Addressing the spatial disconnect between national‐scale total maximum daily loads and localized land management decisions

Abstract

Regulatory watershed mitigation programs typically emphasize widespread adoption of best management practices (BMPs) to meet total maximum daily load (TMDL) goals. To comply with the Chesapeake Bay TMDL, jurisdictions must develop watershed implementation plans (WIPs) to determine the number and type of BMPs to implement. However, the spatial resolution of the bay-level model used to determine these load reduction goals is so coarse that the regulatory plan cannot consider heterogeneity in local conditions, which affects BMP effectiveness. Using the Topo-SWAT modification of the Soil and Water Assessment Tool (SWAT), we simulated two BMP adoption scenarios in the Spring Creek watershed in central Pennsylvania to determine if leveraging fine-scale spatial heterogeneity to place BMPs could achieve the same (or better) nutrient and sediment reduction at a lower cost than the state-level WIP BMP adoption recommendations. Topo-SWAT was initialized with detailed land use and management practice information, systematically calibrated, and validated against 12 yr of observed data. After determining individual BMP cost effectiveness, results were ranked to design a cost-effective BMP adoption scenario that achieved equal or greater load reduction as the WIP scenario for 74% of the cost using eight management-based BMPs: no-till, manure injection, cover cropping, riparian buffers, land retirement, manure application timing, wetland restoration, and nitrogen management (15% less N input). Because watersheds of this size typically represent the smallest modeling unit in the Chesapeake Bay Model, results demonstrate the potential to use watershed models with finer inference scales to improve recommendations for BMP implementation under the Chesapeake Bay TMDL.

The USDA‐ARS Experimental Watershed Network: Evolution, Lessons Learned, Societal Benefits, and Moving Forward

“…The small fields of this region, often <3 ha, offer the opportunity to target management within hydrologic gradients (Piechnik et al, 2012; Veith et al, 2005) and support nutrient management strategies that can be applied at field and watershed scales (Amin et al, 2018; Buda et al, 2009). Hydrologic research within the upper Chesapeake Bay watershed underpins modern critical source area management strategies, now adopted by 47 of 50 U.S. states (Sharpley et al, 2003), and locally serves as the basis for nutrient management in the six states participating in the Chesapeake Bay total maximum daily load (Amin et al, 2020; USDA‐ARS 2010). Simulations with SWAT in the Mahantango Creek Experimental Watershed (MCEW) illustrate how targeting practices to fields with high runoff potential prevent roughly three times more N and P annually from reaching the streams, for 30% less than the cost of implementing practices under conventional, blanket strategies.…”

The Role of Ponds in Pesticide Dissipation at the Agricultural Catchment Scale: A Critical Review

“…An integrated modelling approach predicting pesticide transfer in agricultural basins should include spatially distributed land use and agricultural management practices, soil characteristics and hydro-climatic conditions, upstream transfer risks (Figure 1D) and dissipation processes in ponds (Figure 1C). Such an integrated approach remains scarce and concerns mainly the pond hydrological dynamics [69] or the dissipation efficiency of macro-pollutants, such as nitrogen or phosphorus [70,71].…”

Valuing water quality benefits from adopting best management practices: A spatial approach

“…Models were run using weather data for the years 2007-2014. Details of Topo-SWAT model implementation can be found in Amin, Veith, Shortle, Karsten, and Kleinman (2019).…”