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Using a New Groundwater-Regression Model to Forecast Nitrogen Loading from the Delmarva Peninsula. Ward Sanford, USGS, Reston, Virginia Jason Pope, USGS, Richmond, Virginia David Selnick, USGS, Reston, Virginia. Objectives:. - PowerPoint PPT Presentation
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Using a New Groundwater-RegressionModel to Forecast Nitrogen Loading
from the Delmarva Peninsula
Ward Sanford, USGS, Reston, VirginiaJason Pope, USGS, Richmond, VirginiaDavid Selnick, USGS, Reston, Virginia
Objectives:· To develop a groundwater flow model that can simulate return-times to streams
(base-flow ages) on the Delmarva Peninsula
· To explain the spatial and temporal trends in nitrate on the Delmarva Peninsula using a mass-balance regression equation that includes the base-flow age distributions obtained from the flow model
· To use the calibrated equation to forecast total nitrogen loading to the Bay from the Eastern Shore
· To forecast changes in future loadings to the bay given different loading application rates at the land surface
· To develop maps that will help resource managers target areas that will respond most efficiently to better management practices
Groundwater Model—Delmarva Peninsula
MODFLOW 2005500 ft cell resolution7 Model Layers4+ million active cells30-m DEM, LIDAR300 ft deepSteady State FlowMODPATH travel timesSanford and others (2012)
USGS Open File Report2012-1140 (in press).
1 2
34
5
6
7
Seven watersheds hadsubstantial stream nitrateData and were used:
1. Morgan Creek
2. Chesterville Branch
3. Choptank River
4. Marshyhope Creek
5. Nanticoke River
6. Pocomoke River
7. Nassawango Creek
1950 1960 1970 1980 1990 2000 2010 20200.00.20.40.60.81.01.21.41.61.82.0
Choptank River near Greensboro, MD
Annual Averages
Multi-Year Averages
YEAR
Nitra
te a
s N,
in m
g/L
1950 1960 1970 1980 1990 2000 2010 20200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0Nanticoke River near Bridgeville, DE
Yearly Averages
Multi-Year Averages
YEAR
Nitra
te a
s N,
in m
g/L
1950 1960 1970 1980 1990 2000 2010 20200.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.6
4.0Morgan Creek near Kennedyville, MD
Yearly AveragesMulti-Year Averages
YEAR
Nitra
te a
s N,
in m
g/L
1 10 100 1000 100000
1
10Choptank River near Greensboro, MD
Discharge, in Cubic Feet per Second
Nitra
te a
s N,
in m
g/L
Nitrate Mass-Balance Regression Equation
Simulatedsurface waterconcentration
in stream
=
Concentrationat water table
at recharge year
SoilTerm
RiparianTermX
Denitrification
Simulatedgroundwaterconcentrationin ag field well
=
Concentrationat water table
at recharge year
XSoilTerm
Concentrationat water table
at recharge year= Fertilizer
Load [ XPoultryLoad
RechargeRate ]X X{ [] }1 - 1 -FUE PUE+
FUE & PUE =Fertilizer and PoultryUptake Efficiencies
SoilTerm = (S/5)m
Denitrification ratealong flow path
RiparianTerm = (AREA)n
S = soil drainagefactor
AREA is for the watershedIn square miles
Sn=1
No.pathlines
XX
Denitrification ratealong flow pathX
0
10
20
30
40
50
60
1940 1950 1960 1970 1980 1990 2000 2010
Year
Nitr
ogen
Loa
ding
from
Fer
tiliz
er, m
g/L
Kent
New CastleSussex
CarolineCecil
Dorchester
KentQueen Annes
Somerset
Talbot
WicomicoWorcester
Accomackaverage
1 4 7 10 13 16 19 22 25 28 310.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Stream and Riparian Denitrification
Euivalent distance traveled along the stream, in miles
Frac
tion
Nitra
te R
emai
ning
For calibrated watershed areaexponent parameter = -0.119
Soil Factor (S) in Equation:
1. Very poorly drained2. Somewhat poorly drained3. Poorly drained4. Moderately well drained5. Well drained6. Somewhat excessively drained7. Excessively drained
1 2 3 4 50.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Soil Factor, S
Frac
tion
Nitra
te R
emai
ning
For calibrated soil drainageexponent parameter = 0.337
Very poorlydrained
Welldrained
Fertiliz
er in Rec
harge
After C
rop Uptake
After S
oil Den
itrific
ation
After n
on-ag di
lution
After p
re-ag
dilutio
n
After r
iparian
denitri
ficati
on
observe
d0
5
10
15
20
25
30
35
40
45
50
Morgan Creek
Pocomoke River
Process Leading to Nitrate Loss or Dilution
Con
cent
ratio
n on
Nitr
ate
as N
, in
mg/
L
Regression Number
Fertilizer
Uptake
Efficiency
Manure Uptake Efficiency
Percent Increase in
Uptake Efficiencies
Riparian and Stream
Denitrificait
on loss exponent
Soil Deintirficaiton loss
exponent
Number of
Parameters
estimated
Sum of Squared
Weighted Residual
s
Standard Error of
Regressi
on
1 83% 83% 0 0 0 2 6141 89
2 82% 70% 0 0 0.670 3 5721 83
3 72% 63% 0 -0.152 0 3 2394 35
4 72% 46% 0 -0.146 0.425 4 2139 31
5 67% 47% 24% -0.119 0.377 5 1651 25
10% upper parameter value
limit70% 62% 40% -0.120 0.77 5 2056 40
10% lower parameter value
limit64% 32% 12% -0.155 0.1 5 2056 40
10% limits as percent of value 4% 32% 38% 13% 82% 5 2056 40
1950 1960 1970 1980 1990 2000 20100.00.20.40.60.81.01.21.41.61.82.0
Choptank River near Greensboro, MD
Yearly AveragesMulti-Year AveragesRegression Model
YEAR
Nitra
te a
s N,
in m
g/L
Best Fit for Four Parameterswith constantFertilizer and ManureUptake Efficiencesthrough Time
1950 1960 1970 1980 1990 2000 20100.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0Nanticoke River near Bridgeville, DE
Yearly AveragesMulti-Year AveragesRegression Model
YEAR
Nitra
te a
s N,
in m
g/L
1950 1960 1970 1980 1990 2000 2010 20200.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.6Morgan Creek near Kennedyville, MD
Yearly AveragesMulti-Year AveragesRegression Model
YEAR
Nitra
te a
s N,
in m
g/L
1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 20500
4
8
12
16
20
24 Forecast of Nitrogen Loading
Total Flow N Loading
Had there been no BMPs
High Flow Component
YEAR
Nitr
ogen
Loa
d to
the
Bay
, in
Mill
ions
of P
ound
s pe
r Yea
r
1980 1990 2000 2010 2020 2030 2040 20500
2
4
6
8
10
12
14
16
18
20
Forecast of Nitrogen Loading
13% load reduction
40% load reduction
100% load reduction
0% load reduction
YEAR
Nitr
ogen
Loa
d to
the
Bay
, in
Mill
ions
of P
ound
s pe
r Yea
r
EPA TARGET
Targeting Matrix
Targeting that Includes Response Timeand Nitrogen Delivered to the Bay
Groundwater Return Time
< 7 yrs 7 - 20 yrs > 20 yrs
NitrateConcentration
< 4 mg/L
5 - 7 mg/L
>7 mg/L
Targeting Matrix
Targeting that Includes Response Timeand Nitrogen Delivered to the Bay
Groundwater Return Time
< 7 yrs 7 - 20 yrs > 20 yrs
NitrateConcentration
< 4 mg/L
5 - 7 mg/L
>7 mg/L
Summary and ConclusionsResults from a groundwater flow model were coupled to a nitrate-mass-
balance regression model and calibrated against stream nitrate data.
The calibrated model suggests that nitrogen uptake efficiencies on the Eastern Shore may be improving over time.
Response time of nitrogen delivery to the Bay on the Eastern Shoreis on the order of several decades
EPA targets are for reduced loading of ~20% (3 million lbs/yr) on the Eastern Shore. This cannot be accomplished by reducing landsurface applications by 20%, as loads will continue to rise 13%.
The new model can help target areas where reduced nitrogen loadings would be the most beneficial at reducing total loadings to the Bay.