Annemieke Kooijman, Casper Cusell, Roos Loeb & José van Diggelen

Natuurherstel, waterkwaliteit, verzuring, P-limitatie, N-depositie

Mesotrophic succession and the preservation of mineral-rich floating fens in the Netherlands

Nature restoration, water quality, acidification, P limitation, P-limitatie, N-deposition

For many wetland areas, the Natura 2000 goals include a favourable conservation status of all habitats characteristic for succession, such as H3140 (hard oligomesotrophic waters with benthic vegetation), H3150 (natural eutrophic lakes with magnopotamion or hydrocharition-
type vegetation), H7140 (transition fens), H4010 (Northern Atlantic heaths with Erica tetralix) and H91D0 (bog woodland). Within the transition fens, two subtypes are important: H7140A (mineral-rich f loating fens), and H7140B (sphagnum reed lands). In the 1970s, aquatic vegetation had largely collapsed due to deteriorating water quality. However, in areas such as Weerribben-Wieden, water quality has clearly improved, and early stages of terrestrialization are present again. Nevertheless, succession towards base-rich f loating fens, with the most unfavourable conservation status, has not yet occurred. At the same time, existing rich fens, which are base-rich, but P-limited, are threatened
by eutrophication of surface water and high atmospheric N-deposition, which both lead to acidification and dominance of sphagnum spp. It is however possible to maintain existing fens by regular inundation with mineral-rich and nutrient-poor water. Sphagnum reed lands and to some extent Atlantic heaths and bog woodlands are threatened by high N-deposition as well. Although nature management can help to some extent, measures to further reduce water pollution and N-deposition are urgently needed.


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