The effect of drawdown on the movement of groundwater invertebrates

Groundwater abstraction is a global problem limiting water resources and impacting dependent ecosystems. Groundwater invertebrates provide important services in their ecosystems. This study aims to clarify the role of sediment characteristics, invertebrate traits and drawdown rate on the response of groundwater invertebrates to water level changes. Column experiments using one of three sediment types and two groundwater invertebrate species were used with three drawdown rates. Hypotheses tested are: 1) coarse sediments and slower rates best facilitate the downward movement of invertebrates, 2) copepods and syncarids will differ in their downwards movement and 3) coarse sediment and fast rates will best facilitate the downwards movement of dead copepods. It was found that: 1) the proportion of copepods and syncarids stranded was not significantly different for the drawdown rates or sediment sizes, 2) copepods and syncarids were not found to differ significantly in their ability to move downwards and 3) sediment size and drawdown rate had no significant effect on the distance travelled by dead copepods. 11 % of copepods in the drawdown columns were stranded across all sediment types and rates, while 5 % of syncarids were stranded in the large sediment across all rates. While no statistically significant results were found the results here suggest that stranding does occur despite some capacity for invertebrates to follow a declining water table. The number of invertebrates stranded here under these conditions suggests that management of groundwater abstraction is needed to protect groundwater biodiversity and groundwater ecosystems.