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

在蒙大拿州弗拉黑德河的尼亚克洪泛区的研究地点，从分布在洪泛区的井中抽取的地下水中发现了大量的水生无脊椎动物，从微小的桡足类到大型石蝇和甲壳类。附近的河道从藻类和树叶等陆地资源中获取太阳能和食物，而地下水则必须从河流或洪泛区土壤中输入食物和营养物质。我们的研究表明，地下水中的食物资源非常少。那么，这么多无脊椎动物是如何在食物如此匮乏的地区生活的呢？为了解决这个问题，我们正在开发地下水系统的碳预算，调查各种有机物来源；从河水中，从上覆的土壤中，或者随着时间的推移河流改变河道而被掩埋的植物物质中。这些有机物质被微生物消耗，反过来又为无脊椎动物提供食物。有了这项提案的资助，我们将以两种方式改进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产生二氧化碳）；(2)使用碳和氮的稳定同位素（这是河流与土壤来源所特有的）。呼吸实验将使我们能够计算出各种生物体所消耗的能量，并将其与从整个含水层中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水室，通过呼吸作用来告诉我们生物体对来自土壤或河流水源的碳添加的反应有多强烈。智力优势：这一建议将大大增加我们对生活在河流相连的河漫滩含水层中的生物的基本生物学的理解。更广泛的影响：在西部，山谷和洪泛平原是人口、农业和饮用水重叠的地方。通过观察一个原始的含水层，这项研究将告诉我们地下水系统是如何工作的，这对理解人类的影响很重要

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