walnut creek: monitoring, modeling, and optimizing prairie restoration sergey rabotyagov 1, keith...
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![Page 1: Walnut Creek: Monitoring, Modeling, and Optimizing Prairie Restoration Sergey Rabotyagov 1, Keith Schilling 3, Manoj Jha 2, Calvin Wolter 3, Todd Campbell](https://reader030.vdocuments.mx/reader030/viewer/2022032723/56649cf85503460f949c83b2/html5/thumbnails/1.jpg)
Walnut Creek: Monitoring, Modeling, and Optimizing Prairie Restoration
Sergey Rabotyagov1, Keith Schilling3, Manoj Jha2, Calvin Wolter3, Todd Campbell2
Affiliations: 1. College of Forest Resources, University of Washington, Seattle, 2. Center for Agricultural and Rural Development, Iowa State University, Ames, IA. 3. Iowa DNR-Geological Survey
Gulf Hypoxia WorkshopAmes, Iowa
October 16, 2008
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Walnut Creek Watershed Restoration
• The project was established in 1995 in relation to watershed restoration activities at Neal Smith National Wildlife Refuge located near Prairie City, Iowa
• Large areas of the Walnut Creek watershed have been converted from row crop to native prairie by the US Fish and Wildlife Service
• Paired watershed approach - Walnut Creek is 12,890 ac (treatment watershed) and Squaw Creek is 11,714 ac (control watershed)
• Watersheds share a basin divide and have similar basin characteristics
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Watershed Info
• Since 1993, 3,023 ac of prairie planted in Walnut Creek watershed – most located in core of watershed between two stream gauges (23% of watershed)
• 3.7% of watershed – rented to area farmers
• From 1992 to 2005: row crop land use decreased from 69 to 54% in WC and increased from 71 to 80% in Squaw Creek
• Nitrogen applications reduced 21%; Pesticide use reduced by 28%
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1990 Land Cover
69-71% row crop
2005 Land Cover
54.5% row crop in Walnut Creek
80.6% row crop in Squaw Creek
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Nitrate Concentrations and Loads
Dis
char
ge (
cfs)
0.1
1
10
100
1000
10000
Nitr
ate-
N C
once
ntra
tion
(mg/
l)
0
4
8
12
16
0.1
1
10
100
1000
10000
Water Year
0
4
8
12
16
WNT2
SQW2
1996 1998 2000 2002 2004
WNT2 range 0.5 to 14 mg/l
SQW2 range 2.1 to 15 mg/l
Exceeded 10 mg/l (MCL) 32.8% in Walnut Creek 51.5% in Squaw Creek
Similar temporal pattern of detection – higher in spring and early summer
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Subbasin WNT5 45.9% prairie
Subbasin WNT6 14.3% prairie
Subbasin WNT335.7% prairie
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NO
3-N
Co
nce
ntr
atio
ns (
mg/
l)
0
5
10
15
20
Water Year
0
5
10
15
200
5
10
15
20
0
5
10
15
20
WNT 1
WNT 2
SQW 1
SQW 2
199
61
997
199
81
999
200
02
001
200
22
003
200
42
005
199
61
997
199
81
999
200
02
001
200
22
003
200
42
005
Annual Changes in Nitrate
NO
3-N
Con
cent
ratio
ns (
mg/
l) 0
5
10
15
20WNT 3
0
5
10
15
20
Water Year
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
0
5
10
15
20
WNT 5
WNT 6
NO
3-N
Con
cent
ratio
ns (
mg/
l) 0
5
10
15
20SQW 3
0
5
10
15
20
Water Year
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
0
5
10
15
20
SQW 4
SQW 5
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Conclusions from monitoring
Project results indicate that prairie reconstruction can improve water quality in agricultural watersheds
Many years are needed to detect changes in nitrate due to slow groundwater flow velocities in glacial till catchment
Much more in Schilling and Wolter’s work
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Questions we would like to address
1. Given the location of prairie restoration, what does water quality modeling tell us about the “prairie effect”: the impact of prairie restoration on nutrient loadings?
2. If we wish to achieve nutrient loading reductions at least cost, where should we have put the prairie?
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The “Prairie Effect” We wish to isolate the effect of
prairie restoration Land use has changed in the rest of the
watershed, which confounds the impact of the restoration
Create a “counterfactual” scenario by overlaying 2005 prairie area onto the 1990 land use map of the watershed
Run the SWAT model for the actual 1990 land use and the counterfactual to isolate the impact of the prairie
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The Prairie Effect and Cost-Effectiveness
For example, suppose prairie restoration is predicted to reduce nitrate loadings from N0 to N1
Can (could) one do better? Either achieve the
same level of nutrient reductions at lower cost or
Achieve higher nutrient reductions at the same cost
N
Cost
R1
N0
Current: R
N1
R2
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Why is this important?
1. We are looking for a modeling confirmation of the effectiveness of restoration
2. We are looking to develop the capability to efficiently locate future prairie restoration (or other conservation practices) in the watershed
3. We are looking to inform restoration policies elsewhere
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Fundamental Questions To select the mix and location of
agricultural conservation practices to meet water quality improvement objectives at least cost Here we focus on prairie restoration
What are the trade-offs between costs and water quality improvements?
Conceptually, we wish to solve a multiobjective problem:
min (Cost, Pollutant 1, … , Pollutant K) Subject to
Conservation technology and physical constraints
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Tradeoff Frontier: “Conservation PPF”
The solution is a set of prescriptions for location of conservation practices which yield Pareto-efficient outcomes in (Cost, Pollutant 1, … , Pollutant K) space
For convenience, call this frontier of outcomes a “conservation PPF”
N
Cost
R1
N0
Current: R
N1
R2Conservation PPF
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Solution Framework We wish to approximate the solution
to: min (Cost, Nitrate, Phosphorus)
Looking for a 3-dimensional conservation PPF
Of the 3 objectives to be minimized only cost can be readily computed (as cost of land retirement)
Nutrient loadings need to be simulated Combine:
An evolutionary algorithm, SPEA2 Hydrologic model, Soil and Water Assessment
Tool (SWAT) Sometimes referred to as simulation-
optimization framework
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One possible watershed configuration (a candidate
solution)
a
db
ab
c
a
d
a
b
a a
a
13 Fields 2 conservation practices213 (8192) possible configurationsWe end up with over 1300 hundred “fields”
Practice options = (Leave As Is, Convert to Prairie)Population = set of configurations
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Algorithm progression
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Results
“Prairie Effect” is estimated to be: 28% reduction in Nitrate-N 18% reduction in Total P
Preliminary findings suggest that It could be possible to achieve the same
nutrient reductions for about 30% cheaper
It could be possible to obtain up to an additional 14% reduction in N and 10% reduction in P for the cost of existing prairie
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Where could the prairie be located to achieve same reductions at lower cost?
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Where could the prairie be located to achieve higher reductions at the same
cost?
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Preliminary Conclusions and Future Work
Preliminary modeling suggests that restoration is indeed quite effective in reducing nutrient loadings
We could do “better” if our only objectives were nutrient reductions (but prairie restoration has other goals!)
We develop a framework which Can suggest the cost-effective
placement of additional prairie or other conservation practices in Walnut Creek
Can accompany future restoration efforts