katrinteubner

geographical location of the lake in the austrian alps and its ecology

Lake Attersee, 2001:
View over the lake from the south-west shore. Lake Attersee (47°52’29.9''N, 13°32’54.5''E) is located in the Salzkammergut district in Austria at 469 m above sea level. This lake lies between Mondsee S and Traunsee S, about 10 or 20 km away only. The three alpine lakes Attersee, Mondsee and Traunsee are, therefore, in close proximity. According to its lake water volume of 3,945 x 10⁶ m³, Attersee is the largest lake in Austria. The lake is further characterised by an area of 45.9 km² and a maximum depth of the water basin of 170 m. Attersee is hence 20 m shallower than the deepest and second largest lake in Austria, lake Traunsee, but considerably 100 m deeper than Mondsee. Despite the almost same lake depth for Attersee and Traunsee, the two deep lakes are hydrologically very different. The mean water retention time of Attersee is seven years and hence six years longer than that of Traunsee (Table 1 in Dokulil & Teubner 2002 R, Table 1 in Dokulil et al. 2006 R; see also the large discharge of the River Traun and the history of salt mining in case of the alpine lake Traunsee S).
In view of lake ecology, Attersee relates closer to the relatively shallow lake Mondsee than deep Traunsee, as Attersee and Mondsee are located in the same catchment disconnected to the catchment of Traunsee.

The nutrient status of Attersee is ultra-oligotrophic. The main limiting nutrient element, phosphorus, is particular low. Annual averages of total phosphorus concentration are usually below 0.5 µg per L. This nutrient-poor status corresponds to a low biomass of photosynthetic microorganisms and refers to chlorophyll-a values of 0.6-1.4 µg per L (Fig.8 in Dokulil & Teubner 2002 R). Secchi transparency depth in summer is still high, namely on average about 7-9 m in June and July. During the non-growing peak season Secchi depth is even much higher, namely e.g. about 19 m in early spring (see values for March in Fig.8 in Dokulil & Teubner 2002 R). According to low phosphorus concentration and various typical phytoplankton species, in concert with a common lake hydrology, lake Attersee is described as the reference ecosystem for alpine lakes in the Austrian Salzkammergut district by the rules of the European Water Framework Directive (WFD). The phytoplankton assessment of Austrian lakes in view of WFD (Dokulil & Teubner 2005 R) reveals that the phytoplankton biomass in lake Attersee is mainly built by species, which are known to be most abundant in oligotrophic alpine lakes (such lakes are popularly described as ‘nutrient-poor’, ‘natural pure-water’ or 'crystal-clear' lakes). In addition to this ecological assessment, aspects of the legal meaning of WFD, which refer again i.a. on Austrian lakes, are, for example, described in Berl (2014).

Lake Attersee, 2002:
The crystal-clear water of Attersee convinces well of the reference ecosystem for all the other alpine lakes in the Salzkammergut district. Lake Attersee, 2001:
View over the lake from the west shore. The road (seen right side of the picture) and areas used to build up new constructions are almost everywhere close to the shoreline and are shrinking ecologically valuable areas of the natural land-water interface.

Lake Attersee is still a popular tourist attraction. The excellent transparency of lake water goes hand in hand with low-nutrition in the alpine catchment of the lake, benefiting from sustainable agriculture and sewage treatment plants. The pure lake water, however, goes not together with an ‘untouched nature’ of landscape near the shore. The road traffic is very close to the shoreline almost everywhere around lake Attersee. Natural habitats of the land-water interface (wet meadows) are largely replaced as traditional farming has been more and more substituted by vacation settlements. Limited areas of narrow rocky shorelines that are unsuitable for residential areas are still less impacted. 

the catchment of alpine lakes in the Salzkammergut district: sustainable animal husbandry in lower valleys and higher pastures

Traditional animal husbandry in the Salzkammergut lake district:
Livestock is grazed in high pasture during summer.
Photo: Lake Tappenkarsee, 2002. Traditional animal husbandry in the Salzkammergut lake district:
Suckler cow husbandry; herds are grazed in high pasture during summer.
Photo: Pasture 'Schafberg-Winkl', 2005.

Deep living Planktothrix rubescens is an exception to the rule of planktonic primary producers in a lake. Different from Planktothrix rubescens most photosynthetic organisms need much higher light intensities than dim light for photosynthesis. Hence the primary producers are growing in the surface layer in lake Mondsee. This lake surface layer inhabiting commonly photosynthetic organisms extends from the top 100% light intensity to deeper strata where at least 1% of surface light intensity is penetrating. This surface layer is called the euphotic zone. Phytoplankton organisms, however, are not necessary evenly distributed in the euphotic zone along the vertical profile. The near-surface maximum of phytoplankton biomass most days a year or at least on calm days without mixing by wind, is found at the shallow depth with 11-12% of surface light intensity. Such light intensities are typically found at 2-5m water depth in an alpine lake like Mondsee. At the very near surface, at 0-0.5m, usually not that many phytoplankton organisms are occurring in Mondsee as stress of high light intensity and UV radiation are inhibiting photosynthesis and hence reduce phytoplankton growth rates on the top surface of the lake.

Traditional high pasture dairy farming in the Salzkammergut lake district :
In front is seen the residential house of an alpine farmer family, taking care their cattle in high pasture during summer time. The house is further used as a small alpine restaurant/alpine hut ('Almhütte' ).  The cattle shed (small building left side) is here separately from the residential house. This is rather different from common high pasture dairy farms where the residential area/restaurant is an annex building to the cow stable.
Insert: Livestock is grazed in high pastures, suckler cow husbandry.
Photo: Lake Hinterer Gosausee, Pasture 'Holzmeisteralm', 2000. Traditional lower valley dairy farming in the Salzkammergut lake district:
Many of such small modern stables are built according to the traditional architecture where the residential area of farmer’s family and the stable with the boxes for the cows are joined by an indoor access. To run such a dairy farm by ‘living under one roof’ means to take care the cows all day- and night-time, to milk them twice every day the week and weekend, throughout the four seasons. Usually, part-time farmers operate such small size farm facilities. This means that the farmer is employed somewhere else and helps milking the cows in the early morning (4 am) and late afternoon (4 pm) and is doing other physically demanding farming work. The farmer’s wife, however, does most of the taking care of the dairy cows, from milking to cattle trade.
Photo: District Mondseeland, 2005.

Aquatic plants, called macrophytes, grow well on a wetland close to the shoreline or under-water (littoral) until at water-depth where sufficient light is still available for plant growth. The morphology of the water basin of deep alpine lake Mondsee refers to steep shores and hence, the shallow zone of the shore, the littoral zone of the lake, is narrow for macrophyte stands living in the water. In addition, a coarse grained sometimes even rocky underground at the bottom in the littoral zone, is not beneficial for macrophyte rooting and sprouting. Expanded macrophyte stands cannot be expected in lake Mondsee as found, for example, from riverine shallow lakes in North Europe or from mouths of large rivers as e.g. the Danube delta. Nevertheless, some macrophytes inhabit naturally the lake Mondsee. The macrophyte Phragmites australis for example, reed, occurs in lake Mondsee. This species is common in the world. Littoral reed belts are known to contribute to ecosystem health in many ways. They provide microhabitats for attached living algae (benthic algae, here mainly diatoms), which compete well for phosphorus and hence can be seen to control to some extent the growth of other algae as phytoplankton species. Further, non-living particles such as, for example, dead cells of phytoplankton, are settling in littoral reed stands. This organic material mineralised by microorganisms is fertilizing the sprouts of Phragmites. Underground rhizomes of Phragmites are known to contribute to an aeration of sediment. And it shouldn’t be forgotten that littoral reed belts serve as valuable habitats for many animals as molluscs, crustaceans, insects, fish and water birds.

High pasture animal husbandry in the Salzkammergut lake district:
Mountain huts are embedded in high pasture.
Photo: Pasture 'Genneralm Faistenau-Hintersee', 2002. High pasture dairy farming in the Salzkammergut lake  district:
The manageable number of milk churns seen on the photo refers to a ‘countable number' of cows being milked every day in the small stable. Traditionally, the annex to the stable serves as a living room for the farmer family nighttime and as a small alpine restaurant daytime in high mountain pasture. On sunny days, local food mainly produced by the farmer’s family is served outside.
Photo: Pasture 'Genneralm Faistenau-Hintersee', Hut Posch'n Hütte, 2002.

Traditional dairy farming in the Salzkammergut lake district:
Small mountain huts (‘Almhütten’) are nestled in high pastures and invite to have a rest enjoying the local food that is prepared by the farmer’s family. Such mountain hut is commonly the annex building to the stable of the dairy cow farm.
Photo: Pasture 'Postalm', Hut Postalmhütte, 2004. Traditional animal husbandry Salzkammergut lake district:
In tourist regions, it is attractive for the farmer’s family to serve food mainly produced by their own dairy farm. The food is prepared in form of popular simple dishes, e.g. cakes, salads, soups or cheese and cold or hot sausages served with bred and milk.
Photo: Pasture 'Eisenaualm', Hut Buchberghütte 2001.

The depth of the euphotic zone (euphotic depth) may vary among seasons and years. According to measurements of underwater light climate, the euphotic depth was on average at 11.3m in 1999 and at 11.1m in 2000 for lake Mondsee. In the case of only a few floating organisms, as in winter or in years of low nutrient concentrations, light is less absorbed or scattered by particles and can hence penetrate into deeper strata than at higher particle densities as in summer or nutrient-rich years. For practical reasons, the euphotic depth is usually not directly measured by a light sensor but is visually estimated by Secchi disc transparency (Secchi depth). Absorption and scattering properties by living particles containing even pigments are distinct from those of non-living particles and hence the conversion factor between both methods change with the season. During the growing season, when water transparency is mainly reduced due to living algal particles, i.e. from May to September, the Secchi depth might be multiplied by the factor 3.42 to calculate the euphotic depth.

Sustainable dairy farming in lower valleys in the Salzkammergut lake district:
Farmer’s wife usually does haymaking on this farm. The tractor is hence equipped with a child safety seat to take care of young children while doing fieldwork.
Photo: District Mondseeland, 2001. Sustainable dairy farming in lower valleys in the Salzkammergut lake district:
After the second time of haymaking, i.e in mid to late summer, the herd is grazed daytime in low pasture until late autumn.
Photo: District Mondseeland, 2000.