Stratification and Oxygen Depletion in Lower Lough Erne 1991-2000

Abstract

Seasonal stratification in Lower Lough Erne, north-west Ireland was studied between 1991 and 2000. Oxygen depletion rates from the profundal water (below 40m depth) are reported for each year. The mean depletion rate for all years was 0.459g O₂ m⁻² d⁻¹. Values varied approximately two-fold between individual years, and there was no trend in depletion rate with time. The water mass used for the calculation of the oxygen deficit gained heat throughout the stratified period, but there was no correlation between the oxygen deficit and bottom water heating. The rate of oxygen depletion in the lake was not related to plankton crops in individual years. A provisional carbon budget suggests that advected carbon is the dominant carbon flux to the sediment. The spring diatom crop accounts for only a small fraction of the total carbon deposition, but it may explain up to half of the summer oxygen demand in the bottom water of Lower Lough Erne.