Stable carbon isotope variations in surface bloom scum and subsurface seston among shallow eutrophic lakes

Carbon stable isotope analysis of surface bloom scum and subsurface seston samples was conducted in shallow eutrophic lakes in China during warm seasons from 2003 to 2004. δ¹³C values of bloom scum were always higher (averaged 5‰) than those of seston in this study, and the possible reasons were attributed to (i) direct use of atmospheric CO₂ at the air–water interface, (ii) decrease in ¹³C fractionation due to higher carbon fixation, (iii) active CO₂ transport, and/or (iv) HCO₃⁻ accumulation. Negative correlation between δ¹³C_scum − δ¹³C_seston and pH in the test lakes indicated that phytoplankton at the subsurface water column increased isotopic enrichment under the carbon limitation along with the increase of pH, which might in turn decreased the differences in δ¹³C between the subsurface seston and the surface scums. Significant positive correlations of seston δ¹³C with total concentrations of nitrogen and phosphorus in water column suggested that the increase in δ¹³C of seston with trophic state was depending on nutrient (N or P, or both) supply. Our study showed that δ¹³C of phytoplankton was indicative of carbon utilization, primary productivity, and nutrient supply among the eutrophic lakes.     

MACRO-PATTERNS AND PREDICTIVE MODELS OF ZOOBENTHOS ON MID-LOWER YANGTZE SHALLOW LAKES北大核心CSCD

The Yangtze floodplain is one of the most important wetlands in the world. For decades, many lakes in this region have suffered from multiple stressors, such as over-exploitation fishery resources and cultural eutrophication. To solve these problems, it is necessary to establish a quantitative lake ecosystem management platform at a regional scale. Recognizing the lack of regional scale zoobenthos models with high predictive power, we carried out 105 lake-time investigations on 46 small-to medium-sized lakes along the mid-lower Yangtze River in this study. The results showed that the density and biomass of zoobenthos of these lakes were (847±248) ind./m2 (mean±SE) and (29.41±3.97) g/m2, respectively. The density and biomass of oligochaetes, gastropods and chironomids were (403±225) ind./m2 and (1.12±0.39) g/m2, (82±20) ind./m2 and (26.38±3.99) g/m2, and (356±62) ind./m2 and (1.86±0.58) g/m2, respectively. Further analyses showed that water depth, Secchi depth, water temperature, total phosphorus, phytoplankton chlorophyll a, and submersed macrophyte biomass were the important factors affecting the standing crops of zoobenthos. A series of models were therefore established. The explanation of variations in zoobenthos density among lakes was generally better than that of biomass. The explantion percentage of simple regression models were between 18%—33% for density and 7%—18% for biomass. In the multiple regression models, the explanation percentage was 46%—49% for density and 16%—55% for biomass. Considering the large sampling size of this study, the explanation of these research models was significantly higher than that of previous studies. When comparing the percentage predictive errors (PPE), the simple models and multiple models showed similar results: PPE was 76%—171% for density and 115%—1034% for biomass in simple models, and 88%—114% for density and 141%—1015% for biomass in multiple models. Therefore, these simple regression model with relatively few variables and good predictive power are suggested in practical application. © 2019, Institute of Hydrobiology, Chinese Academy of Sciences. All rights reserved.     

The new alkaliphilic bacteriochlorophyll <Emphasis Type="Italic">a</Emphasis>-containing bacterium <Emphasis Type="Italic">Roseinatronobacter monicus</Emphasis> sp. nov. from the hypersaline Soda Mono Lake (California,United States)

Two strains of pink-colored aerobic bacteriochlorophyll a-containing bacteria were isolated from aerobic (strain ROS 10) and anaerobic (strain ROS 35) zones of the water column of Mono Lake (California, United States). Cells of the bacteria were nonmotile oval gram-negative rods multiplying by binary fission by means of a constriction. No intracellular membranes were detected. Polyphosphates and poly-β-hydroxybutyric acid were the storage compounds. Pigments were represented by bacteriochlorophyll a and carotenoids of the spheroidene series. The strains were obligately aerobic, mesophilic (temperature optimum of 25–30°C), alkaliphilic (pH optimum of 8.5–9.5), and moderately halophilic (optimal NaCl concentration of 40 g/l). They were obligately heterotrophic and grew aerobically in the dark and in the light. Respiration was inhibited by light at wavelengths corresponding to the absorption of the cellular pigments. The substrate utilization spectra were strain-specific. In the course of organotrophic growth, the bacteria could oxidize thiosulfate to sulfate; sulfide and polysulfide could also be oxidized. The DNA G+C content was 59.4 mol % in strain ROS 10 and 59 mol % in strain ROS 35. In their phenotypic properties, the new strains were close but not identical to the alkaliphilic bacterium Roseinatronobacter thiooxidans. The distinctions in the nucleotide sequences of the 16S rRNA genes (2%) and low DNA-DNA hybridization level with Rna. thiooxidans (22–25%) allow the new strains to be assigned to a new species of the genus Roseinatronobacter, Roseinatronobacter monicus sp. nov. with the type strain ROS 35^T (=UNIQEM U-251^T = VKM B-2404^T).     

Phytoplankton structure and dynamics in a volcanic lake in Deception Island (South Shetland Islands,Antarctica)

This work constitutes the first floristic and ecological analysis of the phytoplankton community of a volcanic freshwater lake in Deception Island (62°57′S, 60°38′W, South Shetland Islands, Antarctica). The main limnological features and phytoplankton size fractions were analyzed. Samples were taken during the austral summer of 2002 at two opposite sites. According to ANOVA results performed with abiotic variables, no significant differences between sites were found. The phytoplankton community showed low algal species richness, with an important contribution of the tychoplanktonic taxa. In terms of species number, Bacillariophyceae was the dominant class. Autotrophic picoplankton registered the highest densities from the second sampling date onwards. Nanophytoplankton was represented by unidentified chrysophycean organisms, which showed different distribution patterns between sites. The net phytoplankton abundance remained low during the sampling period and was strongly correlated with chlorophyll a concentration. Both nutrient concentrations and chlorophyll a values indicated oligotrophic conditions.     

Morphometric variation in bluegill Lepomis macrochirus and green sunfish Lepomis cyanellus in lentic and lotic systems

Bluegill Lepomis macrochirus and green sunfish Lepomis cyanellus were examined using geometric morphometrics to evaluate the variation in morphology between fishes that reside in lentic (e.g. lakes) and lotic (e.g. streams) ecosystems. Live fishes were collected from reservoirs and rivers in central Indiana, while additional fishes were sampled from museum collections at Ball State University and the Illinois Natural History Survey. Male and female L. macrochirus and female L. cyanellus from lentic systems display a deeper body than those from lotic systems, while no differences were found in male L. cyanellus morphometry. A deeper body promotes greater manoeuverability, typically desirable in lentic systems. In contrast, the more streamlined body of the fishes found in lotic systems reduces drag as it contends with flowing water, ultimately maximizing energy efficiency. The absence of morphological differences, such as those found in male L. cyanellus, may be caused by fish occupying both lentic and lotic systems, from the population not having been present in the body of water long enough to display any adaptations, or from a lack of statistical power caused by the small sample size.     

Evidence for an active rare biosphere within freshwater protists community

Studies on the active rare biosphere at the RNA level are mainly focused on Bacteria and Archaea and fail to include the protists, which are involved in the main biogeochemical cycles of the earth. In this study, the richness, composition and activity of the rare protistan biosphere were determined from a temporal survey of two lakes by pyrosequencing. In these ecosystems, the always rare OTUs represented 77.2% of the total OTUs and 76.6% of the phylogenetic diversity. From the various phylogenetic indices computed, the phylogenetic units (PUs) constituted exclusively by always rare OTUs were discriminated from the other PUs. Therefore, the rare biosphere included mainly taxa that are distant from the reference databases compared to the dominant ones. In addition, the rarest OTUs represented 59.8% of the active biosphere depicted by rRNA and the activity (rRNA:rDNA ratio) increased with the rarity. The high rRNA:rDNA ratio determined in the rare fraction highlights that some protists were active at low abundances and contribute to ecosystem functioning. Interestingly, the always rare and active OTUs were characterized by seasonal changes in relation with the main environmental parameters measured. In conclusion, the rare eukaryotes represent an active, dynamic and overlooked fraction in the lacustrine ecosystems.     

Occurrence,Dynamics and Production of Picoplankton in Hungarian Shallow Lakes

Phototrophic picoplankton were detected in 10⁵-10⁶ cells/ml concentrations in seven water bodies of differing chemistry and trophic level. Dominant picoplankters were, at all sites, coccoid cyanobacteria of 0.8-1.2 μm dimensions, exhibiting red or yellow autofluorescence. Apart from the effects of water temperature their quantitative dynamics were significantly influenced by the nitrogen supply and the herbivorous zooplankton (Cladocera). Their maximum contribution to the total planktonic primary production was about 50%, both in mesotrophic and hypereutrophic environments. However during the bloom of filamentous nitrogen-fixing blue-greens their role became negligible. In phytoplankton communities the significance of picoplankton is overestimated several times, when based on the cell count, while it is underestimated on the basis of biomass. The most useful characteristics of phytoplankton size groups was the total surface area of their cells.     

Picoplankton in Six New Zealand Lakes: Abundance in Relation to Season and Trophic State

The abundance of picoplankton (0.2-2 μm) was measured seasonally in the surface waters of six New Zealand lakes that represent a range of trophic states. The lakes were: Wakatipu, Te Anau, Manapouri, Hayes, Mahinerangi and Ross Creek Reservoir. Among the lakes, picoplankton abundance was associated positively with temperature; picoplankton were most abundant in summer and autumn when they attained densities of 108,000-270,000 cells/ml in the oligotrophic lakes. In these lakes, prokaryotic picoplankton was generally an order of magnitude more abundant than eukaryotic picoplankton. Consistent with the hypothesis that picoplankton are more important in oligotrophic than eutrophic ecosystems, there was a weak negative correlation between the density of prokaryotic picoplankton in the lakes and the level of chlorophyll a. The presence of large numbers of chroococcoid cyanobacteria in the guts of Ceriodaphnia dubia and Bosmina meridionalis implies that prokaryotic picoplankton are collected, but not digested, by these species.