Abstract
(Englisch)
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1. Parameterization of longwave atmospheric radiation at high mountain environments
2. Suspended erosion particles as ecological determinants in high mountain lakes
3. Dating and heavy metal contents of sediment cores of a high-alpine, remote lake
4. Seasonal dynamics and phytoplankton diversity in high mountain lakes
5. Microbial food web in an oligotrophic high mountain lake
The study on 'Bacterial Diversity in High Mountain Lakes ' by Munti Yuhana is still in progress.
1. Parameterization of longwave atmospheric radiation at high mountain
environments.
Some ecological applications and energy budget calculations of the earth's surface require the accurate estimation of incoming longwave radiation. Because cloud cover observations are not conducted frequently in high mountain environments, a new model for the parameterization of daily mean incoming longwave radiation is proposed based on global radiation instead of cloud cover. Besides global radiation the new model requires data for air temperature, relative humidity and an estimate of daily mean clear sky global radiation. The model was calibrated with data of high mountain and lowland stations and the results compared to existing models. The new model yielded consistent results under all cloud cover conditions, for different sites and all seasons. For the conditions tested, the absolute mean bias error was generally less than 10 Wm -2 and the root mean square error was always between 11 Wm -2 and 16 Wm -2 . Of the other tested models, some did not perform well under clear sky conditions, others yielded large errors under overcast conditions or were not applicable to high mountain sites. The new model is a viable alternative to the existing longwave parameterization models especially for high mountain environments and it can be applied without the resource-consuming observation of cloud cover.
2. Suspended erosion particles as ecological determinants in high mountain lakes
The optical properties of a turbid high mountain lake were analyzed over a period of three years with respect to particle input and distribution. Inorganic erosion particles originating from a glacier in the lake's catchment dominate the attenuation of light in the water column. The turbidity patterns in the lake vary enormously within a year and between years creating attenuation coefficients between 0.4 and almost 1.8. Low particle concentrations before ice-melt are followed by large particle input to the hypolimnion during summer. When the lake destratifies during the fall, the particles are mixed throughout the entire water column which leads to a rapid increase of the attenuation coefficients near the surface. This causes the euphotic depth to decrease from 11 m to less than 5 m. The extension of the lake habitat where organisms can be photosynthetically active is therefore subject to large variations which is reflected in the chlorophyll concentration depth profiles. Particle concentrations and distribution are important physical determinants for glacial lake ecosystems, since they define the light field and thus the extent of the compartments suitable for phototrophic life. They might contribute to the selection of the mixotrophic phytoplankton communities which dominate in these ecosystems.
3. Dating and Heavy Metal Contents of Sediment Cores of a High-alpine, Remote Lake
Sediment cores were collected at Jörisee III. The goal of the analysis was to date the sediment cores in order to correlate actual input conditions of nutrients and pollutants at this high-alpine, remote site, to historical situations. The sediment cores were dated by determining gamma rays of Pb-210 and Cs-137. The calculated sedimentation rate is 0.1 cm/year. Leaching techniques were used to investigate redox sensitive species. The results give evidence for post depositional recycling in case of Fe and Mn. In contrast, the heavy metals Pb, Zn, Cr and Ni are not affected by existing redox gradients. Sediment samples were leached with diluted nitric acid to determine anthropogenic input of Pb, Zn, Cr and Ni. Concentrations of these heavy metals reflect changes in the input conditions since the beginning of industrialization, which is the examined time period.
4. Seasonal Dynamics and Phytoplankton Diversity in High Mountain Lakes
The development of the phytoplankton in two years with very distinct weather situations was compared. In 1996, the ice on Jöri lake III melted in mid June, summer stratification persisted during two months, and ice began to build up again in mid October. In 1997, the ice melted only at the end of July, which strongly influenced the development of the phytoplankton. Stratification persisted during two months and the lake froze up towards the
end of October. The average chlorophyll a concentrations were lower in 1996 than in 1997, which reflects the rather high temperatures and stable weather conditions in 1997 after the late melting of the ice. These observations lead us to suggest that the duration of the ice-free season is less decisive for biomass production than the weather conditions during this period. However, the date and duration of melting of the lake ice strongly influence the development of algal species that are typically observed in early season.
5. Microbial Food Web in an Oligotrophic High Mountain Lake
Jöri lake III (2512 m a.s.l., zm = 22 m, A = 57.81 * 103 m2, V = 601.1 * 103 m3) is situated in the Vereina region in the eastern part of the Swiss Alps. We studied microbial grazing on bacteria and bacterial productivity during the ice-free period. The lake normally gets thermally stratified for two months between July and September. In 1996, chlorophyll a concentrations varied from 0.5 to 2.0 µg l-1 with maximum values just below the thermocline (6 m depth), in 1997, they were between 0.6 and 5.0 µg l-1 with maximum values at 10 m depth - several meters below the thermocline. Bacterial densities varied between 0.7 and 1.7 * 106 ml-1 with maxima in the thermocline, one to two meters above the chlorophyll maximum. The areal bacterial biomass (volume beneath 1 m2 to a depth of 8 m) was 10 µg C l-1 which remained more or less constant for the periods investigated. In 1997, bacterial growth rate and production rates were determined using [3H]-thymidine incorporation. The rates were as low as 0.002 to 0.006 h-1 and 0.01 to 0.03 µg C l-1 h-1, respectively. We found a carbon ratio of bacteria, phytoplankton, and autotrophic picoplancton (APP) of 1.5 : 1.1 : 1 which shows a rather high abundance of bacteria and autotrophic picoplankton (APP) compared to larger phytoplankton. Bacterial growth followed a temperature dependence similar to the one observed for bacteria from Lake Zürich, a prealpine and mesotrophic lake which was studied for comparison. Microbial food web in Jöri lake III was not top down controlled during the periods of our study and mixotrophic algae like Dinobryon cylindricum var. alpinum and autotrophic nanoflagellates (ANF) were the dominant bacterial grazers observed.
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