The temporal and spatial distribution of planktonic and benthic protozoan communities in a small productive lake

An investigation into the spatial and temporal distribution of protozoa in Esthwaite Water, a small eutrophic lake in the English Lake District, was carried out from mid-June until late September, 1977, during the period of summer stratification. Quantitative analyses of planktonic protozoan populations were performed on water samples collected at 1 m intervals throughout the water column and individual depth-time distribution profiles were constructed for the major ciliate species. Population density and species succession of the benthic protozoa was also studied.     

Studies on ciliated protozoa in eutrophic lakes: 1. Seasonal distribution in relation to thermal stratification and hypolimnetic anoxia

An investigation into the spatial and temporal distribution of ciliate populations in a small monomictic eutrophic lake was carried out over a one-year period. A community of large cilates dominated by Loxodes striatus, L. magnus, Spirostomum teres and Frontonia leucas occurred in the deep water sediments during the period of winter mixis. These cilates vacated the sediment during summer stratification, progressively colonising the hypolimnion in phase with the upwards spread of anoxic conditions, returning once more to the sediment following destratification. The possible significance of this ciliate community is discussed.     

Distinct and diverse anaerobic bacterial communities in boreal lakes dominated by candidate division OD1

Lakes have a central role in the carbon cycle of the boreal landscape. These systems typically stratify in summer and their hypolimnetic microbial communities influence burial of biogenic organic matter in sediments. The composition of bacterial communities in these suboxic habitats was studied by pyrosequencing of 16S rRNA amplicons from five lakes with variable dissolved organic carbon (DOC) concentrations. Bacterioplankton communities in the hypolimnetic waters were clearly different from the surface layer with candidate division OD1, Chlorobi and Bacteroidetes as dominant community members. Several operational taxonomic units (OTUs) affiliated with candidate division OD1 were abundant and consistently present in the suboxic hypolimnion in these boreal lakes. The overall representation of this group was positively correlated with DOC and methane concentrations. Network analysis of time-series data revealed contrasting temporal patterns but suggested similar ecological roles among the abundant OTUs affiliated with candidate division OD1. Together, stable isotope data and taxonomic classification point to methane oxidation and autotrophic denitrification as important processes in the suboxic zone of boreal lakes. Our data revealed that while hypolimnetic bacterial communities are less dynamic, they appear to be more diverse than communities from the oxic surface layer. An appreciable proportion of the hypolimnetic bacteria belong to poorly described phyla.     

The distribution of temperature,oxygen and nutrients in Lake Bukoni,Uganda

Temperature, oxygen and nutrients were determined in the permanently stratified Lake Bukoni from July 2004 to December 2005. Meromixis has resulted from the nature of the surrounding hilly topography and the almost vertical crater walls that exclude the effects of light winds. These circumstances and the tropical temperature regime ensure permanent stratification in the offshore part of the lake. From about 20 m to the bottom, the water was out of circulation and devoid of oxygen. Water samples from such depths had a strong smell of hydrogen sulphide gas. The inshore site, with greater turbulence and littoral area, had a uniformly oxygenated water column compared with the offshore site. According to information from members of the community around the lake, ‘fish kills’ have taken place but on irregular occasions. The nutrients (N, P and Si) were well distributed in the inshore site. In the offshore site, the concentrations were generally lower in the uppermost 20 m but more than double near the mud surface. Soluble reactive phosphorous was the least abundant nutrient while soluble reactive silicon was the most abundant nutrient. The high Si : P ratios have led to the dominance of species like Synedra ulna Ehr.     

Population dynamics of hypolimnetic rotifers in the Pluss-see (North Germany)

The hypolimnetic rotifer populations of the Pluss-see (Keratella hiemalis, Filinia terminalis, Filinia hofmanni) show similar patterns of changing population parameters indicating that they respond to particular environmental signals in the same way.     

Seasonal development of hypolimnetic ciliate communities in a eutrophic pond

Abstract The ciliated protozoan communities in the hypolimnion of a highly produtive pond were investigated over two years. Three physiological groups could be distinguished: stratified water column; (b) anaerobic ciliates with endosymbiotic methanogens; and (c) anaerobes without endosymbiotic methanogens. Both groups of anaerobes were confined to the anoxic zone of the hypolimnion. Community biomass was dominated by microaerobic ciliates which had on average 20 times larger cells than anaerobic ciliates. Abundance and biomass of microaerobic ciliates decreased over the summer, while anaerobic ciliates increased. This reflected a spatial shift in the availability of inorganic nutrients and, as a result, of ciliate food from the epi- and metalimnion to the hypolimnion. The low biomass production of anaerobic ciliates was consistent with the low theoretical growth efficiency of anaerobic metabolism. Ciliate species displayed characteristic spatial and seasonal distribution patterns within the water column which were similar in both years investigated. Spatial and temporal distribution was mainly governed by two factors: (1) the distribution of dissolved oxygen; and (2) the availability of food. Distribution patterns were not related to chemical gradients other than the oxygen gradient, but they were correlated with the distribution of major food sources.     

Ordinational analysis of benthic communities upstream and downstream of a prairie storage reservoir

Ordinational analysis of 445 benthic samples taken over the years 1975 through 1979 revealed at least three distinct benthic communities; upstream of the reservoir, in the hypolimnion influenced area, and in the recovered downstream areas. In addition to previously reported influences of thermal constancy, Ca/Na ratio increases in the hypolimnion influenced areas showed high correlation with the dominance of molluscs in the cold water area. Increases in Ca/Na ratios allowed greater reproductive success and better ability to regulate ion concentration in molluscan forms. Combined with thermal regime alterations and high algal cover, most aquatic insects were excluded from this area. The hypolimnion release reservoir and associated downstream areas act as barriers, both thermal and geographical, to aquatic insect dispersal resulting in an impoverished benthic community in thermally recovered areas downstream of the reservoir. This barrier effect, as well as the probability of increased availability of detrital material (from increased periphyton growth in hypolimnion influenced areas) and more uniform flows, has caused changes in dominance structures of benthic communities in recovered downstream areas compared to upstream areas.