渤海中部COD的时空分布特征及其对富营养化的贡献分析

摘要

The temporal and spatial distribution of chemical oxygen demand (COD) in different water layers, and its source and contribution to eutrophication were analyzed in this study based on data collected in the Bohai Sea in all 4 seasons of 2013. The results showed that the highest average concentration of COD appeared in summer, followed by autumn; while the lowest concentration appeared in spring. The analysis about vertical distribution of COD showed that the highest and lowest concentrations of COD appeared in the surface and middle layers in spring, and they appeared in the surface and bottom layers respectively in summer; in autumn and winter they were observed in the middle and bottom layers. As for the horizontal distribution the average COD concentration was distributed quite evenly in spring; in summer COD concentration was the highest in the western sea area and displayed a gradual decrease from the west to the east; in winter the highest concentration was detected in the northern area and it dropped from the north to the south. During the survey period, the COD level in most stations met the first-class seawater quality standard. TheE value ranged from 0.088 to 2.995, and the average was 0.337±0.403. There were 25 stations in which theE values were above 1, including 20 stations in autumn and 5 stations in winter. These results indicated that the surveyed regions might not undergo eutrophication. The contribution of COD to eutrophication ranged from 46.15% to 141.41%, and the average was (71.36±14.98)%, which suggested that COD played an important role in the eutrophication of the Bohai Sea.%以2013年春、夏、秋、冬4个季节对渤海中部海区的调查数据为依据，对调查海域表、中、底层水体的化学耗氧量(Chemical oxygen demand, COD)的时空分布、来源及其对富营养化的贡献等进行了分析。结果显示，调查海域COD平均含量以夏季最高，秋季次之，春季最低。垂直分布差异表现为春季表层最高，中层最低；夏季表层最高，底层最低；秋季和冬季均为中层最高，底层最低。各站位 COD 平均浓度水平分布在春季无明显的高值出现，含量分布较均匀，夏季 COD从西向东呈降低趋势，高值主要分布于西部海域；秋季和冬季COD从北向南呈递减趋势，高值分布于调查海域北部。调查海域各站位营养指数E值变化范围为0.088–2.995，平均值为0.337±0.403，大于1的站位有25个，其中，秋季20个，冬季5个，表明大部分调查海域水质未达到富营养化状态，处于较低营养水平。COD 对调查海域富营养化的贡献率为46.15%–141.41%，平均值为(71.36±14.98)%，表明COD在渤海海区富营养化中占据了主要地位。