Collaborative Research: Evolution of Dissolved Organic Nitrogen (DON) from the Headwaters to the Catchment Outlet: Sources, Variation with Scale, and Differences with DOC.

该提案旨在促进我们对流域溶解性有机氮（DON）的运输和归宿的理解。我们解决了三个新的问题，以前没有研究过：（一）什么是陆地与水生（在流）源/汇上的DON和生物可利用（BDON）动态的相对影响在不同的点沿着排水路径？(b)DON和BDON出口如何随流域规模变化？以及（c）DON动力学与DOC动力学有何不同，造成这些差异的机制是什么？我们解决这些问题在不同的时间尺度从基流风暴事件和跨季节。预计来自不同流域来源的DON的贡献在基流和风暴事件条件之间会发生显着变化，而季节变化尤其会影响BDON。调查的集水资源包括？降水、穿透降水、树干径流、森林地面、山坡土壤水、湿地土壤和地下水、地下水渗漏、潜流带和径流。我们不仅将研究各种汇水源中DON的量如何影响DON输出，还将研究各种溶解有机物（DOM）组分（例如，疏水和亲水级分）调节DON输出。特别注意DON和DOC响应的水文流动路径，风暴事件的大小和季节性时间，前期集水区湿度，氧化还原条件的差异。我们解决这些问题在零至三阶森林覆盖的大麋鹿溪流域在东北马里兰州，这是代表皮埃蒙特流域在大西洋中部地区。集水区已经密集地安装了仪器，自2007年3月以来，可以获得该地点的初步数据。我们将在集水区的多个点实施端元混合分析（EMMA），以表征径流源和DON贡献的空间格局。创新的，新的，荧光光谱工具，如特定的紫外吸收（苏瓦）和激发-发射矩阵（EEMs）用于表征DOM的组成，包括一个原位测井荧光计。一个强大的跨学科科学家团队，具有不同的优势，但互补的利益将评估的问题。我们预计，这项研究将导致第一个概念模型的DON的特点，陆地和institutional过程的相对影响，在不同的集水scales.Results从这项研究将有直接的实际意义：（a）饮用水研究，因为DON有助于形成有毒消毒副产品;和（B）营养富集的沿海河口（例如，切萨皮克湾），因为DON是生物可利用的。将创建一个在线数据档案，以传播本研究的数据和结果。该数据档案将通过特拉华州大学临界区中心（CCZ）和特拉华州水资源中心（DWRC）的网站链接。向美国自然资源保护局、美国林务局、美国环保局和马里兰州的区域办事处的从业人员分发情况说明书？美国林务局应该扩大拟议研究的影响。该仪表化分水岭将（正在）用作？示范？和教育流域实验室。这将使我们能够与UD内外的其他科学家和学生建立新的跨学科伙伴关系。该项目将为生物资源工程，地质学，植物和土壤科学以及地理系的本科生和研究生提供宝贵的跨学科研究经验。PI和Co-PI将积极招募代表性不足的群体？这是为了填补两个或两个以上的本科生和研究生助教奖学金。一名女研究生将担任该项目的博士生。该项目的最后一个推广部分将涉及费尔山自然中心及其经验丰富的环境和经验教育教师。费尔山自然中心是一个非营利实体，教育k-8学生负责任的环境管理。费尔山自然中心每年为8，000多名学童提供教育。该项目的PI将积极参与费尔山自然中心的教师和工作人员，提供关于流域，土壤和森林的教育研讨会，并将参加学生实地考察仪表流域。

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.