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At least 127 records · Page 7Linked to original sources
PubMed2001

A blind test of the MOIRA lake model for radiocesium for Lake Uruskul, Russia, contaminated by fallout from the Kyshtym accident in 1957.

This paper presents results of a model-test carried out within the framework of the COMETES project (EU). The tested model is a new lake model for radiocesium to be used within the MOIRA decision support system (DSS; MOIRA and COMETES are acronyms for EU-projects). This model has previously been validated against independent data from many lakes covering a wide domain of lake characteristics and been demonstrated to yield excellent predictive power (see Håkanson, Modelling Radiocesium in Lakes and Coastal Areas. Kluwer, Dordrecht, 2000, 215 pp). However, the model has not been tested before for cases other than those related to the Chernobyl fallout in 1986, nor for lakes from this part of the world (Southern Urals) and nor for situations with such heavy fallout as this. The aims of this work were: (1) to carry out a blind test of the model for the case of continental Lake Uruskul, heavily contaminated with 90Sr and 137Cs as a result of the Kyshtym radiation accident (29 September 1957) in the Southern Urals, Russia, and (2) if these tests gave satisfactory results to reconstruct the radiocesium dynamics for fish, water and sediments in the lake. Can the model provide meaningful predictions in a situation such as this? The answer is yes, although there are reservations due to the scarcity of reliable empirical data. From the modelling calculations, it may be noted that the maximum levels of 137Cs in fish (here 400 g ww goldfish), water and sediments were about 100,000 Bq/kg ww, 600 Bq/l and 30,000 Bq/kg dw, respectively. The values in fish are comparable to or higher than the levels in fish in the cooling pond of the Chernobyl NPP. The model also predicts an interesting seasonal pattern in 137Cs levels in sediments. There is also a characteristic "three phase" development for the 137Cs levels in fish: first an initial stage when the 137Cs concentrations in fish approach a maximum value, then a phase with relatively short ecological half-lives followed by a final phase with long ecological half-lives more or less corresponding to the physical decay of radiocesium.

Animals↗
PubMed1988

Climatological observations and predicted sublimation rates at Lake Hoare, Antarctica.

In December 1985, an automated meteorological station was established at Lake Hoare in the dry valley region of Antarctica. Here, we report on the first year-round observations available for any site in Taylor Valley. This dataset augments the year-round data obtained at Lake Vanda (Wright Valley) by winter-over crews during the late 1960s and early 1970s. The mean annual solar flux at Lake Hoare was 92 W m-2 during 1986, the mean air temperature -17.3 degrees C, and the mean 3-m wind speed 3.3 m s-1. The local climate is controlled by the wind regime during the 4-month sunless winter and by seasonal and diurnal variations in the incident solar flux during the remainder of the year. Temperature increases of 20 degrees-30 degrees C are frequently observed during the winter due to strong föhn winds descending from the Polar Plateau. A model incorporating nonsteady molecular diffusion into Kolmogorov-scale eddies in the interfacial layer and similarity-theory flux-profiles in the surface sublayer, is used to determine the rate of ice sublimation from the acquired meteorological data. Despite the frequent occurrence of strong winter föhns, the bulk of the annual ablation occurs during the summer due to elevated temperatures and persistent moderate winds. The annual ablation from Lake Hoare is estimated to have been 35.0 +/- 6.3 cm for 1986.

Antarctic Regions↗
PubMed2003

Dynamic modelling of recovery from acidification of lakes in Killarney Park, Ontario, Canada.

During much of the 1900s, the lakes in Killarney Provincial Park have been exposed to high levels of acid deposition due to sulfur emissions from the nearby metal smelters in Sudbury. The sulfur emissions from this large point source have decreased to about 10% of what they were in the 1960s. Lake water quality in Killarney Park has greatly changed in response to reduced emissions, with noticeable declines in sulfate, aluminum and calcium concentrations. Here we apply the dynamic acidification model MAGIC to 3 lakes in Killarney Park. The lakes, which have different buffering capacities and response times, were selected to represent fast, intermediate and slow recovery from acidification. The model was calibrated to match observed data for the lakes and 4 different forecast scenarios for future sulfur deposition reductions were applied. The results indicate that there is still a large potential for improvement in the water quality in Killarney. The recovery time for the different lakes varies greatly. For the lake having the slowest response time several decades are needed for the chemistry to stabilize after implementation of deposition reductions.

Acid Rain↗
PubMedDate not supplied

Toxaphene in the Great Lakes.

This paper presents the most current data for toxaphene in the water, sediments, and biota of the Laurentian Great Lakes of North America. Concentrations in water range from 1.1 ng/L in Lake Superior to 0.17 ng/L in Lake Ontario. Lake Superior has the highest water concentration, which is contrary to the pattern seen for other pollutants. The observed log particle-water partition coefficient was 4.5. Recent sediments had similar concentrations among the lakes (approx. 15 ng/g dry weight), but different homolog compositions. The log bioaccumulation factors (BAFs) normalized to lipid or organic carbon were 5.8, 6.5, 6.3, 6.7, 6.7, and 7.0 for phytoplankton, net zooplankton, Mysis, Bythotrephes, sculpin, and lake trout. These data clearly show that toxaphene biomagnifies in the foodweb.

Animals↗
PubMed1993

A predictive model for the behavior of radionuclides in lake systems.

This paper describes a predictive model for the behavior of 137Cs in lacustrine systems. The model was tested by comparing its predictions to contamination data collected in various lakes in Europe and North America. The migration of 137Cs from catchment basin and from bottom sediments to lake water was discussed in detail; these two factors influence the time behavior of contamination in lake water. The contributions to the levels of radionuclide concentrations in water, due to the above factors, generally increase in the long run. The uncertainty of the model, used as a generic tool for prediction of the levels of contamination in lake water, was evaluated. Data sets of water contamination analyzed in the present work suggest that the model uncertainty, at a 68% confidence level, is a factor 1.9.

Cesium Radioisotopes↗
PubMed2006

Agricultural lakes in Finland: current water quality and trends.

Agriculture is the largest source of nutrients into surface waters in Finland, and yet relatively little is known about the actual impact of the agricultural load on the state of lakes. We analysed the water quality data of 20 Finnish agricultural lakes and found that they had higher levels of nutrients, chlorophyll a and turbidity than did the other types of lakes (e.g. those receiving point-source load) in the national monitoring network (the Finnish Eurowaternet). Currently, six of the agricultural lakes can be classified as eutrophic and 14 as hypertrophic. Trend analysis (based on Kendall's tau-b) indicated that during 1976-2002 the water quality of the lakes either remained constant or showed signs of increasing eutrophication and elevated turbidity. Decreasing nutrient concentrations were found only in one intensively restored lake. In none of the lakes had the chlorophyll a concentration decreased. The results of the trend analysis are compatible with the recent finding that, despite vigorous efforts, the nutrient load from agriculture has not declined in Finland. Recovery of the most eutrophied agricultural lakes would call for a drastic reduction in the external nutrient load, possibly supplemented with in-lake restoration.

Agriculture↗
PubMed2004

Rural-urban differences in cancer care: results from the Lake Superior Rural Cancer Care Project.

Past studies have shown significant differences between rural and urban cancer patients in many measures of cancer care. There is little recent information about this disparity, which generally has shown disadvantages in rural populations. This study reports the rural and urban differences in cancer care using data from the Lake Superior Rural Cancer Care Project. The study used a prospective, population-based design that included all incident cases of breast, colorectal, lung, and prostate cancers diagnosed in northeastern Minnesota, northwestern Wisconsin, and the western portion of Michigan's Upper Peninsula from 1992 to 1997. The outcome measures were 9 endpoints that represented state-of-the-art cancer care during the study. Rural cancer patients as compared with their urban counterparts were disadvantaged in proportion staged, stage at diagnosis, initial management procedures, post-treatment surveillance testing, and participation in cancer clinical trials. These findings are similar to previously published studies. Further research is needed to determine more clearly the barriers in rural cancer care and to find more effective strategies.

Adult↗
PubMed1998

Development of fish mercury concentrations in Finnish reservoirs from 1979 to 1994.

Mercury (Hg) concentrations in burbot (Lota lota), perch (Perca fluviatilis), northern pike (Esox lucius), roach (Rutilus rutilus), whitefish (Coregonus lavaretus) and peled (C. peled) were monitored in 18 reservoirs situated in western and northern Finland over a period of 16 years (1979-1994). The reservoirs were impounded from 1964 to 1980. The surface areas ranged between 1 and 417 km2. Data from downstream sites and reference lakes were compared to reservoir mercury data. Generally, fish Hg concentrations in reservoirs exceeded those in natural lakes. Shortly after inundation, fish mercury concentrations clearly increased and remain 15-25 years above background concentrations. The mean Hg concentrations in standardized 1 kg pike from 1989 to 1993 was 0.45 mg/kg in natural lakes and 0.58 mg/kg in reservoirs. The 1 mg/kg fish Hg level recommended by health authorities as the upper limit for human consumption was still exceeded in two reservoirs 20 years old or more. The two largest reservoirs (24 and 27 years old in 1994) with significant commercial fishing had Hg levels below 0.5 mg/kg in all fish species studied. Statistical models for predicting the Hg concentrations in the weight standardized pike were verified with the observed data. For most of the reservoirs, predictions from models based on pH, organic matter (COD) in water, the extent of water level regulation and reservoir age agreed well with observed data. In the most southern, new (under 20 years old) and heavily regulated reservoirs, pike Hg concentration followed a logarithmic function of reservoir age. Model predictions of mercury in pike in the planned Vuotos reservoir (in northern Finland) predicted that Hg would exceed 1 mg/kg Hg for the first 12 years after the flooding.

Animals↗
PubMedDate not supplied

Comparisons of likelihood and machine learning methods of individual classification.

Classification methods used in machine learning (e.g., artificial neural networks, decision trees, and k-nearest neighbor clustering) are rarely used with population genetic data. We compare different nonparametric machine learning techniques with parametric likelihood estimations commonly employed in population genetics for purposes of assigning individuals to their population of origin ("assignment tests"). Classifier accuracy was compared across simulated data sets representing different levels of population differentiation (low and high F(ST)), number of loci surveyed (5 and 10), and allelic diversity (average of three or eight alleles per locus). Empirical data for the lake trout (Salvelinus namaycush) exhibiting levels of population differentiation comparable to those used in simulations were examined to further evaluate and compare classification methods. Classification error rates associated with artificial neural networks and likelihood estimators were lower for simulated data sets compared to k-nearest neighbor and decision tree classifiers over the entire range of parameters considered. Artificial neural networks only marginally outperformed the likelihood method for simulated data (0-2.8% lower error rates). The relative performance of each machine learning classifier improved relative likelihood estimators for empirical data sets, suggesting an ability to "learn" and utilize properties of empirical genotypic arrays intrinsic to each population. Likelihood-based estimation methods provide a more accessible option for reliable assignment of individuals to the population of origin due to the intricacies in development and evaluation of artificial neural networks.

Animals↗
PubMed2002

Lake Baikal: a unique place to study evolution of sponges and their stress response in an environment nearly unimpaired by anthropogenic perturbation.

Lake Baikal is considered as a unique place to study evolution. In this review, we report on recent data on the evolution of endemic freshwater sponges of this ancient lake. Nucleotide sequence data support the idea that these sponges are of monophyletic origin and evolved from Spongillidae. Baikalian sponges form the dominating biomass in the benthos of the lake. Data on the expression of the biomarker heat shock protein 70, revealed that the endemic sponge species of Lake Baikal are useful as bioindicators to assess the anthropogenic impact on the lake.

Animals↗
PubMed2000

Bacterioplankton Community Composition in Five Lakes Differing in Trophic Status and Humic Content.

To investigate the relation between lake type and bacterioplankton community composition, five Swedish lakes, which differed from each other in nutrient content and water color, were studied. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA was used to examine community composition. The DGGE-patterns of the different samples were analyzed in relation to physical, chemical, and biological data from the lakes by canonical correspondence analysis (CCA). The three variables found to most strongly correlate with the DGGE patterns were biomasses of microzooplankton, cryptophytes, and chrysophytes, suggesting that these biota had an impact on bacterioplankton community structure. Two of the three factors were, in turn, significantly correlated to parameters associated with the trophic status of the lakes, indicating that the nutrient content of the lakes, at least indirectly, influenced the structure of the bacterioplankton community. The relation to water color was less pronounced.

Journal Article↗
PubMed2003

Distribution and fluxes of total and methylmercury in Lake Superior.

Despite the importance and size of Lake Superior, little is known regarding the biogeochemical cycling or distribution of mercury within its waters. We present the results from two research cruises on total Hg (HgT) and methylmercury (MeHg) distributions in aqueous and particulate phases, and in offshore sediments. Open waters of Lake Superior are similar in HgT content to Lakes Michigan and Ontario (sub-ng L(-1)), whereas MeHg was only 1% of HgT. Seasonality in aqueous HgT distribution was observed, most likely from tributary inputs during Spring snowmelt. Suspended particles were enriched in MeHg relative to water and surficial sediments, suggesting enhanced particle partitioning followed by demethylation in the water column and in surface sediments. Distribution coefficients for mercury in surficial sediments were lower than those in suspended material, likely due to remineralization. Preliminary estimates of mass balance indicate that air-water exchange processes such as evasion and wet deposition dominate the HgT budget, due to the basin's relatively small watershed area relative to lake area. In contrast, methylmercury cycling within Lake Superior is influenced more strongly by watershed sources, as well as by sedimentary sources and photodemethylation. The Hg cycle in Lake Superior is unique in that it is more similar in many aspects to that in marine systems than in small lakes, where management data for freshwaters typically originates.

Environmental Monitoring↗
PubMed2006

Forecasting the spread of invasive rainbow smelt in the Laurentian Great Lakes region of North America.

Rainbow smelt (Osmerus mordax) have invaded many North American lakes, often resulting in the extirpation of native fish populations. Yet, their invasion is incipient and provides the rationale for identifying ecosystems likely to be invaded and where management and prevention efforts should be focused. To predict smelt presence and absence, we constructed a classification-tree model based on habitat data from 354 lakes in the native range for smelt in southern Maine. Maximum lake depth, lake area, and Secchi depth (surrogate measure of lake productivity) were the most important predictors. We then used our model to identify lakes vulnerable to invasion in three regions outside the smelt's native range: northern Maine (52 of 244 lakes in the non-native range), Ontario (4447 of 8110), and Wisconsin (553 of 5164). We further identified a subset of lakes with a strong potential for impact (potential-impact lakes) based on the presence of fish species that are affected by rainbow smelt. Ninety-four percent of vulnerable lakes in the non-native range in Maine are also potential-impact lakes, as are 94% and 58% of Ontario and Wisconsin's vulnerable lakes, respectively. Our modeling approach can be applied to other invaders and regions to identify invasion-prone ecosystems, thus aiding in the management of invasive species and the efficient allocation of invasive species mitigation and prevention resources.

Animals↗
PubMed2005

Chemolithotrophic haloalkaliphiles from soda lakes.

This paper summarizes recent data on the occurrence and properties of lithotrophic prokaryotes found in extremely alkaline, saline (soda) lakes. Among the chemolithotrophs found in these lakes the obligately autotrophic sulfur-oxidizing bacteria were the dominant, most diverse group, best adapted to haloalkaline conditions. The culturable forms are represented by three new genera, Thioalkalimicrobium, Thioalkalivibrio and Thioalkalispira in the Gammaproteobacteria. Among them, the genus Thioalkalivibrio was most metabolically diverse, including denitrifying, thiocyanate-oxidizing and facultatively alkaliphilic species. Culturable methane-oxidizing populations in the soda lakes belong to the type I methanotroph group in the Gammaproteobacteria, mostly in the genus Methylomicrobium. The nitrifying bacteria in hyposaline soda lakes were represented by a new species Nitrobacter alkalicus (Alphaproteobacteria), and by an alkaliphilic subspecies of Nitrosomonas halophila (Betaproteobacteria). Both belonged to the low salt-tolerant alkaliphiles. The facultatively autotrophic haloalkaliphilic isolates able to grow with hydrogen as electron donor were identified as representatives of the alpha-3 subclass of the Proteobacteria (aerobic) and of the Natronolimnicola - Alkalispirillum group in the gammaproteobacteria (nitrate-reducing). While all chemolithotrophic isolates from soda lakes belong to the alkaliphiles with a pH optimum for growth around 10, only the sulfur-oxidizing group included species able to grow under hypersaline conditions. This indicates that carbon and nitrogen cycles in the hypersaline alkaline lakes might not be closed.

Fresh Water↗
PubMed1999

Microorganisms in the accreted ice of Lake Vostok, Antarctica.

Analysis of a portion of Vostok ice core number 5G, which is thought to contain frozen water derived from Lake Vostok, Antarctica (a body of liquid water located beneath about 4 kilometers of glacial ice), revealed between 2 x 10(2) and 3 x 10(2) bacterial cells per milliliter and low concentrations of potential growth nutrients. Lipopolysaccharide (a Gram-negative bacterial cell biomarker) was also detected at concentrations consistent with the cell enumeration data, which suggests a predominance of Gram-negative bacteria. At least a portion of the microbial assemblage was viable, as determined by the respiration of carbon-14-labeled acetate and glucose substrates during incubations at 3 degrees C and 1 atmosphere. These accreted ice data suggest that Lake Vostok may contain viable microorganisms.

Acetates↗
PubMed2005

Genetic variability and phylogeography of the invasive zebra mussel, Dreissena polymorpha (Pallas).

The zebra mussel, Dreissena polymorpha (Pallas), a bivalve species originally native to the Black and Caspian seas, has invaded Ireland in the last decade. Five microsatellite loci were used to investigate genetic diversity and population structure in 10 populations across Europe (Ireland, UK, the Netherlands and Romania) and the Great Lakes (Lake Ontario and Lake St Clair). Levels of allelic diversity and mean expected heterozygosity were high for all populations (mean number of alleles/locus and H(E) were 10-15.2 and 0.79-0.89, respectively). High levels of polymorphism observed in Irish populations suggest that the Irish founder population(s) were large and/or several introductions took place after foundation. Significant deficits of heterozygotes were recorded for all populations, and null alleles were the most probable factor contributing to these deficits. Pairwise comparisons using Fisher exact tests and F(ST) values revealed little genetic differentiation between Irish populations. The UK sample was not significantly differentiated from the Irish samples, most probably reflecting an English origin for Irish zebra mussels. No significant differentiation was detected between the two Great Lakes populations. Our data support a northwest rather than a central or east European source for North American zebra mussels.

Animals↗
PubMedDate not supplied

Characterizing land surface erosion from cesium-137 profiles in lake and reservoir sediments.

Recognition of the threat to the sustainable use of the earth's resources posed by soil erosion and associated off-site sedimentation has generated an increasing need for reliable information on global rates of soil loss. Existing methods of assessing rates of soil loss across large areas possess many limitations and there is a need to explore alternative approaches to characterizing land surface erosion at the regional and global scale. The downcore profiles of 137Cs activity available for numerous lakes and reservoirs located in different areas of the world can be used to provide information on land surface erosion within the upstream catchments. The rate of decline of 137Cs activity toward the surface of the sediment deposited in a lake or reservoir can be used to estimate the rate of surface lowering associated with eroding areas within the upstream catchment, and the concentration of 137Cs in recently deposited sediment provides a basis for estimating the relative importance of surface and channel, gully, and/or subsurface erosion as a source of the deposited sediment. The approach has been tested using 137Cs data from several lakes and reservoirs in southern England and China, spanning a wide range of specific suspended sediment yield. The results obtained are consistent with other independent evidence of erosion rates and sediment sources within the lake and reservoir catchments and confirm the validity of the overall approach. The approach appears to offer valuable potential for characterizing land surface erosion, particularly in terms of its ability to provide information on the rate of surface lowering associated with the eroding areas, rather than an average rate of lowering for the entire catchment surface.

Cesium Radioisotopes↗
PubMed1988

Schistosomiasis in Kano State, Nigeria. II. Field studies on aestivation in Bulinus rohlfsi (Clessin) and B. globosus (Morelet) and their susceptibility to local strains of Schistosoma haematobium (Bilharz).

Aestivation patterns in Bulinus rohlfsi and B. globosus were studied by digging transects across the floor of their dried habitats and by monitoring changes in snail population structure during the period when the habitats were flooded. Bulinus rohlfsi, which inhabited a small man-made lake, was found to aestivate towards the bottom of its habitat, aestivation occurring during the last six weeks before the lake dried. The data on B. globosus from a temporary pool are less complete, but they show that this species also aestivates at the bottom of its habitat and can be found buried at depths up to 3 cm. A wide size range of both species of snail were found to aestivate, but there was differential mortality of young B. rohlfsi soon after the lake re-filled, and the optimally surviving size group of B. globosus was 9 mm. The beginning of aestivation in B. rohlfsi did not correlate with any of the physical parameters measured, but it coincided with the dying off of a bloom of unicellular algae. The importance of stimuli other than desiccation in the aestivation process of bulinids is stressed. Laboratory infections with isolates of Schistosoma haematobium showed that both Bulinus species were capable of transmitting local strains of the parasite and indicated the presence of snail host-specific strains.

Adaptation, Physiological↗