Diatom assemblage change in agricultural alluvial plains streams: Application to nutrient management

Authors: HICKS, MATTHEW - Us Geological Survey (USGS); Taylor, Jason

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2018
Publication Date: 11/1/2018
Citation: Hicks, M.B., Taylor, J.M. 2018. Diatom assemblage change in agricultural alluvial plains streams: Application to nutrient management. Journal of Environmental Quality. 48:83–92. https://doi.org/10.2134/jeq2018.05.0196.
DOI: https://doi.org/10.2134/jeq2018.05.0196

Interpretive Summary: Excess nutrients from wastewater and agricultural runoff globally threaten freshwater and marine ecosystems. Widespread recognition of the negative impacts of phosphorus and nitrogen enrichment has led to considerable efforts to develop and implement best management practices that reduce nutrient impacts to critical water resources. Establishing relationships between ecological measures and nutrients is critical to establishing realistic nutrient reduction goals and measuring success of implementation of best management practices. An ARS research ecologist and his USGS collaborator demonstrate that diatom (algae) species are sensitive to nutrient enrichment in streams located in the Mississippi Alluvial Plain, a critical agricultural region of national importance. These measures may serve as indicators of ecological improvements in response to nutrient reductions associated with best management practices implemented by farmers in the region.

Technical Abstract: Streams within large river floodplain regions are generally habitat-limited due to altered geomorphological and hydrologic regimes and have the potential for widespread nutrient enrichment associated with intensive agricultural production. These factors hamper development of field-derived stressor-response relationships for establishing nutrient reduction goals that promote ecological integrity. To address science based nutrient reduction goals, diatom assemblages were sampled from 25 streams located within the Mississippi Alluvial Plain (MAP) that drain portions of upstream ecoregions with greater variation in land management and associated phosphorus (P) and nitrogen (N) inputs. From August through September 2015, epidendric diatom assemblage samples were collected from instream woody debris, the primary stable habitat for diatom colonization found within the study systems. Field nutrient gradients were skewed toward higher concentrations, and ranges of previously reported diatom assemblage response-thresholds indicative of oligotrophic conditions were not well represented. Ordination analysis identified a gradient in species composition associated with increasing P and decreasing dissolved oxygen. A significant shift in diatom assemblage structure was observed between streams representing moderately and highly P enriched conditions in the MAP. Highly-enriched systems were represented by a distinct set of indicator species, lower abundances of ubiquitous species, greater abundances of highly tolerant species, and greater abundances of high P indicator species. No relationships were observed between diatom assemblage measures or traits with increasing N. Current results do not address potential criteria for identifying high quality, oligotrophic streams. However, measures of diatom assemblage structure have potential for helping set benchmarks to reduce nutrient impacts and monitor effects of agricultural best management practices within MAP streams.