北海近岸海域化学需氧量分布特征及其影响因素研究

Distribution Characteristics and the Influencing Factors of COD in the Coastal Waters of Beihai

关键词:  化学需氧量  分布  季节变化  影响因素

Key words:  chemical oxygen demand  distribution  seasonal variation  influencing factors

摘要:

[目的]系统分析北海近岸海域化学需氧量(COD)的平面分布特征及季节变化,探讨不同环境要素对COD分布的影响。[方法]根据2010年6月~2011年3月期间在北海近岸海域4个航次20个站位的生态环境调查数据,采用标准指数法、相关性系统法等对该海域的COD时空分布及其环境影响因子进行分析讨论。[结果]COD高值区及超标的站位主要位于河口附近海域,其余大部分海域COD标准指数均<1,处于一类海水水质范围。除夏季外,调查海域各个季节COD浓度与温度之间的相关系数均为正值,且大于0.45;各季节COD浓度与盐度之间的相关系数普遍高于0.5,两者之间呈较好的负相关关系;春、夏及秋季COD与叶绿素之间的相关指数均较高;COD与悬浮物含量呈正相关性,除夏季较小相关系数为0.596外,其余季节的相关系数均在0.7以上。[结论]各季节调查海域表层海水COD的平面分布特征基本一致,主要表现为近岸高、外海低,由沿岸向离岸方向呈逐渐降低的趋势。COD主要来源于陆源输入,尤其是河流输入。

Abstract:

[Objective] Distribution and seasonal variation of chemical oxygen demand (COD) were investigated,and the effects of environmental factors on the distribution of COD was discussed.[Methods] Based on the field data from four cruises of oceanographic survey carried out in the coastal waters of Beihai in June,September,December and March of 2010~2011,standard index method and correlation analysis method were conducted for the study area.[Results] The result indicated that the high concentrations of COD with COD standard index >1 occurred in coastal waters,especially in river estuaries.The concentrations of COD in most of stations were classified as the first-rate National Seawater Quality Standard.Except in summer,the COD concentrations and temperature showed a positive correlation in other season and the correlation coefficient was larger than 0.45.COD concentrations were in significant negative correlation to salinity (r<-0.5,P<0.05).Additionally,COD concentrations were significantly correlated with chlorophyll a in spring,summer and autumn.The correlation coefficient between the concentrations of COD and suspended solids was 0.596 in summer and over 0.7 in other seasons,which indicated a strong correlations between the COD and suspended solids.[Conclusion] Horizontal distribution of COD showed similar patterns in different seasons.High COD areas were found offshore while COD concentrations in open sea were relatively low.COD concentrations decreased gradually from offshore to open sea.Furthermore,the COD concentrations in the coastal waters of Beihai mainly correlated with terrestrial input,especially the river runoff.