katrinteubner

geographical location of the peat pond

Pond Bergknappweiher (47°51’9.99''N, 11°14’18''E) is situated in the pre-alpine region in Bavaria (Germany), about 50 km southwest of the city of Munich. The pond is very close to the both lakes Ammersee S and Starnberger See, about 15  km and 6 km away, respectively. This pond was created by peat cutting.

the dystrophic character and seasonal phytoplankton development

Cyanobacteria in Bergknappweiher, 2001:
The cyanobacterial surface scum of this dystrophic pond in autumn is mainly composed of bundles of Aphanizomenon flos-aquae but also of various Microcystis and few Anabaena taxa. The photos in the gallery illustrate the appearance throughout the seasons of Bergknappweiher. It is a dystrophic pond, which means that the water contains high concentrations of dissolved organic carbon (DOC). DOC makes water looking yellow-brownish (see photo 8 in the above gallery). The colour of the water, or more specifically the high concentrations of DOC, is, however, harmless for bathers and life in the peat pond. It could even be seen as a positive environmental factor as a water body with high DOC content filters out much stronger UV in comparison with a pond or lake with clear water. For example, in a clear water lake in the alpine region (low DOC concentration), Lake Lucerne at 454 m above sea level in the Swiss Alps, UV significantly inhibits the photosynthesis of primary producers within the top 5 m on a sunny day (see Fig.2 in Teubner et al. 2001 R). Measuring photosynthesis at water surface at 0 and 2 m depth in lake Lucerne, the water samples that were shielded from the UV-A-part of the spectrum, yielded much higher photosynthetic rates than those samples at the same depth but without UV-protection. It could be further seen from the vertical profile of photosynthetic rates that the inhibition effect by UV decreases with depths below 2 m. At a depth of about 5m the photosynthetic rates of UV-protected and non-protected samples were in the same range. Pond Bergknappweiher is located in the pre-alpine region at about 617 m above sea level, but DOC might shield primary producers from UV even at the top surface of pond water. The aquatic life in water basins in the alpine region can become more vulnerable against UV in case the water basins are at high altitude and of low DOC concentration.
In Bergknappweiher, the high concentration of DOC is due to ‘old’ humic substances that are naturally occurring as organic components from the soil (‘fresh/young’ DOC in a water for example can be released by algae being alive in the water body). The pond was created by peat cutting and is still surrounded by meadows and also woodland. The meadows are today mainly used as pastures for cattle or haymaking. Further details about sustainable animal husbandry in this pre-alpine region are illustrated on the website about Ammersee S, for the alpine region in the Salzkammergut district in Austria on the website about Ammersee S.

Bergknappweiher, 2001:
Meadows and woodland are surrounding the pond. . Bergknappweiher, 2001:
Tufted forms of large Carex species (Carex acutiformis/riparia, here seen as still small plants in spring, are found at the pond’s edge.

Along the shore of Bergknappweiher, 2001:
This photo is taken on the road going along the shore of the pond. Sustainable animal husbandry in this pre-alpine region in Bavaria (Germany) is in a more detail illustrated on this website about Ammersee S. See also sustainable agriculture in the alpine region in Upper Austria on the website about Attersee S. Landscape nearby Bergknappweiher, 2001:
Small ponds created by peat cutting are quite common in this area. The pond seen on the photo is in the close neighbourhood of the described pond Bergknappweiher.

Plants grow, bloom and built-up fruits and thus change the appearance of the meadows and woodland in the course of a year. However, not only communities of plants and animals living around a water basin change with seasons, but also the communities of aquatic microorganisms inhabiting the basin do so. The seasonal changes are usually not by chance but follow a pattern driven by the changing environment throughout the seasonal cycle. The development of phytoplankton in pond Bergknappweiher will be illustrated in a greater detail in the following paragraph, as the seasonal pattern described here can be typically found in eutrophied small basins of stagnant water.

Phytoplankton of Bergknappweiher, 2000/2001:
Seasonal development of phytoplankton biovolume observed from December 2000 to November 2001. The DIC-photos are from light microscopy (DIC = differential interference contrast). The graph on the right side shows the relative contribution of monthly biovolume to the annual biovolume of phytoplankton for the studied period. The seasons are indicated in white for winter, green for spring, blue for summer and orange for autumn. The figure on the left side illustrates the monthly shifts among phytoplankton species and phytoplankton biovolume throughout the year. The lowest phytoplankton biovolume is estimated for the wintertime (see white labelled area in the circular graph). Some diatoms (e.g. Aulacoseira as seen for winter on the microscopical photo leftside) and chlorophytes are found in the water column during the cold season. With increasing day length, the phytoplankton cells are growing and build a spring peak of biovolume. With regard to the chilly period from early autumn to late spring (September to May), highest biovolumes can be developed in March, as there are sufficient nutrients available for an unlimited growth. The nutrients were accumulated over the cold season. They are now well distributed along the water column due to spring turnover (mixing) and can be thus utilized by phytoplankton organisms floating in the water body. During this period early in the year the exponential growth of fast growing small-sized single-cell phytoplankton species such as small centric diatoms, needle-shaped diatoms and small cryptophytes and chlorophytes predominates. The dominance of small species in spring can be identified by peak values of the cell-surface to cell-volume ratio of phytoplankton (see dynamic of this ratio in riverine lakes described on the website of Grosser Mueggelsee S). A few weeks later, in April, the biovolume is again remarkable low. It is almost the lowest for the whole year in Bergknappweiher as seen in the circular diagram. This weak phytoplankton biovolume is due to grazing of zooplankton. The growth of zooplankton depends more on temperature than photosynthetic organisms, i.e. phytoplankton organisms. As there is a time shift between the increase of day length and an increase of WATER temperature (see Mondsee S and Ammersee S about coherence and time-shifts between annual peaks of temperature related parameters referring to lake physics and lake biota), a time-lag between phytoplankton and zooplankton species can be often seen. After the clearance of phytoplankton cells the numbers of zooplankton organisms are also lowering as no further food is available anymore. This short interim scenario of a low number of biotic particles in the water column (almost no phytoplankton and also no zooplankton) is reflected by a temporarily high water transparency lasting few days to a week and is called ‘clear water phase’. In May, the phytoplankton species are growing well again even if the species composition is quite different than in early spring. The phytoplankton composition is now dominated by large diatoms and large colonial green algae (Coenochloris spec.). During summer, i.e. the period from June to August, about 70% of the annual phytoplankton biovolume are built up in Bergknappweiher as indicated by the large blue area in the circle diagram. The month with the highest biovolume development here is July. The summer biovolume is mainly built up by cyanobacteria. It might be worth emphasizing that the contribution of species to higher taxa as e.g. the cyanobacteria may change drastically from month to month. In June, some chroococcale cyanobacteria as Microcystis (among other M. viridis) are predominant while in July and August filamentous cyanobacterial forms as Anabaena spp. and Aphanizomenon flos-aquae are common in Bergknappweiher. Many of the cyanobacteria seen on these photos are known to produce toxins. The summer cyanobacteria in Bergknappweiher built large colonies and are usually not the preferred food for zooplankton for many reasons. Due to the shallowness of the pond, the water is well mixed throughout summer. Consequently, autumnal turnover is not important to replenish the nutrients from the deep near-sediment zone and hence no further peak, i.e. no autumnal phytoplankton peak, can be expected. This contrasts with the situation in spring where the biovolume development did not succeed evenly month by month, the phytoplankton biovolume in autumn lowers successively. Cyanobacterial forms that were dominant in late summer persist throughout autumn (see also summer/autumn and winter/spring phytoplankton composition described for riverine lake on the website Grosser Mueggelsee S). As seen on the microscopical photomicrograph for the September sample, Aphanizomenon flos-aquae already forms dormancy stages to survive well during the non-growing season. Bergknappweiher provides an example for dynamic phytoplankton development in terms of biovolume evolvement and species composition throughout the year. How many samples at what time in the year should be taken to get reliable data assessing such an ecosystem? Is one sample a year sufficient or do we need to spend more effort and need to take samples two or four or six times a year to get a reliable data set to assess such a water body? Scientists and government agencies, and also landscape planners constructing swimming pools, need to answer such questions about the schedule of useful sampling intervals. Some aspects of taking samples in a deep lake with a deep chlorophyll layer are discussed on the website about Mondsee S. Some further background about general pattern of seasonal development of phytoplankton and of nutrient availability is described on the websites about Grosser Mueggelsee S.

In summary, Bergknappweiher provides an example of a shallow water body, which is covered by a cyanobacterial scum on calm days during the growing season. Many cyanobacteria are present on the top water surface, giving the water in particular a greenish hue. Cyanobacterial scum or blooms in stagnant water bodies are not a phenomenon of a certain country or region but occurs worldwide. Cyanobacterial blooms are often associated with nutrient enrichment of the water body. They are described on this website for shallow lakes as Old Danube S , Grosser Mueggelsee S & Langer See S, Taihu S, Poyang S and other ponds such as Biotop Auersthal S. Cyanobacteria, hoewever, can be also abundant in deep lakes such as Ammersee S and Mondsee S. Some further aspects about the seasonal development of phytoplankton in shallow lakes are described on the page about Grosser Mueggelsee S.