Export and metabolism of carbon in urban watersheds: Climate implications Rose M. Smith 1, Sujay S. Kaushal 1 1 University of Maryland College Park Motivation Urbanization and climate change influence riverine carbon fluxes to estuaries by altering the hydrologic regime, water temperature, and anthropogenic sources of organic matter. Carbon cycling has implications for freshwater food webs, estuarine ecosystems, and greenhouse gas emissions, however little is known about how land use and climatic factors influence carbon processing and transport in rivers. Objectives 1) Quantify rates of carbon transport and metabolism in four urban watersheds which vary in catchment size 2) Develop a conceptual framework for understanding shifts in carbon export, quality, and metabolism across flow conditions in developed watersheds Methods -Dissolved C Export: 3 years of biweekly sampling + USGS LOADEST model -Metabolism: Baysean Metabolic model (BaMM) used to estimate GPP and ER based on diurnal DO and temperature over 2 years -Organic Matter Quality: Lability metrics quantified based on spectrofluorometric excitation-emission measurements. -CO 2 concentrations: Measured DIC and pH biweekly and determined the proportion of dissolved CO 2 using CO2SYS model of the inorganic carbon system. Acknowledgements: National Science Foundation, Maryland Sea Grant Fellowship Program, Maryland Water Resources Research Center, University of Maryland Graduate Summer Research Fellowship; ESSIC/Geology Travel Grant Conclusions -Annual DOC export from highly developed streams was comparable to forested streams in similar regions and DOM quality resembles soil/leave despite reduced forest cover. -Light availability may limit GPP more than nutrients. -CO 2 concentrations are on par with DOC, and streams were net sources of CO 2 throughout the year. -Greenhouse gas implications of C and N loading in urban areas warrant further study DEPARTMENT OF GEOLOGY 1. Dissolved Carbon form and quality varies with flow : DOC was flushed and DIC was diluted with increasing flow. Dissolved organic matter (DOM) character became less labile at high flows. 4. Net Ecosystem Productivity across flow conditions. NEP (net ecosystem productivity, GPP-ER) was greatest at medium flows for all sites. Periods of positive NEP were greater in the open-channel site compared to smaller streams with seasonal shading from riparian trees. Sampling sites in the Anacostia Watershed Results 2. Daily stream metabolism and seasonal variations: Streams were generally heterotrophic (ER>GPP) with limited periods of net- production (GPP>ER) during spring. Data shown from one site (Northeast Branch). 3. Carbon Dioxide: concentrations of CO 2 was super-saturated compared to the atmosphere on all dates. Paint Branch Northeast Branch Northwest Branch Sligo Creek Conceptual Framework 5. Conceptual Framework highlighting the influence of flow on carbon cycle parameters in urban streams. As DOC fluxes increase, DOM quality becomes less labile. Anthropogenic influences such as warming, salinization, sewage, and stormwater may influence DOC fluxes and DOM quality. In-stream GPP and ER rates peaked during moderate flow conditions and reduced during low-flow due to seasonal shading from riparian trees which coincides with high evapotranspiration. Shaded headwaters Non-shaded River