Evaluating the longevity of in-stream phosphorus legacies: A downstream cascade of recovery following point source remediation

Kevin Wallington, Ximing Cai, Margaret Kalcic

Research output: Contribution to journalArticlepeer-review


In-stream phosphorus (P) legacies cause lags between upstream remediation and downstream load reductions. However, the length of these lags is largely unknown, especially for long stream distances. As a result, lag time estimates at the large-watershed scale have been abstract and sometimes understated. Here, we leverage a large area watershed model with newly improved in-stream P simulation (SWAT+P.R&R) to evaluate the magnitude, longevity, and spatial cascade of legacy P remobilization in a U.S. corn belt watershed. Our results illustrate the “spiraling recovery” of P loads after a hypothetical point source remediation, where locations further downstream take longer to recover to baseline load levels. At the watershed outlet, in-stream legacy P contributions are equivalent to 30% of the baseline average annual P loads for three years after remediation. In-stream legacies do not approach exhaustion (95% remobilized) until at least 9 years after remediation. In hypothetical weather scenarios beginning with dry years, legacy contributions persist even longer. These findings (1) suggest that in-stream legacies could impact P loads for years to decades in large river basins, (2) support explicit accounting for spatial scale in future studies of in-stream legacies, and (3) provide concerning implications for water quality recovery in large river basins.

Original languageEnglish (US)
Article number168711
JournalScience of the Total Environment
StatePublished - Feb 20 2024


  • Eutrophication
  • Gulf of Mexico hypoxia
  • Nutrient spiraling
  • Scaling
  • Soil and Water Assessment Tool
  • Watershed modelling

ASJC Scopus subject areas

  • Pollution
  • Waste Management and Disposal
  • Environmental Engineering
  • Environmental Chemistry


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