## 4 Discussion
### Organic Carbon and Nutrient Fluxes
Strong NO\({}_{3}\)\({}^{-}\) reduction in March causes NO\({}_{2}\)\({}^{-}\) release into the water column (Figure 6). The efflux does not cause a concentration increase in mangrove effluents (Figure 2) because NO\({}_{2}\)\({}^{-}\) undergoes either reoxidation to NO\({}_{3}\)\({}^{-}\) or further reduction to N\({}_{2}\) in the water column. As the incubation experiment yields net fluxes that are the sum of a combination of processes, specific process-based experiments are desirable to assess their relative importance. Concentrations of Si and PO\({}^{4^{-}}\) in pore water generally increase with sediment depth because of the dissolution of siliceous material [26] and remineralization of organic matter [112,113], as well as desorption from particles [22,114]. While this creates concentrations gradients between pore water and water column, the flux direction depends on microbial activity at the interface [26,28,37,55,86]. In the Nanliu mangrove forest, microhyotbenthos abundance and species number are dominated by diatoms [115], which have been suggested to cause Si influx despite high pore water concentrations [116]. Uptake from the pore water pool is indicated by the steepening of the concentration gradient in surface sediments (Figure 3). Utilization by diatoms appears to intercept all diffusive Si efflux in the dark, and increased demand during production in light causes additional uptake from the water column (Figure 6). Influx from the water column is low compared to other studies [28,55], as would be expected from a relatively low GPP. Though data on benthic PO\({}_{4}\)\({}^{-}\) fluxes in mangroves are scarce, comparison with earlier results suggests that influxes in the Nanliu mangrove forest are stronger than in other areas [28,55,86]. Direct uptake by microorganisms [36] may cause low concentrations in surface sediments, particularly in spring, when supply from deeper sediments is slow compared to regular summer conditions. Lower dark influx in March and dark efflux in October (Figure 6a) are likely due to reduced interceptive uptake of PO\({}_{4}\)\({}^{3^{-}}\) by primary producers in the absence of light. Additional removal of PO\({}_{4}\)\({}^{3^{-}}\) from the water column and pore water might be due to adsorption to iron(III)-oxyhydroxides (e.g., [26]), which is important in removing PO\({}^{4^{-}}\) from pore water and the water column in the study area [117]. Since it is likely that the described processes act simultaneously, process-based experiments are required to show their relative contribution to nutrient dynamics. Temporal variability in mangrove nutrient dynamics are largely governed by short-term forcing such as light availability [56,118], inundating water nutrient concentrations [45], and precipitation patterns [16,119], while seasonality may generally be weak [58,88,120]. Sediment core incubations (Figure 6) and pore water profiles (Figure 3b,c) show that benthic nutrient dynamics, particularly of nitrogen, change fundamentally after a storm event. Following tropical storm Nesat in October, DIN reduction in the surface and subsurface sediment decreased, as seen from the decreases in NH\({}_{4}\)\({}^{+}\) accumulation and NO\({}_{3}\)\({}^{-}\) decline (Figure 3b,c), and the reversed flux of NH\({}_{4}\)\({}^{+}\) into the sediment (Figure 6). The oxygenation of pore waters during sediment mobilization and ventilation by Nesat probably decreased denitrification [96,121] and enhanced nitrification of NH\({}_{4}\)\({}^{+}\) to NO\({}_{3}\)\({}^{-}\)[37,59], causing significantly higher NO\({}_{3}\)\({}^{-}\) and lower NH\({}_{4}\)\({}^{+}\) concentrations in bottom and surface sediment pore waters (Figure 3c). Due to the deeper penetration of O2 and NO3-, the SO42- reduction observed in the top 5 cm during September (Figure 4b) ceased after the storm (Figure 4c). Reducing processes dominate in deeper sediment and NO3- and NO2- are net removed from bottom (Figure 6) and pore waters (Figure 3c).