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

Abstract

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 1483.7 and 14234.1 mg·kg-1, with a mean value of 5054.9 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 1964.4 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.