云南昭通渔洞水库枯水期水质及其变化特征

Characteristics and Variation of Water Quality During Dry Season in Yudong Reservoir of Zhaotong District in Yunnan Province

云南昭通渔洞水库集城市供水、农业灌溉、防洪、发电、渔业等功能,了解其枯水期水质及变化对指导水力调度,保障水库水质和水量稳定具有重要的科学意义。该文通过在库区不同水域布设30个监测点,在1月和5月对水库表层、中层和底层水样进行采集,分析了水质主要理化参数和营养物浓度,并利用综合指数法对水质进行了评价。结果表明:从1月到5月,水库水温、电导率和pH显著升高(P<0.05),但表层水透明度显著地下降(P<0.05)。平均COD从(8.21±3.10) mg/L降至(7.68±2.26) mg/L。水域和水层不同,COD各异,但总体上差异不明显(P>0.05)。1月份水库平均TN为(2.65±0.35) mg/L,其中NO_(3)^(-)-N占约90%,NH_(3)-N仅1.5%,平均值则主库区显著低于库湾(P<0.05);而到了5月份,平均TN为(0.96±0.12) mg/L,NO_(3)^(-)-N占约74%,NH_(3)-N仅6.7%,且底层显著高于表层(P<0.05)。水库TDP和SRP在1月份分别为(4.92±1.36)μg/L和(2.25±1.89)μg/L,且水域不同,它们的含量各异;到了5月份,则分别上升至(11.6±11.0)μg/L和(6.72±9.38)μg/L。综合指数评价结果说明,渔洞水库在1月为Ⅲ类水质,但到了5月上升至Ⅱ类,表明渔洞水库在枯水期具有较强的自净能力。枯水期渔洞水库的自净能力可能与硅藻生长有关。水柱中溶解硅较高,水温升高利于硅藻生长,从而消耗了水柱中的NO_(3)^(-)-N和溶解硅,水质得到了提升。

Yudong Reservoir of Zhaotong District in Yunnan Province plays an important role of local drinking water supply,irrigation,flood control,electric power generation,and fisheries.It is of great scientific significance to understand the water quality and changes during the dry period to guide hydraulic scheduling and ensure the stability of water quality and quantity in the reservoir.In this paper,by setting 30 monitoring points in different water fields of the reservoir and collecting water samples from the surface,middle and bottom layers of the reservoir during the dry period(January and May),the main physicochemical indicators and nutrient concentrations of water quality were analyzed and the water quality was evaluated by using the integrated index method.The results showed that that water temperature,conductivity and pH were significantly increased from January to May(P<0.05),but transparency was significantly decreased(P<0.05).Mean COD in whole reservoir was decreased from(8.21±3.10)mg/L in January to(7.68±2.26)mg/L in May.Water fields and layers differed,COD presented in difference indeed,but not reaching a significant level(P>0.05).Mean TN was(2.65±0.35)mg/L in January,in which NO_(3)^(-)-N and NH_(3)^(-)N accounted for 90%and 1.5%,respectively,and it was significantly lower in main reservoir area than bays(P<0.05).However,TN decreased to(0.96±0.12)mg/L in May,in which NO_(3)^(-)-N and NH3-N accounted for 74%and 6.7%,respectively,and it was significantly higher in bottom water layers than surface water layers(P<0.05).Mean TDP and SRP in January were(4.92±1.36)μg/L and(2.25±1.89)μg/L,respectively,and changed with different water fields.However,TDP and SRP in May increased to(11.6±11.0)μg/L and(6.72±9.38)μg/L,respectively,in which different water fields increased by different extents.The integrated indictor showed that the water quality in whole reservoir was in a range of StandardⅢgrade(GB 3838-2002),but it raised toⅡgrade in May,suggesting the reservoir had a strong self-purification potential during dry season.The self-purification potential shall be attributed to the growth of diatoms in surface water layers.A high dissolved Si in the water column and the increase in water temperature during dry season can promote the growth of diatoms,which can consume NO_(3)^(-)-N and dissolved Si with the reservoir water quality improved.