Ecological assessment of salt ponds on St. John, USVI

Abstract

Salt ponds serve several valuable ecological functions in the United States Virgin Islands (USVI), although they have traditionally been undervalued and poorly understood. This thesis describes an ecological assessment performed to provide baseline information on salt ponds on St. John, U.S. Virgin Islands, to recommend a range of indicators to determine the water quality of a salt pond, and to suggest areas of further research to help maintain the value that salt ponds provide to the island. Quantitative and qualitative data were collected for fifteen ponds on the island. These data consist of a descriptive habitat assessment including pond classification, shore characteristics, water characteristics, biota characteristics, specific pond descriptions, as well as macro-invertebrates and chlorophyll a levels sampled in each of the ponds. Findings are presented by salinity, housing density, nitrate levels, dissolved oxygen, macro-invertebrates, species richness, and chlorophyll a. To determine correlation between variables measured, data are then analyzed by pair regression analysis. Multivariate regression results are presented for three independent variables: species richness, chlorophyll a, and dissolved oxygen. In the multivariate regression analysis of species richness, the most significantly correlated factors are berm height, temperature, pH, dissolved oxygen, and nitrate levels; chlorophyll is significantly related to temperature, pH, dissolved oxygen, nitrate levels, and salinity levels; and dissolved oxygen is significantly correlated with depth, berm height, temperature, and pH. The results of this study seem to contradict the original hypothesis-that salt pond health is adversely affected by human development. A series of recommendations are proposed including monitoring sentinel species and metrics, beginning an ongoing salt pond measurement program, performing a nitrogen balance for the ponds, conducting sediment studies on the ponds, and considering the implementation of buffer zones around the ponds.