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Linking terrestrial phosphorus inputs to riverine export across the United States
Citation:
Metson, G., J. Lin, J. Harrison, AND J. Compton. Linking terrestrial phosphorus inputs to riverine export across the United States. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 124:177-191, (2017).
Impact/Purpose:
Human activities have altered the cycling of nitrogen and phosphorus through applications of fertilizers, manures, sewage and septic releases. Phosphorus is of particular interest because it is an important driver of freshwater food webs and too much phosphorus has resulted in a growing number of harmful algal blooms across the US in recent years. A group of scientists from the National Research Council, US EPA and Washington State University are assembling a current inventory of phosphorus inputs to the conterminous US landscape. These data will become part of EPA's EnviroAtlas, so that others can access and use it. The study compares inputs of phosphorus to runoff into rivers in 94 US watersheds, and focuses on determining the controls on phosphorus losses from watersheds in to inform management. This paper contributes to a deliverable for SHC 4.61.
Description:
Humans have greatly accelerated phosphorus (P) flows from land to aquatic ecosystems, causing eutrophication, harmful algal blooms, and hypoxia. A variety of statistical and mechanistic models have been used to explore the relationship between P management on land and P losses to waterways, but our ability to predict P losses from watersheds remains limited and lags behind our ability to predict watershed nitrogen losses. Here we constructed spatially explicit datasets of terrestrial P inputs and outputs across the conterminous U.S. (CONUS) for 2012. We use this novel dataset to improve understanding of P balances at the national scale and to investigate whether high spatial resolution P application and removal data can improve predictions of aquatic P loading at the continental scale. We estimate that in 2012 agricultural lands received 0.19 Tg more P as fertilizer and confined manure than was harvested in major crops. We estimate that 0.06 Tg P was lost to waterways as sewage and detergent nationally, a mass of P that is 1.5 times larger than NPDES-based estimates of major P points sources. TP and DIP concentrations and TP yields were generally correlated more strongly with runoff than with P inputs or P balances, and even the relationships between runoff and P export were weak. Including P inputs as independent variables increased the predictive capacity of the best-fit models by at least 20%, but together inputs and runoff explained just 40% of the variance in concentration and 46-54% of the variance in yield. By developing and applying a novel, high-resolution P budget for the CONUS this study provides new insight into continental-scale P dynamics and suggests that both hydrology and P inputs and sinks play important roles in aquatic P loading. While greatly improving our predictive capacity over runoff alone, high-resolution data on terrestrial P, without considering other mediating factors, will not dramatically improve predictions of aquatic P loading.
