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Title: Integrating watershed- and farm-scale modeling framework for targeting critical source areas while maintaining farm economic viability

Author
item GHEBREMICHAEL, LULA - Pennsylvania State University
item Veith, Tameria - Tamie
item HAMLETT, JAMES - Pennsylvania State University

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2012
Publication Date: 11/26/2012
Citation: Ghebremichael, L.T., Veith, T.L., Hamlett, J.M. 2012. Integrating watershed- and farm-scale modeling framework for targeting critical source areas while maintaining farm economic viability. Journal of Environmental Management. 114(0):381-394.

Interpretive Summary: Watershed models, such as SWAT, are great tools for identifying critical source areas (CSAs) for non-point source pollution and for evaluating the mitigating effectiveness of best management practices (BMPs). However, watershed models do not take into account the economic impact at the farm scale of implementing these BMPs. We integrated the use of SWAT with IFSM, a farm-scale model that can be used to evaluate the environmental and economic impact of BMPs, in an iterative approach to select appropriate BMPs for two dairy farms in the Northeast. The goal was to select BMPs that improved water quality at the watershed scale and improved economic return to the farmer. Several different BMPs were considered in SWAT, providing a reduction in total P loss from 5% to almost 50%. IFSM indicated that farm net return for these practices ranged from -68 to +253 $/year/cow. Selecting BMPs that meet water quality goals and improve farmer net return will be essential to successful mitigation of non-point source pollution.

Technical Abstract: Quantitative risk assessments of pollution and data related to the effectiveness of mitigating best management practices (BMPs) are important aspects of nonpoint source (NPS) pollution control efforts, particularly those driven by specific water quality objectives and by measurable improvement goals, such as the total maximum daily load (TMDL) requirements. Targeting critical source areas (CSAs), areas within a watershed that generate disproportionately high pollutant loads, is a crucial step in successfully controlling NPS pollution. The importance of watershed simulation models in assisting with the quantitative assessments of CSAs of pollution, relative to their magnitudes and extents, and of the effectiveness of associated BMPs has been well recognized. However, due to the distinct disconnect between the hydrological scale in which these models conduct their evaluation and the farm scale at which feasible BMPs are actually selected and implemented, and due to the difficulty and uncertainty involved in transferring watershed model data to farm fields, there are limited practical applications of these tools in the current NPS pollution control efforts by conservation specialists for delineating CSAs and planning targeting measures. There are also limited approaches developed that can assess impacts of CSA-targeted BMPs on farm productivity and profitability together with the assessment of water quality improvements expected from applying these measures. This study developed a modeling framework that integrates watershed- and farm-level assessments through joint use of watershed- and farm-scale models, and it applies a tiered approach in addressing environmental concerns, such as identification and mitigation of CSAs, while maintaining and improving the farmers' economic viability. This paper also outlines steps needed in extracting important CSA-related information from a watershed model to help inform targeting decisions on farms. The modeling framework is demonstrated with two unique case studies in the northeastern United States, with supporting data from numerous published, location-specific studies at both the watershed and farm scales. The application of this approach helped to assess the practical and economic feasibility of watershed-level targeted BMPs on farms and the changes in farm system components needed in order for these potential BMPs to be implemented without negative consequences to farm production and net return. Such comprehensive evaluations can only be accomplished by integrating the use of watershed and farm scale models. This multi-scale modeling approach can be used in the multi-objective task of mitigating CSAs of pollution to meet water quality goals while maintaining farm-level economic viability.