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Simulating critical source areas
1. Simulating critical source areas across
scales using watershed models
Margaret McCahon Kalcic (kalcic.4@osu.edu), Rebecca Logsdon
Muenich, Yu-Chen Wang, Anna Apostel, Awoke Teshager, Jay
Martin, Donald Scavia
Ohio State University and University of Michigan
SWCS International Annul Conference, Field to Watershed Session
Monday, July 31, 2017
2. Cover crop
Grassed
waterway
Wetland
Watershed modeling with SWAT
“The objective of the SWAT model is to predict the effect of management decisions on water,
sediment, nutrient and pesticide yields with reasonable accuracy on large, ungaged river basins.”
Acronyms:
CSA Critical Source Area
TP Total Phosphorus
DRP Dissolved Reactive Phosphorus
SWAT Soil and Water Assessment Tool
3. Two case studies
1. Maumee case study
Multiple model comparison in the Maumee
River watershed
Simulated sub-watershed CSAs before vs.
after improved agricultural management
2. Raisin case study
Sensitivity of field-level CSAs to management
assumptions in the River Raisin watershed
Baseline calibrated model vs. farmer
surveys
Maumee
Raisin
4. 1. Maumee case study
Multiple watershed modeling teams:
Multiple models guide strategies for
agricultural nutrient reductions. 2017.
Frontiers in Ecology and the
Environment.
Funding from the Erb Foundation and
Ohio Department of Higher Education
Rem Confesor
Jay Martin
Noel Aloysius
Jeffrey Kast
Marie Gildow
Anna Apostel
Don Scavia
Margaret Kalcic
Rebecca Muenich
Yu-Chen Wang
Awoke Teshager
Joe DePinto
Todd Redder
Chelsie Boles
Haw Yen
Jeff Arnold
Mike White
Dale Robertson
SPARROW model (SPAtially Referenced
Regressions On Watershed attributes)
Richard Becker
In only one of the two studies:
SWAT models (Soil and Water Assessment Tool)
5. 1. Maumee case study
Before
Previous Project
After
Current Project
Point source inputs Updated to
monthly average
Updated to monthly, included combined sewer
overflows
Climate inputs Updated Updated
Farm management
inputs/assumptions
Unchanged 1. Updated existing BMPs (cover crops, buffer
strips, no-tillage, fertilizer placement)
2. County-specific manure and fertilizer
application rates
Data sources: CEAP surveys, Robyn Wilson
surveys, Fertilizer Institute Data, Ag. Census
Calibration and years Unchanged (run
2005-2014)
Recalibrated to flow, sediment, and nutrients
near outlet, 2005-2015
8. 8
0
1
2
4
5
3
0
1
2
4
3
Number of watershed
models in agreement about
P critical source areas*
TP DRP
* CSAs are sub-
watersheds contributing
the 20% highest area-
weighted P load.
Estimated P Delivery to Lake Erie
(multi-model agreement)
PreviousProjectCurrentProject
1. Maumee case study
9. 1. Maumee case study
Findings about sub-watershed CSAs:
CSAs differed among multiple models
Each modeler set different farm management assumptions
CSAs changed with improved management assumptions
county-level fertilizer and manure applications
10. 2. Raisin case study
SWAT model calibrated to flow and nutrients near outlet
Used in a Pay-for-Performance study enrolling farmers in
conservation for TP reduction
Comparison of field-level outputs for:
A. Baseline calibrated model
B. Model modified to incorporate farmer survey data
12. Farm size (ha)
2. Raisin case study
Estimated TP Export from Fields
Each figure show’s one farmer’s fields
13. Farm size (ha)
2. Raisin case study
Estimated DRP Export from Fields
Each figure show’s one farmer’s fields
14. 2. Raisin case study
Findings about field-scale CSAs:
CSAs differed considerably between baseline and farm survey
Calibration farm management assumptions vs. surveyed
In most cases P losses were greater from farm surveys
15. Moving forward
What can we say about the confidence of simulated CSAs?
Depends on confidence of farm management data at field scale
Useful for regional planning?
How does uncertainty due to farm management assumptions
compare to other aspects of model? (parameter, structural)
Other forms of uncertainty are more readily quantified and reported
Creating online tools where farmers can input management
Funding from Erb Family Foundation, the Ohio Department of Higher Education, and the
Great Lakes Restoration Initiative
Notas del editor
Session 3. Field to Watershed: Connecting Local Scale Influence to Larger Scale Significance
Conservation efforts can be performed at different temporal and spatial scales. Complex management strategies such as nutrient trading can have a tremendous impact on water quality within and beyond a specific watershed, but a simple grassed waterway can also have a positive impact in the overall water quality of an area. This specialty track will explore scale issues of conservation practices and their impacts. Case studies that highlight the connection between local to watershed or regional scale are encouraged.
Title:
Simulating critical source areas across scales using watershed models
Authors: Margaret Kalcic, Rebecca Muenich, Yu-Chen Wang, Anna Apostel, Awoke Teshager,
Jay Martin, Donald Scavia
Abstract:
Watershed models are powerful tools for simulating water quality impacts of agricultural practices at large and small scales. The Soil and Water Assessment Tool (SWAT) can estimate critical source areas—either fields or subwatersheds—contributing nutrients and sediments to streams, rivers, and lakes. Yet the validity of these estimates depends on detailed input data on land management and validation against measured data at comparable scales to the critical source areas. Over time we have improved land management assumptions in SWAT models for major watersheds draining to Lake Erie’s western basin. We are analyzing the changes to predicted critical source areas at a field and subwatershed level, and testing the sensitivity of the model to improved land management inputs. We also compared field-level results from the calibrated model to those of the model with data from farm surveys, and find that fields simulated with surveyed land management practices have far greater variability in nutrient export than subwatersheds. This suggests field-level targeting of conservation should yield greater water quality improvement at the watershed outlet than a focus on the subwatersheds with highest simulated loading.