Waterbirds can impact aquatic ecosystems by adding nutrients through their droppings, potentially leading to eutrophication and weed growth. A study used a model to show that phosphorus from waterbird guano makes up most of the nutrient input to a lake. The model found that the exchange of phosphorus between water and sediment is crucial, and phosphorus in zooplankton is highly sensitive. The study suggests that internal nutrient cycling is key for sustaining productivity in the ecosystem. This type of modeling can help address issues like eutrophication and excessive plant growth in lakes.