This proposal is to evaluate the use of tropical storm precipitation, especially that from hurricanes, as a natural tracer of groundwater movement. Precipitation from tropical storms is known to have a special oxygen and deuterium isotope composition that distinguishes it from normal precipitation. Because tropical storms also produce many times as much rain as normal storms, they are capable of adding a large batch or slug of water to an aquifer during a single event. The objective of this study is to determine whether that slug of isotopically labeled water can be traced by stable isotope measurements as it moves through an aquifer. This research could establish a powerful new technique to study groundwater in tropical areas where hurricanes are frequent. It is difficult to plan and set up an experiment suitable for monitoring a hurricane, and it would be expensive to establish a large network of monitoring stations purely on the chance that a tropical storm might occur somewhere within that network. That is what adds an element of urgency to this proposal. Hurricane Isadore recently passed over the northern Yucatan Peninsula, an area where the PI has previously obtained background data on the isotopic composition of the local groundwater. Northern Yucatan is especially well suited for a trial of this monitoring technique: its karst aquifer is extremely permeable, insuring rapid groundwater movement; it has almost no soil that might impede rapid movement of the hurricane precipitation into the aquifer; and the aquifer is relatively uncomplicated. Thus, it will be relatively easy to monitor changes in the composition of water in this aquifer as the hurricane precipitation moves through. Samples of groundwater will be collected in three sampling trips over a period of one year. These will be obtained from municipal wells, covered karst sinkholes, and piezometers (where available). Students will be involved in collecting the samples and analyzing the data. Isotopic analyses will be performed in the stable isotope laboratory of the Universidad Nacional Autonoma de Mexico. Intellectual merit of this project will be a better understanding of the behavior of groundwater, a precious resource, and the development of a new, non-polluting technique for charting its movement. The broader impacts of this activity will include: 1) development of information on groundwater movement that can lead to better management and protection of groundwater in the very sensitive Yucatan aquifer (essential for human health, agricultural productivity, industrial development, and tourism), 2) establishment of closer collaboration between Mexican scientists and scientists in the United States, accomplished by close collaboration in this research, and 3) education of students in the procedures used to collect meaningful samples of groundwater and to evaluate the analytical results of this study.
