Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Hicks M., Taylor J., Devilbiss S.

Large alluvial plain landscapes, such as the Mississippi Alluvial Plain (MAP) ecoregion, are some of the most agriculturally productive lands in the world but often have modified stream ecosystems due to cultivation history. This context requires consideration when establishing water quality management goals and expectations. We analyzed state water quality databases to demonstrate MAP streams are distinct from streams in other ecoregions of Mississippi. Streams in the MAP have elevated alkalinity, specific conductivity, and nutrients and lower macroinvertebrate diversity compared to streams in other ecoregions. Our results also suggest that water-quality between MAP-confined drainages and MAP-Mississippi Valley Loess Plain drainages differs substantially and should be considered when setting water quality goals and expectations for streams in the MAP. We also explored whether the use of threshold indicator taxa analysis (TITAN) could effectively be used to assess the biological health of the study drainages. Our results from TITAN suggest that macroinvertebrate taxa responses in MAP streams occurred at higher concentrations of alkalinity, total organic carbon, and total phosphorus in comparison to other ecoregions in Mississippi. In addition, many indicator taxa identified by TITAN were only responsive in MAP streams suggesting that biological responses in the MAP are driven by unique taxa that respond to water-quality gradients at higher levels as compared to other ecoregions. We establish the potential for a taxa-based approach to provide a tool for guiding and monitoring success of nutrient reduction efforts in MAP watersheds and other alluvial plain agroecosystems where local and regional taxa pools are less diverse and may not support full recovery of ecological assemblages.