Hydrochemistry of rich fen and water management

Abstract

Rich fen, a type of wetland characterised by calciphyte species, is strictly related to high groundwater levels with high contents of calcium and bicarbonate ions in the soil water. Rich fen is threatened by changes in the water management of surrounding areas. With a view to preserve suitable conditions for rich fen conservation by water management, hydrochemistry of a small rich fen was studied in relation to its hydrology. In order to know whether high groundwater levels are maintained by impeded drainage or seepage of groundwater from the aquifer water balances have been calculated. Chemical balances have been made to decide whether calcium bicarbonate ions originate from local on-site sources or from weathering processes in the aquifer and subsequent seepage to the fen. Vegetation development of rich fen appeared to be conditioned by upward seepage of groundwater having a low redox status and containing high contents of calcium and bicarbonate ions. Rich fen is capable to retain calcium ions in its topsoil only if the redox status can be maintained on a level that prevents pyrite oxidation. Conservation of rich fen must include regional water management to prevent hydraulic heads in the aquifer to fall to such a level that no seepage can take place. Local water management should be directed to decrease drainage in combination with stimulating surface runoff.