This proposal seeks to advance our understanding of the transport and fate of dissolved organic nitrogen (DON) in watersheds. We address three novel questions which have not been studied previously: (a) what is the relative influence of terrestrial versus aquatic (in-stream) sources/sinks on DON and bioavailable (BDON) dynamics at various points along the drainage path? (b) how do DON and BDON exports vary with catchment scale? and (c) how do DON dynamics differ from DOC and what mechanisms are responsible for these differences? We address these questions across varying temporal scales from baseflow to storm events and across seasons. Contributions of DON from various catchment sources are expected to change dramatically between baseflow and storm-event conditions while seasonal changes can especially influence BDON. Catchment sources investigated include ? precipitation, throughfall, stemflow, forest floor, hillslope soil water, wetland soil and ground water, groundwater seeps, hyporheic zone, and streamflow. We will not only investigate how the amounts of DON in various catchment sources influence DON export, but also investigate how the mobility (adsorption-desorption kinetics) and lability of various dissolved organic matter (DOM) constituents (e.g., hydrophobic and hydrophilic fractions) regulate DON export. Special attention is given to differences in DON and DOC responses in light of hydrologic flow paths, storm event magnitude and seasonal timing, antecedent catchment wetness, and redox conditions. We address these questions across zero- to third-order forested catchments of the Big Elk Creek in NE Maryland, which are representative of Piedmont catchments in the mid-Atlantic region. The catchments have already been intensively instrumented, and preliminary data from the site is available since March 2007. We will implement end member mixing analysis (EMMA) at multiple points in the catchments to characterize the spatial pattern of runoff sources and DON contributions. Innovative, new, spectrofluorometric tools such as specific UV absorbance (SUVA) and excitation-emission matrices (EEMs) are used to characterize DOM composition including an in-situ logging fluorometer. A strong interdisciplinary team of scientists with diverse strengths but complimentary interests will evaluate the questions. We anticipate that this study will result in the first conceptual model of DON that characterizes the relative influences of terrestrial and instream processes across various catchment scales. Results from this study will have direct practical implications for: (a) drinking water research since DON contributes to the formation of toxic disinfection by-products; and (b) nutrient enrichment of coastal estuaries (e.g., Chesapeake bay) since DON is bioavailable. An on-line data archive will be created to disseminate the data and results from this study. This data archive will be linked through the web site of the Center for Critical Zone (CCZ) at the University of Delaware and the Delaware Water Resources Center (DWRC). Dissemination of fact sheets to practitioners in regional offices of the US Natural Resources Conservation Service, US Forest Service, US EPA, and Maryland?s Forest Service should broaden the impact of the proposed research. The instrumented watershed will be (is being) used as a ?demonstration? and educational watershed laboratory. This will enable us to develop new interdisciplinary partnerships with other scientists and students within and outside UD. This project will provide valuable interdisciplinary research experiences for undergraduate and graduate students from the Bioresources Engineering, Geology, Plant and Soil Sciences, and Geography Departments. Under-represented groups will be actively recruited by the PI and Co-PI?s with the intention of filling two or more undergraduate and graduate assistantships. A female graduate student will be the PhD student on this project. The final outreach component of this project will involve the Fair Hill Nature Center and its experienced staff of environmental and experiential education teachers. The Fair Hill Nature Center is a non-profit entity, educating k-8 students about responsible environmental stewardship. The Fair Hill Nature Center educates over 8,000 school children annually. PIs on this project will be actively involved with the teachers and staff of the Fair Hill Nature Center staff to provide educational seminars on watersheds, soils, and forests and will participate in student field trips to the instrumented watershed.
