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At least 343 records · Page 19Linked to original sources
PubMed2002

Phototransfomation of ticlosan in surface waters: a relevant elimination process for this widely used biocide--laboratory studies, field measurements, and modeling.

The phototransformation of the widely used biocide triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) was quantified for surface waters using artificial UV light and sunlight irradiation. The pH of surface waters, commonly ranging from 7 to 9, determines the speciation of triclosan (pKa = 8.1) and therefore its absorption of sunlight. Direct phototransformation of the anionic form with a quantum yield of 0.31 (laboratory conditions at 313 nm) was identified as the dominant photochemical degradation pathway of triclosan. Combining the photochemical parameters with actual meteorological data and field measurements allowed us to validate a model describing the behavior of triclosan in the water column of a Swiss lake (Lake Greifensee). From August to October 1999, direct phototransformation accounted for 80% of the observed total elimination of triclosan from the lake. The remaining major sink for triclosan was the loss in the outflow. Thus, during the summer season, direct phototransformation appears to be a major elimination pathway of triclosan in this lake. Based on absorption spectra and quantum yield data, the phototransformation half-lives of triclosan were calculated under various environmental conditions typical for surface waters. Daily averaged half-lives were found to vary from about 2 to 2000 days, depending on latitude and time of year.

Anti-Infective Agents, Local↗
PubMed2026

Nitrogen sources and concentrations shape algal odor compounds: Key drivers of β-cyclocitral and β-ionone in water bodies of the lower Yangtze River.

Taste and odor (T&O) compounds derived from cyanobacterial blooms pose escalating threats to freshwater security worldwide, yet the drivers of specific T&O metabolites remain poorly constrained. Here, we investigated the dual effects of nitrogen (N) sources and concentrations on the production of β-cyclocitral and β-ionone, two algal-derived T&O compounds, through integrated field surveys (54 sites across lakes and rivers) in the eutrophic lower Yangtze River, China, and laboratory cultivation of typical cyanobacteria (Microcystis aeruginosa and Pseudanabaena cinerea). Our field data revealed that the concentrations of β-cyclocitral and β-ionone in lakes and rivers were not significantly different, but increased with the trophic level index. Redundancy analysis and Mantel analysis showed that Microcystis and Pseudanabaena were potentially dominant contributors to β-cyclocitral and β-ionone in the water column. Structural equation modeling and variation partitioning analysis showed that enhanced nitrate (NO3--N) significantly promoted the production of these compounds. Laboratory experiments demonstrated that inorganic N (NaNO₃) maximized total T&O yields by promoting algal biomass, whereas organic N (urea and glutamic acid) elevated the T&O production per unit biomass by 1.5- to 9.5-fold. Notably, Pseudanabaena exhibited a 2.3-fold higher β-ionone yield than Microcystis, with greater sensitivity to N concentrations. Our study highlights the critical role of nitrogen pollution, both source and concentration, in the production of T&O compounds by phytoplankton and provides reference data for managing T&O issues in rivers and shallow lakes.

Norisoprenoids↗
PubMed1998

Viruses in Antarctic lakes.

Water samples collected from four perennially ice-covered Antarctic lakes during the austral summer of 1996-1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double-stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice-covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacteria] secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.

Antarctic Regions↗
PubMedDate not supplied

Evaluation of the phosphorus index in watersheds at the regional scale.

Agricultural losses of phosphorus (P) in runoff are a primary cause of eutrophication in many freshwater systems. A modified version of the P Index originally developed jointly by the USDA (Agricultural Research Service [ARS], Cooperative State Research, Education, and Extension Service [CSREES], and Natural Resources Conservation Service [NRCS]) was used to prioritize P loss vulnerability at the regional scale from 60 watersheds located within Minnesota using readily available data related to the transport and sources of P. This modified version of the P Index was created for a regionally based analysis of the index. Validation of the P Index rating was conducted using long-term water quality monitoring data consisting of total P concentrations collected from watersheds and lakes. The modified version of the P Index produced a strong correlation between P Index rating and total P stream monitoring data in watersheds (r2 = 0.70) excluding the Red River Basin. An equally strong relationship was observed between P Index rating and lake water quality (r2 = 0.68) using the modified P Index. The P Index ratings for the Red River Basin showed good correlation with observed total P stream monitoring data (r2 = 0.51); however, the P Index ratings were smaller than in other basins. The results of this study suggest that, with certain limitations, the P Index can be used at the regional scale to prioritize P loss vulnerability using state and national databases. Regional P Index ratings represent the average risk for agricultural land within the entire watershed.

Agriculture↗
PubMed2005

[Research advance on lake ecosystem dynamic models].

Starting with the role of system analysis in lake ecosystem research, this paper summarized the tentative procedures and softwares for studying the dynamics of lake ecosystem. There are several main stages in modeling the dynamics of lake ecosystem, namely, problems identification, mathematical formulation, computation, validation, sensitive analysis, calibration, and verification. In the modeling, selecting temporal and spatial scales is essential but complex. Since 1960s, a rapid progress has been made in modeling the dynamics of lake ecosystem, being developed from simple zero-dimension models to complex ecological-aquatic-hydrodynamic ones, among which, exergy was applied popularly as an objective function in modeling. In this paper, LakeWeb and LEEDS (Lake Eutrophication, Effect, Dose, and Sensitivity model) were analyzed as examples. In China, the development of lake ecosystem dynamic models could be traced back to 1980s, and most of them were focused on Lake Dianch, Lake Taihu, Lake Chaohu and Lake Donghu. Some softwares such as CE-QUAL-ICM, WASP, AQUATOX, PAMOLARE and CAEDYM were developed to simulate lake ecosystem dynamics, among which, CE-QUAL-ICM is more suitable for long and narrow water bodies. WASP consists of three parts, i. e., DYNHYD, EUTRO, and TOXI. AQUATOX is an ecological risk model, and the parameters are mainly calibrated in U. S. A, which has limited its further application in China. The software ECOPATH for simulating the energy flows in lakes was also described in this paper. There are still many shortages in the lake ecosystem dynamic models, e. g., the lack of sufficient monitoring data for validation, insufficient consideration of uncertainties and the role of bacteria, and inconsistent relationship with watershed changes. The uncertainties are mainly from the intrinsic uncertainties in aquatic ecosystem, in modeling, in parameters selection, and also in forecast and application. Setting up long-term monitoring and data sharing mechanism, using interpolation to make data more densely, introducing objective functions, dealing with uncertainties, and constructing watershed-lake ecosystem dynamic model could be the available ways for overcoming the shortages.

China↗
PubMed2005

Limnothrix redekei (Van Goor) Meffert (Cyanobacteria) strains from Lake Kastoria, Greece form a separate phylogenetic group.

Three strains of Limnothrix (Cyanobacteria) isolated from Lake Kastoria, Greece, were characterized based on their morphological features and 16S rRNA gene sequences. The Limnothrix isolates 007a, 165a, and 165c can morphologically be assigned to Limnothrix redekei (Van Goor) Meffert. The 16S rRNA gene of the Limnothrix strains showed a 99% similarity to the 16S rRNA gene of Planktothrix sp. FP1. Limnothrix redekei strains 165a, 165c, 007a and Planktothrix sp. FP1 formed a separate cluster in the cyanobacterial 16S rRNA gene tree. It was distinct from the Pseudanabaena cluster, which included the other Limnothrix strains isolated from northern temperate lakes. This is the first report on the phylogeny of L. redekei strains originating from a Mediterranean lake (southern Europe) and provides new data about the genus Limnothrix.

Analysis of Variance↗
PubMed1992

A classification of acidified catchments in Britain.

To compare catchments of possible acidified waters in Britain an extensive database was compiled for nearly 600 catchments of lakes and streams for which chemical data were available. Information on the database included map-derived data, pollutant deposition estimates and hydrological characteristics. To stratify the catchment database a randomly selected subset of 328 catchments was used to derive eight classes of catchments using the classification program TWINSPAN. Several classifications were generated by this method using an increasing number of catchment parameters. TWINSPAN classes were defined on the basis of some catchment parameters (indicators) but were shown to be associated with other variables. A general linear model (GLM) analysis of the available chemical data was used to test the different classifications. A TWINSPAN classification which excluded soil and geology characteristics gave the best GLM model because soil and geology types were poorly correlated with other catchment parameters. However, because of the recognized importance of soils and geology in acidification processes, these parameters were introduced into the GLM model as separate GLM classes. The resulting three-class model (TWINSPAN class, soil type, geology type) proved superior to both the one-class model and to two-class models which included either soil or geology. It was demonstrated that the TWINSPAN classes were associated with particular geographical areas and particular monitoring programmes. The TWINSPAN classification was used to evaluate a set of catchments selected as long-term monitoring sites for Britain. In general, the set covered a wide range of catchment types as defined by the classification. It was possible to identify minor shortfalls in classes of catchment selected and suggest possible additions to the sampling programme. Whilst the classification procedure has been applied to possible acidified waters, the method is of general relevance to all catchments and waters of more diverse nature.

Journal Article↗
PubMed1991

The activity of glutathione S-transferase in hepatopancreas of Procambarus clarkii: seasonal variations and the influence of environmental pollutants.

1. The glutathione S-transferase activity in hepatopancreas of the American red crayfish Procambarus clarkii after 15 days' acclimatization in tap water aquaria was measured in specimens collected monthly for a whole year, and shows seasonal variation. 2. Previous data on the environmental pollution of Lake Albufera suggest a possible correlation with the activity tested in the different seasons of the year considering the results of non-acclimatized animals.

Animals↗
PubMed2005

Nitrate leaching as a confounding factor in chemical recovery from acidification in UK upland waters.

Over the period 1988-2002, data from 18 of the 22 lakes and streams in the UK Acid Waters Monitoring Network (AWMN) show clear trends of declining excess sulphate concentrations in response to reductions in sulphur deposition, but fewer trends in increasing pH or alkalinity. There has been no significant decline in the deposition of total nitrogen over the same period, and no sites show a trend in nitrate concentration. Peak nitrate concentrations have already surpassed excess sulphate on occasion in half of the AWMN sites. Furthermore, current understanding of terrestrial N saturation processes suggests that nitrate leaching from soils may increase, even under a constant N deposition load. Best-case projections indicate that nitrate will overtake sulphate as the major excess acid anion in many sites within 10 years, while worst-case predictions with steady-state models suggest that in the longer-term, nitrate could become the dominant excess acid anion in most of the UK.

Acid Rain↗
PubMed2001

Development of the phytoplankton community in a pit-lake in relation to water quality changes.

An open pit-lake was formed at a Northern Saskatchewan mine site after flooding with lake water in early 1992. Since then, water and phytoplankton samples have been collected regularly from the artificial lake over seven years. The resulting data set provides a unique opportunity to examine the physical and chemical changes in water quality and phytoplankton community over time. Seventeen major variables were examined in a principal component analysis. Axes 1, 2 and 4 are significantly correlated to other three variables, the number of days (since the first sampling after flooding of the pit), water temperature and depth, respectively. Total suspended solid (TSS), dissolved oxygen, total phosphorus (Total-P), arsenic, and iron decreased over time while Mg, Ca, K, Na, total organic carbon and HCO3 increased. Canonical correspondence analysis was used to infer the relationship between water quality variables and phytoplankton community structure, which changed substantially over the survey period. TSS, Total-P and arsenic were considered to be the key factors driving the change in phytoplankton community composition.

Canada↗
PubMed2005

A predictive approach to nutrient criteria.

Violation of a water quality standard triggers the need for a total maximum daily load (TMDL); this should result in actions that improve water quality, but sometimes at significant cost. If the standard is well-conceived, a designated-use statement characterizes societal values, and a criterion provides a measurable surrogate for designated use. This latter provision means that scientists measure the criterion and view violations of the criterion as equivalent to noncompliance with the designated use. However, if a criterion is not a good indicator of designated use, it is apt to result in misallocation of the limited resources for water quality improvement through the TMDL process. This concern provides the basis for our assessment of the national nutrient criteria strategy recently proposed by the U.S. EPA. We acquired data sets for four case studies (Lake Washington, Neuse River Estuary, San Francisco Bay, and Lake Mendota) and then used expert elicitation to quantify designated-use attainment for each case. Applying structural equation modeling, we identified good water quality criteria as the best predictors of the designated use elicited response variable. Further, we used the model to relate the level (concentration) of each criterion to the probability of compliance with the designated use; this provides decision-makers with an estimate of risk associated with the criterion level, facilitating the selection of appropriate water quality criteria.

Forecasting↗
PubMed2004

Effects of historical lake level and land use on sediment and phosphorus accumulation rates in Lake Kinneret.

Current paradigms of reservoir ontogeny suggest that water-level fluctuations may increase sedimentary nutrient release, causing long-term eutrophication of water bodies formed by dryland flooding. Less is known of the changes in nutrient status following conversion of natural lakes into reservoirs. Here, we use historical hydrological and limnological data and paleolimnological records of sedimentary P accumulation to evaluate changes in nutrient storage in Lake Kinneret, Israel since approximately 1860. Impoundment in 1932 increased water level fluctuations and altered seasonal hydrologic patterns in the lake. Geochemical analysis of sediment deposits indicated that bulk sediment and P accumulation rates in the central lake increased >600% following dam installation (1930s), draining of Lake Hula wetlands (1951-1957), and diversion of surface water outflow (1964 to present). Further, comparison of sedimentary P stratigraphies with long-term chemical records showed that the period of maximum P deposition corresponds to observed increases in whole-lake and in hypolimnetic P content, as well as epilimnetic biological changes indicative of ongoing eutrophication. Together, these patterns suggest that hydrologic management of natural lakes can increase sedimentary nutrient flux under circumstances where lake volume and water levels become more variable.

Agriculture↗
PubMed2006

Estimation of the uptake rate constants for polycyclic aromatic hydrocarbons accumulated by semipermeable membrane devices and triolein-embedded cellulose acetate membranes.

In this paper we report an extension of our previous work on the triolein-embedded cellulose acetate membrane (TECAM) as a passive sampling device (PSD) and describe the results from simultaneous exposure of TECAMs and triolein-containing semipermeable membrane devices (SPMDs) to PAHs in lake water for 16 days. The data obtained provided a comparison of the uptake rates of specific PAHs by the two PSDs. Using 16-day accumulation tests, similar PAH distribution patterns in TECAMs and in SPMDs (R2 = 0.89, p < 0.0001) were observed. However, it was noted that TECAMs could take up greater amounts of PAHs than SPMDs (735 ng/g of TECAM vs 630 ng/g of SPMD). Uptake rate constants of TECAMs and SPMDs for 16 priority pollutant (PP) PAHs, corrected for dissolved organic carbon, ranged from 0.28 to 2.94 L d(-1) and from 0.16 to 0.91 L d(-1), respectively. The elimination rate constants of TECAMs were 1.4-6.7 times greater than those observed for SPMDs, thereby indicating that PAHs required shorter times to achieve equilibrium in TECAMs than in SPMDs. Thus, the results of the present study suggest that TECAMs have significant potential as a good monitor to assess the pollution of hydrophobic pollutants in aquatic environments.

Cellulose↗
PubMed2007

Phylogenetic measures of biodiversity.

We developed a theoretical framework based on phylogenetic comparative methods to integrate phylogeny into three measures of biodiversity: species variability, richness, and evenness. These metrics can be used in conjunction with permutation procedures to test for phylogenetic community structure. As an illustration, we analyzed data on the composition of 58 lake fish communities in Wisconsin. The fish communities showed phylogenetic underdispersion, with communities more likely to contain closely related species. Using information about differences in environmental characteristics among lakes, we demonstrated that phylogenetic underdispersion in fish communities was associated with environmental factors. For example, lakes with low pH were more likely to contain species in the same clade of acid-tolerant species. Our metrics differ from existing metrics used to calculate phylogenetic community structure, such as net relatedness index and Faith's phylogenetic diversity. Our metrics have the advantage of providing an integrated and easy-to-understand package of phylogenetic measures of species variability, richness, and evenness with well-defined statistical properties. Furthermore, they allow the easy evaluation of contributions of individual species to different aspects of the phylogenetic organization of communities. Therefore, these metrics should aid with the incorporation of phylogenetic information into strategies for understanding biodiversity and its conservation.

Animals↗
PubMed2004

Reconciling geography and genealogy: phylogeography of giant freshwater prawns from the Lake Carpentaria region.

There is convincing geological evidence for the historical existence of an ancient lake on the Australian-New Guinea continental shelf during the late Pleistocene. Lake Carpentaria was a vast fresh- to brackishwater lake that would presumably have provided habitat for, and facilitated gene flow among, aquatic taxa that tolerate low to moderate salinities in this region. Moreover, it has been argued that the outflow of Papua New Guinea's Fly River was diverted westward into Lake Carpentaria during this period, although this hypothesis is controversial. We predicted that these events, if a true history, would have promoted gene flow and population growth via range-expansion events in the giant freshwater prawn (Macrobrachium rosenbergii) and restricted gene flow subsequently by way of a vicariant event as sea levels rose during the late Pleistocene, and a marine environment replaced Lake Carpentaria. We tested these hypotheses using phylogeographical and phylogenetic analyses of mitochondrial DNA variation in M. rosenbergii populations sampled from the Lake Carpentaria region. Our results support the hypothesis that Lake Carpentaria facilitated gene flow among populations of M. rosenbergii that are today isolated, but contest claims of a westward diversion of the Fly River. We inferred the timing of initial expansion in the 'Lake Carpentaria lineage' and found the timing of this event to be broadly concordant with geological dating of the formation of Lake Carpentaria. Reconciling geological and molecular data, as presented here, provides a powerful framework for investigating the influence of historical earth history events on the distribution of biological (i.e. molecular) diversity.

Animals↗
PubMed2002

[Hand injuries in workers on the eastern shore of Marcaibo Lake in the state of Zulia, Venezuela, 1986-1993].

In order to analyze the frequency, injury rate and cause of on site accidents to the hands of workers on the east coast of lake of Maracaibo in Zulia State, data was obtained from the accident reports registered with the Venezuelan Institute of Social Security. An occupational hand injury was defined as a traumatic injury to the hands, fingers or wrists that occurred while the employee was at work; that resulted from a single exposure to a hazardous agent. The following variables were analyzed: age, severity, economic activity, material agent, mechanic cause, type of injury, type of accident and unsafe action. The frequency rate was used to analyze the annual accident rate. During the period under study 2.456 injuries to the hand were registered, representing 36% of the total injuries reported; 95% were light injuries, 5% incapacitating and two cases resulted in the death of the worker. 72% of the injuries were located in the fingers, 22% in the hands and 6% in the wrists. The greatest frequency of injuries were found in the economic activity in mines and quarries with a rate of 123.1 per thousand. The age group most affected was of 20-29 years (42%), Wounds or contusions and crushings were the injuries most commonly reported, in 39% and 36% of the cases respectively. The main type of injuries were caused by run over, running into or blow from objects. The principal agents causing injuries were materials, substances and radiations in 45% of the cases. It is concluded that the hand injury rate is very high in the exploitation of mines and quarries and represents the main cause of worker's disability.

Accidents, Occupational↗
PubMed2006

Remote sensing and GIS techniques for selecting a sustainable scenario for Lake Koronia, Greece.

During recent decades, Lake Koronia has undergone severe degradation as a result of human activities around the lake and throughout the basin. Surface and groundwater abstraction and pollution from agricultural, industrial, and municipal sources are the major sources of degradation. Planning a restoration project was hampered by lack of sufficient data, with gaps evident in both spatial and temporal dimensions. This study emphasized various remote sensing and geographic information system techniques, such as digital image processing and geographic overlay, to fill gaps using satellite imagery and other spatial environmental, hydrological, and hydrogeological data in the process of planning the restoration of Lake Koronia, following Ramsar guidelines. Current and historical remote sensing data were used to assess the current status and level of degradation, set constraints and define the ideotype for the restoration, and, finally, define and select the best restoration scenario.

Geographic Information Systems↗
PubMed2006

Gross photoreduction kinetics of mercury in temperate freshwater lakes and rivers: application to a general model of DGM dynamics.

Previous published measurements of mercury photoreduction are for net-photoreduction, since photooxidation processes occur simultaneously. In this research we combine continuous dissolved-gaseous mercury (DGM) analysis with a photoreactor and a quartz sparger in order to derive mercury gross photoreduction rate constants for UVB and UVA irradiations. The DGM concentration in each filter-sterilized freshwater was measured at 5 min intervals over a period of 23 h. Photoreduction proceeded for the initial 200 min, after which, reducible mercury was depleted in the sample. Substantial losses in DOC fluorescence were observed during the incubations for UVA radiation but not for UVB; therefore, UVB photoreduction dynamics are not linked to a loss in DOC fluorescence. Pseudo first-order reaction kinetics fit the data well (r2 > 0.87). The rate constants appear divided between lakes and rivers with the mean lake UVB rate constant (kUVB = 8.91 x 10(-5) s(-1)), significantly less than the mean rate constant (kUVB = 1.81 x 10(-4) s(-1)) for the river samples. However, while there were differences for the UVB rates between lakes and rivers, the mean and median rate constants for UVA in lakes (kUVA = 7.76 x 10(-5) s(-1)) did not differ significantly from the mean rate constant forthe river sites (kUVA = 1.78 x 10(-4) s(-1)). Here, we propose a model for mercury photoredox dynamics for both temperate lake and river systems. The lake model was validated using principal axis analysis to compare observed and predicted DGM data (n=279) from a variety of lake sites in Nova Scotia and Central Quebec. Principal axis analysis found a linear fit (correlation = 0.81; slope = 2.13) between predicted and observed environmental DGM values when log-normalized. The constant bias on the predicted values was attributed to estimates of available reducible mercury and the effect of DGM volatilization on observed data.

Fresh Water↗