The response of zooplankton network indicators to winter geothermal water warming in shallow reservoirs

Abstract

Abstract. The increase in the temperature of surface waters has been studied for many decades, and various methods have been used to predict the most probable scenarios. The present study was undertaken to test the following research hypothesis: the warming of surface waters in winter (caused by the inflow of geothermal water) significantly modifies the dynamics, significance and type of relationships in zooplankton communities colonizing mine pit reservoirs. These relationships were examined with the use of network graph analysis for three thermal variants: warm winters (WW), moderate winters (MW), and cold winters (CW). The CW network was most cohesive, and it was controlled by eutrophic Rotifera (Trichocerca pusilla, Pompholyx sulcata, Keratella tecta) and Copepoda, with an equivalent number of positive and negative interspecific relationships. An increase in water temperature in winter led to a decrease in primary production, a decrease in the values of centrality attributes in MW and WW networks, and an increase in the significance of species that communicated with the highest number of species across sub-networks. Moderate winters increased the role of ecologically and functionally diverse species, which contributed to the heterogeneity of the MW network. The WW network was least cohesive, and it was controlled by small-sized psammophilous and phytophilous rotifers (Monommata maculata, Cephalodella spp.) and littoral cladocerans Alona spp. Adults Copepoda were not identified in the network, and the significance of antagonistic relationships decreased, which indicates that the WW network structure was weak and unstable. The results of the impact of warm winters and the flattening of the annual water temperature amplitude on the zooplankton network may be a projection of the expected global changes. These effects are particularly important in water reservoirs exposed to anthropogenic pressure and where changes in the thermal regime can influence future ecosystem services.