Identification of groundwater nitrogen point source contribution through combined distribute temperature sensing and in-situ UV photometry

农业是生态系统氮的主要贡献者，包括有机和无机肥料。硝酸盐渗透到地下水，并进一步运输到地表水被认为是氮素命运的主要途径之一。地下水和相关的硝酸盐流向溪流的定量仍然具有挑战性。特别是因为我们缺乏对地下水和相关NO3-通量的空间分布和时间变化的了解。在这项初步研究中，我们将把重点放在高分辨率分布式光纤温度传感（DTS）和原位紫外光度测定（ProPS）相结合的地下水和相关硝酸盐通量的识别和量化上。DTS是一种新的技术，能够测量千米范围内的温度，空间分辨率为~1米，精度为0.01 K。它已成功地应用于确定和量化地下水排放到溪流的来源。ProPS是一种潜水紫外过程光度计，它使用高精度的光谱分析来提供单一物质浓度，在我们的例子中是NO3-，以分钟为间隔，检测限小于0.05 mg l-1（≈0.01 mg NO3—Nl-1）。我们将使用人工侧向流入点源进行现场实验，以测试基于DTS和ProPS的量化方法，并估计其不确定性。选定的研究区域是德国黑森州的施温巴赫集水区，该地区具有良好的监测基础设施。水文通量的初步研究和野外观测表明，该流域有利于预期的研究。

Agriculture is the major contributor of nitrogen to ecosystems, both by organic and inorganic fertilizers. Percolation of nitrate to groundwater and further transport to surface waters is assumed to be one of the major pathways in the fate of this nitrogen. The quantification of groundwater and associated nitrate flux to streams is still challenging. In particular because we lack understanding of the spatial distribution and temporal variability of groundwater and associated NO3- fluxes. In this preliminary study we will focus on the identification and quantification of groundwater and associated nitrate fluxes by combining high resolution distributed fiber-optic temperature sensing (DTS) with in situ UV photometry (ProPS). DTS is a new technique that is capable to measure temperature over distances of km with a spatial resolution of ~1 m and an accuracy of 0.01 K. It has been applied successfully to identify and quantify sources of groundwater discharge to streams. ProPS is a submersible UV process photometer, which uses high precision spectral analyses to provide single substance concentrations, in our case NO3-, at minute intervals and a detection limit of less than 0.05 mg l-1 (≈0.01 mg NO3--Nl-1). We will conduct field experiments using artificial point sources of lateral inflow to test DTS and ProPS based quantification approaches and estimate their uncertainty. The selected study area is the Schwingbach catchment in Hessen, Germany, which has a good monitoring infrastructure. Preliminary research on hydrological fluxes and field observations indicate that the catchment favors the intended study.