## 5 Conclusions  
In this study we employed pore water concentration profiles, intact sediment core incubations, and tidal sampling of estuarine waters and mangrove effluents to investigate nutrient dynamics in a subtropical mangrove forest. Results show that the combination of methods aids the understanding of processes at different system levels.  
Mangrove sediments are a source for NH\({}_{4}\)+ and Si due to the exchange of NH\({}_{4}\)+- and Si-enriched pore waters across the sediment-water interface. Enhanced demand for oxidizing agents during early digenetic processes leads to sediment-directed fluxes of NO\({}_{3}\)- disclosing the mangrove sediments as a sink for nitrate. Although PO\({}_{4}\)[3]- is released into the pore water during sedimentary organic matter degradation processes, enhanced PO\({}_{4}\)[3]- utilization by benthic microalgae and mangrove trees may make the mangrove a net sink for PO\({}_{4}\)[3]-. The difference in pore water fluxes expected from concentration profiles and measured total benthic fluxes indicates that sub-surface nutrient processing does directly translate into sediment-water exchange, probably due to mediation by surface microorganisms.  
The total filtration capacity of the Naniu mangrove is low due to the small forest area and strong anthropogenic inputs. Thus, coastal nutrient management needs to concentrate on reduction of nutrient inputs, mainly from excessive fertilization in agriculture but with additional focus on growing aquaculture.  
While seasonal climatic variability influences the magnitude of sedimentary processes, storm events cause a release of nutrients from pore waters during sediment displacement and ventilation of the surface sediment, inducing changes in sedimentary redox processes, which may lead to the reversion of benthic flux directions. The influence of such extreme events may persist longer for redox-sensitive nutrients like NO\({}_{3}\)- and NH\({}_{4}\)+ than for Si. The physical redistribution of sediments may also enhance the transport of organic matter into deeper sediment layers. However, the mechanism of organic matter transport and burial in mangrove sediments has not been part of this study and deserves its own research focus. Future studies should also aim to investigate individual processes causing observed nutrient fluxes and include wider spatiotemporal resolution in order to enhance the quality of filtration budgets.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **River Discharge** & **Shrimp Pond Effluents** & **Mangrove Filtration** \\ \hline NO\({}_{3}\)– & [10\({}^{3}\) mol\(\cdot\)day\({}^{-1}\)] & 2007.8 & 5.3 & \(-\)9.6 to \(-\)1.4 \\  & _\% of total input_ & _99.7_ & _0.3_ & _\(-\)0.1 to \(-\)0.5_ \\ PO\({}_{4}\)– & [10\({}^{3}\) mol\(\cdot\)day\({}^{-1}\)] & 33.3 & 0.9 & \(-\)0.41 to \(-\)0.40 \\  & _\% of total input_ & _97.4_ & _2.6_ & _\(-\)1.2 to \(-\)1.2_ \\ \hline \end{tabular}
\end{table}
Table 3: Mangrove filtration efficiency for NO\({}_{3}\)– and PO\({}_{4}\)[3]– relative to land-derived riverine input, based on daily fluxes and a mangrove area of 515 ha. Daily nutrient inputs from [PERSON] (unpublished [124], but see [50] for seasonal values).