Ecological Risk Assessment Of Herbicide In Sanggou Bay And The Herbicide Ecotoxicity On Seagrass

In recent decades,the invention and wide use of herbicides have greatly saved the labor force and played an important role in world agriculture.However,with the wide use some herbicides enterd the estuaries and coastal ecosystems through above-ground/underground runoff,threatening the health of the non-target angiosperm plant,seagrass.Since the last century,seagrass has severely declined under the influence of natural and human activities.The threat of herbicides to seagrass has received more and more attention.In order to protect China's seagrass resources,we studied the ecological functions of seagrass:carbon sequestration,environmental improvement and food provision in Sanggou Bay,Shandong Province.A preliminary analysis was conducted to investigate the herbicide contamination in this bay.Then we compared the toxicity of herbicides atrazine and prometryn,which were found to have a high residual concentrations,to 4 seagrass species.The chronic effects of atrazine on the physiology,sexual reproduction,and metabolism of eelgrass?Zostera marina L.?were conducted.In addition,the metabolic response of eelgrass to short term high-temperature and the combined effect of high temperature and herbicides on eelgrass was also studied.This work will provide a theoretical basis for the protection of seagrass in China,and it will also facilitate the managing of the coastal environment and the make of related laws.The main findings are as follows:1)Ecological functions of seagrass in Sanggou BayThe biomass,primary productivity,and tissue carbon content of eelgrass in the eelgrass bed in Sanggou Bay,Shandong Province,were investigated.The carbon sequestration of the primary carbon sequestration were calculated.The results showed that biomass of eelgrass varied between 313.5 and 769.3g DW m^-2,with the maximum of 738.1g DW m^-2 in summer.Primary production was about 2.0-6.4 g DW m^-22 day^-1 and tissue carbon content was 35.5%.Storied carbon of the eelgrass meadow from primary production was about 543.5 g C m^-2yr^-1.We compared the water temperature and dissolved oxygen in the eelgrass patches with the adjacent sandflat.of a sea cucumber pond.Water temperature in the bottom of eelgrass patch was 0 to 0.33?lower than the naked sandflat,while in area with mid to high?50-100%?eelgrass coverage,resolved oxygen in surface water was 0.12-0.57 mg l^-1 higher.Stable isotope signatures?¹³C and?¹⁵N of sea cucumbers A.japonicus was differed from those in adjacent costal seagrass habitat.A strong role of Z.marina matter as sea cucumber food sources was indicated from the estimation of SIAR mixing model.However in adjacent coastal seagrass bed the contribution of seagarass Z.caespitosa matter to A.japonicus was lower than SPOM and brown seaweeds.These results demonstrate that Z.marina could reduce the bottom temperature in the pond and increase surface dissolved oxygen.Cultured A.japonicus consume relatively higher amounts of Z.marina than other organic sources implied the importance of seagrass habitat in the pond environment.2)Herbicide risk assessment in surface waters and the surrounding area of Sanggou BayThis study investigated the residual atrazine in surface waters and the surrounding area of Sanggou Bay during the summer wet season in 2015.The results showed that the average concentration of atrazine was 106.3 ng l^-1 in Sanggou Bay.The trend of the distribution showed higher concentrations along the southwest terrestrial coast than within the bay.The risk index of primary producers in the environment was 0.081.However,higher atrazine concentrations were observed in the surrounding freshwater basins,with a maximum of up to 489.1-701.2 ng l^-1 and a risk quotient of 0.41-0.58.Sanggou Bay is an important bay for mariculture and seagrass distribution in China and cautions should be taken when a combination of atrazine and other environmental factors threaten primary producers or cultured organisms.3)Comparison of the herbicide atrazine and prometryn's acute toxicity on four seagrass speciesExperiments were conducted to compare the effects of the photosystem II?PSII?inhibiting herbicide atrazine and prometryn(1?g l^-1,5?g l^-1 and 25?g l^-1)on four species of seagrass?Z.marina,Z.caespitosa,Z.japonica and Phyllospadix iwatensis M.?in north China.Results showed that maximum quantum yield of Z.japonica was significantly depressed at 1?g l^-1 prometryn and 5?g l^-11 atrazine during 72h exposure,while Z.marina and Z.caespitosa was depressed at 5?g l^-1 prometryn and atrazine.In the same concentration prometryn showed higher toxicity than atrazine for all of the species in this study and Z.japonica was the more sensitive one.4)Chronic effects of atrazine on the physiology,sexual reproduction,and metabolism of eelgrassWe exposed seagrass Z.marina L.,which were in the process of sexual reproduction,to elevated atrazine concentrations(1,3 and 10?g l^-1)for 30 days.Results showed that atrazine significantly inhibited photosynthetic efficiency??F/F'm and Fv/Fm?,while did not affected the sexual reproductive ability?i.e.,number of ovaries?of Z.marina.Atrazine changed the tissue nitrogen content and C:N ratio and also reduced levels of sugars and TCA intermediate.This study shows that long term atrazine exposure(10?g l^-1)decreased energy supply and changed carbon and nitrogen metabolism.Atrazine-induced increases in?-aminobutyric acid?GABA?and 1-aminocyclopropane carboxylic acid?ACC?,which may be involved,either in combination or individually,in metabolic or signal transduction processes.5)Photosynthetic and metabolic responses of eelgrass Z.marina L.to short-term high-temperature exposure and the combined effects of high temperatures and the herbicide,atrazine.Photosynthetic physiology and metabolic changes of eelgrass in responding to48h exposure to 32°C were investigated.The results showed that high temperature induced significant inhibition of photosynthetic efficiency??F/Fm'??23.9%lower than the control?,enhanced respiration?58.3%higher?,and decreased the contents of carbohydrate decomposition products and the tricarboxylic acid?TCA?cycle intermediate products,indicating that the energy supply of the eelgrass may be insufficient at a high temperature.The combined effects of thermal stress?at 26-32??and the herbicide atrazine(at concentrations of 0,3 and 10?g L^-1)on eelgrass were studied in a 7-day exposure experiment.The results showed that both atrazine and temperatures above 30?inhibited the photosynthetic efficiency and energy conversion potential of the photosystem II?PSII?as indicated by the effective quantum yield??F/F'm?and the maximum yield?Fv/Fm?,respectively.High temperatures?of 31 and 32??decreased the Chl a content and stopped the leaf growth of eelgrass.Atrazine concentration had no effect on the photosynthetic pigments at all temperatures;however,decreased leaf growth rate was detected at30?.A high level of agreement between the observed and predicted inhibition of photosynthesis by an Independent Action?IA?model demonstrates that the combined effects of high temperature and atrazine are more harmful to eelgrass than is a single pressure.The present study adds further evidence for seagrass protection and environmental management under the hypothesis that thermal stress combined with herbicides pose a greater threat to seagrasses.