Impact of urbanization and agriculture on zooplankton interactions: A network modelling approach in a lowland river

Land use patterns play a critical role in shaping abiotic conditions, which in turn influence interspecies interactions within aquatic ecosystems. This study tested the hypothesis that catchment management practices significantly alter water parameters and consequently affect the dynamics, importance, and nature of relationships within the zooplankton community structure of a postglacial river (northern Poland). Zooplankton interspecies interactions were assessed using network graph modeling across four diverse catchment sections: natural (NAT), urban (URB), urban/agricultural (URB/AGR), and agricultural (AGR). The NAT network was the most cohesive, dominated by taxa feeding on various food sources (Asplanchna priodonta, Testudinella patina, Chydorus sphaericus, Thermocyclops crassus), with balanced positive and negative interactions, what sign of ecosystem balance and resistance. The intensification of urban and agricultural pressures led to a weakening of the strength and significance of negative interspecies relationships, causing decentralization of the URB and AGR networks. Small, common bacterio-detritophagous and actively feeding rotifers (Filinia terminalis, Anuraeopsis fissa, Polyarthra longiremis) played a key nodal role there, which indicates homogenization and reduced ecosystem resistance. The graph layout highlighting connected components allowed us to observe the environmental filtering process between the studied sections, identifying phenomena of adaptation, or elimination of zooplankton species. This study provides an innovative approach to understanding the functioning of biotic structures in rivers and underscores the importance of sustainable management strategies of river basins undergoing urbanization and agricultural expansion.