仙女湖富营养化特征与水环境容量核算

以典型的亚热带大型水库——江西省仙女湖为例,于2011~2013年季节性监测了仙女湖水体理化指标。采用综合营养状态指数法对其富营养化状态进行了评价,并采用沃伦威德尔模型(Vollenweider)和狄龙模型(Dillon)计算了COD、NH₃-N、TN和TP的水环境容量。结果表明:仙女湖水质总体处于地表水Ⅱ类~Ⅲ类标准,TN 0.32~0.91 mg/L、平均0.59 mg/L,NH₃-N 0.012~0.59 mg/L、平均0.31 mg/L,TP 0.017~0.080 mg/L、平均0.028 mg/L,COD_Mn 1.61~5.59 mg/L、平均2.85 mg/L,Chl-a 0.37~0.95 μg/L、平均0.56 μg/L。从湖区上游到下游,各指标尤其是总氮、总磷、透明度和氨氮呈现明显的趋优变化特征,除TP出现Ⅲ类水质外,其余指标多年持续处于Ⅱ类水质状态;从单因子状态指数来看,采用透明度评价的营养状态最高,大部分湖区持续处于轻度富营养状态;TN和TP评价的营养状态次之,处于中营养水平。仙女湖COD、NH₃-N、TN和TP水环境容量分别为21 208.0、3 528.8、4 991.2和248.1 t/a,分别剩余容量比率56.88%、68.25%、62.89%和13.67%,影响仙女湖水环境容量最突出的环境因子为TP。同时,基于对水环境容量影响因素的分析,最后提出了提高仙女湖区水环境容量的建设性方案。

EUTROPHICATION ASSESSMENT AND ESTIMATION OF WATER ENVIRONMENTAL CAPACITY IN LAKE XIANNV OF JIANGXI

Lake/reservoir eutrophication has become a more and more serious problem. Watershed pollution prevention is the key of eutrophication control. Calculation of water environmental capacity is the important basis of both the pollution prevention and the capacity distribution in the basin. This study is aimed to assess the eutrophic status and estimate the environmental capacity of the Lake Xiannv in Jiangxi Province, a lake with good water quality, in order to provide the reference for the aquatic environmental protection and capacity gross control of main pollutants in this important ecological function zone. From the year of 2011 to 2013, seasonal monitoring of physical and chemical parameters in Lake Xiannv was carried out and parameters included total nitrogen (TN), ammonia nitrogen (NH₃-N), total phosphorous (TP), transparency (SD), chemical oxygen demand (COD_Mn) and chlorophyll a (chl_a). Samples were collected at 4 sites, located in the upper lake-Qianyang Lake (S1-S2) and the lower lake-Wulong Lake (S3-S4), respectively. A comprehensive eutrophic state index was applied to assess the trophic status, and the Vollenweider-Dillon model was employed to analyze the nutrient loading and assimilation capacity of Lake Xiannv. COD, ammonia, TN and TP were used as the control index in calculation of the water environment capacity. Results showed that the water quality of Lake Xiannv could meet Level Ⅱ-Ⅲ standards of water quality for surface water. The mean values (range in parentheses) for TN, TP, NH₃-N, COD_Mn and chl_a were 0.59 mg/L (0.32-0.91 mg/L), 0.028 mg/L (0.017-0.080 mg/L), 0.31 mg /L (0.012-0.59 mg/L), 2.85 mg/L (1.61-5.59 mg/L) and 0.56 μg/L (0.37-0.95 μg/L), respectively. The water quality tended to improve from the upper lake zone to the lower one of the lake. TP was in the status of Level Ⅲ standards in some months, whereas the other indicators were steadily in Level Ⅱ standards. In general, Lake Xiannv was mesotrophic, with higher nutrient levels in the Qianyang Lake area, and the Secchi depth was in the highest trophic state (slightly eutrophic) by the analysis of the single factor index. Loading of COD, ammonia, TN and TP in Lake Xiannv were 21 208.0 t/a, 3 528.8 t/a, 4 991.2 t/a and 248.1 t/a, respectively. The ratio of the remaining capacity of these four pollutants were 56.88%, 68.25%, 62.89% and 13.67%, respectively. TP was selected out as the greatest impact factor on water environmental capacity of the lake. Nutrient loading should be reduced by 72% for phosphorus to achieve water quality meeting Level II standards throughout Lake Xiannv. In this study, the main factors influenced on water environment carrying capacity were analyzed, as well as the variation tendency of water quality and how to improve the water quality of the lake. Based on the analysis of the main influence factors on water environmental capacity, the constructive scheme was proposed for improving water environment carrying capacity in the end.