Solar circulator to restore dissolved oxygen in a hypoxic ice-covered lake

Abstract

Hypoxia is common to shallow ice-covered lakes during the winter season, and restorative actions to prevent impacts to aquatic ecosystems are desired yet untested in remote settings. The use of a solar photovoltaic circulator was investigated for reoxygenation in a shallow hypoxic lake in the northern Rocky Mountains. During the fall of 2019, a solar powered lake circulator (SolarBee SB10000LH; hereinafter circulator) was installed near the center of Upper Red Rock Lake, Montana USA (latitude 44° 36’N) and dissolved oxygen (DO), temperature, turbidity, and changes to ice formation were monitored until ice-out the following spring of 2020 using an array of real-time and data logging sondes. Observations indicate the circulator formed a polynya that lasted until late November, did not increase lake turbidity, and facilitated oxygen exchange through the circulator-created-polynya for at least 3 weeks after an adjacent lake became ice covered. Thereafter, operation of the solar circulator failed from accumulation of snow and ice on the solar panels such that the lake froze completely over during a period of low light in December. From that point on throughout the winter, DO subsequently declined from supersaturation to hypoxia over a 41-day period and remained that way for nearly four months until ice-out in April. Based on this outcome, additional work is required to improve the solar-powered circulator design before attempting comparable applications elsewhere as a means of reducing the severity of hypoxia in shallow-lake systems during winter.