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At least 37 records · Page 2Linked to original sources
PubMed2001

A semi-operative approach to lake water quality retrieval from remote sensing data.

A semi-operative approach to retrieve chlorophyll-a concentration from airborne/spaceborne spectrometer observations has been developed and tested using the airborne imaging spectrometer (AISA) data from 11 lakes located in southern Finland. The retrieval approach is empirical and requires nearly simultaneous in situ training data on water quality for the determination of regression coefficients. However, the training data does not have to be collected from every lake under investigation. Instead, the results obtained indicate that reliable estimates on the level of chlorophyll-a (chl-a) for an individual lake can be achieved without employing in situ data representing this specific lake. This enables the estimation of water quality from remotely sensed data for numerous lakes with the aid of reference data only for a few selected lakes representing the region under investigation. In addition, it is shown that the remotely sensed spectrum shape characteristics are highly affected by the trophic and humic state of the lake water.

Chlorophyll↗
PubMed1993

Direct sequencing of the polymerase chain reaction-amplified 16S rRNA gene of Flavobacterium gondwanense sp. nov. and Flavobacterium salegens sp. nov., two new species from a hypersaline Antarctic lake.

Phenotypic data and phospholipid ester-linked fatty acid profiles indicate that pigmented bacterial strains isolated from a hypersaline Antarctic lake are members of the "flavobacterium-bacteroides" phylum and may represent new taxa. Nearly complete 16S rRNA sequences were obtained for representative strains by directly sequencing the polymerase chain reaction-amplified 16S rRNA gene. Sequence signatures confirmed that these organisms were members of the flavobacterium-bacteroides phylum. A phylogenetic analysis, in which the sequences of the Antarctic strains were compared with a large number of sequences available for members of the flavobacterium-bacteroides phylum, showed that the Antarctic strains were phylogenetically distinct. The new species cluster with a group of organisms that contains the type species of the genus Flavobacterium, Flavobacterium aquatile. Two new species are described, for which the names Flavobacterium gondwanense and Flavobacterium salegens are proposed; strains ACAM 44 (= DSM 5423) and ACAM 48 (= DSM 5424) are the type strains of F. gondwanense and F. salegens, respectively.

Antarctic Regions↗
PubMed1999

More than 200 meters of lake ice above subglacial Lake Vostok, Antarctica.

Isotope studies show that the Vostok ice core consists of ice refrozen from Lake Vostok water, from 3539 meters below the surface of the Antarctic ice sheet to its bottom at about 3750 meters. Additional evidence comes from the total gas content, crystal size, and electrical conductivity of the ice. The Vostok site is a likely place for water freezing at the lake-ice interface, because this interface occurs at a higher level here than anywhere else above the lake. Isotopic data suggest that subglacial Lake Vostok is an open system with an efficient circulation of water that was formed during periods that were slightly warmer than those of the past 420,000 years. Lake ice recovered by deep drilling is of interest for preliminary investigations of lake chemistry and bedrock properties and for the search for indigenous lake microorganisms. This latter aspect is of potential importance for the exploration of icy planets and moons.

Antarctic Regions↗
PubMed2005

Passive and active air samplers as complementary methods for investigating persistent organic pollutants in the Great Lakes Basin.

Data obtained using passive air samplers (PAS) are compared to active high-volume air sampling data in order to assess the feasibility of the PAS as a method, complementary to active high-volume air sampling (AAS), for monitoring levels of organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in the Laurentian Great Lakes. PAS were deployed at 15 of the Integrated Atmospheric Deposition Network (IADN) sites on a quarterly basis between July 2002 and June 2003, and PAS and AAS results are compared. Levels for the OC pesticides are typically highest in agricultural areas, with endosulfan I dominating air concentrations with values ranging between 40 and 1090 pg x m(-3), dieldrin values between 15 and 165 pg x m(-3), and gamma-HCH values between 13 and 100 pg x m(-3). alpha-HCH was seen to be relatively uniform across the Great Lakes Basin with values ranging between 15 and 73 pg x m(-3). Large urban centers, such as Chicago and Toronto, have the highest levels of PCBs and PBDEs that range between 400 and 1200 pg x m(-3) and 10 and 70 pg x m(-3), respectively. Comparison of the AAS and the PAS data collected during this study shows good agreement, within a factor of 2 or 3, suggesting that the two sample methods produce comparable results. It is suggested that PAS networks, while providing data that are different in nature from AAS, can provide a cost-effective and complementary approach for monitoring the spatial and temporal trends of persistent organic pollutants.

Air Pollutants↗
PubMed2003

A comparison of sediment and monitoring data: implications for paleomonitoring a small lake.

Long-term limnological monitoring data (from 1971 to 2001) were compared with sediment core record in Lake Viitna Linajärv (hereafter L. Viitna), a small lake in northern Estonia. The monitoring data show that L. Viitna changed from mesotrophic in the 1970s to eutrophic in the 1990s. The trends of paleodata that integrate the changes in the biogeochemical matter cycling in the lake over 2-3 years have clear signals about changes in the state of the ecosystem in L. Viitna during the last decades. A gradual increase in organic productivity should reflect a greater oxygen demand in the hypolimnion. As a result the hypolimnion became seasonally anoxic earlier and its pH level remained low for a longer time. These fundamental changes near the sediment-water interface were recorded in the sediment core. The greatest changes occurred at the beginning of the 1980s (layers at a depth of ca. 20 cm), when the meso(eu?)trophic conditions in L. Viitna started to become increasingly more eutrophic. The variations of paleorecords in the upper part of the sediment core coincide temporally with changes in the water level of the lake.

Ecosystem↗
PubMed2006

Nitrate degradation without 15N enrichment: a hydrochemical and isotopic study of a fractured rock aquifer including embedded lakes.

Water samples from three quarry lakes and the surrounding fractured rock aquifer were investigated for delta18O and delta2H (H2O), delta15N and delta18O (NO3-), as well as anions and cations. Lake water and groundwater can be distinguished by their different chemical and isotopic composition. Because of evaporation processes, 18O and 2H are enriched in the lake water and can be used as natural tracers for the water dynamic of the lakes. The groundwater is characterised by high nitrate concentrations (up to 120 mg/l). Lake internal processes reduce the nitrate concentration in the quarry lakes. However, no enrichment of delta15N and delta18O in nitrate, typical for microbial nitrate degradation, is observed in the lake water. Because of the complex flow paths in the fractured rock aquifer and the intense chemical transformations at the interface between groundwater and lake water, isotopic and hydrochemical data of lake water and groundwater alone do not conclusively explain hydrological and hydrochemical processes of the investigated lake-groundwater system.

Deuterium↗
PubMedDate not supplied

Changes in acid precipitation-related water chemistry of lakes from southwestern New Brunswick, Canada, 1986-2001.

Between 1986 and 2001, thirty-nine lakes in southwestern New Brunswick in Atlantic Canada were surveyed for acid precipitation-related water quality changes. Most of the study lakes are located on granite bedrock and represent the most acid sensitive lakes in the province. Between 1987 and 1992, hydrogen ion deposition to the lake study area averaged 452 eq ha(-1) yr(-1), compared to 338 eq ha(-1) yr(-1) between 1993 and 2000, a 25% reduction. The lake chemistry data were evaluated by dividing the lakes into four clusters for each survey year based on their acid neutralizing capacity. Twenty percent of the lakes (cluster IV) had an average ANC of 40 microeq L(-1) or greater and maintained an average pH of greater than 6 over the duration of the study period. A pH of 6 or greater is considered a healthy benchmark for maintaining biodiversity. The remaining 31 lakes (clusters I to III) had an average ANC of less than 40 microeq L(-1) and maintained an average pH of less than 6. Other lake chemistry changes included a general decline in lake sulphate and colour over the duration of the survey period, followed by more recent improvements in calcium ion, pH and ANC, and notably higher but declining aluminum levels in lower ANC and pH lakes. Nitrate accounted for 37% of the acid deposition to the study area, however it was not detectable in the lakes. Although acid deposition has declined and these lakes are beginning to show signs of acid recovery, 80% of the study lakes remain acid sensitive having little buffering capacity with low calcium, pH and ANC.

Acid Rain↗
PubMedDate not supplied

[Protist plankton from the Khanka lake].

We present data on studies of protists in Lake Khanka in late August-early September. A total of 99 species of protists have been found, of them 14 phytoflagellates, 14 zooflagellates, five sarcodins, two heliozoans, 62 infusoria, and two suctorians. Small infusoria from the class of Kinetophragminophora, order Oligotrichida, as well as suborder Tetrahymenina were most numerous. The density of many protist species in Lake Khanka exceeds markedly that in several other high-productivity water reservoirs. Most of the protists belong to bacteriovores (bacteriophages). Many of the found species have high density. This is evidence of the production of bacterial plankton in the lake. In view of very high water turbidity in the lake, we assume that the total production of phytoplankton is not that high. In this connection, an abundance of protists (protist plankton) indicates is an indication for the existence of an additional source of organic matter in Lake Khanka.

Animals↗
PubMed2003

Application of ultrafiltration and stable isotopic amendments to field studies of mercury partitioning to filterable carbon in lake water and overland runoff.

Results from pilot studies on colloidal phase transport of newly deposited mercury in lake water and overland runoff demonstrate that the combination of ultrafiltration, and stable isotope amendment techniques is a viable tool for the study of mercury partitioning to filterable carbon. Ultrafiltration mass balance calculations were generally excellent, averaging 97.3, 96.1 and 99.8% for dissolved organic carbon (DOC), total mercury (Hg(T)), and methylmercury (MeHg), respectively. Sub nanogram per liter quantities of isotope were measurable, and the observed phase distribution from replicate ultrafiltration separations on lake water agreed within 20%. We believe the data presented here are the first published colloidal phase mercury data on lake water and overland runoff from uncontaminated sites. Initial results from pilot-scale lake amendment experiments indicate that the choice of matrix used to dissolve the isotope did not affect the initial phase distribution of the added mercury in the lake. In addition there was anecdotal evidence that native MeHg was either recently produced in the system, or at a minimum, that this 'old' MeHg partitions to the same subset of DOC that binds the amended mercury. Initial results from pilot-scale overland runoff experiments indicate that less than 20% of newly deposited mercury was transported in the filterable fraction (<0.7 microm). There is some indication of colloidal phase enrichment of mercury in runoff compared to the phase distribution of organic carbon, but the mechanism of this enrichment is unclear. The phase distribution of newly deposited mercury can differ from that of organic carbon and native mercury, suggesting that the quality of the carbon (available ligands), not the quantity of carbon, regulates partitioning. Further characterization of DOC is needed to clarify the underlying mechanisms.

Biological Availability↗
PubMed1983

[Characteristics of karyosphere formation in the lake frog. Light microscopy data].

Morphological peculiarities of the oocyte nuclear organization were examined in R. ridibunda during winter and spring (February-March). Numerous nucleoli were seen to be assembled around regressive lampbrush chromosomes in the centre of the nucleus, and a central body was formed to which the chromosomes were attached. As result, a structural complex is constituted that involves a karyosphere and a capsule. Nucleoli are characterized by segregation and intensive fragmentation of their material. In result, a considerable part of nucleolar DNA is eliminated in the form of ring and polymorphous structures (micronucleoli). Besides the membranous component of nucleoli (nucleolar threads or tails) is lost. Towards the end of this period, nucleoli with complicated morphology become spherical again. The formation of the central body is started from the appearance of some small optically-light protein structures 5-20 nm in diameter (central body precursors-CBP). CBP are closely surrounded with ring micronucleoli to make intimate contact with the chromosomes and nucleolar threads. CBP commonly lie in one region of the nucleus not far from each other. The formation of a definitive central body obviously occurs due to a fusion of some small CBP. A conclusion is made of the nucleolar origin of the ring and polymorphous structures and of their essential role in the central body formation. The participation of chromosomal and eliminated nucleolar DNA in this process is discussed.

Animals↗
PubMed1984

[Characteristics of karyosphere formation in the lake frog. Electron microscopic data].

The ultrastructural organization of the karyosphere in oocytes of R. ridibunda during formation of its central body (CB) was examined. It is shown that the material of CB consisting of pores similar to those of the nuclear envelope makes some intimate contact with DNA-containing fibrillar micronucleoli (MN). In the zone of this contact a transfer of MN fibrils into CB is observed. The electron microscope data on the nucleolar origin of numerous MN are provided. It is suggested that MN supply the material for the formation of CB. The participation of r-DNA in this process is discussed.

Animals↗
PubMed2004

Development of nestedness: host biology as a community process in parasite infracommunities of yellow perch (Perca flavescens (Mitchill)) from Garner Lake, Alberta.

Infracommunity data from 60 perch collected from Garner Lake, Alberta, in 1992 were examined to determine whether ontogenetic shifts in host diet or habitat could produce a nested subset pattern of infracommunity structure. The host by parasite matrix showed significant nesting. Host idiosyncratic temperatures, which are indicative of differing "biogeographic histories," were determined primarily by the presence of Ergasilus caeruleus in depauperate communities, or its absence in richer communities, and covaried positively with host age and the associated variables of host length, mass, and infracommunity richness. Idiosyncratic host temperatures did not differ significantly between male and female perch when the effect of age was controlled for by analysis of covariance. Although an ontogenetic diet shift can be ruled out as producing the observed nested pattern, it is possible that the observed nested subset pattern is the result of an ontogenetic habitat shift.

Age Factors↗
PubMed2004

Detection of perfluorooctane surfactants in Great Lakes water.

Widespread use of perfluorooctane surfactants has led to ubiquitous presence of these chemicals in biological tissues. While perfluorooctane surfactants have been measured in blood and liver tissue samples of fish, birds, and mammals in the Great Lakes region, data for the aqueous concentrations of these compounds in the Great Lakes or other ambient waters is lacking. Sixteen Great Lakes water samples were analyzed for eight perfluorooctane surfactants. The monitored perfluorooctane surfactants were quantitatively determined using single quadrupole HPLC/MS and qualitatively confirmed using ion trap MS/MS. Additionally, PFOS was quantitatively confirmed using triple quadrupole LC/MS/MS. Concentrations of PFOS and PFOA in the two lakes ranged from 21-70 and 27-50 ng/L, respectively. Analysis also showed the presence of PFOS precursors, N-EtFOSAA (range of 4.2-11 ng/L) and FOSA (range of 0.6-1.3 ng/L), in all samples above the LOQ. PFOSulfinate, another precursor, was identified at six of eight locations with a concentration range, when present, of <2.2-17 ng/L. Other PFOS precursors, N-EtFOSE, PFOSAA, and N-EtFOSA were not observed at any of the sampling locations. These are the first reported concentrations of perfluorooctane surfactants in Great Lakes water and the first report of PFOS precursors in any water body.

Alkanesulfonic Acids↗
PubMed1999

Geomicrobiology of subglacial ice above Lake Vostok, Antarctica.

Data from ice 3590 meters below Vostok Station indicate that the ice was accreted from liquid water associated with Lake Vostok. Microbes were observed at concentrations ranging from 2.8 x 10(3) to 3.6 x 10(4) cells per milliliter; no biological incorporation of selected organic substrates or bicarbonate was detected. Bacterial 16S ribosomal DNA genes revealed low diversity in the gene population. The phylotypes were closely related to extant members of the alpha- and beta-Proteobacteria and the Actinomycetes. Extrapolation of the data from accretion ice to Lake Vostok implies that Lake Vostok may support a microbial population, despite more than 10(6) years of isolation from the atmosphere.

Antarctic Regions↗
PubMed1992

Changes in ice cover thickness and lake level of Lake Hoare, Antarctica: implications for local climatic change.

We report results from 10 years of ice thickness measurements at perennially ice-covered Lake Hoare in southern Victoria Land, Antarctica. The ice cover of this lake had been thinning steadily at a rate exceeding 20 cm yr-1 during the last decade but seems to have recently stabilized at a thickness of 3.3 m. Data concerning lake level and degree-days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier-derived meltwater entering Lake Hoare each summer. From these latter data we infer that peak summer temperatures have been above 0 degrees C for a progressively longer period of time each year since 1972. We also consider possible explanations for the thinning of the lake ice. The thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer. We suggest that the term most likely responsible for the change in the ice cover thickness at Lake Hoare is the extent of summer melting, consistent with the rising lake levels.

Antarctic Regions↗
PubMed1999

Plasma steroid concentrations and male phallus size in juvenile alligators from seven Florida lakes.

Neonatal and juvenile alligators from contaminated Lake Apopka in central Florida exhibit abnormal plasma sex steroid concentrations as well as morphological abnormalities of the gonad and phallus. This study addresses whether similar abnormalities occur in juvenile alligators inhabiting six other lakes in Florida. For analysis, animals were partitioned into two subsets, animals 40-79 cm total length (1-3 years old) and juveniles 80-130 cm total length (3-7 years old). Plasma testosterone (T) concentrations were lower in small males from lakes Apopka, Griffin, and Jessup than from Lake Woodruff National Wildlife Refuge (NWR). Similar differences were observed in the larger juveniles, with males from lakes Jessup, Apopka, and Okeechobee having lower plasma T concentrations than Lake Woodruff males. Plasma estradiol-17beta (E(2)) concentrations were significantly elevated in larger juvenile males from Lake Apopka compared to Lake Woodruff NWR. When compared to small juvenile females from Lake Woodruff NWR, females from lakes Griffin, Apopka, Orange, and Okeechobee had elevated plasma E(2) concentrations. Phallus size was significantly smaller in males from lakes Griffin and Apopka when compared to males from Lake Woodruff NWR. An association existed between body size and phallus size on all lakes except Lake Apopka and between phallus size and plasma T concentration on all lakes except lakes Apopka and Orange. Multiple regression analysis, with body size and plasma T concentration as independent covariables, explained the majority of the variation in phallus size on all lakes. These data suggest that the differences in sex steroids and phallus size observed in alligators from Lake Apopka are not limited to that lake, nor to one with a history of a major pesticide spill. Further work examining the relationship of sex steroids and phallus size with specific biotic and abiotic factors, such as antiandrogenic or estrogenic contaminants, is needed.

Alligators and Crocodiles↗
PubMed2002

Application of an ecosystem model for aquatic ecological risk assessment of chemicals for a Japanese lake.

The Lake Suwa version of the comprehensive aquatic systems model (CASM-SUWA) was developed using field data from Lake Suwa and evaluated to examine the utility of CASM-SUWA for assessing the ecological risk of chemicals for aquatic ecosystems. The calibration of the parameters for the model provided that the established reference model simulation could reproduce complex seasonal biomass behavior of populations that were not significantly different from the general seasonal pattern for the Lake Suwa ecosystem. The sensitivity analyses revealed the potential importance of indirect effects and demonstrated that the parameter values of all the trophic levels were important in determining the biomass of each trophic level in the model. The risk estimation of linear alkylbenzene sulfonates (LAS) demonstrated that the model estimated the risks of direct toxic effects on each population and the indirect ecological effects that propagate through the food-web in the model ecosystem. The CASM-SUWA-derived benchmark levels were approximately one order of magnitude less than the field-derived NOECs in literature. The analyses of the comparison implied that the model could provide a good basis in determining an ecological protective level of a chemical of concern in aquatic ecosystem. This modeling study demonstrated that the model can be used to provide additional information for the decision-making process in the management of the aquatic ecological risk of chemicals.

Benchmarking↗