Aquatic insect response to flow regimes and climate change in two terminal basins

The focus of this research is the flow-ecology relationship and climate vulnerability of two terminal basins on two continents: the Great Basin in the United States (US-TB) and the Central Asian Internal Drainage in Mongolia (MN-TB). These northern hemisphere basins are located within two of the largest temperate steppe biomes in the world and correspond to semiarid desert steppes. Comparison of these terminal basins can help us understand both similarities and differences within similar ecoregions that are widely separated geographically. A comparison of streamflow characteristics was conducted using streamflow variabilities at Functional Process Zones (FPZs), which are the study units of macroscale comparison with different valley-scale hydrogeomorphic characteristics. The streamflow variabilities calculated from continuous daily streamflow data spanning 1990-2014; indicated that streamflow was characterized by longer seasonal high flow in MN-TB and larger minimum flow in US-TB, and four distinct streamflow patterns were established: extended high flow and frequent flooding in MN-TB and highly variable and large baseflow in US-TB. Hence, the larger minimum flow defined high taxa richness in US-TB and the longer seasonal high flow was responsible for the high heterogeneity of aquatic insect assemblages in MN-TB, whereas the four streamflow patterns selected taxa with relatively different functional traits. Among taxa with climate-sensitive traits at FPZs with the four streamflow patterns, warm-water taxa were predicted to be more vulnerable when they also have a preference for slow-moving water conditions. Among the four streamflow patterns, FPZs with the highly variable flow were the most sensitive to projected climate change. Despite similar limiting physiographic conditions such as lacking outlets and connectivity to outside watersheds, these two terminal basins have different flow regimes, which further define the patterns of aquatic insects and vulnerability to climate change. The differences in flow regimes and aquatic insect assemblages indicate that these two terminal basins were driven by differences in continental climate rather than their ecoregional affiliations. Even though the sample sites were located in the same type of ecoregions, continental level variables drove differential responses in the flow-ecology and predicted responses to climate change. Therefore, when examining similar systems, global and continental-scale effects should be taken into effect for designing large-scale natural resource management of rivers.