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Tracking persistent declines in suspended sediment in the Lower Mississippi and Atchafalaya Rivers, 1992–2021: Harnessing WRTDSplus to characterize longitudinally varying trends and explore connections to streamflow

Journal of Hydrology
By: , , and 
https://doi.org/10.1016/j.jhydrol.2025.133885

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Abstract

Suspended sediment (SS) continues a century-long decline in the Lower Mississippi and Atchafalaya Rivers, United States. In this study, we use the WRTDSplus model to estimate concentrations and loads for total, fine (<0.0625 millimeter (mm)), and coarse (≥0.0625 mm) SS for 11 sites. This extension of the Weighted Regressions on Time, Discharge, and Season (WRTDS) model allows a fourth explanatory variable in the model formulation. We incorporated hysteresis terms for most models based on a residual analysis, which allowed for the identification of decreased flushing over time at some sites. Total, fine, and coarse SS concentrations and loads decreased at all sites over two trend periods (water years (WY) 1992–2021 and WY 2012–2021). Declines were largely due to changes in fine SS (mud and silt) but decreases in coarse SS (sands) were also widespread. On average, recent declines are more severe in the Lower Mississippi River below the Old River Control Complex (ORCC, −3.7 mg per liter per year (mg/L/yr)) compared to the Atchafalaya River (−2.0 mg/L/yr), although there is longitudinal variability within each river. The reach below the ORCC is a net SS sink, leading to complex temporal changes for the sites in this area. Streamflows (low, moderate, and high) have increased over these periods, with the last decade being particularly wet. Increasing streamflow and decreasing SS, with little evidence of amelioration, may influence spillway operations during floods, sediment diversion construction and operation, coastal restoration efforts, and aquatic health.

    Suggested Citation

    Murphy, J.C., Schafer, L.A., Mize, S., 2025, Tracking persistent declines in suspended sediment in the Lower Mississippi and Atchafalaya Rivers, 1992–2021: Harnessing WRTDSplus to characterize longitudinally varying trends and explore connections to streamflow: Journal of Hydrology, v. Volume 662, no. Part A, 133885, 14 p., https://doi.org/10.1016/j.jhydrol.2025.133885.

    Study Area

    Publication type Article
    Publication Subtype Journal Article
    Title Tracking persistent declines in suspended sediment in the Lower Mississippi and Atchafalaya Rivers, 1992–2021: Harnessing WRTDSplus to characterize longitudinally varying trends and explore connections to streamflow
    Series title Journal of Hydrology
    DOI 10.1016/j.jhydrol.2025.133885
    Volume Volume 662
    Issue Part A
    Publication Date July 16, 2025
    Year Published 2025
    Language English
    Publisher Elsevier
    Contributing office(s) Lower Mississippi-Gulf Water Science Center, Central Midwest Water Science Center
    Description 133885, 14 p.
    Country United States
    State Louisiana, Mississippi
    Other Geospatial Lower Mississippi and Atchafalaya Rivers
    Additional publication details