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Diatom Communities and Metrics as Indicators of Urbanization Effects on Streams and Potential Moderation by Landscape Green Infrastructure
Citation:
Smucker, N., N. Detenbeck, AND A. Morrison. Diatom Communities and Metrics as Indicators of Urbanization Effects on Streams and Potential Moderation by Landscape Green Infrastructure. Presented at New England Association of Environmental Biologists (NEAEB) 36th Annual Meeting, Falmouth, MA, March 21 - 23, 2012.
Impact/Purpose:
Urbanization can negatively affect the structure and function of stream ecosystems by altering water chemistry, habitat, and nutrient, sediment, and hydrological regimes. As the foundation of primary production in streams, algal biomass and diatom community structure are important indicators of nutrients, conductivity, and habitat conditions, all of which are affected by urbanization and management practices. We studied diatom assemblages collected from 160 sites in New England and found that community structure and metrics had threshold responses to increased impervious cover in upstream watersheds between 1-5%. Above these thresholds, sensitive taxa and low nutrient taxa substantially decreased, and high nutrient taxa, high conductivity taxa, and motile taxa increased in relative abundances. Boosted regression trees indicated that maintaining >65-80% green infrastructure in 120 meter near-stream buffers could potentially reduce watershed IC effects on diatom assemblages by 20-25%. These results are important for future monitoring and management efforts, and they emphasize the importance of implementing protective measures in the future, especially in watersheds near these IC thresholds, and the potential to reduce urban effects on streams by restoring and conserving near-stream green infrastructure.
Description:
Diatoms are very useful and important indicators of anthropogenic impacts on streams because they are the foundation of primary production and are responsive to nutrients, conductivity, and habitat conditions. We characterized relationships of diatom assemblages with water chemistry and land cover for 160 sites in New England. Diatom community structure was strongly related to urban land cover in upstream watersheds, conductivity, and concentrations of P and N. Diatom metrics indicative of high or low nutrient concentrations, high conductivity, altered hydrology, and sedimentation were significantly correlated with land cover in upstream watersheds and changes in community structure. Threshold Indicator Taxa Analysis and nonparametric change-point analysis identified impervious cover (IC) thresholds around 3% at which substantial changes in diatom community structure occurred. Boosted regression trees (BRTs) showed that diatom metrics had similar threshold responses from 1-5% IC, at which low nutrient and sensitive taxa decreased in relative abundances and high nutrient, high conductivity, motile, and prostrate taxa increased in relative abundances. Interaction plots of BRTs indicated that maintaining >65-80% green infrastructure in 120 m near-stream buffers could potentially reduce watershed IC effects on diatom assemblages by 20-25%. High conductivity diatoms and motile diatoms greatly increased with less GI in buffers and were less affected by watershed % IC, potentially indicating that disturbed areas with near proximity to streams contributed more salts and sediments than areas farther away. Restoring and maintaining near-stream green infrastructure may effectively benefit stream condition in urban areas and reduce watershed impervious cover effects on diatom communities.