Microbial food web in an oligotrophic high mountain lake (Jöri Lake III, Switzerland)

• Published in: Journal of limnology 1999-08, Vol.58 (2), p.162-168
• Main Authors: HINDER, Brigitte, BAUR, Isabel, HANSELMANN, Kurt, SCHANZ, Ferdinand
• Format: Article
• Language: English
• Subjects: Algae; alpine lake, microbial food web, bacterial growth rates, autotrophic picoplankton, mixotrophic algae; Bacteria; Freshwater
• ISSN: 1129-5767; 1723-8633
• DOI: 10.4081/jlimnol.1999.162

Jori Lake III (2512 m a.s.l., z sub(m) = 22 m, A = 57.81 ' 10 super(3) m super(2), V = 601.1 ' 103 m super(3)) 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 mu g l super(-1) with maximum values just below the thermocline (6 m depth), in 1997, they were between 0.6 and 5.0 mu g l super(-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 mu g C l super(-1) which remained more or less constant for the periods investigated. In 1997, bacterial growth rate and production rates were determined using [ super(3)H]-thymidine incorporation. The rates were as low as 0.002 to 0.006 h-1 and 0.01 to 0.03 mu g C l super(-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 Zurich, a prealpine and mesotrophic lake which was studied for comparison. Microbial food web in Jori 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.