Study On Pollution Stress And Ecological Damage Assessment Of Oil Spill In Estuarine Tidal Flat Ecosystem

The Yangtze River Estuary is a biodiversity reserve and one of the most important ecological sensitive areas in the world,with its special habitat conditions and global significance.At the same time,with the development of the Yangtze River shipping,the probability of sudden pollution accidents,especially oil spill accidents,are becoming more and more serious.Not only structure and function of estuarine tidal flat ecosystem,but also urban ecological security would be taken a great threat.In this paper,taking the " 12.30" typical estuary oil spill as an example in the Yangtze River estuary,we study the pollution effects of sediment and water on the estuarine wetland environment,as well as the dynamic response characteristics of macrobenthic community and typical species at the tidal flat under pollution stress after accident occurred.We also carried out the ecological damage assessment of estuary oil spill,and put forward the ecological environment pollution damage assessment system proposal.It will provide scientific evidence and technical support for further establishment and improvement of estuary oil spill accident emergency disposal,investigation,evaluation,management,repair technology and the managCement system.The main results are as follows:1)About 90%of the oil was adsorbed to the estuary shoreline wetlands after oil spills occurred,because of the terrain,tides,waves and other synergies.After emergency treatment,the content of TPH and PAHs in the sediments of the high tidal flat was significantly higher than those in the control point and the corresponding low tidal flat(P<0.01),and it also presented a discontinuous gradient distribution.There was a significant positive correlation between TPH and PAHs in sediments of high tidal flat(P<0.01).In C7?C36 TPH composition was the highest,and PAHs were mainly composed of 2?3 rings.Tidal sediments in this research area were obvious affected by the heavy oil pollution of the accident.2)After the emergency treatment,the content of PAHs in the surrounding waters around beach continued to decline,and the sediments were disturbed during the secondary restoration and released the pollutants.As the time went on,the proportion of PAHs in water was increasing.The sump simulation experiments show that,under the action of tidal scouring,TPH in surface sediments can be released into water at a certain rate(water temperature 27.5?,Csed = 78731e-0.083t).The TPH in the bottom sediments was more difficult to release,and the water temperature had a great effect on the release of TPH in sediments.The lower the temperature was,the slower the release rate was.3)When oil spill accident happened,benthic taxa like mollusk and crustacea,which were dominant species in the region originally were replaced by annelid like the resistance groups of animals(such as hypertrichiasis,oligochaeta).After two years,the crustacean would become the dominant group again,and annelid would still occupy a certain advantage than mollusk.At this time;the average habitat density and biomass of macrobenthic fauna in this region were 53.44 ind./m2 and 6.66 g/m2,compared with the post-emergency treatment was increased(38.19 ind./m2 and 5.15 g/m2),but there was still a large gap compared with the region's historical data(582.23 ind./m2 and 171.08 g/m2).4)For Chiromantes dehaani,the content of TPH in different tissues and organs was significant different.Besides,the visceral tissue was more likely to accumulate contaminants than muscle tissue,and there was the significant positive correlation between them(P<0.01).At the time scale,the content of TPH in organisms decreased significantly than one year before(P<0.05),and it decreased much in the visceral tissue.The content of TPH in muscle and visceral tissue were linearly correlated with the content of TPH in the corresponding point sediments,indicated that the TPH content in organisms can be directly affected by the accumulation of TPH in sediments.5)This oil spill accident brought about a huge loss,which included 281100 yuan in the supply of terrestrial ecosystem products,5266100 yuan in regulation services,13079100 yuan in ecological support services,1393000 yuan in cultural and entertainment services,and the total loss of the ecosystem services in that year was 20019300 yuan.The actual accident emergency disposal cost,secondary rehabilitation cost and the total investment was 8422100,13461600,and 21883700 yuan,respectively.Oil spill in estuarine beach region caused a loss of value in unit area of ecosystem services of 294400 yuan per hectare per year,and a clean-up project investment of 321800 yuan per hectare.In c.onclusion,the results indicate that the pollution stress and the ecological damage in estuarine beach region caused by oil spill has the unique characteristics,and it can be affected by combined factors,such as tides and habitats.This paper explores the damage of typical oil spill to the environment and biology in the wetland,and makes cooperative analysis on the TPH and PAHs pollution in the sediments.It is also illustrated the dynamic changes of TPH distribution in macrobenthic and the TPH distribution in organisms based on the nearly 3-year field observation,which further confirms the causal relationship between the environmental pollution and the biological damage of the oil spill,and also makes up for the lack of research on the Yangtze River estuary area and can be the foundation of the investigation,disposal,assessment and repair for similar oil spill accidents.