AN ASSESSMENT OF DISSOLVED OXYGEN LEVELS IN ALASKA SMALL BOAT HARBORS

Abstract

The Alaska District of the U.S. Army Corps of Engineers, under its Civil Works program, actively studies, designs, and manages the construction of small boat harbors throughout Alaska. Based partially upon input from other Federal, state, and local agencies, these harbors are designed to ensure they promote adequate water quality. In particular, small boat harbors are designed to ensure that they provide adequate circulation. Harbors with poor circulation can result in concentrations of hydrocarbons, toxins or, low dissolved oxygen that can be detrimental to the health of marine organisms (Smith et al., 2002). To date, little analysis has been done to determine the quality of water present within small boat harbors in Alaska. The Environmental Protection Agency has identified a nation wide lack of quantitative harbor water quality data and has recommended the measurement of dissolved oxygen concentration reductions within small boat harbors (USEPA 1985). In this analysis, multiple vertical profile data sets of dissolved oxygen concentrations were collected within thirteen individual small boat harbors located throughout Alaska. This data was compared to ambient dissolved oxygen concentrations collected from outside each harbor. Analysis of this data indicated that one harbor, the Saint Paul Small Boat Harbor in Kodiak, Alaska, had depressed dissolved oxygen concentrations during sampling. Previously recorded dissolved oxygen concentrations that were assimilated as part of this investigation also indicate that the Seward Small Boat Harbor in Seward, Alaska may be prone to periodic depressed concentrations of dissolved oxygen. Further data collection and the establishment of a water quality monitoring plan at these two harbors, as well as the Valdez Small Boat Harbor in Valdez, Alaska, are recommended to confirm and identify the source of depressed dissolved oxygen concentrations . Based upon the results of this further research, the pollution prevention plans of the harbors can be updated to incorporate those best management practices that will best minimize future depletions of dissolved oxygen within the harbors. The results of a draft version of a numerical harbor circulation model based upon theoretical relationships between harbor geometry and harbor water exchange for the thirteen harbors investigated were compiled. The qualitative results of the model and the quantitative dissolved oxygen concentrations collected as part of this investigation were compared to determine if there is a correlation between the model results and dissolved oxygen concentrations within the harbors. This analysis showed that there was no apparent correlation. Harbors that were deemed to have poor circulation characteristics by the model most often did not possess depressed dissolved oxygen concentrations.