Are nutrient loading effects on stream nutrient processing driven by shifts in biofilm community dynamics?

Document Type

Conference Proceeding

Publication Date



Stream biofilm community composition may be influenced by nutrient stoichiometry, and in turn, may affect the storage, processing and export of nutrients. We experimentally tested the responses of autotroph and heterotroph components of biofilm communities to nutrient concentrations by adding variable amounts of nitrogen (NO3-, 0.8 –490 µg/L-N), phosphorus (PO4-3, 1.2-35 µg/L-P) and/or dissolved organic carbon (DOC-glucose, 1.2 –7.1 mg/L), in replicated laboratory mesocosms. We hypothesized that increased DOC concentrations would shift biofilm composition toward heterotrophs, and that decreased DOC relative to NO3- or PO4-3 concentrations would increase the relative dominance of autotrophs. Biofilm chlorophyll a concentrations did not respond to DOC or PO4-3 addition, but increased with NO3- addition, which suggested an increase in the N-limited algal assemblage. In contrast to our expectation, fungal ergosterol concentrations decreased with DOC addition, and did not respond to NO3- or PO4-3. Shifts in heterotroph compared to autotroph dominance in response to resource availability suggest that biofilm community interactions may be an important mechanism controlling nutrient uptake. Understanding these complex interactions may help explain patterns of accumulation and downstream export of nutrients.

Publication Title

American Society of Limnology and Oceanography and the North American Benthological Society Joint Meeting 2010