Obersee (Zürichsee)

reed belt at Busskirch

Following a 1978 inventory, in 1988 the University of Geneva took a second inventory of aquatic plants in the riparian zone of the entire lake area. The lake shore in the Canton of St. Gallen was divided into 50 portions of approximately 500 metres (1,640 ft) in length and described by 12 different parameters. The most important are the plants environmental information on aquatic plants (macrophytes), divided into reeds, floating plants and submerged vegetation (pondweed and stoneworts). The dense vegetation zones are generally between 1 metre (3.3 ft) and 4 metres (13.1 ft) up to 5 metres (16.4 ft) depth. Instead of nutrients there is a high a load with floating mineral particles which prevents colonization of the sea floor in greater depths. The grade of colonization of the shallow water zone has risen again since the last observation in 1978, which is directly related to the increase in the maximum colonization zone. The vegetation consists four-fifths of submerged plants and only about one-fifth of emerging plants. The latter includes the reedbed: In 1850 90 hectares (222 acres) of reed beds were alone in the lower lake area yet been demonstrated. A comparison of aerial photographs from 1954 and 1987 shows in most shore sections of the machining area a significant decrease in the reed beds. The reed area has increased from 1978 to 1987 in the upper lake from 15 to 16 ha. It can be concluded that the reed banks are mostly declined in the 1960s and 1970s, but that since then at a low level takes place a slight recovery. Lily as floating leaf plants covered on Untersee 0.4 ha, with a declining trend; in contrast, a doubling Obersee on 2 ha can be detected. 56 of the 61 species in the entire Zürichsee colonize the upper lake and the lower lake 34. Most frequently represented are the pondweed (Potamogeton); 24 species are considered rare, more than 15 very rarely.[1]

Bollingen peninsula

In fact, there are no more original riverside forests on lake shore, except on steep slopes like the Fuchsberger Horn where a species-rich forest with oak and pine trees breeds. Also worth mentioning is the small wooded area at the far end of the upper Bollingen peninsula. Outside of urban areas, the bank is often planted with different density and broad trees stocks. Extensive shore sections are occupied by large, private gardens and parks. Although often non-native and exotic shrubs and trees species occur and the lawns usually are intensively cultivated, the upstream water habitats often form relatively low-noise buffer areas to the underlying recreation, transport and settlement areas. At several banks sections butt agricultural meadows and pastures directly to the water. However, the upper Bollingen peninsula is the only major agricultural area with lake access. All remaining grasslands have less than 50 metres (164 ft) lake access and are usually relatively little interference. A disadvantage often is the missing, extensively used transition to riparian vegetation.[1]

Stampf area, mouth of the Jona (river)

Geotopes comprise geological outcrops, boulders and river delta formations. Geological rock outcrops, i.e. scenically striking rocky ridges are found in Fuchsberg and Stafflen in Jona, Heilig Hüsli in Rapperswil and the Hörnli glacial erratic in Oberbollingen. Extensive river deltas included that of the Jona and Aabach in Schmerikon, to a lesser degree of Sägenbächlein, Wagner and Lehholz in Jona and the Linth with side channels in Schmerikon.[1]

Netta rufina at Jona Stampf

Wursmbach reeds

Perennial systematic birdwatching and studies illustrate the importance of reed beds as an outstanding habitat for many bird species. Among the 15 most valuable ornithological reeds on Obersee include (Canton St. Gallen) Rapperswil Strandweg (rank 4), Bollingen Unter Stafflen (rank 7), Wurmsbach bay (rank 11), Wurmsbach nunnery (rank 12), and Schmerikoner Allmeind (rank 13). The extensive area of shallow water with its diverse flora and the still widespread shore trees play an extremely important role for many bird species, both as food, breeding and resting place. A critical phase in the evolution of birds is the time of moulting, during which they are more or less incapable of flying and depending on quiet water areas. The Reed warblers inhabit the seaward edges of the reed belts and need significantly more space than other reed birds. Due to the decline of the reed banks and the increase in interference from recovery operations and water sports on the lake shore, the number of breeding pairs is constantly decreasing. Today the Great reed warbler is acutely threatened. According to the Red List of endangered species in Switzerland, it is listed in the top risk category of disappearing birds whose survival in Switzerland is unlikely if the threats continue. In Obersee area are three important resting places of waders: Joner Allmeind annually depending on the water level in spring and autumn, Rapperswil in winter and Schmerikoner Allmeind in spring and autumn.[1]

Many amphibian species are dependent on both natural waters for spawning, as well as on adjacent food and wintering areas. Because the connection between these two partial habitats is interrupted by settlement patterns and transport systems, the amphibians have declined in these landscapes. With regard to a cross-linking of priority areas by the lake with the backlands, the most important amphibian spawning areas have been identified in 1997. Amphibian spawning areas of national importance are situated at the Allmeind areas in Jona and Schmerikon. At the Joner Allmeind two endangered species on the Red List (Yellow-bellied toad and Pelophylax) can be found in large to very large populations. Schmerikoner Allmeind is home to the same two endangered species. For both areas the preservation and promotion of natural corridors are required, and in Schmerikon along the Linth and the side channels a large-scale networking with Kaltenbrunner Riet and other protected areas in the Linthebene region.[1]

Podiceps cristatus and its prey, alongside the lake bridge crossing near Hurden

The few existing inventory data are compiled by the competent fisheries overseer respectively a report in 1993. This is a rough, spatially highly generalized statement to the spawning grounds of Northern pike, Coregonus and Coregonus zugensis (commonly Albeli). In addition to these specific fishing information, ecological data and studies on the other species of fish and their habitat requirements, but also to other creatures, such as crabs and mussels is missing, no data are available.[1]

For the inventory of the national fen asset protection zones, the Canton of St. Gallen evaluated and proposed, in accordance with the provisions in the national fen regulation, appropriate buffer zones, among them as fens of national importance: the lakeshore marshes west of Busskirch, Joner Allmeind marshes, the lakeside read area east of Wurmsbach, reed at Schmerikon and the reed area in front of HSR area and Knie's Kinderzoo in Rapperswil. Fens of regional and local importance include the reed area east of the Busskirch church, the reed area south of Hessenhof, the small area at the parking side of the Jona mouth (Stampf), the embankment and so-called Kormoraninsel at Stampf, as well as the bay to the west of the upper Bollingen peninsula.[1]

Heilig Hüsli lake islands as seen from Holzbrücke Rapperswil-Hurden

After the Seedamm causeway was built in 1878, the Heilig Hüsli chapel was the only remaining structure of the prehistorical and medieval lake crossings. It stood isolated in the lake and was not accessible to visitors until the reconstruction of the former wooden bridge was erected in 2001. The lake and the small islands between the chapel, the timber piles of the Rapperswil–Hurden bridge and the Seedamm are designated as a nature reserve. Together with an artificial island made of gravel, they form one of the most important waterfowl breeding areas. For this reason, fishing from the wooden bridge is prohibited, as is swimming and mooring boats in the area. Among the area around the Seedamm lake crossing and between Rapperswil and Busskirch, there are some more protected areas around Obersee.

Frauenwinkel protected area as seen from Seedamm towards Untersee, Ufenau island and Zimmerberg plateau in the background

The Frauenwinkel protected area is situated on the Seedamm area in Hurden. Its reed and marsh belt has a maximal width of about 1 kilometre (0.6 mi) from the west to the east and a length of about 1.5 kilometres (0.9 mi) from the north to the south. The lake area towards Lützelau and Ufenau islands it also part of the protected area of about 3.5 kilometres (2.2 mi). Landward there is reed vegetation with large and small sedge flora, rushes, Iris sibirica, and the rare Gentiana pneumonanthe. In certain places even transition and high marsh occurs. In the nature reserve there are European rarities, among them Phengaris alcon, Eurasian curlew and Gentiana pneumonanthe, as well as Ruspolia nitidula, a small snail.[3]

Nuoler Ried is a reed located on the north end of a large plane that was filled by the Wägitaler Aa and Spreitenbach streams. This delta is larger than those of Frauenwinkel or of the Jona river and Wurmsbach stream. The present marshes only comprise a small fraction of the formerly extensive, extensively used reed and meadows which offered numerous animals and plants a wide habitat. Larger areas of the present nature reserve, such as the so-called Schüttinsel, were created on the deposits of non-recyclable residual material from the nearby gravel extraction.[4]

Schmerikoner Ried

Schmerikoner Ried is a reed located on the northeastern lake shore in the Linthebene area towards the Grynau Castle. The protected area was set under federal protection as a low-moor bog of national importance (German: Bundesinventar der Flachmoore von nationaler Bedeutung) in 1994.[5]

Grynau Castle on the eastern slope of the Buechberg hill

On the southwestern side, between Grynau and Lachen there is namely the bird reserves of national importance Güntliweid up to Bätzimatt at Buechberg.[6] The reserve is located on the south lake shore, at the foothills of Buechberg, and extends from the south of Bätzimatt at Schmerikon to Güntliweid east of Lachen.[7] It is considered as a particularly valuable resting place for waders, and may be obtained as resting place for waders on the train,[8] although there is a quarry that mines Bollinger Sandstein.[9]