Assessment of submarine groundwater discharge into the Wuyuan bay via continuous Radon-222 measurements

作者：Guo Zhan Rong^*; Li Kai Pei; Yuan Xiao Jie; Zhang Bin; Ma Zhi Yong

来源：Advances in Water Science, 2012, 23(2): 263-270.

DOI：CNKI:32.1309.P.20120224.2002.008

• Average values
• Bay areas
• Decay products
• Diffusive flux
• Dynamic variations
• Effective tool
• Geochemical tracer
• Input rate
• Intensive research
• Mass balance
• Mass budget
• Naturally occurring
• Pore waters
• Radon-222
• Semi-diurnal
• Submarine groundwater discharge
• Weighted averages
• Wind speed
• Wuyuan Bay

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.

• 出版日期2012
• 单位厦门大学