A GEOCHEMICAL COMPARISON OF SPITTAL POND AND WARWICK POND, BERMUDA

Spittal Pond is a marine pond located on the southeastern coast of Bermuda. It consists of two relatively deep basins (~60-80 cm deep) separated by a shallow basin (~5-35 cm deep). Warwick Pond is a single basin of uniform depth (~20 cm) and is the only naturally occurring "freshwater" pond on Bermuda. We believe that these two ponds are representative of the range of the geochemical conditions of Bermuda's ponds and have conducted a study which documents and compares their geochemistry. This documentation provides a much-needed foundation for future studies on the island including the calibration of hydrogeologic models and environmental geochemical studies.

Our study involves field and lab analysis of both pond and sediment pore waters. Pond waters were sampled at the water surface and at depth (near the sediment-water interface). Dissolved oxygen, pH, conductivity, temperature, ORP, and alkalinity were measured in the field and the samples were quantitatively analyzed in the lab for cations and anions using ICP-AES and IC. Analyses indicate that both ponds are vertically well-mixed and that Spittal Pond is saline (~20,000 mg/l) while Warwick Pond is brackish (~2,000 mg/l). Data also indicate that while the chemistry across Warwick Pond is nearly constant, the chemistries of the eastern and western basins of Spittal Pond are significantly different, suggesting that the pond waters in Spittal Pond do not mix freely.

Eleven sediment cores (150-400 cm long) were pulled from the ponds using a Vibracorer. Each of the cores was sampled at 10 cm intervals and analyzed for water content and major ion concentrations. Water content of the sediment ranges from 40% for the basal clays to 80% for surface sediments and, in general, decreases with depth. Major cation and anion analyses of the pore waters were conducted on water extracted from the cores. Geochemical profiles of the cores will be presented and discussed.