Abstract Title: Role of Lake Morphometry on Hypolimnetic Oxygen Demand and Deep-Water Oxygen Depletion

Abstract Submitted to: HYDROLOGY

Abstract Text:

Temperate lakes often experience the seasonal loss of dissolved oxygen as thermal stratification disconnects deep waters from the atmosphere. Hypolimnetic oxygen demand can reduce habitat availability and alter lake biogeochemical processes. Deep water dissolved oxygen depletion is further expected to increase as waters warm and global change alters the physical limnology of lakes. To better understand spatial variation in hypolimnetic dissolved oxygen depletion, we collected monthly vertical water quality profiles in 16 lakes located in the Kawartha Highlands region of Ontario, Canada. Lakes sampled differed in morphometry but occupied similar landscapes surrounded by a mixture of wetlands, mixed hardwood forests, and some recreational property development. Despite their similarities, summer hypolimnion dissolved oxygen concentrations range considerably in theses lakes (0.746 to 11.01 mg O₂/L). Like dissolved oxygen concentrations, we observed variation in dissolved oxygen depletion rates (0.123 to 0.383 g O₂/m² per day). However, the large range in dissolved oxygen depletion rates was driven by a select few lakes with rates in most lakes being comparable (inter-quartile range = 0.212 to 0.276 g O₂/m² per day). Differences in summer dissolved oxygen concentration but a relatively uniform biological oxygen demand suggests that morphometry may play a simple yet large role in the dissolved oxygen budget of a lake. There is still, however, unexplained variation in dissolved oxygen depletion rate and thus more work is needed to understand the physicochemical drivers behind the observed differences.