Individual study: Digging of new turf ponds for early successional aquatic plant communities, Westbroek Polder, Utrecht, the Netherlands
Beltman B. & Allegrini C. (1997) Restoration of lost aquatic plant communities: new habitats for Chara. Aquatic Ecology, 30, 331-337
In the Netherlands, base-rich fen peat was excavated for fuel until around 1950. This gave rise to shallow waterbodies ('turf ponds'), and aquatic plants colonised along with associated fauna. Succession over the years has resulted in many of the open water communities and early terrestrialization stages becoming very rare; terrestralization from open water to fen communities takes about 50 years. Work commenced in 1991 to restore these early successional calcareous communities by excavating new turf ponds at Westbroek Polder, one of the polders of the Vechtplassen.
Study area: The new turf ponds were created in the Westbroek Polder, located 2-3 km west of the village of Maartensdijk, northwest of the city of Utrecht.
Turf pond creation: Between October 1991-December 1993, 16 open water bodies, 1 m deep and 30-40 m wide 100-700 m in length were excavated in former alder Alnus glutinosa fen carr by Staatsbosbeheer (nature managers of the Forestry Service). In several, remnants of aquatic vegetation and/or floating fens were left as source of propagules (seeds or vegetative organs). Some ponds were completely bare as they were excavated down to the underlying sandy mineral soil.
Vegetation monitoring: Subsequent to the turf pond creation work, for three years the vegetation was recorded and mapped along transects every 10 or 20 m, perpendicular to the length of the ponds.
In 1993, 90 ‘bank’ plant species were recorded, most being those reorded previously. Three years (or less) after excavation, the water quality was excellent (due to groundwater discharge of oligo-mesotrophic and calcareous water) and ponds had been colonized by substantial beds of submerged aquatic vegetation; the first aquatic plant species appeared within 6 months of excavation.
In June and September 1993, surveys revealed 19 aquatic species. Stoneworts Chara spp. were early colonizers with three species present: C.vulgaris, C.globularis delicatula (commonly present in ditches), and notably the regionally rare C. major (syn. hispida). Broad-leaved pondweed Potamogeton natans, fennel-leaved pondweed P.pectinatus and Nuttal’s pondweed Elodea nutallii were also early colonizers.
In the new ponds however, the number of Potamogeton spp. was rather limited and water soldier Stratiotes aloides was absent; some species are unable to colonise from adjacent waterbodies if there is no connecting open water. Management measures, such as manual re-introduction of such species to some of the ponds, are being considered.
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