Understanding how river food webs respond to hydroclimatic extremes, including drought and river drying, is critical for predicting freshwater biodiversity dynamics into the future. Our NSF-funded work (DEB-2047324, DEB-1802714) focuses on an under-researched, yet consequential area of research: the interactive effects that local drought stress and watershed-level fragmentation can have on river food webs and the ecosystem processes that these food webs control.

UC Berkeley Scientists Publish Research on Pinnacles National Park | Institute for Parks, People, and Biodiversity

When rivers run dry, predators are often unable to move freely across the river network, and prey are forced to coexist at high densities in isolated river pools. As a consequence, unique food-web structures emerge. Using a combination of field experiments and modeling of long-term hydrologic and ecological data, we showed that biota persisting in the dry riverbed (i.e., the animal ‘seedbank’) uniquely contributes to post-drought community recovery; flow connectivity mitigates the effects of drought via compensatory dynamics; and regional drought can synchronize metapopulation dynamics of stream invertebrates across large river networks – increasing risk of extinction of drought-sensitive species, and risk of disassembly of whole food webs.

A significant focus of our research is understanding the ecological consequences of flow intermittency (i.e., streams ‘running dry’). We maintain a long-term monitoring program at the Chalone Creek watershed (Pinnacles National Park, California), in collaboration with the National Park Service. This intermittent river network is densely instrumented and has been sampled seasonally for the past 10 years. In this system, drought-resistant stoneflies persist in hyporheic habitats, and three-spined stickleback periodically leave perennial habitats to colonize intermittent stream sections. The relatively simple, yet highly-dynamic nature of this food web makes it an ideal study system to probe the mechanisms and limits of river biodiversity persistence to drought.

Water flows through a series of concrete channels that zig-zag across a dry, grassy mountainside. In the foreground, a person sits on the edge of one of the channels watching a white contraption that is floating in the water. Snowy mountain peaks rise in the background.

In the Sierra Nevada, climate change threatens snow-dependent rivers by reducing snowpack and prolonging summer droughts. These changes elevate water temperature and reduce flow velocity, impacting stream biodiversity and ecosystem processes. Our research at the Sierra Nevada Aquatic Research Laboratory (SNARL) and the Kings River Experimental (KREW) has shown, via large-scale experiments and long-term monitoring respectively, that invertebrate community composition and phenology (life cycles), predator diets, and overall food-web structure is poised to shift in response to novel snow regimes.

Many river networks in the U.S. West and across mountain ranges globally are drying for the first time in the period of record, or experiencing unprecedented declines in their snowpack. By integrating approaches and insights learned across model systems, scales, and approaches (experimental vs. observational), we seek to increase our predictive ability of climate change impacts on river ecosystems – and inform conservation and monitoring strategies accordingly.

Related grants

2021-26 Sole PI, NSF CAREER: Drought and metacommunity stability in riverine networks (DEB-2047324).

2019-23 PI. NSF MSB-FRA: Scaling Climate, Connectivity, and Communities in Streams (DEB-1802714).

2020-21 Sole PI, Hellman Fellows Fund. Drought on Riverine Networks: How Does Flow Intermittency Disrupt Stream Ecosystem Processes?

2019-20 Sole PI, California Institute for Water Resources (CIWR) Water Research Program. Towards a Mechanistic Understanding of the Multi-Scale Effects of Drought on Riverine Biodiversity.

Selected publications

Leathers, K., Herbst. D., de Mendoza, G., Doerschlag, G. & A. Ruhi (2024). Climate change is poised to alter mountain stream ecosystem processes via organismal phenological shifts. Proceedings of the National Academy of Sciences of the USA, 121(14):e2310513121.

Carlson, S.M., Ruhi, A., Bogan, M.T., Wölfle Hazard, C., Ayers, J., Grantham, T.E., Batalla, R.J. & C. Garcia (2024). Losing flow in free-flowing, Mediterranean-climate streams. Frontiers in Ecology and the Environment, p.e2737.

Fournier, R., de Mendoza, G., Sarremejane, R. & A. Ruhi (2023). Isolation controls reestablishment mechanisms and post-drying community structure in an intermittent stream. Ecology, 104(2):e3911.

Sarremejane, R., Stubbington, R., England, E., Sefton, C.E.M., Eastman, M., Parry, S. & A. Ruhi (2021). Drought effects on invertebrate metapopulation dynamics and quasi-extinction risk in an intermittent river network. Global Change Biology, 27(17):4024–4039.

Vander Vorste, R, Stubbington, R., Acuña, V., Bogan, M.T., Bonada, N., Cid. N., Datry, T., Storey, R., Wood, P.J. & A. Ruhi (2021). Climatic aridity increases temporal nestedness of invertebrate communities in naturally drying rivers. Ecography, 44(6):860-869.

Palmer, M. & A. Ruhi (2019) [equal contribution]. Linkages between flow regime, biota, and ecosystem processes: implications for river restoration. Science, 365(6459):eaaw2087.