From groundwater abstraction to vegetative response in fen ecosystems

Abstract

Hydrological effects of groundwater abstraction near a Danish river valley have been assessed by integrated hydrological modelling. The study site contains groundwater‐dependent terrestrial ecosystems in terms of fen and spring habitats that are highly dependent on regional and local scale hydrology. Fens are rare and threatened worldwide due to pressures from agriculture, to lack of appropriate management and to altered catchment hydrology. A solid foundation for hydrological modelling was established based on intensive monitoring at the site, combined with full‐scale pumping tests in the area. A regional groundwater model was used to describe the dynamics in groundwater recharge and the large‐scale discharge to streams. A local grid refinement approach was then applied in a detailed assessment of damage in order to balance the computational effort and the need for a high spatial resolution. A considerable flow reduction in the natural spring was monitored during a full‐scale pumping test while no significant effects on the water table in the fen habitats were observed. A modelled abstraction scenario predicted a lowering of 2–3 cm in the centre of the main fen area during summer periods. The predicted change in water table conditions in the fen habitat is compared to the variability found in 35 Danish fens, and the ecological response is discussed based on statistical water‐level vegetation relations. The results provide a rare quantitative foundation for decision making in relation to management of groundwater‐dependent terrestrial ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.

Groundwater–surface water interaction in Denmark

“…Pumping changes how regional flow discharges to riparian zones and streams (as streambed seepage, drainage, or groundwater-fed surface flow or springs). Johansen et al (2011Johansen et al ( , 2014 were the first studies on how groundwater seepage affects fen ecosystems (groundwater-dependent ecosystems). A pumping experiment in a shallow chalk aquifer showed that outflow through springs was reduced, while the shallow water table in the fen ecosystems was relatively unaffected (Johansen et al, 2011) and the effect on vegetation was minimal (Johansen et al, 2014).…”

“…Johansen et al (2011Johansen et al ( , 2014 were the first studies on how groundwater seepage affects fen ecosystems (groundwater-dependent ecosystems). A pumping experiment in a shallow chalk aquifer showed that outflow through springs was reduced, while the shallow water table in the fen ecosystems was relatively unaffected (Johansen et al, 2011) and the effect on vegetation was minimal (Johansen et al, 2014). Many of these studies were supported by numerical modeling.…”

“…In the field of wetland restoration, problems due to the release of phosphate are a new concern (Audet et al, 2020). Previous studies on water-ecosystems interactions (Johansen et al, 2011(Johansen et al, , 2014 were followed by a nationwide survey of relations between vegetation and water level in 35 wetlands, demonstrating that absolute water level and water level variability affect species diversity (Johansen et al, 2018). Anthropogenic effects on the chemical characteristics of water were studied, for example, the implementation of controlled drainage to generate anoxic conditions to minimize the impact on harvest yields (Carstensen et al, 2019), the implications of human-made drain management on stream-riparian zones (Steiness et al, 2019), and the bypass effect of drains or geological conditions (Steiness et al, 2021).…”

“…Another cause for concern related to ecological processes is the effects of groundwater abstraction on gaining reaches of rivers and groundwater-dependent wetlands, since alteration of the streamflow regime can potentially have an adverse effect (Danapour et al, 2021). It remains unclear whether the magnitude of these changes can be comparable with natural variations (Johansen et al, 2011(Johansen et al, , 2014, and ultimately it will depend on the amount of groundwater extracted and the hydraulic connectivity between groundwater and wetlands/streams. These studies can also be seen in the context of climate change, as variations in recharge conditions would lead to modifications of the groundwater-dependent ecosystems.…”

Applicability of Geostatistical Tools and Fractal Theory for the Estimation of the Effect of a River on Water Relations in Adjacent Area

“…The issue of the effect of rivers or lakes on the water relations in adjacent areas can be analysed through the application of hydrological mathematical models (Ha et al, 2008;Guay et al, 2013;Johansen et al, 2014;Mosley et al, 2014) or through statistical analyses (Aguilera et al, 2013;Sahoo and Jha, 2013;Varouchakis and Hristopulos, 2013).…”