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Georgia Journal of Science

Article Title

TESTING PRECISION LIMITS IN ALGAL COMMUNITY ANALYSES FOR USES IN WATER QUALITY ASSESSMENT

Abstract

Diatoms, a common group of algae in lotic environments, have cell walls made of hydrated silica, or glass, that survive and function as robust biological indicators. Accurate identification of diatom species is essential. USGS Shenandoah Best Management Practices (BMP’s) in watersheds, for the protection of the Chesapeake Bay, have been implemented in order to restore water quality and nutrients. In this research diatom community metrics from streams located in the Shenandoah River Valley in the Chesapeake Bay were analyzed. Data was used to assess how levels of diatom enumeration can be used to infer improvement due to BMPs. Algal community data complemented macroinvertebrate and physiochemical data. Fourteen streams were sampled, processed following standard protocol, and diatoms were enumerated as composite samples. At random, 3 streams with 3 field sample replicas each were selected and compared to the composite analyses. Within-stream replicas had high similarity, but lower species richness justifying replica counts per stream. Species richness and Shannon diversity were significantly higher in the composite samples (p<0.001). Within replicated counts, individual species abundances were consistent, no taxon had higher than 34% relative abundance. Relative abundance was sample and species specific. Achnanthidium deflexum (Reimer) Kingston, a common low nutrient indicator stayed at 12-14% relative abundance regardless of valves enumerated. Evenness also stayed high with a relatively stable average (ranging between 69.4-89.6%). Percent similarity based on species composition was high, 50.5-58.6%, which would indicate that diatom analyses for BMP’s assessment would be accurate. Results of this research suggest that both: shorter counts from field replicas or longer counts of a single composite sample can be used, dependent on the research objective. Diatom community indices and low abundance of Naviculoid diatoms suggested reduction in nutrients and eutrophication from agricultural areas around the Chesapeake Bay watershed, reducing risk of harmful algal blooms.

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