我国南方桉树(Eucalyptus)人工林区水库突发性泛黑形成机理初探

Mechanism of “black-water ” occurrence in the reservoirs with Eucalyptus plantation,southern China

桉树(Eucalyptus)在我国南方大规模种植,最快两三年成材,经济价值高,但近来却被认为是"抽水机"、"绿色沙漠",甚至传言"有毒".特别是近年来桉树人工林区水库出现的"泛黑"现象——水体呈现黑褐色并伴有涩味,给种植地附近居民造成了很大的恐慌.并且其黑水形成机理、物质来源及触发条件等尚不清楚.基于此,本文选取我国南方桉树人工林区典型水库,开展了水体"泛黑"现象成因研究:于2015年8月2016年4月对广西南宁市那降水库、天雹水库、百合水库分别进行了4次水体垂直分层采样,测定其理化指标,并结合当地水库管理站提供的水文数据进行综合分析.结果表明,桉树人工林区水库泛黑与特定季节及特殊气候条件有关,水体温度分层结构失稳是黑水物质运移的主要动力因素;夏季水库水温分层结构稳定,限制了底层致黑物质向上迁移,溶解氧等水质指标分层明显,秋冬季节分层消失,水体发生垂直交换,给底层致黑物质提供了上翻的作用力,导致"泛黑"现象发生.硫化物、单宁酸、铁、锰等物质季节性及空间分异特征与水温季节性分层特性密切相关.桉树林区水库水体铁和锰浓度最高可达2.93和3.46 mg/L,桉树茎、叶在水体中浸出大量单宁酸,在硫化物、单宁酸、铁、锰同时存在的条件下,发生铁、锰与硫化物,硫化物与单宁酸,铁、锰与单宁酸等一系列反应,生成黑色络合物,导致水库泛黑.研究结果可为保障桉树人工林区饮用水源地安全提供指导,并为桉树人工林区水库黑水深入研究奠定基础,引领更多学者进行深入研究.

Eucalyptus can grow into wood in two or three years and has large-scale cultivation in the southern China,with high economic value. Recently it is considered"pump","green desert",and even rumoured"toxic. "The water in the reservoir in Eucalyptus planting area appeared"black"sporadically. The water was dark brown with a pungent smell,which has caused great panic within local residents. The phenomenon is associated to Eucalyptus trees plantation. To explore the mechanism of"blackwater"in the reservoir in Eucalyptus plantation,southern China,three typical reservoirs( Najiang,Tianbao,Baihe Reservoirs) were selected in Eucalyptus planting area. Main water quality variables including hydrological and environmental factors were observed 4times,from August 2015 to April 2016. The physicochemical indexes of water were determined,and then synthetic analysis was performed combined with hydrological data provided by the Nanning Metrological Station. The results indicate that reservoirs in Eucalyptus forest area blackening are associated with a particular season and special climatic conditions. Meanwhile,the instability of water temperature stratification structure is the main driving factor of black materials transport. In summer,hierarchical structure,the water temperature in reservoirs keeping thermal stratification structure stable,results in dissolved oxygen and other water quality indexes were changing with stratification and limits transporting upward. In autumn and winter,stratification disappears,and vertical exchange of water body provides the underlying pollutants with upward force. Finally,pollutants spread the whole body and lead"blackwater"phenomenon. Seasonality and spatial heterogeneity of sulfide,tannic acid,iron,manganese and other materials is closely related to the seasonal characteristics of water temperature stratification. In the Eucalyptus forest reservoirs,iron and manganese concentrations are up to 2. 93 and 3. 46 mg/L,respectively. A large amount of tannic acid appeared when Eucalyptus leaves soaked in the water. When sulfide,tannic acid,iron and manganese exist together,a series of reactions such as iron,manganese and sulphur,sulphur and tannic acid,iron,manganese and tannic acid can produce black complex. Our results can provide guidance in guaranteeing the safety of drinking water sources in Eucalyptus planting area and lay the foundation for the further research of black water.