katrinteubner

die geografische Lage des Sees in den österreichischen Alpen

Alpiner Hallstätter See, 2000:
Blick vom Wanderpfad „Ostuferweg“ nordwärts auf den See. Der Hallstätter See (47°34’26.8''N, 13°39’26.3''E) ist ein alpiner See im Salzkammergut in Oberösterreich (Österreich), der 508 m über dem Meeresspiegel liegt. 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.

Fluß Traun, 2005:
Dieser Fluss durchfliesst die beiden Alpenseen Hallstätter See und Traunsee. Der starke Traun-Durchfluss bewirkt eine relativ kurze theoretische Verweilzeit des Wassers in beiden Seen trotz der großen tiefen Seebecken. Stadt Bad Dürrenberg nahe der Stadt Halle, 2005:
Sole wurde nicht nur für die Salzgewinnung im Mittelalter, sondern auch für Heilzwecke und Wellness bis jetzt verwendet, wie es hier für die Kurstadt Bad Dürrenberg (Deutschland) gezeigt ist. Auch die Orte in der Nähe von Hallstatt (Österreich) waren beliebt für Wellness. Das Foto zeigt Salzverkrustungen des Gradierwerkes. Eingefügtes Foto: Gradierwerk mit Holzrahmenkonstruktionen, die mit Reisig von Prunus spinosa gefüllt sind. Die Sole wird von oben über die Reisigzweige verrieselt. Mit der Verdunstung des Wassers lagern sich Salzkrusten auf dem Reisig ab. Es wird gesagt, dass das Einatmen des Sole-Aerosols der Gesundheit gut tut. Das Flanieren entlang eines Gradierwerks soll einem Spaziergang am Meer gleichen.

Hallstatt is famous for saltmining 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.

Stadt Hallstatt am Hallstätter See, 2005.
Viele Häuser der kleinen mittelalterlichen Stadt sind in den steilen Bergklippen am Ufer des Sees gebaut.Dieselben Häuser wie auf den Foto links, aber 2010 fotografiert.
Autos werden in dieser kleinen Stadt, einem Ort mit einer alten Kulturgeschichte, „gut versteckt“. Der Verkehr wird über ein Tunnelsystem entlang dem Rand der Stadt geleitet. Besucher parken ihre Autos auf den Tunnel-Terrassen an den Klippen oder auf Parkflächen, die einen etwa 15-minütigen Spaziergang entfernt vom Stadtzentrum liegen.

Menschen Zuhörend: 'Ja, es ändert sich so manches mit der Zeit, gerade heutzutage, wo vieles leider so arg kurzlebig ist. Oft denk’ ich so. Aber nicht, wenn ich hier auf der Terrasse steh’ und hinunter auf das kleine Hallstatt schau. Hier ist alles noch wie es vor Jahren war – zumindest über die Jahre gesehen, über die ich Hallstatt von Zeit zu Zeit besucht habe. Hier kann ich mich darauf verlassen, dass der Ort so aussieht, wie ich ihn schon oft geseh’n habe, am Ufer vom kristallklaren Hallstätter See, eingebettet in die Berge! Das ist Hallstatt! Wie oft war ich schon hier? Mit der Familie und mit Freunden! Ich weiß nicht, wie oft ich schon auf dieser Terrasse gestanden bin, wage es nicht mal dies grob abzuschätzen. Egal! Es zählt halt der Augenblick heute wieder einmal hier sein zu können, und das freut. Und heute bin ich hier mit Joe. Ich dreh mich vom See weg und schau verträumt hangaufwärts auf die weißen Häuser. Diese Häuser sind quasi mit dem Berg verwachsen! Wie werden sie wohl innen aussehen? Wer mich kennt, weiß wie gern ich dort mal einen Blick hineinwagen würde. Diese Häuser faszinieren mich immer wieder von neuem, sodass es jedes Mal ein Muss ist, sie nochmals zu fotografieren: mal sind sie von Schnee umgeben, mal im Regen, mal inmitten von Frühlingsgrün, in der gleißenden Sonne im Sommer oder eingeschlossen in den bunten Herbstfarben der Sträucher und Bäume. Und so fotografiere ich diese weißen Häuser auch heute wieder. Wunderschön! Wenn ich diese Häuser betrachte, kommt mir kaum in den Sinn, dass es für so manche Bergbaufamilie ganz sicher nicht leicht war an diesem Ort zu leben. Ich genieße den Blick hinunter auf den kleinen Markt von Hallstatt und sage zu Joe: „Die Aussicht ist herrlich! Und da oben, diese weißen Häuser, wie sie am Hang kleben, die haben es mir besonders angetan. ’s muss wohl leicht beschwerlich sein, seinen wöchentlichen Einkauf dorthin zu tragen?! ABER ich glaub’ mit einem zuverlässig funktionierenden Internetanschluss würde es mir gefallen dort zu wohnen. Das wär’ urnett! Joe, könntest du dir auch vorstellen hier zu wohnen?“ Joe antwortet nicht gleich, schaut vom Tal den Hang rauf und wieder hinunter auf den See und meint dann allmählich: „Also, ehrlich gesagt, für mich wär’ das nix. Ich würde hier nicht leben wollen. Der Ort ist überhaupt nicht gut zum Leben.“ Und während er dies sagt, schaut er leicht kopfschüttelnd über den See und das Tal dahin. „Da ist ja überhaupt kein Platz“, fährt er fort, „du kannst da keinen Getreideacker haben, kein Viehzeug, nicht mal Hühner! Gar nichts! Und überhaupt ist diese Bergwelt ja völlig ungeeignet für einen Weingarten.“ Und hier überzieht nun ein Lächeln sein Gesicht. Mit Augenzwinkern und abwinkender Hand fährt er munter fort: „Ja, ich würde hier meinen Weingarten vermissen! Samt dem alten Kirschbaum!“ „Ach komm, Joe“, sage ich, „wozu hat man einen Kirschbaum auf dem Weinberg?“ „Ich kann dir sagen, wozu ein Kirschbaum gut ist“, entgegnet Joe lachend. „Früher haben sie oft Kirschbäume mitten in die Weinberge gepflanzt. Warum? Sie haben die Kischbäume angebaut um Schutz zu haben. Man hatte Schatten um Mittag, wenn man eine Stunde mittags draußen auf dem Weinberg seine Jaus’n gegessen hat. Auch konntest du dich da bei Regen kurz unterstellen. UND - MAN KONNTE DAS PFERD ANBINDEN!!!!“ sagt Joe bedeutungsvoll mit leicht erhobenen Finger und mit nem Schmäh in den Augen fährt er betonend fort: „Und auch das Pferd braucht den Schatten. Und nicht zu vergessen, die Kirschen hatte man auch“, lacht er. „O.k., verstehe“ sage ich und lache mit! Ja, ja, die Zeiten, wie sehr sie sich doch geändert haben!’

Stadt Hallstatt und der Hallstätter See, 2005.
Wie links aber leicht geschwenkte Ansicht, 2005.

Wie oben, aber 2007.
Wie oben, aber 2007.
.

Wie die beiden Fotos oben, aber 2010.
Blick auf das Zentrum der kleinen mittelalterlichen Stadt und den See. Das Foto ist von den Parkplatz-Terrassen aus aufgenommen, die vor wenigen Jahrzehnten gebaut wurden.Wie die beiden Fotos oben, aber 2010.
Blick auf den südlichsten Teil des Hallstätter Sees.

Der Ort Hallstatt, der in der Dachstein-Gebirgsregion der österreichischen Alpen gelegen ist, ist Teil des UNESCO-Weltkulturerbes. Diese Region wird hier als „Hallstatt-Dachstein Salzkammergut Kulturlandschaft“ bezeichnet. Eine detaillierte anschauliche Beschreibung dieses Standortes zusammen mit den sieben übrigen Welterbestätten in Österreich ist in Linder & Dröscher (2007, R) ausgeführt.

Rückblick aus dem Jahr 2013 auf frühere SeenUntersuchungen: Der Hallstätter See hat das Interesse der Wissenschaftler seit mehr als 160 Jahre angezogen.

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

Hallstätter See, 2005:
Links eingefügte Grafik - Tiefenprofile der Wassertemperatur im Jahre 1849 gemessen und veröffentlicht von Simony (1850). Die Linie mit den Datenpunkten zeigt die Messdaten für den 31. August 1849. Die anderen Linien sind Messungen vom April, Mai und November desselben Jahres.
Rechts eingefügte Grafik - wie links, aber in den letzten Jahrzehnten gemessen. Es werden hier nur die Werte für den Sommer (Juli, August) gezeigt (Sommerdaten vom '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 fromthe 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).

Meeresbälle, 2013:
Aus Fasern gebildete Meereskugeln sowie Muscheln am Strand des Mittelmeeres. Die Form und das Aussehen dieser Bälle ähnelt den Kugeln, die im See Hallstätter See gefunden werden. Sie werden hier nach Morton als “Die Hallstätter Seekugeln“ oder “Lärchennadel-Bälle“ benannt. Solche Seekugeln wurden auch von anderen Seen in Österreich beschrieben. Meeresbälle, 2013:
Wie das Foto links, aber als Detailansicht. Diese Kugeln vom Meer schauen weniger grob gefasert aus als die der Seen, die durch Nadeln aufgebaut sind.

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.

anzeichen einer ökologischen unstimmigkeit in diesem salzhaltigen see: Ist das kristallklare Wasser des Hallstätter Sees tatsächlich ein Ausdruck eines gesunden Ökosystems?

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

Hallstätter See, 2005:
Das kristallklare Wasser verspricht auf den ersten Blick eine hohe Wasserqualität dieses Alpensees: Zeigt es hier zugleich den Status eines uneingeschränkt gesunden Ökosystems an? 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.

Das Ostufer vom Hallstätter See, 2005:
Der beliebte Wanderweg “Ostuferweg“ geht durch Wiesen, Obstgärten und Wälder entlang dem Seeufer.Das Ostufer vom Hallstätter See, 2001:
Streuobstwiese mit frisch gefallenem Schnee zu Ostern (April) am Seeufer. Rechtsseitig ist ein Bootshaus zu sehen.

Das Ostufer vom Hallstätter See, 2001:
Traditionelle alpine Holzhäuser von Streuobstwiesen umgeben liegen nahe der Wasserkante vom Seeufer. Das Ostufer vom Hallstätter See, 2000.
Blühende Sommerwiese mit Glatthafer (Arrhenatherum elatius) und Habichtskraut (Crepis spec.) unweit vom Seeufer.

Das Ostufer vom Hallstätter See, 2005.
Nachhaltige Tierhaltung auf kleinen Bauernhöfen befindet sich am Ufer von diesem Alpensee.Das Ostufer vom Hallstätter See, 2001.
Wälder aus Buchen (Fagus sylvatica) und Fichten (Picea abies) erstrecken sich entlang dieses Alpensees.

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.