DISSERTATION RESEARCH: Energy Flow and Carbon Sources in a Montane Floodplain Aquifer

在我们位于蒙大拿州弗拉海德河Nyack泛滥平原的研究地点，从分布在泛滥平原上的井中抽取的地下水中发现了大量的水生无脊椎动物，从微型的桡足类动物到大型的石蝇和甲壳类动物。与附近的河道相比，附近的河道从藻类生产和陆地来源(如树叶)获得太阳能和食物，地下水必须从河流或通过泛滥平原土壤进口食物和养分。我们的研究表明，地下水中的食物资源非常少。那么，这么多无脊椎动物怎么会生活在食物如此匮乏的地区呢？为了解决这个问题，我们正在制定地下水系统的碳平衡，以调查各种有机物质来源；来自河水、来自上覆土壤的有机物质，或来自河流随时间改变其河道的埋藏植物物质。这些有机物被微生物消耗，微生物反过来喂养无脊椎动物。在这项提案的资助下，我们将通过两种方式完善我们对有机预算的理解：通过(1)呼吸实验(无脊椎动物和细菌和真菌消耗氧气来产生二氧化碳)，以及(2)使用稳定的碳和氮同位素(这是河流和土壤来源所独有的)。呼吸实验将使我们能够计算各种生物所使用的能量，并将这些能量与从整个含水层采集的水样的测量结果进行比较。在另一个实验中，我们将使用一个建造的地下洞室，利用呼吸作用告诉我们，生物对来自土壤或河流水源的碳添加的反应有多强烈。智力价值：这一建议将显著提高我们对生活在河流相连的河漫滩中的生物的基本生物学的了解。广泛的影响：在西部，山谷和漫滩是人口、农业和饮用水重叠的地方。通过观察原始含水层，这项研究将告诉我们地下水系统是如何在理解人类影响的重要方面发挥作用的。

At our study site on the Nyack floodplain of the Flathead River, Montana, large numbers of aquatic invertebrates, from microscopic copepods to large stoneflies and crustaceans, are found in groundwater pumped from wells distributed across the floodplain. Compared to the nearby river channel, which receives solar energy and food from algal production and terrestrial sources such as leaves, the groundwater must import food and nutrients from the river or through the floodplain soil. Our research has shown that food resources in the groundwater are very low. So, how can so many invertebrates live in an area with so little food? To address this question, we are developing a carbon budget for the groundwater system investigating the various organic matter sources; from river water, from overlying soils, or as buried plant matter as the river shifts its channel over time. This organic matter is consumed by microbes, which in turn feed the invertebrates. With funding from this proposal, we shall refine our understanding of the organic budget in two ways: through (1) respiration experiments, (consumption of oxygen to produce carbon dioxide by invertebrates and bacteria & fungi), and; (2) use of stable isotopes of carbon and nitrogen (that are unique to river vs. soil sources). The respiration experiments will let us calculate the energy used by various organisms and compare these to measurements from water samples taken from across the whole aquifer. In another experiment, using a constructed groundwater chamber, we will use respiration to tell us how strongly the organisms respond to carbon additions from soil or river water sources. Intellectual Merit: this proposal will significantly increase our understanding of the basic biology of organisms that live in river-connected river floodplain aquifers.Broader Impacts: In the west, mountain valleys and floodplains are where human population, agriculture, and drinking water overlap. By looking at a pristine aquifer, the research will tell us how groundwater systems work in ways important to understanding human impacts