Environmental Engineering Reference
In-Depth Information
ways. Some stands were transformed into alkali meadows. In some cases, decreased water
table resulted in the leeching of the alkali salts from the upper layers of the soil leading to a
significant decrease in abundance of halophytes. Loosing the alkali character of the soil often
facilitated the invasion of reed (Bart et al. 2006) even in alkali marshes characterised by
Bolboschoenus
and
Schoenoplectus
.
In parallel with the regional-scale changes in the water regime, the land use system also
changed markedly during the past centuries. As a part of this process, free-ranging grazing
was reduced or even ceased in many regions (Isselstein et al. 2005). Traditional breeds were
replaced by intensive ones, such as Holstein Friesian and Hungarian Red, which were not able
to graze in marshes (Šefferová-Stanová et al. 2008). Cessation of grazing resulted in the
homogenisation of alkali marsh vegetation and enhanced litter accumulation in some stands.
Alkali reeds have been used for reed harvesting since historical times, when reed harvest
had a little impact on reed beds, as the intensity of the harvests was lower. The intensive,
industrial-scale reed harvesting started in the 20
th
century and affected both alkali and non-
alkali reed beds negatively (Valkama et al. 2008). As reed from alkali habitats has excellent
mechanical structure for industrial purposes, reed companies prefer alkali reed beds for
harvesting. Harvesting often results in a considerable decrease of habitat diversity by
decreasing the number of alkali marsh types present in the area mainly by the expansion of
reed into neighbouring habitats (see the habitat maps in Figure 5). Regular harvesting
generally decreases the patchiness of alkali marshes (Valkama et al. 2008). While a fine-scale
mosaic of old (with a high proportion of standing dead reed) and emerging young patches
(with low amount of dead plant material) is typical in unmanaged natural alkali reed stands, in
regularly harvested stands young reed forms a dense, uniform structure. In these regularly
harvested stands subordinate forb species are generally suppressed or even missing.
Figure 5. Habitat maps of a frequently harvested (A) and an unmanaged (B) alkali marsh stand (each
100×100 metres).
Alkali marshes are also threatened by considerable changes in land use. In some cases
stands of alkali marshes disappeared due to the establishment of fishponds. Stands affected by
the most severe decrease in water supply were sometimes ploughed. Alkali marshes are often
surrounded by arable lands, thus they can be subjected to infiltration of fertilisers and
pesticides.
