Restoration of hypolimnetic dissolved oxygen through light irradiation‐induced periphyton production: Fid-Bau Portal

Restoration of hypolimnetic dissolved oxygen through light irradiation‐induced periphyton production

Kishimoto, Naoyuki / Mawatari, Koichi

Large quantities of detritus can accumulate on the bottom sediments of eutrophic lakes, leading to depletion of dissolved oxygen (DO) in the hypolimnion. Decreased redox potential associated with low hypolimnetic DO concentrations can accelerate the remobilization of ammonia and phosphorus from the sediments back into the water column. As maintenance of aerobic conditions in the hypolimnion is an important consideration for successful lake management, this research focused on the use of periphyton production of DO to control hypolimnetic DO levels. To augment periphyton photosynthesis, light was irradiated to the bottom sediments via glass fibres, in order to examine the effects of light irradiation on DO restoration on bottom sediments in test chambers. Dissolved oxygen restoration by periphytic photosynthesis was confirmed in these experiments, with both temperature and light intensity having positive effects on the areal net oxygen production rate. The Q₁₀ temperature coefficient for net oxygen production was estimated to be 2.24. In typical temperate‐zone lakes, the hypolimnetic water temperature is <15 °C, resulting in an expected areal net oxygen production rate ranging from 100 to 200 mg O₂ m⁻² day⁻¹ at a light irradiation of 50 μE m⁻² s⁻¹. Based on these experimental results, the condenser area required to achieve DO restoration under hypolimnetic light irradiation alone was estimated to be 3.2–4.1% of the hypolimnetic area. Thus, hypolimnetic light irradiation combined with hypolimnetic aeration can reduce energy consumption required for hypolimnetic aeration in DO restoration efforts.