The Impact of Water Table Drawdown and Drying on Subterranean Aquatic Fauna in In-Vitro Experiments

The abstraction of groundwater is a global phenomenon that directly threatens groundwater ecosystems. Despite the global significance of this issue, the impact of groundwater abstraction and the lowering of groundwater tables on biota is poorly known. The aim of this study is to determine the impacts of groundwater drawdown in unconfined aquifers on the distribution of fauna close to the water table, and the tolerance of groundwater fauna to sediment drying once water levels have declined. A series of column experiments were conducted to investigate the depth distribution of different stygofauna (Syncarida and Copepoda) under saturated conditions and after fast and slow water table declines. Further, the survival of stygofauna under conditions of reduced sediment water content was tested. The distribution and response of stygofauna to water drawdown was taxon specific, but with the common response of some fauna being stranded by water level decline. So too, the survival of stygofauna under different levels of sediment saturation was variable. Syncarida were better able to tolerate drying conditions than the Copepoda, but mortality of all groups increased with decreasing sediment water content. The results of this work provide new understanding of the response of fauna to water table drawdown. Such improved understanding is necessary for sustainable use of groundwater, and allows for targeted strategies to better manage groundwater abstraction and maintain groundwater biodiversity.

地下水抽取是一种全球性现象，直接对地下水生态系统构成威胁。尽管该问题具有全球重要性，但人们对地下水抽取及地下水位下降对生物群落的影响仍知之甚少。本研究旨在探究无压含水层（unconfined aquifers）内地下水位下降对地下水位附近动物群分布的影响，以及水位下降后地下动物群（stygofauna）对沉积物干燥的耐受能力。为此，本研究开展了一系列柱实验，分别探究饱和状态下，以及地下水位快速、缓慢下降后，不同地下动物群（包括合虾总目（Syncarida）和桡足类（Copepoda））的深度分布特征；同时测试了地下动物群在沉积物含水量降低条件下的存活情况。研究结果显示，地下动物群对水位下降的分布与响应具有类群特异性，但部分类群会因水位下降而暴露搁浅，这是共通的响应特征。此外，地下动物群在不同沉积物饱和水平下的存活情况也存在差异：合虾总目（Syncarida）相较于桡足类（Copepoda）更能耐受干燥环境，但随着沉积物含水量降低，所有类群的死亡率均会上升。本研究结果为阐明生物群落对地下水位下降的响应机制提供了新的认知。这一认知的提升对于地下水的可持续利用至关重要，同时可为制定针对性策略以优化地下水抽取管理、保护地下水生物多样性提供依据。