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Evaluation of δ15N in stream biota and periphyton in an urban watershed
Citation:
Serbst, J., A. Kuhn, AND Jim Lake. Evaluation of δ15N in stream biota and periphyton in an urban watershed. SETAC North Atlantic Chapter, 28th Annual Meeting 2022, Groton, CT, June 27 - 28, 2022.
Impact/Purpose:
Human sources of nitrogen resulting from landscape development in watersheds are primary sources of negative impacts in aquatic ecosystems. Measurements of nitrogen stable isotopes in aquatic organisms are often used as indicators of these impacts. The present study measured nitrogen ratios in macroinvertebrates and surface growths (periphyton) collected from 12 stream sites in Rhode Island and Massachusetts, USA in 2012, 2013 and 2018 to compare their usefulness for indicating human impact in streams and to assess their variability over time.
Description:
Background/Question/Methods. Anthropogenic sources of nitrogen resulting from landscape development in watersheds are primary sources of negative impacts in aquatic ecosystems. Measurements of nitrogen stable isotopes (δ15N) in aquatic biota are often used as indicators of these influences. This study measured δ15N ratios in periphyton (surficial growths) and macroinvertebrates collected from 12 stream sites in Rhode Island and Massachusetts in 2012, 2013 and 2018 to compare the utility of both periphyton and macroinvertebrates for indicating anthropogenic impact in streams and to assess their temporal variability. We used a spatially balanced stratified random stream survey design to sample across a continuous environmental gradient in the Narragansett Bay watershed in southeastern New England. Sites were sampled once in 2012 and seasonally in 2013 and 2018. Periphyton was collected off submerged rocks and macroinvertebrate samples were collected at each stream. δ15N was measured in samples of dried periphyton and macroinvertebrates by isotope ratio mass spectrometry. Organisms were separated into two feeding groups: predators and consumers. Results/Discussion. Comparisons of δ15N in periphyton (δ15NPeriphyton) among years and seasons showed a high level of correspondence, indicating low temporal variability. Across the 12 stream sites sampled in 2012 and seasonally in 2013 and 2018, comparisons of regression lines of annual mean δ15N in the macroinvertebrate feeding group as a function of annual mean δ15NPeriphyton were, for predators: (R2 = 0.79) in 2012, (R2 = 0.85) in 2013 and (R2 = 0.73) in 2018. For consumers, the δ15N relationships were: (R2 = 0.89) in 2012, (R2 = 0.88) in 2013, and (R2 = 0.85) in 2018. Comparisons of these lines showed 95% confidence intervals overlapped for the slopes and intercepts for predators and consumers indicating no significant difference over the six-year time interval. These results demonstrate a consistent responsiveness and low temporal variability providing strong support for utilizing δ15NPeriphyton in streams as an indicator of anthropogenic development, as an alternative to the more intensive collection, identification, and enumeration of macroinvertebrates.
