Collaborative Research: Evaluating how the sampling integration scale affects field estimates of groundwater transit time and nitrogen fluxes

地下水从地下水位的补给到溪流的排放的过渡时间是一个基本的含水层特征，与地下水中污染物的输送速率和水资源管理的其他方面有关。该项目的目标是对三种新方法进行严格的定量比较，以估计与过境时间和非点源硝酸盐污染有关的三个变量：(a)地下水在含水层中的平均过境时间（MTT）， (b)从含水层到溪流的水和硝酸盐通量的大小，以及(c)地下水在渗入溪流之前发生的硝酸盐降解量。这三种方法都是基于地下水和河流水文和示踪剂测量，然而，数据收集方法和分析策略差异很大。对阐明优势和局限性的方法进行并排评估并不存在，将由本项目在北卡罗来纳州沿海平原农业区的两条溪流中完成。该项目将在纽瑟河流域进行，这是北卡罗来纳州雄心勃勃的全流域监管努力的所在地，旨在减少纽瑟河河口的氮(N)污染和相关的有害藻华和鱼类死亡。几年的努力并没有减少河口的氮输入。地下水中氮的运移时间可以延长几十年，这可能是一个重要的影响因素。通过比较三种测量MTT、硝酸盐通量和硝酸盐降解的新方法，本项目将更好地确定这些方法的优缺点。研究结果将为改进适用于水资源和土地管理的评价战略提供实际指导。该项目将为两所大学（北卡罗来纳州立大学和犹他大学）的学生提供高级水文学培训，并为处理非点源污染物的州监管机构提供实际结果和见解。

The transit time of groundwater, from recharge at the water table to discharge at streams, is a fundamental aquifer characteristic relevant to rates of contaminant transport in groundwater and other aspects of water resource management. The project goal is a rigorous quantitative comparison of three novel approaches for estimating each of three variables related to transit time and non-point-source nitrate contamination: (a) the mean transit time (MTT) of groundwater in aquifers, (b) the magnitude of water and nitrate flux from aquifers to streams, and (c) the amount of nitrate degradation occurring in groundwater prior to seepage into streams. Each of the three approaches is based on groundwater and stream hydrologic and tracer measurements, however, the data collection methods and analysis strategies differ greatly. A side-by-side evaluation of the approaches elucidating strengths and limitations does not exist and will be completed by this project in two streams in an agricultural region of the N.C. Coastal Plain.The project will take place in the Neuse River watershed, site of an ambitious basin-wide regulatory effort by the state of N.C. to reduce nitrogen (N) contamination and associated harmful algal blooms and fish kills in the Neuse River estuary. Several years of effort have not reduced estuarine N input. Groundwater transit times for N, which can extend for decades, are potentially an important contributing factor. By comparing three novel approaches to measuring MTT, nitrate flux, and nitrate degradation, this project will better define the pros and cons of the approaches. The results will provide practical guidance to improve assessment strategies applicable to water resource and land management. The project will provide advanced hydrologic training for students at two universities (N.C. State and the Univ. of Utah), and practical results and insight for state regulators dealing with non-point-source pollutants.