Bacterial dynamics in two high-arctic lakes

The heterotrophic planktonic bacteria in two high-arctic lakes were studied by direct microscope count and the enzymatic uptake of ¹⁴C labelled glucose which generally conformed to Michaelis-Menten kinetics. Bacterial numbers and activity in oligo-trophic Char Lake ranged from 0.1 to 2.0×10^?3 bacteria/l and a maximum uptake velocity (V_max) of 1.8 × 10^?3μg glucose l^? h^?1. Nearby Meretta Lake received waste water from the Department of Transport Base at Resolute and this eutrophication was reflected in higher bacterial numbers of 2-80 × 10⁸/1 and Kmax of 0.1 × 10^?1-7.5 × 10^?1 fig glucose l^?1 h^?1 The Kmax per cell in Char Lake was 3 × 10^?11μg glucose l^?1 h^?1 and changed little between the period of solid ice cover in May and ice-free conditions in August. Bacterial cycles could not be related to phytoplankton cycles in either lake. Comparison of kinetic data from several lakes suggests a relationship between the bacterial uptake rate of glucose and phytoplankton production. Both bacterial numbers and activity in Char Lake may be very close to the minima to be expected in undisturbed freshwater environments.     

Plant community structure determines primary productivity in shallow,eutrophic lakes

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Life on the edge: the plankton and chemistry of Beaver Lake, an ultra-oligotrophic epishelf lake, Antarctica

1. Beaver Lake, a large epishelf lake in eastern Antarctica was sampled on two occasions during the austral summer of 2000. Two sites, one 1 km offshore and another 6 km offshore were sampled at intervals to depths of 40 and 110 m, respectively. 2. The lake is an end member of ultra‐oligotrophic lake systems with a very low carbon pool. Dissolved organic carbon concentrations ranged between 95 and 652 μg L^–1. Nutrient levels were generally low with soluble reactive phosphorus ranging from undetectable to 8.4 μg L^–1, ammonium ranged between 1.8 and 5.0 μg L^–1, nitrate from undetectable to 161 μg L^–1 and nitrite 1.1–5.3 μg L^–1. 3. Chlorophyll a concentrations (0.39–4.38 μg L^–1) showed an unusual distribution with the highest levels close to the lake bottom at the offshore site (110 m) where the phototrophic nanoflagellates (PNAN) displayed strong autofluorescence. 4. Bacterial concentrations were low, with a maximum of 7.60 × 10⁷ L^–1, as were the concentrations of heterotrophic nanoflagellates that exploit them. 5. Primary production ranged between 19.7 and 25.49 μg C L^–1 day^–1 and bacterial production from 0.32 to 1.15 μg C L^–1 day^–1. 6. In common with other continental Antarctic lakes, the system was dominated by a microbial plankton. However, a dwarf variety of the calanoid copepod, Boeckella poppei, occurred below 25 m at concentrations of 3–5 L^–1. 7. The data suggest that primary production and bacterial production were not limited by nutrient availability, but by other factors, e.g. in the case of bacterial production by organic carbon concentrations and primary production by low temperatures.     

Effects of humic stress on the zooplankton from clear and DOC‐rich lakes

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Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency

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Connectivity and complexity of floodplain habitats govern zooplankton dynamics in a large temperate river system

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Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer

1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L^?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 10⁴ L^?1 ± 33.5 (23rd December) and 130.9 × 10⁴ L^?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L^?1 h^?1 ± 0.002 and 0.579 μg C L^?1 h^?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 10⁷ L^?1 ± 1.2 (23rd December) and 14.0 × 10⁷ L^?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L^?1 h^?1 ± 0.8 and 12 ng C L^?1 h^?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L^?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 10⁴ L^?1 ± 14.2 (23rd December) to 133.8 × 10⁴ L^?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L^?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle.     

Microplankton dynamics in a perennially ice-covered Antarctic lake – Lake Hoare

1. Temporal and spatial variation in planktonic abundance, biomass and composition were determined in Lake Hoare (McMurdo Dry Valleys, Antarctica) over two summer seasons (1996–97 and 1997–98). 2. Phototrophic nanoflagellates (PNAN) dominated planktonic biomass, with a mean monthly biomass ranging between 27.3 and 40.4 μg C L^?1. The deep chlorophyll maximum was mainly composed of cryptophytes (>87% of total PNAN biomass) and varied in depth between 6 and 12 m. 3. Maximum bacterial concentration was 11.8 × 10⁵ cells mL^?1. Bacterial abundance showed relatively little temporal variation, with the exception of a drop in numbers that occurred in late November of both years studied. 4. Ciliates were the most successful heterotrophic protozoan group, with a mean monthly biomass (1.2–3.2 μg C L^?1) being typically at least double that of heterotrophic nanoflagellate (HNAN) biomass (0.1–0.7 μg C L^?1). 5. Microbial processes within this lake appear to be dominated by bottom up control. The relative importance of allochthonous inputs into the lake (from the ice‐cover and stream flow) and autochthonous recycling (by microzooplankton regeneration) are considered. 6. Results from a horizontal transect indicate that the permanence of the main sample hole may have enhanced planktonic biomass over a relatively small spatial scale.     

Climate and productivity shape fish and invertebrate community structure in subarctic lakes

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Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus‐rich lakes

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Epiphytic diatoms in two freshwater maritime Antarctic lakes

SUMMARY.

• 1 An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.
• 2 A diverse community of 104 epiphytic taxa was identified. Twenty-eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.
• 3 A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.
• 4 Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.
• 5 A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).

     

Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria. 2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m² m^?2 river bottom were found in a 6.6 km river stretch. 3. The epiphyton supported a bacterial production of 5–58 ng C cm^?2 h^?1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L^?1 h^?1, and abundance was 4.0–7.8 × 10⁹ cells L^?1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm^?3 h^?1, and abundance from 0.84 to 6.7 × 10⁹ cells cm^?3. Bacteria were larger and more active in sediments than in the pelagic zone. 4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column. 5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes. 6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.     

Lake‐type‐specific seasonal patterns of nutrient limitation in German lakes,with target nitrogen and phosphorus concentrations for good ecological status

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Field measurements of ingestion and assimilation for the Australian brine shrimp Parartemia zietziana Sayce (Crustacea: Anostraca)

Ingestion and assimilation of the brine shrimp Parartemia zietziana were measured in the field. Populations in Pink Lake and Lake Cundare were used; both lakes are shallow (< 1 m), saline (> 60°/00), and located in western Victoria; they have tow primary production. P. zietziana relies largely on organic matter in lake sediment for food. Ingestion rate was measured in situ in Pink by following the uptake of ¹⁴C from labelled sediment. The rate of faecal pellet production was measured (in both lakes) by allowing animals to defaecate for 24 h in a net suspended in the lake. Ingestion rate varied from 0.35 to 13 01 × 10^–1 mg dry wt h^-1 individual^-1 for a range in dry weight of shrimp from 0.2 to 2.3 mg individual^-1; for a similar range in weight, defaecation varied from 0.08 to 2.03 × 10^-1mg dry wt h^-1 individual^-1. These rates were converted to joules and assimilation efficiencies of 30–60% calculated. Regressions showed that change in dry weight of shrimp accounted for > 90% of the variance in both rates.     

Enhancing ethanol production from cellulosic sugars using <Emphasis Type="Italic">Scheffersomyces (Pichia) stipitis</Emphasis>

Studies were performed on the effect of CaCO₃ and CaCl₂ supplementation to fermentation medium for ethanol production from xylose, glucose, or their mixtures using Scheffersomyces (Pichia) stipitis. Both of these chemicals were found to improve maximum ethanol concentration and ethanol productivity. Use of xylose alone resulted in the production of 20.68 ± 0.44 g L^?1 ethanol with a productivity of 0.17 ± 0.00 g L^?1 h^?1, while xylose plus 3 g L^?1 CaCO₃ resulted in the production of 24.68 ± 0.75 g L^?1 ethanol with a productivity of 0.21 ± 0.01 g L^?1 h^?1. Use of xylose plus glucose in combination with 3 g L^?1 CaCO₃ resulted in the production of 47.37 ± 0.55 g L^?1 ethanol (aerobic culture), thus resulting in an ethanol productivity of 0.39 ± 0.00 g L^?1 h^?1. These values are 229 % of that achieved in xylose medium. Supplementation of xylose and glucose medium with 0.40 g L^?1 CaCl₂ resulted in the production of 44.84 ± 0.28 g L^?1 ethanol with a productivity of 0.37 ± 0.02 g L^?1 h^?1. Use of glucose plus 3 g L^?1 CaCO₃ resulted in the production of 57.39 ± 1.41 g L^?1 ethanol under micro-aerophilic conditions. These results indicate that supplementation of cellulosic sugars in the fermentation medium with CaCO₃ and CaCl₂ would improve economics of ethanol production from agricultural residues.     

Effects of warming on annual production and nutrient‐use efficiency of aquatic mosses in a high Arctic lake

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Seasonal Viral Loop Dynamics in Two Large Ultraoligotrophic Antarctic Freshwater Lakes

The effect of viruses on the microbial loop, with particular emphasis on bacteria, was investigated over an annual cycle in 2003–2004 in Lake Druzhby and Crooked Lake, two large ultraoligotrophic freshwater lakes in the Vestfold Hills, Eastern Antarctica. Viral abundance ranged from 0.16 to 1.56 × 10⁹ particles L^-1;1 and bacterial abundances ranged from 0.10 to 0.24 × 10⁹ cells L^-1;1, with the lowest bacterial abundances noted in the winter months. Virus-to-bacteria ratios (VBR) were consistently low in both lakes throughout the season, ranging from 1.2 to 8.4. lysogenic bacteria, determined by induction with mitomycin C, were detected on three sampling occasions out of 10 in both lakes. In Lake Druzhby and Crooked Lake, lysogenic bacteria made up between 18% and 73% of the total bacteria population during the lysogenic events. Bacterial production ranged from 8.2 to 304.9 × 10⁶ cells L^-1;1 day^-1;1 and lytic viral production ranged from 47.5 to 718.4 × 10⁶ viruslike particles L^-1;1 day^-1;1. When only considering primary production, heterotrophic nanoflagellate (HNF) grazing and viral lysis as the major contributors to the DOC pool (i.e., autochthonous sources), we estimated a high contribution from viruses during the winter months when >60% of the carbon supplied to the DOC pool originated from viral lysis. In contrast, during the summer <20% originated from viral lysis. Our study shows that viral process in ultraoligotrophic Antarctic lakes may be of quantitative significance with respect to carbon flow especially during the dark winter period.     

Viruses in the plankton of freshwater and saline Antarctic lakes

1. Virus‐like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra‐oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 10⁶ mL^–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 10⁶ mL^–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter. 2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star‐like particles of about 80 nm diameter. 3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P < 0.01). 4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus‐like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy. 5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.     

Virus dynamics in a large epishelf lake (Beaver Lake,Antarctica)

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Total phosphorus thresholds for regime shifts are nearly equal in subtropical and temperate shallow lakes with moderate depths and areas

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