Seasonal Fluctuations of Nutrient Characteristics and Interfacial Fluxes in Mangrove Intertidal Groundwater

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Abstract
Mangrove ecosystems are vital intertidal transition zones where nutrient cycling sustains productivity and function. However, studies on the spatiotemporal distribution, transport fluxes, and controlling mechanisms of nutrient cycling in mangroves under land–sea interactions remain limited. In this study, we investigated the spatiotemporal distributions and fluxes via submarine groundwater discharge (SGD) of dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) with different seasons (autumn, winter and summer) and depths in a subtropical mangrove wetland. Research results indicated that mangrove ecosystems exhibited overall phosphorous limitation, especially in summer. Moreover, the spatiotemporal patterns and cycling of nutrients were influenced by land–sea interactions, mangrove development, sediment composition, and microbial processes, showing pronounced spatial heterogeneity. Higher nutrient fluxes from submarine groundwater discharge occurred in summer, and groundwater end‐member selection significantly influenced flux estimates. Nitrogen cycling shifted along the groundwater flow path from dissimilatory nitrate reduction to ammonium (DNRA) to nitrification in fringe mangroves, and from nitrification to denitrification and anammox in interior mangroves, driving nitrogen loss. Nitrogen loss was enhanced in winter, whereas nitrogen fixation was strengthened in summer. Seasonal changes further regulated phosphorus cycling, such that its release peaked in winter, while mobilization was offset by biological uptake in summer. These findings enhance our understanding of biogeochemical cycling in mangrove groundwater and support coastal mangrove ecosystem management.
Funding Information
  • Ministry of Education of the People's Republic of China (D20020)

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