Lake Erie Central Basin Oxygen Depletion Changes from 1929–1980

Abstract

The hypolimnetic oxygen depletion rates of the Lake Erie central basin have been reassessed using a new approach. In the past, the central basin rates have been calculated using the available data, excluding some areas based on either temperatures and/or depth definition. The high spatial variability in the data caused uncertainties in the mean value which were sufficiently large to prevent a statistically meaningful interval oxygen depletion rate time-trend analysis. The new approach reduces the effect of spatial variability (80%) on the calculation of the interval oxygen depletion rates and hence permits the identification of a time-trend with more precision, particularly when the data are corrected for the effects of vertical mixing, temperature effects on metabolic rates by using Q 10 coefficient, variable hypolimnion thicknesses, and seasonal variability. A linear regression analysis of the final corrected depletion rates with time shows a significant increase in the yearly average hypolimnetic oxygen depletion rate of 0.030 gm·m· −3mo· −1 yr· −1 between 1929 and 1980. This increase in the rate accounts for a loss of 4 to 5 gm·m −3 of oxygen from the central basin hypolimnion since the earliest oxygen records in 1929. This increase may be directly related to an increase in the trophic level of the central basin, since most of the major limnological variables which affect the depletion rate have been accounted for.