Controlling internal nitrogen and phosphorus loading using Ca-poor soil capping in shallow eutrophic lakes: Long-term...

Area of Science:

• Environmental Science
• Limnology
• Geochemistry

Background:

• Eutrophic lakes suffer from internal nutrient loading, hindering recovery and macrophyte growth.
• Clean soil capping is a potential solution, but its long-term efficacy and mechanisms require investigation.

Purpose of the Study:

• To evaluate the long-term performance of clean soil capping in controlling internal nutrient loading in Lake Taihu.
• To elucidate the mechanisms behind clean soil's nutrient adsorption and retention.
• To assess the impact of capping on sediment properties and macrophyte recovery.

Main Methods:

• A three-year in-situ field experiment using intact sediment cores.
• In-situ porewater sampling, isotherm adsorption experiments, and analysis of sediment nitrogen and phosphorus fractions.
• Comparison of capped sediments with control sediments.

Main Results:

• Clean soil significantly mitigated ammonium (NH₄⁺-N) and soluble reactive phosphorus (SRP) fluxes at the sediment-water interface for one year.
• Clean soil demonstrated excellent phosphorus adsorption and retention, primarily through cation exchange (Al³⁺) for NH₄⁺-N and Al/Fe reactions and Ca-bound P (Ca-P) precipitation for SRP.
• Macrophyte recovery was observed during the growing season, but capping benefits diminished after one year as sediment properties reverted.

Conclusions:

• Clean, Ca-poor soil is a promising, ecologically safe capping material for short-term nutrient control and macrophyte restoration in eutrophic lakes.
• The nutrient control effect of clean soil capping is temporary, lasting approximately one year under in-situ conditions.
• Further research is needed to enhance the longevity of clean soil capping as a sustainable geoengineering technology for lake management.