Collaborative Research: Sediment stabilization by animals in stream ecosystems: consequences for erosion, ecosystem processes, and biodiversity

San Francisco State University, San Francisco CA

Investigators

Abstract

Many of the world's environmental problems are exacerbated by changes in both biological and physical conditions that jointly influence sediment erosion. In freshwater habitats, major progress toward clearly linking biology and geomorphology to address environmental problems includes incorporating the role of the many small animals that live in streams into our understanding of erosion. This research project investigates how bottom-dwelling invertebrates in streams influence flood disturbance by regulating the stability of the riverbed. Sediment erosion is a critical variable in freshwater ecosystems because it influences freshwater biodiversity, insect and fish egg survival, changes the composition and activity of algae, and alters carbon and nutrient cycling. An understanding of sediment erosion that includes the impacts of bottom-dwelling animals will address a range of practical problems relevant to society, including informing models to predict erosion in landscapes altered by land use, predicting the impacts of floods that are being altered worldwide as a result of changes to water levels caused by climate warming and diversion for agriculture, and protecting and restoring habitat for threatened freshwater organisms such as fish. This project will provide research opportunities for one PhD student, two Master students, and four undergraduate students, develop workshops to teach concepts related to bottom-dwelling invertebrate influences on sediment erosion to high school teachers, and produce outreach videos documenting sediment erosion. To investigate how animals in streams influence physical resistance to flood disturbance with consequences for aquatic benthic communities and ecosystem processes, the researchers will study common aquatic ecosystem engineers, web-spinning hydropsychid caddisfly larvae (Trichoptera:Hydropsychidae). These aquatic insects build silk structures that can bind riverbed sediment together, increase the force required to move sediments, and reduce bedload flux. The researchers will quantify sediment stabilization effects by caddisfly larvae from grain to landscape scales. They will also document how changes in sediment disturbance due to caddisfly silk structures influence ecosystem productivity, nutrient cycling, and the recovery of benthic communities following floods. The researchers will use a combination of controlled laboratory experiments, caddisfly density manipulations in natural streams, field surveys, and sediment transport models to identify how caddisfly ecosystem engineering affects sediment transport regimes across landscapes. Together, the series of studies will quantify how much these abundant ecosystem engineers can regulate erosional processes in streams.