| The interaction between sediment and water(the circulation of nutrients,migration and storage of nutrients)has an important impact on the neritic ecological environment.Sediment-water interface is one of the most important interfaces in coastal shallow waters.The exchange of nutrients at sediment-water interface has a significant impact on the maintainance of marine primary productivity and the balance of water nutrients.Control of sediment water interface between the main factors of nutrient migration including diffusion,adsorption desorption,precipitation(mineralization),dissolution and decomposition of organic matter.In the process,temperature,dissolved oxygen,p H,salinity,bioturbation and the physico-chemical properties of sediment can promote or inhibit the exchange of nutrients between the sediment and water.At present,most scholars have studied the influence of a single factor on nutrient exchange,but the factors that affect nutrient exchange at sediment-water interface are not independent,which will act on the exchange process together.This thesis takes the marine ranching of Haizhou Bay as an example,and is carried out a study on the exchange of nutrients at the sediment-water interface characteristics based on the orthogonal design and the biological disturbance experiments,which is expected to provided basic information for restoring and building the ecological model in Haizhou Bay,and also servesa as a theoretical basis for the restoration of water environment.The nutrient exchange fluxes at sediment-water interface of 3 stations in Haizhou Bay in May 2016 was studied.The effects of sediment type,temperature,DO and p H on nutrient exchange fluxes at sediment-water interface were analyzed.In October 2016,Scapharca subcrenata were directly sampled from the culture area in Haizhou Bay.This study also investigated the effects of bioturbation and density of S.subcrenatas on the nutrient exchange in SWI based on laboratory experiments.And the following research results are obtained:The effects of sediment type,temperature,DO and p H on the exchange fluxes of nutrients between sediment and water interface were analyzed.The primary and secondary relations of various factors above affecting nutrient fluxes could be observed from the experiment results.With respect to NH4+-N,its influencing factors were shown as follows,DO>temperature>sediment type;for NO3-+NO2--N,sediment type>DO>temperature;for PO43--P,DO>sediment type>temperature;for Si O32--Si,temperature>p H.The interaction among these factors was found as an important effect on the fluxes of nutrients,which should be taken into account in the establishment of the sediment-water interface nutrients exchange model.Results in this study on the effect of sediment types,temperatures,dissolved oxygen,and p H on the nutrient exchange fluxes in Haizhou Bay were basically consistent with the investigation data of Haizhou Bay in former years.Results showed that the biological effects of S.subcrenatas could increase the diffusion depth and rate of the nutrients in the sediments.The bioturbation of S.subcrenatas could allow the nutrients to permeate into the surface sediments at the depth of 6~10 cm and significantly increase the release rate of nutrients in the sediment-water interface.A tendency was observed that the average nutrient fluxes migrated from pore water to the overlying water during the experiment period.The releasing fluxes of DIN and PO43--P in the culture area is around three times higher than that in the non-cultured region,and the releasing flux of Si O32--Si is about twice higher than that in non-cultured region.The overall exchange of nutrients in the sediment-water interface would provide 49% DIN,74% PO43--P and 27% Si O32--Si for the aquaculture farm through culturing S.subcrenata in Haizhou Bay.In this study,S.subcrenata culture has been proved as an important contributor to nutrient exchange across the sediment-water interface(SWI)in the farming area of Haizhou Bay. |
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