The left side of Figure 2.1 illustrates the connections both between the various basin floor vadose zone projects and with projects in other thrust areas. The research of Small, Hendrickx and Phillips are all closely related and aimed at achieving a better understanding of the basin floor vadose zone. The sum of these research projects will be a better conceptual understanding of how the basin floor functions hydrologically and a model component for a basin scale model in TA4. Field work for these vadose zone studies are taking place, in part, at the Jornada and Savilleta long-term ecological research sites (LTER's). Accordingly, these research projects can take advantage of long term records of vegetation changes, soil moisture, etc. Because this vadose zone research is interested in recharge rates, there are connections with the infiltration / runoff studies in TA1. In addition, the work of Small involves micrometeorological flux measurements; this work will have close connections with other micrometeorological studies in TA1 and TA3. The micrometeorological data will also be used to calibrate land surface models in TA4. Finally within this group, the research of Ekwurzel involves the development of 32Si as a tracer for recharge. This research will take advantage of sites being investigated within TA2, the alluvial recharge sites in TA1, and sites being studied by the USGS in the San Pedro Basin.

The right side of Figure 2.1 illustrates the integration of projects investigating basin-scale hydrologic systems. The work of Wilson, investigating mountain block recharge, has close ties with the TA1 work on the water balance above the mountain front. Results from the TA1 group will be used to constrain the amount of water that travels through the mountain block. In addition, Wilson's research will employ environmental tracers for determining the source and rate of recharge through the mountain block and will be closely tied with the work of Long and Eastoe. Ultimately, a hydrologic model will be developed for the mountain block and the interface with the basin aquifer system. This model component will be added to the integrated model effort of TA4. The work of Long and Eastoe employs a variety of environmental tracers to determine areas of recharge, groundwater flowpaths and ultimately discharge. Such environmental tracers will be valuable for understanding the paths and rates of groundwater flow within basins. Preliminary results indicate that these tracers are especially sensitive to alluvial recharge. As such, this research will have close ties with various groups investigating recharge, such as the alluvial recharge work of TA1. Tracing groundwater flowpaths to discharge into river drainages will link the work of Long and Eastoe to the work of Phillips et al. on solute balances of basin river systems. The solute balance research of Phillips et al. will link with Duffy's low-dimensional models through investigating how the solute balance of a river system changes with climatic perturbations. Furthermore, investigation of the river solute balances will have direct linkages to nutrient cycling in riparian areas (TA3) (nutrients are biologically important solutes) and to river management in TA5 (URGWOM Model, etc.). Finally, Duffy's research investigates how long-term changes (climate, vegetation, human use) propagate through a basin hydrologic system and result in changes in river discharge and solute burden. These results will be used to develop a low-dimensional model for a basin system and ultimately incorporated within the basin-scale systems modeling (Coarse Resolution / Lumped) effort of TA4.

This group has also developed several important collaborations outside of SAHRA. These include a study funded by the New Mexico Interstate Stream Commission (NM-ISC) to investigate surface water-groundwater interactions in the Middle Rio Grande from San Acacia to Elephant Butte reservoir. There is a collaborative research project with the CEA-CREST (Center for Environmental Analysis - Centers of Research Excellence in Science and Technology) group at Cal State LA focused on understanding the flowpaths, residence times and sources of salinity within the Hueco Bolson near El Paso, TX and Juarez, MX. Finally, the isotopic analyses of the Rio Grande will be incorporated into the International Atomic Energy Agency's (IAEA) worldwide investigation into isotopic mass balances for river basins.