Mercury Dynamics and Influencing Factors During the Decomposition of Urban Green Space Litter: In Situ Control Trials from Changchun, China

Litter decomposition is crucial for the mercury biogeochemical cycle, though urban disturbances often disrupt this process. This study simulated urban conditions to investigate how ecological factors affect litter decomposition and mercury dynamics, while assessing ecosystem service values. In the planted forests within the urban areas of northeast China, controlled experiments were conducted to study the effects of different light-transmittance treatments on the decomposition of litter and changes in mercury content. Results showed that decomposing litter continuously adsorbs atmospheric mercury, with accumulation peaking in summer, at 170.71 ng/g, and enhancing urban mercury retention. Light conditions significantly regulated both mercury fixation efficiency and ecosystem service value; specifically, 25% light transmittance maximized mercury absorption, and moderate shading improved the ecological service value of decomposition. Urban green space litter functions as a mercury sink driven by multiple factors. Besides light, decomposition duration, precipitation, temperature, litter chemical properties, and urban disturbances collectively regulate decomposition rates and mercury accumulation. These findings advance the understanding of urban mercury cycling and verify that moderate shading enhances mercury retention. Ultimately, this research supports evidence-based urban green space planning to improve environmental purification services and mitigate heavy metal pollution.