Citation:

Smucker, N., E. Pilgrim, H. Wu, C. Nietch, J. Darling, M. Molina, B. Johnson, AND L. Yuan. Characterizing temporal variability in streams supports nutrient indicator development using diatom and bacterial DNA metabarcoding. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 831:154960, (2022). https://doi.org/10.1016/j.scitotenv.2022.154960

Impact/Purpose:

Nutrient pollution is a widespread problem for freshwater ecosystems throughout the United States and around the world. Its negative effects on biota and ecosystems increase as human populations grow and as watersheds become increasingly altered to produce food and to meet housing and socioeconomic demands. As a result, interest in developing diatom and bacterial indicators of nutrients continues to grow because their relationships with nutrient concentrations can help inform the assessment, conservation, and management of stream ecosystems and watersheds. However, temporal variability could affect their applications in monitoring programs. Here, we used DNA metabarcoding of diatoms (rbcL) and bacteria (16S) to characterize how temporal variability potentially affects their use as total phosphorus (TP) and total nitrogen (TN) indicators.

Description:

Interest in developing periphytic diatom and bacterial indicators of nutrient effects continues to grow in support of the assessment and management of stream ecosystems and their watersheds. However, temporal variability could confound relationships between indicators and nutrients, subsequently affecting assessment outcomes. To document how temporal variability affects measures of diatom and bacterial assemblages obtained from DNA metabarcoding, we conducted weekly periphyton and nutrient sampling from July to October 2016 in 25 streams in a 1293 km2 mixed land use watershed. Measures of both diatom and bacterial assemblages were strongly associated with the percent agriculture in upstream watersheds and total phosphorus (TP) and total nitrogen (TN) concentrations. Temporal variability in TP and TN concentrations increased with greater amounts of agriculture in watersheds, but overall diatom and bacterial assemblage variability within sites—measured as mean distance among samples to corresponding site centroids in ordination space—remained consistent. This consistency was due in part to offsets between decreasing variability in relative abundances of taxa typical of low nutrient conditions and increasing variability in those typical of high nutrient conditions as mean concentrations of TP and TN increased within sites. Weekly low and high nutrient diatom and bacterial metrics were more strongly correlated with site mean nutrient concentrations over the sampling period than with same day measurements and more strongly correlated with TP than with TN. Correlations with TP concentrations were consistently strong throughout the study except briefly following two major precipitation events. Following these events, biotic relationships with TP reestablished within one to three weeks. Collectively, these results can strengthen interpretations of survey results and inform monitoring strategies and decision making. These findings have direct applications for improving the use of diatoms and bacteria, and the use of DNA metabarcoding, in monitoring programs and stream site assessments.

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