Does it matter at which point of time groundwater fauna is carried out?
14.5 in Young Hydrogeologists Forum
Eight groundwater springs were sampled in four times for ecological purpose in Baumberge and Schöppinger Berg (Münsterland area, North-Rhine Westphalia). The sampling times were in November 2018 and January 2019 with low groundwater level in the associated groundwater system and April 2019 with a high level. In July 2019, it gradually returned to a low level. The main goal of this study is the investigation of the relationship between groundwater level, Physico-chemical parameter and stygofauna abundance and diversity.
Groundwater fauna has been captured with plankton nets, which were installed at the direct outflow of the spring on several consecutive days. After about 24 hour’s collection period, the captured groundwater fauna was prepared for the laboratory. Field parameters of the spring water outflow were taken at the same time included pH value, temperature, electrical conductivity, dissolved oxygen concentration and the average spring water discharge. In the laboratory the groundwater fauna was subdivided into stygobiont, stygophil and stygoxen fauna; furthermore, only the stygobiont fauna, the so-called stygofauna, were further processed and subdivided into different taxonomic classes or orders of stygofauna.
Field parameter data showed, there were no significant differences in sampling time visible except in electrical conductivity values. The electrical conductivity was found to be most high in April and gradually decreasing in other months. There was a slight correlation of the electrical conductivity with the groundwater level except for sampling times with high short-term local groundwater recharge.
The results of the faunistic analysis showed that different animal sizes (from meiofauna to macrofauna) were present in the eight springs at all sampling times. Copepoda (cyclopoids and harpacticoids) was the dominated fauna in both groundwater systems. The other fauna such as Ostracoda, Isopoda, and Amphipoda were distributed with different ratios. The number of very small Nauplius larvae was very high, but since it was not clear whether they would develop into stygobiont species, they were excluded from further analysis.
In summary, it was found that stygofauna abundance increased when the groundwater level in the associated groundwater system and the average spring discharge was low and decreased when the groundwater water level was high. This could mean that at high hydraulic pressures and thus higher groundwater flow velocities, individuals retreat into protected areas (e.g. smaller fissures and pores). At that time, they cannot be trapped, or only in small numbers, in the spring water outflow. At lower groundwater level, the samples showed both higher abundance and higher diversity of captured individuals. Thus, the relatively large amphipods were only detected in some springs at times with low groundwater level. In summary, an investigation of abundance and diversity of groundwater fauna at low groundwater levels and higher electrical conductivities can be recommended.