Climate-induced shift in hydrological regime alters basal resource dynamics in a wilderness river ecosystem

1. We integrated a 20-year ecological data set from a sparsely inhabited, snowmelt-dominated catchment with hydrologic models to predict the effects of hydrologic shifts on stream biofilm. 2. We used a stepwise multiple regression to assess the relationship between hydrology and biofilm ash-free dry mass (AFDM) and chlorophyll-a (chl-a) under recent climate conditions. Biofilm AFDM was significantly related to the timing of peak streamflow, and chl-a was significantly related to the timing of median streamflow. We applied these results to output from the variable infiltration capacity hydrologic model, which predicted hydrology under a baseline scenario (+0 degrees C) and a range of warming scenarios expected with climate change (+1, +2 or +3 degrees C). 3. When compared to the baseline, the results indicated that earlier peakflows predicted under warming scenarios may lead to earlier initiation of biofilm growth. This may increase biofilm AFDM during the summer by up to 103% (+/- 29) in the +3 degrees C scenario. Moreover, interannual variability of AFDM was predicted to increase up to 300%. Average chl-a during the summer increased by up to 90% (+/- 15) in the +3 degrees C scenario; however, its response was not significantly different from baseline in most years. 4. Because hydrologic change may alter the temporal dynamics of biofilm growth, it may affect the seasonal dynamics of biofilm quality (i.e. chl-a-to-AFDM ratio). The results indicated that hydrologic shifts may increase biofilm quality during the spring, but may decrease it during the summer. Thus, we provide evidence that predicted hydrologic shifts in snowmelt-dominated streams may alter the quantity and quality of an important basal resource. However, the magnitudes of these predictions are likely to be affected by other environmental changes that are occurring with climate change (e.g. increased wildfire activity and stream warming).