Baltimore Ecosystem Study Institute of Ecosystem Studies

2011 BES Annual Meeting Presentation and Poster Abstracts

Sources and Transformations of Carbon and Nitrogen in the Potomac River Estuary
Pennino, Michael
Co-Authors: Sujay Kaushal, and Sudhir Murthy

Abstract: This study examines the capacity of a major tributary of the Chesapeake Bay, the Potomac River, to transform nitrogen (N) and carbon (C) inputs from the world's largest advanced wastewater treatment facility. Surface water and effluent samples were collected monthly for one year, along longitudinal transects of the Potomac River. Water samples were analyzed for the major dissolved and particulate forms of C and N. Nitrate stable isotopes were used to trace the fate of wastewater nitrate, and other nitrate sources. Carbon sources were traced using fluorescence excitation emission matrices (EEMs), and PARAFAC modeling. Preliminary results indicate that levels of nitrate increase within the vicinity of the wastewater treatment outfall, but decrease rapidly downriver, potentially indicating nutrient uptake and/or denitrification. Data from fluorescence EEMs indicate that organic matter inputs from wastewater effluent disappears within 1-2 km downriver. Nitrate isotope data shows 15N-NO3-, which is characteristic of wastewater sources, increases downriver of the wastewater treatment plant, but the 15N signal disappears after about 30 km downriver. Nitrate isotope data also indicate potential sources of nitrate from upriver animal farm inputs and downriver marine nitrate inputs. Additionally, both wastewater effluent samples and downriver samples show evidence for denitrification. Majors rivers like the Potomac may have a huge capacity for transforming and processing large carbon and nitrogen inputs within a short distance. Greater knowledge of how land management and climate change impacts these transformations will be important in predicting changes in the amounts and forms of nutrient loads to coastal waters.