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Site-specific Water Quality Trading Ratio Analysis

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2007 ASAE Annual Meeting  072179.(doi:10.13031/2013.22975)
Authors:   Ming-chieh Lee, Kyle R Mankin
Keywords:   Water Quality Trading, Trading Ratio, Non-Point Source Pollution, Watershed Modeling, GIS

Nutrient loading from non-point sources is the single largest remaining source of water quality impairments in the State of Kansas. Water Quality Trading (WQT) is one of the potential methods to reduce nutrient loads, allow point sources to meet the required water quality criteria, and achieve both economic and environmental benefits. Even though WQT has been promoted for decades, the trading volume and cases were significant smaller than expected. Recent studies have shown that the most likely impediment to WQT might be the failure to address uncertainties inherent to using fixed, empirical trading ratio. The goals for this study are to analyze and quantify nutrient load reductions with combined watershed model and GIS techniques, and then to estimate site-specific load reduction ratio and trading ratios for every potential scenario. The nutrient loading changes among 36 land management practice scenarios have been modeled at Lower Kansas subbasin in northeastern Kansas. We evaluated four tillage-practice, three crop types, two fertilizer-application methods, and with/without edge of field BMP scenarios. The trading ratios were estimated through statistical analyses which estimate load uncertainties with designated confidence levels for every potential scenario. The modeled pollutant load reductions show significant spatiotemporal differences among the subwatersheds. The annual and monthly site-specific average load reductions, reduction rates, uncertain ratios and trading ratios were determined to address the heterogeneous physical properties within the watershed.

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