Dissertation research -- The role of mineralization in nutrient spiralling in heterotrophic streams

人类活动极大地增加了氮和磷等营养物的用量，这些营养物被用于全球景观。这些营养负荷中的大部分通过溪流和河流输送到沿海地区。然而，溪流不是被动的管道，而是重要的养分转化场所。营养物质可能以溶解的无机形式进入溪流，被水流输送一定距离，并最终被溪流生物转化为有机形式，这些生物需要这些化学物质来维持和生长。这项研究将集中在这个循环的最后阶段，在这个阶段，溪流生物，如细菌、真菌和昆虫，将多余的营养物质归还给水。具体而言，本研究将确定增加的营养输入对河流生物的营养转化的影响及其影响下游营养运输的能力。研究人员将使用一种稳定的氮同位素在野外和实验室环境中测量几种营养处理指标。这种综合方法将允许描述跨越时间和空间的广泛模式，以及确定负责观察到的模式的具体机制。全球范围内不断增加的营养负荷正在引起一系列环境问题，包括生物多样性下降、饮用水污染和沿海水域缺氧。河流在将这些多余的营养物质从陆地运输到海洋系统中的作用，使得了解河流中营养物质的命运对试图减轻营养负荷负面影响的决策者至关重要。这项研究的时间和空间范围将有助于填补对河流养分循环理解的空白，并将增加政策制定者可用的知识体系。这项研究也为本科生提供了参与科学过程的机会，并有助于理解相关的环境问题。

Human activity has greatly increased the amount of nutrients, such as nitrogen and phosphorus, applied to the global landscape. Much of this nutrient load is transported to coastal areas by streams and rivers. However, streams are not passive conduits but are sites of significant nutrient transformation. Nutrients may enter streams in dissolved inorganic forms, are transported a certain distance by water flow, and are eventually transformed into organic forms by stream organisms, which need these chemicals for maintenance and growth. This research will focus on the final stage of this cycle where stream organisms, such as bacteria, fungi, and insects, return excess nutrients to the water. Specifically, this research will determine the effect of increased nutrient input on nutrient transformations by stream organisms and their ability to influence the transport of nutrients downstream. The investigators will use a stable isotope of nitrogen to measure several nutrient processing metrics in both field and laboratory settings. This combined approach will allow for the description of broad patterns across time and space as well as the determination of specific mechanisms responsible for the observed patterns. The increased nutrient loading occurring around the globe is causing a suite of environmental problems including declines in biodiversity, contamination of drinking water, and anoxia of coastal waters. The role of streams in transporting these excess nutrients from terrestrial to marine systems makes understanding the fate of nutrients within streams vital to policy makers attempting to mitigate the negative effects of nutrient loading. The temporal and spatial scope of this research will help fill a gap in the understanding of stream nutrient cycling and will add to the body of knowledge available to policy makers. This research also provides opportunities for undergraduate students to participate in the scientific process and contribute to the understanding of a relevant environmental issue.