Internal cycling, not external loading, decides the nutrient limitation in eutrophic lake: A dynamic model with...

Area of Science:

• Environmental Science
• Limnology
• Ecosystem Dynamics

Background:

• Lake eutrophication is driven by excessive nitrogen (N) and phosphorus (P) from human activities and internal nutrient cycling.
• While external nutrient loading is understood, the precise contribution of internal cycling to lake eutrophication remains unclear.

Purpose of the Study:

• To quantify the contributions of internal nutrient cycling versus external loading to eutrophication in Lake Dianchi.
• To explore seasonal nutrient dynamics and N and P limitation of phytoplankton growth using a dynamic mass-balance model.

Main Methods:

• Developed a dynamic mass-balance model incorporating a temporal Bayesian Hierarchical Framework (BHM).
• Simulated key state variables (chlorophyll a, total phosphorus, ammonia, nitrate, organic N) and estimated critical parameters (growth, sediment exchange, nitrification, denitrification rates).

Main Results:

• The model accurately simulated observed dynamic patterns of nutrient variables.
• Internal cycling of N and P was found to contribute more to water column nutrient changes than external loading.
• Phosphorus limitation was primarily determined by sediment P exchange, while nitrogen was often limiting due to denitrification.

Conclusions:

• Lake Dianchi's recovery requires managing internal nutrient cycling, not just reducing external watershed loads.
• Inhibiting sediment nutrient release and promoting denitrification are key strategies for eutrophication management in Lake Dianchi.