Assessment of submarine groundwater discharge into the Wuyuan bay via continuous Radon-222 measurements
Assessment of submarine groundwater discharge into the Wuyuan bay via continuous Radon-222 measurements
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通过连续 Radon-222 测量评估排入五缘湾的海底地下水
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发表时间：
2012
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通讯作者：
Ma, Zhi-Yong1
中科院分区：
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作者：
Guo, Zhan-Rong1;Li, Kai-Pei1;Yuan, Xiao-Jie1;Zhang, Bin1;Ma, Zhi-Yong1
近年来，利用放射性核素222（222 Rn）对五原湾海底地下水排泄进行了研究，并对该海域的地下水排泄进行了定量分析。我们连续测量了海水222 Rn和226 Ra的活度、近海面空气222 Rn、风速、在此基础上，利用222 Rn培养装置测量了222 Rn在沉积物和孔隙中的扩散通量。根据~（222）Rn通量的质量平衡原理，对实测海水~（222）Rn进行了母源~（226）Ra衰变产物、潮汐效应、大气损失、沉积物扩散通量结果表明，相对保守的估算，SGD引起的222 Rn通量在0 ~ 126.7 Bq/（m2·h）之间，约占海水中222 Rn的54%。计算得到的SGD输入速率变化范围为0 ~ 29.3cm/d，平均值为9.3cm/d，端元由地下水和孔隙水~（222）Rn活度的加权平均值组成，SGD输入速率的波动周期为12 h，五缘湾的SGD输入量可达1.86×105 m3/m3，d如果在假设平均SGD输入率适用于整个海湾地区的情况下进行估算，则在五缘湾，若淡水输入量占SGD输入总量的10%，则五缘湾的地下水年平均排放量约为1.86×104 m3/d。
In recent years,submarine groundwater discharge(SGD) has been recognized as an important process in land-ocean interactions in the coastal zone(LOICZ).The subject has thus become the focus of intensive research.Geochemical tracers can be effective tools for estimating SGD in LOICZ.The objective of this study is to estimate SGD in the Wuyuan Bay using Radon-222(222Rn) as naturally occurring tracer.The dynamic variation of SGD can thus be subsequently assessed.We continuously measure the seawater 222Rn and 226Ra activities,the near-sea surface air 222Rn,wind speed,sea water temperature and depth for two consecutive days.We also deploy an incubation device to measure the diffusive flux of 222Rn from sediments and the pore-water 222Rn activities.Based on the mass balance principle for the 222Rn flux,the measured seawater 222Rn are corrected for the decay product of parent 226Ra,the effects of tides,the losses to the atmosphere,the diffusive influxes from the sediments,and the mixing with offshore seawaters.The result shows a conservative estimate of 222Rn flux attributed to SGD is between 0 and 126.7 Bq/(m2 h),which can account for 54% 222Rn in seawater.Taking a SGD end-member as example,the calculated SGD input rates range from 0 to 29.3 cm/d with an average value of 9.3 cm/d.The end-member is made of the weighted average of groundwater and pore-water 222Rn activities.The fluctuation in the SGD input rate has a 12-h period,which matches well with the semi-diurnal tides in this region.The SGD input to the Wuyuan Bay could be as much as 1.86×105 m3/d if the estimation were made under the assumption that the average SGD input rate is applicable to the entire bay area.The input of terrestrially derived fresh groundwater in the Wuyuan Bay could be approximately 1.86×104 m3/d if the fresh groundwater were 10% of the total SGD input.