A management model to predict seasonal variability in oxygen concentration and oxygen consumption in thermally stratified coastal waters

Abstract

There are many indications of increasing eutrophication problems in the Baltic Sea. In the coastal zone, problems manifested as low near bottom oxygen concentrations and oxygen depletion are no longer unusual. The aim of this paper is to present a practically useful model to predict seasonal variability in oxygen concentration and oxygen consumption. In the model, empirical variations in deep water oxygen concentrations (late summer values) among 20 Baltic coastal areas were explained by variations in organic load and deep water turnover time. Regressions between modelled values and empirical data yielded r 2-values from 0.84 to 0.90. The mean oxygen consumption rate (March–October) for the 20 areas was calculated to 23 l O 2/m 2 ∗ month. The predicted rate is in the same order of magnitude as literature data from the Öresund area and a calculated default rate for the Baltic Sea. The model can be used to predict the lowest oxygen concentration during the year and to identify coastal areas where low concentrations are likely to appear. Furthermore, the sensitivity of a coastal area to an increased organic load can be assessed. Such information is useful when planning for example new locations for sewage treatment plants and/or fish farms, which increase the load of biodegradable substances.