Cross-ecosystem linkages are vital for the stability of the Earth’s ecosystems. Rivers and lakes play a crucial role in fertilizing the surrounding watersheds by exporting insect prey that sustain riparian predators such as insectivorous birds, lizards, and bats. In turn, aquatic ecosystems often receive large amount of organic matter that gets conditioned and decomposed in the aquatic environment. The magnitude and timing of these fluxes of organisms and materials, known as cross-ecosystem subsidies, can be thus affected by changes in both the terrestrial and aquatic environment.

One of our new research lines focuses on the role of trees in mediating key ecohydrological processes in riparian ecosystems. In Chalone Creek, Pinnacles National Park (California), we study how trees use and move water. Using sap flow data, stable isotope source water sampling, and long-term groundwater depth data, we are identifying the sources, magnitude, and timing of water uptake and redistribution by riparian trees. This research is critical for understanding how trees provide moist refugia for drought-stressed organisms, particularly the invertebrate “seedbank” in the hyporheic zone during seasonal drying. As droughts become more frequent and severe, understanding these processes becomes increasingly important for conserving riparian ecosystems. We are also experimentally testing the rates of tree leaf litter decomposition in these intermittent streams – and how intermittency may alter ecosystem process rates by altering shredder invertebrate composition, tree leaf quality, and hydroperiod length.

Emerging aquatic insects are another vital component of cross-ecosystem subsidies, playing a significant role in linking river and forest ecosystems. In a recent study where we experimented with novel low flows simulating a climate change scenario in the Sierra Nevada, we found that the early snowmelt treatment controlled the abundance of stream insects metamorphosing, leading to earlier, more abundant pulses of flying bugs that in turn attracted riparian birds.

Compared to their terrestrial counterparts, aquatic insects can be rich in long-chain polyunsaturated fatty acids (LCPUFA) that are essential for the development of brain and muscle in vertebrates. Our preliminary research indicates that riparian predators may time their breeding to coincide with the peak abundance of nutrient-rich aquatic insects. However, droughts can disrupt this synchrony, and may devalue river-derived prey if these are forced to survive in dark, detrital-based habitats. A new projected funded by the Winkler Scholars Award seeks to understand the potential role of drought in altering the quantity and quality (fatty acid signature and amount) of stream insects emerging from intermittent streams – a crucial step for predicting the impacts of climate change on riverine-riparian food webs.

Related grants

2024 Sole PI, Winklers Scholars Award. Will drought disrupt key river-to-forest connections?

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.