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Quantifying stream periphyton assemblage responses to nutrient amendments with a molecular approach
Citation:
Hagy, J., K. Houghton, D. Beddick, J. James, S. Friedman, AND R. Devereux. Quantifying stream periphyton assemblage responses to nutrient amendments with a molecular approach. Freshwater Science. The Society for Freshwater Science, Springfield, IL, 39(June 2020):292-308, (2020). https://doi.org/10.1086/708935
Impact/Purpose:
The objectives of this study were to investigate relationships between land use and water quality in streams, characterize periphyton community responses to water quality, and develop new sensitive and nutrient-specific periphyton indicators of water quality using a molecular approach based on analysis of DNA sequences. The most important and novel aspect of the research was use of DNA sequences to characterize microbial community composition of periphyton and develop indicators, providing an alternative to traditional approaches using microscopy. The manuscript should be of interest to scientists and water quality managers interested in methods for evaluating biotic condition in streams, specifically in relation to nutrient pollution. The manuscript should be especially of interest to those working to advance application of molecular methods evaluating stream periphyton communities.
Description:
Nutrient (nitrogen [N] and phosphorus [P]) pollution is a pervasive water quality issue in the USA for small streams and rivers. The effect of nutrients on the biotic condition of streams is often evaluated with biological indicators such as macroinvertebrate assemblages or periphyton assemblages, particularly diatoms. Molecular approaches facilitate the use of periphyton assemblages as bioindicators because periphyton is diverse and its composition as a whole, rather than just diatoms, soft-bodied algae, or any single group, may convey additional information about responses to nutrients. To further develop the concept that a taxonomically-broad evaluation of periphyton assemblages could be useful for developing stream bioindicators, we examined microbial assemblage composition with both 16S and 18S rRNA genes, enabling us to evaluate composition in 3 domains. We measured otherwise unknown nutrient responses of different periphyton groups in situ with experiments that used glass fiber filters to allow diffusion of amended nutrients into a stream. We deployed these experimental setups in 2 streams that differ in the extent of agricultural land-use in their catchments in the southeastern USA. Experiments consisted of controls, N amendments, P amendments, and both N and P amendments. Periphyton assemblages that grew on the filters differed significantly by stream, date or season, and nutrient treatment. Assemblage differences across treatments were more consistent among Bacteria and Archaea than among eukaryotes. Effects of nutrient amendments were more pronounced in the stream with less agricultural land use and, therefore, lower nutrient loading than in the stream with more agricultural land use and higher nutrient loading. Combined N and P amendments decreased species richness and evenness for Bacteria and Archaea by ~36 and ~9%, respectively, compared with controls. Indicator species analysis revealed that specific clades varied in their response to treatments. Indicators based on the responses of these indicator clades were related to nutrient treatments across sites and seasons. Analyses that included all the taxa in a domain did not resolve differences in responses to N vs P. Instead, better resolution was achieved with an analysis focused on diatoms, which responded more strongly to P than N. Overall, our results showed that in situ nutrient-diffusing substrate experiments are a useful approach for describing assemblage responses to nutrients in streams. This type of molecular approach may be useful to environmental agencies and stakeholders responsible for assessing and managing stream water quality and biotic condition.
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DOI: Quantifying stream periphyton assemblage responses to nutrient amendments with a molecular approach