Ecological Engineering 17 (2001) 21 – 31 Rehabilitation of acidified and eutrophied fens in The Netherlands: Effects of hydrologic manipulation and liming B. Beltman a, *, T. Van den Broek a , A. Barendregt b , M.C. Bootsma b , A.P. Grootjans c a Department of Geobiology, Section of Landscape Ecology, Utrecht Uniersity, PO Box 800 84, NL-3508TB Utrecht, The Netherlands b Department of Enironmental Studies, Utrecht Uniersity, PO Box 801 15, NL-3508TC Utrecht, The Netherlands c Department of Plant Ecology, Uniersity Groningen, PO Box 14 NL-9750AA Haren, The Netherlands Accepted 28 July 2000 Abstract Mosaic fen communities with many rare plant species were outcompeted by fast-growing bryophyte stands (Sphagnum flexuosum/Sphagnum fallax and Polytrichum commune ). Eutrophication and acidification were the main causes. Management experiments were carried out to set back this succession by restoring the former abiotic conditions (high pH, low nutrients). The management options investigated were: sod removal, lime application, drainage improvements (digging ditches and trenches) and combinations of sod cutting and liming, respectively, with drainage improvements. Four pilot projects are discussed, one in the brackish (oligohaline) peat area, one freshwater site with floating Carex -dominated fens and two freshwater sites with purple-moor grassland (Cirsio dissecti – Molinietum) in the holocenic peatlands of The Netherlands. Plant species, soil and water chemistry were monitored. The evaluation after five years showed that some of the desired plant species had returned, e.g. Viola palustris, Hydrocotyle ulgaris, whereas others had increased in cover. e.g. Scirpus lacustris spp. tabernaemontani (brackish site), Pedicularis palustris, Calliergonella cuspidata (fen site) and Gentiana pneumonante and Carex panicea (C. dissecti – Molinietum peatland). This happened, however, only in restricted strips along trenches and ditches. In the combined measure of drainage improvement and sod cutting, the Sphagnum species declined permanently, but after sod cutting only, they recovered within three years to the previous cover of ca. 80%. The sod–cutting measure and the control treatment showed no differences in the presence of a rain water lens, whereas drainage and combination treatments showed narrow (0.5–2 m wide) zones with intrusion of surface water. Soil and water pH and Electric Conductivity (EC) showed a sharp decrease within 0.5 m from the trenches (pH from ca. 6 to ca. 4). Also the cations Ca 2 + and Mg 2 + and the anions Cl - and SO 4 2 - showed this sharp decline. www.elsevier.com/locate/ecoleng * Corresponding author. E-mail address: b.beltman@bio.uu.nl (B. Beltman). 0925-8574/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0925-8574(00)00128-2