Basal food resource quality and trophic energy flow across the biofilm-consumer interface: aquatic ecosystem response to environmental stressors

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Agriculture is the dominant contributor to eutrophication in many watersheds in Canada. Adequate monitoring of potential impacts from agriculture is thus essential to make informed management decisions for freshwater resources. Biological assessment is an approach that provides information on the response of organisms subjected to environmental pressures, allowing for an evaluation of how anthropogenic activities are affecting the biota. To date, bioassessment of aquatic ecosystems has generally been based on changes in taxonomic composition of assemblages. Yet, despite providing reliable estimates of ecosystem health, taxonomy-based indices are focused on individual organism groups (e.g. algae, invertebrates) without evaluating impacts across the food web, and provide limited insight into the effects of stressors that act at the ecosystem scale. There is thus a need to develop biomonitoring tools that incorporate community function and food web dynamics to reflect ecological attributes of whole ecosystems. Fatty acid (FAs) are vital for organisms (e.g., energy, reproduction, cell membranes). Certain essential FAs are transferred from food sources to consumers with no or minimal modification, which is fundamental for invertebrate growth/reproduction and for energy transfer efficiency to higher trophic levels. FA profiles in stream biofilms thus represent a proxy for basal resource quality, i.e., the nutritional quality at the base of the food web. FA profiles change under various conditions, and could be used as a biomarker to evaluate the effects of anthropogenic stressors such as eutrophication and climate warming. However, new knowledge is needed to support the use of FAs in biomonitoring, in particular to confirm the response of this biomarker to eutrophication from agricultural land use in combination with warmer water temperatures. With this NSERC-Discovery grant, I will address five short-term objectives: (1)Quantify the spatial and temporal variability in biofilm FAs; (2)Quantify the response of biofilm FAs under different phosphorus conditions and the relationship with algal taxonomic composition and diatom-based index values; (3)Establish relationships between land use and biofilm FAs to identify thresholds of change; (4)Determine the relationship between biofilm FAs and primary consumer FAs under eutrophic conditions characteristic of agricultural streams; (5)Assess whether the effects of eutrophication on biofilm FAs at the base of the trophic chain are exacerbated by increased water temperatures. My NSERC-Discovery program involves fundamental and applied research based on mesocosm experiments and field studies. The results will improve our comprehension of threats to biodiversity and ecosystem function by providing a better understanding of how food webs will be impacted by agricultural land use and eutrophication in a warming climate.