Lake Neusiedl

Ecological characterization

- Figure 12. Lake Neusiedl

Lake Neusiedl is situated in the border region between Austria and Hungary (Figure 12) and represents the westernmost steppe lake of the Euro-Asiatic continent (Bekesi, 2007). In the region of Lake Neusiedl–Seewinkel several natural sanctuaries have been established over the years: partial nature reserve and protected landscape (since 1962), biosphere reserve (since 1977), Ramsar-protective area (since 1982), National Park (since 1993), European biogenetic reserve, Site of Community Interest, Special Protection Area. Due to its geomorphological, chemical and biological peculiarities the lake was finally nominated as Natura 2000 site and since 2001 also world cultural heritage of UNESCO.

During the retreat of the Tethys sea 13 million years ago, a large amount of salt was dropped and enormous amounts of sediments (forming a 400-600 m thick layer) were deposited in the area covering the Vienna Basin and the Hungarian Plain. After a consequent tectonic subsidence, postglacial feeder streams and precipitation began to fill the tectonic depression about 19000 years BP.

Today, the north and the east sides of the lake are formed by Danubian and glacial danubian gravels. The west side consists of limestone, called “Leithakalk”, while the south-east area is covered by the Hanság (Fen in Hungarian), a former bog and marsh land which has been partly transformed in moist meadows after partial drying out (Figure 13).

- Figure 13. The Hungarian Hanság around Lake Neusiedl.

The drainage of the swamps in the south-east areas of the lake (Hansag or Waasen-region) and the transmutation to agricultural land resulted in the disappearance of wetland species in these regions. In the 20th century the reed belt (Phragmites australis) started to extend occupying both shores and open water, covering 54% of the whole lake surface (Dinka et al., 2004). Presently the lake consists of more reed (178 km²) than open water (143 km²). Ecologically the reed belt took over the role of the former Hansag-Waasen-wetlands and consequentely many autochthonous animal and plant species moved their habitats (Führer, 2010)

The lake covers a total area of about 315 km2 and has a mean depth of 1.2 m, with a catchment area/lake area ratio of about 3:1, quite unusual for such a large lake (Figure 14). The average water depth of 1,4 m with a maximum depth of 1,8 m result in a small water volume.

Figure 14 report 5.1.4 fig. 68 pag.106

The climate of the region Burgenland is continental and characterized by annual average precipitation (574 mm) even a little lower than the annual potential evaporation (630 mm), resulting in a net water loss in dry years. The summer months are hot and dry and the winter months fall below 0 °C for short periods.

The present water budget of Lake Neusiedl mainly depends on precipitations that contribute 78% (ca. 184,3 Mio. m³ y

) to the water gains of the lake. A small input is provided by the inflow of the River Wulka that contributes about 20 % (47,2 Mio. m³ y-1), while the contribution of ground water inflow is almost negligible (2 %) (Eitzinger & Kubu, 2005). As the lake has only one artificial outflow (Einser-Kanal) regulated by an Austro-Hungarian lake management contractor, there may be some years where no water at all is drained through the channel. In the average, it is assumed that about 10% of the lake water losses are caused by the channel and 90 % by the natural evaporation from the lake surface.

If the water volume of a shallow lake varies considerably over the years and the seasons, it is evident that the lake area of the lake changes as well. In the past, the area of Lake Neusiedl varied from 0 (lake vanished in 1865-1871) to nearly 500 km² in the 18th century. Today the lake’s area is generally 321 km² because the management contract for the Einser-Kanal is aiming to keep the water level constant at 115,5 m a.s.l. since 1965. However, high precipitations may occasionally cause small-scaled floods of the wetlands near the lake, as happened in 1997. Before the water level regulation, high water levels were observed in 1941 (maximum 116,1 m a.s.l.), and still earlier in the 18th and first half of the 19th century.

Lake shallowness and frequent winds are responsible for the permanently well-mixed conditions of Lake Neusiedl, so that the horizontal variability results more important than the vertical thermal stratification (Dokulil & Padisák, 1994). The water temperature lake ranges from 0°C in winter under the ice cover to 28°C in summer.

The specific salt content of the lake is relatively high compared to other lakes in the Alpine region (about 1700 mg L-1). The main salt is Na2CO3, with NaCl, Na2SO4, and MgSO4 as minor constituents. The lake conductivity is 1300-3500 µS cm–1, and pH 7,7-9,5. In the early 1970s water quality worsened due to anthropogenic impacts. A considerable increase in nutrient concentrations in Lake Neusiedl occurred (Figure 15), triggered mainly by growing tourism and intensification of agriculture, especially expansion of viticulture. Influential causes for eutrophication of the lake were tributaries with high nutrient load, diffuse inputs (erosion by wind and rain from farm land), lodges within the reed belt, anthropic pressure, animals, remobilisation of nutrients from the reed belt and insufficient treated sewage discharge. As a consequence ecosystem changes occurred. Plankton biomass increased considerably and algal blooms appeared, first in autumn of 1977 then again during the e d of the 1990s

- Figure 15. Total phosphorus content (left) and total nitrate content (right) (mg l-1) (annual means of all monitoring stations) in water of Lake Neusiedl. - Figure 16. Lake Neusiedl and the surrounding communities.

After beginning of sewage treatment in early 1980s (see below), TP gradually decreased to the present annual average of ca. 50 µg L-1. On the other hand, nitrate concentration showed a uninterrupted increasing trend since the 1960s, with present annual concentration around 300 µg L-1 NO3-N. Nitrogen concentrations appear to be positively correlate with precipitation (Herzig & Dokulil, 2001) (Figure 15). According to the present P level Lake Neusiedl is classified as mesotrophic (eutrophic within the reed stands).

Lake Neusiedl is surrounded by more than 20 directly adjacent communities (Figure 16). With the exception of Neusiedl am See all the surrounding cities and the cities and municipalities within the catchment area of the river Wulka discharge their (treated) wastewater into the lake today. The amount of wastewater in the year 2010 was more than 22,106 m³. Due to adaptation measures at the wastewater treatment plants in the last 30 years it was possible to strongly reduce nutrient concentration.

Also due to the amelioration of water quality, tourism markedly increased since the 1960s and at present represents the most important economical activity for the region. The Lake Neusiedl, named the “Vienna’s Beach”, offers many kind of sports, a wide range of excursions and cultural events.

Traditionally fishing was the most important resource for the local population, because of the presence of high number of fish species. Since the second half of XX century husbandry became important, with herds of cattle, horses and pigs grazing on common pastures, and the agriculture was intensified, in particular viniculture and other cultures such as wheat and rye, oil crops, grape and sunflower.

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