Effects of groundwater inputs on algal assemblages and cellulose decomposition differ based on habitat type in an agricultural stream

Stream communities and processes are known to differ among reaches and habitat types in accordance with environmental variation. However, groundwater input has not been well-explored as a driver of ecological heterogeneity among stream reaches and habitats. We assessed stream biofilm communities (biomass and diatom assemblage composition) and cellulose decomposition in run and riffle habitats across three stream reaches with high, moderate, and low groundwater input in Kintore Creek, Ontario, Canada. Algal biomass, as well as density and composition of diatom assemblages, differed between runs and riffles in reaches with moderate and high groundwater inputs, but not in the low groundwater reach. Reaches with moderate and high groundwater input had faster streambed cellulose decomposition in riffles than in runs, whereas the reach with low groundwater input had no difference in streambed cellulose decomposition. Subsurface cellulose decomposition in riffles and runs was fastest in the high groundwater reach. We found that measured environmental variables did not explain the apparent effects of groundwater inputs. Findings from this study highlight the covarying influence of groundwater input and habitat type in altering in stream ecological response in enriched streams.