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

Abstract

Knowledge of the hydrological mechanisms that underlie stable plant communities within natural fens is essential for the improvement of current fen restoration and conservation strategies. In this study, steady-state groundwater modelling was performed to quantify the impact of throughflow mechanisms on the presence of exfiltrated, alkaline groundwater across a near-natural fen in the Biebrza River catchment (Poland). Alkaline groundwater is considered essential for the existence of low-productive fen plants. The results indicate that throughflow redistributes exfiltrated groundwater, mixed with locally infiltrated precipitation, in various concentrations across the fen. The throughflow model provides an explanation for the major patterns in the plant alliances that have a preference for minerotrophic or ombrotrophic habitat conditions. These patterns could not be reproduced with groundwater models that did not account for the existence of throughflow on a regional scale. We conclude that throughflow (1) enables a spatially contiguous supply of exfiltrated groundwater across fens, and thereby (2) facilitates abiotic conditions suitable for fen plants outside the zones that are directly supplied by exfiltrated groundwater. These new insights into landscape hydrological mechanisms that drive abiotic conditions within natural fens necessitate the reprioritisation of current hydrological fen restoration strategies.