第三节 海水碱度

CHAPTER 3 SEAWATER CHEMISTRY——Section 3 Alk of Seawater in the Xiamen Harbour

碱度(Alk)是水体中氢离子接受体(如弱酸根、多元酸根、氢氧根等等)浓度的总和。它与温、盐、深、生物活动及碳酸盐的溶解和沉淀等有关;在河口港湾中,则主要受大陆径流、潮汐作用等水文因素影响,其次还受生物活动的影响。本调查区中Ⅰ区碱度的时空分布受河水和潮汐的影响较小,呈现浅海碱度的时空分布特征;Ⅲ区碱度的时空分布则受九龙江水和潮汐的强烈影响,呈现河口海域碱度的时空分布特征;Ⅱ区或多或少地受九龙江淡水的影响,其时空变化也或多或少地具有Ⅰ区和Ⅲ区的某些特征,大致呈过渡状态。本调查区碱度与盐度(或氯度)存在着紧密的正相关关系。

The distribution of alkalinity presented a large variation with range of 0.75—2.38 meq/L and an increasing trend from southwest(estuarine area at areaⅢ)to northeast(bay mouth at areaⅠ).Relatively small variation of alkalinity appeared at latteral transects,stratification distribution with low value at the upper layer and high value at the lower layer appeared at transects near the estuary;the distribution at longitudinal transect was a typical wedge form,Its vertical,diurnal and annual variations were all larger at areaⅠthan at areaⅡand smallest at areaⅠ.The diurnal variation of alkalinity at areaⅢfeatured clear tidaI influence For the annual variation,in area two high and two low value trends,the peak vaIues appeared in October 1980 and February 1981,the iowest values appeared in December 1980 and June-August 1981;the difference in the year of the mean values was less than 0.4 meq/L in areaⅡandⅢ,the annual variations were similar to those in areaⅠexcept for a secend highest value in August 1981,The difference of average value in the year reached 0.68 meq/L for surface layer and 0.38/L for bottom layer in areaⅢand 0.36 meq/L surface water and 0.26meq/L for bottom layer in areaⅡ.The average ratios of alkalinity to chloride were 0.125—0.126 for areaⅠandⅡ,similar to those of open ocean water and 0.132—0.136 for areaⅢobviously higher than those of open ocean water,A close Positive correlationship existed between alkalinity and chloride for the survey areas,its empiric formula was as follows:Alk=0.5396+0.09794C1(n=169,r=0.991)during dry seasonAlk=0.5228+0.09166C1(n=222,r=0.993)during wet seasonThe differences of measured alkalinity and calculated alkalinity obtained from the above equations are less than 0.10 meq/L The temporal variation of the alkalinity-chlorinity ratios indicates that ratios of the entering-harbour seawater in winter are obviously higher than those in summer,which shows that the seawater mass influencing the survey area in dry season and wet season is differens,it maybe the Min-Zhi coastal current moving southward in winter and the South China seawater in summer.