白洋淀水体富营养化和沉积物污染时空变化特征

Spatio-temporal Variations in the Characteristics of Water Eutrophication and Sediment Pollution in Baiyangdian Lake

雄安新区成立以后,在白洋淀流域实施了一系列污染综合整治措施.为评估白洋淀污染状况并识别主要污染来源,本文在淀内采集了30个水体样品和29个沉积物样品,分析了水体中的COD、TP、TN、NH4^+-N和Chla这5项指标和沉积物中TN、TP和重金属(Cd、Zn、Cu、Pb、Ni、As和Cr),结合历史监测数据分析了白洋淀污染时空分布特征及其影响因子.结果表明, 2019年白洋淀淀内水体整体处于富营养化状态, 30个采样点中"轻度富营养化"点位8个,"中度富营养化"16个,"重度富营养化"6个,与1991~2017年相比,淀区北部地区多数点位的营养程度明显下降,污染整治措施基本上遏制了水体污染加重趋势.沉积物营养盐污染依然严重,TN含量在1 483.7~14 234.1 mg·kg^-1之间,平均值为5 054.9 mg·kg^-1,变异系数高达46.5%,TP含量在360.3~1 964.4 mg·kg^-1之间,平均值为925.4 mg·kg^-1,变异系数为25.7%.重金属地累积指数计算表明沉积物中Igeo平均值均小于1,属于清洁或轻度污染,主要污染物为Cd、Zn和Cu.重金属生态风险除部分点位(L3、L21、L28和L29)处于重度和严重生态风险等级外,淀区整体处于中等风险水平.整体上,白洋淀水体污染区域正在从北部向南部转移,主要影响因素从外源污染向淀中村和沉积物污染引起的内源污染转变.

Since the establishment of Xiong’an New District, a series of comprehensive pollution control measures have been implemented in Baiyangdian Lake. To evaluate the pollution status and identify the main sources of pollution of Baiyangdian Lake, 30 water samples and 29 sediment samples were collected in the lake. Five water quality indexes(i.e., concentrations of chemical oxygen demand, total phosphorus(TP), total nitrogen(TN), NH4^+-N, and chlorophyll-a) and three sediment quality indexes(i.e., concentrations of TN, TP, and heavy metals) were measured. Along with historical monitoring data, the spatio-temporal pollution characteristics and their influencing factors in Baiyangdian Lake were analyzed. The results show that the Baiyangdian Lake water is eutrophicated. Of the 30 sampling sites, 8 are "mildly eutrophicated"(accounting for 26.7%), 16 are "moderately eutrophicated"(accounting for 53.3%), and 6 are "severely eutrophicated"(accounting for 20%). Compared with the periods between 1991 and 2017, the water quality of most sampling sites, especially in the northern parts, has improved a lot. This shows that the pollution control measures have basically curbed the gradually increasing trend of pollution in the waterbody. The nutritive pollution in sediment is severe. The concentrations of TN are between 1 483.7 and 14 234.1 mg·kg^-1, with a mean value of 5 054.9 mg·kg^-1, and the concentration coefficient variation in different sites is as high as 46.5%. The concentrations of TP are between 360.3 and 1 964.4 mg·kg^-1, with a mean value of 925.4 mg·kg^-1, and the concentration coefficient variation in different sites is 25.7%. Geoaccumulation index calculation shows that the mean Igeo value of heavy metals in sediments is less than 1, which indicates cleanness or slight pollution. The main contributions to heavy metal pollution are Cd, Zn, and Cu. Regarding ecological risk of heavy metals, only some sites(i.e., L3, L21, L28, and L29) are at high and very high risk level, while the remaining sites are at moderate risk level. Overall, the pollution of Baiyangdian Lake changes from the northern part to the southern part, and the main influencing factors also change from external pollution to endogenous pollution caused by the discharge of villages in the lake and the sediments.