Environmental Challenges (Dec 2022)
Scenario analysis with a simulation model of the effect of waterbirds on phosphorus dynamics of a shallow freshwater ecosystem
Abstract
Many freshwater systems throughout the world support a high number of waterbird congregations. Previous works suggest waterbirds have the potential to deposit a considerable amount of nutrients into the waterbody that may cause eutrophication. To investigate the effect of the waterbirds on the dynamics of the ecosystem, we developed a process-based model incorporating waterbirds as a forcing function, namely GUANOTROPHY_P. In this work, the model is perturbed to understand the dynamics of different state variables to different scenarios of changing waterbird number of various feeding guilds, the digestive performance of waterbirds, P concentration in waterbird faeces, temperature, dissolved oxygen and initial biomass of macrophytes. It is found that an increase in ornithogenic nutrient load the system responds with increased concentrations of abiotic state variables (highest in organic phosphorus). At the same time, zooplankton is most positively sensitive to changes in waterbird numbers among biotic state variables. Grazing by waterbirds negatively affected the P concentration of all state variables. Temperature positively affects all state variables except sediment total phosphorous because sediment total P decreased by temperature-induced resuspension of organic P and desorption of inorganic P from sediment. Among the biotic state variables, phytoplankton was most sensitive to temperature. Dissolved oxygen was found to have minimal impact on the ecosystem and maximum effect on soluble reactive phosphorous concentration in water. At last, some lacunae of the model are highlighted as found in the scenario analysis.
