katrinteubner

geographical location of the lake in the austrian alps

Alpine lake Hallstaetter See, 2000:
View from the popular trail "Ostuferweg" northward onto the lake. Hallstaetter See (47°34’26.8''N, 13°39’26.3''E) is an alpine lake in the Salzkammergut district in Upper Austria, at 508 m above the sea level. The lake basin area is 8.6 km², the water volume 557 x 10⁶ m³ and the maximum depth 125 m. The lake has an elongated shape, which extends over a distance of about 8 km from north to south. The deep lake belongs to the same catchment as lake Traunsee.
The theoretical water retention time of Hallstätter See is a half-year only (Table 1 in Dokulil & Teubner 2002 R, Table 1 in Dokulil et al. 2006 R) . This is even shorter than for lake Traunsee, having about a four times higher lake water volume than Hallstaetter See. As described for lake Traunsee, the reason for the particular short water retention despite the large size of deep alpine water basins is the large discharge of the river Traun, which flows through both lakes.

Alpine lake Hallstaetter See, 2001:
View southward onto the lake elongated between north and south. In the back, on the west bank of the lake, the town Hallstatt can be seen.
The water retention time of large deep lakes, however, is usually much longer, as already discussed on the website of lake Traunsee S comparing Traunsee and Mondsee. Mondsee S has about the same water volume (510 x 10⁶ m³) as lake Hallstätter See, is also located in the Salzkammergut district in Upper Austria but in the neighbouring catchment and has a theoretical water retention time of 1.7 years. Lakes of very short water retention lasting from days to a few months are typically flushed shallow lakes in lowland river-floodplains and are called 'riverine lakes' S and hence have a quite different limnology compared to that of deep alpine lakes.
The Hallstatt area is an ancient place. The importance of Hallstatt is mirrored in the eponymously named period of Early Iron Age ( ‘Hallstatt’ culture). This populated site is also rich in Late Iron Age history ( ‘Celtic’ culture). Palaeolimnological studies on sediments of lakes in this alpine region describe very well the impact of climate and land use for this mountain area from these prehistoric periods until recent times (see e.g. Schmidt et al. 2008 R & 2009 R).

The medieval town Hallstatt is located in the south of the west bank of the lake. According to descriptions by Simony in 1866/67 (see page 51 in Grims 1996 R), all early morning many salt miners travelled in wooden barges (boats) on lake Hallstaetter See to Hallstatt, and were then hiking the mountain Hallberg (Salzberg at Hallstatt) via serpentines to go to work. Even in recent times, a few decades ago, this small town was still a remote place as paths on the western lake shore were too narrow to allow traffic to pass to this area. A tunnel system of roads and parking terraces along the rocky west lake bank now enables local people and visitors to get easy access to this place.

River Traun, 2005:
This river connects the both alpine lakes Hallstaetter See and Traunsee. Its large discharge causes the short theoretical water retention time despite the large size of water basin of these both deep lakes. Town Bad Duerrenberg near city Halle, 2005:
Brine was not only used for salt production in the middle ages but was also used as a spa until now as illustrated here for the spa town Bad Dürrenberg (Germany). Also towns near Hallstatt (Austria) were popular as spas. The photo shows a detail of encrusted salt from a graduation tower. Inset: Graduation tower with wooden frame constructions stuffed with brushwood of Prunus spinosa. Brine (‘Sole’) is pumped onto the top and trickles then along the brushwood. While water evaporates, salt encrusts the brushwood. It is said that breathing the aerosol while strolling along the graduation tower is like a walk in sea air benefiting health.

Hallstatt is famous for salt mining in the Austrian Alps. It is one of the oldest salt mining places around the world and was used for more than 7000 years. It is suggested that the name ‘Hall’ does not refer to the word ‘salt’ of Celtic Language but to the technically newly introduced treatment for salt crystallization commonly described in the language of High and Middle German in the middle age, to the name of a processing plant, where underground brine is heated up in a ‘salt pan’ (Sudpfanne, Salzsiedepfanne, Saltzpan) to get solid salt (Stifter 2004/2005 R). Simony wrote that the house with the salt pan was the heart of Hallstatt , and that it was the working place for about 70-80 people (“Das Pfannhaus ist das Herz Hallstatts,…”; page 52 in Grims 1996 R). Such houses (Pfannhaus, Sudhaus, Siedehaus) with ‘Salzsiedepfannen’ were frequently used to produce salt in the middle age in Europe, at places where natural and artificially underground brine (in German ‘Sole’) was available (e.g. the region around the city Halle in Germany and small towns in the neighbourhood such as Bad Duerrenberg and Bad Koesen). This technique of salt production via underground produced brine was efficient in the medieval period but needed lots of firewood. High amounts of wood ash (in German ‘Asche’) containing waste of salt compounds needed to be handled. In Bad Duerrenberg, a small town near Halle for example, the waste of salt production by encrustation of brine was transferred by small railway containers (Loren, Güterloren) to a salt mine waste tip (ash-salt tip, ‘Ascheberg in Bad Dürrenberg’ at ‘Salinenstrasse’, road section between Ostrauer Strasse and Merseburger Strasse, 51°18’2.1''N, 12°3'844.08''E). This salt mine tip is now moderately covered by vegetation. Among other halophilic plants, dense stands of the yellow flowering Horned Poppy (Glaucium flavum) can be there found at the surface where soil is mixed up with plate-shaped mineral salt crusts, the deposited waste from salt pans. Different from Bad Dürrenberg in the low land, in Hallstatt the area needed for the deposition of salt waste was limited in the mountain environment. The ash-salt waste was simply dumped into the lake for hundreds of years. At the time of the visits by Simony in 1866/68, one third of brine only was treated to make salt in Hallstatt. The remaining brine was pumped via pipelines to the village Ebensee at Traunsee, to the ‘Sudwerk’ that was founded years ago, in 1607 (page 52 in Grims 1996 R). In recent decades, the brine was not yet treated in Hallstatt, but all transferred via pipelines to the plant in Ebensee at lake Traunsee (see also on this website the effluence of mineral industrial tailings in the recent period in Traunsee until the soda production ended in 2005). Salt mining in this alpine region played an important economic role but also affected both the large lake ecosystems, Traunsee and Hallstaettter See. The impact on Hallstaetter See is shortly described in the following section about the limnology of this lake. For Traunsee S see limnological details on the respective lake website.

Town Hallstatt at Hallstaetter See, 2005.
Many houses of the small medieval town are built into the steep cliffs of the lake bank. Houses as left but the photo is taken in 2010.
Cars are somehow hidden in this town, a place of ancient history. Traffic passes through a tunnel system to get access to the town. Visitors leave their cars on parking terraces at the cliffs or at a distance of a 15-minute walk away from the centre of the small middle-aged town.

Listening To People: 'Times change, I sometimes think, but looking at the medieval town Hallstatt from this scenic point might tell a different story: Did this view onto the town from this parking terrace always look the same?! The same beautiful scenery as the first time I have visited this place, and this is absolutely great! You feel relaxed when you arrive over here, as you know: That's how it should be: This is Hallstatt! How many times have I been here and shared this view with family and friends? I haven’t counted these visits yet! This time I was here with Joe and said: “Look, what a scenic view onto the lake. How lovely this town looks! This gorgeous view downhill onto the market of Hallstatt! I admire these white-painted houses uphill! They are looking as if they have grown into the mountain, aren’t they?” Every time I am in Hallstatt, it is a must to look at these houses on the rocks, and then I just take a photo standing right here. And indeed, just having finished saying this sentence, I took another photo. Enjoying the romantic scenery it does not cross one’s mind how hard life must have been for numerous miner families who have lived or worked at this place. “The white houses look marvellous”, I continued to Joe, “this is one of my favorite places, surrounded by such a fabulously beautiful landscape? Just being connected to the world via the Internet, it might be fantastic to live at such a place!!! Do you think so too, Joe?” - Joe did not reply promptly and after a while he slowly said: “Well, to be honest, I would not want to live here. This place is not convenient for living here at all” – and while telling he took another look around and gently shook his head. “The space is too narrow”, he said, “you could not have your own grain field, no livestock and even no poultry - nothing. And this mountain place is even unsuitable for vineyards.” Joe smiled when he continued talking with a twinkle in his eye. He said that he would miss the vineyard and would also miss the old large cherry tree right on top of the vineyard. “Come on, Joe”, I replied, “what would you need a cherry tree in a vineyard for?” “Well, I can tell you this!”, said Joe, “In the past, they used to plant a cherry tree for shelter, for being protected from rain; also for having a shade at noon, when you had a one-hour lunch break in the yard, AND you simply could use the tree to tie up the horse!!! The shade of the tree is also convenient for the horse! And don’t forget that you can enjoy eating some cherries”, he laughed. “Ok”, I said, and was thinking: “Indeed, times have changed!” ’

Town Hallstatt and lake Hallsteatter See, 2005.
As the left photo but slightly turned view, 2005.

As above but 2007.
As above but 2007.
.

As two photos above but 2010.
This scenic view onto the centre of the small medieval town and the lake is taken from the car parking terraces, which were built in recent history.As the two photos above but 2010.
Slightly turned view onto the most southern part of lake Hallstaetter See.

Town Hallstatt, which is located in the mountain range Dachstein of the Austrian Alps, is part of the UNESCO World Cultural Heritage. It is declared as the ‘Hallstatt-Dachstein Salzkammergut Cultural Landscape’. A description of this site together with another seven World Heritage sites in Austria is given in Linder & Dröscher (2007, R).

we look back at the lake in year 2013: lake hallstaetter see has attracted lake scientists for more than 160 years

Lake Hallstaetter See, 2005:
Left inset – Depth profiles of lake water temperature measured in 1849 and published by Simony in 1850. The plotted data points show the graph for the date 31. August 1849, the other graphs are for April, May, and November.
Right inset - same as left but measured in recent decades and for lake water temperature in summer only (July, August). Summer data from 'Bundesamt für Gewässerökologie, Fischereibiologie und Seenkunde' .There is hardly any other lake in the Salzkammergut district that attracted naturalists for more than 160. Early studies in Hallstätter See were mainly based on the temperature depth profiles, and hence introduced limnological research in the alpine region and in Austria. Probably, the most popular publication of early measurements is by Friedrich Simony released in 1850 and was entitled ‘Die Seen des Salzkammergutes’ (‘The lakes of the Salzkammergut district’). Grims (1996) describes Simony as a naturalist, who was focused on land surveying of alpine mountains and of lake basins, but had also broad interests on glaciers, climatic ice age, mineralogy & geology and botany & zoology.
Simony used a minimum thermometer developed by Kapeller to measure water temperature along vertical depths in the alpine lakes in the Salzkammergut district (Simony, 1850). He wrote that eight minutes were sufficient enough for the thermal adjustment of the thermometer in the depth to measure reliable data. According to his description, the replicated measurements varied in the narrow range of 0.05 °C only. The temperature profiles of Hallstätter See by Simony are drawn in the left inset of the right photo. The graph for summer measured on the date on August 31 in 1849 is marked by plotting the individual data points, difficult to confuse with lines of the other measurements in April, May and November in 1849. This summer depth profile illustrates well that only the upper stratum of the lake, the layer of about 40 (to 60) m is warmed up in summer. This phenomenon of thermal stratification is common in deep lakes but was rather unknown at that time. With increasing air temperature from spring to summer, the lake heats up successively from the surface to deeper layers. This includes that (1) surface water of the lake is getting warmer, (2) the thickness of the warmed up surface layer increases consecutively (3) the thermocline 'grows up' and moves downward into deeper layers (4) and the resistance against vertical mixing increases (thermal stability of water column increases). According to these thermal gradients, the water body of a deep lake reaches a stabile thermal stratification in late summer. Further descriptions about the thermocline, the metalinmion and the thermal stability of water bodies is presented in the section ‘annual cycles by heating and cooling of the water body’ on the website about lake Mondsee S, and in the section ‘Ammersee and Mondsee: two lakes but one story’ on the website about lake Ammersee S. It is worth mentioning here, that the thermal gradients in Hallstaetter See are partly interfered with by a stronger salinity gradient promoting a particular type of mixing, the meromixis as it will be described under the section below.
Looking at recent temperature depth profiles for July and August from the seventies to nineties shown in the right inset, it reminds us that the summer water surface temperature may vary a lot among years in Hallstaetter See. These summer temperature records ranged at the near surface of 2 m from 9.7 to 18.5 °C and at depth of 9.5m from 9.5 to 13.15. The individual measurements on August 31 in 1949 by Simony at 2 and 9.5 m refer to a bit lower temperatures, namely to 9 and 7.3 °C respectively. Taking into account the different equipment that was used about 160 years ago, the temperature records by Simony should be interpreted with caution when compared with recent temperature data sets. Besides this uncertainty, however, one may say that Simony has just measured in a year of a particularly cold summer. Others might claim that warming by climate change might be most responsible that the temperature measured by Simony is rather an outlier than within the range of statistical deviation from the expectation when compared with recent times.
According to monthly means of surface temperature in August, measured in Hallstatt, the temperature tended indeed to increase by about 1.326 degree over a period of 100 years (1901-2000), namely from 14.9 °C to 15.74. During this period, in 54 years occurred a negative anomaly in August, which was on average –1.15 °C. In the remaining 46 years, a positive temperature anomaly was recorded and here the mean temperature in August was on average 1.38 °C warmer than expected by the long-term trend. In extreme years, the surface temperature in August could be even 3.28°C lower or 4.16 higher, respectively. These few numbers illustrate the range of temperature variation in August in individual years during the 20th century. It shows that the measurements by Simony are not that extreme as at first glance they might have seemed when comparing the temperature depth profiles of both discussed graphs. Climate warming, however, does not follow necessarily linear trends over too long periods and therefore, the trend estimated for the 20th century cannot be simply used to calculate backwards what the usual temperature in August 1849 would have been. For this reason, the question is not yet answered here to what extent climate warming or an extreme cold summer or simply the uncertainty caused by the use of different instruments was most responsible that Friedrich Simony had written in his notes the numbers of a relatively cold-water body in August 1849. The climate response on the WHOLE water body of Hallstaetter See will not be described on this page.
Evidence for significant DEEPWATER warming at depths of 80, 100 and 120m in Hallstaetter See, however, was found in a recent study (Table 2 and Fig.2 I in Dokulil et al. 2006 R). These statistically significant trends in Hallstaetter See were in concert with other lakes of the Salzkammergut district and also lakes across Europe. Other deep alpine lakes in Austria, however, seemed to respond more closely to global climate signals than Hallstaetter See (see the correlation with the NAO-index integrated over the period January to May in Table 4 and Fig.3 in Dokulil et al. 2006 R; NAO signal see also Mondsee S and Ammersee S). The reason for the individual lake response of Hallstaetter See can be attributed to the low wind-exposure of the alpine valley lake basin, which extends from north to south (see page 2789 in Dokulil et al. 2006 R). It is further argued, that Hallstätter See is locally surrounded by a cold environment as the lake receives on average about five hours less sunshine than other alpine lakes in it’s neighbourhood. This situation thus counterbalances the impact of global warming and explains why the significant increase of deepwater warming is not that strong compared to other neighbouring lakes (e.g. see for lake Traunsee Table 2 and Fig.2 J in Dokulil et al. 2006 R).
Another reason for the individual lake response to climate signals can be found when considering the study by Ficker et al. (2011 R), even the impact of climate was not mentioned in their analysis. They observed two water-mixing regimes that occurred alternatively from time to time in recent decades in Hallstaetter See, the meromixis and holomixis. The shifts among the both mixing regimes were linked to the many ups and downs of water density in the salt-mining lake, namely by the sudden increase of chloride concentrations after every brine spill, on the one hand, and a decrease by washing-out on the other (Fig.2 in Ficker et al. 2011 R). While periods of high chloride were associated with meromictic mixing, periods below a certain threshold concentrations of chloride referred to holomixictic mixing. The toggled two mixing regimes that were mainly linked to fluctuations of chloride concentration (and not primarily to temperature effects) might thus also explain the more individual lake response to climate signals (NAO) in Hallstaetter See than compared with other deep alpine lakes.

Two studies - by Liburnau (1898) mainly about zooplankton and by Keissler (1903) about phyto- and zooplankton – describe very early the planktonic species in lake Hallstaetter See. Keissler used an Apstein plankton net to take samples, and hence he describes only large or colonial phytoplankton species as e.g. the green algae Staurastrum paradoxum, Sphaerocystis schroeteri and Botryococcus braunii, the diatoms Cyclotella comta and Asterionella formosa, the chrysophyte Dinobryon divergens and the dinoflagellates Ceratium hirundinella and Peridinium cinctum. The size of these phytoplankton forms is larger than (30 -) 50µm. Large species are, however, usually much less abundant in alpine lakes than small species. It could be shown for other alpine lakes in Austria and in Switzerland, that the  small cell size fraction of only 0-10 µm contributes more than 50% to the total chlorophyll concentration of phytoplankton (Teubner et al. 2001 R). In this way, the samples by Keissler certainly missed main components of phytoplankton. Despite these uncertainties, Kreissler is probably right to emphasize that the abundance of the species found in net phytoplankton from Hallstaetter See was in particular low when compared with those of other lakes in the Salzkammergut district. He also stated that phytoplankton was only found in the upper 60 meters, which corresponds to the warmed up top layer described by Simony. Taking depth integrated net samples, Keissler also measured the water transparency (see details in the section below).

Sea balls, 2013:
Fibrous sea balls and mussels on the beach of the Mediterranean Sea. The shape of these sea balls looks very similar to the lake balls found in lake Hallstätter See (called ‘Die Hallstätter Seekugeln’ or ‘Lärchennadelnbälle’ acc. to Morton). The lake balls are also found in other lakes in Austria. Sea balls, 2013:
Same as the left photo but a detailed view. These balls from a marine environment are looking less coarse than those of lakes built by needles.  

The fibrous spherical to ellipsoid formations found in the littoral zone and on the shore of Hallstätter See are perhaps the greatest curiosities for people enjoying nature and lakes, and were described first for Hallstaetter See by Friedrich Morton. He called these fibre-lake-balls ‘Die Hallstätter Seekugeln‘ ('The lake balls from Hallstaetter See', Morton, 1924 R R), and in a later publication ‘Lärchennadelnbälle’ (‘Balls made by larch needles’). These balls are processed from needles of Larix decidua. Morton wrote that he found them most abundant in shallow shore areas of Hallstätter See, where the needles built a dense layer of about 10 centimetres on littoral sediment washed on the waves. The intertwining of plant fibres of Larix needles begins on small pieces of rhizomes e.g. of Carex from the littoral or other material of rough surface. The initial small balls grow up further in the moved shallow water. According to Morton, these balls were common on the south-east shore of the lake, between the inlet of River Obertraun and the village Winkl; and were also found but more rare along the west shore between ‘Lahn und dem Landungsplatze im Markte’. These natural fibre marbles actually might have fascinated him, as he published a series of seven (!) short notes on ‘Lärchennadelbälle’ found in Hallstätter See (the first was published in 1934, see all references in Müller & Werth, 1982 R) and one publication for a lake nearby, the Offensee (balls were found close to the outlet of stream Offenbach; Morton, 1964 R). Such fibrous balls (‘Seebälle / Meeresbälle’ ; ‘sea balls / marine balls’) seem to be more common in the Mediterranean Sea than in lakes (see the two photos above). Sea balls are built by other plant fibres than Larch needles, but look very like the lake balls, which are shown in photos published by Morton 1964 R.

the gap in this saline aquatic ecosystem: is the crystal-clear water of Hallstaetter See indeed the signature for a healthy environment?

Lake Hallstaetter See, 2005:
The crystal clear water promises at first glance the high water quality of this Alpine lake: Does it indicate here indeed a healthy ecosystem? One may argue that water transparency is the best parameter describing water quality of inland waters. According to Keissler (1903), the Apstein plankton net was visible up to 3 to 6 m below the water surface during sampling from July to September 1902 in Hallstaetter See (the average was 4 m, 12 measurements). The standard measurement with a Secchi disk (see preface S) in recent decades revealed a Secchi transparency depth of about 4 to 5 m in June and August in this lake, respectively (ranging from 1.5 to 7 m, see Fig.8 in Dokulil & Teubner 2002 R). The water transparency depends mainly on the amount of floating particles in the water column, which are described as inorganic and organic suspended solids. The latter are mainly phyto- and zooplankton that are most abundant during growing season (see seasonal development of phytoplankton on the page about Bergknappweiher S). When Secchi depth is measured in winter or before the spring peak development, the values can be even higher. In the case of Hallstaetter See the Secchi depth is early spring about 8 m, ranging from 7-10 m (see data for March in Fig. 8 in Dokulil & Teubner 2002 R). Such crystal-clear water, as found in Hallstaetter See, seems to be very attractive for tourists to visit and enjoy the alpine lake region. Only in few lakes in the Salzkammergut district, as e.g in lake Attersee S (see Fig. 8 in Dokulil & Teubner 2002 R) is the water transparency even higher than in Hallstaetter See.

The east shoreline of Hallstaetter See, 2005:
The popular trail 'Ostuferweg' takes through meadows, orchards and woods along the shore. The east shoreline of Hallstaetter See, 2001:
Meadow orchard covered with fresh snow at Easter, in spring (April). On the rightside a boat house is seen.  

The east shoreline of Hallstaetter See, 2001:
Traditional wooden alpine house surrounded by meadow orchards. The east shoreline of Hallstaetter See, 2000.
Blossoming summer meadow with false oat-grass (Arrhenatherum elatius) and hawksbeard (Crepis spec.).

The east shoreline of Hallstaetter See, 2005.
Sustainable animal husbandry and small farmyards at this alpine lake. The east shoreline of Hallstaetter See, 2001.
Woods along the lake (European spruce, Picea abies and European Beech, Fagus sylvatica).

In view of biota living in the lake water body, water transparency refers to the underwater light climate that controls the growth of microbial primary producers (e.g. algae). The Secchi depth of about 4.5 m in summer and 8 m in early spring in Hallstaetter See corresponds to an euphotic depth covering about the top 15 and 27 m, respectively (see also underwater light climate described on the page for Mondsee S and Traunsee S). The epilimnetic layer (see depth profiles for summer water temperature shown in the figure above) might thus largely exceed the euphotic layer. The proportion between the concentration of chlorophyll-a (Chl-a), which is used as a rough estimator for biovolume of phytoplankton, and the concentration of total phosphorus (TP) in Hallstaetter See, is relative low when compared with the Chl-a:TP proportion in other alpine lakes of the Salzkammergut district, like Attersee, Mondsee, Traunsee and Wolfgangsee (see Fig. 6.54 in Dokulil et al. 2000). In other words: It seems that the phytoplankton yield is much less than might be expected from the total phosphorus pool size in Hallstaetter See (see also Fig. 8 in Dokulil & Teubner 2002 R). Even though the water looks crystal-clear the surprisingly low phytoplankton biomass raises questions about the ecosystem integrity or the ecosystem health. One reason among others could be perhaps the mismatch between the euphotic depth and mixing depth described for this lake before. Another impact might be due to the large discharge by the River Traun, which is passing the lake Hallstaetter See (see the plume horizon of the River Traun identified in the top 6.5 to 20 m along the 140 m depth profile in Traunsee S). Salinity, however, might not simply explain the unexpected low biovolume of phytoplankton as values for conductivity and chloride are much lower in lake Hallstaetter See than in lake Traunsee. Further, the low nutrient concentration, in particular of phosphorus, would not contribute to understanding the low phytoplankton development in Hallstaetter See, as phosphorus concentration in Attersee is even much lower than in Hallstaetter See but the amount of phytoplankton biovolume relative to the total phosphorus pool is commonly higher in Attersee than in Hallstaetter See. As lake Attersee S is an ultra-oligotrophic lake and as the lake was not used for salt mining at all, phytoplankton assemblages of this lake occur in a pristine alpine ecosystem. In view of the European Water Framework Directive lake Attersee is thus described as reference ecosystem for the Austrian alpine lakes in the Salzkammergut district. For many reasons, however, coarse and simple monitoring measurements in Hallstaetter See in comparison to other mentioned alpine neighbouring lakes, that strictly satisfy the rules of European Water Framework Directive, do not provide a satisfying perspective to understand the complexity or functioning of these ecosystems. A subtler approach, however, seems to be more appropriate to answer the question of unexpected low biomass of primary producers in Hallstaetter See. An advanced ecosystem study might cover the utilization and turnover of nutrients (in particular of phosphorus, see small scale phosphate acquisition on the page preface S), the potential growth inhibition of biota and the match or mismatch of allocation pattern among various planktonic organisms - bacteria, cyanobacteria, algae and the many types of zooplankton -, and also fish. Such a more detailed study about the interaction of aquatic organisms with their environment along depth layers would be essential to answer the question how efficiently nutrients can be exploited by biota in Hallstaetter See.