Ecosystem models indicate zooplankton biomass response to nutrient input and climate warming is related to lake size

Zooplankton is an essential part of the simulation in ecological process-based models and rigorous calibration of the zooplankton module lacks relevant modeling research that can predict the response of zooplankton biomass to varied environmental factors. The paper therefore builds a one-dimensional lake ecology model PCLake, which quantifies the dynamic effects on zooplankton in small water bodies distinguished by lake size and eutrophication status in warming climates. Based on the main geometric characteristics among a series of shallow water bodies, we constructed three lake models, namely, a northern lake with a larger area (> 0.1 ha) in Poland (Lake NL), a northern lake with a smaller (< 0.1 ha) area in Poland (Lake NS), and a southern lake with the smallest area in Croatia (Lake SS). Data from 2017 to 2018, including water temperature, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chl a), and zooplankton, were used to calibrate and verify models for three shallow water body categories and uncertainty analyses were carried out to support the credibility of our models. Further, to discuss the potential driving forces of environmental factors on zooplankton, we set up a series of scenarios in which atmospheric temperature and nutrient input were changed. Zooplankton are only considered as a common pool and therefore only how biomass varied can be obtained. Warming resulted in a decline of zooplankton in the lakes located in Northern Europe, with peak decreases in zooplankton biomass more than four times higher in Lake NS than in Lake NL. In addition, due to multiple nutrient loading scenarios, incoming nitrogen and phosphorus concentrations were found to have a huge impact on zooplankton biomass in Lake NL. Specifically, relative to the original eutrophic level, the average annual biomass of zooplankton increased by 90% with a 75% increase in organic nitrogen over the original eutrophic level and decreased by more than 50% with a 75% decrease in inorganic phosphorus. Hence, lake size characteristics should be taken into account in management and restoration as they may be synergistic with in-lake biological and abiotic processes under complex environmental forces.