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中溶解有机氮（DON）的运输和命运的理解。我们解决了三个以前没有研究过的新问题：(a)陆地与水生（流内）源/汇对沿排水路径各点的DON和生物可利用性（BDON）动态的相对影响是什么？(b)污水处理厂和污水处理厂的出口如何因应集水区的规模而变化？(c) DON动力学与DOC有何不同，造成这些差异的机制是什么？我们跨越从基流到风暴事件和季节的不同时间尺度来解决这些问题。不同流域源对DON的贡献在基流和风暴条件下预计会发生巨大变化，而季节变化尤其会影响BDON。调查的集水区来源包括？降水、透雨、茎流、森林地表、山坡土壤水、湿地土壤和地下水、地下水渗漏、潜流带和溪流。我们不仅将研究不同流域来源中DON的数量如何影响DON的输出，还将研究各种溶解有机物（DOM）成分（例如疏水和亲水组分）的迁移性（吸附-解吸动力学）和不稳定性如何调节DON的输出。在水文流动路径、风暴事件强度和季节时间、先前的流域湿度和氧化还原条件下，特别关注DON和DOC响应的差异。我们在马里兰州东北部的大麋鹿溪的零到三级森林集水区解决了这些问题，这些集水区是大西洋中部地区皮埃蒙特集水区的代表。集水区已经进行了密集的仪器测量，自2007年3月以来，该地点的初步数据已经可用。我们将在流域的多个地点实施末端成员混合分析（EMMA），以表征径流源和DON贡献的空间格局。创新的荧光光谱测量工具，如特定紫外吸收（SUVA）和激发发射矩阵（EEMs），用于表征DOM成分，包括原位测井荧光仪。一个强大的跨学科科学家团队，他们拥有不同的优势，但兴趣互补，将评估这些问题。我们预计，这项研究将产生第一个DON概念模型，该模型表征了不同流域尺度上陆地和河流过程的相对影响。这项研究的结果将对以下方面产生直接的实际影响：(a)饮用水研究，因为DON会形成有毒的消毒副产物；(b)沿海河口（如切萨皮克湾）的营养富集，因为DON是生物可利用的。将建立一个在线数据档案，以传播这项研究的数据和结果。该数据档案将通过特拉华大学关键区域中心（CCZ）和特拉华水资源中心（DWRC）的网站进行链接。向美国自然资源保护局、美国林业局、美国环保署和马里兰州的区域办事处的从业人员分发情况说明书？美国林务局应扩大拟议研究的影响。仪器化分水岭将（正在）用作示范。以及教育分水岭实验室。这将使我们能够与特拉华大学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系、地质系、植物与土壤科学系和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。S的目的是填补两个或两个以上的本科生和研究生的助教。一名女研究生将担任该项目的博士生。这个项目的最后一个扩展部分将涉及费尔希尔自然中心及其经验丰富的环境和体验教育教师。费尔希尔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。费尔希尔自然中心每年为8000多名学童提供教育。参与该项目的专业人员将与费尔希尔自然中心的教师和工作人员积极合作，提供有关流域、土壤和森林的教育研讨会，并将参加学生对仪器化流域的实地考察。

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.