Synergistic impact of socio-economic and climatic changes on the ecosystem of a deep dam reservoir: Case study of the Dobczyce dam reservoir based on a 30-year monitoring study

Highlights: • Socio-economic and climatic changes are important factors affecting water quality. • Global warming causes an extension of water column thermal stratification. • Land use type in the catchment affects water quality in the dam reservoir. • Positive effects of socio-economic changes may veil the consequences of climate change. Climate change, increasing inequality in freshwater supply and consumption, as well as human land use activities are remarkable drivers of the alteration of the water cycle on the Earth. The aim of our research was to determine if socio-economic and climatic changes affected the ecosystem of a deep dam reservoir which is used for drinking water. A 30-years data series showed that suburbanization did not negatively affect the quality of the water. Moreover, 30 years of socio-economic and political changes resulted in land use changes (increase of forest from 45 to 50% and decrease of agricultural land from 53 to 43%) and better management of the catchment, as well as the modernization and introduction of new technologies. Furthermore, simultaneous climatic changes affected various physical and chemical features of the studied reservoir, and the most important finding is that the thermal stratification period is extended as an effect of global warming (begins earlier and lasts longer). The complexity of the processes contributing to the functioning of the ecosystem is large, so some processes might be a result of synergistic effects of global warming and socio-economic changes. Our 30-year monitoring study explicitly shows how the ecosystem of a deep dam reservoir reflected these changes.