Modeling impact of culture facilities on hydrodynamics and solute transport in marine aquaculture waters of North Yellow Sea

An increasing number of marine aquaculture facilities have been placed in shallow bays and open sea,which might significantly affect hydrodynamic and solute transport processes in marine aquaculture waters.In this study,a coupled hydrodynamic and solute transport model was developed with high-resolution schemes in marine aquaculture waters based on depth-averaged shallow water equations.A new expression of drag force was incorporated into the momentum equations to express the resistance of suspended culture cages.The coupled model was used to simulate the effect of suspended structures on tidal currents and the movement of a contaminant cloud in the marine aquaculture of the North Yellow Sea,China.The simulation results showed a low-velocity area appearing inside the aquaculture cage area,with a maximum reduction rate of velocity close to 45%under high-density culture.The results also showed that tidal currents were sensitive to the density of suspended cages,the length of cages,and the drag coefficients of cages.The transport processes of pollutants inside aquaculture facilities were inhibited away from the vicinity of the culture cage area because of the diminished tidal currents.Therefore,the suspended cages significantly affected the transport processes of pollutants in the coastal aquaculture waters.Furthermore,the reduced horizontal velocity significantly decreased the food supply for the aquaculture areas from the surrounding sea.

The Impact of Marine Aquaculture on the Environment;the Importance of Site Selection and Carrying Capacity

A growing increase in the world’s population and a gradual decline in poverty necessitate a search for new sources of protein in order to guarantee food security. Aquaculture has been identified as a potential sector capable of meeting the requirements for increased protein production without making excessive demands on the ecosystem. Although water makes up 70% of the earth’s surface, aquaculture cannot feasibly be practised everywhere;it requires a unique set of natural, social and economic resources to be managed in an environmentally responsible way. Finding suitable sites for aquaculture is becoming an ever increasing problem in the development of the sector as precautions need to be taken in setting up sites to ensure appropriate environmental characteristics exist and that good water quality can be maintained. Additionally, the effects of aquaculture on coastal and inland resources must be clearly determined to implement policies and regulatory frameworks to control its impact. Marine cage farming is gaining momentum, specifically in the Mediterranean and Black Sea coastal regions. For these sites to be further developed there is a need to minimize the effects on the environment and conflicts with other coastal users. To this aim the concept of allocated zones for aquaculture (AZA) is being adopted to provide specific areas for marine aquaculture to avoid environmental degradation. When choosing an (AZA) suitable site, it is vital to calculate ‘carrying capacity’ to reduce the risks and to protect the marine ecosystems. In this study the MERAMOD model was used to investigate the carrying capacity of marine fish farms. Modelling offers the possibility to simulate and predict the environmental impact of fish farms.

Marine aquaculture regulates dissimilatory nitrate reduction processes in a typical semi-enclosed bay of southeastern China

Marine aquaculture in semi-enclosed bays can significantly influence nutrient cycling in coastal ecosystems.However,the impact of marine aquaculture on the dynamics of dissimilatory nitrate reduction processes(DNRPs)and the fate of reactive nitrogen remain poorly understood.In this study,the rates of DNRPs and the abundances of related functional genes were investigated in aquaculture and non-aquaculture areas.The results showed that marine aquaculture significantly increased the denitrification(DNF)and dissimilatory nitrate reduction to ammonium(DNRA)rates and decreased the rate of anaerobic ammonium oxidation(ANA),as compared with non-aquaculture sites.DNF was the dominant pathway contributing to the total nitrate reduction,and its contribution to the total nitrate reduction significantly increased from 66.72%at non-aquaculture sites to 78.50%at aquaculture sites.Marine aquaculture can significantly affect the physicochemical characteristics of sediment and the abundances of related functional genes,leading to variations in the nitrate reduction rates.Although nitrate removal rates increased in the marine aquaculture area,ammonification rates and the nitrogen retention index in the aquaculture areas were 2.19 and 1.24 times,respectively,higher than those at non-aquaculture sites.Net reactive nitrogen retention exceeded nitrogen removal in the aquaculture area,and the retained reactive nitrogen could diffuse with the tidal current to the entire bay,thereby aggravating N pollution in the entire study area.These results show that marine aquaculture is the dominant source of nitrogen pollution in semi-enclosed bays.This study can provide insights into nitrogen pollution control in semi-enclosed bays with well-developed marine aquaculture.

Interactions of fluoroquinolone antibiotics with sodium hypochlorite in bromide-containing synthetic water:Reaction kinetics and transformation pathways

Seven popular fluoroquinolone antibiotics(FQs)in synthetic marine aquaculture water were subject to sodium hypochlorite(NaClO)disinfection scenario to investigate their reaction kinetics and transformation during chlorination.Reactivity of each FQ to NaClO was following the order of ofloxacin(OFL)>enrofloxacin(ENR)>lomefloxacin(LOM)>ciprofloxacin(CIP)?norfloxacin(NOR)>>pipemedic acid(PIP),while flumequine did not exhibit reactivity.The coexisting chlorine ions and sulfate ions in the water slightly facilitated the oxidation of FQs by NaClO,while humic acid was inhibitable to their degradation.The bromide ions promoted degradation of CIP and LOM,but restrained oxidation of OFL and ENR.By analysis of liquid chromatography with tandem mass spectrometry(LC-MS/MS),eight kinds of emerging brominated disinfection byproducts(Br-DBPs)caused by FQ S were primarily identified in the chlorinated synthetic marine culture water.Through density functional theory calculation,the highest-occupied molecular orbital(HOMO)and the lowest-unoccupied molecular orbital(LUMO)characteristic as well as the charge distribution of the FQs were obtained to clarify transformation mechanisms.Their formation involved decarboxylation,ring-opening/closure,dealkylation and halogenation.Chlorine substitution occurred on the ortho-position of FQs's N4 and bromine substitution occurred on C8 position.The piperazine ring containing tertiary amine was comparatively stable,while this moiety with a secondary amine structure would break down during chlorination.Additionally,logK_(ow)and log BAF of transformation products were calculated by EPI-Suite^(TM)to analyze their bioaccumulation.The values indicated that Br-DBPs are easier to accumulate in the aquatic organism relative to their chloro-analogues and parent compounds.