Towards an efficient watershed-specific management plan using a variable source area hydrology watershed model

Authors: AMIN, MOSTOFA - Bangladesh Agricultural University; Veith, Tameria - Tamie; SHORTLE, JAMES - Pennsylvania State University; KARSTEN, HEATHER - Pennsylvania State University; Kleinman, Peter

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2019
Publication Date: 3/23/2020
Citation: Amin, M.G., Veith, T.L., Shortle, J.S., Karsten, H.D., Kleinman, P.J. 2020. Towards an efficient watershed-specific management plan using a variable source area hydrology watershed model. Journal of Environmental Quality. 1-15. https://doi.org/10.1002/jeq2.20051.
DOI: https://doi.org/10.1002/jeq2.20051

Interpretive Summary: Agricultural best management practices (BMPs) are common and beneficial in reducing nutrient loading from fields. However, their effectiveness in reducing nutrients varies based on where they are placed as well as the physical and management characteristics of the surrounding land. We studied the effectiveness of eight agricultural BMPs of interest by stakeholders in the Spring Creek Watershed by using a hydrologic simulation model (Topo-SWAT) to represent the impact of placing those BMPs in various combinations and locations throughout the watershed. Additionally, we calculated the cost-effectiveness of nutrient reduction for each BMP based on the average cost and nutrient reduction simulated by each individual BMP in the watershed. By careful placement of the most cost-effective BMPs within the watershed we found that we could meet or exceed nutrient reduction goals for watersheds in the Chesapeake Bay at a cost of 26% less than our simulated estimate of the state’s Phase II Watershed Implementation Plan for the Spring Creek Watershed.

Technical Abstract: Watershed mitigation programs typically emphasize widespread implementation of best management practices (BMPs) to meet total daily maximum load (TMDL) goals. However, BMP effectiveness in improving water quality varies with individual placements within a watershed and also with hydrological and geochemical conditions across watersheds. To understand options for BMP implementation under the Chesapeake Bay TMDL, we investigated alternative scenarios for the 370 km2 Spring Creek watershed in Centre County, PA. The Topo-SWAT modification of the Soil and Water Assessment Tool was initialized with detailed land use and management practice information, systematically calibrated, and validated against 12 years of observed data. BMP cost-effectiveness was quantified through individualized simulations, and BMPs were ranked accordingly. Implementing no-till, manure injection, cover cropping, riparian buffer strip, land retirement, manure application timing, and wetland restoration reduced nutrients and sediment loads at varying rates. Nitrogen (N) management (15% less N input) reduced N loss, but increased total phosphorus (P) and soil losses. Combinations of these BMPs were included in Topo-SWAT scenarios simulating a TMDL-derived watershed implementation plan (WIP-2025) and a cost-effective practice implementation plan. Both scenarios achieved TMDL load reductions by the target date of 2025. However, the later scenario cost 26% less to implement and more evenly reduced N, P, and sediment load at the watershed outlet. Because watersheds of this size typically represent the smallest modeling unit in the Chesapeake Bay Model, results demonstrate the potential to apply watershed models with finer inference scales to improve recommendations for BMP implementation under the Chesapeake Bay TMDL.