Dissolved inorganic nutrients (NO-N, NO-N, NH-N, and PO-P) play a critical role in the effective management of water quality and prevention of fish and shrimp diseases in aquaculture systems. In this study, dissolved inorganic nutrient concentrations in the water column and sediment porewater, and the fluxes across the sediment-water interface (SWI) were investigated in three intensive shrimp ponds with zero water exchange to examine nutrient cycling during the different growth stages of shrimps. Distinct changes in the dissolved inorganic nutrient concentrations in both the water column and sediment porewater were observed among the three growth stages. Average NO-N, NO-N, NH-N, and PO-P concentrations in the sediment porewater were 3.53, 2.81, 29.68, and 6.44 times higher, respectively, than those in the water column over the study period, indicating that the pond sediment acted as a net source of nutrients to the water column. This was further supported by the net release of nutrients from the sediments to the water column observed during the incubation experiment. Nutrient fluxes were dominated by NH-N, while NO-N (NO-N and NO-N) and PO-P fluxes remained low. The high rates of NH-N release from the sediment highlight the need of taking into account the biogeochemical role of sediments in mitigating the problem of water quality degradation in coastal shrimp ponds. Based on a total water surface area of mariculture ponds and a total mariculture production of 2.57×10ha and 2.30×10kg, respectively, we estimated conservatively that approximately 4.77×10tons of total nitrogen and 3.75×10tons of total phosphorus are being discharged annually from the mariculture ponds into the adjacent coastal zones across China. Results demonstrated the importance of aquaculture pond effluent as a major contributor of water pollution in the coastal areas of China, and called for actions to properly treat these effluents in alleviating the eutrophication problem in the Chinese coastal zones.

Land‐use/land‐cover change (LULCC) often results in degradation of natural wetlands and affects the dynamics of greenhouse gases (GHGs). However, the magnitude of changes in GHG emissions from wetlands undergoing various LULCC types remains unclear. We conducted a global meta‐analysis with a database of 209 sites to examine the effects of LULCC types of constructed wetlands (CWs), croplands (CLs), aquaculture ponds (APs), drained wetlands (DWs), and pastures (PASs) on the variability in CO2, CH4, and N2O emissions from the natural coastal wetlands, riparian wetlands, and peatlands. Our results showed that the natural wetlands were net sinks of atmospheric CO2 and net sources of CH4 and N2O, exhibiting the capacity to mitigate greenhouse effects due to negative comprehensive global warming potentials (GWPs; −0.9 to −8.7 t CO2‐eq ha−1 year−1). Relative to the natural wetlands, all LULCC types (except CWs from coastal wetlands) decreased the net CO2 uptake by 69.7%−456.6%, due to a higher increase in ecosystem respiration relative to slight changes in gross primary production. The CWs and APs significantly increased the CH4 emissions compared to those of the coastal wetlands. All LULCC types associated with the riparian wetlands significantly decreased the CH4 emissions. When the peatlands were converted to the PASs, the CH4 emissions significantly increased. The CLs, as well as DWs from peatlands, significantly increased the N2O emissions in the natural wetlands. As a result, all LULCC types (except PASs from riparian wetlands) led to remarkably higher GWPs by 65.4%−2,948.8%, compared to those of the natural wetlands. The variability in GHG fluxes with LULCC was mainly sensitive to changes in soil water content, water table, salinity, soil nitrogen content, soil pH, and bulk density. This study highlights the significant role of LULCC in increasing comprehensive GHG emissions from global natural wetlands, and our results are useful for improving future models and manipulative experiments.

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Mariculture shrimp ponds are important CH4 sources to the atmosphere. However, the spatiotemporal variations of CH4 concentration and flux at fine spatial scales in mariculture ponds are poorly known, particularly in China, worlds largest aquaculture producer. In this study, the plot‐scale spatiotemporal variations of water CH4 concentration and flux, both within and among ponds, were researched in shrimp ponds in Shanyutan wetland, Min River Estuary, Southeast China. The average water CH4 concentration and diffusion flux across the water‐air interface in the shrimp ponds over the shrimp aquaculture period varied from 2.29 ± 0.29 to 50.48 ± 20.91 μM and from 0.09 ± 0.01 to 2.32 ± 0.95 mmol·m−2·hr−1, respectively. The CH4 emissions from the estuarine ponds varied greatly between seasons, with peaks in August and September, which was similar to the trend of water temperature and dissolved oxygen concentrations. There was no remarkable difference in CH4 concentration and flux between shrimp ponds but significantly spatiotemporal differences in CH4 concentration and flux within the ponds. Significantly higher emissions occurred in the feeding zone, accounting for approximately 60% of total CH4 emission flux, while much lower CH4 emissions appeared in aeration zone, contributing 14% to total flux. This study suggests the importance of considering spatiotemporal variation in the whole‐pond estimates of CH4 concentration and flux. In light of such high spatial variation within ponds, improving aeration and feed utilization efficiency would help to mitigate CH4 emissions from mariculture ponds.

Coastal reservoirs are potentially CH4 emission hotspots owing to their biogeochemical role as the sinks of anthropogenic carbon and nutrients. Yet, the fine-scale spatial variations in CH4 concentrations and fluxes in coastal reservoirs remain poorly understood, hampering an accurate determination of reservoir CH4 budgets. In this study, we examined the spatial variability of diffusive CH4 fluxes and their drivers at a subtropical coastal reservoir in southeast China using high spatial resolution measurements of dissolved CH4 concentrations and physicochemical properties of the surface water. Overall, this reservoir acted as a consistent source of atmospheric CH4, with a mean diffusive flux of 16.1 μmol m -2 h -1 . The diffusive CH4 flux at the reservoir demonstrated considerable spatial variations, with the coefficients of variation ranging between 199 and 426% over the three seasons. The shallow water zone (comprising 23% of the reservoir area) had a disproportionately high contribution (56%) to the whole-reservoir diffusive CH4 emissions. Moreover, the mean CH4 flux in the sewage-affected sectors was significantly higher than that in the nonsewage-affected sectors. The results of bootstrap analysis further showed that increasing the sample size from 10 to 100 significantly reduced the relative standard deviation of mean diffusive CH4 flux from 73.7 to 3.4%. Our findings highlighted the role of sewage in governing the spatial variations in reservoir CH4 emissions and the importance of high spatial resolution data to improve the reliability of flux estimates for assessing the contribution of reservoirs to the regional and global CH4 budgets.