Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

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Budding and prosthecate bacteria from freshwater habitats of various trophic states

Budding and prosthecate bacteria were enumerated in spring and summer by viable counting procedures in several freshwater habitats in Australia including oligotrophic lakes, a mesotrophic lake, and eutrophic ponds.Caulobacter spp. were the most numerous type encountered. They were present in the highest concentrations (exceeding 1000/ml) in the mesotrophic lake during the summer. Their proportion to total viable heterotrophic bacteria was also highest (35.1 to 37.7) in this habitat. From 17 to 330/mlCaulobacter spp. were counted in the eutrophic habitats where their proportion to total viable numbers was less than 1.0%. In the oligotrophic lakes they varied from 5 to 23/ml and comprised greater than 5% of the total viable count.Hyphomicrobium- like bacteria were also numerous in the mesotrophic lake and in one oligotrophic lake during the summer sampling period.Ancalomicrobium spp. occurred in high concentrations (130/ml) in the mesotrophic lake. Budding bacteria of thePlanctomyces-Pasteuria group were most numerous in the eutrophic habitats where as many as 240/ml were counted; their proportion to total heterotrophs remained relatively constant regardless of trophic state, however. A similar pattern was observed withProsthecobacter spp.     

Increased Diversity of Predacious <Emphasis Type="Italic">Bdellovibrio</Emphasis>-Like Organisms (BLOs) as a Function of Eutrophication in Kumaon Lakes of India

Predation by Bdellovibrio-like organisms (BLOs) results in bacterial community succession in aquatic ecosystems. The effects of nutrient loading on the distribution and phylogeny of BLOs remain largely unknown. To this end, we present our findings on BLO diversity from four north-Indian lakes that are variable in their trophic status; Nainital is eutrophic, both, Bhimtal and Naukuchiatal are mesotrophic and Sattal remains oligotrophic, respectively. Initially, total heterotrophic bacteria and BLOs were quantified by most probable number (MPN) analyses using Pseudomonas putida and Escherichia coli as prey bacteria. Total bacterial numbers were at least two-logs higher in the eutrophic lake samples compared with oligotrophic lake. Similarly, BLO numbers were approximately 39-fold higher using Pseudomonas sp., which is likely the preferred prey within these lakes. Conversely, significant differences were not observed between mesotrophic and oligotrophic BLO numbers when E. coli was used as the prey. PCR-RFLP of small subunit rDNA (SSU rDNA) of BLOs, followed by cloning, sequencing, and taxonomic categorization revealed distinct differences such that, eutrophic lake consisted of higher BLO diversity compared with mesotrophic and oligotrophic lake, most likely due to both, higher numbers and availability of a diverse population of prey bacteria resulting from nutrient loading in this ecosystem.     

Identification and characterization of 10 microsatellite primers for the calanoid freshwater copepods Eudiaptomus gracilis and E. graciloides using enriched genomic libraries

The calanoid copepods Eudiaptomus gracilis and Eudiaptomus graciloides are widespread among European lakes. We constructed enriched genomic libraries for both species in order to isolate and characterise microsatellite markers. The obtained 7 polymorphic microsatellite‐loci for E. gracilis and 3 for E. graciloides are the first for any freshwater copepod. They display an expected heterozygosity ranging from 0.60 to 0.96 and 0.63 to 0.94 and observed heterozygosity ranging from 0.53 to 0.87 and 0.57 to 0.87, respectively. We were not able to cross‐amplify the isolated loci across species, indicating long divergence among both congeneric species despite morphological similarity.     

Dissolved Organic Carbon as Major Environmental Factor Affecting Bacterioplankton Communities in Mountain Lakes of Eastern Japan

Relationships between environmental factors and bacterial communities were investigated in 41 freshwater lakes located in mountainous regions of eastern Japan. Bacterioplankton community composition (BCC) was determined by polymerase chain reaction-denaturing gradient gel electrophoresis of the 16S rRNA gene and then evaluated on the basis of physicochemical and biological variables of the lakes. Canonical correspondence analysis revealed that BCC of oligotrophic lakes was significantly influenced by dissolved organic carbon (DOC) content, but its effect was not apparent in the analysis covering all lakes including mesotrophic and eutrophic ones. The generalized linear model showed the negative association of DOC on the taxon richness of bacterioplankton communities. DOC was positively correlated with the catchment area per lake volume, suggesting that a large fraction of DOC supplied to the lake was derived from terrestrial sources. These results suggest that allochthonous DOC has a significant effect on bacterioplankton communities especially in oligotrophic lakes. The genus Polynucleobacter was detected most frequently. The occurrence of Polynucleobacter species was positively associated with DOC and negatively associated with total phosphorus (TP) levels. In addition, TP had a stronger effect than DOC, suggesting that oligotrophy is the most important factor on the occurrence of this genus.     

Fossil record of cladoceran and algal responses to fishery management practices

1. We hypothesized that the fishery management practices of toxaphene application and trout stocking would affect non-target organisms in lakes. Because these practices were rarely monitored in the past, cladoceran and algal assemblages were quantified in sediment cores from two lakes treated 30+ years ago to determine the long-term response of organisms near the base of the food chain. 2. Chydorids were remarkably resistant over the short term (a few years) in both the oligotrophic and eutrophic lakes despite toxaphene treatments that extirpated native fish and other invertebrates. In the oligotrophic lake (Annette Lake), six chydorid taxa were less abundant in the years following treatment, although no loss of species richness was detected. In the eutrophic lake (Chatwin Lake), the dominant Chydorus cf. sphaericus declined coincident with toxaphene treatment, but longer-term declines of all taxa were probably related to food web or other changes rather than to toxaphene toxicity. Cause and effect coupling was complicated by the fact that many chydorids were present at low concentrations in some pretreatment samples. 3. The algal communities (as fossil pigments) responded to treatment differently in the two lakes. In the oligotrophic lake, planktonic diatoms, dinoflagellates and chlorophytes were replaced as dominants by deep-water or benthic blooming cryptophytes, chrysophytes and cyanobacteria. This shift occurred along with increases in large daphnids and the ‘grazing indicator’, pheophorbide a. While both lakes appear to have had enhanced pigment preservation following treatment, the eutrophic lake encountered few long-term changes in its fossil pigment assemblage. Redundancy analysis estimated that the presence or absence of stocked trout explained much of the variation in the algal assemblages, particularly in the oligotrophic lake. 4. Toxaphene remained elevated in profundal sediments from these lakes 30 and 35 years after treatment.     

Seasonal Changes in Chlorophyll-containing Picoplankton Populations of Ten Lakes in Northern England

Key features of photosynthetic picoplankton populations were compared during 1988 in ten lakes in northern England ranging from oligotrophic to slightly eutrophic; two of the three eutrophic lakes were shallow and lacked a thermocline. Measurements were made at 0.5 m depth of temperature, total chlorophyll a, chlorophyll-containing picoplankton cell density, mean picoplankton cell volume and percentage of phycoerythrin-rich cells in the total picoplankton population. All lakes showed maxima for total chlorophyll concentration and picoplankton cell density in mid- to late summer. The maximum value for picoplankton density ranged from 3.4 × 10³ (Esthwaite Water) to 1.3 × 10⁶ cells ml⁻¹ (Ennerdale Water). There was a significant negative relationship (p < 0.05) between log₁₀ of maximum picoplankton cell density and maximum total chlorophyll, the latter being taken as an indicator of lake trophic status. The ratio of maximum to minimum picoplankton density during the year in a particular lake ranged from 39 to 2360 and showed no obvious relationship to lake type. Overall, the seasonal range in picoplankton density was about one order of magnitude greater than the range in total chlorophyll a, but there were considerable differences between lakes. Phycoerythrin-rich picoplankton as a percentage of total picoplankton reached a maximum in summer in all lakes. Values were always very low (<5%) in the two shallow eutrophic lakes, but reached 97% and over in the four most oligotrophic lakes. In two of the oligotrophic lakes, Wast-water and Ennerdale Water, phycoerythrin-rich picoplankton was a major component of the summer phytoplankton biomass.     

Lipid content and utilization of lipids in planktonic copepods in Lake Pääjärvi,southern Finland

The variation of the lipid content of a planktonic copepod species, Eudiaptomus gracilis G. O. Sars, was studied in an oligotrophic lake, Pääjärvi, southern Finland, during 1982. The variation was caused by changes in the food resources and by the use of lipids for reproduction. The lipids are partly present in the form of droplets, which provide an energy reserve for some of food shortage, or may be used in reproduction. The utilization of lipid droplets for nutrition was studied by culturing specimens of two species, Eudiaptomus gracilis and Thermocyclops oithonoides G. O. Sars, in the absence of food. It was found that about half of the energy required for the 30-hour experimental period was obtained from the lipid droplets. However, not all the animal groups could use their lipid droplets and they had to use other reserves to satisfy their energy requirement. Lipid droplets seemed to have only a minor effect on the sinking rate of Eudiaptomus gracilis.     

Relation between nematode communities and trophic state in southern Swedish lakes

The aim of this study was to examine whether littoral nematode community patterns are shaped by lake trophic state. It was hypothesized that trophic level is associated negatively with the proportion of omnivores and positively with the percentages of bacterial feeders, but not at all with the diversity, abundance, and biomass of freshwater nematodes. Sediment samples were taken at littoral sites of eight southern Swedish lakes of different trophy in spring and autumn 2007. Trophic level was found to strongly influence species richness, as oligotrophic and mesotrophic lakes supported the greatest species numbers, whereas nematode abundance, biomass, and Shannon index were unaffected. Furthermore, our results indicated effects on the nematode community’s trophic structure, with a larger proportion of predatory nematodes in oligotrophic and mesotrophic lakes but no differences in the other feeding types (bacteria, algae and suction feeders, omnivorous species). Multivariate analysis indicated a shift in species compositions along the threshold from mesotrophic to eutrophic conditions, with the presence of Tobrilus gracilis, Monhystera paludicola, Brevitobrilus stefanskii, and Ethmolaimus pratensis related to the latter. Nematode communities in oligotrophic and mesotrophic lakes were characterized by a similar species composition, with pronounced occurrences of Eumonhystera longicaudatula, Semitobrilus cf. pellucidus, Prodesmodora circulata, and Rhabdolaimus terrestris. Overall, the results suggested that lake trophic state is a major factor structuring littoral nematode communities, although intra-lake variations might be of importance as well.     

Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ?

The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l^-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5 and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l^-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2 and N. integer in lakes with a salinity above 0.5. Above 2 the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5.     

Zooplankton and environmental factors of a recovering eutrophic lake (Lysimachia Lake, Western Greece)

The present study investigates the zooplankton community dynamics and the abiotic environment in the eutrophic Lake Lysimachia (western Greece). The lake is considered to be recovering from eutrophication after the termination of an urban sewage inflow in 2000, and its waters are replenished constantly from the nearby oligotrophic Lake Trichonis. The results show that, although a decrease in nutrient concentrations was observed compared to the past, the lake still has eutrophic characteristics. This was reflected in the zooplankton community which is typical of those found in eutrophic lakes where rotifers prevail. Similarities among this lake and other nearby lakes were found considering the zooplankton community composition and seasonal variation. However, Lake Lysimachia is inhabited also by a number of different and even unique species (e.g., Moina micrura), suggesting that this ecosystem may be an important biodiversity refuge. Most of the zooplankton species were correlated with water temperature and, to a lesser extent, eutrophication key-water quality variables. Although there are few available data on the zooplankton of the lake, the abundance and composition of the community presenting characteristics indicative of intermediate trophic conditions and suggesting that the lake is probably under a kind of “biological” recovery.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake’s ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970’s, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978–1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.

Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.

Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.

     

The distribution of calanoid copepods in the plankton of Wisconsin Lakes

Zooplankton communities from 499 lakes were examined for calanoid copepod species. Limnocalanus macrurus and Senecella calaloides are confined to Lakes Michigan, Superior and one inland lake each. Eurytemora affinis has recently become established in the coastal waters of Lakes Michigan and Superior. Epischura lacustris is present in the summer plankton of a wide variety of lake types. Aglaodiaptomus leptopus is sensitive to fish predation and confined to small lakes without fish. Leptodiaptomus ashlandi is restricted to Lakes Michigan and Superior, but L. sicilis is also found in some inland lakes. Leptodiaptomus minutus is a boreal species found mostly in lakes of the far north. Skistodiaptomus oregonensis is the most commonly occurring calanoid and seems well adapted to lakes of the meso-to low eutrophic types. Skistodiaptomus pallidus is also generally distributed throughout the state, but less common than oregonensis and adapted to more eutrophic lakes. Leptodiaptomus siciloides and A. clavipes are western species, adapted to eutrophic lakes, which are expanding their ranges eastward, aided by cultural eutrophication.     

The seasonal dynamics of Copidodiaptomus numidicus (Gurney, 1909) and Thermocyclops dybowskii (Lande, 1890) in Castelo-do-Bode Reservoir

We investigated the population dynamics of Copidodiaptomus numidicus (Copepoda: Calanoida) and Thermocyclops dybowskii (Copepoda: Cyclopoida) in Castelo-do-Bode Reservoir (Portugal). Both species in the reservoir were regulated mainly by food availability during the summers of 1993 and 1994. C. numidicus was always more abundant than T. dybowskii in the reservoir. C. numidicus produced two generations during the sampling period of both years whereas T. dybowskii produced two and three generations in 1993 and 1994, respectively. Because of high temperatures and low rainfall in 1994, the reservoir was more eutrophic than in 1993. Higher clutch size and a higher percentage of ovigerous females suggest that both species were benefiting from better feeding conditions in 1994. Despite this, population growth was reduced in 1994 relatively to 1993. Vertebrate predation and predation by copepods seem to have been minor factors in explaining this decline. However, the presence of Mesostoma sp. in the reservoir may have contributed to the reduction of both copepod populations during specific periods in 1994 although the calanoid was more affected than the cyclopoid by this predation.     

Genetic diversity of Potamogeton pectinatus L. in relation to species diversity in a pair of lakes of contrasting trophic levels

Understanding the correlation between genetic diversity and species diversity in freshwater communities is important to elucidate the influences of local selective forces on the genetic diversity of local aquatic plant populations across different communities. This study employed amplified fragment length polymorphism (AFLP) to assess the genetic diversity of Potamogeton pectinatus L. populations between two sister-lakes with contrasting trophic levels, eutrophic and oligotrophic, in the Yunnan Plateau in southwest of China. The results showed high genetic differentiation between eutrophic lake and oligotrophic lake. The genetic distances between P. pectinatus populations were significantly correlated with the species evenness, but not with difference in species richness of aquatic plant communities. The results underpinned that genetic diversity at inter-population levels and local species diversity in plant communities are positively correlated. In addition, our results also suggested that habitat types might play an important role in the genetic diversity of the P. pectinatus populations between these two lakes.     

The photosynthetic and growth rate responses of two freshwater angiosperms in lakes of different trophic status: responses to light and dissolved inorganic carbon

SUMMARY 1. Two rooted freshwater macrophytes ( Lagarosiphon major (Ridley) Moss; Myriophyllum triphyllum Orchard) were grown in two lakes of differing trophic status on sediments collected from an eutrophic lake. In the two experiments (summer and winter) in the oligotrophic lake (Lake Taupo, New Zealand), the relative growth rates of both species were approximately double those recorded in the experiments in the eutrophic take (Lake Rotorua, New Zealand). These growth responses occurred even though the light and temperature regimes were similar at the experimental sites in both lakes and the concentrations of inorganic nutrients were higher in the eutrophic lake water.
2. Dissolved inorganic carbon (DIC) analysis of both lake waters indicated that the oligotrophic water had approximately 10-fold more DIC than the eutrophic water. This corresponded, at natural pH, to a 2-fold higher concentration of free-CO₂ in the oligotrophic lake water (49 μM) than in the eutrophic lake water (23 μM). Photosynthetic experiments demonstrated that the maximum rates of photosynthesis were 2.46 and 2.25-fold higher in L. major and M. triphyllum , respectively, when the shoots were incubated in Lake Taupo water at Lake Taupo levels of free-CO₂ relative to Lake Rotorua water at Lake Rotorua levels of free-CO₂.
3. It is concluded that these differences in photosynthetic rates would lead approximately to a 2-fold difference in growth rate, thus explaining the growth responses observed in the field experiments.     

Nematodes from saline and freshwater lakes of the Vestfold Hills,East Antarctica,including the description of <Emphasis Type="Italic">Hypodontolaimus antarcticus</Emphasis> sp. n.

The invertebrate fauna of many Antarctic ice-free areas, even those close to permanent research stations, can be poorly known. Here we describe some nematodes from freshwater and saline, marine-derived lakes of the Vestfold Hills, East Antarctica. The freshwater lakes contained the widespread East Antarctic endemic species, Plectus frigophilus Kirjanova, 1958. The saline lakes were inhabited by two recently described species, Halomonhystera halophila Andrássy, 2006 and Halomonhystera continentalis Andrássy, 2006, and by a new species described in this report, Hypodontolaimus antarcticus sp. n. Originally marine but now brackish Highway Lake contained a nematode fauna with both freshwater and marine-derived components. The nematode fauna of Antarctica now consists of 54 named species, 22 of which are found in East Antarctica.     

Abundance and diversity of iron reducing bacteria communities in the sediments of a heavily polluted freshwater lake

Iron reduction mediated by Fe(III)-reducing bacteria (FeRB) occurs in aqueous environments and plays an essential role in removing contaminates in polluted freshwater lakes. Two model FeRB species, Shewanella and Geobacter, have been intensively studied because of their functions in bioremediation, iron reduction, and bioelectricity production. However, the abundance and community diversity of Shewanella and Geobacter in eutrophic freshwater lakes remain largely unknown. In this work, the distribution, abundance and biodiversity of Shewanella, Geobacter and other FeRB in the sediments of a heavily polluted lake, Chaohu Lake, China, across four successive seasons were investigated. Shewanella, Geobacter, and other FeRB were found to be widely distributed in the sediment of this heavily eutrophic lake. Geobacter was abundant with at least one order of magnitude more than Shewanella in cold seasons. Three Shewanella-related operational taxonomic units were detected and sixty one Geobacter-related operational taxonomic units were grouped into three phylogenetic clades. Thiobacillus, Desulfuromonas and Geobacter were identified as the main members of FeRB in the lake sediments. Interestingly, nutrients like carbon, nitrogen, and phosphorus were found to be the key factors governing the abundance and diversity of FeRB. Total FeRB, as well as Geobacter and Shewanella, were more abundant in the heavily eutrophic zone than those in the lightly eutrophic zone. The abundance and diversity of FeRB in the sediments of freshwater lakes were highly related with the degree of eutrophication, which imply that FeRB might have a great potential in alleviating the eutrophication and contamination in aqueous environments.

     

Phototrophic Picoplankton in Temperate Lakes: Seasonal Abundance and Importance along a Trophic Gradient

The seasonal development of autotrophic picoplankton was investigated in seven Danish lakes representing a eutrophication gradient. Highest cell abundance between 1.5 to 6 × 10⁵ cells ml⁻¹ were found in mid-summer. Minor peaks were observed in spring. In winter, densities were below 10³ ml⁻¹. The highest relative picoplankton contribution to total autotrophic biomass also occurred in mid-summer. In the eutrophic lakes and one humic lake the average seasonal contribution of picoplankton to total chlorophyll was below 1% increasing to 5-8% in the meso- and oligotrophic clear water lakes. During short periods the proportion of picoplankton did reach 25%. The higher relative importance of picoplankton in less productive lakes was not due to higher actual chlorophyll concentrations, but due to a much more pronounced response by larger algae at higher nutrient loading. Both cyanobacteria and eukaryote organisms were present as picoplankton. Only eukaryotes were found in one eutrophic lake and an acidic, humic lake. In the eutrophic lakes eukaryote picoplankton was dominant; both with respect to cell densities and biovolume, whereas cyanobacteria dominated the two meso-oligotrophic lakes. Autotrophic picoplankton were present in all lake types, however their importance seemed to be less in most eutrophic lakes than in less productive, meso-oligotrophic lakes.