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The importance of ciliates as a trophic link, which is defined as a fraction of the energy bound by primary producers that is transferred through the ciliate community, was assessed in the pelagic zones of shallow, eutrophic, and estuarine lakes. The study was conducted in Lake Gardno and Lake Łebsko located in northern Poland. Each of these lakes is characterized by very high mean annual ciliate biomasses of 115 μg C -1 (Lake Gardno, April 2006 – April 2007), 107 μg C L-1 (Lake Gardno, February 2007 – February 2008), 85 μg C L-1 (Lake Łebsko, April – November 2007), and 127 μg C L-1 (Lake Łebsko, April – September 2008). Ciliate production was estimated using allometric equations and was compared to primary production measured with the light-and-dark bottles method. Annual, depth-integrated ciliate secondary production corresponded to 9 and 11% (Lake Gardno, two consecutive years studied) and 12% (Lake Łebsko, the same value for two growing seasons studied) of primary production. These values exceed the majority of other estimates in the literature, which indicates the high importance of ciliates in such highly-productive, shallow lakes.
Shallow lakes, defined as ‘nonstratifying’, polymictic water bodies are usually eutrophic and highly productive, and more turbid than deeper lakes due to bottom sediment resuspension. Gross primary production (GPP) and total planktonic community respiration (TCR) were measured in a very shallow (on average 1.2 m deep) and large (area 25 km²), polymictic, eutrophic Lake Gardno (Baltic coastal lake, Northern Poland) with the light-and-dark bottle method. The aim was to compare GPP to TCR ratio in the pelagic zone in a course of a year and identify factors governing these processes. Identified factors governing GPP were light conditions and temperature, with Q₁₀ = 2.23 in the 2–24.5°C temperature range, whereas TCR was driven by water temperature (Q₁₀ = 2.15 in the same temperature range) and by organic matter content in water. TCR was correlated with total suspended matter (effect of bottom sediment resuspension due to wind action in a very shallow lake), however not with chlorophyll content. During two-year measurement period (years 2006 and 2007), annual GPP amounted to 402 and 471 g C m⁻², and TCR amounted to 192 and 223 g C m⁻² respectively. Lake Gardno pelagic system seemed to be net autotrophic on annual basis; GPP to TCR ratio = 2.1. Part of the organic matter produced in pelagial is probably deposited in bottom sediments decomposed there. Wind induced resuspension increases matter content in water (measured here as TSM content) and thus contributes to pelagic respiration processes (TCR).
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