Dissolved oxygen concentrations in Lake Erie (U.S.A.-Canada): 1. Study of spatial and temporal variability using cluster and regression analysis

Abstract

A non-hierarchical nearest-centroid clustering method was used to separate data pairs consisting of the dissolved oxygen (DO) concentration and temperature into four groups corresponding to hypolimnetic and non-hypolimnetic water of the Central and Eastern Basins of Lake Erie. For the stations which were common to all cruises within a year and were classified as being in the hypolimnion, initial DO concentrations and depletion rates were calculated and tests about their constancy were performed using weighted regression analysis and regression models with the time structure of the data explicitly incorporated in the models. The yearly uncorrected depletion rates for 1967–1980 were similar to values previously reported by several authors, indicating that this semi-objective clustering procedure provides a practical alternative to subjective selection of data. The conclusions about constancy of initial concentrations and depletion rates based on an unweighted regression analysis were shown to differ from those of weighted regression. Using regression with empirical weights, it was found that neither the initial DO concentration nor the depletion rate remained constant between 1967 and 1980 in the Central Basin but that the depletion rate remained constant and the initial DO concentration varied in the Eastern Basin.