Collaborative Research: Interactive effects of temperature and nutrient supply on the structure and function of stream ecosystems

现在很多科学研究都集中在植物和动物将如何应对气候变暖上。这是至关重要的，但也非常困难，因为有许多其他全球变化同时发生。例如，人类广泛传播了大量的氮和磷，这是重要的肥料。但是，随着全球变暖，主要沉积在陆地上、然后流入水生生态系统的过量营养物质会产生什么影响尚不清楚。因此，我们需要研究这些全球性变化是如何同时相互作用的。该研究项目的目标是探索淡水生态系统如何同时对变暖和养分富集做出反应。这项研究很重要，因为营养物质的富集可能会极大地改变变暖对溪流和河流的影响，因此，在社会试图适应更温暖的环境时，研究结果应该是有用的。研究结果还将为试图利用基本原理来理解物种和生态系统如何应对全球变化的生态学理论提供信息。教育计划将是这个项目的一个组成部分，将包括电影纪录片的开发，学生播客，以及对本科生和研究生以及研究技术人员的更传统的培训。该项目将在冰岛西南部的一个地热活跃地区进行，那里的溪流环境温度变化很大，背景化学成分没有显著差异，否则会影响结果。研究小组将利用河流之间的自然温度差异来研究营养供应和温度如何共同影响溪流和河流的生态。第一个目标是量化变暖和营养物对碳和氮的来源和归宿的影响（例如，生态系统生产力、营养物吸收和固氮）。然后，该团队将把生态系统规模的氮和磷添加与受控的河滨通道实验结合起来，研究变暖对溪流和河流生态的影响如何受到营养供应的影响，以及对变暖的短期反应是否与长期观察到的自然生态系统不同。这些生态系统级过程的反应也应该塑造能量和物质如何通过食物网从藻类流向鳟鱼。第二个目标是量化温度和营养物质对河流和溪流食物网中能量和物质路径的相互作用。将使用稳定（即非放射性）同位素示踪剂添加、二次生产测量和流动食物网分析的组合来跟踪食物网对不同温度流之间营养物质的反应。这项研究将提供关于两个主要的全球变化驱动因素，变暖和养分富集，如何相互作用影响重要淡水栖息地的生物多样性和生态系统功能的急需信息。

A lot of scientific effort is now being focused on how plants and animals will respond to a warming climate. This is critically important, but very difficult because there are many other global changes occurring at the same time. For example, humans have widely spread large amounts of nitrogen and phosphorus, which are important fertilizers. But what effects excess nutrients that are deposited mainly on land but then wash into aquatic ecosystems will have as the world warms is not clear. So studies are needed that examine how multiple global changes like these interact at the same time. The goal of this research project is to explore how freshwater ecosystems respond to warming and nutrient enrichment simultaneously. The research is important because nutrient enrichment may drastically alter the effects of warming on streams and rivers and so the results should be useful as society tries to adapt to warmer conditions. Results will also inform ecological theory that attempts to use basic principles for understanding how species and ecosystems may respond to global change. An education program will be an integral part of this project and will include the development of film documentaries, student podcasts, and the more traditional training of undergraduate and graduate students, as well as research technicians. This project will be conducted in a geothermally active region of southwestern Iceland, where streams exhibit a wide range in ambient temperature without significant differences in background chemistry that would otherwise influence results. The research team will use the differences in natural temperature between streams to examine how nutrient supply and temperature together influence the ecology of streams and rivers. The first objective is to quantify effects of warming and nutrients on the origin and fate of carbon and nitrogen (e.g., ecosystem productivity, nutrient uptake, and nitrogen-fixation). The team will then combine ecosystem-scale nitrogen and phosphorus additions with controlled streamside channel experiments to examine how the influence of warming on the ecology of streams and rivers is affected by nutrient supply, and whether short-term responses to warming differ from those observed in natural ecosystems over longer periods. Responses of these ecosystem-level processes should also shape how energy and materials flow through food webs from algae to trout. The second objective is to quantify the interactive effects of temperature and nutrients on the routes of energy and materials through river and stream food webs. Food web responses to nutrients between streams of varying temperatures will be tracked using a combination of stable (i.e., non-radioactive) isotope tracer additions, secondary production measurements, and flow food web analyses. This research will provide much needed information about how two dominant global change drivers, warming and nutrient enrichment, interact to influence biodiversity and ecosystem function in an important freshwater habitat.