Changes in nitrogen and phosphorus concentrations in Lake Taihu, 1985-2015

分析了太湖水体氮、磷浓度1985-2015年的演变趋势.结果表明，近30年来，全太湖水体氮、磷指标总体呈先恶化、后好转的波动变化趋势.总氮（TN）浓度年均值在1.79～3.63 mg/L之间，30年平均值为2.62±0.03 mg/L，总磷（TP）浓度年均值在0.04～0.15 mg/L之间，30年平均值为0.086±0.001 mg/L，1996年全太湖TN （3.84 mg/L）和TP （0.15 mg/L）浓度年均值均达历史峰值.氮、磷逐月浓度变化情况显示，TN浓度呈明显季节性变化规律，最高值集中出现在3、4月，概率分别为67%和33%，最低值则分布在8、9、10、11月，概率分别为18%、41%、29%和12%，而TP浓度则没有明显的季节性变化规律.太湖各湖区水体氮、磷浓度变化空间异质性明显，西部水域和北部水域变化幅度大于东部水域、南部水域和湖心区.太湖水体氮、磷浓度的长期变化趋势显然和流域经济发展及各项环保管理措施的实施密切相关，同时也受到重大水情变化的影响.此外，在相对封闭的局部湖湾水体可以通过水利调度等综合治理措施短时期内改善氮、磷指标，但大太湖水质的改善任重而道远.;This paper analyzed the evolution trends of nitrogen and phosphorus concentrations of Lake Taihu for a period from 1985 to 2015. The result showed that there occurred water deteriorating at first years by records of the nitrogen and phosphorus indicators, and then the water improved in the whole Lake Taihu during the past three decades. The annual average of total nitrogen(TN) varied between 1.79 and 3.63 mg/L, and the thirty-year-average is 2.62±0.03 mg/L. The annual average of total phosphorus(TP) varied between 0.04 and 0.15 mg/L, and the thirty-year average is 0.086±0.001 mg/L. In 1996, the annual average of TN and TP concentrations in the whole Lake Taihu reached the historical peaks of 3.84 and 0.15 mg/L, respectively. Monthly records showed that, there was significant seasonal variation in the TN concentrations, in which the maximum usually appeared in March and April with the probability of 67% and 33%, respectively. The minimum usually appeared in four months between August and November, with the probability of 18%, 41%, 29% and 12%, respectively. However, the TP did not show significant seasonal variations. There were spatial changes in nitrogen and phosphorus concentrations in different areas of the lake. The water bodies in the western and northern showed greater changes than in areas of the eastern, southern and center. The long term changes in TN and TP of Lake Taihu are closely linked with the drainage economy development and the environment protection actions. As an example of Lake Wuli, a small water body in the northern Lake Taihu, there occurred remarkable decreases in the N and P concentrations in 2015 after many years of treatments such as water interception, water source control, and dredging and ecological restoration. The successful experience for Lake Wuli leads us to believe that it is possible to manage the small water bodies well, although waive for efforts on the improvement of the whole Lake Taihu.