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Differentiation of microbial loop components in small anthropogenic reservoirs

Mieczan T.

Polish Journal of Ecology

2014

Vol. 62, nr 2

323--334

The interactions between bacteria and heterotrophic protists are essential for the ecosystem ecology of freshwater. The basic objective of the study was to analyse the seasonal dynamics of changes in particular elements of the microbial loop (bacteria, flagellates and ciliates) in various types of small water bodies. The classification into particular trophic groups of ciliates and the role of the organisms in the functioning of the microbial loop was also analysed. The abundance and biomass of microbial communities has been assessed in eight reservoirs of varied origin (peat pits, clay pits and post-mining reservoirs), in order to test a hypothesis that the microbial communities differed among reservoirs and that differences could be related to fertility of habitats. Fieldwork was done from April to November 2010-2012. From each reservoirs once a month, three samples were collected with a 5-litre planktonic sampler. Samples were taken on two stations: pelagic – located in the deepest part of each reservoirs and littoral. The density and biomass of bacteria and protists significantly differed between the studied reservoirs, with the lowest numbers in the peat pits and clay pits and the highest in the post-mining reservoirs. All of the studied reservoirs were generally dominated by ciliates belonging to the orders Oligotrichida and Scuticociliatida constituted > 30% of the total numbers. In all reservoirs bacterivorous ciliates occurred in the highest numbers, while predators ones in the lowest. Generally, concentrations of nutrients (especially total phosphorus) is not a factor having the strongest effect on the abundance of bacteria and heterotrophic flagellates and the number and strength of correlations between microbial loop components. The relations demonstrated between bacteria and protists point to an important process of matter and energy flow from bacteria to higher trophic levels. In peat pits, relations between bacteria and ciliates were stronger. Only in clay pits and postmining reservoirs the correlation between bacteria and heterotrophic flagellates were found. Consuming much of bacterial productions, protozoa become an important link between bacteria and micrometazoans.

Bacteria, nanoflagellates and ciliates as components of the microbial loop in three lakes of different trophic status

Kalinowska K.

Polish Journal of Ecology

2004

Vol. 52, nr 1

19-34

The major components of the microbial loop (dissolved organic carbon, bacteria, nanoflagellates and ciliates) were examined in three Polish lakes (Masurian Lakeland, North-Eastern Poland): highly eutrophic (Lake Ryńskie), mesotrophic (Lake Kuc) and humic, acid (Lake Smolak Duży). Microbial loop was distincly differentiated among studied lakes. In the eutrophic lake, the microbial loop was characterized by a widevariety of biotic components, great taxonomic, trophic and size differentiation of ciliates (dominated by bacterivorous and predatory taxa.) Probably, in this lake autochthonous dissolved organic carbon (DOC) prevailed. In the mesotrophic lake, the microbial loop comprised fewer components and the taxonomic andtrophic variability of ciliates (dominated mainly by bacterivorous and algivorous taxa) was smaller. This lake contained almost the same amount of DOC, but part of it was probably less available and allochthonous origin. Much of the DOC in the humic lake being poorly available (humic substances prevailed) and hence there were lower densities of bacteria and still lower of nanoflagellates and ciliates (dominated by large-sized mixotrophic and small-sized bacterivorous species). The only significant correlation between bacteria and ciliates suggests that the food chain in this lake is short and that the high concentrations of DOC of allochthonous origin are not readily assimilated. Additionally, low pH values restricted growth of the studied groups of organisms and decomposition of DOC by bacteria. The number of significant correlations differed among lakes and in different temporal scales. In the eutrophic lake the relationships were stronger in both seasonal and diel cycle. Practically no relationships were found in the humic lakes in both scales. Generally, diel correlations were stronger than those in the seasonal scale.