Oxygen flux and penetration depth in the sediments of aerated and non-aerated lake basins

The effects of hypolimnetic aeration on oxygen penetration depth and oxygen flux into the sediment (DOU) were studied during two successive years. The study was conducted by comparing data from the aerated Enonselka basin with the non-aerated Kajaanselka basin of Lake Vesijarvi (southern Finland). Aeration increased the average O2 concentration in near-bottom layers. This was mainly due to shortened stratification period in the aerated basin, which was again attributed to the positive effect of aeration on hypolimnetic water temperature. Aeration did not prevent hypoxia during summer stratification and oxygen penetration depth in the sediment and DOU did not increase. During summer stratification DOU was even lower at the aerated than at the non-aerated basin. The weak effect of aeration on DOU and oxygen penetration was mostly due to the minor effect on hypolimnetic oxygen concentrations. The positive effect of aeration on hypolimnetic O2 concentration was negated by the positive effects of aeration on hypolimnetic temperature and turbulence that increase oxygen consumption in the water column. Due to the generally low effect on DOU, the present aeration effort in Enonselka does not have positive effects on sediment quality.