Appendix 4. Step-trend Analysis of Changes in Laboratory ...The overall purpose of this appendix is to augment the long-term (10-year to 40-year) trend analyses for the national

Appendix 4.

Step-trend Analysis of Changes in Laboratory Analysis and Sample Collection Methods

2 Appendix 4

Appendix 4

Introduction 3

IntroductionFor the trend results described in the main report, four

trend assessment periods with different specified starting years were analyzed: 1972–2012, 1982–2012, 1992–2012, and 2002–12. Based on the screening criteria presented in the “Water-Quality Data Preparation” section of the main body of this report, subsets of all compiled U.S. Geological Survey (USGS) and outside-agency sampling sites with adequate sampling coverage for analyzing trends were selected for each parameter and each trend assessment period. Changes in flow-normalized mean concentrations from the beginning to the end of each period, determined by using the Weighted Regressions on Time, Discharge, and Season (WRTDS) method (Hirsch and others, 2010) in the R package Exploration and Graphics for RivER Trends (EGRET) (Hirsch and De Cicco, 2015a, b), were used for assessing trends. The number of sites with adequate sampling coverage for a particular parameter and assessment period generally consisted of a small subset of the total number of sites in the compiled dataset of all available USGS and outside-agency sampling sites.

In this appendix, a less rigorous but more inclusive (in terms of spatial coverage and trend assessment periods) trend analysis is described. Step trends rather than gradual (linear) trends are analyzed because a primary goal of this analysis is to determine if and when potential changes in laboratory analytical methods or sample collection and preservation methods might lead to bias in some of the trend results. Such bias, if large enough in relation to environmental trends, may affect the interpretive and causal analyses. The reported concentration of a particular target parameter is a random variable that depends not only on the true riverine concentration but also on the way the sample is collected and preserved. For example, total phosphorus concentration in a grab sample from the middle of a river channel might differ from the concentration in a depth- and width-integrated sample unless the concentration is uniform with respect to depth and lateral position in the river cross section. Furthermore, total phosphorus concentration determined from whole (unfiltered) water samples depends on the sample preservation method (such as chilling and [or] adding a reagent such as sulfuric acid before shipping to the laboratory). Preservation methods are used to prevent additional chemical reactions that may consume phosphorus between the time the sample was collected and when it is analyzed by the laboratory. In some cases, less effective preservation methods (which produce downward bias in concentration) may be replaced with more effective preservation methods that reduce or eliminate downward bias. In addition, dissolved concentrations are generally determined by filtering the raw sample though a filter with specified properties and then preserving the filtered sample before shipment to the lab. Changes in the filter types or properties through time can change the resulting concentrations. Changes in equipment and methods used by laboratories to measure chemical concentrations also can change reported concentrations irrespective of the sample

collection or preservation methods. Although quality-assurance procedures should be used to minimize potential analytical bias, in many cases the method change may not be well documented or there may be inadvertent errors in the calibration process or in computation of bias-correction factors, if applicable.

It is assumed in this appendix that an analytical or sample collection and preservation method change would tend to produce a rapid, step-like trend rather than a gradual trend and that the step trends would be similar in direction and magnitude for all sites from the particular sampling agency, or agencies, making the change. Although non-method-related changes could cause step trends as well, those step trends would generally show a different geospatial pattern compared to method-related changes. For example, a sewage-treatment plant upgrade, removal or construction of a dam, or major change in water withdrawals might be expected to cause step trends, but such trends would occur only downstream of the change and would be unrelated to the sampling agency or laboratory providing the data. Conversely, water-quality trends due to regional-scale environmental (or socioeconomic) drivers, such as land-use change, crop or fertilizer price changes, or regulatory changes, would be expected to produce gradual incremental changes rather than step-like trends because the changes often take place over a number of years, and there may be long lag times before the environmental changes are fully manifested as water-quality changes. Such changes also should be independent of the agency collecting the data and thus not restricted to sites from a single agency. The previous discussion suggests that a method-related change should manifest itself as a step-like trend occurring at the same time and same direction for all sites corresponding to the agency (or agencies) making the change but with no similar step trends occurring at neighboring or overlapping sites from other agencies. A regional environmental change should manifest itself as a gradual change (incremental step changes over a number of years) that is consistent across a large region consisting of sites from multiple agencies.

To help distinguish data changes that may have resulted from environmental changes from those that may have resulted from changes in laboratory analysis or field sampling methods at USGS, step trends were analyzed for each 4-year sliding window beginning with 1972–75 (January 1, 1972, through December 31, 1975) and ending with 2009–12. A 4-year window was considered to be the smallest window for which reliable step trends could be determined, and using a wider window reduces the ability to discern the precise timing and extent (with respect to sampling agencies or regions) of the trends. Although environmental trends may be more gradual than step trends, if large enough, they would be expected to produce significant estimated step trends; therefore, analysis of consistent (among multiple sampling agencies and [or] regions) patterns in the step trends can provide information on the timing and spatial extent of environmental trends and thus may be helpful for interpretive and causal analyses.

4 Appendix 4

Step trends caused by changes in laboratory analysis or field sampling methods likely will be limited to data reported by a single agency. Therefore, to help distinguish data changes potentially caused by laboratory analysis and [or] field sampling method changes from those caused by environmental changes, step trends in USGS data were compared to those in data collectively obtained from all available outside data-collection agencies (ODCA). Correspondence between the step trends in USGS and ODCA data was interpreted to be indicative of environmental changes that would be expected to produce trends of similar direction, regional extent, and timing across multiple sampling agencies; a lack of correspondence between step trends in USGS and OCDA data was interpreted to be indicative of a potential data change that may have resulted from changes in laboratory analysis or field sampling methods at USGS. Information on the timing of laboratory analysis and [or] field sampling method changes at USGS was used as an additional line of evidence (appendix 3). Because information on the timing of laboratory analysis and [or] field sampling method changes was only readily available for USGS data, the same analysis could not be conducted for other agencies. In addition, because the analyzing agency field is not universally populated in the National Water Information System (NWIS) database, it was assumed that all data in NWIS were analyzed at a USGS laboratory. There likely is a small percentage of data in NWIS that is not analyzed at a USGS laboratory, but that percentage was not expected to be large enough to affect the analysis.

The overall purpose of this appendix is to augment the long-term (10-year to 40-year) trend analyses for the national trend assessment sites included in the main body of this report by analyzing a more complete set of sites and focusing on short-term, abrupt trends. Specific objectives are to (1) provide results of regional step-trend analyses of USGS and ODCA data to use as supplementary information for interpreting trends for the final trend assessment sites; and (2) describe instances of major inconsistencies in timing, direction, and extent of trends between different sampling agencies or between USGS and ODCA data that may be the result of non-environmental causes, such as changes in laboratory analytical methods or field sampling methods.

MethodsThe water-quality data sources and data compilation

methods are described in the “Water-Quality, Pesticide, and Ecology Data Compilation” section of the main body of this report. For each parameter and water-quality sampling site, concentration data were merged with concurrent daily streamflow values from a USGS streamgaging station at or near the sampling site. Sites with streamflow data from a source other than USGS are not included in this analysis. To improve the flow-normalization process, described later in this

section, streamflow anomalies (Ryberg and Vecchia, 2012) also were computed and merged with the concentration data. Flow anomalies have been shown in many cases to explain more flow-related variability in concentration than can be achieved by using just concurrent streamflow (Vecchia, 2003, 2005; Vecchia and others, 2008; Battaglin and others, 2009; Ryberg and others, 2010; Garrett, 2012). The flow anomalies are defined by expressing log-transformed daily streamflow in terms of an annual (365-day), 30-day, and 1-day flow anomaly by using the following equation:

(1)

where log denotes base-10 logarithm; Q(t) is daily mean streamflow, in cubic feet per

second, for decimal day t; M is the mean of log-transformed streamflow

for a specified analysis period; and A365d(t), A30d(t), and A1d(t) are the 365-day, 30-day, and 1-day

anomalies (dimensionless), respectively.Daily streamflows were downloaded from the USGS National Water Information System (U.S. Geological Survey, 2016), and the anomalies were computed by using the R package waterData (Ryberg and Vecchia, 2012; R Core Team, 2016). Flow-related variability in concentration was modeled and removed by using a two-stage flow-normalization process:

(2)

log ( ) ( ) ( ) ( )Q t M A t A t A td d d− = + +365 30 1

log ( ) ( ), ( ) ( )C t Loess A t A t R td d= { }+1 365 30 1

R t Loess A t t t R td1 2 1 22 2( ) ( ),cos( ),sin( ) ( )= { }+π π (3)

where C(t) is concentration, in milligrams per liter,

computed from a sample collected on day t;

Loess1 is a locally weighted regression model with degree of polynomial used (degree) equal to 1 and the proportion of points used in each neighborhood for fitting the polynomial (span) equal to 0.75 (R Core Team, 2016) and is based on the 365-day and 30-day flow anomalies;

R1(t) is the residual from Loess1; Loess2 is a locally weighted regression model

with degree 1 and span 0.75 and is based on the 1-day anomaly and the cosine (cos) and sine (sin) functions; and

R2(t) is the residual from Loess2, hereafter referred to as “flow-normalized concentration.”

Examples 5

Flow normalization using the flow anomalies (equations 2 and 3) is referred to as “compound flow-normalization” (Vecchia, 2003) to distinguish it from simple flow-normalization, which is based on concurrent streamflow and cosine and sine functions and is calculated by using the following equation:

(4)

As illustrated in the “Examples” section later in this appendix, using equations 2 and 3 often results in the removal of more flow-related variability than using equation 4. Removing as much flow-related variability as possible was considered important for analyzing step trends for the short (4-year) time windows.

The flow-normalized concentrations analyzed in this appendix differ from flow-normalized concentrations determined by using the WRTDS model (Hirsch and others, 2010). For the WRTDS model, the dependence of concentration on flow and season varies smoothly through time, and trends are evaluated for long-term (multidecadal) time periods. In this appendix, the relation of concentration to flow and season is fixed for each 4-year window, and flow anomalies are used to remove as much flow-related variability as possible for the 4-year window.

For each combination of parameter and site and each 4-year time window with sufficient data, flow-normalized concentrations computed using equations 2 and 3 were tested for a difference between the mean of the first 2 years of data and the mean of the last 2 years of data:

(5)

where Stp(T) is the step trend for year T; T is the decimal time corresponding with

January 1 of calendar year T; and mean{.} is the mean over all nonmissing

concentration values for the respective periods.

Data were considered sufficient for computing the step trend for a given parameter and site and time window under the following conditions:

1. less than 20 percent of the concentrations for the 4-year time window were censored;

2. there were at least six samples per year for each of the 4 calendar years in the window; and

3. there were no sampling gaps longer than 4 months during the 4-year window.

The compiled data were interval-censored by using the methods described in the “Calculation of Target Parameters” sections of the main body of this report. For this analysis, a fixed concentration value was computed from the censoring limits as follows:

(6)

where VL ≥ 0 is the lower censoring limit, and VU > 0 ≥ VL is the upper censoring limit.If VL ≥ 0.5VU (including the case when VL = VU, meaning that the concentration value is known), then the concentration value was assumed to equal the average of VL and VU and was considered uncensored. If VL < 0.5VU (including the case when VL = 0, meaning that the data are right-censored), then the concentration value was assumed to equal VU and was counted as a censored value. If more than 20 percent of the values were censored, the step trend was not analyzed. The p-value for determining whether a step trend was significantly different from zero was computed by using ordinary least-squares regression with a dummy variable to model a change in the intercept; thus, it is assumed that the variance is the same before and after the step trend and that the flow-normalized concentrations are approximately normally distributed.

ExamplesBefore describing the overall results, some examples

for total phosphorus concentration will be used to illustrate the methodology. Figure 4–1 shows the results of the step-trend analysis for total phosphorus concentrations for the 2003 (January 1, 2001, through December 31, 2004) window. There were 159 USGS sites with sufficient data for this window—77 with uptrends and 82 with downtrends. Of these trends, 14 uptrends and 14 downtrends were significant at the 10-percent level (two-sided p-value less than 0.1). Under the null hypothesis that the data are trend free, we expect 10 percent of the 159 sites, or about 16 sites, to have significant trends, with half (8) of the significant trends being uptrends and half being downtrends. On the basis of a binomial distribution, there is a p=0.029 chance of at least 14 significant uptrends when we expect 8. In the “Results” section, if this binomial probability is less than 0.025, then there is said to be more significant uptrends than expected. There were 361 OCDA sites for this window, with 25 significant uptrends and 41 significant downtrends. In this case, there are more significant downtrends than expected (p<0.001). For this window and others, particularly after 1999, there were some States with a large number of sampling sites. For example, Iowa, Oklahoma, and Indiana all had a high density of sites for the 2003 window compared to other States and compared to the USGS sampling network. To avoid skewing the overall findings too much toward these high-density networks, for each time window, the sites for any State with more than 20 OCDA sites in that window were thinned to 20 sites. The thinning was accomplished by ordering the sites by gaging station number, from smallest to largest, and systematically thinning sites by gage number. For example, if a State had

log ( ) log ( ),cos( ),sin( ) ( )C t Loess Q t t t R t= { }+2 2π π

Stp T R t T t T R t T t T( ) ( ); ( );= ≤ ≤ +{ }− − ≤ <{ }mean mean2 22 2Stp T R t T t T R t T t T( ) ( ); ( );= ≤ ≤ +{ }− − ≤ <{ }mean mean2 22 2

V C t VL U≤ ( ) ≤

6 Appendix 4

USGS sites

Step trends for total phosphorus for 2003 (January 1, 2001, to December 31, 2004) window

Nonsignificant trend

Significant (p<0.1) uptrend, larger than 30 percent

Significant (p<0.1) uptrend, smaller than 30 percent

Significant (p<0.1) downtrend, smaller than −20 percent

Significant (p<0.1) downtrend, larger than −20 percent

U.S. Geological Survey

Outside data collection agency

77 uptrends, 14 significant82 downtrends, 14 significant

ODCA sites

158 uptrends, 25 significant203 downtrends, 41 significant [*][*] more significant uptrends or downtrends than expected

EXPLANATION

Figure 1.

USGS

ODCA

Figure 4 –1. Maps showing national step trends for total phosphorus for the 2003 (January 1, 2001, to December 31, 2004) window.

Examples 7

25 sites, every fifth site, starting with the fifth, was thinned; if there were 30 sites, every third site was thinned. Figure 4–2 shows the results for the thinned set of sites and looks similar overall to figure 4–1. There were 260 OCDA sites in the thinned network, with 17 significant uptrends and 23 significant downtrends. All trend results from hereinafter are based on the thinned network of sites.

It is important when analyzing trends for short time windows to remove as much flow-related variability as possible so that regional patterns unrelated to streamflow (or climate) variability can be more clearly revealed. As mentioned in the previous section, for some parameters, compound flow normalization (equations 2 and 3) can be more effective than simple flow normalization (equation 4). The difference between compound and simple flow normalization is indicated in figure 4–3, which shows the same sites as in figure 4–2, but uses simple flow normalization instead of compound flow normalization. There were many more significant trends in figure 4–3 compared to figure 4–2. For example, there were 36 significant downtrends for the USGS sites (compared to 14 for fig. 4–2) and 54 significant downtrends for the OCDA sites (compared to 23 for fig. 4–2). Most of the significant downtrends were for the Middle Atlantic States, and these trends became largely nonsignificant, or in some cases significantly upward, for the compound flow-normalization model (fig. 4–2).

The difference between compound and simple flow normalization is further illustrated in figure 4–4, which shows the observed and fitted total phosphorus concentrations and estimated step trends for a site from the Chesapeake Bay drainage, South Fork Quantico Creek near Independent Hill, Virginia, for the 2003 window. The compound flow-normalization model is shown in figures 4–4A and 4–4B. For this site, there was substantial lower frequency (seasonal to interannual) flow-related variability in the concentrations, as indicated by the line showing the fitted concentrations for stage 1 (equation 2), and the combination of the stage 1 and stage 2 (equation 3) models, which explained much of the variability in the raw concentrations. After removing the flow-related variability, there was an estimated step trend of 10.5 percent and a p-value of 0.072. For the simple flow-normalization model (figure 4–4C and 4–4D), the lower frequency flow-related variability was not captured, and there was not as much overall variability that could be explained. This is especially evident during 2002, which had high concentrations compared to the other years and for which the simple flow-normalization model underestimated the high concentrations compared to the compound flow-normalization model. For the simple flow-normalization model, there was an estimated step trend of -21.7 percent and a p-value of 0.0046, mainly as a result of the high concentrations during 2002 that were still high after simple flow normalization.

Another example showing the difference between compound and simple flow normalization is shown in figure 4–5, which shows the observed and fitted total phosphorus concentrations and estimated step trends for the Des Moines River near Tracy, Iowa, for the 2003 window. Compared to the previous example, there was not as much contrast between the compound and simple flow-normalization models; however, the compound flow-normalization model again explained more lower frequency variability compared to simple flow normalization, especially during 2001–2. For this example, there was an estimated step trend of 14.4 percent (p-value of 0.016) for the compound flow-normalization model compared to an estimated step trend of 5.6 percent (p-value of 0.39) for the simple flow-normalization model.

It is also important that trends not caused by flow-related variability can be detected with reasonable power. To illustrate this, an artificial uptrend of 30 percent was added to the raw (non-flow-normalized) concentrations of the figure 4–2 dataset for the second half of the window (2003 and 2004); the step-trend results for the “spiked” data are shown in figure 4–6. Compared to the original data (fig. 4–2), there is a much greater number of significant uptrends. For the USGS sites, there are 52 significant uptrends (compared to 14 for fig. 4–2), and for the OCDA sites, there are 76 significant uptrends (compared to 17 for fig. 4–2). Also, most of the significant downtrends in figure 4–2 became either nonsignificant or significantly upward in figure 4–6. The modeled concentrations and step trends for the two sites in Virginia and Iowa discussed previously are shown in figure 4–7, which can be compared with the A and B plots in figures 4–4 and 4–5. For the Virginia site, the spiked data (fig. 4–7) had an estimated step trend of 19.2 percent (p-value of 0.0029) compared to 10.5 percent (p-value of 0.072) for the raw data (fig. 4–4). Although the uptrend was larger and more significant for the spiked data, the difference (about 9 percent) was considerably smaller than 30 percent. Unfortunately, the presence of lower frequency flow-related variability (as well as gradual environmental trends) can, in some cases, make it harder to detect and (or) accurately estimate step trends; however, for the Iowa site (fig. 4–7C and 4–7D) spiked data, there was an estimated step trend of 41.3 percent (p-value less than 0.0001) compared to 14.4 percent (p-value of 0.016) for the raw data (fig. 4–5A and 4–5B). The difference (26.9 percent) was nearly equal to 30 percent. The degree of confounding between step trends and lower frequency flow-related variability depends on the timing and nature of the variability in relation to the step trend.

8 Appendix 4

USGS sites



ODCA sites


Figure 2.








EXPLANATION

USGS

ODCA

Figure 4 –2. Maps showing national step trends for total phosphorus for the 2003 (January 1, 2001, to December 31, 2004) window after thinning to at most 20 sites per state.

Examples 9

USGS sites


77 uptrends, 16 significant [*]82 downtrends, 36 significant [*][*] more significant uptrends or downtrends than expected

ODCA sites


Figure 3.








EXPLANATION

USGS

ODCA

Figure 4 –3. Maps showing national step trends for total phosphorus for the 2003 (January 1, 2001, to December 31, 2004) window, using simple flow normalization.

10 Appendix 4

−2.2

−2.4

−2

−1.8

−1.6

−1.4

−1.2

−1

−0.8

−0.6

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion

Fitted (stage 1)Fitted (stage 1) + Fitted (stage 2)

EXPLANATION

−0.6

−0.4

−0.2

0

0.2

0.4

2001 2002 20042003 2005

Flow

-nor

mal

ized

conc

entra

tion

Step trend

percentage change = 10.53p-value = 0.072

EXPLANATION

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

2001 2002 2003 2004 2005

Flow

-nor

mal

ized

conc

entra

tion

Step trend

percentage change = −21.69p-value = 0.0046

EXPLANATION

−2.4

−2.2

−2

−1.8

−1.6

−1.4

−1.2

−1

−0.8

−0.6

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion

Fitted (simple flow model)

EXPLANATION

A

B

C

D

Figure 4 –4. Graphs showing fitted total phosphorus concentrations and step trend for the 2003 window for South Fork Quantico Creek near Independent Hill, Virginia, using compound-flow normalization (A, B) and simple flow normalization (C, D).

Examples 11

−1

−1.2

−0.6

−1.4

−0.8

−0.4

−0.2

0

−1.2

−1.4

−1

−0.8

−0.6

−0.4

−0.2

0

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion


−0.6

−0.4

−0.2

0

0.2

0.6

0.4

2001 2002 20042003 2005

Flow

-nor

mal

ized

conc

entra

tion

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion

Fitted (simple flow model)

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

2001 2002 2003 2004 2005

Flow

-nor

mal

ized

conc

entra

tion

Step trend


Step trend


EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

A

B

C

D

Figure 4 –5. Graphs showing fitted total phosphorus concentrations and step trend for the 2003 window for Des Moines River near Tracy, Iowa, using compound-flow normalization (A, B) and simple flow normalization (C, D).

12 Appendix 4

USGS sites


130 uptrends, 52 significant [*]29 downtrends, 5 significant[*] more significant uptrends or downtrends than expected

ODCA sites


Figure 6.








EXPLANATION

USGS

ODCA

Figure 4 –6. Maps showing national step trends for total phosphorus for the 2003 (January 1, 2001, to December 31, 2004) window with artificial uptrend of 30 percent.

Examples 13

−1.6

−1.8

−2

−1.2

−2.2

−1.4

−1

−0.8

−0.6

−1.2

−1.4

−1

−0.8

−0.6

−0.4

−0.2

0

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion


−0.6

−0.4

−0.2

0

0.2

0.4

2001 2002 20042003 2005

Flow

-nor

mal

ized

conc

entra

tion

2001 2002 2003 2004 2005

Base

-10

loga

rithm

of c

once

ntra

tion

−0.8

−0.6

−0.4

−0.2

0

0.2

0.4

0.6

2001 2002 2003 2004 2005

Flow

-nor

mal

ized

conc

entra

tion

Step trend

Step trend

EXPLANATION


EXPLANATION

EXPLANATION

EXPLANATION

percentage change = 19.17 p-value = 0.0029

percentage change = 41.29 p-value = 0

A

B

C

D

Figure 4 –7. Graphs showing fitted total phosphorus concentrations and step trends for the 2003 window for South Fork Quantico Creek near Independent Hill, Virginia (A, B), and Des Moines River near Tracy, Iowa (C, D), using compound flow normalization and including an artificial uptrend of 30 percent.

14 Appendix 4

ResultsFor presentation and discussion of results in this

section, emphasis is placed on identifying anomalous trend patterns that may reflect non-environmental factors such as changes in analytical (laboratory) or field sampling methods. Occasionally, strong regional trend patterns that appear to be consistent across multiple agencies and thus probably reflect changes in environmental factors, such as land use, will be contrasted with anomalous trend patterns. Note that the lack of obvious anomalous trend patterns for some parameters could mean that there are indeed no anomalous trends for those parameters or that the anomalous trends cannot be detected given the limitations of the data and statistical methodology.

Results are grouped by general categories of nutrients, sediment, major ions and salinity, and carbon. Specific information on the parameters (such as units, methods for combining parameter codes from different agencies) is described in detail in the “Water-Quality Data Preparation” section of the main body of this report. Target parameters discussed in the main body of this report, but not included in this appendix, had site densities too low for meaningful regional or interagency comparisons.

The sites were divided into three overlapping regions on the basis of the gaging station number associated with each site. Region 1 (East) has the first two digits of the gaging station number equal to 01 through 04 and covers roughly the eastern third of the conterminous United States, including the New England, Mid-Atlantic, Great Lakes, Ohio, and Tennessee Basins. Region 2 (Central) has the first two digits equal to 03 through 07 and includes the Great Lakes and Mississippi (including the Ohio, Tennessee, and Missouri) Basins. Region 3 (West) has first two digits equal to 05 through 14, and covers roughly the western two-thirds of the conterminous United States, including most of the Mississippi Basin (excluding the Ohio Basin), the Texas-Gulf Basins, and all basins west of the Continental Divide. The sites were divided into regions to help account for the effects of non-uniform and variable (through time) site locations and coverage. Large overlapping regions were selected to increase the number of windows with sufficient population of sites for regional comparison between the USGS and ODCA sites. For both USGS and ODCA data, a particular region and trend window was required to have at least 20 step-trend results for making regional comparisons. Note that because the regions used for the trend results overlap, the regional trend totals do not add up to the national totals.

Nutrients

Total PhosphorusA summary of the regional trend results for total

phosphorus are given in table 4–1. Only the trend results for which at least 20 step trends could be analyzed for a particular

region and trend window are reported. Early trend windows (in this case, only 1974) were omitted from the table if there were no trend results that could be reported (for either USGS or ODCA sites) for those windows. Blue cells indicate cases for which there were both more downtrends than expected (based on a binomial distribution with success probability 0.5 and exceedance probability less than 0.025) and more significant downtrends than expected (based on a binomial distribution with success probability 0.05 and exceedance probability less than 0.025). Similarly, red cells indicate cases for which there were both more uptrends and more significant uptrends than expected. The first condition (more than expected number of trends in a particular direction) was imposed because method bias was expected to cause consistent step changes in one direction or the other, and the second condition (more than expected number of significant trends in the same direction) was imposed to highlight cases where the trends tended to be relatively large in relation to natural variability. Note that shaded cells indicate significant results for each individual window/region, and thus in a table such as table 4–1 we would have a substantial probability (much higher than 5 percent) of having one or more shaded cells by chance, even if there were no trends. The approach used here is exploratory and descriptive in nature. Developing rigorous hypothesis tests on the basis of multiple comparisons was beyond the scope of this study.

For the 1980 window, there was a strong tendency for uptrends in total phosphorus for USGS sites (fig. 4–8, table 4–1). Note that the regions used for the trend results shown in table 4–1 and subsequent tables overlap, so the regional trend totals do not add up to the national totals shown in figure 4–8. Although ODCA sites for this window were sparse, there was a general tendency for downtrends for those sites. The uptrends for USGS sites were particularly strong for the West (56 uptrends out of 85, 13 significant) and East (34 uptrends out of 48, 6 significant) regions. In contrast, for the ODCA sites, there were only 11 uptrends out of 31, none significant, for the West region and 9 uptrends out of 21, none significant, for the East region. Although the sparse density of ODCA sites for the western and southeastern United States makes for tenuous comparisons, the increase in USGS concentrations in about 1980 may be related to a change in sample preservation methods (appendix 3, table 3–3) that occurred about that time and may have resulted in higher concentrations compared to earlier years (that is, downward bias prior to 1980).

From 1981 to 2012, there were generally consistent total phosphorus trend results between the USGS and ODCA sites, with predominantly downtrends for many years for the East region and mixed trends for the remaining regions. For example, for the 1991 window (fig. 4–9, table 4–1), there were more downtrends than expected for both the USGS and ODCA sites for the East region. Although the method timeline analysis (appendix 3, table 3–3) indicates that a possible increase in USGS total phosphorus concentrations may have occurred about this time, there is no indication of an anomalous upward step trend for the USGS sites.

Results

15Table 4–1. Summary of regional step-trend analysis for total phosphorus.

[USGS, U.S. Geological Survey; ODCA, outside data collection agency; sig., number of trends that are significant (p-value <0.1); -, less than 20 available trends, insufficient data for regional analysis; blue shading indicates higher than expected number of downtrends; red shading indicates higher than expected number of uptrends]

Center of trend window

(year)

Trend countsRegion 1 (East) Region 2 (Central) Region 3 (West)

TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends

(sig.)USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA

1975 12 2 - - - - 17 13 - - - - 30 11 22(9) - 8(0) -1976 22 4 10(2) - 12(4) - 25 26 14(1) 16(1) 11(2) 10(1) 44 26 26(2) 18(1) 18(3) 8(0)1977 41 10 27(8) - 14(2) - 50 29 30(3) 9(4) 20(6) 20(15) 72 30 43(3) 7(3) 29(8) 23(15)1978 42 15 32(11) - 10(2) - 53 30 31(7) 10(2) 22(3) 20(7) 82 32 43(6) 12(2) 39(5) 20(6)1979 46 20 25(7) 12(4) 21(2) 8(2) 56 34 29(5) 15(2) 27(3) 19(6) 80 33 37(5) 16(1) 43(11) 17(4)1980 48 21 14(2) 12(4) 34(6) 9(0) 63 33 29(5) 21(5) 34(8) 12(0) 85 31 29(5) 20(4) 56(13) 11(0)1981 38 25 15(0) 15(3) 23(2) 10(2) 46 28 25(5) 19(4) 21(2) 9(2) 66 27 34(6) 17(3) 32(4) 10(1)1982 27 30 9(2) 16(4) 18(2) 14(2) 25 26 12(1) 13(2) 13(3) 13(4) 45 30 22(2) 14(0) 23(4) 16(4)1983 27 47 19(1) 24(3) 8(1) 23(4) 21 28 11(0) 15(1) 10(0) 13(1) 40 36 21(0) 17(1) 19(1) 19(3)1984 27 47 18(4) 23(6) 9(3) 24(4) 22 33 11(2) 25(10) 11(0) 8(2) 34 42 15(2) 27(9) 19(1) 15(1)1985 34 49 22(2) 26(9) 12(1) 23(3) 22 42 10(3) 22(6) 12(2) 20(3) 34 52 16(4) 24(7) 18(1) 28(1)1986 44 50 22(3) 32(15) 22(3) 18(2) 32 42 14(1) 22(5) 18(3) 20(2) 39 55 22(2) 26(1) 17(3) 29(5)1987 47 54 28(6) 44(25) 19(1) 10(2) 35 45 22(6) 26(7) 13(1) 19(2) 42 55 25(6) 30(6) 17(1) 25(3)1988 51 57 26(6) 36(13) 25(3) 21(1) 38 45 25(5) 24(5) 13(3) 21(2) 49 54 32(6) 31(5) 17(4) 23(3)1989 52 59 30(4) 38(14) 22(3) 21(5) 38 24 15(1) 9(2) 23(1) 15(3) 51 33 24(2) 17(2) 27(1) 16(0)1990 39 55 23(4) 33(14) 16(3) 22(4) 42 25 24(1) 9(5) 18(7) 16(5) 60 33 38(3) 13(2) 22(7) 20(3)1991 35 59 25(8) 35(11) 10(1) 24(5) 13 25 - 13(4) - 12(4) 28 32 15(2) 12(2) 13(0) 20(4)1992 35 82 24(9) 49(8) 11(2) 33(1) 14 29 - 20(3) - 9(1) 28 27 16(2) 17(0) 12(2) 10(1)1993 25 101 11(5) 53(13) 14(2) 48(2) 11 67 - 30(7) - 37(7) 26 53 14(2) 27(5) 12(2) 26(7)1994 23 109 10(4) 46(16) 13(1) 63(12) 9 70 - 36(12) - 34(8) 21 53 11(5) 30(7) 10(4) 23(4)1995 21 106 10(2) 61(22) 11(2) 45(8) 23 61 13(5) 34(8) 10(4) 27(8) 38 45 22(7) 28(9) 16(5) 17(5)1996 15 110 - 68(29) - 42(9) 10 82 - 33(3) - 49(11) 26 56 7(2) 25(1) 19(2) 31(4)1997 17 104 - 63(15) - 41(7) 10 80 - 36(7) - 44(9) 24 54 10(3) 23(5) 14(1) 31(8)1998 18 96 - 60(13) - 36(6) 18 78 - 42(10) - 36(6) 33 53 18(5) 28(3) 15(3) 25(1)1999 25 99 14(2) 62(8) 11(0) 37(2) 30 87 7(2) 45(5) 23(5) 42(6) 47 61 16(4) 31(2) 31(6) 30(5)2000 38 101 19(3) 58(18) 19(5) 43(10) 34 94 13(1) 48(14) 21(5) 46(12) 57 74 25(4) 37(8) 32(8) 37(8)2001 46 116 22(3) 67(32) 24(4) 49(12) 50 127 29(3) 64(11) 21(3) 63(10) 84 109 46(6) 52(3) 38(6) 57(8)2002 54 120 20(4) 61(16) 34(4) 59(18) 55 165 26(4) 85(15) 29(7) 80(20) 91 142 48(8) 72(11) 43(8) 70(12)2003 64 116 27(2) 63(9) 37(8) 53(13) 68 151 43(8) 87(17) 25(5) 64(9) 95 144 55(12) 79(14) 40(6) 65(4)2004 48 132 32(5) 80(16) 16(3) 52(6) 70 136 35(9) 75(20) 35(4) 61(14) 98 121 45(14) 64(18) 53(8) 57(13)2005 48 145 28(10) 92(35) 20(2) 53(16) 70 140 31(10) 69(15) 39(3) 71(21) 95 122 48(8) 59(9) 47(8) 63(12)2006 38 124 19(7) 64(19) 19(5) 60(17) 76 144 33(9) 77(13) 43(10) 67(14) 98 141 44(10) 79(14) 54(10) 62(3)2007 40 112 29(10) 70(16) 11(2) 42(11) 71 127 31(3) 64(9) 40(6) 63(12) 97 131 37(6) 67(15) 60(13) 64(5)2008 64 102 39(8) 61(15) 25(5) 41(5) 73 124 29(4) 66(8) 44(11) 58(5) 102 130 51(6) 68(7) 51(10) 62(4)2009 74 101 38(9) 48(12) 36(4) 53(8) 76 129 33(5) 72(19) 43(7) 57(10) 95 137 55(15) 76(19) 40(7) 61(11)2010 71 100 42(10) 68(23) 29(2) 32(7) 70 93 35(5) 55(10) 35(4) 38(6) 81 91 41(8) 52(8) 40(4) 39(5)2011 60 83 35(12) 44(15) 25(4) 39(5) 74 89 48(11) 46(6) 26(7) 43(6) 94 87 48(9) 41(6) 46(14) 46(7)

16 Appendix 4

USGS sites



ODCA sites


Figure 8.








EXPLANATION

USGS

ODCA


Results 17

USGS sites



ODCA sites


Figure 9.








EXPLANATION

USGS

ODCA


18 Appendix 4

Trends for the 1999 window (fig. 4–10, table 4–1) indicate several significant uptrends for the USGS sites in the Central region and a generally consistent pattern for the ODCA sites. The change in field treatment protocols for USGS sites during this time (appendix 3, table 3–3) apparently did not affect total phosphorus concentrations enough to stand out from the natural variability and (or) environmental trends for the sites analyzed. Another example for the 2007 trend window (fig. 4–11, table 4–1) illustrates the general consistency between the USGS and ODCA sites. For this window, there were more downtrends than expected for the East region for both the USGS and ODCA sites. Although there were more uptrends than expected for the USGS sites for the West region and that pattern was not confirmed by the ODCA sites, this discrepancy probably reflects differences in site locations.

Filtered OrthophosphateThe step-trend results for filtered orthophosphate are

given in table 4–2. For this parameter, there were no step trends to report prior to the 1982 window, and for the USGS sites, there were few trend results to report prior to the mid-1990s. The generally sparse site coverages are illustrated for the 1994 window in figure 4–12. Although site coverage is sparse, there seems to be general consistency between the USGS and ODCA results for this window and other windows in the 1990s. There may be an anomalous pattern for the 2000 window, shown in figure 4–13. For this window, there were more uptrends than expected for the ODCA sites for the East region, and the uptrends were consistent across multiple State agencies; however, there was no indication of similar uptrends for USGS sites. Although differences in site locations between USGS and ODCA sites could be a factor, there may be an anomalous decrease in USGS concentrations that corresponds with a laboratory method change about this time (appendix 3, table 3–3).

The USGS laboratory method timeline also indicates a filtered orthophosphate method change in about 2006 (appendix 3, table 3–3). The trend windows for 2006 and 2007 (figs. 4–14 and 4–15) may indicate that the method change resulted in an anomalous upward step trend for USGS sites. For the 2006 window, there were more downtrends than expected for the ODCA sites for the East and Central regions (table 4–2), and these downtrends were not indicated for the USGS sites. Furthermore, there were more pronounced uptrends for the USGS sites for the West region compared to the ODCA sites for both the 2006 and 2007 windows.

Total NitrogenResults of the step-trend analysis for total nitrogen are

given in table 4–3. Like total phosphorus (fig. 4–8), for the 1980 window (fig. 4–16, table 4–3), there was a large number of significant uptrends in total nitrogen (41 uptrends out of 55, 15 significant) for the USGS sites for the West region.

Although there were few ODCA sites to compare to USGS sites, the abrupt and widespread nature of the total nitrogen uptrends and the similarity with the total phosphorus uptrends may indicate that the sample preservation change in about 1980 (appendix 3, table 3–2) caused an anomalous uptrend for the USGS sites.

The methods timeline indicates potential upward bias in total Kjeldahl nitrogen concentration, one of the parameters often used to compute total nitrogen, during 1986–92 (appendix 3, table 3–2); however, as shown for the 1986 window in figure 4–17, there were no indications of anomalous uptrends in total nitrogen for USGS sites during that time. Likewise, the 1992 window (not shown) had no indications of anomalous downtrends. The bias apparently was not large enough to be readily distinguished from natural variability and (or) environmental trends. Similarly, for the 1999 window (fig. 4–18), there were no indications of anomalous trends for the USGS sites (as compared to ODCA) caused by the change in sample preservation methods at that time (appendix 3, table 3–2).

The method timeline indicates an analytical change in 2004 (probably affecting certain sites but not others) that may cause downward bias in USGS total nitrogen concentrations (appendix 3, table 3–2); however, as shown in figure 4–19, for the 2004 window, there generally were small mixed upward and downward trends for both USGS and ODCA sites, and therefore the downward bias may not be large enough to be distinguished from natural variability and (or) environmental trends, or it was not extensive enough with respect to the sites analyzed to cause an obvious regional pattern.

Nitrate

Results of the step-trend analysis for nitrate are given in table 4–4. Detailed examination of the trend plots for each window indicated that the USGS and ODCA sites for the various State agencies generally showed similar regional trend patterns, and no readily identifiable anomalous patterns were indicated. For example, unlike total phosphorus and total nitrogen (figs. 4–8 and 4–16, respectively), there were no indications of anomalous uptrends for nitrate from USGS sites for the 1980 window (fig. 4–20). This provides more evidence that the increase in total nitrogen may be due to a change in preservation methods (appendix 3, table 3–2) that affected the unfiltered parameters (such as total Kjeldahl nitrogen) more than the primarily dissolved parameters such as nitrate. The nitrate trends for the 1999 window (fig. 4–21) indicated general agreement between agencies and with the total nitrogen trends for the same window (fig. 4–18), providing more evidence that the change in USGS field methods at that time did not substantially affect the nutrient trends. Nitrate trends for the 2004 window (fig. 4–22, table 4–4) indicate more uptrends for the West region for the USGS sites compared to the ODCA sites, but this probably reflects differences in site locations.

Results 19

USGS sites



ODCA sites


Figure 10.








EXPLANATION

USGS

ODCA


20 Appendix 4

USGS sites



ODCA sites


Figure 11.








EXPLANATION

USGS

ODCA


Results

21Table 4–2. Summary of regional step-trend analysis for filtered orthophosphate.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.) TotalDowntrends

(sig.)Uptrends (sig.)

USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA USGS ODCA 1982 0 22 - 8(1) - 14(2) 1 6 - - - - 1 9 - - - -1983 0 27 - 10(1) - 17(2) 1 8 - - - - 2 9 - - - -1984 5 31 - 12(5) - 19(2) 7 12 - - - - 12 10 - - - -1985 7 32 - 23(11) - 9(1) 4 11 - - - - 10 11 - - - -1986 6 33 - 24(16) - 9(1) 6 17 - - - - 10 23 - 12(1) - 11(0)1987 8 30 - 15(8) - 15(3) 5 19 - - - - 9 27 - 15(5) - 12(2)1988 10 34 - 20(6) - 14(2) 10 23 - 10(4) - 13(2) 16 30 - 11(2) - 19(4)1989 8 33 - 18(4) - 15(3) 10 24 - 10(2) - 14(2) 17 27 - 10(3) - 17(0)1990 7 33 - 13(2) - 20(6) 11 25 - 9(3) - 16(7) 22 26 13(2) 13(3) 9(1) 13(3)1991 7 26 - 13(7) - 13(4) 11 23 - 10(4) - 13(4) 19 26 - 11(0) - 15(5)1992 6 39 - 17(7) - 22(3) 12 25 - 13(8) - 12(2) 20 25 7(3) 12(3) 13(3) 13(1)1993 6 41 - 24(8) - 17(7) 9 27 - 12(8) - 15(3) 17 28 - 14(9) - 14(2)1994 8 41 - 27(9) - 14(3) 7 21 - 18(10) - 3(0) 17 27 - 24(8) - 3(0)1995 15 42 - 24(8) - 18(7) 14 18 - - - - 27 24 16(6) 19(8) 11(3) 5(0)1996 13 42 - 28(13) - 14(4) 8 26 - 15(3) - 11(3) 25 35 9(3) 20(1) 16(1) 15(0)1997 14 41 - 25(6) - 16(5) 10 32 - 25(9) - 7(3) 25 40 15(5) 27(9) 10(1) 13(3)1998 16 36 - 27(5) - 9(3) 17 32 - 19(6) - 13(3) 31 44 14(3) 22(6) 17(4) 22(0)1999 19 38 - 18(1) - 20(3) 22 43 16(2) 26(8) 6(1) 17(3) 44 58 27(4) 35(12) 17(2) 23(2)2000 20 42 11(4) 10(0) 9(5) 32(10) 26 43 12(3) 15(0) 14(2) 28(15) 52 61 32(7) 27(1) 20(0) 34(11)2001 20 50 12(4) 21(6) 8(3) 29(9) 29 33 10(3) 12(1) 19(2) 21(10) 59 53 29(6) 28(1) 30(2) 25(8)2002 22 53 11(1) 18(7) 11(3) 35(10) 33 42 21(6) 22(3) 12(4) 20(6) 61 66 37(10) 32(2) 24(7) 34(4)2003 21 52 10(1) 31(4) 11(2) 21(4) 38 55 22(11) 30(7) 16(5) 25(8) 63 79 38(17) 39(7) 25(6) 40(7)2004 23 54 17(4) 33(7) 6(0) 21(4) 42 64 23(8) 24(6) 19(7) 40(7) 67 87 29(11) 32(5) 38(10) 55(9)2005 21 57 13(7) 38(18) 8(1) 19(6) 41 65 23(7) 35(10) 18(3) 30(6) 64 75 33(12) 33(5) 31(6) 42(6)2006 22 57 8(0) 39(12) 14(2) 18(1) 48 65 16(1) 42(9) 32(6) 23(3) 69 85 28(5) 51(11) 41(10) 34(4)2007 30 61 18(1) 35(8) 12(3) 26(8) 50 79 11(1) 25(6) 39(11) 54(15) 74 96 22(2) 43(12) 52(18) 53(11)2008 39 65 19(2) 34(10) 20(5) 31(10) 63 76 24(2) 45(4) 39(3) 31(5) 90 91 35(2) 51(5) 55(7) 40(5)2009 48 68 22(6) 35(13) 26(9) 33(9) 69 76 37(6) 50(9) 32(6) 26(6) 99 91 56(7) 57(9) 43(8) 34(6)2010 48 64 29(11) 42(15) 19(4) 22(7) 63 61 47(6) 33(9) 16(5) 28(7) 83 80 57(9) 49(12) 26(9) 31(3)2011 35 50 21(8) 27(7) 14(1) 23(7) 63 53 50(12) 32(8) 13(3) 21(3) 85 74 59(12) 43(9) 26(4) 31(4)

22 Appendix 4

USGS sites

Step trends for filtered orthophosphate for 1994 (January 1, 1992, to December 31, 1995) window


ODCA sites


Figure 12.








EXPLANATION

USGS

ODCA

Figure 4 –12. Maps showing national step trends for filtered orthophosphate for the 1994 (January 1, 1992, to December 31, 1995) window.

Results 23

USGS sites



ODCA sites

66 uptrends, 21 significant [*]37 downtrends, 1 significant [*] more significant uptrends or downtrends than expected

Figure 13.








EXPLANATION

USGS

ODCA


24 Appendix 4

USGS sites



ODCA sites


Figure 14.








EXPLANATION

USGS

ODCA


Results 25

USGS sites



ODCA sites

79 uptrends, 19 significant [*]78 downtrends, 20 significant [*] [*] more significant uptrends or downtrends than expected

Figure 15.








EXPLANATION

USGS

ODCA


26

Appendix 4Table 4–3. Summary of regional step-trend analysis for total nitrogen.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1976 17 12 - - - - 10 2 - - - - 22 1 10(0) - 12(3) -1977 23 18 5(0) - 18(7) - 17 2 - - - - 36 3 15(1) - 21(6) -1978 23 12 6(0) - 17(3) - 20 2 9(0) - 11(2) - 49 3 25(4) - 24(4) -1979 25 15 19(2) - 6(2) - 22 8 9(1) - 13(3) - 43 4 13(2) - 30(7) -1980 49 19 29(3) - 20(2) - 45 8 20(1) - 25(7) - 55 5 14(0) - 41(15) -1981 40 27 12(1) 11(0) 28(5) 16(1) 34 7 10(0) - 24(4) - 39 5 10(0) - 29(6) -1982 26 38 4(1) 22(2) 22(8) 16(1) 19 6 - - - - 29 6 8(1) - 21(2) -1983 28 46 14(1) 27(5) 14(1) 19(0) 23 7 11(0) - 12(1) - 32 10 18(0) - 14(1) -1984 27 46 11(1) 32(10) 16(3) 14(2) 22 14 13(1) - 9(2) - 31 19 20(3) - 11(2) -1985 35 46 25(5) 25(6) 10(2) 21(4) 25 13 18(3) - 7(2) - 33 19 22(4) - 11(3) -1986 39 37 21(3) 21(5) 18(2) 16(5) 29 10 13(2) - 16(1) - 34 24 15(3) 16(2) 19(2) 8(2)1987 38 34 24(4) 16(4) 14(2) 18(5) 30 13 17(4) - 13(2) - 36 28 19(4) 14(0) 17(3) 14(1)1988 40 53 30(7) 26(7) 10(1) 27(4) 28 15 22(7) - 6(0) - 36 29 26(7) 15(3) 10(1) 14(2)1989 38 54 26(5) 21(6) 12(1) 33(2) 27 14 14(0) - 13(3) - 37 24 21(2) 15(3) 16(4) 9(0)1990 35 49 20(1) 18(3) 15(1) 31(6) 31 15 9(0) - 22(10) - 42 18 17(2) - 25(11) -1991 31 51 19(5) 33(5) 12(2) 18(2) 13 14 - - - - 25 10 7(0) - 18(3) -1992 25 72 14(4) 46(13) 11(1) 26(3) 15 15 - - - - 25 7 14(2) - 11(2) -1993 19 79 - 48(18) - 31(4) 12 22 - 15(10) - 7(1) 23 8 13(3) - 10(2) -1994 19 88 - 58(24) - 30(2) 10 27 - 19(12) - 8(1) 22 15 12(5) - 10(2) -1995 19 89 - 61(14) - 28(8) 23 29 13(1) 16(6) 10(1) 13(6) 37 18 22(4) - 15(1) -1996 21 91 5(2) 46(7) 16(6) 45(8) 7 47 - 30(9) - 17(7) 21 34 9(2) 22(5) 12(2) 12(3)1997 23 85 16(3) 53(14) 7(0) 32(7) 8 47 - 26(3) - 21(5) 22 36 14(3) 15(2) 8(1) 21(4)1998 26 84 21(3) 57(14) 5(0) 27(2) 14 46 - 29(10) - 17(5) 28 35 10(1) 18(4) 18(3) 17(7)1999 34 93 16(1) 36(5) 18(2) 57(17) 25 57 6(0) 22(8) 19(7) 35(16) 46 40 15(2) 17(5) 31(7) 23(11)2000 39 99 14(5) 41(4) 25(4) 58(21) 29 66 12(3) 25(4) 17(3) 41(19) 58 58 24(7) 29(8) 34(8) 29(6)2001 47 121 22(7) 53(13) 25(5) 68(21) 47 96 24(5) 18(0) 23(1) 78(22) 84 87 44(8) 27(3) 40(4) 60(9)2002 51 120 28(4) 49(12) 23(6) 71(16) 53 130 29(4) 47(7) 24(6) 83(19) 91 118 40(8) 53(7) 51(14) 65(13)2003 59 118 38(6) 60(14) 21(0) 58(10) 62 130 32(6) 85(17) 30(8) 45(5) 86 127 39(12) 84(12) 47(11) 43(5)2004 49 134 28(3) 58(11) 21(5) 76(14) 64 132 34(9) 62(15) 30(6) 70(13) 89 123 54(15) 62(15) 35(7) 61(8)2005 48 145 27(6) 81(27) 21(4) 64(12) 69 132 31(7) 65(14) 38(6) 67(16) 91 117 44(13) 52(9) 47(11) 65(12)2006 38 131 20(8) 88(23) 18(3) 43(4) 73 139 31(4) 84(23) 42(9) 55(13) 96 136 36(6) 70(10) 60(12) 66(14)2007 39 120 23(7) 74(15) 16(5) 46(9) 69 120 29(7) 59(8) 40(8) 61(18) 97 120 40(8) 55(8) 57(10) 65(14)2008 60 103 42(15) 45(11) 18(2) 58(10) 74 106 40(1) 52(10) 34(5) 54(7) 89 113 45(4) 49(7) 44(9) 64(9)2009 73 104 48(14) 50(6) 25(8) 54(11) 75 102 31(8) 58(11) 44(11) 44(9) 80 109 34(9) 60(13) 46(10) 49(8)2010 74 94 36(11) 44(15) 38(4) 50(12) 75 63 33(5) 33(8) 42(5) 30(7) 83 63 36(7) 35(6) 47(6) 28(5)2011 62 87 36(11) 52(17) 26(3) 35(7) 78 65 37(8) 34(5) 41(4) 31(3) 97 66 44(6) 31(4) 53(6) 35(3)

Results 27

USGS sites

Step trends for total nitrogen for 1980 (January 1, 1978, to December 31, 1981) window







ODCA sites


EXPLANATION

Figure 16.Figure 4 –16. Maps showing national step trends for total nitrogen for the 1980 (January 1, 1978, to December 31, 1981) window.

28 Appendix 4

USGS sites



ODCA sites


Figure 17.








EXPLANATION

USGS

ODCA

Figure 4 –17. Maps showing national step trends for total nitrogen for the 1986 (January 1, 1984, to December 31, 1987) window.

Results 29

USGS sites



ODCA sites

80 uptrends, 28 significant [*]53 downtrends, 10 significant [*] more significant uptrends or downtrends than expected

Figure 18.








EXPLANATION

USGS

ODCA


30 Appendix 4

USGS sites



ODCA sites


Figure 19.








EXPLANATION

USGS

ODCA


Results

31Table 4–4. Summary of regional step-trend analysis for nitrate.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 10 11 - - - - 13 13 - - - - 34 9 24(9) - 10(1) -1975 16 24 - 14(4) - 10(1) 18 16 - - - - 40 15 21(6) - 19(2) -1976 26 25 11(1) 13(0) 15(3) 12(2) 25 31 12(1) 15(0) 13(2) 16(3) 47 30 17(3) 11(0) 30(3) 19(4)1977 47 29 16(0) 17(3) 31(10) 12(3) 47 35 14(3) 8(1) 33(6) 27(13) 68 36 28(6) 5(2) 40(7) 31(12)1978 49 28 17(4) 15(2) 32(5) 13(3) 48 37 19(3) 7(0) 29(7) 30(12) 70 42 36(9) 7(1) 34(9) 35(11)1979 52 35 27(5) 23(10) 25(5) 12(2) 53 47 28(2) 22(6) 25(5) 25(8) 69 47 34(4) 22(4) 35(6) 25(6)1980 60 41 26(5) 20(0) 34(5) 21(5) 70 43 35(6) 18(5) 35(7) 25(8) 83 39 43(6) 19(8) 40(6) 20(6)1981 52 48 18(2) 17(2) 34(11) 31(7) 53 40 17(3) 17(7) 36(7) 23(6) 63 39 22(6) 19(6) 41(9) 20(6)1982 34 52 12(1) 25(4) 22(3) 27(5) 32 41 8(0) 23(10) 24(4) 18(3) 45 44 15(4) 25(9) 30(5) 19(2)1983 35 73 19(6) 28(5) 16(0) 45(4) 35 42 14(1) 22(9) 21(1) 20(2) 48 43 21(1) 24(12) 27(1) 19(1)1984 34 79 17(7) 37(8) 17(3) 42(7) 36 48 16(2) 18(8) 20(5) 30(3) 48 53 22(3) 26(9) 26(9) 27(3)1985 35 79 15(3) 42(10) 20(2) 37(7) 39 47 23(4) 25(3) 16(5) 22(2) 50 55 29(6) 29(5) 21(10) 26(2)1986 37 73 9(0) 38(7) 28(6) 35(8) 42 44 17(2) 30(8) 25(4) 14(2) 52 58 21(3) 39(4) 31(4) 19(3)1987 40 73 13(1) 30(7) 27(7) 43(8) 42 43 18(4) 33(11) 24(1) 10(0) 51 61 23(4) 38(11) 28(2) 23(1)1988 49 77 20(1) 39(5) 29(7) 38(5) 43 46 28(6) 28(2) 15(2) 18(2) 53 60 31(7) 32(1) 22(4) 28(7)1989 50 79 26(2) 29(2) 24(5) 50(11) 42 26 17(1) 10(1) 25(5) 16(6) 53 35 24(2) 18(1) 29(6) 17(4)1990 41 75 24(4) 26(5) 17(1) 49(11) 50 30 11(4) 10(3) 39(14) 20(14) 64 32 18(5) 14(1) 46(18) 18(9)1991 37 76 22(7) 50(15) 15(5) 26(1) 25 27 11(2) 13(5) 14(1) 14(4) 41 28 17(1) 9(1) 24(5) 19(5)1992 37 94 13(1) 57(19) 24(3) 37(3) 29 37 20(0) 24(9) 9(3) 13(3) 48 37 31(1) 21(6) 17(4) 16(4)1993 28 108 13(3) 62(14) 15(1) 46(5) 21 70 8(1) 42(18) 13(1) 28(2) 39 60 20(3) 33(13) 19(4) 27(2)1994 28 114 16(7) 74(30) 12(1) 40(4) 18 75 - 48(24) - 27(5) 33 64 16(7) 37(14) 17(7) 27(3)1995 25 115 9(1) 60(14) 16(2) 55(18) 34 74 19(1) 30(7) 15(2) 44(12) 50 56 25(2) 26(8) 25(4) 30(6)1996 22 119 8(3) 50(9) 14(8) 69(16) 22 97 11(2) 34(10) 11(3) 63(17) 40 84 16(2) 32(7) 24(2) 52(6)1997 24 113 18(2) 58(13) 6(0) 55(7) 27 98 11(1) 47(12) 16(2) 51(13) 46 83 17(4) 35(9) 29(10) 48(11)1998 26 106 20(5) 61(21) 6(1) 45(5) 31 96 15(0) 48(16) 16(5) 48(13) 52 82 22(3) 38(10) 30(14) 44(14)1999 36 106 15(0) 52(10) 21(1) 54(7) 36 101 9(0) 40(9) 27(4) 61(23) 60 92 14(5) 42(8) 46(8) 50(21)2000 42 101 18(5) 44(8) 24(2) 57(15) 40 95 19(9) 42(4) 21(4) 53(21) 68 104 37(16) 56(7) 31(8) 48(12)2001 51 136 19(5) 66(14) 32(7) 70(20) 45 148 19(4) 49(2) 26(4) 99(28) 78 142 35(7) 59(3) 43(8) 83(20)2002 61 133 39(6) 58(9) 22(6) 75(13) 51 159 27(5) 79(15) 24(2) 80(22) 86 159 45(13) 77(14) 41(8) 82(23)2003 73 134 41(6) 75(16) 32(1) 59(4) 64 165 27(4) 90(18) 37(12) 75(4) 87 171 38(8) 92(18) 49(16) 79(7)2004 64 136 26(5) 64(12) 38(5) 72(14) 67 158 30(9) 90(19) 37(7) 68(19) 91 164 35(8) 95(20) 56(19) 69(18)2005 57 135 33(9) 68(19) 24(7) 67(16) 67 140 35(7) 78(19) 32(4) 62(14) 92 155 42(7) 67(11) 50(11) 88(20)2006 48 130 30(6) 87(20) 18(8) 43(11) 72 141 37(6) 82(19) 35(7) 59(13) 95 155 47(11) 75(12) 48(7) 80(14)2007 50 126 27(4) 79(15) 23(5) 47(9) 70 140 23(6) 78(14) 47(8) 62(18) 98 160 43(16) 81(19) 55(9) 79(15)2008 66 132 43(18) 69(15) 23(5) 63(9) 74 134 38(3) 75(13) 36(6) 59(13) 88 153 47(6) 84(17) 41(11) 69(14)2009 76 140 44(23) 77(10) 32(2) 63(5) 77 139 42(10) 84(30) 35(9) 55(7) 83 158 45(9) 88(31) 38(9) 70(9)2010 71 139 37(11) 63(17) 34(4) 76(13) 76 91 37(6) 41(17) 39(5) 50(10) 84 110 35(6) 44(17) 49(8) 66(18)2011 60 122 32(14) 53(11) 28(3) 69(13) 72 81 38(9) 45(11) 34(9) 36(7) 86 99 42(6) 50(10) 44(11) 49(11)

32 Appendix 4

USGS sites

Step trends for nitrate for 1980 (January 1, 1978, to December 31, 1981) window


ODCA sites


Figure 20.








EXPLANATION

USGS

ODCA

Figure 4 –20. Maps showing national step trends for nitrate for the 1980 (January 1, 1978, to December 31, 1981) window.

Results 33

USGS sites



ODCA sites


Figure 21.








EXPLANATION

USGS

ODCA


34 Appendix 4

USGS sites



ODCA sites


Figure 22.








EXPLANATION

USGS

ODCA


Results 35

Ammonia

Results of the step-trend analysis for ammonia are given in table 4–5. The sparse and variable site coverage for both USGS and ODCA sites made it difficult to make meaningful regional comparisons. For example, the ammonia trends for the 1981 window (fig. 4–23, table 4–5) indicated more downtrends than expected for the ODCA sites for the Central and West regions, but this was due to a large concentration of sites in Kansas. The USGS sites indicated more uptrends than expected for the West region, but site coverage was sparse and did not overlap with the ODCA sites. For the 1986 window (fig. 4–24), there were more downtrends than expected for the ODCA sites for all regions and for the USGS sites for the West region, but the ODCA sites were clustered in a few States, and again there was minimal overlap between USGS and ODCA sites.

Sediment

Suspended Sediment

As described in the “Sediment Parameters of Interest and Harmonization” section of the main body of this report, there are two parameters related to sediment transport—suspended sediment, collected primarily by USGS, and total suspended solids, collected primarily by State agencies. The field methods and analytical methods used for the two parameters differ, and thus concentrations can differ substantially depending on streamflow conditions and sediment properties. Meaningful regional comparisons between USGS and OCDA data, or between suspended sediment and total suspended solids, could not be made; however, a regional step-trend analysis for each parameter is presented here for completeness.

Step-trend results for suspended sediment are given in table 4–6. During the 2000s, there were several distinct and variable regional patterns. For example, for the 2002 window (fig. 4–25), there were many downtrends for the East and Central regions. In 2004 (fig. 4–26), this pattern shifted to mostly uptrends for the same sites. The well-defined geographical boundaries, abrupt nature, and opposite signs of the trends for 2002 and 2004 may indicate either a strong regional environmental cause or perhaps downward bias for those sites during about 2002–4. A similar pattern was not observed in previously discussed parameters, such as total phosphorus or total nitrogen, which would be expected to be positively correlated with suspended sediment concentration. In addition, total suspended solids (described in the “Total Suspended Solids” section of this appendix), which would also be expected to be positively correlated with suspended sediment, did not show a similar pattern. More detailed investigation is required to determine the potential cause for this anomaly.

Total Suspended SolidsStep-trend results for total suspended solids are given in

table 4–7. During the 2000s, there were generally consistent regional trend patterns for ODCA sites across multiple agencies. These patterns are illustrated for the 2002, 2004, and 2005 windows in figures 4–27, 4–28, and 4–29, respectively. The regional patterns, though generally extending across multiple States, were complex and highly variable from window to window; however, in each case, the trends for each State appear to be consistent with trends from one or more neighboring States. Compared to the results for suspended sediment for the 2002 and 2004 windows (figs. 4–25 and 4–26), the regional patterns for total suspended solids differ substantially. Although suspended sediment and total suspended solids concentrations are expected to differ, the strong contrast between the trend patterns may provide further evidence for a downward bias in USGS suspended sediment concentrations during 2002–4.

Major Ions and Salinity

SulfateResults of the step-trend analysis for sulfate are given in

table 4–8. For the 1970s and 1980s, there were too few ODCA sites to make meaningful regional comparisons; however, there may be anomalous step trends for the USGS sites for the 1987 and 1989 windows (figs. 4–30 and 4–31), during which the methods timeline indicates possible upward bias for USGS sulfate concentrations (appendix 3, table 3–4). In particular, for USGS sites in the East region, there were strong uptrends (27 uptrends out of 33, 11 significant) for the 1987 window and strong downtrends (41 downtrends out of 44, 20 significant) for the 1989 window. The ODCA sites, though few, did not indicate a similar pattern, and thus upward bias in USGS sulfate concentrations during this time may be causing the anomalous trends. The same pattern was not evident for the Central and West regions, which may indicate that either the bias was restricted to the East region or that there was too much natural variability for sites in the other regions to detect the bias.

During the 1990s, there were more ODCA sites but too few USGS sites to make meaningful regional comparisons. This is evident for the 1995 window (fig. 4–32). There may have been negative method bias for USGS sites during this time (appendix 3, table 3–4), but without more USGS sites, it is difficult to determine how extensive the bias may have been.

During the 2000s, there was much better site coverage for both USGS and ODCA sites, and the regional trend patterns were generally consistent among the various agencies. For example, for the 2002 window (fig. 4–33, table 4–8), there were mostly downtrends for the USGS sites for the Central and West regions, and these downtrends were generally consistent with the overlapping ODCA sites; however, there were uptrends for the ODCA sites along the gulf coast but no overlapping USGS sites in that area.

36

Appendix 4Table 4–5. Summary of regional step-trend analysis for ammonia.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1976 9 1 - - - - 2 25 - 20(4) - 5(0) 9 26 - 20(4) - 6(0)1977 13 6 - - - - 5 25 - 8(0) - 17(4) 12 26 - 8(0) - 18(4)1978 14 10 - - - - 6 28 - 4(0) - 24(13) 20 32 9(2) 4(0) 11(2) 28(13)1979 14 13 - - - - 5 31 - 18(3) - 13(1) 15 34 - 18(2) - 16(1)1980 27 16 15(3) - 12(0) - 28 33 15(1) 32(24) 13(1) 1(0) 35 31 18(4) 31(23) 17(5) 0(0)1981 23 16 7(0) - 16(4) - 21 36 4(1) 30(16) 17(3) 6(1) 26 36 6(3) 28(15) 20(5) 8(1)1982 18 16 - - - - 11 37 - 20(1) - 17(6) 20 41 4(1) 21(1) 16(5) 20(7)1983 19 22 - 10(0) - 12(2) 14 29 - 10(3) - 19(3) 24 33 12(2) 11(4) 12(1) 22(3)1984 21 21 6(0) 13(2) 15(1) 8(3) 15 29 - 18(6) - 11(1) 24 44 14(1) 27(10) 10(1) 17(2)1985 28 23 14(3) 18(4) 14(1) 5(1) 18 21 - 12(2) - 9(0) 26 37 16(3) 26(4) 10(1) 11(0)1986 32 26 18(4) 19(7) 14(0) 7(0) 20 20 14(6) 17(5) 6(1) 3(0) 29 36 21(8) 29(12) 8(1) 7(0)1987 30 29 19(3) 25(5) 11(1) 4(0) 19 23 - 19(6) - 4(0) 27 39 14(4) 28(7) 13(1) 11(1)1988 29 32 23(6) 21(3) 6(2) 11(0) 22 21 14(2) 9(0) 8(1) 12(0) 31 35 16(3) 15(2) 15(1) 20(3)1989 25 27 20(9) 20(3) 5(0) 7(1) 22 16 15(2) - 7(0) - 33 29 21(3) 17(1) 12(2) 12(2)1990 24 27 17(5) 15(2) 7(1) 12(1) 27 16 22(5) - 5(0) - 38 24 27(9) 15(6) 11(1) 9(2)1991 22 29 14(3) 13(2) 8(1) 16(1) 21 14 10(0) - 11(0) - 31 21 15(1) 9(0) 16(2) 12(2)1992 23 31 10(2) 17(3) 13(2) 14(1) 20 14 8(1) - 12(2) - 30 18 12(1) - 18(2) -1993 19 28 - 16(3) - 12(0) 20 12 12(0) - 8(4) - 32 14 18(1) - 14(6) -1994 20 27 12(3) 19(1) 8(1) 8(3) 12 15 - - - - 17 18 - - - -1995 18 28 - 17(3) - 11(0) 20 16 15(3) - 5(0) - 24 20 19(4) 8(0) 5(0) 12(5)1996 13 25 - 13(1) - 12(1) 13 25 - 9(1) - 16(8) 16 33 - 14(1) - 19(8)1997 14 24 - 16(2) - 8(0) 11 26 - 10(0) - 16(0) 14 35 - 10(0) - 25(9)1998 13 20 - 14(0) - 6(0) 7 27 - 23(14) - 4(1) 11 36 - 23(14) - 13(9)1999 12 20 - 9(0) - 11(0) 4 29 - 22(7) - 7(0) 8 42 - 23(7) - 19(2)2000 17 25 - 13(2) - 12(1) 5 30 - 14(0) - 16(2) 11 50 - 22(3) - 28(3)2001 20 45 11(4) 23(3) 9(0) 22(3) 7 16 - - - - 13 36 - 18(2) - 18(3)2002 18 52 - 20(2) - 32(8) 6 17 - - - - 10 45 - 21(4) - 24(3)2003 22 51 15(1) 25(2) 7(0) 26(2) 12 20 - 13(2) - 7(1) 13 53 - 35(8) - 18(4)2004 16 52 - 23(2) - 29(4) 15 20 - 8(1) - 12(0) 19 60 - 31(8) - 29(2)2005 17 55 - 35(7) - 20(2) 20 12 8(2) - 12(0) - 25 51 10(2) 17(2) 15(0) 34(2)2006 20 43 10(3) 31(6) 10(0) 12(0) 19 9 - - - - 24 46 13(3) 25(7) 11(0) 21(6)2007 23 39 12(3) 22(2) 11(1) 17(0) 17 23 - 6(0) - 17(2) 22 51 15(0) 19(3) 7(0) 32(7)2008 27 49 20(3) 29(3) 7(1) 20(2) 14 28 - 4(0) - 24(2) 20 55 7(0) 20(6) 13(5) 35(5)2009 32 50 13(3) 28(10) 19(4) 22(2) 14 35 - 9(0) - 26(4) 19 59 - 24(1) - 35(4)2010 26 66 10(2) 25(3) 16(3) 41(4) 13 19 - - - - 19 27 - 15(2) - 12(2)2011 23 48 14(6) 17(5) 9(1) 31(8) 11 11 - - - - 20 19 8(1) - 12(0) -

Results 37

USGS sites

Step trends for ammonia for 1981 (January 1, 1979, to December 31, 1982) window


ODCA sites


Figure 23.








EXPLANATION

USGS

ODCA

Figure 4 –23. Maps showing national step trends for ammonia for the 1981 (January 1, 1979, to December 31, 1982) window.

38 Appendix 4

USGS sites

Step trends for ammonia for 1986 (January 1, 1984, to December 31, 1987) window


ODCA sites


Figure 24.








EXPLANATION

USGS

ODCA

Figure 4 –24. Maps showing national step trends for ammonia for the 1986 (January 1, 1984, to December 31, 1987) window.

Results

39Table 4–6. Summary of regional step-trend analysis for suspended sediment concentration.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 1 1 - - - - 13 1 - - - - 22 0 10(2) - 12(4) -1975 2 2 - - - - 17 2 - - - - 31 0 19(4) - 12(3) -1976 10 2 - - - - 20 2 10(0) - 10(1) - 32 0 20(7) - 12(1) -1977 22 2 12(5) - 10(2) - 36 2 24(7) - 12(3) - 58 0 38(10) - 20(5) -1978 21 2 13(0) - 8(2) - 35 3 20(5) - 15(2) - 69 1 31(13) - 38(8) -1979 23 2 14(5) - 9(2) - 40 3 18(5) - 22(3) - 69 1 25(5) - 44(14) -1980 31 2 16(5) - 15(1) - 49 4 25(11) - 24(2) - 73 2 37(11) - 36(6) -1981 24 2 15(3) - 9(1) - 35 5 14(0) - 21(3) - 56 3 31(5) - 25(4) -1982 9 0 - - - - 17 3 - - - - 39 3 13(1) - 26(2) -1983 8 0 - - - - 19 3 - - - - 27 3 13(3) - 14(2) -1984 5 0 - - - - 20 3 13(2) - 7(2) - 27 3 15(2) - 12(4) -1985 10 0 - - - - 18 3 - - - - 26 3 9(4) - 17(5) -1986 15 0 - - - - 21 2 11(2) - 10(1) - 29 2 13(4) - 16(2) -1987 17 0 - - - - 20 3 8(1) - 12(1) - 27 3 12(2) - 15(2) -1988 17 0 - - - - 23 2 13(1) - 10(0) - 31 2 19(3) - 12(1) -1989 16 0 - - - - 25 2 14(2) - 11(2) - 44 2 25(7) - 19(2) -1990 15 0 - - - - 23 2 11(5) - 12(3) - 43 2 19(10) - 24(7) -1991 16 0 - - - - 17 1 - - - - 39 1 12(5) - 27(8) -1992 17 5 - - - - 17 1 - - - - 41 1 26(7) - 15(4) -1993 15 5 - - - - 15 1 - - - - 43 1 25(7) - 18(11) -1994 9 5 - - - - 10 1 - - - - 28 1 10(3) - 18(8) -1995 12 5 - - - - 17 1 - - - - 33 1 19(6) - 14(3) -1996 15 5 - - - - 19 1 - - - - 34 1 12(5) - 22(4) -1997 13 0 - - - - 20 1 7(3) - 13(6) - 36 1 11(2) - 25(7) -1998 16 0 - - - - 31 1 11(3) - 20(5) - 57 1 26(8) - 31(6) -1999 24 0 18(3) - 6(2) - 40 1 27(7) - 13(3) - 69 1 41(12) - 28(5) -2000 29 1 8(2) - 21(7) - 41 2 23(6) - 18(4) - 72 2 40(10) - 32(9) -2001 34 6 15(7) - 19(5) - 48 2 26(4) - 22(6) - 75 2 45(8) - 30(4) -2002 42 6 24(10) - 18(4) - 50 2 36(19) - 14(4) - 80 2 55(23) - 25(3) -2003 42 6 22(7) - 20(3) - 55 2 40(12) - 15(2) - 80 2 50(12) - 30(3) -2004 41 5 18(3) - 23(4) - 56 1 27(5) - 29(14) - 80 2 37(7) - 43(19) -2005 30 5 18(6) - 12(3) - 55 1 24(9) - 31(7) - 83 1 43(8) - 40(8) -2006 21 3 11(4) - 10(3) - 60 1 30(12) - 30(6) - 93 1 39(12) - 54(12) -2007 23 3 12(4) - 11(1) - 55 1 29(6) - 26(8) - 88 6 42(6) - 46(12) -2008 27 3 19(9) - 8(2) - 51 1 19(5) - 32(7) - 87 5 43(7) - 44(8) -2009 30 3 12(4) - 18(4) - 51 1 22(11) - 29(11) - 84 5 51(20) - 33(14) -2010 35 6 16(3) - 19(6) - 52 0 26(7) - 26(4) - 78 4 43(11) - 35(8) -2011 33 3 19(3) - 14(6) - 60 0 30(11) - 30(10) - 87 4 40(14) - 47(16) -

40 Appendix 4

USGS sites

Step trends for suspended sediment for 2002 (January 1, 2000, to December 31, 2003) window


ODCA sites


Figure 25.








EXPLANATION

USGS

ODCA

Figure 4 –25. Maps showing national step trends for suspended sediment for the 2002 (January 1, 2000, to December 31, 2003) window.

Results 41

USGS sites

Step trends for suspended sediment for 2004 (January 1, 2002, to December 31, 2005) window


ODCA sites


Figure 26.








EXPLANATION

USGS

ODCA

Figure 4 –26. Maps showing national step trends for suspended sediment for the 2004 (January 1, 2002, to December 31, 2005) window.

42

Appendix 4Table 4–7. Summary of regional step-trend analysis for total suspended solids.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1976 0 3 - - - - 0 25 - 21(8) - 4(1) 5 28 - 24(8) - 4(1)1977 1 4 - - - - 0 31 - 25(12) - 6(0) 7 40 - 28(11) - 12(0)1978 1 3 - - - - 0 32 - 15(0) - 17(2) 6 45 - 24(2) - 21(2)1979 1 13 - - - - 2 36 - 10(0) - 26(7) 6 48 - 16(2) - 32(5)1980 4 14 - - - - 16 25 - 9(0) - 16(1) 17 40 - 18(2) - 22(3)1981 4 15 - - - - 15 23 - 12(1) - 11(1) 14 43 - 25(4) - 18(0)1982 6 21 - 8(2) - 13(3) 18 24 - 9(1) - 15(5) 17 47 - 25(2) - 22(6)1983 6 44 - 14(4) - 30(1) 23 24 9(1) 13(5) 14(3) 11(3) 22 48 10(1) 22(4) 12(2) 26(6)1984 6 53 - 28(8) - 25(7) 28 37 15(3) 27(8) 13(3) 10(3) 27 58 14(2) 34(6) 13(3) 24(4)1985 6 55 - 29(2) - 26(5) 31 43 16(2) 21(5) 15(2) 22(5) 29 65 16(2) 37(8) 13(2) 28(1)1986 6 52 - 37(6) - 15(3) 33 44 16(2) 16(4) 17(4) 28(6) 31 69 15(3) 28(5) 16(4) 41(8)1987 7 52 - 34(6) - 18(1) 34 46 12(1) 23(5) 22(1) 23(6) 32 71 12(2) 34(3) 20(1) 37(7)1988 7 55 - 26(3) - 29(3) 29 49 18(4) 31(4) 11(1) 18(1) 28 72 18(3) 39(5) 10(1) 33(5)1989 7 56 - 20(2) - 36(10) 28 29 13(0) 12(2) 15(1) 17(4) 29 47 14(0) 20(3) 15(1) 27(5)1990 7 56 - 13(2) - 43(6) 29 29 11(0) 13(2) 18(3) 16(4) 31 41 15(0) 17(1) 16(4) 24(6)1991 7 60 - 28(4) - 32(2) 12 27 - 13(5) - 14(3) 17 37 - 15(2) - 22(4)1992 9 63 - 41(11) - 22(0) 13 31 - 21(5) - 10(1) 18 36 - 21(1) - 15(2)1993 3 71 - 38(12) - 33(5) 11 60 - 38(13) - 22(4) 18 58 - 40(4) - 18(2)1994 4 76 - 35(10) - 41(9) 10 64 - 40(20) - 24(8) 14 66 - 33(16) - 33(10)1995 4 83 - 43(11) - 40(10) 13 67 - 44(16) - 23(7) 17 68 - 37(10) - 31(6)1996 4 68 - 33(6) - 35(10) 5 72 - 32(5) - 40(9) 8 89 - 30(2) - 59(13)1997 7 71 - 32(6) - 39(7) 7 70 - 28(3) - 42(12) 10 86 - 45(2) - 41(9)1998 7 65 - 39(7) - 26(4) 6 69 - 42(11) - 27(10) 10 89 - 52(12) - 37(10)1999 5 63 - 34(13) - 29(4) 8 78 - 38(9) - 40(8) 11 106 - 55(9) - 51(8)2000 5 70 - 50(18) - 20(3) 6 79 - 52(16) - 27(4) 9 111 - 71(11) - 40(3)2001 5 96 - 54(13) - 42(10) 5 106 - 55(22) - 51(11) 8 156 - 84(23) - 72(7)2002 9 101 - 54(14) - 47(8) 4 113 - 62(13) - 51(11) 7 164 - 75(8) - 89(15)2003 14 107 - 51(18) - 56(8) 8 119 - 69(19) - 50(7) 9 174 - 91(8) - 83(13)2004 6 124 - 68(13) - 56(13) 12 127 - 77(24) - 50(14) 15 167 - 107(28) - 60(13)2005 7 124 - 71(22) - 53(15) 11 129 - 59(13) - 70(25) 14 159 - 81(9) - 78(16)2006 7 124 - 53(11) - 71(12) 13 128 - 54(7) - 74(17) 14 164 - 77(9) - 87(16)2007 4 112 - 44(5) - 68(15) 12 106 - 51(6) - 55(14) 14 139 - 77(11) - 62(8)2008 11 126 - 70(12) - 56(13) 18 95 - 46(9) - 49(11) 19 126 - 64(14) - 62(8)2009 15 122 - 62(10) - 60(10) 22 95 10(1) 48(12) 12(1) 47(13) 23 131 9(1) 71(11) 14(1) 60(13)2010 21 123 10(5) 68(19) 11(1) 55(11) 19 75 - 52(12) - 23(2) 20 110 11(2) 54(8) 9(2) 56(13)2011 24 106 18(5) 72(24) 6(0) 34(3) 15 61 - 32(7) - 29(12) 14 79 - 36(1) - 43(17)

Results 43

USGS sites

Step trends for total suspended solids for 2002 (January 1, 2000, to December 31, 2003) window


ODCA sites


Figure 27.








EXPLANATION

USGS

ODCA

Figure 4 –27. Maps showing national step trends for total suspended solids for the 2002 (January 1, 2000, to December 31, 2003) window.

44 Appendix 4

USGS sites



ODCA sites


Figure 28.








EXPLANATION

USGS

ODCA


Results 45

USGS sites




Figure 29.

ODCA sites








EXPLANATION

USGS

ODCA


46

Appendix 4Table 4–8. Summary of regional step-trend analysis for sulfate.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 22 3 15(9) - 7(0) - 32 1 18(6) - 14(1) - 72 1 48(17) - 24(4) -1975 19 3 - - - - 39 1 20(4) - 19(2) - 81 0 43(11) - 38(6) -1976 19 3 - - - - 45 1 18(6) - 27(6) - 87 2 42(13) - 45(8) -1977 33 7 8(0) - 25(3) - 74 1 27(4) - 47(10) - 115 4 49(8) - 66(22) -1978 30 11 12(1) - 18(2) - 74 1 23(4) - 51(17) - 124 3 39(11) - 85(27) -1979 37 13 22(6) - 15(4) - 82 2 44(10) - 38(10) - 124 5 61(13) - 63(18) -1980 47 15 20(4) - 27(6) - 86 1 50(15) - 36(12) - 125 5 74(26) - 51(14) -1981 47 14 20(4) - 27(5) - 69 1 46(14) - 23(1) - 102 7 65(20) - 37(6) -1982 34 16 11(4) - 23(7) - 46 1 33(8) - 13(3) - 84 9 54(14) - 30(7) -1983 36 16 15(2) - 21(3) - 43 3 17(1) - 26(4) - 76 13 34(3) - 42(5) -1984 33 16 19(3) - 14(3) - 44 4 20(3) - 24(6) - 70 21 33(4) 10(2) 37(10) 11(2)1985 28 19 18(1) - 10(0) - 37 3 25(4) - 12(3) - 61 24 35(7) 12(3) 26(6) 12(1)1986 30 18 12(2) - 18(5) - 39 3 23(8) - 16(2) - 61 23 34(10) 12(2) 27(5) 11(1)1987 33 18 6(2) - 27(11) - 42 5 21(2) - 21(4) - 65 24 30(7) 10(1) 35(8) 14(5)1988 37 22 20(5) 11(0) 17(2) 11(0) 43 7 19(2) - 24(2) - 71 24 34(8) 12(1) 37(5) 12(4)1989 44 22 41(20) 12(1) 3(0) 10(1) 44 7 26(4) - 18(4) - 69 22 39(6) 9(4) 30(7) 13(2)1990 31 24 20(2) 9(1) 11(1) 15(2) 45 7 23(5) - 22(6) - 78 24 37(8) 11(3) 41(9) 13(3)1991 25 44 11(4) 23(3) 14(3) 21(4) 19 8 - - - - 46 23 22(5) 8(1) 24(6) 15(3)1992 24 47 13(2) 26(7) 11(2) 21(4) 20 12 11(2) - 9(0) - 43 20 23(7) 4(1) 20(2) 16(5)1993 14 57 - 29(7) - 28(5) 17 12 - - - - 41 20 18(5) 9(0) 23(8) 11(2)1994 14 51 - 35(7) - 16(4) 11 11 - - - - 26 21 18(4) 10(3) 8(2) 11(0)1995 11 52 - 28(7) - 24(9) 14 10 - - - - 30 21 19(5) 9(2) 11(0) 12(1)1996 9 53 - 21(3) - 32(9) 8 25 - 19(11) - 6(1) 22 36 10(3) 24(12) 12(2) 12(3)1997 10 55 - 37(8) - 18(1) 12 25 - 18(3) - 7(2) 31 38 16(5) 23(7) 15(4) 15(3)1998 11 48 - 38(16) - 10(2) 17 29 - 14(4) - 15(5) 37 39 21(10) 18(4) 16(3) 21(3)1999 17 50 - 25(2) - 25(5) 30 34 15(3) 20(9) 15(1) 14(5) 49 38 28(6) 18(9) 21(2) 20(2)2000 27 37 14(1) 18(4) 13(2) 19(4) 35 39 13(3) 23(8) 22(4) 16(2) 55 39 24(6) 21(5) 31(8) 18(4)2001 31 45 12(3) 21(4) 19(2) 24(6) 43 70 24(10) 41(12) 19(5) 29(8) 68 91 43(14) 52(10) 25(6) 39(8)2002 36 50 25(5) 32(13) 11(1) 18(7) 41 72 28(11) 44(20) 13(2) 28(8) 66 86 45(15) 44(13) 21(5) 42(7)2003 43 51 29(9) 36(11) 14(0) 15(5) 54 98 21(5) 46(14) 33(4) 52(8) 73 116 36(10) 46(12) 37(10) 70(11)2004 46 57 25(4) 37(11) 21(1) 20(4) 52 104 25(7) 51(10) 27(4) 53(19) 70 111 32(9) 46(7) 38(5) 65(17)2005 37 58 14(4) 33(14) 23(3) 25(10) 44 88 23(1) 46(16) 21(4) 42(10) 57 93 23(3) 39(8) 34(6) 54(10)2006 33 53 21(3) 40(15) 12(1) 13(3) 53 89 25(5) 61(26) 28(9) 28(3) 62 100 25(7) 45(15) 37(11) 55(6)2007 31 54 17(8) 33(13) 14(3) 21(0) 44 94 24(10) 59(22) 20(2) 35(3) 58 95 32(12) 54(16) 26(2) 41(5)2008 31 48 20(8) 32(13) 11(1) 16(5) 51 87 34(4) 55(11) 17(1) 32(9) 61 95 40(6) 57(8) 21(5) 38(9)2009 33 51 24(7) 24(2) 9(0) 27(11) 55 86 25(5) 37(10) 30(7) 49(11) 60 95 30(5) 44(10) 30(8) 51(8)2010 35 39 22(9) 13(7) 13(2) 26(9) 55 57 22(7) 26(12) 33(10) 31(5) 61 49 26(7) 19(7) 35(11) 30(4)2011 22 30 16(5) 9(4) 6(1) 21(8) 52 36 27(8) 13(4) 25(7) 23(7) 69 36 36(9) 12(1) 33(8) 24(7)

Results 47

USGS sites

Step trends for sulfate for 1987 (January 1, 1985, to December 31, 1988) window



Figure 30.

ODCA sites








EXPLANATION

USGS

ODCA

Figure 4 –30. Maps showing national step trends for sulfate for the 1987 (January 1, 1985, to December 31, 1988) window.

48 Appendix 4

USGS sites




Figure 31.

ODCA sites








EXPLANATION

USGS

ODCA


Results 49

USGS sites




Figure 32.

ODCA sites








EXPLANATION

USGS

ODCA


50 Appendix 4

USGS sites




Figure 33.

ODCA sites








EXPLANATION

USGS

ODCA


Results 51

Chloride

Results of the step-trend analysis for chloride are given in table 4–9. With the exception of the mid-1990s when few USGS sites could be analyzed, there was generally overall consistency between the regional trends for USGS and ODCA sites. For example, for the 1985 window (fig. 4–34), there were many uptrends for the East region for both USGS and ODCA sites. For the 1995 window (fig. 4–35), there were many uptrends for ODCA sites in the northeast and south-central United States but too few USGS sites to verify the uptrends. For the 2001 window (fig. 4–36), there were many uptrends for the East and Central regions for both USGS and ODCA sites.

Sodium, Potassium, Magnesium, Calcium, and Total Dissolved Solids

Results of the step-trend analysis for sodium, potassium, magnesium, calcium, and total dissolved solids are given in tables 4–10 to 4–14, respectively. Site coverage for these parameters was much sparser compared to the previous parameters, especially for ODCA sites, so few direct comparisons between USGS and ODCA sites could be made. Furthermore, the USGS method timeline analysis indicated no notable method changes (appendix 3, table 3–4). Detailed examination of the trend results from tables 4–10 to 4–14 and the trend maps (not shown) indicated no apparent anomalous trends for any of the parameters. The few instances when the tables may indicate conflicting results between USGS and ODCA sites were probably caused by differences in site locations and densities; however, because of the sparse site coverage, it is likely that any anomalous trends that did occur would not be readily detected.

Carbon

AlkalinityResults of the step-trend analysis for alkalinity are

given in table 4–15. Detailed examination of the trend results indicated general overall consistency between the regional trends for USGS and ODCA sites, with no obvious anomalous patterns. For example, for the 1985 window (fig. 4–37), there were more uptrends than expected for the USGS sites for the East (22 uptrends out of 29, 10 significant) and Central (26 uptrends out of 38, 9 significant) regions. The ODCA sites also had mostly uptrends for the East (24 out of 38 uptrends, 5 significant) region, but there were few ODCA sites in the upper Midwest where an abundance of uptrends were evident for USGS sites. For the 2000 window (fig. 4–38), there were many more uptrends than expected for the East region for both USGS and ODCA sites, along with mostly downtrends for the West region.

Total Organic CarbonTotal organic carbon was the only carbon-related parameter

besides alkalinity for which site coverage was minimally sufficient to make regional comparisons. Results of the step-trend analysis for that parameter are given in table 4–16. There were too few USGS sites to make regional comparisons for all but a few cases; however, examination of the trends for the ODCA sites for the later windows indicated general agreement between the regional trends from the various agencies. For example, the total organic carbon trends for the 2004 window (fig. 4–39) indicated widespread downtrends for the ODCA sites for the East region and widespread uptrends for the Central and West regions.

52

Appendix 4Table 4–9. Summary of regional step-trend analysis for chloride.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 21 5 11(1) - 10(0) - 31 11 17(1) - 14(3) - 73 27 45(11) 16(6) 28(6) 11(1)1975 18 5 - - - - 38 16 24(7) - 14(2) - 81 19 49(12) - 32(8) -1976 25 5 7(0) - 18(5) - 43 21 25(4) 11(1) 18(2) 10(5) 88 26 50(12) 12(1) 38(9) 14(5)1977 43 8 10(1) - 33(11) - 71 21 23(1) 14(3) 48(13) 7(2) 115 28 44(3) 15(3) 71(19) 13(2)1978 40 13 16(1) - 24(8) - 73 22 20(3) 13(6) 53(15) 9(0) 125 31 50(13) 20(7) 75(25) 11(0)1979 48 14 32(12) - 16(2) - 81 21 48(10) 10(5) 33(9) 11(4) 124 30 69(16) 17(7) 55(11) 13(4)1980 53 15 30(4) - 23(2) - 84 21 39(7) 7(0) 45(8) 14(4) 122 30 62(10) 12(3) 60(10) 18(6)1981 53 14 23(3) - 30(7) - 67 21 33(10) 9(2) 34(6) 12(5) 99 32 55(11) 14(4) 44(8) 18(5)1982 34 16 7(3) - 27(4) - 44 23 24(5) 17(2) 20(4) 6(0) 77 35 42(8) 22(4) 35(5) 13(4)1983 37 18 15(2) - 22(4) - 39 26 15(3) 18(4) 24(5) 8(0) 69 38 31(6) 23(6) 38(5) 15(4)1984 33 18 8(1) - 25(7) - 40 28 20(2) 13(3) 20(4) 15(6) 63 41 34(2) 22(4) 29(8) 19(5)1985 28 21 8(0) 0(0) 20(5) 21(9) 33 27 19(3) 10(3) 14(4) 17(8) 55 42 27(6) 21(6) 28(7) 21(7)1986 31 19 12(1) - 19(2) - 35 26 13(4) 16(4) 22(2) 10(3) 55 43 24(8) 29(10) 31(4) 14(3)1987 33 7 11(3) - 22(9) - 40 27 11(2) 20(4) 29(10) 7(1) 62 43 25(6) 29(7) 37(11) 14(1)1988 37 7 19(4) - 18(0) - 38 26 17(5) 12(5) 21(2) 14(5) 66 43 33(8) 18(4) 33(3) 25(8)1989 45 7 32(7) - 13(2) - 41 6 21(2) - 20(3) - 63 22 30(3) 11(3) 33(7) 11(2)1990 32 9 14(2) - 18(1) - 41 7 19(3) - 22(8) - 72 23 26(3) 13(2) 46(15) 10(4)1991 25 28 8(2) 24(11) 17(2) 4(1) 18 9 - - - - 45 25 17(2) 11(0) 28(5) 14(1)1992 23 29 7(0) 15(5) 16(3) 14(7) 19 12 - - - - 44 22 22(5) 8(3) 22(6) 14(2)1993 14 41 - 15(1) - 26(12) 15 32 - 16(1) - 16(2) 42 44 27(5) 23(1) 15(4) 21(1)1994 13 45 - 19(9) - 26(16) 11 40 - 14(4) - 26(10) 31 47 19(9) 21(7) 12(2) 26(4)1995 10 49 - 22(12) - 27(12) 14 43 - 13(2) - 30(14) 36 48 16(5) 20(3) 20(4) 28(11)1996 8 53 - 18(3) - 35(12) 8 63 - 18(4) - 45(17) 28 68 17(6) 25(4) 11(3) 43(13)1997 9 62 - 36(10) - 26(3) 12 70 - 24(7) - 46(18) 34 78 19(6) 31(6) 15(4) 47(17)1998 11 69 - 40(9) - 29(4) 17 78 - 37(12) - 41(10) 45 77 22(5) 44(13) 23(6) 33(8)1999 17 65 - 18(1) - 47(14) 30 86 12(0) 33(10) 18(4) 53(20) 57 84 27(4) 38(10) 30(10) 46(11)2000 27 46 6(0) 18(1) 21(10) 28(14) 35 87 11(1) 30(6) 24(12) 57(24) 63 86 33(6) 39(7) 30(11) 47(12)2001 31 67 3(0) 27(6) 28(15) 40(16) 44 131 15(3) 53(6) 29(4) 78(23) 77 133 36(7) 61(7) 41(5) 72(12)2002 35 68 14(4) 34(10) 21(8) 34(8) 41 131 22(7) 59(12) 19(2) 72(14) 73 133 41(10) 63(9) 32(4) 70(15)2003 43 65 16(1) 30(6) 27(4) 35(8) 51 155 17(0) 59(9) 34(9) 96(29) 77 164 28(2) 65(13) 49(17) 99(29)2004 45 68 22(0) 27(4) 23(7) 41(13) 48 159 18(0) 75(13) 30(9) 84(28) 74 162 25(1) 74(11) 49(16) 88(21)2005 35 64 14(4) 30(14) 21(7) 34(11) 40 139 23(2) 56(18) 17(2) 83(20) 62 151 26(3) 58(12) 36(8) 93(23)2006 30 66 23(12) 39(22) 7(2) 27(7) 48 145 20(4) 71(26) 28(7) 74(18) 68 164 32(11) 75(16) 36(11) 89(23)2007 28 58 18(8) 35(13) 10(3) 23(6) 40 143 11(2) 75(16) 29(4) 68(19) 64 162 24(6) 83(15) 40(5) 79(22)2008 28 68 12(4) 37(17) 16(8) 31(5) 46 126 23(5) 75(25) 23(0) 51(16) 65 152 38(8) 76(22) 27(3) 76(21)2009 30 70 11(2) 20(5) 19(8) 50(16) 48 122 30(5) 66(26) 18(1) 56(14) 63 143 39(7) 75(28) 24(4) 68(13)2010 33 65 10(4) 21(4) 23(14) 44(17) 49 95 20(5) 50(15) 29(12) 45(7) 65 101 29(7) 53(14) 36(11) 48(8)2011 27 63 18(8) 29(8) 9(3) 34(12) 49 63 27(7) 33(6) 22(4) 30(9) 69 73 40(11) 38(8) 29(3) 35(8)

Results 53

USGS sites

Step trends for chloride for 1985 (January 1, 1983, to December 31, 1986) window



Figure 34.

ODCA sites








EXPLANATION

USGS

ODCA

Figure 4 –34. Maps showing national step trends for chloride for the 1985 (January 1, 1983, to December 31, 1986) window.

54 Appendix 4

USGS sites




Figure 35.

ODCA sites








EXPLANATION

USGS

ODCA


Results 55

USGS sites




Figure 36.

ODCA sites








EXPLANATION

USGS

ODCA


56

Appendix 4Table 4–10. Summary of regional step-trend analysis for sodium.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 14 0 - - - - 29 0 14(3) - 15(5) - 62 0 32(7) - 30(8) -1975 11 0 - - - - 35 4 20(4) - 15(5) - 74 4 41(9) - 33(10) -1976 15 0 - - - - 45 0 27(6) - 18(4) - 92 0 59(18) - 33(9) -1977 31 1 7(1) - 24(9) - 74 0 32(5) - 42(16) - 119 0 56(9) - 63(16) -1978 30 1 11(3) - 19(3) - 75 0 26(4) - 49(13) - 128 0 52(15) - 76(20) -1979 39 1 20(9) - 19(3) - 83 0 38(11) - 45(11) - 127 1 64(15) - 63(15) -1980 48 1 22(5) - 26(4) - 80 0 36(6) - 44(10) - 122 0 59(14) - 63(13) -1981 49 0 21(4) - 28(9) - 62 0 32(7) - 30(4) - 98 0 45(11) - 53(7) -1982 23 0 8(0) - 15(6) - 34 0 24(4) - 10(3) - 72 0 47(12) - 25(6) -1983 24 0 13(3) - 11(2) - 30 0 9(2) - 21(4) - 62 0 32(3) - 30(5) -1984 23 2 10(4) - 13(5) - 36 1 18(0) - 18(6) - 58 14 28(1) - 30(7) -1985 18 0 - - - - 25 1 12(2) - 13(0) - 45 18 22(6) - 23(1) -1986 21 0 11(0) - 10(3) - 31 2 17(6) - 14(1) - 49 22 28(9) 11(6) 21(1) 11(2)1987 23 0 11(2) - 12(3) - 35 3 15(1) - 20(7) - 55 23 24(5) 9(2) 31(8) 14(3)1988 27 0 10(3) - 17(4) - 41 1 17(1) - 24(7) - 67 19 29(3) - 38(11) -1989 35 0 24(5) - 11(1) - 44 1 26(5) - 18(3) - 69 18 33(6) - 36(9) -1990 22 0 14(0) - 8(0) - 44 1 21(6) - 23(5) - 78 16 34(9) - 44(10) -1991 17 0 - - - - 16 1 - - - - 44 15 24(3) - 20(3) -1992 16 0 - - - - 16 3 - - - - 40 13 17(4) - 23(2) -1993 8 0 - - - - 12 3 - - - - 38 12 19(4) - 19(6) -1994 13 0 - - - - 6 4 - - - - 20 12 14(4) - 6(0) -1995 10 0 - - - - 10 3 - - - - 25 12 14(4) - 11(3) -1996 9 0 - - - - 8 1 - - - - 22 10 10(5) - 12(3) -1997 10 0 - - - - 12 7 - - - - 28 16 13(2) - 15(7) -1998 12 0 - - - - 17 7 - - - - 37 19 18(5) - 19(4) -1999 18 0 - - - - 31 8 13(3) - 18(6) - 49 23 27(8) 14(4) 22(6) 9(1)2000 23 0 6(0) - 17(6) - 27 11 9(1) - 18(6) - 37 18 16(3) - 21(7) -2001 15 4 - - - - 29 32 19(7) 14(2) 10(0) 18(4) 41 52 27(9) 21(2) 14(0) 31(6)2002 14 4 - - - - 22 30 15(5) 13(5) 7(0) 17(7) 36 51 24(6) 29(9) 12(0) 22(8)2003 16 3 - - - - 25 31 7(0) 9(1) 18(4) 22(8) 39 57 10(1) 19(3) 29(10) 38(10)2004 19 2 - - - - 26 33 10(1) 16(3) 16(5) 17(6) 38 61 13(3) 25(3) 25(5) 36(11)2005 20 13 9(1) - 11(4) - 25 20 14(2) 11(3) 11(2) 9(0) 36 50 13(1) 22(5) 23(3) 28(6)2006 19 16 - - - - 28 25 11(2) 20(9) 17(5) 5(0) 41 57 18(4) 41(15) 23(6) 16(0)2007 19 18 - - - - 22 27 8(0) 20(3) 14(4) 7(2) 37 47 17(2) 34(9) 20(4) 13(2)2008 19 13 - - - - 23 31 14(3) 9(3) 9(1) 22(10) 35 51 27(7) 15(4) 8(3) 36(11)2009 21 11 8(1) - 13(3) - 29 29 15(2) 6(1) 14(2) 23(10) 38 64 25(3) 27(7) 13(3) 37(13)2010 25 10 9(2) - 16(5) - 33 29 11(1) 11(1) 22(8) 18(3) 44 54 18(3) 29(8) 26(7) 25(3)2011 24 7 14(4) - 10(3) - 32 28 11(0) 12(5) 21(7) 16(3) 47 51 20(4) 24(8) 27(7) 27(3)

Results

57Table 4–11. Summary of regional step-trend analysis for potassium.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 13 0 - - - - 28 0 14(3) - 14(2) - 60 0 24(7) - 36(7) -1975 10 0 - - - - 34 4 17(2) - 17(4) - 72 4 34(7) - 38(7) -1976 14 0 - - - - 44 0 28(7) - 16(2) - 90 0 61(15) - 29(6) -1977 32 1 11(0) - 21(4) - 72 0 36(6) - 36(8) - 116 0 66(15) - 50(11) -1978 31 1 11(3) - 20(2) - 72 0 27(4) - 45(16) - 124 0 51(14) - 73(26) -1979 39 1 27(11) - 12(0) - 80 0 30(7) - 50(13) - 124 1 50(8) - 74(16) -1980 48 1 32(8) - 16(0) - 78 0 44(10) - 34(5) - 119 0 59(15) - 60(5) -1981 48 0 32(4) - 16(0) - 62 0 41(9) - 21(1) - 97 0 59(19) - 38(1) -1982 24 0 15(2) - 9(2) - 32 0 17(6) - 15(2) - 70 0 37(9) - 33(3) -1983 25 0 9(0) - 16(2) - 28 0 14(2) - 14(1) - 61 0 34(4) - 27(2) -1984 24 2 10(0) - 14(3) - 34 1 16(4) - 18(2) - 58 14 29(5) - 29(5) -1985 18 0 - - - - 24 1 13(1) - 11(1) - 46 15 28(4) - 18(2) -1986 21 0 6(1) - 15(1) - 28 2 20(0) - 8(4) - 49 20 30(1) 11(1) 19(6) 9(0)1987 23 0 12(1) - 11(0) - 34 3 26(7) - 8(0) - 56 21 38(9) 15(3) 18(2) 6(0)1988 27 0 9(2) - 18(3) - 40 1 32(6) - 8(0) - 67 18 48(9) - 19(3) -1989 35 0 11(0) - 24(6) - 43 1 23(5) - 20(4) - 69 17 33(5) - 36(4) -1990 21 0 9(0) - 12(1) - 43 1 18(2) - 25(6) - 78 14 39(5) - 39(7) -1991 16 0 - - - - 15 1 - - - - 43 14 18(2) - 25(3) -1992 16 0 - - - - 15 3 - - - - 40 13 22(2) - 18(1) -1993 8 0 - - - - 10 3 - - - - 36 12 21(3) - 15(3) -1994 13 0 - - - - 6 8 - - - - 20 13 16(4) - 4(0) -1995 10 0 - - - - 10 7 - - - - 25 12 14(2) - 11(1) -1996 9 0 - - - - 8 16 - - - - 22 22 7(3) 3(1) 15(0) 19(11)1997 10 0 - - - - 12 22 - 5(1) - 17(8) 28 28 15(1) 7(2) 13(0) 21(9)1998 12 0 - - - - 16 23 - 18(14) - 5(0) 36 33 25(6) 21(14) 11(3) 12(3)1999 18 0 - - - - 30 24 21(5) 20(13) 9(1) 4(3) 48 39 32(7) 29(14) 16(2) 10(3)2000 23 0 6(0) - 17(6) - 25 27 8(1) 8(0) 17(4) 19(3) 35 33 19(4) 11(0) 16(2) 22(3)2001 15 3 - - - - 27 32 10(2) 19(3) 17(5) 13(3) 39 37 20(4) 20(3) 19(5) 17(4)2002 14 4 - - - - 20 30 14(2) 15(2) 6(0) 15(2) 34 34 20(4) 17(4) 14(0) 17(4)2003 16 2 - - - - 22 30 8(0) 9(0) 14(4) 21(8) 36 36 8(1) 11(1) 28(13) 25(7)2004 19 1 - - - - 23 32 6(0) 16(2) 17(7) 16(4) 35 40 7(0) 17(2) 28(9) 23(7)2005 20 13 13(1) - 7(3) - 23 20 12(2) 10(1) 11(0) 10(0) 34 29 12(4) 14(3) 22(2) 15(0)2006 19 15 - - - - 26 25 9(0) 14(0) 17(7) 11(1) 39 36 14(2) 23(4) 25(8) 13(1)2007 19 18 - - - - 22 27 6(1) 14(1) 16(9) 13(3) 37 34 13(2) 18(2) 24(11) 16(3)2008 19 13 - - - - 23 30 13(1) 16(5) 10(1) 14(5) 35 37 22(4) 16(4) 13(2) 21(7)2009 19 11 - - - - 29 28 19(6) 17(6) 10(4) 11(3) 38 50 27(7)* 30(9) 11(4) 20(3)2010 23 10 16(7) - 7(0) - 33 28 16(4) 16(5) 17(5) 12(1) 44 48 23(6) 29(10) 21(5) 19(1)2011 21 7 11(3) - 10(2) - 32 27 16(4) 11(0) 16(6) 16(2) 47 43 24(7) 21(4) 23(10) 22(2)

58

Appendix 4Table 4–12. Summary of regional step-trend analysis for magnesium.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 15 0 - - - - 33 0 11(3) - 22(8) - 75 0 35(11) - 40(11) -1975 18 0 - - - - 39 0 17(2) - 22(3) - 83 0 34(5) - 49(9) -1976 18 0 - - - - 46 0 22(2) - 24(2) - 92 0 51(10) - 41(4) -1977 34 1 12(0) - 22(5) - 75 0 32(10) - 43(10) - 118 0 57(18) - 61(18) -1978 32 1 15(4) - 17(3) - 76 0 38(11) - 38(9) - 127 0 64(19) - 63(14) -1979 40 1 24(9) - 16(4) - 84 0 51(18) - 33(7) - 127 1 75(28) - 52(11) -1980 46 1 30(7) - 16(0) - 79 0 41(13) - 38(11) - 122 0 63(19) - 59(17) -1981 47 0 16(0) - 31(6) - 62 0 23(4) - 39(7) - 99 0 41(6) - 58(11) -1982 22 0 3(0) - 19(8) - 36 0 21(5) - 15(4) - 76 0 45(10) - 31(7) -1983 23 0 15(3) - 8(0) - 33 0 15(2) - 18(1) - 68 0 34(6) - 34(3) -1984 23 2 16(1) - 7(1) - 39 1 16(1) - 23(1) - 64 14 23(2) - 41(4) -1985 18 0 - - - - 28 1 14(5) - 14(1) - 51 18 27(7) - 24(5) -1986 30 0 7(0) - 23(6) - 34 2 17(4) - 17(1) - 55 20 30(5) 14(1) 25(4) 6(2)1987 33 0 8(0) - 25(10) - 38 3 16(1) - 22(5) - 59 21 25(5) 5(2) 34(8) 16(1)1988 36 0 6(1) - 30(14) - 42 1 17(4) - 25(5) - 68 18 32(4) - 36(7) -1989 44 0 27(6) - 17(4) - 45 1 28(6) - 17(2) - 71 17 38(7) - 33(5) -1990 30 0 19(2) - 11(0) - 46 1 22(4) - 24(5) - 81 15 38(9) - 43(8) -1991 24 0 15(4) - 9(0) - 21 1 13(0) - 8(2) - 50 14 28(5) - 22(4) -1992 23 0 8(2) - 15(1) - 21 3 7(1) - 14(2) - 46 13 21(4) - 25(4) -1993 14 0 - - - - 19 3 - - - - 45 12 20(6) - 25(7) -1994 13 0 - - - - 13 4 - - - - 27 12 18(7) - 9(3) -1995 10 0 - - - - 17 3 - - - - 32 12 20(4) - 12(1) -1996 9 0 - - - - 11 1 - - - - 25 10 11(5) - 14(4) -1997 10 0 - - - - 15 7 - - - - 32 16 14(4) - 18(7) -1998 12 0 - - - - 20 7 9(3) - 11(3) - 48 19 23(8) - 25(5) -1999 18 0 - - - - 33 8 9(1) - 24(5) - 63 24 34(9) 17(5) 29(5) 7(2)2000 23 0 7(0) - 16(3) - 29 11 11(5) - 18(3) - 52 21 26(10) 8(1) 26(6) 13(2)2001 15 4 - - - - 31 32 22(6) 16(3) 9(1) 16(6) 48 54 32(11) 24(5) 16(2) 30(10)2002 14 4 - - - - 25 31 17(5) 17(3) 8(0) 14(4) 42 53 26(6) 30(3) 16(0) 23(4)2003 16 3 - - - - 32 31 15(2) 11(2) 17(6) 20(9) 49 62 17(4) 30(5) 32(12) 32(11)2004 19 2 - - - - 33 34 9(0) 17(6) 24(7) 17(5) 48 68 15(1) 32(10) 33(9) 36(10)2005 22 13 13(2) - 9(0) - 31 21 13(0) 10(2) 18(3) 11(0) 55 66 18(1) 31(9) 37(11) 35(11)2006 19 16 - - - - 35 27 16(2) 16(1) 19(3) 11(2) 60 74 31(6) 42(13) 29(8) 32(5)2007 19 18 - - - - 30 31 17(6) 17(2) 13(3) 14(1) 58 69 31(14) 39(9) 27(6) 30(6)2008 19 13 - - - - 31 45 23(4) 27(7) 8(2) 18(4) 58 83 39(5) 32(10) 19(6) 51(12)2009 21 11 13(8) - 8(3) - 39 41 21(6) 20(4) 18(5) 21(4) 58 75 30(8) 44(10) 28(6) 31(7)2010 25 10 13(4) - 12(3) - 43 39 14(0) 21(6) 29(11) 18(2) 64 64 24(3) 38(15) 40(13) 26(2)2011 24 7 5(2) - 19(5) - 42 38 15(3) 21(5) 27(9) 17(2) 67 60 30(6) 35(10) 37(10) 25(3)

Results

59Table 4–13. Summary of regional step-trend analysis for calcium.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 15 0 - - - - 33 0 12(3) - 21(7) - 76 0 36(12) - 40(9) -1975 17 0 - - - - 39 0 20(5) - 19(1) - 85 0 44(7) - 41(3) -1976 16 0 - - - - 45 0 27(7) - 18(3) - 94 0 61(16) - 33(3) -1977 33 1 9(0) - 24(5) - 74 0 34(5) - 40(10) - 119 0 64(7) - 55(14) -1978 31 1 14(1) - 17(3) - 74 0 34(8) - 40(11) - 127 0 63(16) - 64(17) -1979 39 1 27(8) - 12(4) - 82 0 52(21) - 30(7) - 126 1 77(34) - 49(10) -1980 47 1 35(13) - 12(1) - 77 0 43(16) - 34(5) - 121 0 65(24) - 56(7) -1981 48 0 17(1) - 31(9) - 61 0 27(3) - 34(9) - 99 0 40(5) - 59(16) -1982 22 0 6(0) - 16(8) - 36 0 18(7) - 18(7) - 75 0 40(13) - 35(8) -1983 23 0 15(4) - 8(0) - 33 0 17(3) - 16(0) - 68 0 37(4) - 31(0) -1984 23 2 13(3) - 10(0) - 39 1 16(1) - 23(2) - 64 14 28(3) - 36(5) -1985 18 0 - - - - 28 1 9(2) - 19(1) - 51 18 23(3) - 28(5) -1986 30 0 12(2) - 18(5) - 34 2 17(4) - 17(3) - 55 20 28(9) 12(3) 27(3) 8(1)1987 33 0 13(4) - 20(8) - 38 3 19(5) - 19(2) - 59 21 29(9) 12(1) 30(5) 9(0)1988 38 0 9(2) - 29(10) - 43 1 19(3) - 24(5) - 68 17 33(6) - 35(7) -1989 46 0 23(5) - 23(4) - 46 1 25(0) - 21(2) - 71 16 30(1) - 41(6) -1990 31 0 22(3) - 9(2) - 46 1 17(2) - 29(8) - 80 15 27(4) - 53(12) -1991 25 0 14(4) - 11(3) - 22 1 12(1) - 10(4) - 50 14 25(4) - 25(7) -1992 25 0 12(1) - 13(2) - 22 3 13(0) - 9(0) - 46 13 28(6) - 18(2) -1993 14 0 - - - - 19 3 - - - - 45 12 22(5) - 23(6) -1994 13 0 - - - - 13 6 - - - - 27 14 13(5) - 14(3) -1995 10 0 - - - - 17 5 - - - - 32 14 20(4) - 12(1) -1996 9 0 - - - - 11 16 - - - - 25 25 14(5) 18(9) 11(2) 7(1)1997 10 0 - - - - 15 22 - 14(2) - 8(0) 32 31 16(5) 20(3) 16(5) 11(1)1998 12 0 - - - - 20 23 12(3) 14(3) 8(3) 9(3) 48 35 28(10) 22(6) 20(5) 13(3)1999 18 0 - - - - 33 24 13(1) 11(4) 20(4) 13(4) 63 40 35(8) 24(9) 28(4) 16(4)2000 23 0 6(0) - 17(6) - 29 27 12(1) 13(4) 17(3) 14(7) 52 36 28(5) 16(4) 24(4) 20(8)2001 15 4 - - - - 31 32 19(5) 15(3) 12(1) 17(4) 48 54 31(11) 22(4) 17(2) 32(8)2002 14 4 - - - - 25 31 17(4) 18(2) 8(1) 13(2) 42 53 28(6) 36(7) 14(2) 17(2)2003 16 3 - - - - 32 31 12(0) 11(0) 20(4) 20(6) 50 62 15(3) 29(8) 35(11) 33(9)2004 19 2 - - - - 33 34 10(1) 16(6) 23(7) 18(5) 49 68 15(2) 24(7) 34(9) 44(13)2005 22 13 13(0) - 9(0) - 31 21 13(2) 10(2) 18(1) 11(1) 56 67 18(3) 28(8) 38(11) 39(12)2006 19 13 - - - - 35 27 18(5) 14(0) 17(3) 13(1) 61 75 33(12) 43(9) 28(7) 32(3)2007 19 15 - - - - 30 31 16(3) 16(2) 14(4) 15(3) 59 70 30(11) 39(9) 29(6) 31(6)2008 19 10 - - - - 31 46 20(4) 22(4) 11(2) 24(5) 58 85 39(8) 32(4) 19(6) 53(12)2009 21 8 13(6) - 8(2) - 39 41 22(6) 26(3) 17(5) 15(5) 58 76 30(7) 45(6) 28(5) 31(9)2010 25 7 14(6) - 11(1) - 43 39 14(1) 19(6) 29(8) 20(0) 64 65 25(5) 34(10) 39(10) 31(4)2011 24 7 14(2) - 10(1) - 42 38 18(4) 20(5) 24(2) 18(5) 67 61 33(8) 27(7) 34(4) 34(5)

60

Appendix 4Table 4–14. Summary of regional step-trend analysis for total dissolved solids.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 17 1 - - - - 32 1 11(3) - 21(5) - 74 2 42(15) - 32(7) -1975 15 1 - - - - 40 3 18(3) - 22(2) - 83 4 49(18) - 34(5) -1976 21 1 12(0) - 9(0) - 47 11 32(8) - 15(3) - 94 13 60(23) - 34(5) -1977 48 0 11(1) - 37(8) - 74 30 29(9) 21(6) 45(16) 9(3) 120 37 62(19) 23(7) 58(19) 14(4)1978 45 0 19(2) - 26(5) - 75 31 31(8) 19(7) 44(14) 12(2) 128 41 59(16) 24(8) 69(20) 17(4)1979 50 0 28(6) - 22(0) - 81 32 44(10) 19(5) 37(11) 13(5) 125 42 63(16) 25(7) 62(16) 17(5)1980 55 0 30(1) - 25(0) - 79 24 38(5) 7(2) 41(7) 17(4) 122 28 60(13) 9(2) 62(15) 19(6)1981 52 0 26(1) - 26(5) - 58 20 31(6) 5(1) 27(5) 15(4) 96 24 50(12) 6(1) 46(12) 18(6)1982 30 1 8(1) - 22(7) - 16 21 - 12(2) - 9(0) 42 27 31(8) 16(3) 11(3) 11(0)1983 32 1 19(2) - 13(1) - 14 22 - 16(2) - 6(1) 37 29 26(6) 22(4) 11(0) 7(2)1984 27 2 20(4) - 7(0) - 14 22 - 10(1) - 12(4) 31 32 15(4) 15(2) 16(3) 17(5)1985 19 1 - - - - 10 26 - 16(2) - 10(3) 26 40 15(4) 24(4) 11(4) 16(6)1986 23 1 9(0) - 14(1) - 12 28 - 18(3) - 10(2) 27 49 12(2) 32(11) 15(1) 17(2)1987 23 0 4(0) - 19(5) - 14 27 - 15(2) - 12(1) 31 45 18(4) 26(5) 13(2) 19(1)1988 29 0 9(0) - 20(3) - 18 26 - 8(1) - 18(2) 40 46 17(2) 15(4) 23(3) 31(8)1989 34 0 23(3) - 11(1) - 19 6 - - - - 37 21 17(2) 8(1) 20(3) 13(2)1990 27 0 18(0) - 9(0) - 18 12 - - - - 39 26 20(2) 6(1) 19(5) 20(9)1991 23 0 13(2) - 10(1) - 15 14 - - - - 29 22 17(2) 10(0) 12(3) 12(1)1992 24 1 7(1) - 17(2) - 13 16 - - - - 26 24 12(1) 12(5) 14(2) 12(0)1993 13 2 - - - - 8 40 - 25(7) - 15(0) 25 47 12(1) 29(7) 13(6) 18(0)1994 13 3 - - - - 6 48 - 24(4) - 24(4) 17 51 - 25(5) - 26(4)1995 10 20 - 11(3) - 9(0) 5 49 - 18(4) - 31(12) 16 50 - 20(3) - 30(13)1996 8 21 - 3(0) - 18(7) 4 59 - 23(2) - 36(9) 14 58 - 23(2) - 35(7)1997 9 23 - 6(0) - 17(7) 6 40 - 10(2) - 30(8) 16 39 - 12(3) - 27(8)1998 11 31 - 16(1) - 15(4) 13 49 - 19(1) - 30(7) 27 40 14(4) 19(4) 13(4) 21(4)1999 17 36 - 14(1) - 22(4) 25 59 11(2) 25(3) 14(2) 34(9) 41 45 23(8) 18(3) 18(2) 27(6)2000 22 40 5(0) 10(0) 17(7) 30(6) 21 57 6(2) 24(3) 15(4) 33(8) 28 45 13(3) 24(4) 15(2) 21(4)2001 14 39 - 14(0) - 25(6) 22 76 13(4) 31(5) 9(1) 45(11) 27 82 13(4) 37(6) 14(3) 45(8)2002 14 38 - 25(7) - 13(5) 17 83 - 37(11) - 46(10) 24 87 13(4) 36(7) 11(3) 51(9)2003 18 38 - 26(6) - 12(1) 22 87 10(1) 38(8) 12(3) 49(15) 29 95 15(3) 38(7) 14(3) 57(16)2004 17 38 - 23(7) - 15(2) 19 84 - 37(6) - 47(8) 26 89 15(1) 37(5) 11(4) 52(10)2005 23 39 13(2) 28(7) 10(2) 11(0) 22 83 11(1) 48(7) 11(3) 35(4) 30 90 10(0) 48(6) 20(2) 42(7)2006 21 40 14(3) 26(9) 7(0) 14(0) 27 97 10(1) 57(11) 17(6) 40(9) 31 120 9(1) 65(13) 22(6) 55(14)2007 22 39 10(1) 28(6) 12(1) 11(1) 20 82 9(1) 51(14) 11(0) 31(5) 25 101 12(2) 52(11) 13(0) 49(8)2008 22 41 6(1) 28(8) 16(4) 13(4) 22 75 13(5) 43(12) 9(2) 32(8) 29 92 20(7) 42(11) 9(3) 50(13)2009 24 42 13(3) 20(6) 11(2) 22(3) 28 71 20(4) 30(8) 8(1) 41(5) 32 88 19(5) 45(14) 13(1) 43(4)2010 29 32 15(4) 14(1) 14(3) 18(1) 40 64 18(0) 29(6) 22(7) 35(6) 48 70 19(4) 38(8) 29(10) 32(5)2011 27 43 18(4) 20(5) 9(0) 23(2) 37 65 20(5) 34(12) 17(3) 31(6) 48 74 26(10) 39(12) 22(5) 35(5)

Results

61Table 4–15. Summary of regional step-trend analysis for alkalinity.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1974 18 3 - - - - 35 4 12(3) - 23(8) - 75 4 34(11) - 41(10) -1975 19 4 - - - - 42 16 22(6) - 20(3) - 84 17 44(12) - 40(11) -1976 18 9 - - - - 51 26 30(10) 6(0) 21(3) 20(5) 97 30 59(19) 7(1) 38(6) 23(5)1977 31 14 10(1) - 21(3) - 75 26 41(8) 17(3) 34(7) 9(6) 120 30 70(19) 19(6) 50(13) 11(7)1978 30 22 21(4) 13(1) 9(0) 9(1) 75 29 50(12) 18(7) 25(7) 11(4) 129 35 79(22) 21(13) 50(10) 14(4)1979 38 22 25(3) 13(2) 13(0) 9(0) 81 30 57(13) 21(9) 24(3) 9(1) 126 35 82(23) 26(13) 44(8) 9(1)1980 49 19 24(6) - 25(5) - 82 30 39(11) 13(5) 43(8) 17(5) 122 32 59(17) 19(5) 63(9) 13(3)1981 52 19 12(1) - 40(4) - 66 30 16(2) 3(0) 50(13) 27(15) 100 34 28(6) 6(0) 72(21) 28(13)1982 31 21 11(0) 11(4) 20(5) 10(2) 40 31 17(5) 12(2) 23(4) 19(5) 76 37 27(10) 19(2) 49(10) 18(6)1983 31 21 22(9) 14(2) 9(1) 7(2) 40 32 22(3) 22(6) 18(1) 10(2) 71 40 36(2) 26(6) 35(0) 14(1)1984 29 34 13(2) 17(3) 16(4) 17(4) 45 36 23(7) 24(6) 22(3) 12(0) 72 50 40(7) 26(6) 32(3) 24(3)1985 29 38 7(0) 14(2) 22(10) 24(5) 38 35 12(3) 17(2) 26(9) 18(3) 63 50 28(7) 25(6) 35(8) 25(4)1986 35 32 15(1) 13(0) 20(9) 19(8) 41 31 17(3) 18(3) 24(11) 13(5) 63 50 33(6) 24(5) 30(12) 26(8)1987 37 47 16(5) 27(8) 21(7) 20(1) 47 34 25(5) 23(6) 22(1) 11(0) 70 51 38(7) 33(9) 32(2) 18(4)1988 41 43 11(3) 25(4) 30(9) 18(0) 50 30 24(2) 13(1) 26(1) 17(1) 75 50 37(2) 24(2) 38(5) 26(4)1989 44 41 18(6) 13(1) 26(5) 28(4) 46 10 22(0) - 24(5) - 76 29 37(7) 15(7) 39(7) 14(3)1990 33 50 22(6) 30(7) 11(0) 20(5) 48 11 20(3) - 28(7) - 84 28 34(5) 13(2) 50(10) 15(4)1991 28 61 12(1) 27(4) 16(4) 34(8) 27 11 14(0) - 13(1) - 57 28 28(2) 14(4) 29(7) 14(2)1992 28 75 11(2) 31(11) 17(0) 44(11) 32 18 13(1) - 19(3) - 60 29 31(3) 19(2) 29(4) 10(0)1993 19 93 - 44(6) - 49(12) 27 48 16(7) 28(6) 11(2) 20(5) 57 46 29(12) 31(4) 28(8) 15(3)1994 21 87 11(3) 51(13) 10(2) 36(6) 19 45 - 22(11) - 23(2) 35 51 16(7) 20(7) 19(3) 31(3)1995 18 88 - 44(7) - 44(12) 35 44 15(1) 18(6) 20(4) 26(15) 51 51 20(1) 21(5) 31(7) 30(12)1996 15 89 - 37(4) - 52(8) 28 48 14(4) 23(4) 14(3) 25(5) 42 58 19(5) 33(4) 23(7) 25(3)1997 21 90 12(2) 36(7) 9(3) 54(12) 35 57 22(6) 26(8) 13(0) 31(4) 52 65 26(6) 32(5) 26(5) 33(3)1998 23 81 11(2) 37(10) 12(5) 44(8) 41 53 22(8) 22(3) 19(1) 31(5) 61 59 27(10) 25(7) 34(7) 34(4)1999 31 80 11(0) 38(10) 20(8) 42(4) 44 54 28(4) 25(7) 16(2) 29(5) 62 66 38(6) 32(10) 24(4) 34(6)2000 36 57 7(0) 6(0) 29(10) 51(16) 48 51 25(9) 21(10) 23(5) 30(6) 71 69 41(13) 38(12) 30(4) 31(1)2001 39 77 12(2) 24(7) 27(8) 53(22) 56 105 21(7) 43(8) 35(10) 62(17) 86 129 42(12) 62(7) 44(9) 67(11)2002 48 84 31(8) 39(17) 17(4) 45(7) 58 107 31(8) 61(20) 27(5) 46(7) 86 136 50(17) 73(16) 36(7) 63(9)2003 52 90 29(3) 59(20) 23(5) 31(2) 64 114 23(1) 65(17) 41(12) 49(6) 86 143 35(9) 70(13) 51(17) 73(21)2004 37 97 23(3) 68(24) 14(1) 29(2) 51 144 28(6) 72(19) 23(4) 72(14) 73 165 32(7) 71(12) 41(9) 94(31)2005 32 105 23(5) 64(14) 9(0) 41(6) 47 148 23(9) 82(13) 24(2) 66(10) 61 173 23(5) 86(13) 38(6) 87(20)2006 26 93 12(3) 48(10) 14(1) 45(3) 50 136 19(2) 64(15) 31(17) 72(12) 66 186 31(9) 94(24) 35(18) 92(16)2007 26 93 10(1) 51(8) 16(4) 42(13) 49 141 12(0) 72(10) 37(15) 69(16) 69 180 29(3) 88(20) 40(15) 92(19)2008 39 99 10(1) 39(6) 29(8) 60(15) 56 132 33(6) 67(17) 23(1) 65(9) 70 170 43(6) 84(24) 27(6) 86(17)2009 41 108 20(7) 49(11) 21(5) 59(14) 57 129 34(9) 78(12) 23(4) 51(14) 66 166 33(10) 99(21) 33(9) 67(14)2010 43 109 31(11) 67(20) 12(4) 42(7) 56 100 27(4) 49(10) 29(7) 51(15) 65 132 28(2) 68(19) 37(9) 64(15)2011 34 87 17(4) 45(9) 17(2) 42(7) 49 67 35(8) 33(10) 14(2) 34(6) 64 94 43(11) 48(11) 21(4) 46(14)

62 Appendix 4

USGS sites

Step trends for alkalinity for 1985 (January 1, 1983, to December 31, 1986) window



ODCA sites








EXPLANATION

USGS

ODCA

Figure 4 –37. Maps showing national step trends for alkalinity for the 1985 (January 1, 1983, to December 31, 1986) window.

Results 63

USGS sites

Step trends for alkalinity for 2000 (January 1, 1998, to December 31, 2001) window



ODCA sites








EXPLANATION

USGS

ODCA

Figure 4 –38. Maps showing national step trends for alkalinity for the 2000 (January 1, 1998, to December 31, 2001) window.

64

Appendix 4Table 4–16. Summary of regional step-trend analysis for total organic carbon.



(year)


TotalDowntrends

(sig.)Uptrends

(sig.)Total

Downtrends (sig.)

Uptrends (sig.)

TotalDowntrends

(sig.)Uptrends


1977 20 5 11(4) - 9(0) - 2 4 - - - - 10 6 - - - -1978 17 5 - - - - 1 4 - - - - 13 6 - - - -1979 20 5 17(11) - 3(1) - 9 4 - - - - 22 6 3(0) - 19(8) -1980 17 5 - - - - 2 4 - - - - 5 6 - - - -1981 16 8 - - - - 1 0 - - - - 4 4 - - - -1982 16 20 - 20(10) - 0(0) 1 3 - - - - 4 7 - - - -1983 18 20 - 15(3) - 5(0) 3 4 - - - - 5 11 - - - -1984 19 20 - 9(0) - 11(1) 3 5 - - - - 5 18 - - - -1985 19 20 - 9(1) - 11(1) 3 3 - - - - 3 18 - - - -1986 20 0 1(0) - 19(6) - 3 0 - - - - 3 19 - - - -1987 25 1 14(1) - 11(1) - 3 0 - - - - 3 20 - 18(5) - 2(0)1988 30 1 21(8) - 9(1) - 3 0 - - - - 2 17 - - - -1989 34 1 18(0) - 16(6) - 7 0 - - - - 4 12 - - - -1990 24 24 12(1) 10(0) 12(2) 14(2) 8 4 - - - - 5 9 - - - -1991 24 39 17(5) 23(0) 7(2) 16(2) 2 3 - - - - 3 9 - - - -1992 24 54 12(3) 17(1) 12(4) 37(7) 2 3 - - - - 5 5 - - - -1993 12 71 - 33(9) - 38(5) 0 12 - - - - 4 18 - - - -1994 12 70 - 31(5) - 39(8) 0 13 - - - - 1 22 - 16(5) - 6(4)1995 9 53 - 26(4) - 27(6) 0 14 - - - - 0 23 - 12(2) - 11(4)1996 8 55 - 21(3) - 34(5) 0 16 - - - - 0 27 - 14(0) - 13(2)1997 14 50 - 18(0) - 32(9) 0 17 - - - - 0 39 - 24(8) - 15(5)1998 16 36 - 7(2) - 29(12) 0 19 - - - - 0 37 - 22(7) - 15(2)1999 17 43 - 18(3) - 25(0) 0 29 - 16(2) - 13(1) 0 50 - 30(8) - 20(7)2000 18 58 - 41(18) - 17(1) 1 39 - 26(12) - 13(1) 2 41 - 30(11) - 11(1)2001 19 71 - 47(18) - 24(5) 2 57 - 40(9) - 17(2) 3 56 - 44(9) - 12(2)2002 25 73 11(1) 27(4) 14(4) 46(7) 1 63 - 25(5) - 38(2) 2 65 - 28(7) - 37(2)2003 24 78 12(0) 37(6) 12(2) 41(6) 3 86 - 42(8) - 44(14) 1 86 - 36(8) - 50(14)2004 11 75 - 51(15) - 24(3) 5 88 - 25(3) - 63(21) 4 105 - 31(0) - 74(28)2005 18 72 - 54(21) - 18(3) 6 86 - 28(2) - 58(16) 4 93 - 28(3) - 65(22)2006 20 57 16(5) 34(15) 4(2) 23(17) 7 81 - 33(8) - 48(23) 4 86 - 34(9) - 52(7)2007 18 56 - 24(8) - 32(10) 8 71 - 42(11) - 29(10) 5 76 - 45(17) - 31(8)2008 30 68 14(6) 33(13) 16(7) 35(12) 9 55 - 42(15) - 13(1) 6 64 - 44(11) - 20(1)2009 28 65 17(4) 40(9) 11(2) 25(5) 8 55 - 46(14) - 9(2) 4 66 - 48(13) - 18(4)2010 29 73 24(10) 44(19) 5(0) 29(11) 10 43 - 35(16) - 8(2) 7 59 - 32(16) - 27(9)2011 27 72 16(2) 44(12) 11(2) 28(3) 5 35 - 24(7) - 11(0) 5 44 - 25(7) - 19(0)

Results 65

USGS sites

Step trends for total organic carbon for 2004 (January 1, 2002, to December 31, 2005) window



ODCA sites








EXPLANATION

USGS

ODCA

Figure 4 –39. Maps showing national step trends for total organic carbon for the 2004 (January 1, 2002, to December 31, 2005) window.

66 Appendix 4

Summary and Conclusion

Given the limitations of the data and statistical methods, there were few instances for the parameters analyzed in this appendix when anomalous step trends could be identified on the basis of regional comparison of step trends for U.S. Geological Survey (USGS) and multiple outside data-collection agency (ODCA) sites; therefore, in most cases, laboratory or field sampling method changes that took place probably had limited effect on flow-normalized concentrations compared to regional environmental variability or change. It is likely that more instances of laboratory or field method changes did occur and that some of these changes may have caused method bias, but ability to detect the relatively small effects of these changes would require a combination of higher (and more uniform) sampling frequencies, more nearby (or co-located) sites from USGS and ODCAs, field replicate samples, and (or) more detailed information on timing and nature of the changes. In particular, the highly variable (through time) and lack of overlapping (in space) site locations for USGS and ODCA data made it difficult to rigorously test whether the anomalous trends were due to laboratory or field method changes and not due to random spatially correlated perturbations or environmental trends in flow-normalized concentrations. Despite these limitations, a few cases were identified where potential USGS laboratory or field method changes could have produced bias that was large enough to affect interpretation of trends on a regional to national scale:

1. Uptrends in total nitrogen and total phosphorus concentrations for USGS sites in about 1980. The uptrends appear to be widespread nationally and are not evident in filtered (dissolved) nutrient concentrations for USGS sites or in total or filtered nutrient concentrations for ODCA sites. The likely cause was a sample preservation change that eliminated (or reduced) downward bias in the nutrient concentrations prior to 1980.

2. Downtrends in filtered orthophosphate concentrations for USGS sites in about 2000. The cause may be an analytical method change.

3. Uptrends in filtered orthophosphate concentrations for USGS sites in about 2006. Again, the cause may be an analytical method change.

4. Uptrends in suspended sediment concentrations for USGS sites in the central and northeastern United States in about 2002, followed by downtrends in 2004. Although there are no documented method changes during this time, there was no indication of similar trends in any of the parameters, such as total phosphorus or total suspended solids (from ODCAs) that would be expected to correlate with suspended sediment. The cause of the anomalous trends may require further investigation.

5. Uptrends in sulfate concentrations for USGS sites in about 1987, along with downtrends in about 1989. The cause may be previously documented upward bias during that time.The general consistency of regional trend patterns for

USGS and ODCA data and for ODCA data from different States indicates that analyzing trends by combining USGS sites with sites from the ODCAs should provide a better representation of trends than analyzing only USGS data. Using ODCA data increases site density and coverage, making regional trend patterns more readily defined and increasing the robustness of the trend results; however, similarity of the step trends does not necessarily imply that there is no bias in the concentration data from USGS or ODCAs. The similarity only implies that changes in bias through time are probably not large enough in most cases to cause false interpretation of environmental trends that may be confounded with laboratory or field method changes.

Irrespective of the causes of the trends, there were widespread occurrences of significant and regionally coherent step trends for many parameters and time periods, and the regional trend patterns were often highly complex and variable on a regional to national scale. In addition to helping avoid method-bias-induced misinterpretation of trends, the step-trend results should provide a valuable supplement to the national trend assessment effort by helping to determine the timing, regional extent, and causes of long-term regional and national scale water-quality trends.

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68 Appendix 4

Documents

Appendix 4. Step-trend Analysis of Changes in Laboratory ...The overall purpose of this appendix is to augment the long-term (10-year to 40-year) trend analyses for the national