Citation:

Yuan, L., N. Smucker, C. Nietch, AND E. Pilgrim. Quantifying spatial and temporal relationships between diatoms and nutrients in streams strengthens evidence of nutrient effects from monitoring data. Freshwater Science. The Society for Freshwater Science, Springfield, IL, 41(1):100-112, (2022). https://doi.org/10.1086/718631

Impact/Purpose:

Nutrient pollution has widespread negative effects on freshwater ecosystems throughout the United States and around the world. However, changes in phosphorus and nitrogen concentrations in streams are usually associated with changes in other environmental factors, and this phenomenon complicates efforts to understand the effects of nutrients on stream biological assemblages. This work describes an approach for analyzing field, observational data to estimate quantitative effects of increased nutrients on diatom assemblages by comparing relationships estimated in time at 25 individual stream sites and in space among these sites. Diatoms are particularly useful for assessing nutrient effects on streams because they are a highly diverse group of unicellular algae found in nearly all aquatic environments and are sensitive responders to increased nutrient concentrations. Results from temporal, within-site models and a spatial, among-site model provide evidence of a causal effect of increased phosphorus on diatom assemblage structure.

Description:

Changes in phosphorus and nitrogen concentrations in streams are usually associated with changes in other environmental factors, and this phenomenon complicates efforts to understand the effects of nutrients on stream biological assemblages. Controlled experimental manipulations can isolate the effects of nutrients, but such experiments usually require some simplification of the stream ecosystem. Observational data can be collected from a wide variety of streams but must address the possible effects of confounding factors. Here, we propose a new approach for analyzing field, observational data, in which we compare the effects of changes in nutrient concentrations in time within individual sites and in space among many sites. We apply this approach to metagenomic data collected in the East Fork of the Little Miami River watershed (Ohio). The analysis indicates that changes in diatom assemblage structure are consistently associated with changes in the concentration of total reactive phosphorus in time and in space. In contrast, estimated effects of ammonia and urea differed when estimated in time versus in space. We suggest that the results of this analysis provide evidence of a causal effect of increased phosphorus on diatom assemblage structure.

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