Effect Of Eutrophication And Ocean Acidification On The Physical And Ecologycial Characteristics Of Phytoplankton

Anthropogenic activity,such as the extent application of fertilizer and large discharge of sewage,had resulted in severly nutrient disorder in water,not only on their loadings,but also their forms and ratios.Meanwhile,the enormous emission of CO2 lowered the pH value in ocean.The significantly envrionmental changes lead to the loss of biodiversity and intensively the ocurrence of harmful algal blooms dominated by dinoflagellate or cyanobacteria.It may also promote proliferation of toxic dinoaflagellate and its toxin production,bringing about severe shellfish poisoning through food web.Effect of eutrophication and ocean acidification on the physiological and ecological characteristic of specific community of phytoplankton,in situ Microcystis spp.in Lake Taihu and unicell-cultivated Alexadrium fundyense were the target species.Firstly,kinetic and nutrient enrichment experiments were conducted to assess N uptake rates under differing conditions,and to examine effects of changes in N forms(NH4+,NO3-and urea)and P availability on phytoplankton community physiology.The results showed that the(1)utilization of NH4+,NO3-and urea by Microcystis-dominated communities was not efficient at low ambient substrate concentrations.(2)Maximum uptake rates by these phytoplankton was achieved on NH4+ and these rates were significantly higher than those on NO3-or urea with or without nutrient pretreatment.(3)High amounts of NH4+ may have inhibited or repressed the uptake of NO3-at certain times in these studies.(4)In the diurnal study,dissolved inorganic carbon and pH changed substantially throughout the day.The resulting high pH altered N and P in ways that may help to sustain nutrient cycling for the blooms.Secondly,the physiological and toxicological response of Alexandrium fundyense on the effect of ocean acidification(OA)was conducted.The results indicated that:(1)The addition of CO2(1000ppm and 1300ppm),compared to the normal condition(?450ppm),would lead the bloom duration to extend 6 more days and biomass to increase by 64.8%?77.3%.(2)The particulate organic carbon(POC)of Alexandrium fundyense at stationary phase was raised with the enriched CO2,indicating the potential stronger carbon-fixation capability in the more acidic water.(3)OA may stimulate the PSP toxin production,with a certain threshold.(4)OA promoted the production of carbamate toxins(GTX3)but repressed the production of N-sulfonamide toxins(C2),causing the increased cell toxicity.In summary,eutrophication and ocean acidification played very important roles in the structure and function of phytoplankton community.The positive feedback interactions of algal accumulation,dissolved inorganic carbon(DIC),pH elevation,and nutrient efflux(N,P)contributed to the N and P in ways that may help to sustain nutrient cycling for the blooms.Likewise,ocean acidification,in present study,was suggested to exacerate the blooms of"Alexandrium fundyense" and its potentically toxic impacts.All these research will provide scientific guidance to regulate nutrient discharge and give support on preventing the harmful algae bloom.