THE POTENTIAL IMPACT OF TERRESTRIAL RUNOFF ON AN ADJACENT CORAL REEF: ROATAN, BAY ISLANDS HONDURAS

The Potential Impact Of Terrestrial Runoff On An Adjacent Coral Reef: Roatan, Bay Islands, Honduras MODLEY, MEG and Mehrtens, Char, Department of Geology, University of Vermont, Burlington, VT., 05405, mmodley@zoo.uvm.edu, cmehrten@zoo.uvm.edu

The coral reef surrounding the island of Roatan is under stress from changing water quality and siltation. Extreme seasonality is reflected in both total suspended solids (TSS) in the water column over the reef range from 8-70mg/l in the summer to 20-163mg/l in the winter and sedimentation rates on the reef ranging from 0.13- 7.07mg/cm2/day in the summer to 41-71 mg/cm2/day in the winter. Summer (dry season) values are similar to those from other Caribbean reefs, however winter (rainy season) values are 10x those described in the literature from elsewhere in the Caribbean. In order to evaluate the contribution of terrestrial runoff from a tropical island experiencing changing land use, we sampled four streams, two of these over a three year period and two for one season each. Water samples were collected from streams during the summer and winter. TSS values range from a low summer value of 0.004g/l to a winter storm-runoff high of 146g/l. Measurements were made on the streams in order to determine stream discharge and resulting suspended sediment loading into the adjacent lagoon. The results of this study reflect sampling confined to a limited time interval however comparison to long term precipitation data suggests that they record very typical seasonal rainfall. We therefore feel that these values are an accurate first order estimate of terrestrial runoff. Finally, we have attempted to correlate runoff values to watershed characteristics, including its current land use.