Our research aims to inform solutions to global water challenges that sustain biodiversity, satisfy human needs, and promote environmental stewardship. Key themes of our work include understanding drivers of hydrologic variability, quantifying ecological responses to flow variation and alteration, and characterizing the diversity and stability of freshwater populations and communities. Much of our research also directly guides the management and conservation of freshwater ecosystems for sustainable stewardship of water, fisheries, and the environment.
We use multiple methods in our research. We tag and track fish, sample benthic macroinvertebrates from streams, observe organisms underwater in their natural environment by snorkeling or with videography, and survey birds and vegetation. We deploy a wide variety of sensors at our study sites to characterize environmental conditions, including temperature, light, water quality parameters, and streamflow. We conduct field experiments, manipulating environmental variables and communities to understand ecological relationships and responses to environmental change. In the laboratory, we sequence genes, process stable isotopes, analyze otoliths, and identify macroinvertebrates. We use a wide variety of data sources, analytical tools, and modeling approaches to characterize ecosystem dynamics and gain insight into the causes and consequences of environmental change on aquatic species and the benefits that people derive from healthy freshwater ecosystems.
Hydrologic variability and change in freshwater ecosystems
Streamflow is a master variable in freshwater ecosystems. Variation in flow across days, seasons, and years affects the structure and functions of rivers, streams, wetlands, and estuaries, ultimately controlling the diversity, abundance, and health of aquatic organisms. Human activities, including anthropogenic climate change, are disrupting the water cycle, affecting the timing, seasonality, and magnitude of flows as well as the frequency and intensity of extreme floods and drought. Research in our group aims to understand how humans are altering natural flow regimes, especially from dam operations, water withdrawals, and climate change. We also study the effects of human activities on flow-dependent environmental variables, including stream network connectivity and water quality. Our work also aims to assess and predict the potential for freshwater ecosystems to experience major shifts in hydrologic regimes, such as the transition of perennial- to intermittent-flowing systems.
See our list of publications under “hydrologic variability” theme for more information.
Ecological responses to flow variation and alteration
The modification of hydrologic (streamflow) regimes is a primary driver of ecosystem degradation and biodiversity loss. Our group investigates how different levels of biological organization – from populations to food webs – respond to hydrologic variation and changes in hydrologic regimes within streams, rivers, and in estuaries. This research includes studies that explore the effects of natural and artificial stream drying on macroinvertebrates, stream fish, and stream food webs; the effects of dam operations on fish populations and community composition; and effects of wastewater discharges on benthic macroinvertebrates, birds, and riparian vegetation. Our work also explores the effects of extreme flow events, including droughts and floods, on the life history traits, survival, abundance, and composition of freshwater species and communities.
See our list of publications under “flow alteration” theme for more information.
Diversity and stability of salmon and freshwater food webs
Populations of Pacific salmon that breed and rear in different environments often differ in aspects of their life histories (e.g., timing of migrations, age at maturity, etc.). Such diversity within and among populations contributes to the overall stability and resilience of their population complexes. Our group studies how critical elements of life history diversity can be lost, as well as strategies for recovering trait diversity in imperiled populations. In particular, we are interested in how the expression of diverse life history traits in spatially-structured populations lead to asynchronous dynamics, promoting stability, much like a well-built financial portfolio. We also explore how such stabilizing portfolio effects can be observed at the community level, driven not only by environmental variation, but also in the response diversity of the multiple species making up a community.
As we advance understanding of individual species responses to global change stressors, important gaps remain around the scaling of processes from individual sites to whole river networks, and from individual populations to whole food webs. Species interactions (e.g., predation and competition) may dampen or amplify impacts of environmental stress on individual species. Effects on predators may ripple across whole food webs; and changes in basal productivity may increase animal productivity–affecting not only the riverine environment but also the adjacent riparian habitat. A central focus of our work is to probe, via field experiments and analysis of long-term monitoring data, the mechanisms that control how whole food webs are responding to a changing climate.
One of the most consistent signatures of global change are shifting phenologies, or shifts in the timing of key life cycle events. Our groups are interested in understanding the causes and consequences of phenological shifts, including in the timing of spawning, migration, or productivity. We are especially interested in the potential for phenological shifts to cause mismatches that influence dynamics, such as mismatches between salmon arrival timing to the ocean and ocean conditions, and trophic mismatches between forage fishes and their aquatic prey, or between emerging insects and their terrestrial predators. This work aims to reveal how community dynamics are driven by the underlying temporal dynamics of environmental conditions, often mediated through food web interactions.
See our list of publications under “diversity and stability” theme for more information.
Restoration, management, and conservation of freshwater ecosystems
Much of our work is designed to inform management decisions, with the aim of conserving biodiversity and the many benefits that people derive from healthy freshwater ecosystems. One major topic in this research theme is environmental flow science – an interdisciplinary field focused on understanding the quantity and quality of river flows needed to sustain aquatic species and their habitats. This work includes applying knowledge of ecological-flow relationships to guide dam (re)operation, water diversion management, and establishment of environmental flow requirements in rivers and streams. Research in this theme also informs dam removal decisions and habitat restoration planning–from headwaters to tidal estuaries, where formerly levied wetland ecosystems are being reconnected to tidal action. Much of our research is intended to support salmon conservation and recovery, including studies to identify strategies for rebuilding abundance and diversity of different runs and life histories. Work in this area includes studies to understand the impact of habitat loss and change, the impact and control of invasive species, as well as studies to improve hatchery practices and support sustainable fisheries. Finally, our work includes the development decision-support tools to inform long-term water allocation planning, the design of environmental monitoring networks, and freshwater biodiversity conservation.
See our list of publications under the “management and conservation” theme for more information.