基于^(222)Rn质量平衡模型的胶州湾海底地下水排泄

The Evaluation of Submarine Groundwater Discharge in Jiaozhou Bay Based on ^(222)Rn Mass Balance

海底地下水排泄(SGD)作为全球水循环的一个组成部分,近年来成为陆海相互作用的研究热点。地球化学示踪法是研究海底地下水排泄的主要手段。本文以环境同位素222Rn作为示踪剂,通过构建222Rn质量平衡模型来评价胶州湾的海底地下水排泄,并进一步估算地下水输入的营养盐。222Rn质量平衡模型的源项考虑了河流的输入、沉积物的扩散、母体226Ra的支持,汇项考虑了222Rn的自身衰变、222Rn散逸到大气的损失以及与湾外海水的混合损失,源汇项的差值则作为地下水输入的222Rn通量。结果表明,2011年9—10月胶州湾海底地下水排泄通量为24.2 L?m–2?d–1,2012年4—5月胶州湾海底地下水排泄通量为7.8 L?m–2?d–1。丰水季节地下水输入胶州湾的营养盐低于河流输入的,但是枯水季节地下水输入的营养盐接近河流输入的,特别是输入的活性磷酸盐和硅酸盐很接近。

Submarine groundwater discharge （SGD）, an important part of global water cycle, has recently been a research focus in the field of land-ocean interaction along the coastal zone. Geochemical tracing is a major tool to study submarine groundwater discharge. Taking natural occurring isotope ^222Rn as a tracer, the authors built ^222Rn mass balance model to estimate groundwater discharge to Jiaozhou Bay, and also evaluated the nutrient fluxes transported via groundwater. River input, dispersion of sediments, and support from parent ^226Ra are considered to be the sources of ^222Rn mass balance model, whereas radioactive decay, escape from sea-water interface to air and loss in mixing with the low activity water from open ocean are considered to be the sink of the model. Thus, the imbalance of budget from the model is attributed to submarine groundwater discharge. Calculations show that submarine groundwater discharge flux to Jiaozhou Bay was 24.2 L·m^-2·d^-1 from September to October in 2011, and 7.8 L·m^-2·d^-1 from April to May in 2014, respectively. The results of the study also indicate that the nutrient fluxes derived from groundwater during the wet season are lower than those transported by the local rivers, whereas the nutrient fluxes derived from groundwater during the dry season are close to those transported by the local rivers and, what is more, soluble reactive phosphate and silicate fluxes from both groundwater and fiver are very close to each other.