Organic carbon is the source of the energy that fuels biological production at the base of the foodweb. In aquatic ecosystems, organic matter derives from broken-up pieces of plants, algae and phytoplankton in the water and soil. Some sources of organic matter are imported by rivers from upland sources including soils and plant detritus (terrigenous sources), which tends to be lower in quality and less useful to aquatic organisms as a food source. Other sources of organic matter are produced within marshes, lakes and other aquatic systems and tend to be of higher nutritional value. In recent decades, human activities have altered aquatic ecosystems by changing freshwater flow, introducing exotic or non-native species, contributing to declining water quality through nutrient enrichment, and by the construction of dams. These activities have altered the amount, sources, and quality of carbon supplied to aquatic ecosystems. This project will use the Sacramento-San Joaquin River Delta, CA (referred to as the "Delta" hereafter) as a model system for understanding how human modifications influence the abundance, sources and age of carbon in sediments representing the past 100-200 years. The project will examine the organic carbon composition of sediments collected from sites representing key sub-environments of the Delta using "biomarkers", naturally-occurring chemical tracers that allow us to identify the sources of organic carbon. The objectives of this study will be to use these "biomarkers" to: (1) identify the sources of the aquatic and terrigenous components of sedimentary organic matter (SOM) currently being deposited within sub-habitats of the Delta; (2) determine how anthropogenic activities have altered the composition of organic matter delivered to the Delta using biomarker distributions in sediment cores, and (3) use the natural abundance of radiocarbon to determine the average age of organic carbon (TOC) and source-specific biomarkers to apportion organic matter sources and determine the radiocarbon ages of aquatic and terrigenous components of the SOM.
Broader Impacts This project will address basic questions related to human impacts on carbon quality in a representative highly modified ecosystem-the Sacramento-San Joaquin River Delta and will test fundamental hypotheses about the determinants of community structure and degradation of deltaic habitats. Deltaic habitats provide habitat for fishes and invertebrates that feed a large proportion of the world's human population and sustaining these dynamic ecosystems is of clear scientific, social and economic significance. To the best of our knowledge, our study will be the first to apply a multi-biomarker approach to questions of environmental change in deltaic environments and assess these changes within the context of potential restoration issues. The broader impacts of the proposed work also include a unique training opportunities for students to conduct interdisciplinary research that addresses questions of fundamental importance to ecosystem science at the interface between basic and applied research. This project will also engage under-represented groups and students at various stages in their training (high school, undergraduate and graduate) in aquatic sciences research through specialized programs at the three institutions involved in this study.
