Abstract:

Evaluation of coastal water quality and identification of the main factors affecting water quality were the prerequisites for the targeted implementation of environmental protection measures, which would help to improve the coastal water quality and promote the construction of regional marine ecological civilization. This study area included 32 cities along the coastline of South China. Firstly, coastal water quality was evaluated using the single factor standard and comprehensive evaluation index. Second, canonical correspondence analysis and stepwise linear regression analysis were used to explore the correlations between the various impact factors and the quality indicators of coastal water. The results showed that the quality of coastal water of South China in 2017 was mainly influenced by inorganic nitrogen (N), active phosphate (P), and suspended solids (SS). The N and P contents significantly exceeded the Chinese national standards in Xiamen, Ningde, Fuzhou, Zhuhai, Shenzhen, and Qinzhou, which were mainly located in the coastlines of Fujian, Guangxi, and Guangdong provinces. Correlation analysis showed that N, P, and SS pollution were closely related to marine aquaculture. The high quantity of domestic wastewater discharge should also be accountable for N and P pollution. The contents of heavy metal and petroleum pollutants in the coastal waters in 2017 did not exceed the national standard along the coastline of most cities in South China. However, analysis results of the integrated water quality indices indicated that coastal water quality would be more likely affected by the heavy metals and petroleum in these cities (such as Huizhou, Zhanjiang, Jiangmen, Shantou, Zhuhai, and Yangjiang) in Guangdong province, in comparison with other cities. This can be attributed to the vigorous development of local industrial production in these cities. Industrialization is usually related to industrial wastewater discharge. As a result, industrial wastewater discharge was directly related to heavy metal and petroleum pollution. Furthermore, the correlation analysis results found that the heavy metal copper (Cu) is more likely related to the influencing factors in comparison with other heavy metals such as cadmium (Cd), mercury (Hg), and lead (Pb). In addition, frequent water traffic might also affect the pollution level of Cu. At the same time, it was also found that there was a positive correlation between the comprehensive water quality index and the regional gross domestic product. This result partially indicated that environmental infrastructure would be more improvable with economic development, and thus, the treatment efficiency of domestic and industrial wastewater was relatively higher in cities with higher economic levels. As mentioned above, to promote the construction of regional ecological civilization and improve the coastal water quality in South China, these measures can be carried out in these relevant cities and regions along the coastline of South China as follows: (1) The scale and intensity of marine aquaculture should be rationally planned and ecological aquaculture should be recommended; and (2) more attention should be paid to the interception and emission reduction of domestic and industrial wastewater. In particular, the removal efficiency of N and P could be largely improved through technical innovation for existing wastewater treatment facilities. Moreover, the construction of environmental infrastructure should be largely strengthened in these undeveloped cities; and (3) it was also noteworthy that an environmental risk assessment should be carried out before entering the sea for these ships using Cu ion antifouling paint or ships made by Cu-containing metals.

Key words: coastal waters in South China, water quality evaluation, heavy metals, canonical correspondence analysis, stepwise linear regression