三峡水库典型支流上游区和回水区营养状态分析

Trophic status analysis of the upper stream and backwater area in typical tributaries,Three Gorges Reservoir

2006年3、5、8月,对三峡水库成库后5条支流的上游区和回水区水质参数及营养因子分布进行了初步研究.研究结果表明,支流高锰酸盐指数范围在1.00-2.50mg/L、COD范围为6.00-26.5mg/L,上游区与回水区有机物含量差异不大,支流目前未受到有机物污染影响.NH_4^+-N范围为0.039-0.367mg/L,各支流含量均为丰水期最大.TN范围在0.58-1.67mg/L,TP范围在0.005-0.133mg/L,支流回水区TN和TP含量均远高于水体发生富营养化的最低限制值,水体存在发生富营养化的风险.大多支流N/P比值处于适宜藻类生长范围.Chl.a浓度范围为0.94-28.9mg/m^3,各支流回水区Chl.a浓度均为5月最大河流回水区Chl.a浓度高于上游区,上游区、回水区Chl.a含量有显著差异.选用修正的Carlson营养状态指数(Trophic State Index)TSI_M法,评价了支流水体营养状态,TSI_M指数范围在36.0-64.2,上游区除龙河、澎溪河5月达到富营养水平外,其余支流均为贫-中营养水平.回水区各支流均达到中-富营养水平.支流回水区营养状态指数均高于上游区,但各支流增加幅度不同.支流回水区水体营养状态明显受三峡水库蓄水水体流速减缓的影响.Chl.a与COD(n=15,P<0.01)呈极显著正相关,与其它营养因子无明显相关关系.三峡水库完工后,支流回水区水体流速减缓,富营养化趋势可能加重.

Through sampling and analyzing in 5 typical tributaries of Three Gorges Reservoir, parameters of the water quality and main nutrients were monitored in Mar. , May and Aug. of 2006. The variation of perruenganate index of oxygen demand and COD ranged from 1.00 -2.50mg/L and 6.00 -26.5mg/L respectively. Concentration of organic contamination was not discrepancy in upstream and backwater areas. Values of ammonia nitrogen （ NH4^＋ -N ）, total nitrogen （TN） and total phosphorus （TP） were 0. 039-0. 367mg/L, 0.58- 1.67mg/L and 0. 005 -0. 133mg/L, respectively. Concentration of NH4^＋ -N in Aug. was higher than thoses in Mar. and May, when concentrations of TN and TP were largely exceed the minimum limited value of eutrophic state. The ratio of TN and TP were favored well for algae growth in nearly all tributaries. Chl. a ranged from 0.94 - 28.9mg/m^3. Chl. a values in backwater areas of tributaries wcrc exceed upstream and the concentration of Chl. a in May was higher than in Mar. and Aug. Utilizing the method of modified Carlson trophic state index （ TSIM ） has assessed the trophic states of the studied area. The values of TSIM ranged from 36.0 - 64.2, showing that the trophic state of upstream area was oligotropher to mesotropher and the backwater areas were mesotropher to cutrophcr. Trophic state of backwater areas were poorer than upstream, and was affected by impoundment of the Three Gorges Reservoir. There was a significant positive correlation between Chl. a and COD, but Chl. a wasnot significant correlation with other nutrient factors. After the Three Gorges Reservoir was completed in 2009, eutrophic trend of tributaries in backwater areas would be more serious with the decrease of flow velocity.