海南岛三大流域“十三五”水质变化特征及“十四五”趋势预测

为服务海南自由贸易港水生态环境保护，基于海南省地表水环境质量监测网监测数据，对海南岛南渡江、昌化江、万泉河三大流域“十三五”期间水质状况、主要污染物浓度、综合污染指数变化进行了分析，采用Spearman秩相关系数研判其污染变化特征，并采用均值GM(1,1)模型（EGM）预测“十四五”期间水质变化趋势。结果表明：“十三五”期间，海南岛三大流域水质状况总体呈稳中向好趋势，南渡江、万泉河流域水质优良比例分别上升至96.3%、100%，昌化江流域水质优良比例保持在100%；三大流域COD_Mn、COD_Cr、氨氮、总磷浓度年均值均处于较低水平，低于GB 3838—2002《地表水环境质量标准》Ⅱ类标准限值，其中COD_Cr年均值均低于Ⅰ类标准限值，“十三五”期间除氨氮浓度下降外，其他指标均有不同程度的上升或波动，上升幅度为6.7%~23.8%；干流综合污染指数均小幅下降，下降幅度为0.03~0.04，主要支流综合污染指数自上游到下游呈波动上升的空间变化特征。EGM预测结果表明，“十四五”期间海南岛三大流域干流和绝大部分支流水质综合污染指数呈上升趋势，最大上升幅度达108.3%，三大流域水环境仍面临较大的压力，尤其是支流汇入带来的污染负荷不容忽视。“十四五”期间，应以系统保护思路，落实“六水共治”“一河一策”等措施，进一步改善三大流域水质。

Characteristics of water quality change during the 13th Five-Year Plan period and trend prediction during the 14th Five-Year Plan period in three major basins of Hainan Island

Based on the monitoring data of Hainan Province surface water environment quality network, the water quality, concentration of major pollutants, variation of composite pollution index in three major basins of Nandu River, Changhua River, Wanquan River in Hainan Island during the 13th Five-Year Plan period were analyzed, and Spearman rank correlation coefficient was used to research and judge the pollution changecharacteristic, and the mean GM(1,1) model (EGM) was used to predict the trend of water quality change during the 14th Five-Year Plan period for servicing the water ecological environment protection of Hainan Free Trade Port. The results showed that the water quality of three major basins in Hainan Island was getting better steadily during the 13th Five-Year Plan period. The proportion of Grade Ⅰ-Ⅲ water quality of Environmental Quality Standards for Surface Water (GB 3838-2002) in Nandu River basin and Wanquan River basin increased to 96.3% and 100%, respectively. The proportion of Grade Ⅰ-Ⅲ water quality in Changhua River basin remained at 100%. The average annual concentrations of permanganate index, chemical oxygen demand, ammonia nitrogen and total phosphorus were all at a low level, which were lower than the standard limits of Grade Ⅱ, and the average annual concentration of chemical oxygen demand was lower than the standard limits of Grade Ⅰ. The average annual concentration of ammonia nitrogen was decreased during the 13th Five-Year Plan period. The average annual concentrations of permanganate index, chemical oxygen demand and total phosphorus were increased or fluctuated during the 13th Five-Year Plan period, with an increase range of 6.7% to 23.8%. The composite pollution index of the mainstream declined with a range of 0.03 to 0.04. The composite pollution index of the main tributaries increased with fluctuations from upstream to downstream. EGM predicted that during 14th Five-year Plan period, the comprehensive pollution index of the mainstreams of three major basins and most of the tributaries showed an upward trend, with a maximum increase of 108.3%. The water environment of three major basins in Hainan Island would face high pressure, and especially the pollution load from the tributaries should not be neglected. According to the prediction results, in order to improve the water quality of the three major basins, it was necessary to implement measures such as “Governance of Six Waters” and “One River One Policy” in a systematic protection approach during the 14th Five-Year Plan.