Macroinvertebrate assemblage responses to nutrient stressor gradients in alluvial plain streams: Using taxa-based approaches to delineate assemblage responses in modified agroecosystems

Authors: Taylor, Jason; DEVILBISS, STEPHEN - US Department Of Agriculture (USDA); HICKS, MATTHEW - Us Geological Survey (USGS)

Submitted to: Ecological Indicators
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2023
Publication Date: 5/27/2023
Citation: Taylor, J.M., Devilbiss, S.E., Hicks, M. 2023. Macroinvertebrate assemblage responses to nutrient stressor gradients in alluvial plain streams: Using taxa-based approaches to delineate assemblage responses in modified agroecosystems. Freshwater Biology. 153. Article 110377. https://doi.org/10.1016/j.ecolind.2023.110377.
DOI: https://doi.org/10.1016/j.ecolind.2023.110377

Interpretive Summary: Establishing relationships between fish and insect populations found in streams and the amount of nutrients in the water is necessary to help measure the success of best management practices aimed at improving the quality of water in agricultural watersheds. In the Lower Mississippi River Basin, many streams have been altered and water quality is already poor. This makes it more difficult to see if even small improvements in water quality affect fish and insect responses. We showed that changes in insect populations in streams with different levels of water quality could be detected using sensitive statistical tests. These changes occurred at higher nutrient concentrations when compared to results from other areas with less agriculture. These results demonstrate that current water quality goals for intensive agricultural regions should consider streams have been modified in the past, but this history does not necessarily mean realistic goals cannot be achieved.

Technical Abstract: 1. Alluvial plain landscapes are some of the most agriculturally productive lands in the world but often have modified stream ecosystems due to cultivation history. In the Mississippi Alluvial Plain (MAP), where ~65% of land area is agriculture, streams are chemically and biologically distinct from adjacent regions within the state with far less agricultural influence. This context requires consideration when establishing water quality management goals. 2. Analyses of state water quality databases confirmed that MAP streams have elevated alkalinity (Alk), specific conductivity (SC) and nutrients and lower macroinvertebrate local and regional taxa pools compared to streams in other ecoregions, potentially reducing the efficacy of traditional biomonitoring approaches within the region. To overcome these challenges, we used threshold indicator taxa analysis (TITAN) to compare macroinvertebrate assemblage responses to water quality gradients among ecoregions in Mississippi. 3. Individual taxa and assemblage-level responses occurred at higher concentrations for Alk, total organic carbon (TOC) and total phosphorus (TP), but not total nitrogen (TN) in MAP streams relative to other ecoregions. A large proportion of indicator taxa were only responsive in MAP streams suggesting that assemblage-level responses are driven by unique taxa that respond to water quality (WQ) gradients at higher levels than observed in other ecoregions. 4. Two potential subregions – the transition and the interior – were identified within the MAP based on water quality and macroinvertebrate assemblage patterns. If managed collectively, water quality standards for the interior may be unattainable due to the influence of lower nutrient and ion concentrations in transition streams. Despite this, our TP macroinvertebrate assemblage threshold for MAP streams similar to guidance based on distributional analysis of water quality data within the ecoregion (0.11 vs 0.128 mg L-1). 5. Macroinvertebrate assemblage thresholds identified in this study using a taxa-based approach provide a tool for guiding and monitoring success of nutrient reduction efforts in MAP watersheds and other alluvial plain agroecosystems. Given widespread habitat modification within the MAP, these results should also be compared with more sensitive and less habitat-limited biological assemblages (e.g., algae or bacteria) that may aid managers ability to measure ecological responses to best management practices, particularly in interior MAP streams where local taxa pools are less diverse and may not support recovery of macroinvertebrate assemblages.