The estimated costs of dual-nutrient control are poorly constrained, with the regulated community generally claiming amounts that far exceed the actual realized costs. The unidirectional flow of water and nutrients through streams, rivers, lakes, estuaries and ultimately into coastal oceans adds additional complexity to our understanding, as these ecosystems may be limited by different nutrients. Consequently, the reduction of just one nutrient upstream to control eutrophication can allow the export of other nutrients downstream where they may stimulate algal production…