Controls and consequences of oxygen depletion in lakes

• Main Author: Foley, Brian
• Published: University of Ulster 2011
• Subjects: 551.482
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553864

Estimates of hypolimnetic water column (Jv) and sediment (JA) dissolved oxygen (DO) consumption rates were made using the methodology of Livingstone & Imboden (1996); DO, temperature, chlorophyll a (ChI a) and total phosphorus (TP) concentration, and bathymetric data were collected from five Northern Irish lakes and collated from four lakes in England and Sweden. These data were combined with existing results to examine the influence of physicochemical variables and lake morphometry on the relationships among Jv, JA and lake trophic state. There was a positive relationship between Jv and the growing season (GS) mean ChI a and annual mean (AM) TP concentration, with a maximum Jv evident in eutrophic lakes (0.218±0.015 g O2 m' d-I based on the relationship with GS mean ChI a). The trophic state indicator variables standardised by lake maximum depth (ZMAX) explained the most variation in Jv (83%) and JA (35%). The relationships between Jv, JA and the trophic state indicator variables standardised by ZMAX were employed in the development of a model for predicting hypolimnetic DO concentration-depth profiles. The model was capable of reproducing observed data in four test lakes of varying trophic state and morphometry; the coefficient of determination and standard error of the estimate of the regression between observed and predicted data were 0.62 (P < 0.001) and 1.60 g O2 m", respectively. Long-term data (1968 to 2008) from two lakes were used to examine the effect of a warming climate and eutrophication on hypolimnetic DO resources. The rate of volumetric hypolimnetic DO depletion (VHODobs) ranged from 0.035 to 0.090 g O2 m-3 a' and from 0.131 to 0.252 g O2 m" a' in Windermere South Basin (WSB) and Blelham Tarn (BT), respectively. Mixed layer ChI a concentration in WSB and wind speed over BT were important drivers of the variation in VHODobs. Changes in lake thermal structure resulted in the duration of thermal stratification increasing by 25±8 days and 38±8 days in WSB and BT, respectively, over the study period. Results show that climate warming effects on lake thermal structure have the potential to exacerbate hypolimnetic DO depletion, and may undermine management efforts taken to alleviate the impacts of eutrophication.