The physical limnology of Augher Lough (Northern Ireland)

SUMMARY. The physical limnology of Augher Lough, Northern Ireland (area=9.25 ha. z=5.5 m), including stratification pattern, heat budget, thermocline erosion rate, eddy diffusion rate in the thermocline and hypolimnion and areal hypolimnetic oxygen deficit is described. Oxygen and temperature profiles, recorded at two sites during 1978 and four sites during 1979, showed that spatial variability of these quantities was low and allowed the following lake characteristics to be estimated. Heat budgel was 5.30 kcal cm‐2 (standard deviation=s=0.26) in 1978 and 5.00 (s= 0.26) in 1979. The thermocline depth was 3.5–6.5 m with an erosion rate of 1.9X10‐7 m s‐1 in 1979. Eddy diffusion coefficients of heat in the thermocline and hypolimnion normally ranged from 0.48X 10‐2 cm2 s‐1 (s=0.20X10‐2) to 5.4X10‐2 (s=2.6X10‐2), but reached 10X10‐2 cm2s‐l (s=9X10‐2) in early July 1978 after a cooling‐mixing episode in the epilimnion. The hypolimnetic oxygen deficit was 680 mg O2 m‐2 d‐1 (s=76) and varied strongly with depth. A cooling‐mixing episode in the epilimnion in June‐July 1978 caused the movement of heat down to 8 m, movement of oxygen down to 6 m and increased the eddy diffusion coefficients of heat by an order of magnitude.