洞庭湖出入湖污染物通量特征

采用2010年洞庭湖主要出入湖断面水质、水量监测数据,估算洞庭湖四水(湘江、资江、沅江、澧水)和三口(松滋口、太平口、藕池口)入湖及城陵矶出湖的污染物通量,分析洞庭湖出入湖污染物通量随时间的变化及空间来源组成. 结果表明,2010年洞庭湖经由四水和三口COD_Mn、NH₄+-N、TP入湖通量分别为44.47×104、67.49×103、15.03×103 t,城陵矶出湖通量分别为73.69×104、82.46×103、21.88×103 t. 时间分布上,受水情的影响,洞庭湖污染物入湖通量在年内分配不均,最高值出现在6—7月,三口输入的污染物通量变化与三峡水库下泄流量呈较显著相关；空间分布上,入湖污染负荷主要来源于四水水系(占总入湖污染负荷的82.82%~87.54%),湘江和沅江贡献较大,长江三口入湖量仅占12.46%~17.18%. 此外,与1999—2002年(三峡水库运行前)相比,2010年(三峡水库运行后)洞庭湖三口来水量减少了约1/3,经由三口输入的COD_Mn、NH₄+-N、TP入湖通量减少了49.27%~53.19%,但该变化特征仍需进一步论证. 除入湖河流外,洞庭湖区间径流及湖面受纳降水虽然亦同步影响洞庭湖污染物输入,但该部分污染物通量贡献相对较小. 洞庭湖的污染物控制仍应以强化主要入湖河流输入通量控制为主,并重点兼顾湖区面源污染的治理. 

Characteristics Analysis of Pollutant Influx and Outflux in Dongting Lake

Characteristics analysis of pollutant influx and outflux is important to examine the relationship between Dongting Lake and the Yangtze River, as well as Dongting Lake and its upstream rivers. Based on hydrological and water quality data in the main monitoring sections in 2010, pollutant influxes from four upstream branches (Xiang, Zi, Yuan and Li) and three water inlets (Songzi, Taiping and Ouchi) were calculated for Dongting Lake. The pollutant outflux of Chenglingji outlet was studied as well. Furthermore, spatial-temporal variations and source contributions of pollutant flux were analyzed. The results showed that the pollutant influxes of COD_Mn, NH₄+-N (ammonia nitrogen) and TP (total phosphorus) through the four upstream branches and three water inlets were 44.47×104,7.49×103 and 15.03×103 t, respectively. The total outfluxes of COD_Mn, NH₄+-N and TP were 73.69×104,2.46×103,1.88×103 t in 2010. As for the temporal distributions, uneven monthly pollutant influx during the year was found. A peak value was observed from June to July, which was affected by the characteristics of precipitation and the water flow. The influxes of the three water inlets were significantly correlated with the scheduling operation process of the Three Gorges Reservoir. As for the spatial distribution, the pollutant load of Dongting Lake was mainly from the four rivers system (82.82%-87.54%), with the greatest contribution from the Xiang and Yuan Rivers. The three water inlets in connection with the Yangtze River only contributed 12.46%-17.18% of the total pollutant influx. In addition, more information was achieved based on further analysis of historical documents. Comparing data from 2010 (after the Three Gorges Dam was built) with 1999-2002 (before the dam was built), the runoff from the three water inlets was reduced by one-third, and the influxes of COD_Mn, NH₄+-N and TP were reduced 49.27%-53.19%. However, the characteristics and influence of the change still requires long-term observation and further study. In addition to the four upstream rivers and three water inlets, the runoff around the lake area and precipitation on the surface of the lake also affects the pollutant influx, but the contribution from them is relatively small. For pollution prevention in Dongting Lake, controlling the pollutant influxes from the upstream rivers and water inlets should be the first focus, while non-point source pollution control around the lake area should also be strengthened.