Impacts of Damming on Biogeochemical Cycling of Carbon, Nitrogen, and Phosphorus in Karst Rivers: Insights and Prospects

<p indent="0mm"> Against the backdrop of large–scale hydraulic engineering, dam reservoirs in karst regions play a significant role in regulating the transport and transformation of biogenic elements. This study systematically elucidates the impacts of karst damming on the biogeochemical cycling of carbon, nitrogen, and phosphorus at the watershed scale. The distinctive features of karst systems, including extensive carbonate rock distribution and frequent surface water–groundwater interactions, result in pronounced differences in element cycling compared to non-karst reservoirs. Key distinctions include: (1) The CO₂ emission flux from karst reservoirs <sc>[14.24 mmol/(m</sc>²·d)] was significantly lower than that of non–karst reservoirs <sc>[122.34 mmol/(m</sc>²·d)], as the unique carbonate buffering system in karst regions mitigated carbon emissions. (2) Elevated concentrations of dissolved inorganic carbon (DIC) in karst reservoirs enhanced carbon–nitrogen coupling, stimulating microbial heterotrophic denitrification and increasing N₂O emissions, thereby exacerbating global warming. (3) High Ca²⁺ and HCO₃^– concentrations in karst reservoirs promoted phosphate precipitation, elevating phosphorus retention capacity than non–karst reservoirs. Given the ecological fragility of karst systems and the dual impact of damming on climate change and biogeochemical cycles, future research should prioritize unraveling the mechanisms governing element cycling in ecologically vulnerable karst zones and hydraulic engineering-affected regions, assessing groundwater contributions to biogenic element fluxes in dammed rivers, and developing groundwater–surface water pollution control technologies tailored to these systems. Such efforts would provide a scientific foundation for water environment management in karst regions.