Influence Of Coastal Pollutants On Diatoms Ecosystem Functions And Iron Biogeochemical Cycle

Coastal ecosystems account for over one-third of the world's ecosystems services.Diatoms tend to dominate phytoplankton communities in well-mixed coastal and upwelling regions.Marine diatoms greatly influence marine food webs,global climate,atmospheric carbon dioxide concentration,and marine ecosystem function.Coastal pollutants mainly included inorganic nitrogen,active inorganic phosphorus,and petroleum-derived hydrocarbons.Aquaculture pollution was often exposed to both eutrophication and antibiotic abuse pollution.We used algal cell density,cell growth cycles,protein,chlorophyll a,superoxide dismutase activity(SOD),and malonaldehyde(MDA)for the assessment of algal biomass,lifetime,nutritional value,photosynthesis and respiration,antioxidant capacity,and lipid peroxidation,respectively,and then the risk assessment of the eutrophication,petroleum-derived hydrocarbons,and aquaculture pollution on coastal ecosystem functions is fully investigated.The influence of eutrophication on the iron speciation distribution,iron bioaccessibility,and interspecific competition between diatom species were examined.These studies could be used for risk assessment the ecotoxicity of coastal pollutants on diatoms ecosystems function and iron biogeochemical cycles.The results were shown as follows.(1)As a coastal centric diatom,Conticribra weissflogii can be used as a model of diatom.Here we investigated the effects of nitrate addition(N,8.0,16.0,32.0,64.0 ?mol/L),Petroleum-derived hydrocarbons(WSF,0,0.1,0.5,1.0,5.0 mg L-1),and oxytetracycline(OTC,0,1.0,3.0,5.0,10.0 mg L-1)on the coastal ecosystems function of Conticribra weissflogii.The influence of petroleum hydrocarbons or oxytetracycline on diatoms ecosystems function was more significant than nitrate addition.After N addition is combined with WSF pollution,the cell growth cycles are shortened by 27-44%;the activities of superoxide dismutase are decreased by 1-64%;the cell density,the concentrations of chlorophyll a,protein,and malonaldehyde are decreased by 38-310%,62-712%,4-124%,and 19-233%,respectively.After N addition is combined with OTC pollution,the cell growth cycles are shortened by 27-44%;the activities of superoxide dismutase are decreased by 19-397%;the cell density,the concentrations of chlorophyll a,protein,and malonaldehyde are decreased by 73-121%,52-693%,19-875%,and 66-2733%,respectively.So,the coastal ecosystems function,stability of food chain,and the transfer of energy in food chain could be changed by eutrophication,petroleum-derived hydrocarbons,and oxytetracycline pollution.(2)Two non-toxic coastal diatoms,Skeletonema costatum and Thalassiosira weissflogii were exposed to N,P,and Fe enrichment for four-day.The experimental macronutrient treatments included:total N concentrations of 8,16,32,and 64 ?mol L-1,at a total P concentration of 1.0 ?mol L-1;total P concentrations of 1.5,2.0,and 2.5 ?mol L-1,at total N concentration of 8 ?mol L-1;and 1.8 ?mol L-1 Fe species(Fe(III)-EDTA,Fe(OH)3,dissolved,colloidal,and particulate Fe from culture medium).In coastal environment,S.costatum is coexistence with T.weissflogii,their cell density ratios are 5.57-7.03 times,indicating that S.costatum is more competitive than T.weissflogii,because:Fe bioavailability is controlled by algal secretion;the growth promotion of S.costatum by its cell-free filtrate is more obvious than that of T.Weissflogii;and Fe availability for S.costatum is more than that for T.Weissflogii.Fe bioavailability is a key determinant for the interspecific competition,because:1)under N addition from 8 ?mol L-1 to 32?mol L-1,the adsorption and absorption of Fe per cell and total adsorption,absorption and uptake by S.costatum is higher than T.weissflogii;2)P concentration higher than 1.5 ?mol L-1,the absorption of Fe by T.weissflogii is more than S.costatum;3)the species of Fe in seawater could be affected by the secretions of marine phytoplankton;and 5)all the dissolved,colloidal and particulate Fe from S.costatum and T.weissflogii are available by S.costatum,i.e.the Fe bioavailability by S.costatum is higher than T,weissflogii.