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利用近20年监测数据，对洞庭湖总氮（TN）和总磷（TP）浓度的时空分布特征及其三峡工程运行后的变化进行了分析．结果表明，洞庭湖 TN 和 TP 浓度的年均值分别为1．12—2．06 mg·L－1和0．062—0．146 mg·L－1，TN浓度呈显著上升趋势（P＜0．05），TP浓度变化平稳．TN和TP浓度总体均表现为枯水期＞平水期＞丰水期，其中枯水期、平水期与丰水期TN浓度差异具有统计学意义（ P＜0．05）．下游S6—S11断面TN浓度明显高于上游S1—S5断面，除S6断面外，洞庭湖各断面之间TP浓度相差不大；TN浓度总体表现为东洞庭湖＞南洞庭湖＞西洞庭湖，各湖区相互之间TN浓度差异具有统计学意义（ P＜0．05），TP浓度总体表现为西洞庭湖＞东洞庭湖＞南洞庭湖．三峡工程运行前后，TN浓度的时空分布基本保持一致；TP浓度的季节分布由三峡工程运行前的平水期＞枯水期＞丰水期变化为三峡工程运行后的枯水期＞平水期＞丰水期，其空间分布由三峡工程运行前的东洞庭湖＞西洞庭湖＞南洞庭湖变化为三峡工程运行后的西洞庭湖＞东洞庭湖＝南洞庭湖．洞庭湖TN和TP浓度的空间分布特征与其污染来源有关．三峡工程运行前后洞庭湖TP浓度的时空分布格局变化与其水沙条件变化有关．

Spatial?temporal distribution of total nitrogen ( TN ) and total phosphorus ( TP ) concentrations in Dongting Lak and their changes after Three Gorges Project operation were analyzed using monitoring data for the recent 20 years. The results showed that the annual average
concentrations of TN and TP varied from 1. 12 to 2. 06 mg·L-1 and from 0. 062 to 0. 146 mg·L-1 , respectively. TN concentration showed a significant upward trend ( P<0.05) , while TP concentration had no significant change. Concentrations of TN and TP were generally in the order of low water period>normal water period>high water period, and TN concentrations had statistical significance ( P<0.05) . TN concentration in downstream sections ( S6—S11) were significantly higher than that in upstream sections ( S1—S5 ) . However, TP concentration had no significant differences except section S6. The decreasing order of TN concentration as follows:East Dongting Lake>South Dongting Lake>West Dongting Lake ( P<0.05) . TP concentration was generally in the order of West Dongting Lake>East Dongting Lake>South Dongting Lake. Spatial?temporal distribution of TN concentration remained essentially the same after Three Gorges Project operation. Before the first impoundment of Three Gorges Project, the decreasing order of TP concentration as follows:normal water period>low water period >high water period. After Three Gorges Project operation, TP concentration was highest in low water period. The temporal distribution of TP concentration also changed. The decreasing order of TP concentration before Three Gorges Project operation was as follows:East Dongting Lake>West Dongting Lake>South Dongting Lake. While TP concentration was highest in West Dongting Lake after Three Gorges Project operation. Characteristics of the spatial distribution of TN and TP concentrations were related to their pollution sources. The change of spatial?temporal distribution pattern of TP concentration was related to the changes of water and sediment conditions in Dongting Lake after Three Gorges Project operation.