Spatial and temporal distribution characteristics and influencing factors of nitrogen and phosphorus pollution in Zhanjiang Bay,Guangdong Province
As one of the most productive places on Earth,protecting the bay is an important part of the construction of beautiful bay.Based on the point survey data of Zhanjiang Bay from 2015 to 2021,the spatial and temporal distribution characteristics of seawater quality,oncentration of active phosphate(DIP)and inorganic nitrogen(DIN)in Zhanjiang Bay were analyzed.The eutrophication and nutrient structure of Zhanjiang Bay were evaluated by the N/P ratio,eutrophication index and potential eutrophication assessment model,and discussed the main pollution sources and influencing factors.Results showed that the main area of Zhanjiang Bay were inferior to the fourth category of national sea water quality standard,and the main pollutants were DIP and DIN.The average annual concentration of DIP showed a downward trend,while DIN showed a trend of first increased and then decreased.The areas with high DIP and DIN concentrations were mainly distributed to the northern region of Maxi slope and the eastern of Nanshan waterway of Zhanjiang Bay.And the concentration of DIP and DIN showed a spatial variation trend of decreasing from inside to outside in Zhanjiang Bay.The water quality of Zhanjiang Bay shows obvious different characteristics,which may be affected by the input of terrestrial pollution into the sea and coastal rivers,the biochemical action of organic matter in the bay water,the topography and hydrodynamic conditions of the bay.The DIN/DIP ratio in Zhanjiang Bay is relatively low,ranging from 5.33 to 11.16,and nitrogen was the main potential limitation.The DIN/DIP ratio in the northern,central and southern region of Zhanjiang Bay is relatively low(N/P ≤ 8),land-based emission reduction may be the main reason for the change of nutrient structure.The eutrophication index of Zhanjiang Bay varied from 9.35 to 46.72,has reached a severe eutrophication,with the eutrophication level slightly higher in summer and autumn than in winter and spring due to the influence of a large amount of land-based pollution input in flood season.The potential eutrophication level of Zhanjiang Bay changed from the medium nitrogen limited potential eutrophication to the eutrophication state,which may be related to the influence of Suixi River and land-based pollution of coastal domestic sewage,industrial wastewater and agricultural pollution,and changed the nutrient structure of Zhanjiang Bay.In order to improve the water quality of Zhanjiang Bay,the pollution control of Suixi River and other land-based sources should be promoted simultaneously.The research and the proposed control countermeasures can provide useful reference and support for the precise pollution control in Zhanjiang Bay.
Zhanjiang Baynitrogen pollutionphosphorus pollutionspatial and temporal distributioninfluencing factors
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