UC Riverside

Freshwater systems are irreplaceable natural resources, and they are imperiled globally by both anthropogenic and natural pressures. The Sacramento-San Joaquin river delta (SSJD) in California is among the most heavily human impacted river systems. The SSJD drains the western slope of the Sierra Nevada mountains and serves as a hub for California’s agricultural and municipal water distribution system. Pervasive geomorphological and hydrological alteration have created a novel distribution of water and habitat in the SSJD. Here, I use stable isotope analysis of fatty acids and amino acids to investigate the sources of organic matter available to consumers in the SSJD. Moreover, I elucidate the basal sources of organic matter supporting fish of conservation interest, such as the Chinook salmon (Oncorhynchus tshawytscha). My results confirm the importance of algae for fish in the SSJD. However, I demonstrate that inputs of organic matter derived from fungi, bacteria, and higher plants may be important as well. In Chinook salmon, I show that juveniles rearing in off-channel habitats maintained higher muscular concentrations of fatty acids. In total, my results suggest that availability of off-channel, and floodplain, habitats is important to fish in the SSJD.