基于^(223)Ra和^(224)Ra的桑沟湾海底地下水排放通量  

Submarine groundwater discharge into Sanggou Bay traced by^(223)Ra and ^(224)Ra

作　　者：王希龙[1] 杜金洲[1] 张经[1] 

机构地区：[1]华东师范大学河口海岸学国家重点实验室,上海200062

出　　处：《海洋学报》2017年第4期16-27,共12页

基　　金：科技部973项目"多重压力下近海生态系统可持续产出与适应性管理的科学基础"(2011CB409801);国家自然科学基金项目"我国黄海海底地下水排泄及营养盐入海通量的研究"(41376089)

摘　　要：海底地下水排放(SGD)是陆地向海洋输送水量和营养物质的重要通道之一,对沿海物质通量及其生物地球化学循环有重要的影响,对生态环境起着不可忽视的作用。本文运用天然放射性同位素^(223)Ra和^(224)Ra示踪估算了我国北方典型养殖基地桑沟湾的海底地下水排放通量。结果表明,海底地下水样尤其是间隙水中Ra活度[^(224)Ra=(968±31)dpm/(100L),^(223)Ra=(31.4±4.9)dpm/(100L),n=9]远高于表层海水[^(224)Ra=(38.7±2.0)dpm/(100L),^(223)Ra=(1.70±0.50)dpm/(100L),n=21]。假设稳态条件下,考虑Ra的各源、汇项,利用Ra平衡模型,估算出桑沟湾SGD排放通量为(0.23~1.03)×10~7 m^3/d。潮周期内的观测结果显示,涨潮时,水力梯度较小,SGD排放变弱,落潮时,水力梯度较大,导致了相对较多的SGD排放。在一个潮周期间,基于^(223)Ra和^(224)Ra得到的SGD排放通量平均为0.39×10~7 m^3/d。潮汐动力下的SGD排放平均占总SGD排放的61%,因此桑沟湾沿岸的地下水排放主要受潮汐动力的影响,并对海水组成及海陆间物质交换有显著贡献。Submarine groundwater discharge（SGD）with inputs of nutrients and water into the ocean in certain regions plays a significant role in coastal material fluxes and their biogeochemical cycle,which cannot be ignored for its impact on the eco-system.In this paper,SGD into the typical aquaculture base of northern China,Sanggou Bay,was estimated using naturally occurring radium isotopes,（223）Ra and （224）Ra.Results showed that the radium activities of submarine groundwater,especially in the pore water[（224）Ra=（968±31）dpm/（100L）,（223）Ra=（31.4±4.9）dpm/（100L）,n=9],were obviously greater than those in the surface water[（224）Ra=（38.7±2.0）dpm/（100L）,（223）Ra=（1.70±0.50）dpm/（100L）,n=21].Assuming steady state and using a radium mass balance model with sources and sinks,the SGD rate was estimated to be among（0.23-1.03）×10^7 m3/d.SGD flux varied from spring tide to ebb tide.During spring tide,SGD flux was smaller because of weak hydraulic gradient while it was much larger during ebb tide because of strong hydraulic gradient.During a tidal cycle,the SGD flux was averaged to be 0.39×10^7 m3/d based on （223）Ra and （224）Ra.Tidal-driven SGD can account for 61% of the total SGD.Therefore,the main driving force of SGD into Sanggou Bay was tidal pumping and SGD of Sanggou Bay in coastal zone contributes a lot to seawater composition and material exchange between land and sea.

关 键 词：镭同位素 海底地下水排放 镭库模型 潮汐动力 桑沟湾 

分 类 号：P734.2[天文地球—海洋化学]