As climate-induced flow variability increases in our riverine systems, some rivers with historically perennial flow regimes in the Sierra Nevada Mountains are becoming intermittent. This shift in flow regime could have ramifications to the persistence of many aquatic taxa that rely on constantly flowing streams for reproductive success in the late summer and fall. We simulated future flow loss in this region by utilizing a set of nine experimental stream channels at the Sierra Nevada Aquatic Research Laboratory (SNARL). We conducted an experimental drought study subjecting the aquatic benthic insect community to various levels of flow reduction. We sampled the invertebrate community several times before, during, and after drought treatments were in effect. We were interested in how drought would affect invertebrate persistence and beta-diversity at SNARL, given that aquatic taxa in high elevation regions are adapted to a perennial hydrograph.
Results/Conclusions
Contrary to predictions, taxa at SNARL exhibited high resistance to drought stress until surface flow in the streams was lost. Pools served as a refuge for a longer amount of time than riffles, sustaining higher populations. Pools in channels subjected to extreme drought were still fed by a small amount of hyporheic flow which sustained them throughout the summer. In terms of beta-diversity, community dissimilarity was maintained (turnover), while strong abundance gradients (nestedness) emerged through drought treatments and time. The results of our study highlight the importance of sustained surface flow in perennial systems.