The drying of rivers is becoming increasingly common, but impacts of drying on river ecosystems are not well understood. Previous research has shown that drying is harmful to many species but can be beneficial to some–altering the composition of species found at a given site (i.e., the local communities). However, effects of river drying on biodiversity and ecosystem processes at larger spatial scales, e.g., by altering processes such as dispersal and phenology along the river network, remain largely unknown. Further, the consequences of drying may be mediated by climate, but past studies have rarely compared drying impacts across gradients of aridity. This project sought to examine the effects of drying on stream ecosystems across multiple levels of biological organization (from genes to ecosystems), and to understand how differences in drying effects may be influenced by climatic context. Project team members examined streamflow, aquatic invertebrate communities, and genetic diversity in ten watersheds throughout the United States over the span of three years. Research led by the Ruhi Lab at UC Berkeley focused on how invertebrate communities potentially linked by dispersal (or metacommunities) change over time in response to stream drying. Specifically, we sought to understand when, where, and why drying alters the local and regional processes that generate and support riverine biodiversity. 

In addition to collecting samples of aquatic invertebrates at Pinnacles National Park (Chalone Creek) and in California’s Sierra Nevada (Kings River Experimental Watersheds), our team developed time series analysis and mathematical simulations to test how species respond to a wide range of drying conditions. To date, the project has produced seven peer-reviewed publications, with further papers in development. Main findings led by our group relate to the importance of river drying location (e.g., in headwaters vs. in main river reaches), showing that location, combined with drying severity and extent, determines river biodiversity not just at small (local) spatial scales, but across entire watersheds (Ruhi et al., in prep). We also found that drought can synchronize dynamics of species across large spatial scales, increasing their aggregate extinction risk (Sarremejane et al 2021, Global Change Biology). Further, we showed that thermal vulnerability quickly propagates across the stream network, and that air temperature in Sierra Nevada streams has the greatest influence on water temperature in the late spring and summer, when air and water temperatures peak and organisms are more likely to be stressed (Leathers et al. 2023, Limnology & Oceanography). Understanding how drying may lead to different ecological outcomes (e.g., depending on the geographic context) can help inform and prioritize conservation efforts at the watershed scale. More broadly, work funded by this project has enabled the development of scientific frameworks that connect change in hydrology to changes in species dynamics and ecosystem processes (Palmer & Ruhi 2019, Science). 

Two graduate students, two postdocs, and ten undergraduates were trained through the project resulting in career advancement and graduation. We have also collaborated with Pinnacles National Park to take over groundwater monitoring operations, lead outreach to the public in events like the California Biodiversity Week, and share our research with the public while in the field. The scholarship generated by this award is enabling further downstream science and helping connect scientific advances to river conservation and restoration practices—many of which address the pressing need to anticipate ecosystem responses to drought and flow intermittency.

Last Modified: 03/12/2025
Modified by: Albert RUHI