Abstract
Due to the acceleration of industrialization and urbanization in recent decades, the majority of coastal rivers and estuaries in China have been moderately or severely contaminated by a variety of pollutants. We investigated the spatial and seasonal variations of water nutrients (permanganate index, chemical oxygen demand, biochemical oxygen demand, ammonium, nitrate, total nitrogen, and total phosphorus) and heavy metals (Hg, Pb, Cu, Zn, Se, As, Cd, Cr, Fe, and Mn) in 27 subtropical rivers draining into the South China Sea. Our results indicated that the average concentrations of all water quality parameters except ammonium, total nitrogen, and total phosphorus satisfied the requirements for grade III of the surface water quality standard of China. The concentrations of both nutrients and heavy metals showed a strong spatial variation. Cluster analysis classified the 27 rivers into three spatial clusters corresponding to low, moderate, and high pollution levels. In terms of seasonal variation, the values of chemical oxygen demand and biochemical oxygen demand in wet seasons were significantly lower than those in dry seasons. Multivariate statistical analyses demonstrated that river nutrients might mainly originate from domestic, industrial, and agricultural wastewaters, while heavy metals likely came from industrial activities and natural weathering processes. The findings of this study suggest that for reducing the pollution of subtropical rivers draining into the South China Sea, further efforts should be made to control nitrogen and phosphorus export from catchments.
Highlights
Water quality plays a critical role in determining the ecological conditions and functions of aquatic habitats [1,2]
This study investigated the water nutrient and heavy metal pollution in 27 subtropical rivers draining into the South China Sea and found that the averages of most water quality parameters were lower than the corresponding values of the grade III water quality standard of China
Spatial pattern and cluster analyses revealed that the Lianjiang River was the most polluted, with the highest levels of IMn, COD, BOD5, NH4 +, Hg, Fe, and Mn
Summary
Water quality plays a critical role in determining the ecological conditions and functions of aquatic habitats [1,2]. Excess nutrients and heavy metals in rivers are considered to be the major environmental problems in many countries, and especially in China [3,4,5,6]. Eutrophication, characterized by excessive growth of algae and other aquatic plants, is a common consequence of nitrogen (N) and phosphorus (P) enrichment in rivers and streams [7,8]. Water quality degradation can result in many other ecological problems such as a reduction of aquatic biodiversity, the mortality of benthic communities, and fish deaths [9,10]. Heavy metals can accumulate in the human body via the food chain and lead to serious damage to the nervous system and internal organs [11,12,13,14].
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