防城港近岸表层水化学需氧量的周年变化特征

Annual Variation Characteristics of COD in the Coastal Surface Waters of Fangchenggang

关键词:  化学需氧量  分布  环境因子  防城港

Key words:  chemical oxygen demand  distribution  environmental factors  Fangchenggang

摘要:

[目的]分析防城港近岸海域表层水化学需氧量(COD)的平面分布及周年变化特征,并探讨海域表层水COD分布与不同环境要素的相关性。[方法]根据2010年6月至2011年3月在防城港近岸海域4个航次12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表层水的COD时空分布及其环境影响因子进行分析讨论。[结果]COD超标的站位位于西湾顶部的防城江入海口附近海域,其余站位COD标准指数均<1,处于一类海水水质范围。调查海域各季节COD浓度与水温之间的相关系数均为正值,其中春季最高为0.575;各季节COD浓度与盐度呈显著负相关,其相关系数均高于0.860(P<0.01);在春、冬两季COD与叶绿素a之间的相关指数较高,分别为0.910(P<0.01)及0.957(P<0.01),呈显著正相关,夏、秋两季COD与叶绿素a的相关系数较低,分别为0.606和0.592;COD与悬浮物含量呈正相关,冬季较小,相关系数为0.478,其次为秋季0.694,春、夏季节的相关系数均在0.800以上。[结论]调查期间,防城港海域各季节表层海水COD的平面分布特征基本一致,均体现为近岸高、外海低,由沿岸向离岸方向呈逐渐降低的趋势。其COD主要来源于陆源输入,尤其是河流输入,同时还会受浮游植物等的影响。

Abstract:

[Objective] Distribution and seasonal variation of chemical oxygen demand (COD) in the coastal surface waters of Fangchenggang were analyzed,and the correlation between the environmental factors and the distribution of COD was discussed.[Methods] Based on the field data from four cruises and 12 stations of oceanographic survey carried out in the coastal waters of Fangchenggang from the June 2010 to March 2011,the sea surface water spatial and temporal distribution of COD and its influence factors are discussed by using standard index method and correlation method.[Results] The result indicated that COD standard index > 1 occurred in the top of the West Bay, the Fangcheng river estuaries. The COD concentrations of other stations met the firstrate National Seawater Quality Standard. There was a positive correlation between the COD concentrations and temperature in each season and the larger correlation coefficient was 0.575 in spring. COD concentration was in significant negative correlation to salinity (r < 0.860,P < 0.01). Additionally,COD concentration was significantly correlated with chlorophyll a in spring (r=0.910,P < 0.01) and winter (r=0.957,P < 0.01). In contrast,the correlation coefficient is relatively low in summer(0.606) and the autumn(0.592). The correlation coefficient between the concentration of COD and suspended solids was above 0.800 in spring and summer,0.694 in autumn,and 0.478 in winter.[Conclusion] Horizontal distribution of COD showed similar patterns in different seasons in Fangchenggang. Areas with high value of COD concentration were found offshore while COD concentration in open sea was relatively low. COD concentrations decreased gradually from offshore to open sea. Results showed the COD concentration in the coastal waters of Fangchenggang was mainly correlated with terrestrial input,especially the river runoff. In addition,the COD concentration was also affected by phytoplankton.