Environmental Engineering Reference
In-Depth Information
(
Rallus
spp.); swimming ducks (
Anas
spp
.
), grebes (
Podiceps
spp.) and marsh harrier (
Circus
aeruginosus
) (Ecsedi et al. 2004). Sodic lakes and alkali marshes represent important resting
and foraging sites for many endangered migrating birds, for example, red-breasted
goose(
Branta ruficollis
), lesser white-fronted goose (
Anser erythropus
). One of the largest
migration routes of the common crane (
Grus grus
) leads across alkali marshes of the
Hortobágy National Park, where half of the European breeding population consisting more
than 60,000 cranes stage over (Végvári & Tar 2002). During migration, alkali marshes act as
stepping stones for birds.
Alkali marshes of the Pannonian basin are the westernmost occurrences of alkali
wetlands in the forest steppe zone, which makes Central-European alkali marshes particularly
important (Deák et al. 2014). Alkali habitats (on 80,200 hectares) are best preserved in the
Hortobágy National Park (East-Hungary). Thus, extended alkali marshes of the national park
are one of the last pristine remnants of former alkali wetlands characterised by a nature-close
mosaic pattern. Alkali marshes are included as important wetlands in the Ramsar convention
and as a priority habitat type ―Pannonic salt steppes and salt marshes‖ to the Natura 2000
network.
2.
S
ITE
C
ONDITIONS
Alkali marshes are wetland habitats characterised by high stress levels owing to astatic
water regime and high salt concentration. They are typical in continental climate,
characterised by cold, humid winters and hot, dry summers. Alkali marshes are affected by
astatic water regime: they are present in areas with periodical inundation followed by dry
periods.
They are covered by water between spring and mid-summer (average water depth
reaching 30-50 cm) and often become dry till late summer due to intense evaporation. As
their water supply highly depends on precipitation, they can completely dry out. Water supply
of these habitats is originated from groundwater and surface waters. Surface waters originate
from floods or precipitation (mainly winter precipitation), however, due to the large-scale
river regulation works of the 19
th
century, floods are very scarce nowadays (Túri et al. 2013;
Varga et al. 2013).
High alkalinity is typical in the soil and water of alkali marshes, which results in high
osmotic pressure, unfavourable soil structure and suboptimal pH (Valkó et al. 2014a). The
soil of alkali marshes is characterised by high alkalinity, generally due to sodium and hydro-
carbonate ions. Salts generally originate from groundwater and also from surface water due to
intense evaporation and generally accumulate in the upper soil layers. Human disturbances
can result in a decreased salt content of alkali marshes. For instance, decrease in water table
(drainage) can cause the leeching of the salts, while permanent inundation by freshwater
(when salt marshes are used as water reservoirs or fishponds) can cause a decrease in salt
concentration. This can result in a considerable change or even loss of the alkali marsh
character.
