Deciphering the role of dissolved organic nitrogen in stream nutrient cycling

许多地表沃茨是黄色或棕色的，这是由于存在来自许多自然来源的有机分子，如树叶、土壤和湿地。 这些分子影响水流中的广泛特性，例如光穿透水的能力和水的酸度。 有机分子还可以为河流提供能量和必需的营养物质，如氮和磷。这些有机分子的一种特别重要的形式是溶解的有机氮，它在全球森林，北极苔原，河口和溪流中发现。然而，关于溶解有机氮在何时何地作为能量来源、氮源或两者对生物群落的作用知之甚少。该项目将研究溶解有机氮在跨越不同环境的五个不同森林地区的溪流中的作用，以阐明溶解有机氮的作用。这项研究与水资源管理有关，因为溶解的有机氮是导致河口有毒藻类大量繁殖的过度营养负荷的来源，当在饮用水供应中发现它时，它可以在水处理过程中产生可能危害人类健康的消毒副产品。 这项研究还将把代表性不足的群体纳入该项目所需的实验室工作和实地工作，并为研究生和博士后科学家提供培训机会。区分溶解有机氮（DON）的竞争作用是困难的，因为直接操纵水生生态系统中的DON池最容易通过添加特定化合物如氨基酸，其是市售的，但并不特别代表在环境条件下在溪流和河流中发现的DON。根据初步实验结果，研究人员将在新英格兰、波多黎各、西班牙、捷克共和国和西伯利亚的溪流中进行一系列新颖的实地操作，以更好地了解DON在全球溪流中作为能源或氮源的程度。在新英格兰的初步实验观察表明，DON可以作为氮源和能源，但它的作用似乎随空间和时间而变化。在这里，研究人员将进行额外的实验，将硝酸盐脉冲添加到全球网络的流中，以评估DON主要作为氮源而不是能量（碳）源的频率和条件。这组实验将提供一些第一个实验证据，以评估这两个竞争的驱动程序在调节自然沃茨中的环境DON水平的重要性。

Many surface waters are yellow or brown in color due to the presence of organic molecules which come from many natural sources such as leaves, soils, and wetlands. These molecules affect a wide range of characteristics within streams such as the ability of light to penetrate the water and the acidity of the water. The organic molecules also can provide streams with energy and essential nutrients such as nitrogen and phosphorus. One particularly important form of these organic molecules is dissolved organic nitrogen, which is found globally in forests, arctic tundra, estuaries and streams. However, very little is known about when and where dissolved organic nitrogen serves as a source of energy, a source of nitrogen, or both to biological communities. This project will examine the role of dissolved organic nitrogen in streams across five distinct forested regions spanning a diverse set of environments in an effort to shed light on the role of dissolved organic nitrogen. This research is relevant to water resources management because dissolved organic nitrogen is a source of excessive nutrient loading causing toxic algal blooms in estuaries, and when it is found in drinking water supplies it can produce, during water treatment, disinfection by-products that can harm human health. This research will also integrate under-represented groups into the laboratory work and field work needed for the project and provide training opportunities for a graduate student and a post-doctoral scientist.Differentiating among the competing roles for dissolved organic nitrogen (DON) is difficult, as direct manipulation of the DON pool in aquatic ecosystems is most easily accomplished by addition of specific compounds such as amino acids, which are commercially available but are not particularly representative of the DON found in streams and rivers under ambient conditions. Based on initial experimental results, the researchers will conduct a series of novel field manipulations in streams across New England, Puerto Rico, Spain, Czech Republic, and Siberia to better understand the extent to which DON serves as an energy source or nitrogen source in streams globally. Initial experimental observations in New England show that the DON can serve as both a nitrogen source and an energy source, but its role appears to vary over space and time. Here the researchers will perform additional experiments where nitrate pulses are added to streams across a global network to assess how frequently, and under what conditions, DON serves predominantly as a nitrogen source, versus an energy (carbon) source. This set of experiments will provide some of the first experimental evidence to assess the importance of these two competing drivers in regulating the levels of ambient DON in natural waters.