|Ward, George - UNIV TX AUSTIN|
Submitted to: United States Geological Survey Technical Report
Publication Type: Other
Publication Acceptance Date: October 1, 2001
Publication Date: October 1, 2001
Citation: WARD, G.H., GREEN, B.W. EFFECTS OFSHRIMP FARMING ON THE WATER QUALITY OF EL PEDREGAL AND SAN BERNARDO ESTUARIES, GOLFO DE FONSECA, HONDURAS. UNITED STATES GEOLOGICAL SURVEY TECHNICAL REPORT. 2001. Technical Abstract: An intensive data collection and modeling study was conducted on two channel estuaries, the El Pedregal and San Bernardo, that drain into the Gulf of Fonseca, Honduras. The assimilative capacity of these estuaries, where the Honduran shrimp aquaculture industry is centered, was determined with respect to dissolved oxygen (DO). Data were compiled on shrimp farm configurations, exchange rates, and pond chemistry. Extensive incubations were performed on water samples from selected farms and from the estuaries to determine BOD, and to characterize the time progression of oxygen depletion. Temperature-salinity-dissolved oxygen profiles were measured in the estuary channels as far upstream as navigable in a boat. Generally, the DO's in the main channel of each estuary system are low by estuary standards, being less than 3 mg/L throughout most of their length during the rainy and dry seasons. The two most important factors that govern the longitudinal profile of DO's are the concentration of DO and flow rate of waters flowing into the estuary at its head, and the DO concentration in waters at the estuary mouth. Based upon application of a mathematical model for the estuary oxygen budget, the effect of shrimp farm discharges on DO in these estuaries was found to be an important contributor to the low DO's of the estuaries, but only part of the cause. Also crucial are the low DO concentrations brought into the head of the estuary, due to natural organic oxygen demands and limited reaeration. Even if all shrimp farm discharges were eliminated, much of the estuary length would still be below 3 mg/L DO. In this sense, the carrying capacities of the estuaries already have been exceeded, but were low already.