Local and regional impact of anthropogenic drainage on fen contiguity

Abstract

Abstract. Knowledge of the hydrological mechanisms behind habitat fragmentation of fen plant communities in intensively managed regions like The Netherlands is essential to improve currently utilized fen restoration and conservation strategies. In this study, we analysed the local and regional impact of anthropogenic drainage on the groundwater supply of fens. For this purpose, we developed finescale groundwater flow models and collected empirical data to analyse (1) the differences in groundwater supply between an anthropogenically drained fen and a poorly drained fen in The Netherlands, and (2) the local and regional effects of the elimination of drainage ditches on the groundwater supply of fens. Our results consistently indicated the presence of recently infiltrated precipitation on top of upwelling groundwater across the anthropogenically drained fen, and a mixing gradient of recently infiltrated precipitation and upwelling groundwater across the poorly drained fen. Furthermore, our results showed that the elimination of drainage ditches from the anthropogenically drained fen increased the area and the flux of groundwater supply of both the anthropogenically drained fen and the poorly drained fen. We conclude that anthropogenic drainage not only causes a lowering of groundwater tables, but also (1) enhances the infiltration of local precipitation across fens while simultaneously preventing upwelling groundwater from entering the fen root zone, and (2) reduces the groundwater supply of adjacent fens by intercepting groundwater that is potentially directed to downstream regions. These insights support the need to reconsider the current priorities in hydrological fen restoration strategies.

Impact of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve (the Netherlands)

“…This was also the case in May 2016 although to a minor extent. Furthermore, van Loon et al (2009) showed in a modelling study corroborated with empirical data that in 2006, during periods of precipitation deficit, brackish groundwater were flowing into the fen. Van Loon et al (2009) also suggested that fresh groundwater flow is intercepted by ditches in close-by agricultural land, thereby redirecting it before it can flow to the fen.…”

“…Furthermore, van Loon et al (2009) showed in a modelling study corroborated with empirical data that in 2006, during periods of precipitation deficit, brackish groundwater were flowing into the fen. Van Loon et al (2009) also suggested that fresh groundwater flow is intercepted by ditches in close-by agricultural land, thereby redirecting it before it can flow to the fen. However, we stress that the groundwater that seeps up in the major part of the studied fen comes from a regional freshwater system and is still seeping up into the fen in dry periods.…”

“…In the fen, both fresh and brackish palaeo-groundwater comes to the surface. The brackish groundwater comes from Holocene sea water intrusions which entered the aquifer from above by density flow (Post et al 2003;van Loon et al 2009). The fresh groundwater that seeps up in the fen comes from the adjacent ridge Het Gooi (Fig.…”

Diversity and Distribution of Riparian Plant Communities in Relation to Stream Size and Eutrophication

“…For example, discharge of deep groundwater into a riparian area is associated with low water temperature, low amounts of nutrients, and a steady supply of water (Almendinger and Leete, 1998;van Loon et al, 2009), whereas shallow groundwater can have high levels of nutrients, in particular in catchments with high agricultural activity (Allan et al, 1997;Davies and Neal, 2007). Because diff erent groundwater sources provide habitats for diff erent community types spanning from high-productive types (e.g., high tall herb fringes) to very low-productive types (e.g., alkaline fens) (DeMars et al, 1997;Wassen et al, 2003;Grootjans et al, 2006), a high community richness is likely to evolve in areas with discharge of diff erent types of groundwater (Jansson et al, 2007).…”

Throughflow as a determining factor for habitat contiguity in a near-natural fen

“…Managed fens often have an anthropogenically controlled hydrology to accommodate multiple land uses like housing and agriculture. Tile drains and ditches (Schot et al, 2004;Van Loon et al, 2009b) and groundwater abstractions (Fojt, 1994), for example, intercept groundwater that is potentially directed to the fen surface, and prevent the available groundwater from entering the fen root zone. Furthermore, drainage elements accelerate the discharge of groundwater from fens via surface water, and often prevent the reinfiltration of groundwater into the fen root zone (Wassen et al, 1990).…”