Legacy contributions to diffuse water pollution: Data-driven multi-catchment quantification for nutrients and carbon

Sci Total Environ. 2023 Jun 25:879:163092. doi: 10.1016/j.scitotenv.2023.163092. Epub 2023 Mar 30.

Abstract

Legacy pollutants are increasingly proposed as possible reasons for widespread failures to improve water quality, despite the implementation of stricter regulations and mitigation measures. This study investigates this possibility, using multi-catchment data and relatively simple, yet mechanistically-based, source distinction relationships between water discharges and chemical concentrations and loads. The relationships are tested and supported by the available catchment data. They show dominant legacy contributions for total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) across catchment locations and scales, from local to country-wide around Sweden. Consistently across the study catchments, close relationships are found between the legacy concentrations of TN and TOC and the land shares of agriculture and of the sum of agriculture and forests, respectively. The legacy distinction and quantification capabilities provided by the data-driven approach of this study could guide more effective pollution mitigation and should be tested in further research for other chemicals and various sites around the world.

Keywords: Eutrophication; Groundwater; Land use; Legacy sources; Streams; Water browning.