Diffusion of Nitrogen and Phosphorus Across the Sediment-Water Interface and In Seawater at Aquaculture Areas of Daya Bay, China

Abstract

With the yearly increasing marine culture activities in floating cages in Daya Bay, China, the effects of pollution may overlap and lead to more severe water environmental problems. In order to track the impacts of the marine culture in floating cages on water environment, sediments and overlying water were sampled by cylindrical samplers at three representative aquaculture areas of Daya Bay. The water content, porosity, density of sediments as well as the vertical distributions of ammonia nitrogen and active phosphate in pore water along sediments depth were measured. The release rate and annual released quantity of the nutrients across sediment-water interface were calculated using Fick’s Law. A horizontal two-dimensional mathematical model was developed to compute the spatial and temporal distributions of the nutrients in seawater after being released across the sediment-water interface. The results showed that the sediments, with a high content and a large annual released quantity of nitrogen and phosphorus, constitute a potential inner source of seawater pollution. Influenced by tide and water depth, the scope of diffusion and migration of the nutrients appears as a long belt which is about 1 km long and 50 m wide. Seawater in this area is vulnerable to eutrophication.

Changes in soil and water quality at sediment–water interface ofPenaeus vannameiculture pond at varying salinities

“…Sediments with a high content of nutrients under marine culture in floating cages released a large quantity of nitrogen and phosphorus across the SWI and contribute a lot to the nutrients in the water was observed by Cheng, Zeng, Guo, and Zhu (2014) in a study on the fluxes of nutrients. The phosphorus exchange between sediment and water is influenced by the interaction between abiotic and biotic processes.…”

“…The phosphorus availability in water depends on the pH of water and sediment (Masuda & Boyd, 1994;Moore & Reddy, 1994) and exists in dissolved reactive phosphate form (Cheng et al, 2014). Phosphate content was 2.5 times higher in high saline than low saline water (Figure 7), which is due to the high concentration of sulphate in brackishwater.…”

“…The most active area to understand the release and transport of nutrients including nitrogen and phosphorus is the surface of the sediment within the first four cm vertical depth (Cheng et al, ). Hence, the most significant indicator of pond environment quality is the SWI as it influences both the overlying water quality and sediment by constant interaction and exchange of nutrients from sediment to water and vice versa at the interface area.…”

“…The most active area to understand the release and transport of nutrients including nitrogen and phosphorus is the surface of the sediment within the first four cm vertical depth (Cheng et al, 2014).…”

Effects of Nonaerated Circulation Water Velocity on Nutrient Release from Aquaculture Pond Sediments

“…Given that the N and P released can also boost autotrophic growth in freshwater ecosystems, seriously affecting the biomass and population structures of aquatic species [2][3][4], a great deal of research has focused on the role played by N and P in aquaculture [5,6]. Most previous studies examined the changes in nutrition concentration in the sediment porewater and overlying water and measured the nutrient diffusion flux under still water conditions [7], but the water turbulence caused by storms, aeration, and bioturbation can have a significant impact on the release of N and P at the sediment-water interface [8]. The deposition and resuspension of sediments resulting from water turbulence can prompt the release of nutrients and metals into overlying water [9] and increase the exchange coefficient between the overlying water and sediments, thus accelerating the diffusion of any contaminants present in the sediments into the overlying water and boosting nutrient release.…”