METALIMNETIC OXYGEN DEPLETION - ORGANIC-CARBON FLUX AND CRUSTACEAN ZOOPLANKTON DISTRIBUTION IN A QUARRY EMBAYMENT

Particulate organic carbon (POC) flux and the distribution and abundance of crustacean zooplankton and bacteria associated with formation of a metalimnetic oxygen minimum were examined in a deep embayment of Kentucky Lake, Kentucky. POC measurements from sediment traps placed above and below the metalimnion yielded an estimate of the organic material that was metabolized in the metalimnion. This estimate was the molar equivalent of the oxygen that was depleted from the metalimnion. Calculated zooplankton respiration accounted for 26-31% of the observed oxygen loss, except in midsummer when it accounted for 15%. Estimated bacterial respiration accounted for greater-than-or-equal-to 44% of the observed oxygen loss. The comparison of calculated oxygen demand with observed oxygen loss emphasizes the importance of in situ processes as the cause of the minimum and suggests that metalimnetic deficits may be useful to estimate productivity. The vertical distribution of three species of Daphnia changed as the oxygen minimum formed. Daphnia pulex became entirely hypolimnetic. Thus, changes in chemical structure influence spatial distribution of zooplankton species.