Sedimentation And Spatial Distribution Of Aquaculture-derived Organic Matter From Large Yellow Croaker Cage Farm In Sansha Bay

Sansha Bay,located in the northeastern Fujian Province,represents one of the most typical mariculture bay on the Chinese coasts.The large yellow croaker?Pseudosciaena crocea?cage farm in the area,in particular,numerically dominated in the national total production of the species.The environmental impacts of mariculture practices in Sansha Bay have been addressed by varied authors,many of which were described based on the spatial variability of environmental parameters and macrobenthic community among different areas?finfish cage farm,seaweed raft culture,abalone suspension cage farm and non-farm area?.However,to date,limited information is available on sedimentation and spatial distribution patterns of aquaculture-derived organic matter?AOM?in Sansha Bay,which were the fundamental issues in understanding benthic impacts in the region.Surface sediment and AOM samples under the two typical feeding methods?pelleted feed and raw fish?within a spatial extend 200 m away from the finfish cages were collected,on which based AOM sedimentation rate and its spatial extent,nutritive matters?POM:particulate organic matter;POC:particulate organic carbon;PN:particulate nitrogen;TP:total phosphorus?fluxes were s in this study.The results obtained are as follows:?1?In Sansha Bay,the sedimentation rate of AOM was 563.66±119.18 g m^-2 d^-1in the case of using commercial pellets as feed,which was significantly higher than feeding raw fishes.POM,POC,PN and TP fluxes were much elevated under the circumstance of using commercial feed than using raw fishes,they were 27.25±2.43 g m^-2 d^-1,6.03±0.58 g m^-2 d^-1,0.66±0.06 g m^-2 d^-1and 0.39±0.04 g m^-2 d^-1 in the former experimental condition,and 13.04±1.62 g m^-2 d^-1,3.57±0.45 g m^-2 d^-1,0.51±0.06 g m^-2 d^-1and 0.22±0.04 g m^-2 d^-1 in the latter situation,respectively.However,nutritive matter content were lower in AOM in the case of using commercial feeds as feed.?2?The spatial extent of influence of AOM deposition in Sansha Bay was considered restricted to an area 200 m from the finfish cages.Minor discrepancies were present among the conclusions drawn with the varied sedimentary parameters.For examples,the spatial distribution pattern of AOM sedimentation and stable isotope(?¹³C and?¹⁵N)values indicate an influence area of 50?100 m,which is significantly smaller than the ranges based on the spatial variability of nutrient contents in sediment and sedimentary stable isotope values?150?200 m?.?3?Correlation analysis showed that there was no correlation between the contents of SOC,STN and STP in sediments and the corresponding nutrients deposition fluxes.This result indicated that AOM in Sansha Bay experienced a complex biogeochemical cycle after settling into the sediment environment.Although the AOM sedimentation rates in Sansha Bay were higher than those reported on the Mediterranean and Australian coasts,they are similar with those previously reported in China.The main reasons for the large dispersion range of AOM in Sansha Bay were considered to lie in varied aspects.For example,the water current in prevalent flow direction in near-bottom layer in the study area are relatively strong with an average of 0.22 m/s.It enables high-level sediment resuspensions,which can extend the spatial distances of AOM loading.Additionally,wild and escaped fish outside the cages consumed the waste particles dispersed in the environment around the cage and deposited them elsewhere by defecation.They could also enlarge the distribution areas of AOM from the finfish cages.In Sansha Bay,it is likely that pelleted feed were excessively utilized,as suggested by the relatively large number of AOM.Thus,the improvements of feeding technical are greatly benefits for the alleviating the negative environmental impacts from the finfish cage farm practice.