Skip to content

Longitudinal Patterns in Nitrate Revealed Through Drone-Based Measurements in an Agriculturally Influenced Midwestern U.S. River

Published Article

United States

Publication Date: July 1, 2025

View resource

We used an aquatic drone to map nitrate dynamics along a 12-km reach of the Des Moines River. Results reveal strong spatial and seasonal variability, tributary influences, and subreach nitrate removal patterns, offering insights for managing agriculturally impacted rivers.

 

Subject tags

  • Rivers
  • Agriculture

Abstract

Nitrate concentrations in streams and rivers in the Midwestern United States are often elevated, reflecting the predominance of agriculture in the surrounding landscape. Recent advances in technology, including surface water drones and more precise sensors, provide opportunities to investigate nitrate dynamics with high spatial and temporal resolution. We deployed an aquatic drone, the AquaBOT, in a sixth-order, agriculturally influenced river to examine longitudinal patterns in water quality. Our goal was to measure the spatial and temporal heterogeneity in nitrate and nitrate removal processes and determine the influence of tributary inputs on main stem chemistry. We navigated the drone along a 12-km reach of the Des Moines River (Iowa, USA) nine times between June 2021 and August 2022. Across the deployments, mean nitrate concentration was positively related to discharge and was nearly two orders of magnitude higher in spring than summer. We observed contrasting patterns in main stem nitrate, which decreased downstream during some runs (e.g., 3.1–2.7 mg N L−1 in June 2021), demonstrating net nitrate uptake along the reach, and remained constant on other dates. Similarly, tributaries to the Des Moines had a varied influence on riverine nitrate. Tributaries either increased or decreased main stem nitrate concentrations depending on the tributary and the date. Nitrate removal rates were spatially and temporally variable but showed some consistency at the subreach (2 km) scale, with two subreaches often showing elevated rates of nitrate removal across dates. Our study reveals nuanced heterogeneity in nitrate dynamics of the Des Moines River despite the homogeneity of agricultural land cover in the watershed. 

Citation

Gerhardt, A., Levi, P. S., Griffiths, N. A., DeRolph, C. R., Riggs, J. S., & Fortner, A. M. (2025). Longitudinal patterns in nitrate revealed through drone-based measurements in an agriculturally influenced Midwestern U.S. River. Journal of Geophysical Research: Biogeosciences, 130, e2024JG008342. https://doi.org/10.1029/2024JG008342

Media Contacts