A practical application of Droop nutrient kinetics (WR 1883)

Area of Science:

• Environmental Science
• Aquatic Ecology
• Limnology

Background:

• Eutrophication models are crucial for understanding aquatic ecosystem dynamics.
• Algal growth is often limited by nutrient availability, such as phosphorus.
• Existing models may not fully capture the complex relationship between internal nutrient storage and algal response.

Purpose of the Study:

• To integrate algal growth kinetics based on internal phosphorus concentration into a eutrophication model.
• To evaluate the impact of this integration on simulated algal biomass and nutrient dynamics.
• To assess the model's sensitivity to parameter variations in a real-world aquatic system.

Main Methods:

• Incorporated Droop kinetics, which links algal growth to intracellular nutrient levels, into a pre-existing eutrophication model.
• Applied the modified model to a closed system to observe algal biomass and phosphate dynamics.
• Conducted sensitivity analyses using data from the lower St. Johns River, Florida, by altering key model parameters.

Main Results:

• The model with Droop kinetics exhibited damped oscillations in algal biomass and phosphate compared to a fixed-composition model.
• Peak algal biomass predictions were similar across models, regardless of whether internal phosphorus was considered.
• Sensitivity analyses indicated that parameter variations significantly influenced computed dissolved phosphate concentrations but had minimal impact on chlorophyll levels.

Conclusions:

• Droop kinetics provide a mechanism for regulating computed nutrient concentrations within eutrophication models.
• The model suggests that internal nutrient dynamics play a more significant role in controlling nutrient levels than in directly controlling peak algal biomass.
• The findings highlight the importance of considering intracellular nutrient storage for accurate simulation of aquatic ecosystem responses to nutrient loading.