Tracing Fluxes of Groundwater Through Riparain Food Webs Using Stable Isotopes of Hydrogen and Oxygen

地下水位下降是世界干旱地区（如沙漠）的一个普遍问题。地下水位降低的一个后果是河流边缘生境（称为“河岸”生境）中植物的丰富度和物种数量（称为“物种多样性”）的变化。虽然人们对地下水位降低对植物的影响了解甚多，但对地下水的相对可得性或获取如何影响河岸栖息地动物的丰度和多样性知之甚少。该项目的目标有两个：(1)开发新的工具来量化从地下（地下水）和地表（河流）水源流向动物种群的水量；(2)使用这些工具来量化位于亚利桑那州东南部圣佩德罗河沿岸沙漠栖息地的动物物种的水资源限制。我们将开发的工具将基于氢（2H，或D，“氘”）和氧（18O）的稳定同位素的传统应用，通过植物从环境中追踪水源。稳定同位素是天然存在的非放射性元素，其质量高于这些元素的更常见、更轻的版本（分别为1H和16O）。我们将利用这些稳定同位素在树叶和河水中自然存在的浓度差异来了解动物通过消耗植物材料间接获取水的情况。为了做到这一点，我们将主要关注以死亡有机物为食的无脊椎动物及其捕食者。这个研究系统将使我们能够确定水从地下水流经树木流向居住在地上栖息地的动物的途径。这项研究将通过培养两名研究生和建立将氢和氧的稳定同位素应用于地下水资源管理的基础，产生更广泛的影响。

Water table lowering is a common problem in arid regions of the world such as deserts. One consequence of water table lowering is a change in the abundance and number of species (called "species diversity") of plants in habitats along river margins (called "riparian" habitats). While much is known about the effects of water table lowering on plants, little is known about how the relative availability or access to ground water may affect the abundance and diversity of animals in riparian habitats. The goals of this project are twofold: (1) to develop new tools to quantify the flow of water from sub-surface (groundwater) and surface (river) sources to animal populations and, (2) to use these tools to quantify water limitation in animal species occupying desert riparian habitats along the San Pedro River in southeastern Arizona. The tools we will develop will be based on traditional applications of stable isotopes of hydrogen (2H, or D, for "deuterium") and oxygen (18O) to trace water sources from the environment through plants. Stable isotopes are naturally occurring, non-radioactive elements with higher mass than the more common, lighter versions of these elements (1H and 16O, respectively). We will use differences in naturally occurring concentrations of these stable isotopes in leaves and in river water to understand the indirect acquisition of water by animals via consumption of plant material. To do this we will focus primarily on invertebrates feeding on dead organic matter and their predators. This study system will allow us to determine the pathways by which water flows through trees from groundwater to animals inhabiting above-ground habitats. This research will achieve broader impacts by training two graduate students and by establishing the basis for applying stable isotopes of hydrogen and oxygen to the management of groundwater resources.