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Agricultural nutrient runoff has been a major contributor to hypoxia in many downstream coastal ecosystems. Although programs have been designed to reduce nutrient loading in individual coastal waters, cross watershed interdependencies of nutrient runoff have not been quantified due to a lack of suitable modeling tools. Cross-watershed pollution leakage can occur when nutrient runoff moves from more to less regulated regions. We illustrate the use of an integrated assessment model IAM that combines economic and process-based biophysical tools to quantify Nitrogen loading leakage across three major US watersheds. We also assess losses in consumer and producer surplus from decreased commodity supply and higher prices when nutrient delivery to select coastal ecosystems is restricted. Reducing agricultural N loading in the Gulf of Mexico by 45% (a) increases loading in the Chesapeake Bay and Western Lake Erie by 4.2% and 5.5%, respectively, and (b) results in annual surplus losses of $7.1 and $6.95 billion with and without restrictions on leakage to the Chesapeake Bay and Lake Erie, respectively.

We examine the implications of state water quality regulatory heterogeneity for waste and drinking water violations in the continental US using Environmental Protection Agency data from 2007 to 2017. Using discrete regression analyses, we find some evidence that cumulative violations are higher when additional state water quality standards are introduced. However, one year after a new standard is implemented, cumulative violations seem to decline relative to the number of violations before introducing additional regulations. Compliance may improve after introducing new standards as operations and procedures are modified, the use of inputs like disinfectants is adjusted, or technologies are upgraded in response to new standards.