How important are trophic state,macrophyte and fish population effects on cladoceran community? A study in Lake Erhai

Environmental controls on cladoceran community structure in lake ecosystems are complex and may involve many environmental parameters including trophic state and fish populations. In Lake Erhai, a plateau lake located in southwest China, it was hypothesized that a combination of lake eutrophication and planktivorous fish introduction would increase the abundance of cladoceran, while also decreasing cladoceran size. To test this hypothesis, we examined temporal changes in cladoceran microfossils in the sediments of Lake Erhai over the past century. The influence of changing macrophyte coverage within the littoral region of the lake was also considered. Results demonstrated that cladoceran abundance (measured as flux of cladoceran fossils in the sediments) increased markedly accompanying eutrophication of the lake. In addition, there was a shift in the dominant cladoceran species from those species that prefer oligotrophic conditions to those that prefer mesotrophic and eutrophic conditions. A reduction in the ephippium length of Daphnia spp. was observed and attributed to the introduction of the planktivorous fish Neosalanx taihuensis. Our findings indicated that eutrophication and fish introduction were the main controls affecting cladoceran community structure during the recent decades, and predation by planktivorous fish had an important impact on Daphnia body size.     

从微体化石群看我国沿海早第三纪含油盆地的差异

对我国沿海3个含油盆地－珠江口、北部湾和渤海湾盆地下第三系湖相生油岩中的微体化石群进行比较分析。3个盆地中以渤海湾盆地下第三系湖相化石群最为丰富,数量多,分异度高,而且化石群以地方性属种比例高、咸水类型多,存在“海源陆生生物化石”为特征;北部湾盆地,在涠洲组和流沙港组发现较多的介形类化石及个别腹足类和轮藻化石;而珠江口下经三系湖相地层中,微体化石罕见,只在个别层位发现贝壳碎片。据化石群特征,推测渤海湾盆地早第三纪是封闭型的咸水湖泊,而且部分沉积时期,可能是以Cl^-和Na^ 为主的咸水湖泊;珠江口盆地早第三纪是湖水矿化度低、硬度、pH值也低的淡水湖泊;而北部湾盆地早第三纪可能仍属淡水湖泊,但有一定的矿化度。     

First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong,North China

Organic-walled microfossils offer important information on the biospheric evolution in pre-Cryogenian and provide biostratigraphic implications for many Proterozoic fossiliferous sequences that are poorly age constrained for the lack of reliable radiometric date. Recently, macroscopic carbonaceous compression fossils have been reported for the first time from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China. However, organic-walled microfossils have never been discovered from this formation up till now. To improve our knowledge about Proterozoic biodiversity in North China, we conducted a micropaleontological survey on the argillaceous limestone samples of the Shiwangzhuang Formation, which also contain macroscopic carbonaceous compression fossils, from the Baishicun section in Anqiu, western Shandong, North China. Our investigation shows that the Shiwangzhuang microfossil assemblage is dominated by smooth-walled sphaeromorphic acritarchs and cyanobacterium-like filaments and relatively low abundance of other acritarchs, including 16 taxa, such as Polysphaeroides filliformis, Ostiana microcystis, Simia annulare, ?Jacutianema sp., Arctacellularia tetragonala, Pellicularia tenera, Polythrichoides lineatus, and Navifusa actinomorpha. The Shiwangzhuang organic-walled microfossil assemblage, although consisting of long-ranging and not age diagnostic taxa, is consistent with a Tonian age suggested by macroscopic carbonaceous compression fossils, including the Chuaria-Tawuia and Sinosabellidites-Protoarenicola-Pararenicola assemblages, revealed from the same fossiliferous horizon of the Shiwangzhuang Formation and by organic-walled microfossil assemblage, including the late Mesoproterozoic to Tonian index fossil Trachyhystrichosphaera aimika, from the underlying Tongjiazhuang Formation. However, it is also worth noting that a Cryogenian or Ediacaran age cannot be completely excluded based just on the Shiwangzhuang microfossils because of their limited biostratigraphic utility.     

Tubular microfossils from the Ediacaran Weng’an Biota (Doushantuo Formation,South China) are not early animals

The early Ediacaran Weng’an Biota (ca. 609 Ma) of the Doushantuo Formation (Guizhou Province, China) encompasses an abundant and exquisitely preserved assemblage of phosphatic microfossils that have provided unique insight into the origin and early evolution of multicellular eukaryotes. However, the affinities of these early organisms are far from certain, including the tubular microfossils Crassitubulus, Quadratitubus, Ramitubulus, and Sinocyclocylcicus. These taxa have been widely accepted as stem-cnidarians or, alternatively, interpreted as filamentous cyanobacteria, or multicellular algae. We use high-resolution X-ray tomographic microscopy to analyse the structure and development of the four taxa. Our data and analysis allow us to conclude that these four taxa were not biomineralized. Crassitubulus, Quadratitubus, and Sinocyclocylcicus, may be grouped on the basis that they exhibit alternating complete and incomplete cross walls, and bipolar growth; which makes them favourably comparable to filamentous cyanobacteria. In contrast, Ramitubulus exhibits only complete cross walls, unipolar growth and dichotomous branching. These features are difficult to reconcile with a cyanobacterial interpretation. They are, instead, more indicative of multicellular algae-like Cambrian Epiphyton. Thus, the Weng’an tubular microfossils constitute a disparate assemblage of cyanobacteria and algae, but none represents early Ediacaran animals.     

Mississippian (Lower Carboniferous) microfossils from the Chios Mélange (Chios Island, Greece)

The Chios Mélange is a thick Paleozoic wildflysch sequence that crops out on the Greek island Chios. It is composed of chert, limestone and volcanic blocks floating in a siliciclastic turbiditic matrix. New data suggest that the youngest blocks within the Chios Mélange are clasts of a breccia from the Kouramia-Nenitouria area that contain conodonts of late Visean or early Serpukovian age. The conodont fauna from the breccias is characterized by the genera Gnathodus and Lochriea, which favored deeper-water, open-marine facies. Elsewhere on the island, in the Papalia-Nagos area, calcareous microfossils of middle to late Visean age have been recovered from lime grainstone beds within the Chios Mélange. Allochems making up the grainstones are interpreted to have been transported into deeper-water turbiditic facies, but there is no evidence of stratigraphic reworking. Age-diagnostic calcareous microfossils include the alga Koninckopora inflata and foraminifers in the genus Paraarchaediscus. In situ Mississippian microfossils indicate that the Chios Mélange is older than Pennsylvanian (Upper Carboniferous) - Permian, as previously thought. The revised age suggests that the origin of the Chios Mélange may be related to the development of an accretionary prism during the Hercynian Orogeny.© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

Late Quaternary environmental history of the south-eastern Tibetan Plateau inferred from the Lake Naleng non-pollen palynomorph record

A 17.81 m sediment core from Lake Naleng, a freshwater lake in the south-eastern part of the Tibetan Plateau was examined for its non-pollen palynomorph (NPP) composition. The frequencies of 15 NPPs and three aquatic pollen types were determined in 160 samples. Since the origin of several NPP types is still unknown, multivariate analysis, supported by findings from the corresponding fossil pollen flora, was carried out to extract information about their ecological environments. The analysis allowed a classification of all microfossils in four groups of environmental response, which provided an approach to tracing lake history and palaeoclimatic changes in the area since the Late Glacial (since 17,700 cal years b.p.). Unstable lake conditions and a low organic productivity were reconstructed for the Late Glacial before 14,600 cal years b.p. with high inputs of terrestrial material. Climate conditions became wetter during the Bølling/Allerød interval indicated by high productivity in the lake. After a short climate deterioration (12,500–11,500 cal years b.p.), stable lake conditions were inferred from the record. During the late Holocene (since 2,700 cal years b.p.) changes in the NPP composition might be related to human impact, the latter being inferred from the pollen data through the presence of grazing indicators.     

Diversity of sulfur-cycle prokaryotes in freshwater lake sediments investigated using aprA as the functional marker gene

The diversity of sulfate-reducing prokaryotes (SRPs) and sulfur-oxidizing prokaryotes (SOPs) in freshwater lake ecosystems was investigated by cloning and sequencing of the aprA gene, which encodes for a key enzyme in dissimilatory sulfate reduction and sulfur oxidation. To understand their diversity better, the spatial distribution of aprA genes was investigated in sediments collected from six geographically distant lakes in Antarctica and Japan, including a hypersaline lake for comparison. The microbial community compositions of freshwater sediments and a hypersaline sediment showed notable differences. The clones affiliated with Desulfobacteraceae and Desulfobulbaceae were frequently detected in all freshwater lake sediments. The SOP community was mainly composed of four major phylogenetic groups. One of them formed a monophyletic cluster with a sulfur-oxidizing betaproteobacterium, Sulfuricella denitrificans, but the others were not assigned to specific genera. In addition, the AprA sequences, which were not clearly affiliated to either SRP or SOP lineages, dominated the libraries from four freshwater lake sediments. The results showed the wide distribution of some sulfur-cycle prokaryotes across geographical distances and supported the idea that metabolic flexibility is an important feature for SRP survival in low-sulfate environments.     

Pollen deposition in a small closed drainage basin lake

A moss cushion and fifteen lake bottom samples from a small volcanic crater lake in southeastern South Australia were examined for pollen. The distribution of pollen types is analysed in relation to the distance from source areas of Eucalyptus woodland and Pinus radiata plantations, and in relation to water depth in the lake.Most taxa were only detectable in small quantities within a few metres of the source plants. The decline in these local pollen types led to a relative increase in regional pollen types in the centre of the lake. This is a problem which makes interpretation of the extent of the redeposition factor difficult for some taxa. The redeposition factor was small for extralocal taxa including Pinus radiata and Eucalyptus spp. as their relative frequencies declined noticeably toward the centre of the lake. Regional types included Casuarina stricta, Chenopodiaceae, Polygonaceae and Poaceae pollen. Aquatic pollen was derived within the lake and does not contribute to the regional pollen rain. The majority of these taxa have highest values near the source plants but were also deposited elsewhere in the lake. The exceptions to this were Triglochin and Typha angustifolin pollen; the former showed a distribution pattern which had little relation to the occurrence of the plant while the latter had highest relative frequencies away from the source plants. The implications in relation to water depth interpretation from fossil pollen profiles are discussed.     

Nucleation of Celestite and Strontianite on a Cyanobacterial S-Layer

Synechococcus strain GL24 is a unicellular cyanobacterium that was isolated from Fayetteville Green Lake, New York, a meromictic lake which has high Ca²⁺ and SO₄^2- concentrations. Epicellular mineralization of Synechococcus cells in the lake is the mechanism by which extensive calcitic bioherms (or microbial reefs) have been formed on the lake's shore and a marl sediment has been built on the lake bottom. Previous studies have shown that calcium carbonate (calcite) formation on the Synechococcus surface is dependent upon an alkaline pH, which is produced in the cellular microenvironment by the cells as their activity increases with seasonal warming of the lake water. At the circumneutral pH of bulk lake water, calcium sulfate (gypsum) is formed. In this study, we show that Synechococcus mediates a similar sulfate-to-carbonate transformation when Sr²⁺ is the major divalent cation present, forming celestite and strontianite. In experimental systems to which equimolar amounts of Ca²⁺ and Sr²⁺, Ca²⁺ or Sr²⁺ and Mg²⁺, or all three ions together were added to artificial lake water, Ca²⁺ and Sr²⁺ were incorporated equally into mineral formation to form CaSr(CO₃)₂. No Mg²⁺ -containing carbonates were formed when either or both of the other two ions were present. Mineral formation takes place on a hexagonally arranged proteinaceous template (an S-layer) which forms the outermost surface of the Synechococcus cell. Our results provide evidence that the S-layer exhibits selectivity with respect to the ions bound and subsequently incorporated into carbonate minerals and that celestite and strontianite, previously thought to be purely evaporitic minerals, can be biogenically formed.     

Bacterial Inhibitors in Lake Water

The populations of six bacterial genera fell rapidly after their addition to sterile lake water but not after their addition to buffer. The decline in numbers of two species that were studied further, Klebsiella pneumoniae and Micrococcus flavus, occurred even when the buffer was added to sterile lake water. The inhibition of K. pneumoniae by substances in lake water varied with the season of the year, and the rate and extent of decline of both species were different in sterile samples of different lakes. The extent of reduction in the density of K. pneumoniae was independent of initial population size and was diminished by the addition of 10 μg of glucose per ml of lake water. The toxin was removed from lake water by dialysis and by a cation-exchange resin but not by an anion-exchange resin, and it was destroyed by heating. The inhibition of K. pneumoniae was not evident in lake water buffered at a pH value above 8.0. We suggest that toxins may be important in determining the composition of the bacterial community of lakes.     

Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial Maximum

Aim  There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c . 130,000 yr bp , i.e. prior to the LGM.
Location  Lake Reid, Larsemann Hills, East Antarctica (76°23' E; 69°23' S).
Methods  Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c . 130,000 yr bp .
Results  Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM.
Main conclusion  The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent.     

Aeromonas Distribution and Survival in a Thermally Altered Lake

Par Pond is a thermally enriched monomictic southeastern lake which receives heated effluent from a production nuclear reactor. Fish populations in the lake have lesions of epizooty from which Aeromonas spp. are readily isolated. Distribution and population densities of Aeromonas in the water column were measured along an oxygen and temperature gradient as well as seasonally. Greater population densities of Aeromonas occurred below the oxygen chemocline when the lake was stratified. Survival of Aeromonas hydrophila under in situ conditions in both epilimnetic and hypolimnetic waters was determined through the use of polycarbonate membrane diffusion chambers during two separate reactor operating conditions. Survival levels of pure cultures of A. hydrophila corresponded to the distribution patterns of the naturally occurring Aeromonas-like populations. The greater survival of A. hydrophila during full reactor operation suggests that the fish populations may be exposed to Aeromonas for a longer period of time than when the reactor is not operating.     

Occurrence of Cryptophyceae and katablepharids in boreal lakes

One of the most important algal groups in Finnish lakes are the Cryptophyceae. Changes in the community structure of Cryptophyceae in a total of 22 lakes belonging to the Vuoksi river basin in eastern Finland were studied. The existence of lakes with water qualities varying from oligotrophic to eutrophic, often loaded by human activities, provides a good opportunity to study the effects of environmental variables on the occurrence and size variation of Cryptophyceae. In the Vuoksi river basin, the main soil type is moraine. Twelve of the lakes were large or moderately large and with clear, i.e. oligo-humic water, and one lake could be described as a small clear water lake. Eight large or moderately large lakes were humic, with a water colour number of 40–70 mg l^?1 Pt, including three lakes impacted by nutrient loads. One lake was naturally eutrophic, with a high water colour number of 100 mg l^?1 Pt, and was also impacted by municipal and pulping effluents. CCA-ordination analysis grouped the studied lakes into: (1) clear water lakes, (2) humic lakes and (3) the naturally eutrophic brown water lake. In the CCA-ordination analysis based on cell numbers small Cryptophyceae (Cryptomonadales), Rhodomonas lacustris and the katablepharid Katablepharis ovalis were grouped into the first axis, which was positively correlated with Secchi depth (r=0.58) and NO₃N - nitrogen (r=0.24) and negatively with Ptot (r=-0.69), PO₄P (r=-0.69) and water colour number (r=-0.66). In humic lakes, medium-sized Cryptophyceae were abundant. The naturally eutrophic lake was grouped into first axis, which is positively correlated with Ptot (r=0.69), PO₄P (r=0.69) and water colour number (r=0.66). The lake formed a distinct group with large Cryptophyceae. Only in this lake was the heterotrophic Katablepharis ovalis rather abundant. However, large-sized taxa dominated the biomass of the Cryptophyceae assemblage in all lake types excluding large clear water lakes, where Rhodomonas lacustris dominated and large Cryptophyceae co-dominated.     

Palynomorphs from the Cambrian Series 3, Parahio valley (Spiti), Northwest Himalaya

We present low-diversity acritarch assemblages, including Alliumella baltica, Bavlinella faveolata, Brocholaminaria nigrita, Brocholaminaria sp., Eliasum sp., Leiosphaeridia minutissima, Leiosphaeridia spp., Lophosphaeridium sp., Pterospermella solida, Satka colonialica, Siphonophycus sp., and Synsphaeridium sp., as well as filamentous algae and cryptospore-like microfossils recorded from 45 rock samples around the Oryctocephalus indicus Zone (Cambrian Series 3) in the Cambrian Kunzam La (Parahio) Formation at the Kaltarbo locality in the Parahio valley, Northwest Himalaya. One new species Synsphaeridium parahioense was established. The acritarch assemblages at the basal part of the Cambrian Series 3 in the Kunzam La (Parahio) Formation were dependent on the local marine environment. The new discovery of cryptospore-like microfossils from the Cambrian Kunzam La (Parahio) Formation supports the extensive distribution of possible cryptospores in the Cambrian stratigraphic sequences.     

<Emphasis Type="Italic">Coregonus peled</Emphasis> (Gmelin) transplanted into Ulaagchny Khar lake (western mongolia) showed no evidence of hybridization with other introduced <Emphasis Type="Italic">Coregonus</Emphasis> species

Coregonus peled (Gmelin) (Teleostei: Salmoniformes: Coregonidae), which is considered an important object of coldwater aquaculture, had been successfully introduced into an enclosed Western Mongolian lake Ulaagchny Khar in the early 1980s. At the same time larvae of two other Coregonus species—Baikal omul C. migratorius (Georgi) and least cisco C. sardinella Valenciennes—had also been released into the lake. Baikal omul was then reported as a naturalized species. This might have caused interspecific hybridization and gene introgression. Identification of coregonids by morphology can be problematic, so to determine which species was dominant in the lake (we presumed it was peled) and if its gene pool was affected by other introduced Coregonus species we sampled 40 individuals and analyzed them by sequencing a fragment of mtDNA cyt b and by allozyme electrophoresis. The analysis showed that all the fish belonged to C. peled with no evidence of admixture from other coregonid species. Taking into account mass release of both species in 1980s, it is evident that naturalization of peled in the lake was much more successful than that of Baikal omul.     

The contribution of leaching to nutrient release from leaf litter of two emergent tree species in a Malaysian tropical peat swamp forest

Ostracode faunas changed in Lake Bonneville as the lake rose in the closed basin and became more dilute, then overflowed, and eventually returned to closed-basin hydrology; alkalinity (carbonate + bicarbonate) increased throughout the lake history. Fossil-ostracode faunas in marl deposited in the lake between about 30 and 13 cal ka allow reconstruction of these geochemical changes (as shown by R. M. Forester), and permit stratigraphic correlations within the large lake basin, including into the Sevier subbasin, which was connected to the main body of the lake but had different inflowing rivers. The first ostracode to appear in Lake Bonneville deposits at low altitudes is Limnocythere staplini; it was replaced by L. ceriotuberosa as the lake got larger and the water became more dilute and alkaline. Candona adunca and several species of Fabaeformiscandona mark the freshest-water phases. Cytherissa lacustris appeared in lake-margin settings after lake level dropped and cold, fresh groundwater began to discharge into the lake. Candona sp. cf. eriensis lived in the Sevier subbasin during the transgressive phase of the lake, but did not appear in the main body until late in the regressive phase. Limnocythere sappaensis, which requires high alkalinity, showed up late in the regressive phase in the main body when lake level was very low.     

Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity

Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.     

Fossil diatoms and scales of Chrysophyceae in the recent history of Hall Lake, Washington

SUMMARY. Scales of several members of the Chrysophyceae (family Synuraceae) were examined from a core of the recent sediments of Hall Lake, Washington, in conjunction with a study of fossil diatoms. Both types of microfossils revealed communities changing with the historical development of the lake. Increases in planktonic diatoms and in two species of Mallomonas occurred about the time of European settlement. Several acidophilous species among the Chrysophyta disappeared with the establishment of a sawmill and meromictic conditions in the lake. When extensive road construction around the lake ended the period of meromixis, the ratio of Synuraceae, in general, to diatoms, declined. Besides the change in ratio of Synuraceae to diatoms there was a change in the composition of the community of Synuraceae at that time. Species of Synura that had been rare before became the most abundant, and Mallomonas became relatively rare. Throughout the recent history of the lake the dominant Synuraceae seemed to respond more strongly to disturbance around the lake than the most abundant diatoms; thus, scales of Mallomonas, Synura , and other Synuraceae are valuable microfossils for paleolimnological studies.     

Heterogeneous distribution of a floating-leaved plant,Trapa japonica,in Lake Mikata,Japan, is determined by limitations on seed dispersal and harmful salinity levels

Factors affecting the within-lake distribution of Trapa japonica were analysed in Lake Mikata, Japan, by integrating remote sensing analyses, field surveys, and laboratory experiments. The T. japonica bed has been expanding since 2006 and covered more than 60 % of the lake’s area from 2008 to 2010. However, two parts of the lake, the upper and lower areas, retained open water, even during recent years. A survey of lake-bottom sediments revealed a heterogeneous seed distribution. Although seed density exceeded 13 seeds/m² in the lake’s central area, no seeds were observed in the upper and lower areas. A seed-bag retrieval experiment showed that 75.6 % of seeds at the upper site germinated when seeds were artificially introduced, whereas 6.7 % of seeds germinated at the lower site. These results suggest that seed dispersal opportunities are the primary limitation on the distribution of T. japonica in the upper area. Brackish water was found in springs in the lower area, reflecting an adverse inflow of water from a downstream brackish lake. Laboratory experiments revealed significant adverse effects of water salinity on germination and early growth of T. japonica. Based on these results, we concluded that the heterogeneous distribution of T. japonica within the lake was determined by a combination of two factors: limitations on seed dispersal determined by the inflowing river and harmful salinity levels caused by inflows of seawater from the Sea of Japan via a downstream brackish lake.