Channel morphology and P uptake following removal of a small dam

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Channel morphology and P uptake following removal of a small damAuthor(s) Cailin H Orr Kristy L Rogers Emily H StanleySource Journal of the North American Benthological Society 25(3)556-568 2006Published By The Society for Freshwater ScienceDOI httpdxdoiorg1018990887-3593(2006)25[556CMAPUF]20CO2URL httpwwwbiooneorgdoifull1018990887-359328200629255B5563ACMAPUF5D20CO3B2

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J N Am Benthol Soc 2006 25(3)556ndash568 2006 by The North American Benthological Society

Channel morphology and P uptake following removal of a small dam

Cailin H Orr1 Kristy L Rogers2 AND Emily H Stanley3

Center for Limnology University of Wisconsin 608 North Park Street Madison Wisconsin 53706 USA

Abstract Dam removal is becoming an increasingly common management solution for aging dams andevaluation of the impact of dam removal on basic attributes of streams such as nutrient uptake andtransport is essential The removal of 2 small dams from a forested 2nd-order stream in Wisconsin allowedus to study how nutrient dynamics were influenced by changes in channel geometry and bed material Wecalculated P uptake and transient storage metrics from a series of 19 short-term injections measured cross-sectional profiles and determined benthic sediment size at regular intervals for 2 mo before and after theremovals We also repeated these measurements over the same time period the following year Nutrientuptake was highly variable and the stream changed from being a soluble reactive P (SRP) sink to being asource several times over the study period Uptake lengths increased immediately after dam removal butdifferences between measurements made before and after removal were not significant We found nosignificant relationship between uptake length and benthic sediment composition channel geometry orwater residence time over the course of the dam removals Our results indicate that changes in physicalchannel attributes did not play an important role in controlling SRP retention probably because the impactof dam removal was small compared with the natural variability of this system

Key words dam removal nutrient uptake geomorphology Wisconsin sediments

Dam removal is an increasingly prevalent solutionfor the management of aging dams (Doyle et al2003d) The number of intentional removals in the USis estimated at 417 (Pohl 2002) (cf thousands of damsin existence USACE 1998 Graf 1999) but the potentialfor this management action to become more frequent issubstantial because of growing safety and economicconcerns associated with an aging national daminfrastructure (Born et al 1998 Doyle et al 2003a)Selective removal of dams has been widely promotedas a powerful restoration or enhancement tool for riverecosystems (Hart et al 2002) because removal isexpected to reverse many of the deleterious effects ofdams such as blockage of fish passage flow mod-ification or thermal alteration (Bednarek 2001) How-ever tests of the effects of dam removal on rivers areextremely limited Recent studies describing channelformation (Doyle et al 2003a) macroinvertebratecommunity structure (Bushaw-Newton et al 2002Stanley et al 2002) and fish movement (Kanehl et al

1997) have provided encouraging but limited resultswith respect to rehabilitation of ecosystem functionsfollowing dam removal The number of river restora-tion projects that involve dams is increasing and thistrend has spurred a new interest in determining howphysical alterations such as dam removal impact basicecological patterns and processes in streams (Bednarek2001)

Nutrient retention is a fundamental attribute ofstreams that may be affected by dam removal (Stanleyand Doyle 2002) The concept of spiraling often is usedto describe nutrient cycling in these ecosystems andthe efficiency of nutrient uptake is reported as uptakelength or the average distance a nutrient moleculemoves downstream before it is retained by the benthos(Sw Newbold et al 1981) Short Sws are an indicationof elevated demand and possibly increased limitationof the nutrient of interest However short Sws also canbe caused by changes in water velocity and depthbecause measurement of Sw has a hydrologicalcomponent (Stream Solute Workshop 1990 Simon etal 2005)

Benthic uptake of nutrients has both biotic (periph-yton and biofilm) and abiotic (sediment adsorption)components and several variables can influenceuptake rates simultaneously (Davis and Minshall1999) However nutrient retention is modulated by

1 Present address Carolina Environmental Program CB

1105 University of North Carolina Chapel Hill ChapelHill North Carolina 27599-1105 USA Email chorruncedu

2 E-mail addresses kristyrogerswiscedu3 ehstanleywiscedu

556

the extent or duration of contact between sedimentsand water Thus changes in variables such as watervelocity depth transient storage and channel geo-morphology often affect uptake rates and lengthsbecause of their effects on sedimentndashwater interactions(Valett et al 1996 Alexander et al 2000) Channelmorphology can influence nutrient retention by affect-ing water residence time (Gucker and Boechat 2004)and because sediment composition varies amongdifferent channel forms (Knighton 1998) In particularsmaller particles with relatively large surface areasoften are associated with higher uptake rates of P thanlarger particles with relatively small surface areas(Meyer 1979 Klotz 1988 Valett et al 2002)

Several determinants of the extent of sedimentndashwater interaction and nutrient uptake in streams maybe altered by dam removal (Stanley and Doyle 2002)Down-cutting through reservoir sediment changeschannel geometry and mobilizes sediments (Doyle etal 2003b) The outcome can include a steeper channelslope increased water velocity and alteration of bedmaterial in the reservoir reach Changes also extendbeyond the dammed area and previous studies havedocumented transport of fine reservoir sediment toform depositional bars downstream (Doyle et al2003b) Further disturbance to benthic algae and otherbiota through scouring displacement and sedimentdeposition during dam removal is likely to reducebiotic uptake in a fashion analogous to changes causedby flash floods (eg Martı et al 1997) and subsequentrecolonization after dam removal also may be similarto postflood recovery Doyle et al (2003c) found thatchannel adjustments following dam removal from a5th-order river were associated with decreased Pretention and a modeling exercise relating retentionto flow parameters suggested that up to 40 of thechange in retention was caused by channel adjustmentHowever net Sw was estimated from massndashbalancecalculations because discharge was too high to allowuse of nutrient-addition methods to measure uptakeparameters directly The stream in our study was smallenough to permit direct measurement of Sw before andafter dam removal

We studied a pair of small dam removals in BoulderCreek a 2nd-order stream in south-central Wisconsinto assess the impact of dam removal on physicalvariables benthic sediments and nutrient uptakerates We used the dam removals as an experimentthat altered the abiotic factors that influence uptake toaddress 2 questions 1) How does dam removal affectchannel form and nutrient-uptake efficiency 2) Arethe observed nutrient changes correlated with changesin sediment particle size or waterndashsediment contact

time (measured as water residence time and transientstorage)

We expected Boulder Creek to respond in a mannersimilar to responses observed in other dam removalstudies in Wisconsin (Doyle et al 2003b) We predictedthat 1) water residence time in the dammed reachwould decrease after dam removal and thus sedi-mentndashwater contact would decrease 2) stream slopewould increase resulting in erosion of benthic sedi-ments in the impounded area and deposition ofsediments especially silt and sand downstream and3) cover of the streambed by silt and sand would bepositively correlated with uptake rates (Valett et al2002) These factors together were expected to causeuptake rates to decrease and P concentrations in thewater to increase immediately after dam removal Wetested these predictions by measuring changes in Puptake using solute-injection techniques and quantify-ing bed sediment composition and channel geometryfor several months before and after dam removal inBoulder Creek

Study Site

Boulder Creek is a 2nd-order stream located outsidethe city of Baraboo in Sauk County Wisconsin (Fig 1)Its headwaters are in the Baraboo Hills at lat43827rsquo30rsquorsquoN long 89 38rsquo00rsquorsquoW and it flows 16 km toits confluence with the Baraboo River The 406-km2

watershed is mainly undeveloped and is characterizedas old-growth red oak (Quercus rubra) and sugar maple(Acer saccharum) forest with canopy trees ranging from90 to 120 y old A small farm and orchard were in thewatershed above the study site historically and a smallactive milking operation currently exists immediatelydownstream of the study area The Aldo LeopoldFoundation a nonprofit stewardship group owns andmanages 162 ha of land surrounding the study siteBefore the dam was removed the biological integrityin the stream received an lsquoexcellentrsquo score (20) basedon an EPA index (USEPA 1997) and brook trout(Salvelinus fontinalis) were found in all reaches of thestream above and below both dams (M CatalanoWisconsin Department of Natural Resources personalcommunication)

Two small run-of-river dams were present inBoulder Creek before 2003 The 1st structure at thetop of the study reach (the upper dam) was a 1-m-highconcrete wall with a single centered rectangular watergate Water flowed through the gate into a smallplunge pool with a total change in elevation of 2 mfrom the top of the gate to the dam sill The upstreamreservoir had a surface area of 85 m2 and an averagewater depth of 8 cm at base flow A 2nd larger dam (the

2006] 557STREAM MORPHOLOGY AND P UPTAKE

lower dam) was 180 m downstream of the upper damThe lower dam was built in the 1950s as part of a fishhatchery and was 25 m high with concrete wing wallsthat extended at 308 angles on either side of the mainstructure It was in disrepair and had developed alarge crack so that water flowed through a sinkholeand under the structure The lower reservoir had asurface area of 190 m2 and an average depth similarto the upper reservoir At the beginning of our studyboth reservoirs were filled with silt and sand and hadlittle water retention capacity Both dam structureswere removed on 9 July 2003 They were breachedwith a wrecking ball and moved offsite in pieces overthe course of a few hours Care was taken to disturbthe stream as little as possible minimal shaping wasdone to the channel following the removals and thestream was allowed to adjust through subsequentnatural erosion and deposition processes

A 262-m stream segment from just above thereservoir of the upper dam to 110 m below thelower dam was chosen as the study reach a year before

the dams were removed (Fig 1) This length encom-passed the area most heavily impacted by the damsAverage channel width and depth in the study reachbefore the dam removals were 364 m and 8 cmrespectively (Table 1) and slope was 0036 Averagesummer (MayndashAugust) water depth fluctuated be-tween 4 and 32 cm and water temperatures rangedfrom 05 to 258C Bed substrate consisted mainly ofsand and coarse cobble with larger rock in riffle areasSuspended sediment concentrations were 120 mgL atbase flow soluble reactive P (SRP) concentrationsranged from 0039 to 0044 mgL and NO3 concen-trations were 12 to 13 mgL before the dams wereremoved

Methods

Physical variables

Water stage and dischargemdashBasic monitoring of thestudy site began 1 y before the removal and continuedfor 18 mo after the removal Water depth and temper-

FIG 1 Boulder Creek watershed and study reach Sampling sites are labeled 1 to 10 Stream stage was monitored at the roadculvert adjacent to site 4 Dams were located at 21 m and 193 m downstream of sample site 1

558 [Volume 25C H ORR ET AL

ature were recorded hourly in the middle of the studyreach using an Intech WTDL32000 capacitance-rod datalogger The capacitance rod was installed at the down-stream end of a culvert that captured the entire streamflow (Fig 1) Periodic flow measurements were taken atthe capacitance-rod site using a handheld MarshndashMcBirney FloMate flow meter Triplicate 60-s integra-tions were done and averaged for each measurementFlow data were combined with measures of cross-sectional area at multiple stages to calculate streamdischarge A stagendashdischarge relationship for the culvertoutflow was generated and used to estimate streamdischarge for times when flow was not measured

Channel cross-sectional morphologymdashCross-sectionalsurveys of channel geometry were done using an autolevel and stadia rod at 10 locations within the studyreach including 1 transect within each of the 2impoundments Surveys were conducted weekly inJune to July 2003 before removal (4 dates) in July toAugust 2003 after removal (6 dates) and again in Julyto August 2004 (5 dates) Cross sections wereseparated by a distance of 103 the channel width(30ndash50 m) Channel depth was measured and sedimentsize classes were observed at 20-cm intervals from theright channel bank to the corresponding left bankSediment was inspected visually and assigned to 1 of 4broad size classes silt (0006 cm) sand (0006ndash2 cm)cobble (2ndash10 cm) or rock (10 cm) For consistencythe same investigator conducted all surveys Repeatedsurveys were made from these fixed locations and allcross sections began and ended above the line ofvegetation to ensure they captured the entire activechannel and any changes that occurred as a result ofthe dam removal Sediment loss from the formerreservoir was estimated from the difference in cross-sectional profiles throughout the impounded reachfrom dates before and after removal of the damsAdditional cross sections of the stream wetted perim-eter were completed at 1-wk intervals for 12 evenlyspaced locations in the study reach Lateral measure-ments and water depth were recorded at 20-cmintervals Wetted perimeter measurements were usedto calculate channel width water volume and cross-sectional area for each sampling date

Stream water chemistry

Ambient concentrations of soluble reactive P (SRP)were measured at weekly intervals as part of nutrient-uptake studies (see below) Additional high-frequencysampling was conducted immediately before and afterremoval of the dams Automated ISCOt samplerswere stationed at sites 1 and 10 on 8 July 2003 21 hprior to dam removal and samples were collected at 3-h intervals until 9 July 2003 19 h after the breaching ofthe lower dam Samples were removed from theautomated samplers 3 times during the 40-h monitor-ing period and returned to the laboratory for filtration(07-lm glass fiber filter) and SRP determination usingascorbic acid colorimetry (APHA 1995) Additionalgrab samples were collected at 15- to 60-min intervalsat site 10 during the morning of the dam removal (9July) to characterize the main wave of sediment andwater that was released following breaching of thedam wall

Nutrient uptake

SRP Sw was measured using short-term KH2PO4

additions with NaCl as a nonreactive conservativetracer (Stream Solute Workshop 1990 Webster andEhrmann 1996) P was chosen as the study nutrientbecause surveys of water chemistry in 2002 revealedthat N concentrations were consistently high (12ndash13mgL) leading to NP ratios of 261 to 331 Theseratios suggested that P was the potentially limitingnutrient in Boulder Creek Experimental additionswere done 19 times at approximately weekly inter-vals from May to August 2003 and May to August2004 Six measurements were made before the damremovals and 5 after the removals in 2003 Theremaining 8 injections were done throughout May toAugust in 2004 to compensate for seasonal effects thatmay have confounded pre- and postremoval compar-isons in 2003 sampling and to allow consideration oflonger-term impacts of the removals Injections weredone at roughly the same time of day (0900ndash1000 h) onprecipitation-free days For each injection a solution ofNaCl and KH2PO4 was pumped into a well-mixedsection of stream at 90 mLmin using a battery-

TABLE 1 Mean (SD) channel physical variables before and after dam removal

Preremoval 2003 Postremoval 2003 2004

Width (m) 364 (008) 360 (027) 418 (015)Depth (cm) 8 (1) 7 (2) 11 (1)Cross-sectional area (m2) 025 (003) 024 (008) 044 (006)Water retention time (min) 50 (3) 39 (6) 28 (7)


powered ceramic reciprocating pump (Q431ndash02 FluidMetering Syoset New York) The concentration ofNaCl in the solution was adjusted to elevate Cl

concentrations in the stream water to 23 backgroundconcentrations The PO4 concentration was adjustedwith the goal of elevating the stream SRP concen-tration by the smallest change we could measurereliably to prevent overestimating uptake (Mulhollandet al 2002) The measured increases in SRP were 002to 018 mg PL resulting in increase of 5 to 66 aboveambient (mean and median frac14 28) Backgroundconcentrations and elevated concentrations of bothCl and SRP were all within detectable limitsthroughout the study period

Conductivity was monitored at the downstream endof the study reach with a data-logging conductivityprobe (WTW340i) recording at 1-min intervals begin-ning 60 min before each injection Initial watersamples were collected in duplicate or triplicate at 10points over the study reach downstream of the injectionpoint These points corresponded to the locations of thecross-sectional surveys Samples were collected beforethe addition and after conservative-tracer steady statewas achieved Steady state was indicated by theconductivity-curve plateau at the downstream conduc-tivity probe (90 min after pumping began) Sampleswere filtered in the field at the time of collection (045-lm glass-fiber filter) placed on ice and returned to thelab SRP was measured within 24 h using ascorbic acidcolorimetry (APHA 1995) Cl concentrations weredetermined on an ion chromatograph (Dionex IonpacAS14 A with a 4-mm analytical column) Conductivitymeasurements from the data logger were comparedwith pump start and stop times and were used tocalculate water residence time in the study reach Meanwater residence time was calculated as minutes elapsedfrom pump start to a downstream conductivity readingof frac12 the plateau value (Webster and Ehrmann 1996)Conductivity data were adjusted slightly for probe driftover the duration of measurement on several dates

SRP concentration was corrected for dilution usingthe conservative-tracer data (Webster and Ehrman1996) SRP Sw was calculated according to protocolsand equations in Stream Solute Workshop (1990) andWebster and Ehrman (1996) Regression outliers wereremoved (1 value in each of 7 calculations) wereremoved based on a Bonferroni outlier test andgoodness-of-fit measures were calculated using SY-STAT (version 10 SPSS Chicago Illinois) Values of Sw

are not reported for additions in which we did notdetect a significant negative relationship betweendistance downstream and SRP concentration

For dates when sufficient data were available(conductivity profiles for the duration of the injection

and significant negative Sw regressions) the additionalparameters of uptake rate (U mg m2 min1) anduptake velocity (Vf ms) were calculated using theequations

U frac14 CbQ60

SwwVf frac14

U

Cb60

where Cb is the background concentration of SRP(mgm3) Q is discharge (m3s) Sw is uptake length(m) w is the average stream width for the reach (m)and 60 is a unit conversion factor (Stream SoluteWorkshop 1990)

Transport model

The 1-dimensional transport model OTIS is used tosimulate downstream transport of waterborne solutesusing the assumption that solute concentration variesonly in the longitudinal direction This assumption isreasonable in small well-mixed streams such asBoulder Creek OTIS is based on the advectionndashdispersion equation with terms added to account fortransient storage and lateral inflow (Runkel 19982002) A modified version of OTIS OTIS-P alsoincludes a nonlinear regression model that canestimate stream main-channel cross-sectional area(A) transient storage (As) and storage-zone exchange(a) We used the metric AsA to characterize transientstorage relative to mass transport (Runkel 1998)

A time-variable model was constructed in OTIS andwas run against conductivity data recorded at themost downstream location at 1-min intervals through-out the injection period Adjustments for lateral flowwere not needed to model Boulder Creek flow becausegroundwater input accounted for 5 of the totalchange in solute concentration over the entire studyreach Three upstream boundary conditions were usedto reflect the nutrient addition the initial condition ofbackground conductivity the maximum conductivityresulting from solute addition applied at the time stepassociated with the pump start time and a return tobackground concentration at the time the pump wasstopped For each injection OTIS-P was run 3 times todetermine the optimal set of estimated parametervalues Parameter estimate outputs from each of thefirst 2 runs were used as initial parameter estimates inthe subsequent run (Runkel 1998)

Two sampling dates were modeled 6 July and 8August 2003 These were the dates of the 2 injectionsclosest to either side of the dam-removal date that alsohad measurable nutrient-uptake lengths and goodconductivity data Dates immediately after dam remov-al could not be used for this model because conductivitymeasurements were affected by sediment release from


the lower impoundment The 2 dates also represented

endpoints in measured uptake rates (see Results)

Data analysis

Preremoval 2003 values for mean ambient SRP

concentrations Sw and U were compared with

postremoval 2003 and 2004 values using t-tests Linear

regression was used to analyze relationships between

Sw U and Vf and cover of silt sand siltthorn sand and

mean water retention time Correlation analysis was

used to compare Sw and SRP elevation over ambient

values Variables expressed as percentages were trans-

formed to arcsin values to normalize distributions

Other variables were log-transformed to homogenize

variance before analysis when necessary All statistical

analyses were done using SYSTAT (version 10 SPSSChicago Illinois)

Results

Physical changes

The 2003 summer season was slightly drier thanaverage (National Climate Data Center 2003) and thisdryness was reflected in the discharge data for BoulderCreek Q calculated from hourly stage measurementsand the stage-discharge curve ranged from 021 to 24m3s (mean 6 SE 05 6 02) for all of 2003 but washigher and more variable in 2004 (11 6 06 range013ndash50 m3s)

The channel in the impounded reaches deepenedand narrowed in the area directly upstream of bothdams after dam removal (Fig 2A B) A head cutformed immediately after the lower dam was breachedand moved upstream over several hours stalling at theupper end of the former reservoir 30 m upstream ofthe dam site The channel deepened in this section ofthe stream over the next several weeks but the headcut did not move farther upstream Net transport ofsediment from the lower impounded area from July toAugust 2003 was estimated as 160 m3 Removal of themain wall of the upper dam revealed a mass ofconsolidated clay and rock material which erodedmuch more slowly than the sediment behind the lowerdam A distinct step was visible at this location for 2mo after the removal Channel adjustments in theupper dam area were limited to the former impound-ment area and erosion occurred in the first 19 mupstream of the dam site A cross section below thelower dam was in the lee of a small island and in aposition to receive sediment deposition from both theupper and lower dams This cross section changedvery little over the study period although somedeposition was observed

Overall width and channel surface area did notchange significantly after the removal despite localdecreases in channel widths above both damsChannel adjustment was moderate throughout theentire study reach (Table 1) The average streamwetted-channel width varied from 34 to 44 mthroughout the sampling period (preremoval 2003 vspostremoval 2003 comparison t frac14 070 p frac14 025preremoval 2003 vs postremoval 2004 comparison tfrac14001 p 05) Surface area decreased by only 5 overthe entire study length

Silt and sand together covered 46 to 55 of thebenthic surface in the study reach before the damremovals and bed composition showed minor butconsistent variation from week to week (Fig 3) Coverof silt thorn sand ranged from 42 to 60 and bed

FIG 2 Channel cross-sectional profiles immediately up-stream from the upper (A) and lower (B) dams 1 d before 9 dafter and 27 d after dam removal


composition continued to show weekly changesduring the six 2003 postremoval sampling datesHeadcutting and channel formation upstream of bothdams resulted in erosion and deposition of sedimentbut effects on the stream bed were localized andtransient Changes in bed composition associated withthe removal did not appear to be substantially differ-ent than background levels even for the transectswithin the silt-filled reservoir immediately upstream ofeach dam where the physical impacts of the removalwere greatest Cover of siltthorn sand decreased slightly in2004 However this change was more likely a result ofincreased discharge in 2004 than of dam removal

SRP concentration and uptake

Ambient SRP concentrations were highly variableand often high in both years (Table 2) with valuesranging from 0023 to 007 mgL High-frequencysampling revealed a distinct but extremely brief pulseof SRP generated from the breaching of the dam andrelease of stored reservoir sediments (Fig 4) SRPincreased to 0066 mgL within 10 min of the initialbreach and reached a maximum concentration of 0074mgL 1 h later as the first flush of sediments escapedfrom the reservoir following the removal of most of thedam face Concentrations returned to backgroundlevels within 2 h then rose modestly soon after thebreach of the smaller upstream structure 3 h laterAnother moderate increase in SRP occurred inassociation with a wave of sand and silt passingthrough the sample site during the final 6 h of ISCOsample collection The highest concentrations wereobserved in the 2 wk after the removal (Table 2) butpreremoval and postremoval 2003 concentrations did

not differ significantly (t frac14 01 p frac14 015) Preremoval2003 concentrations were lower than postremoval 2004concentrations (2003 mean 003 mgL 2004 mean004 mgL p frac14 001) and SRP was marginally higherafter dam removal (2003 and 2004 postremoval datestogether) than before dam removal (tfrac14 003 pfrac14 007)

SRP retention changed from one sampling date tothe next and the study reach fluctuated betweenfunctioning as a P sink to functioning as a P sourceseveral times over the course of our study (Table 2 Fig5) On 19 May 2003 Sw was relatively short (169 m)Two weeks later (3 June) Sw was not measurablebecause the relationship between SRP concentrationand distance downstream was not significant On 10June the relationship between distance downstreamand corrected SRP concentrations was significantlypositive (negative Sw) indicating that the stream was asource of SRP at that time This pattern was reversedand then repeated immediately after dam removal andagain in late June and early July 2004 No significantuptake could be measured on 5 of the 19 dates ofnutrient addition (dates when R2 01) and signifi-cant positive relationships between distance down-stream and SRP concentration were found on 3 datesSw was not correlated with elevation in nutrientconcentrations or with background streamwater SRP

The comparison of Sw measurements between yearswas confounded with the slightly higher discharge in2004 but the other spiraling metrics are flow inde-pendent The longest Sw values were found 2 wk afterdam removal (Table 2 Fig 5A) on days when ambientSRP values were within the range of preremoval SRPvalues Sw did not differ between preremoval 2003 andpostremoval 2003 dates (p frac14 015) Sw was marginally

FIG 3 Average composition of benthic sediments for 12 transects in the Boulder Creek study reach before and after damremoval in July 2003


TABLE 2 Observed discharge (Q) and soluble reactive P (SRP) concentrations and calculated values for nutrient uptake length(Sw) uptake rate (U) and uptake velocity (Vf) The R2 and p-values are associated with the regression of SRP on distancedownstream of the dam indicates a significant positive relationship NM frac14 not measurable

Date Q (m3s) SRP (mgm3) Sw (m) R2 p U (mg m2 min1) Vf (mms)

2003

19 May 052 23 169 072 003 116 0843 June 034 29 NM 004 05910 June 043 29 NM 057 00117 June 026 35 278 042 004 056 0271 July 030 37 303 030 012 063 0286 July 039 31 476 054 002 042 02311 July 078 47 NM 077 00015 July 103 70 500 038 006 209 05022 July 052 33 NM 007 0488 August 056 34 1667 062 001 018 00912 August 030 32 1111 079 000 015 008

2004

27 May 109 42 1250 065 0009 052 02116 June 135 57 333 073 0003 312 09123 June 100 43 NM 007 04529 June 082 34 1250 074 000 034 0178 July 100 41 NM 006 04912 July 091 41 NM 053 00312 August 082 35 345 031 012 127 06024 August 082 35 NM 004 086

FIG 4 Soluble reactive P (SRP) concentrations at site 1 (upstream) and site 10 (downstream) in Boulder Creek the day beforedam removal (8 July 2003) and during dam removal (9 July 2003) Circles denote samples collected at 3-h intervals by automatedISCO samplers and the triangles represent grab samples collected at 15- to 60-min intervals at the downstream location 0 hrepresents the initial breach of the lower dam


longer after dam removal (2003 and 2004 postremovaldates together) than before dam removal (p frac14 0065)The range of preremoval 2003 Sw values (169ndash476 mFig 5A) was smaller than the range of postremoval2003 values (500ndash1667 m Fig 5A) The range of 2004Sw values (333ndash1250 m Fig 5B) was similar to therange of 2003 values (169ndash1667 m)

Calculation of uptake is based on a significantpositive Sw value Therefore U and Vf could becalculated only when Boulder Creek was acting as anSRP sink (Table 2) U did not differ between prere-moval 2003 dates (042 to 116 mg m2 min1) andpostremoval 2003 dates (015 to 209 mg m2 min1 pfrac14096) U also did not differ between preremoval 2003dates and all 2003 and 2004 postremoval dates together

(pfrac14039) U was marginally higher in 2004 than in 2003(preremoval and postremoval dates together p frac140057) Vf was variable among preremoval and post-removal dates and between 2003 and 2004 (Table 2)and no comparisons of Vf values from dates before andafter removal or among years were significantCorrelations between uptake parameters and coverof silt sand or water-retention time were low (all R2

037) and not statistically significant

Transport model

Water retention times did not differ betweenpreremoval 2003 and postremoval 2003 dates (meanpreremovalfrac14 50 min mean postremovalfrac14 39 min tfrac14001 p 05) However water retention times were

FIG 5 Soluble reactive P (SRP) uptake length (Sw) in Boulder Creek during summer 2003 (A) and 2004 (B) Diamonds indicatesignificant Sw lengths Triangles indicate dates with significant positive relationships between SRP concentration and distancedownstream during nutrient-addition experiments Uptake and release were not measurable on 3 June and 22 July 2003 and on 23June 8 July and 24 August 2004 The vertical line indicates the date of dam removal


significantly shorter on postremoval 2004 samplingdates than on preremoval 2003 sampling dates (meanpostremoval 2004frac14 28 min tfrac14 451 p 005 Table 1)

The size of the transient storage zone was relativelysmall before and after dam removal (008 and 005 m2respectively Table 3) On 6 July 2003 AsA was 028and a was 13 3 104s The corresponding values for 8August 2003 were 012 and 63 3 104s (Table 3) Thedifferences between these values represent a 54reduction in AsA and an 53 increase in a between6 July 2003 and 8 August 2003 dates

Discussion

Physical and chemical changes associated with dam removal

Physical changes to Boulder Creek that were causedby the dam removals were less pronounced than wehad anticipated Channel adjustment occurred in apattern similar to that observed in other dam removals(Doyle et al 2003b) however the impacts were limitedto the small reservoir areas upstream of both damsCross-sectional surveys directly above each dam in thearea where reduction of base flow had the largestimpact showed that the channels became deeper andnarrower but cross sections farther upstream anddownstream of the dams were essentially unchangedSome sediment movement was observed in associationwith channel adjustment but these changes also werelocalized and sediment appeared to move throughand out of the study reach relatively rapidly Netdifferences in bed-material composition for any singlecross section and for the study reach overall were smalland did not appear to differ from background changesin sediment composition in this high-gradient stream

Water retention time for the study reach decreased

slightly with the removal but year-to-year variabilityin discharge decreased water retention time much morethan dam removal did and probably was responsiblefor the significant differences between preremovaldates in 2003 and postremoval dates in 2004 Thetransport models indicated that transient storage alsodeclined immediately following dam removal in 2003

SRP concentration fluctuated over a fairly widerange of values in both years but dam removal hadonly a very brief effect on ambient concentrations inBoulder Creek These effects took the form of rapidSRP pulses associated with release of the first wave ofsediment from the impoundments

Changes in uptake parameters associated with dam removal

We did not detect a significant effect of dam removalon P uptake parameters in Boulder Creek Sw washighly variable after dam removal suggesting that thestream was changing from a nutrient source to sinkand back again over at least a 2-wk period Udecreased and Sw increased slightly during the 2 wkafter dam removal However whether dam removalcaused these changes is not clear in the context of theentire sampling period The switch from sink to sourcein 2003 just after removal of the dam may have beencaused by the removal but this type of switch also wasobserved in 2003 before removal of the dam and againin 2004 well after removal a pattern that suggests thatsuch variability may be a natural feature of BoulderCreek Moreover dam removal produced only mod-erate localized physical changes to Boulder Creek soit is not surprising that the response of Sw to thedisturbance of dam removal was difficult to detect

We expected bed composition and water retentiontime to change after dam removal and our originalprediction was that uptake parameters would becorrelated with the composition of bed material Forexample we expected to find higher Us associatedwith more silt and sand and greater water residencetime before removal and lower Us associated with anarrower cobble and rock-dominated channel withhigher flow velocities after removal Contrary to theseexpectations U Vf and Sw were not correlated withthe cover of silt sand or siltthorn sand nor with water-residence time

We were able to make only 2 estimates of transientstorage and conclusions are difficult to extrapolatefrom this limited number of estimates because thesimulations are specific for the time and reach lengthwhere the measurements were made (Wagner andHarvey 1997) The results of the models suggested thattransient storage may be important to nutrient dynam-

TABLE 3 Hydrologic properties of surface and storagezones in the Boulder Creek study reach before dam removalon 6 July 2003 and after removal on 8 August 2003

Variable6 July2003

8 August2003

Surface flow

Discharge (m3s) 039 056Cross-sectional area (m2) 027 044Dispersion (m2s) 039 018

Storage zone

Storage zone cross-sectionalarea (m2)

008 005

Storage zonechannel arearatio (m2m2)

028 012

Exchange coefficient (s) 000013 000063

Channel residence time (min) 52 44


ics The uptake rate from 6 July 2003 to 8 August 2003changed in the same proportion as the change in theAsA value between those 2 dates However ourresults do not tell us where the uptake is occurringStream-tracer methods may be more sensitive tochanges in exchange with surface storage zones thanwith hyporheic flow (Harvey et al 1996) but it is notpossible to differentiate between these 2 areas ofstorage using this method

In other systems nutrient Sw has been related toambient nutrient concentration (Dodds et al 2002) anddegree of enrichment presumably because of Michae-lisndashMenton kinetics (Steinman and Mulholland 1996)This relationship between Sw and nutrient concen-tration can make comparisons of measured ratesacross experiments difficult (Mulholland et al 2002)and could potentially cause the type of variation in Sw

found in our study However Sw was not correlatedwith degree of nutrient enrichment in our study andelevated concentrations were consistently within rec-ommended ranges for the method we used (Mulhol-land et al 2002) making it unlikely that the largedifferences observed in uptake were caused by over-enrichment during the nutrient additions

Values of Sw were slightly longer after dam removalthan before but postremoval values remained withinthe range of values observed before dam removal If Pwere the limiting nutrient in Boulder Creek it shouldhave been retained in the stream reach and water SRPconcentrations should have been low However weobserved relatively high SRP concentrations on severaldates before and after removal and it is likely that Pwas not limiting production in Boulder Creek Back-ground SRP concentrations in Boulder Creek wereabove concentrations considered limiting in othersystems (10 lgL Dodds et al 2002) Moreover thefrequency of weak or nonsignificant regressionsbetween dilution-corrected SRP values and distancedownstream for Sw calculations observed in our studyindicate low demand and nonlimiting conditions(Haggard et al 2005) Significant downstream uptakeis possible under nonlimiting conditions (eg Doyle etal 2003c Haggard et al 2005) but limitation of Puptake by other variables (eg light) may haveconfounded our ability to identify the effects of damremoval on uptake dynamics Natural variabilityprobably was another factor that limited our abilityto detect an effect of dam removal on nutrient-uptakeparameters Simon et al (2005) reported that values ofSw showed seasonal ranges from 200 to 600 m basedon monthly measurements in a New Zealand streamThis temporal variability was similar to that observedin our study although the magnitudes of the changes

in values of Sw were lower in the study by Simon et al(2005) than those we measured in Boulder Creek

Our results differed from results of another damremoval in the same region as Boulder Creek (Doyle etal 2003c) Doyle et al (2003c) used a massndashbalanceapproach to measure P retention in a 45-km-longreservoir and found that changes in channel geometrymight explain up to 40 of the measured change in Pconcentration Their model also suggested that channelgeometry would be more influential than Sw whenbiochemical uptake rates were high or had limitedvariability The discrepancy between Doyle et al (2003c)and our study probably is a result of the relativevariability of uptake across stream systems and the scaleof disturbance caused by the dam removals In BoulderCreek Sw was measured directly and was highlyvariable over time Moreover channel changes werelimited to the 20 m directly above the dams in BoulderCreek and probably were not large enough disturbancesfor channel geometry to become more important thanbiochemical uptake In the system studied by Doyle etal (2003c) geomorphic changes following removalproduced significant responses in velocity and depthand measurable decreases in P retention

Implications

Based on experience from other study sites weexpected the removal of the 2 dams to cause a largechange in the channel geometry of Boulder Creek andwe expected this change to reduce nutrient retentionfor some period of time following the removalsHowever both dams were run-of-river with minimalimpounded areas and they did not change flowtiming or water temperature while they were in placeSome fine sediments were deposited preferentiallybehind each dam but the downstream channel wasnot sediment starved to the point that the channel wasdown-cut or excessively armored as has been observedat other dam sites (Collier et al 1996) Dam removalchanges channel geometry (Doyle et al 2003b) but inthe case of Boulder Creek the magnitude of the changein the physical construction of the stream was not largeenough to alter nutrient retention significantly In thefinal analysis removing the dams appears to havebeen a relatively minor disturbance with respect toreach-scale channel form and nutrient retention

This conclusion is not to say that the removal of thedams had no effect on the stream in other waysBiological variables such as primary productivityinvertebrate distribution and fish habitat could havebeen impacted by the sediment transport and deposi-tion we observed Recent studies describing macro-invertebrate community structure (Bushaw-Newton et


al 2002 Pollard and Reed 2004 Sethi et al 2004) andfish movement (Kanehl et al 1997) have providedmixed information on the impact dam removal mayhave on biotic communities

Our study emphasizes the differences between damsand the outcomes of their removal In our study thedams and the disturbance of their removal appear tohave been too small relative to normal backgroundvariation to change basic functions in Boulder CreekHowever studies of larger dams have shown thatremovals can cause substantial changes in the physicalsetting and biological processes of streams (Doyle et al2003c) Most dam removals are of small dams (Doyleet al 2005) and in that regard Boulder Creek may be agood model for studying the effects of removal Incases such as this one where the restoration distur-bance was within the range of natural disturbanceexperienced by the system measurements that show asignificant amount of natural variability (eg nutrient-spiraling parameters) may not be robust enough toshow a clear response to the disturbance

Widespread promotion of selective removal of damsas a tool for restoration or enhancement for riverecosystems (Hart et al 2002) will make understandingthe relationships between dam-related disturbanceand its physical and ecological consequences moreimportant We must continue to evaluate how resultsfrom small systems such as Boulder Creek may or maynot be applied to systems at different scales A recentevaluation of stream-restoration efforts showed thattens of thousands of stream and river restorationprojects are being done in the US However few ofthese efforts have been monitored or evaluated todetermine if they met their goals of improvingecological attributes or processes (Bernhardt et al2005) Measures of ecosystem response to restorationshould be useful for evaluating the success of restora-tion efforts but the processes measured for evaluationshould be chosen to be consistent with the scale andnatural variability of the system under study

Acknowledgements

We thank the Aldo Leopold Foundation and SteveSwenson for access to the study site and for coordinat-ing the dam removals We are indebted to Noah LottigMegan Mezera and Steve Kroiss for their assistance inthe field and David Huyck for the study-site illustra-tion We also thank 2 anonymous referees for theircomments which greatly improved earlier versions ofour paper Funding for the dam removal came in partfrom the US Fish and Wildlife Service and a portion ofour research was funded by a University of WisconsinVilas Association Award to EHS

Literature Cited

ALEXANDER R B R A SMITH AND G E SCHWARZ 2000 Effectof stream channel size on the delivery of nitrogen to theGulf of Mexico Nature 403758ndash761

APHA (AMERICAN PUBLIC HEALTH ASSOCIATION) 1995 Stand-ard methods for the examination of water and waste-water 19th edition American Public Health AssociationAmerican Water Works Association and Water Environ-ment Federation Washington DC

BEDNAREK A T 2001 Undamming rivers a review of theecological impacts of dam removal EnvironmentalManagement 27803ndash814

BERNHARDT E S M A PALMER J D ALLAN G ALEXANDER KBARNAS S BROOKS J CARR S CLAYTON C DAHM JFOLLSTAD-SHAH D GALAT S GLOSS P GOODWIN D HARTB HASSETT R JENKINSON S KATZ G M KONDOLF P SLAKE R LAVE J L MEYER T K OrsquoDONNELL L PAGANO BPOWELL AND E SUDDUTH 2005 Synthesizing US riverrestoration efforts Science 308636ndash637

BORN S M K D GENSKOW T L FOLBERT N HERNANDES-MORA M L KEEFER AND K A WHITE 1998 Socio-economic and institutional dimensions of dam removalsthe Wisconsin experience Environmental Management22359ndash370

BUSHAW-NEWTON K L D D HART J E PIZZUTO J RTHOMSON J EGAN J T ASHLEY T E JOHNSON R JHORWITZ M KEELEY J LAWRENCE D CHARLES C GATENBYD A KREEGER T NIGHTENGALE R L THOMAS AND D JVELINSKY 2002 An integrative approach towards under-standing ecological responses to dam removal Journal ofthe American Water Resources Association 381581ndash1599

COLLIER M R J WEBB AND J SCHMIDT 1996 Damsriversprimer on the downstream effects of dams US Geo-logical Survey Circular 1126 US Geological SurveyTuscon Arizona

DAVIS J C AND G W MINSHALL 1999 Nitrogen andphosphorus uptake in two Idaho (USA) headwaterstreams Oecologia (Berlin) 119247ndash255

DODDS W K A J LOPEZ W B BOWDEN S GREGORY N BGRIMM S K HAMILTON A E HERSHEY E MARTI W HMCDOWELL J L MEYER D MORRALL P J MULHOLLAND BJ PETERSON J L TANK H M VALETT J R WEBSTER AND WWOLLHEIM 2002 N uptake as a function of concentrationin streams Journal of the North American BenthologicalSociety 21206ndash220

DOYLE M W E H STANLEY AND J M HARBOR 2003aTowards policies and decision-making for dam removalEnvironmental Management 31435ndash465

DOYLE M W E H STANLEY AND J M HARBOR 2003bChannel adjustment following two dam removals inWisconsin Water Resources Research 391011ndash1026

DOYLE M W E H STANLEY AND J M HARBOR 2003cHydrogeomorphic controls on phosphorus retention instreams Water Resources Research 391147ndash1164

DOYLE M W E H STANLEY J M HARBOR AND G S GRANT2003d Dam removal in the United States emergingneeds for science and policy Eos 8429ndash36

DOYLE M W E H STANLEY C H ORR A R SELLE S ASETHI AND J M HARBOR 2005 Stream ecosystem response


to small dam removal lessons from the heartlandGeomorphology 7227ndash244

GRAF W L 1999 Dam nation a geographic census ofAmerican dams and their large-scale hydrologic impactsWater Resources Research 351305ndash1311

GUCKER B AND I G BOECHAT 2004 Stream morphologycontrols ammonium retention in tropical headwatersEcology 852818ndash2827

HAGGARD B E E H STANLEY AND D E STORM 2005 Streamnutrient retention efficiency in an enriched systemJournal of the North American Benthological Society2429ndash47

HART D D T E JOHNSON K L BUSHAW-NEWTON R JHORWITZ A T BEDNAREK D F CHARLES D A KREEGERAND D J VELINSKY 2002 Dam removal challenges andopportunities for ecological research and river restora-tion BioScience 52669ndash682

HARVEY J W B J WAGNER AND K E BENCALA 1996Evaluating the reliability of the stream tracer approach tocharacterize stream-subsurface water exchange WaterResources Research 322441ndash2451

KANEHL P D J LYONS AND J E NELSON 1997 Changes in thehabitat and fish community of the Milwaukee riverWisconsin following removal of the Woolen Mills damNorth American Journal of Fisheries Management 17387ndash400

KLOTZ R L 1988 Sediment control of soluble reactivephosphorus in Hoxie Gorge Creek New York CanadianJournal of Fisheries and Aquatic Sciences 452026ndash2034

KNIGHTON D 1998 Fluvial forms and processes a newperspective Arnold Publishers London UK

MARTI E N B GRIMM AND S G FISHER 1997 Pre- and post-flood retention efficiency of nitrogen in a Sonoran Desertstream Journal of the North American BenthologicalSociety 16805ndash819

MEYER J L 1979 The role of sediments and bryophytes inphosphorus dynamics in a headwater stream ecosystemLimnology and Oceanography 24365ndash375

MULHOLLAND P J J L TANK J R WEBSTER W K DODDS S KHAMILTON S L JOHNSON E MARTI W H MCDOWELL JMERRIAM J L MEYER B J PETERSON H M VALETT AND WM WOLLHEIM 2002 Can uptake lengths in streams bedetermined by nutrient addition experiments Resultsfrom an interbiome comparison study Journal of theNorth American Benthological Society 21544ndash560

NATIONAL CLIMATE DATA CENTER 2003 Annual climatologicalsummary 2003 Station 470516 for Baraboo WisconsinNational Oceanic and Atmospheric Administration USDepartment of Commerce Asheville North Carolina(Available from httpwwwncdcnoaagovoancdchtml)

NEWBOLD J D J W ELWOOD R V OrsquoNEILL AND A LSHELDON 1981 Measuring nutrient spiraling in streamsCanadian Journal of Fisheries and Aquatic Sciences 38860ndash863

POHL M M 2002 Bringing down our dams trends inAmerican dam removal rationales Journal of theAmerican Water Resources Association 381511ndash1519

POLLARD A I AND T REED 2004 Benthic invertebrate

assemblage change following dam removal in a Wiscon-sin stream Hydrobiologia 51351ndash58

RUNKEL R L 1998 One dimensional transport with inflowand storage (OTIS) a solute transport model for streamsand rivers US Geological Survey Water ResourcesInvestigation Report 98ndash4018 US Geological SurveyDenver Colorado

RUNKEL R L 2002 A new metric for determining theimportance of transient storage Journal of the NorthAmerican Benthological Society 21529ndash543

SETHI S A A R SELLE M W DOYLE E H STANLEY AND H EKITCHEL 2004 Response of unionid mussels to damremoval in Koshkonong Creek Wisconsin (USA) Hy-drobiologia 525157ndash165

SIMON K S C R TOWNSEND B J F BIGGS AND W B BOWDEN2005 Temporal variation of N and P uptake in 2 NewZealand streams Journal of the North AmericanBenthological Society 241ndash18

STANLEY E H AND M W DOYLE 2002 A geomorphicperspective on nutrient retention following dam remov-al BioScience 52693ndash702

STANLEY E H M A LUEBKE M W DOYLE AND D WMARSHALL 2002 Short-term changes in channel form andmacroinvertebrate communities following low-headdam removal Journal of the North American Bentho-logical Society 21172ndash187

STEINMAN A D AND P J MULHOLLAND 1996 Phosphoruslimitation uptake and turnover in stream algae Pages161ndash190 in F R Hauer and G A Lamberti (editors)Methods in stream ecology Academic Press San DiegoCalifornia

STREAM SOLUTE WORKSHOP 1990 Concepts and methods forassessing solute dynamics in stream ecosystems Journalof the North American Benthological Society 995ndash119

USACE (US ARMY CORPS OF ENGINEERS) 1998 Nationalinventory of dams US Army Topographic EngineeringCenter Alexandria Virginia (Available fromhttpcrunchtecarmymilnidwebpagesnidcfm)

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VALETT H M C L CRENSHAW AND P F WAGNER 2002 Streamnutrient uptake forest succession and biogeochemicaltheory Ecology 832888ndash2901

VALETT H M J A MORRICE C N DAHM AND M E CAMPANA1996 Parent lithology surface-groundwater exchangeand nitrate retention in headwater streams Limnologyand Oceanography 41333ndash345

WAGNER B J AND J W HARVEY 1997 Experimental designfor estimating parameters of rate-limited mass transferanalysis of stream tracer studies Water ResourcesResearch 331731ndash1741

WEBSTER J W AND T P EHRMAN 1996 Solute dynamicsPages 145ndash160 in F R Hauer and G A Lamberti(editors) Methods in stream ecology Academic PressSan Diego California

Received 8 April 2005Accepted 15 March 2006


J N Am Benthol Soc 2006 25(3)556ndash568 2006 by The North American Benthological Society

Channel morphology and P uptake following removal of a small dam

Cailin H Orr1 Kristy L Rogers2 AND Emily H Stanley3

Center for Limnology University of Wisconsin 608 North Park Street Madison Wisconsin 53706 USA

Abstract Dam removal is becoming an increasingly common management solution for aging dams andevaluation of the impact of dam removal on basic attributes of streams such as nutrient uptake andtransport is essential The removal of 2 small dams from a forested 2nd-order stream in Wisconsin allowedus to study how nutrient dynamics were influenced by changes in channel geometry and bed material Wecalculated P uptake and transient storage metrics from a series of 19 short-term injections measured cross-sectional profiles and determined benthic sediment size at regular intervals for 2 mo before and after theremovals We also repeated these measurements over the same time period the following year Nutrientuptake was highly variable and the stream changed from being a soluble reactive P (SRP) sink to being asource several times over the study period Uptake lengths increased immediately after dam removal butdifferences between measurements made before and after removal were not significant We found nosignificant relationship between uptake length and benthic sediment composition channel geometry orwater residence time over the course of the dam removals Our results indicate that changes in physicalchannel attributes did not play an important role in controlling SRP retention probably because the impactof dam removal was small compared with the natural variability of this system

Key words dam removal nutrient uptake geomorphology Wisconsin sediments

Dam removal is an increasingly prevalent solutionfor the management of aging dams (Doyle et al2003d) The number of intentional removals in the USis estimated at 417 (Pohl 2002) (cf thousands of damsin existence USACE 1998 Graf 1999) but the potentialfor this management action to become more frequent issubstantial because of growing safety and economicconcerns associated with an aging national daminfrastructure (Born et al 1998 Doyle et al 2003a)Selective removal of dams has been widely promotedas a powerful restoration or enhancement tool for riverecosystems (Hart et al 2002) because removal isexpected to reverse many of the deleterious effects ofdams such as blockage of fish passage flow mod-ification or thermal alteration (Bednarek 2001) How-ever tests of the effects of dam removal on rivers areextremely limited Recent studies describing channelformation (Doyle et al 2003a) macroinvertebratecommunity structure (Bushaw-Newton et al 2002Stanley et al 2002) and fish movement (Kanehl et al

1997) have provided encouraging but limited resultswith respect to rehabilitation of ecosystem functionsfollowing dam removal The number of river restora-tion projects that involve dams is increasing and thistrend has spurred a new interest in determining howphysical alterations such as dam removal impact basicecological patterns and processes in streams (Bednarek2001)

Nutrient retention is a fundamental attribute ofstreams that may be affected by dam removal (Stanleyand Doyle 2002) The concept of spiraling often is usedto describe nutrient cycling in these ecosystems andthe efficiency of nutrient uptake is reported as uptakelength or the average distance a nutrient moleculemoves downstream before it is retained by the benthos(Sw Newbold et al 1981) Short Sws are an indicationof elevated demand and possibly increased limitationof the nutrient of interest However short Sws also canbe caused by changes in water velocity and depthbecause measurement of Sw has a hydrologicalcomponent (Stream Solute Workshop 1990 Simon etal 2005)

Benthic uptake of nutrients has both biotic (periph-yton and biofilm) and abiotic (sediment adsorption)components and several variables can influenceuptake rates simultaneously (Davis and Minshall1999) However nutrient retention is modulated by

1 Present address Carolina Environmental Program CB

1105 University of North Carolina Chapel Hill ChapelHill North Carolina 27599-1105 USA Email chorruncedu

2 E-mail addresses kristyrogerswiscedu3 ehstanleywiscedu

556






Study Site








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U frac14 CbQ60

SwwVf frac14

U

Cb60


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Variable6 July2003

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Variable6 July2003

8 August2003

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Acknowledgements


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SwwVf frac14

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Variable6 July2003

8 August2003

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Data analysis













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2003


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Variable6 July2003

8 August2003

Surface flow


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Results

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Variable6 July2003

8 August2003

Surface flow


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028 012










Implications







Acknowledgements


Literature Cited



























































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Variable6 July2003

8 August2003

Surface flow


Storage zone


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Variable6 July2003

8 August2003

Surface flow


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028 012










Implications







Acknowledgements


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Variable6 July2003

8 August2003

Surface flow


Storage zone


008 005


028 012










Implications







Acknowledgements


Literature Cited



















































Discussion











Variable6 July2003

8 August2003

Surface flow


Storage zone


008 005


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Implications







Acknowledgements


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Documents

Channel morphology and P uptake following removal of a small dam