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.
