Simulating the effects of aquatic avifauna on the Phosphorus dynamics of aquatic systems

Abstract

Many freshwater ecosystems throughout the world support a high number of waterbirds. Nutrient from droppings of these waterbirds may serve as an important source of nutrients to those systems. Previous works suggest that excess nutrients from waterbirds may lead to eutrophication. The excess nutrients also may induce nuisance growth of aquatic weeds in shallow lakes. However, the aquatic weeds serve as an important food for some avian species. The main objective of this work is to study how the waterbirds affect the dynamics of the aquatic ecosystem through a process-based modelling approach.To understand this, a lake with negligible anthropogenic nutrient influx and the high winter-avian congregation is taken as study site. A process-based dynamic ecological model with six state variables has been developed. Phosphorus (P) is taken as model currency since it is the limiting nutrient in most shallow and present in high concentration in the dropping of waterbirds. Before the model calibration, sensitivity analysis is performed with the data collected during the first year of study. Model is validated with the data collected during the second year of study.As per the model, P from the waterbird guano comprises 98.32% of P input to the lake. Parameters affecting the water-sediment exchange of P are most sensitive. P content in zooplankton is the most sensitive state variable. Nutrient budget analysis reveals that internal cycling of the nutrient is the main pathway to sustain productivity in the system. So far, no process-based modelling has been done on the impact of dropping of waterbird on nutrient dynamics of the aquatic system. This kind of model will be helpful to handle problems like eutrophication and macrophyte overgrowth due to eutrophication.