基于镭同位素示踪的嵊泗高场湾海底地下水排放

Using radium isotopes to estimate SGD flux in Gaochang bay,Shengsi

作为全球水循环的重要组成部分,海底地下水排放(SGD)是营养盐等陆源物质进入海洋的重要途径之一。本文利用天然放射性同位素223Ra、224Ra和228Ra对嵊泗岛高场湾SGD通量及及其所携带的营养盐通量进行了估算。研究表明,地下水中223 Ra(16.7±2.9 dpm/100 L)、224 Ra(479±18 dpm/100 L)、228Ra(97±4 dpm/100 L)的活度远高于近岸水体中223Ra(3.5±0.7 dpm/100 L)、224Ra(80±4 dpm/100 L)、228Ra(31±2 dpm/100 L)的活度。运用潮动力模型,基于223 Ra和224 Ra得到的SGD速率分别为7.6 cm/d和4.1 cm/d,而根据223Ra的离岸输送估算出SGD速率为22 cm/d。结合地下水端元营养盐的浓度计算得SGD携带的溶解无机氮(DIN)、溶解无机磷(DIP)、溶解硅(DSi)的排泄通量分别为593,4.16和241μmol/(m^2?s)。

Submarine groundwater discharge(SGD)has been recognized as an important pathway for nutrients into ocean and plays an important role in global water cycle.In this study,seawater and groundwater samples were collected from the coast of Shengsi Island,Zhejiang Province and radium isotopes(223Ra,224Ra,228Ra)and nutrients were analyzed in the lab.Then SGD and its derived nutrients fluxes were estimated.The results showed that Radium activities in groundwater(223Ra:16.7±2.9 dpm/100 L,224 Ra:479±18 dpm/100 L,228 Ra:97±4 dpm/100 L)were much higher than those in seawater(223Ra:3.5±0.7 dpm/100 L,224Ra:80±4 dpm/100 L,228Ra:31±2 dpm/100 L).Moreover,the tidal-drived SGD rate were calculated to be 7.6 and 4.1 cm/d based on 223Ra and 224Ra,respectively.However,according to the decay of 223Ra with distance offshore,a SGD flux of 22 cm/d was derived.Based on SGD flux,the flux of dissolved inorganic nitrogen(DIN),dissolved inorganic phosphorous(DIP)and dissolved silicon(DSi)were calculated to be 593,4.16 and 241μmol/(m^2?s),respectively.