Fig 1.
Microbial community diversity reflects the introduction of novel microbial taxa with the stream event response to an isolated precipitation event beginning 9 October 2020 on the Marys River, Oregon, USA.
(A) Stable isotope ratios δ2H (purple) and δ18O (pink) measured in the stream (triangles) and in approximately 2-week aggregated precipitation (lines) demonstrate a subtle storm response. (B) Microbial community alpha diversity, including taxonomic richness (number of unique amplified sequence variants; teal squares) and Shannon index (red circles) exhibits dynamics similar to the storm hydrograph. (C) Mean difference from pre-event stable isotope ratios (Euclidean distance; green) and microbial community composition (Bray-Curtis dissimilarity; gold) illustrates the sensitivity of the microbial community to the event. Error bars indicate one standard deviation. Pre-event samples are 6–9 October. (D) Daily precipitation [mm] and Marys River daily observed (shaded) and modeled (lines) discharge [m3/s (CMS)]. Solid line is discharge predicted from multivariate linear regression of first four PCoA components (see Fig 2); dashed and dotted lines show discharge prediction from linear regression of taxonomic richness and Shannon index, respectively.
Fig 2.
Principal coordinates analysis (PCoA) of streamwater microbial beta diversity illustrates a fundamental shift in microbial community structure that persists beyond the stream response to a precipitation event 6–25 October 2020 on the Marys River, Oregon, USA.
Marker color corresponds to daily observed discharge [cms] on the date in October indicated by the marker number. Distances along axes indicate the proportion of differences in discharge explained by each principal coordinate; distances between points correspond to the magnitude of differences in microbial community structure, as measured by Bray-Curtis dissimilarity. Inset shows daily discharge modeled with multivariate linear regression of the first four principal coordinates versus observed discharge, with r2 adjusted for the number of predictors.
Fig 3.
Increasing fractions of mobilized and static taxa in the microbial streamwater community, with a corresponding decrease in the fraction of diluted microbial taxa, detail the shift in microbial community structure associated with the stream response to a precipitation event beginning 9 October 2020 on the Marys River, Oregon, USA.
Fraction is of the total abundance (number of sequences) identified in at least three samples and that were positively correlated (mobilized), not correlated (static), or negatively correlated (diluted) with stream discharge (p < 0.1).
Fig 4.
Patterns in the proportion of microbial taxonomic groups classified as mobilized, static, or diluted with streamflow volume offer evidence of shifting event flow sources in response to precipitation beginning 9 October 2020 on the Marys River, Oregon, USA.
We collected 17 microbial community samples between 6–25 October. Proportions of microbial taxonomic groups identified as mobilized, static, and diluted are shown as a fraction of the total [relative] abundance of each amplified sequence variant (ASV) over the sampling period (left) and as a fraction of the number of unique taxa (right). Diluted, static, and mobilized ASVs are those that were identified in at least three samples and were negatively correlated, not correlated, or positively correlated with stream discharge (p < 0.1), respectively.
Fig 5.
Difference in community representation (%) of each predicted source environment in the early event and post-event microbial communities, relative to the average pre-event community composition, illustrate shifting sources of microbes to the stream during an early season storm in October 2020 on the Marys River, Oregon, USA.
Boxes and whiskers show the distribution of differences in representation from pre-event mean of each source environment in the sampled community during the early and post-event periods. A value of zero indicates no difference from the pre-event community. * indicates p < 0.1 (Mann-Whitney non-parametric U test).