Benthic primary production decreases internal phosphorus loading from lake sediments under light supplement.

Area of Science:

• Environmental Science
• Aquatic Ecology
• Limnology

Background:

• Light penetration to sediment surfaces in shallow lakes influences internal phosphorus (P) release.
• Benthic primary production affects sediment oxidation, pH, and alkaline phosphatase activity.
• Eutrophic conditions exacerbate phosphorus dynamics at the sediment-water interface.

Purpose of the Study:

• To investigate the impact of light exposure on phosphorus dynamics in eutrophic lake sediments.
• To quantify the effects of varying light intensities on internal phosphorus release.
• To elucidate the mechanisms by which light influences phosphorus cycling.

Main Methods:

• A two-month mesocosm experiment using 1000 L tanks.
• Surface sediments from eutrophic Lake Nanhu were exposed to four light intensities (0, 50, 100, 200 μmol m⁻² s⁻¹) using LED lights.
• Measurements included total phosphorus concentration and phosphorus release flux.

Main Results:

• Light treatments significantly reduced total phosphorus concentration and phosphorus release flux compared to the control.
• Benthic primary production directly absorbed soluble reactive phosphorus and increased dissolved oxygen, inhibiting P release.
• Direct absorption and indirect inhibition contributed 23-69% and 31-77% to reduced P release, respectively, varying with light intensity.

Conclusions:

• Supplemental light can decrease internal phosphorus release in eutrophic aquatic ecosystems.
• Benthic primary production plays a dual role in mitigating phosphorus release through direct uptake and indirect oxygenation.
• Light management is a potential strategy for controlling eutrophication by reducing internal phosphorus loading.