Impacts of maricultural activities on characteristics of dissolved organic carbon and nutrients in a typical raft-culture area of the Yellow Sea, North China

Ailian Bay is an integrated multi-trophic aquaculture bay with approximately 60 years maricultural activities in North China. The floating raft culture of kelp and shellfish is the unique mariculture mode. In this study, the impacts of intensive mariculture activities on seasonal carbon and nutrient dynamics in Ailian Bay were systematically analysed via seasonal surveys between 2015 and 2016. The dissolved inorganic nitrogen and silicon reached the maximum concentrations during summer, which were mainly attributed to the release of shellfish metabolic by-products and their filter-feeding effects on diatoms. Dissolved organic carbon (DOC) concentrations were significantly elevated when kelps were rotting in summer and kelp seeding were occurring in winter. Meanwhile, the fluorescence intensity of humic-like chromophoric dissolved organic matter was relatively high in kelp mariculture zone. As most humic-like DOC are potentially refractory substances, we propose that kelp mariculture would contribute importantly to the increase of refractory DOC pool in oceans.