湘江保护治理对水质的影响及原因分析

Analysis of impact and causes on protection and treatment on water quality of Xiangjiang River

湖南省于2016—2018年针对湘江保护和治理开展了第二个“三年行动计划”(简称“行动”),但是其对湘江水系水质的修复效果及其关键因素并不完全清楚。本研究选取湘江干流和支流26个水质监测站的2015—2018年水质逐日监测数据,分析该行动对湘江水系水质变化的影响及其原因。结果表明,调查期间水质各项指标基本保持在国家地表水Ⅲ类水质及以上。水体污染时空变化特征主要表现在:从上游到下游,干流氨氮富集,总磷先上升后下降;支流比干流污染更严重,乡村站点比城镇站点的氨氮浓度低、总磷浓度高;氨氮冬季高、夏季低,总磷秋季达到峰值。水体污染与pH、溶解氧浓度负相关,而与高锰酸钾指数正相关。氨氮和总磷可能的主要来源分别是城镇工业污染排放和农业源排放。本次“行动”使水体氨氮浓度、总磷浓度、高锰酸钾指数分别下降32.24%、30.03%和5.80%,溶解氧浓度增加4.66%。污染改善的主要原因可能在于干流沿岸城镇和工业污染的氮磷协同减排,其次是乡村和支流的农业源减排。因此,湘江流域水体的后期治理应该更多地关注农业源水体污染物尤其是磷的排放。

Hunan Province launched the second“Three-year Action Plan”for protection and treatment of Xiangjiang River from 2016 to 2018.However,restoration effect on water quality of Xiangjiang River and key factors were not entirely clear.In this study,daily water quality monitoring data from 26 water quality monitoring stations in the main stream and tributaries of Xiangjiang River from 2015 to 2018 were selected to analyze impact of action on water quality changes in the Xiangjiang River.The results showed that water qualities indexes remained above class III of national surface water during the investigation period.Temporal and spatial variations were as follows:ammonium was accumulated while total phosphorus was elevated and then declined along the trunk stream.The pollution of tributaries was more serious than that of main stream,and ammonia nitrogen concentration was lower and total phosphorus concentration was higher in rural stations than in urban stations.Ammonia nitrogen concentrations was high in winter and low in summer,while concentrations of total phosphorus peaked in autumn.Water pollutants were negatively related with pH and dissolved oxygen,but positively correlated with potassium permanganate index.The main possible sources of ammonia nitrogen and total phosphorus were industrial and agricultural emissions,respectively.Due to the action,ammonia nitrogen,total phosphorus,and potassium permanganate index reduced by 32.24%,30.03%and 5.80%,respectively,while dissolved oxygen increased by 4.66%.These mitigations were primarily contributed by collaborative control of nitrogen and phosphorus in industrial emissions along trunk stream,and followed by agricultural source emission reduction in villages and tributaries.Therefore,future protection and treatment of Xiangjiang River system should be more focused on the discharge of agricultural pollutants,especially phosphorus.