Investigation On The Ecological Environment In The Coastal Waters Of The Yellow River Delta And Analysis Of Its Changing Trend

The coastal waters of the Yellow River delta is important seawater and freshwater intersection area mainly include the western part of Laizhou Bay and the southern part of Bohai bay.There are 1 national nature reserve,5 national Marine special protection zones,and 3 Marine Germplasm resources protection zones within The coastal waters of the Yellow River delta.A large amount of freshwater and sediment transported by the Yellow River every year contains extremely rich nutrients and is a natural bait for marine life.So the coastal sea area of the Yellow River Delta is the natural spawning,hatching and feeding grounds for marine life.In addition to the Yellow River,the Yellow River Delta has more than ten rivers flowing into the sea,such as the Guangli River,Chao River,and the Tiao River,and there are many industrial parks along the coast that are susceptible to land-based pollution.In recent years,large amounts of land-based pollutants have been discharged into the sea,the construction of large-scale marine projects,tidal flat reclamation,over-fishing and pollution of aquaculture waters have damaged the coastal marine ecosystem and declined the fishery resources.Coastal petrochemical and salt chemical production accidents and offshore oil and gas exploitation,storage and transportation,and other pollutant accidents have occurred from time to time,increasing the risk of pollution and ecological pressure,resulting in outstanding environmental problems.Besides,the Laizhou Bay and the Bohai Bay are semi-closed bays,with shallow water depth and poor water exchange.The seawater quality and marine biodiversity index have declined to varying degrees,affecting marine protection areas and aquatic germplasm resources protection areas,The function of marine functional areas such as coastal wetland typical ecosystem.Through the investigation of the marine ecological environment in the coastal area of the Yellow River Delta,the evaluation of its marine ecological environment status,the analysis of its changing trends,and the suggestion of effective measures are of great scientific significance to the marine ecological environmental protection and resource restoration in the coastal area of the Yellow River Delta.From 2015 to 2018,for four consecutive years in March(winter),May(spring),August(summer),and October(autumn),The environment has been investigated and evaluated,and its changing trend has been analyzed.The main conclusions are as follows:(1)Inorganic nitrogen,chemical oxygen demand,active phosphate and petroleum are the main pollutants in the coastal waters of the Yellow River Delta.The area with more serious pollution is mainly located near the entrance of Guangli River in the west of Laizhou Bay and the entrance of Chaohe River and Tiaohe River in the south of Bohai Bay.In different seasons,the monitoring values of stations near the river estuary fluctuate greatly,which is easy to exceed the standard seriously.(2)The results of comprehensive seawater evaluation show that the seawater quality of the nearshore waters of the Yellow River Delta was poor and nutritious in 2015,with good water quality as a whole;poor and nutritious in 2016,with good water quality as a whole;poor and nutritious in 2017,with good water quality as a whole;slightly nutritious in 2018,with good water quality as a whole.The overall quality of marine sediment is in good condition,meeting the quality standard of class I marine sediment.Only in 2015,individual survey stations were polluted by arsenic factor.The biodiversity index H'of large zooplankton and benthic organisms shows that the marine ecological environment in the coastal waters of the Yellow River Delta is lightly polluted from 2015 to 2018;the biodiversity index H' of phytoplankton and small zooplankton shows,In 2015,2016 and 2018,it was a light pollution level,and in 2017 it was a moderate pollution level.(3)The seasonal changes of water temperature,salinity,pH and dissolved oxygen are obvious,and the annual average change trend is relatively stable;the annual average value of chemical oxygen demand concentration shows a trend of first decreasing and then increasing;the fluctuation of nutrients in the same season in different years is large,The inorganic nitrogen content showed an upward trend as a whole,and the active phosphate content showed an upward trend year by year;the interannual change of petroleum showed an overall downward trend.In 2015-2018,the total number of phytoplankton species and the number of dominant species decreased year by year;the total number of large zooplankton,small zooplankton,benthic species,and the number of dominant species overall declined first and then increased.Interannual trends.