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Regional trends in summer TP concentrations driven by shifts in contemporary and historic phosphorus inputs across the United States
Citation:
Sabo, R., C. Clark, J. Lin, B. Pickard, J. Compton, M. Pennino, S. LeDuc, Jim Carleton, M. Weber, Ryan A. Hill, Steve Paulsen, AND J. Stoddard. Regional trends in summer TP concentrations driven by shifts in contemporary and historic phosphorus inputs across the United States. Interagency Conference on Research in the Watersheds, Tifton, Georgia, March 30 - April 02, 2020.
Impact/Purpose:
Develop statistical models that predict watershed responsiveness to changes in phosphorus inputs and surpluses and use these models to help inform watershed restoration strategies and prioritize candidate watershed for restoration.
Description:
Excess phosphorus (P) loading to lotic, lacustrine, and estuarine ecosystems compromises drinking water supplies, diminishes aquatic biodiversity, and fuels hypoxia across the United States and the globe. Efforts to reduce P loading to surface water and ameliorate these undesired effects through wastewater treatment upgrades and implementation of urban and agricultural best management practices has not resulted in a robust nation-wide improvement in surface water TP loads and concentrations. The spatial heterogeneity in the magnitude of surface water P loads and concentration as well as associated trends across the United States makes it especially difficult to prioritize catchments for restoration and tailor restoration strategies due to uncertainty over the responsiveness of surface water P concentrations and loads to changes in terrestrial P inputs, agricultural legacy P pools, and other management actions. To address the uncertainty of catchment responsiveness to changes in contemporary and historic P inputs, the spatiotemporal relationship between downscaled estimates of terrestrial P inputs/surplus and agricultural legacy P pools from a recently compiled P inventory and summer low flow TP concentrations from national surveys for lakes and streams in the contiguous United States (CONUS) was explored for the 2000-2014 period. Other variables that may influence P spatial and temporal trends like terrestrial net primary productivity, mean climate, soil erodibility, disturbance, and local weather conditions as well as the effect of ecoregion were also considered using a multi-model comparison approach. All linear model combinations of predictor variables will be evaluated, and the most parsimonious models will be identified using the Akaike information criterion. The inventory and environmental predictor datasets have been generated and the statistical analysis will be completed in the fall and winter of 2019 and 2020. We predict that regional shifts in stream and lake concentrations, both positive and negative, can be largely explained by regional changes in contemporary phosphorus inputs and surpluses across the CONUS, thus the lack of nation-wide changes can be mostly attributed to the lack of progress in decreasing P inputs and surplus in specific watersheds.