VERTICAL DISTRIBUTION OF CILIATES AND PHOTOTROPHIC
BACTERIA IN STRATIFIED GREEN LAKE NEAR POMARY
WITH LOW SULFATE CONTENT
M.V. Umanskaya, S.V. Bykova, M.Yu. Gorbunov
Institute of ecology of Volga basin RAS, Togliatti, Russia, [email protected]
The territory of the Vyatka ridge considered a geographical province of
karst lakes. Most of these lakes have a low mineralization of HCO3-Ca type,
and contain low levels of sulfates and chlorides. However the scanty lakes of
this area with anomalous chemical content, highly mineralized with high concentration of sulfates and chlorides, attracts the greatest interest of researchers. Oddly enough, but detailed information about the features of chemical
and physical limnology (detailed chemical composition, patterns of stratification ets.), as well as characteristics of biocenoses of typical, low-mineralized
karst lakes is nearly almost absent.
The Green Lake (Vuver-Er) near settlement of Pomary (Rep. Mari El) is
one of the many typical karst lakes in the region. We have studied it at July,
15 and September, 08, 2013. In the moment of our study the lake water was
of HCO3-Ca type with mineralization 230 mg·L-1 in the surface layer and
330 mg·L-1 and 500 mg·l-1 in the bottom in July and September, respectively.
The main gradient of mineralization was located between 4 and 6 m. Besides,
the rise of the mineralization from 10 m depth to the near-bottom layer occurred in September. The thermocline occupied a wide depth range, from 2.5
to 7 m in July and from 5 to 9 m September, but the maximal temperature
gradient (5–6 °C·m-1) in both months was located between 5 and 6 meters.
In July, a significant deepwater maximum of oxygen concentration was
located at the depth of 4 m; similar but much smaller maximum positioned at
the depth of 8 m in September. Below the maximum, starting at the depth of
7.5 m in July and 8.5 m in September, the redox potential decreased sharply
from +350-450 mV to +120 mV, which indicates the transition from aerobic
to weakly reducing conditions. However, the hydrogen sulfide concentration
below the redoxcline was less than 10 µM, and below the maximum at
a depth of 10 m it decreased slightly to the bottom. The principal reducing
agent in this zone was Fe (II), with the concentration of 2,5–4,4 mg·l-1 at
10 m. It further increased more than order of magnitude in the bottom layer.
The transparency was high, 4.1–-4.5 m, because the Chl a concentration
in the lake epilimnion was only 2 and 0.9 µg·l-1 in July and September, respectively. Below Chl a increased significantly, reaching maximum at
8.5 m, with concentration, respectively, 29 and 19 µg·l-1. In both dates, BChl
a maximum (4.3–4.4 µg·l-1) was located at the same depth, as well as the
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maximum of BChl d (44.6 µg·l-1) in July. In September, the peak of BChl d
descended to the 9 m layer and its concentration increased to 56 µg·l-1.
The phytoplankton of deep chlorophyll maximum was dominated by filamentous cyanobacteria with a predominance of Planktothrix rubescens (De
Candolle ex Gom.) Anagnostidis & Komárek. Along with this species two
other forms with different cell sizes has been observed. Unicellular (Synechocystis spp.) and colonial (mostly Aphanocapsa spp.) picocyanobacteria
formed their maxima above it, at depths of 4 and 7.5 m.
The species of purple sulfur bacteria (genera Thiocapsa and Thiodictyon), filamentous anoxygenic phototrophs (Chloronema giganteum Gorlenko
et Pivovarova) and «Chlorochromatium» consortia of the green sulfur bacteria have been detected in the redoxcline of the lake. In July, two species of
Thiocapsa and Tdc. bacillosum (Winogr.) Pfennig and Trüper were peaked at
a depth of 8 m, while maxima of Chl. giganteum, which dominated by biomass, and «Chlorochromatium» positioned at 8.5 m. In September the peaks
of all species descend 0.5 m down to the bottom, and the biomasses of Chl.
giganteum and «Chlorochromatium» become comparable.
In July, two peaks of total ciliate abundance approximately equal by
magnitude located at 6 m and 9 m layers, the peaks of biomass were at 6 and
8 m. In September common peak of the abundance and biomass was observed
at 8.5 m, together with the maximum in the surface layer.
89 species of ciliates were recorded in 28 samples taken from the lake,
but 25 of them were detected in a single sample. 38 species were present in
the lake in both dates, although the number and distribution of some species
changed significantly. For example, Haplocaulus sp., dominated in lake epilimnion in July, was replaced by Pseudohaplocaulus infravacuolatus Foissner
and Brozek, and Pseudohaplocaulus anabaenae (Stiller) Warren, which, in
July formed a significant part of the abundance and biomass at 6 and 7 m layers, almost disappeared in September. Pelagothrix plankticola Foissner et al.,
dominant by biomass at 8 and 9 m depth, more than tripled its numbers in
September. In both dates a high number of small Cyclidium glaucoma
(O.F.Müll.) concentrated at the depth of 9 m, and obligate anaerobic species
of genera Metopus, Caenomorpha and Plagiopyla inhabited the area below.
Thus, despite the low content of sulfides in the anaerobic zone of the
lake, communities of both phototrophic prokaryotes and ciliates are highly heterogeneous vertically. Characteristic features of the lake are the presence of
filamentous anoxygenic phototroph Chl. giganteum that is uncharacteristic for
high-sulfidic lakes, and also its coexistence with significant populations of filamentous non-heterocystous cyanobacteria.
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