Benthic nutrient fluxes in an integrated multi-trophic aquaculture (IMTA) baySanggou Bay, China -were measured in June and September 2012. The benthic nutrient fluxes and total organic carbon (TOC) of sediment in this IMTA system were significantly lower than in monoculture bays. This was due to the efficient recycling of organic matter in the IMTA system, as revealed by historical data of annual production, dissolved inorganic nitrogen (DIN) concentration in seawater and TOC in sediment. Benthic nutrient fluxes in the IMTA system were mainly controlled by seawater temperature, dissolved oxygen (DO) and nutrient concentrations, which were strongly related to aquaculture activities. In June, the early growth phase of cultured finfish and bivalves contributed little to biodeposition, and benthic nutrient fluxes tended to be from the sediment to the seawater and contributed to algal growth. In September, the active growth of finfish and bivalves resulted in high concentrations of nutrients in the seawater and TOC in the sediment; 64% of the nitrogen and 25% of the phosphorus metabolized by bivalves were transferred from the seawater to the sediment.

Nitrogen transfer processes and NO3− sources in the East China Sea (ECS) were analyzed using dual isotopes of NO3− and NO2−, the concentration and isotopes of dissolved O2 and N2 gases, nutrient concentrations, and the hydrological conditions. It was clear that the δ15N and δ18O values of NO3− in the Changjiang freshwater were 5.6–6.6‰ and 0.6–1.0‰, respectively, affected by human activities (fertilizer, sewage, and manure) and nitrification. Off the Changjiang Estuary to the ECS continental slope, the NO3− concentration was lower or exhausted in the upper water layers, where both available δ15N and δ18O values for NO3− were high related to phytoplankton assimilation. In the lower water layers, organic matter remineralization, nitrification, and coupled sedimentary nitrification and denitrification resulted in low NO3− isotope values. Moreover, in the upper water layers of the ECS continental slope, NO3− showed high δ15N and δ18O values and low Δ(15, 18) values affected by assimilation, nitrification, and N2 fixation. NO2− in the ECS was dominated by NH4+ oxidation, and NO2− oxidation plays an important role in depleting NO2− in δ15N values. An overall NO3− budget is built for the ECS shelf, indicating that open boundary exchanges of NO3− flux and isotopes through Kuroshio invasion and Taiwan Warm Current Water are comparable to outflow off the ECS shelf, and nitrogen transformation processes (such as NO3− assimilation and nitrification) play an important role in nitrogen cycle, and NO3− is modified on the ECS shelf.

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A long-standing enigma in oceanography is why terrestrial organic matter is "missing" in the global ocean, despite the considerable discharge into it every year. Although some explanations, such as mineralogical composition, hydrodynamic processes, and priming effect, have been proposed, we hypothesize that the essential mechanism behind the missing organic matter is microbial processing, for which the underlying coupled geochemical, molecular, and genetic evidence is unknown. An ultra-large-volume, long-term river-seawater stratified simulation system was constructed to unravel the microbially driven fate of terrigenous particulate organic matter (POM) in oceans. Analysis of combining the molecular with POM chemical composition data suggests that Bacteroidetes could act as pioneers in the processing of terrigenous POM in oceans, degrading high-molecular-weight, high-carbon compounds such as polysaccharides. Remaining low-molecular-weight nitrogenous organic matter is subsequently degraded by Planctomycetes and Proteobacteria. Isotopic signals show that this preferential degradation causes a distinct "aging" effect of POM, and along with nitrification enhanced by remineralization, causes a decrease in the POM C : N ratio. Degradation of terrigenous POM and bacterial biomass biosynthesis leads to positive deviations in δ 15 N and δ 13 C. Relatively refractory hydrocarbons, aromatic compounds, and phenols are accumulated by microbial processes in this system. This study provides mechanistic insights into the missing chemical and isotopic signals and microbially driven fate of terrigenous POM in the ocean, with important implications for how riverine material input affects marine carbon and nitrogen cycling.Ongoing climate change is expected to lead to increased global river runoff (Labat et al. 2004;Andersson et al. 2015). Both ecological modeling and field research have indicated that the flux of terrestrial input to oceans increases with increased river runoff (Andersson et al. 2015). However, few molecular signals of abundant terrestrial organic matter are detected in marine environments (Hedges et al. 1997;Bianchi 2011;Kandasamy and Nath 2016), and only a trace of terrigenous organic matter (e.g., lignin) is present in the ocean (Opsahl and Benner 1997). A proposed explanation for this is a priming effect, in which the addition of labile organic carbon increases remineralization of the relatively refractory organic carbon (Bianchi 2011;Morling et al. 2017). Mineralogical composition and characteristics have also been proposed as important factors controlling the fate of continentally