Evolution of water quality and biota in the Panjiakou Reservoir, China as a consequence of social and economic development: implications for synergies and trade-offs between Sustainable Development Goals

Water shortages caused by poor water quality severely affect the sustainable social and economic development of Tianjin City and Tangshan City in China. The Panjiakou Reservoir is located in the Luanhe River mainstream and provides water to the public in both cities since 1983. The evolution of water quality and aquatic community structure in the Reservoir and interactions with the social and economic development of its surroundings (Tangshan City and Chengde City) were analyzed. The relations between these changes and the various interrelated Sustainable Development Goals (SDGs) were also evaluated. From 1984 to 2019, the overall trend of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD Mn ), and ammonia nitrogen (NH 3 -N) concentrations first increased and then decreased with economic growth. The organisms with strong ecological adaptability and pollution resistance became dominant species in the aquatic community. These included chlorophyta, cyanophyta and bacillariophyta among phytoplankton, copepods among zooplankton, and tubificidae and chironomidae among zoobenthos. The completion of Panjiakou Reservoir satisfied the water demand of Tianjin City and Tangshan City as well as benefited the economic and social development of the surroundings. However, high levels of pollutants produced by cage fish culture, mineral processing, and tourism threatened the water environment, which would in turn harm society and the economy. Therefore, fish cages were removed and other environmental protection measures were implemented to ensure the safety of drinking water. This study demonstrated that considering comprehensively the individual needs inside and across catchments to minimize trade-offs and maximize synergies was of great significance for coordinating the relations among society, economy, and water resources to achieve sustainable development at the sub-national scale.