Abstract
A study of variations of the oxygen isotopic composition (δ18O), in precipitation, surface waters and shallow groundwaters collected around the University of Houston Coastal Center (UHCC) in Galveston County, southeast Texas was undertaken.
Isotopic spikes caused by natural atmospheric phenomena were found in a collection of rainfall samples from January 1985. The weighted mean isotopic composition of the rainfalls from January 1985 to December 1989 was about -4.48‰. However, precipitation had a very large variation of oxygen isotopic composition. Especially, two storms in late June (tropical storm “Allison”) and early August (hurricane “Chantal”), 1989 produced heavy rainfall with very low δ18O values, -9.5‰ and -13.6‰, respectively.
Groundwater from shallow wells was monitored for oxygen isotopic composition from January, 1989. The weighted mean oxygen isotopic composition of groundwater was about -4.0‰. Spikes found in the rainfall have not yet been identified in the wells. In sharp contrast to this, the isotopic compositions observed in the surface waters very greatly. This is to be expected because the surface waters receive rainfall runoff after every significant rainfall event whereas the wells contain water representing numerous rainfall events integrated over a long time, or else the recent rainfalls may not have reached the shallow silt layer.
