华北平原深层地下水的更新与资源属性

Groundwater Renewal and Characteristics in the Deep Confined Aquifer in North China Plain

学术界对于华北平原深层地下水的资源属性存在争议,这直接关系到地下水的合理开发利用以及管理方式和开发战略的制定。本文从地下水资源属性的定义、内涵,地下水补给以及开发后含水层系统的响应等方面来讨论深层地下水的更新性。含氚的现代地下水分布在山前平原,其稳定同位素组成接近当地降水加权平均值,说明当地降水补给占有相当的比重,氚含量与深度的关系反映了150m深度以上地下水是可更新的,其更新强度约为3%/a。中东部承压含水层地下水的放射性碳-14年龄为10kaB.P至大于35kaB.P,其稳定同位素δ18O和δD值比现代地下水要低得多,反映了末次冰期补给水的特征。根据水均衡方法估算的河北平原承压含水层1985年～1995年间的平均更新强度为0.09%/a,1990年～2000年间的平均补给强度为0.12%/a,说明大规模开采地下水诱发了一定程度的侧向补给,但是其更新强度仍然小于一般意义上的可更新含水层系统的更新强度0.2%/a。尽管这部分承压地下水并不是严格意义上的"不可更新地下水资源",但因其更新相对比较缓慢,可以看作"不可更新地下水资源",应该按不可更新地下水资源来规划开发与管理。

It is arguable whether we are ＂mining for a non-renewable groundwater resource＂ in the North China Plain. This paper analyzed the renewability of groundwater in the deep confined aquifer through defining the concept of non-renewable resources and aquifer＇ s responses to exploitation, since it was vital for water policy makers to manage groundwater resources. The tracer data showed that there were relatively modern ground waters in the piedmont plain. The contents of stable isotopes samples in the piedmont plain are close to the regional annual weighted average composition of meteoric waters. The concentration of tritium indicated a young post-bomb recharge （〈50yr） and therefore the water recourses were renewable. Their depth-dependence distribution showed local recharge from precipitation. Tritium-free 150m below ground surface indicated an absence of modern post nuclear water recharge. Thus, the active groundwater recharge zone had a depth of up to 150m. Its average renewal rate was estimated as about 3% a^-1. In contrast, ground water in central and littoral parts of the North China Plain may date from 10,000 B.P to more than 35,000 B.P by radiocarbon dating. These waters were isotopically lighter than younger groundwater by up to 2.2%e of δ^18O and 15%e of δD, which indicated that water recharge took place during the past glacial period. The tracers revealed a slow natural replenishment rate in the central plain, where groundwater has been exploited. The estimated renewal rate of deep confined aquifer was about 0.09% a1 from 1985 to 1995 and 0.12% a^-1 from 1990 to 2000. This implied that intensive exploitation of groundwater induced the increase of some lateral recharge from the piedmont, but it was still less than 0.2% a^-1. Groundwater in the highly-confined parts of quaternary aquifer systems could be considered as non-renewable resources because of extremely low renewable rate, though groundwater resources in deep aquifers were not strictly ＂non-renewable＂. Thus, exploitation and management of groundwater should take the characteristics of non-renewable groundwater system into account.