珠江中下游表层水体COD_(Mn)时空分布特征及水环境评价

Spatio-temporal Characteristics of COD_(Mn) in Surface Waters of Middle and Downstream of the Pearl River and Water Environment Evaluations

为了解珠江中下游表层水体中COD_(Mn)的时空特征及影响因素,2015年对该水域进行了季节调查,并对其水环境质量进行了初步分析与评价。调查期间,COD_(Mn)质量浓度范围为1.14~15.8 mg·L^(-1),平均值为3.93 mg·L^(-1)。从季节变化角度看,枯水期(3月和12月)的COD_(Mn)质量浓度明显高于丰水期(6月和9月)。从空间分布特征看,调查区域的COD_(Mn)质量浓度分为3个层次,对应着3个聚群。其中,聚群1代表了西江干流沿线站位,聚群2代表了邻近广州市区的站位,聚群3代表了珠江珠三角河网中部站位。聚群2的COD_(Mn)质量浓度最高,聚群1的质量浓度最低,聚群3介于聚群1和聚群2之间。与其他理化因子的相关分析表明,COD_(Mn)与盐度、电导率及DO呈极显著负相关;与总氮、总磷、硅酸盐及叶绿素a呈极显著正相关。基于COD_(Mn)质量浓度的水环境评价的季节特征显示,丰水期综合水质评价为I类到Ⅱ类水质,而枯水期37.6%的站位未达到Ⅲ类水质标准,总体上丰水期水质优于枯水期。空间特征显示,不同区域的水环境质量存在较大的差别。其中,西江干流沿线的P_i均值为0.47,水体受污染少,全年水质保持在I类到Ⅲ类;广州市区附近的Pi均值为1.21,受污染较重,不符合Ⅲ类水质标准的站位占42.7%;河网中部水域的Pi均值为0.60,仅12.5%调查站位为Ⅳ类水质,其余站位均达到Ⅲ类水质以上。分析认为,径流是影响珠江中下游表层水体COD_(Mn)季节变动的主要因素;人类活动引起的生产和生活排污是影响该水域COD_(Mn)空间分布的重要因素。

In order to understand the spatio-temporal pattern of CODMn and impacting factors in the surface water of the middle and downstream of the Pearl River, seasonal investigations were carried out in 2015. During the investigation, the mass concentration of CODMn was in the range of 1.14~15.8 mg·L^-1, with an average of 3.93 mg·L^-1. For seasonal characteristics, CODMn of the dry season （March and December） was significantly higher than that of the flood period （June and September）. Runoff is the main factor affecting the seasonal variation. As for the spatial distribution pattern, the content of CODMn in the studied area could be divided into three levels, represented by three clusters. Among them, cluster 1 represents the sites along the West River, cluster 2 represents the adjacent sites of Guangzhou city, and cluster 3 represents the central Pearl River Delta. The highest content of CODMn was found in cluster 2, followed by that in cluster 3 and the lowest in cluster 1. Correlation analysis with other physical and chemical factors showed that CODMn had a significant negative correlation with salinity, conductivity and DO, and was significantly positively correlated with total nitrogen, total phosphorus, silicate and chlorophyll a. Pollution conditions and water quality levels based on CODMn was also analyzed. The seasonal results showed that water quality during flood periods was between class I and II, while 37.6% sites showed worse than class III. It was obviously water quality in flood periods was better than that in dry sesons. There is a big difference in water quality in different regions. Among them, mean value of Pi along the West River was 0.47, less polluted, and the annual water quality maintained between class I and class III. The mean value of Pi nearing Guangzhou city was 1.21, heavily polluted, and 42.7% sites did not meet the class III water quality standards. The mean value of Pi in central Pearl River Delta was 0.6, only 12.5% sites were worse than class IV water quality, most were better than class III. Above all, runoff is the main factor affecting the seasonal variation of CODMn in the surface water of the middle and downstream of the Pearl River; production and living pollution caused by human activities is an important factor affecting the spatial distribution of CODMn content in the studied regions. Our results are helpful for understanding pollution conditions and environmental protection in the studied area.