bluuebunny/crossref_metadata_2025 huggingface dataset:
Saltation Layer of Particles in Water Flows Related to Transport Stage
Authors: Mazumder B. S. , Dalal D. C.
Published: May 2018

A theoretical model has been developed to determine the maximum saltation layer thickness of sediment particles in water associated with the migration velocity of particle in the bed layer. This is consistent with Owen's (1964) hypothesis for saltation of uniform grain in air. The equation for mean particle velocity at the bed is derived by balancing the horizontal forces acting on the particle in the bed. The modified expression for mean particle velocity includes the effects of drag and lift coefficients, bed shear stress, coefficient of dynamic friction, settling velocity and pivoting angle. The saltation layer model presented here extends a reasonable physical assumption by converting the average horizontal particle velocity to a vertical component of velocity due to collisions with particles resting on the bed. This explicitly shows a functional dependence of saltation height on mean particle velocity and take-off angle. The proposed model has been tested using available experimental data and the agreement with particle velocities and saltation heights is excellent. An interesting outcome is that a quadratic relationship is suggested between the higher transport stage (upper plane bed) and the take-off angle of particle. This shows that the take-off angle decreases with increase in transport stage.
Comparison of Ground-Based and Airborne Snow Depth Measurements with Georadar Systems, Case Study
Authors: Marchand Wolf-Dietrich , Killingtveit Ånund , Wilén Peter , Wikström Per
Published: May 2018

Snow depth measurements with the help of georadar (Ground Penetrating Radar, GPR) were investigated for almost two decades in Scandinavia. For the first tests in the early 1980s, results were of poor quality. Later, data quality improved when different systems were developed. In Norway, emphasis was put on ground-based snow measurements of scientific character; few attempts for operational use were undertaken. In Sweden, airborne, operational snow measurements with georadar were performed since 1986. A helicopter, flying near to the ground, was used as platform.

The objective of the presented study was to compare results from ground-based and airborne snow measurements. The radar control units used were comparable, but the antenna configuration and frequencies differed. Also radar data interpretation and the conversion of radar signal travel time into snow depth values varied. Measurements were made at common snow courses.

The comparison showed in general high correlation between radar results from both methods. Differing results were found for shallow snow and bare areas. Here, the ground-based method indicated zero or close-to-zero snow depth, whereas the airborne method rarely detected zero snow depth. This phenomenon seemed to be connected to the bigger footprint size of the airborne radar and to the different radar data interpretation methods. On average, the airborne measurements indicated shallower snow depths than ground-based measurements, 4% less in open terrain and 7% less in forest. Comparing snow depth as grid cell values, the best agreement, less than 1% difference, was obtained for the 10 m resolution.
Thermo-hydrological Responses to an Exceptionally Warm, Dry Summer in a High Arctic Environment
Authors: Young Kathy L. , Woo Ming-ko
Published: May 2018

1998 was a very warm year for Canada and the High Arctic was no exception. A typical area was Resolute, Cornwallis Island, Nunavut, where the thaw season was extended and the thawing degree-days were larger than normal. The warm summer was accompanied by early spring melt and low rainfall. This study documents the thermo-hydrological responses including warming of the top soil, deepening of the active layer, alteration of the evaporation pattern, adjustment of the water table positions and runoff. The presence of semi-permanent snowbanks and patchy wetlands buffer some local sites from the warm and dry summer conditions. This and other studies show that the cryospheric and hydrologic systems may or may not recover quickly from the year to year variations in the climate, depending on how readily the storages (snow, ice and basin moisture) can be replenished. In view of the cumulative effects of storage depletion under climatic warming, short-term studies on thermo-hydrological behaviour in the Arctic provide a useful but insufficient analogue to capture the climatic change impacts.
Trends and Characteristics of Hydrological Time Series in Finland
Authors: Hyvärinen Veli
Published: May 2018

Hydrological time series analyses made in Finland up to 2001 show the following: 1) Precipitation has been increasing in southern and central Finland, and also in the north in winter, during the period 1911-2000. There are, however, no harmonized analyses of areal precipitation to show the exact increase. 2) The annual maximum of the areal water equivalent of snow has been increasing in eastern and northern Finland but decreasing in the south and west during the period 1947-2001. 3) The winter runoff has generally been increasing strongly in southern and slightly in central Finland during the 20th century. In northern Lapland there are no signs of increase in winter or annual flow. Annual discharge in the south and west has also increased to some extent. 4) The existing analyses show no signs of long-term trends in annual evapotranspiration. 5) Long-term fluctuations of water stage have been observed in the major groundwater formations. 6) The series of the date of ice break-up in the river Tornionjoki - starting in 1693 – shows that in recent decades the ice cover of the river has broken up about two weeks earlier than in the beginning of the period. 6) Lake ice maximum thickness series show no noticeable trend. 7) Lake water temperature in south-eastern Finland seems to have been increasing slightly during the period starting in 1924; in central and northern Finland no trends in water temperature have been observed.
Seasonal changes in meltwater storage and drainage characteristics of the Dokriani Glacier, Garhwal Himalayas (India)
Authors: Singh Pratap , Haritashya Umesh K. , Kumar Naresh
Published: May 2018

Storage and drainage characteristics of the Dokriani Glacier (9.66 km2) located in the Garhwal Himalayas have been studied. In order to understand these characteristics, clear weather (non-rainy) days data for three ablation seasons (1996–1998) are used because discharge is melt-driven on such days. Moreover, diurnal variations in the discharge on clear days represent the true picture of glacier response to streamflow. Results indicate that meltwater storage characteristics of the glacier lead to high discharges in the stream during the night. Consequently, night-time discharges are comparable with those observed during daytime throughout the melt season. Meltwater storage characteristics of the glacier are much stronger in the early part of the melt season and they weaken as the melt season progresses.

Diurnal variations in the discharge are observed to be clearer with advancement of the melt season providing variations in the timing of peak flow. Maximum discharge for different years was observed between 1700 and 1900 hours, showing a lag of 2 hours in the timing of maximum flow over the ablation period. The time to peak flow varied from 8.5 to 11 hours. For all the years, a strong seasonal trend towards increasing diurnal amplitude in discharge until August and thereafter a decreasing trend, was observed. The time lag between Qmax and Tmax varied from 3–6 hours over the ablation season and recession of melt water became faster with time. The time lag is higher at the beginning of the melt season and reduces as the melt season progresses. Recession trends of the hydrographs with time suggested a similar hydrological response of the glacier in June and September. The basin behaved like a single conceptual linear reservoir for these two months, while for July and August it behaved like two conceptual linear reservoirs, namely, accumulation and ablation reservoirs.
A synthetic groundwater modelling study of the accuracy of GLUE uncertainty intervals
Authors: Christensen Steen
Published: May 2018

Synthetic groundwater flow models with one unknown parameter, the average log transmissivity of the flow domain, and with Gaussian log-transmissivity error structure were used to study the nature and the accuracy of Generalized Likelihood Uncertainty Estimation (GLUE) intervals. The uniform prior distribution of log10 transmissivities was sampled uniformly and 1000 values per log10-transmissivity cycle were required to produce unbiased GLUE results. Because the errors in hydraulic head resulting from the log-transmissivity errors are known to be Gaussian for a linear model for heads, the Gaussian likelihood function was used as the GLUE goodness-of-fit function in most cases studied. The GLUE interval computed for the hydraulic head at different locations within the domain has the characteristics of a confidence interval for the hydraulic heads computed using the spatial average log transmissivity. The GLUE interval does not have the characteristics of a prediction interval, which is a probability interval for an uncertain observation of some variable such as the hydraulic head. The goodness-of-fit function can be corrected so that the resulting GLUE interval has the characteristics of a prediction interval. However, neither the original nor the corrected GLUE interval account for the uncertainty caused by small-scale model errors, which is always present in practical groundwater flow modelling. It is therefore concluded that one should be careful with using the GLUE interval to evaluate the validity of a model's structure. The structure may be valid even though observations fall significantly outside the GLUE interval if the observations are uncertain and the goodness-of-fit function is not corrected to account for this, or if small-scale model error is significant. If small-scale model error does not significantly bias model predictions, the predictions will be useful although uncertain. Small-scale model error did not bias the predictions in the examples studied here except near a strong sink. Changing the goodness-of-fit function from the Gaussian likelihood function to a similar but different function made the resulting GLUE intervals very inaccurate. Changing to a third function based on a fitted model rejection value produced results that were somewhat better than those obtained with the Gaussian likelihood function. However, the results were sensitive to the model rejection value, which in the ideal case should be adjusted for each predicted variable individually. Thus, the third function is not attractive for practical applications with the GLUE methodology.
Climate impacts on the ice regime of an Atlantic river
Authors: Beltaos Spyros
Published: May 2018

Although the sensitivity of river ice processes to climatic inputs is well known, there is very little information on how a changing climate can affect the severity and frequency of ice jam events and their numerous ecological and socio-economic impacts. The present study adds to this information by examining the ice regime of the Southwest Miramichi River, New Brunswick, and identifying recent trends that may be linked to concomitant climatic variations. The timing of freeze-up and breakup, as well as the thickness of the winter ice cover, do not exhibit significant temporal trends. However, spring ice jamming is becoming more severe, and there is increasing potential for devastating mid-winter breakup events. These findings are consistent with increasing rainfall and snowfall amounts, as well as increasing river flows, during the winter and early spring. Unlike in most parts of Canada, slight cooling during the winter months was detected, consistent with cooling trends found elsewhere in Atlantic Canada. Implications for adaptation and infrastructure design are discussed.
Statistical properties of spatial snowcover in mountainous catchments in Norway
Authors: Marchand Wolf-Dietrich , Killingtveit Ånund
Published: May 2018

The spatial distribution of snowcover in a catchment is determined by complex interactions between meteorological and physiographical factors, integrated over time. The snowcover shows variability over scales ranging from centimeters up to hundreds of kilometers.

An important and necessary decision for modelers is to determine spatial resolution in a distributed model. Since the spatial variability in snowcover may be quite large, even within a few meters, it is difficult to use modeling units small enough so that the snow can be assumed evenly distributed within the unit. A possible method to compensate for this is to use larger units, and describe the snow distribution within each unit by a statistical model (e.g. normal, log-normal, gamma, etc). This technique requires information about spatial statistical properties of snowcover within a unit.

As many of the distributed hydrological models operate on a grid basis, it would be desirable to find a statistical distribution on a sub-grid scale. However, as an initial approach, the study presented here was done on a catchment scale. The catchment scale presented the possibility of incorporating data from several historical snow surveys. These surveys were taken at the time of maximum snow accumulation in various mountainous catchments in Norway. Comparing empirical distribution functions with different theoretical distribution functions, it was shown that a mixed distribution combining two separate log-normal distributions clearly gave the best fit in most of the catchments. This seems to indicate that a mixture of at least two different populations of SWE values exists.
Critical bed shear for initial movement of sediments on a combined lateral and longitudinal slope
Authors: Dey Subhasish
Published: May 2018

An experimental study on critical bed shear-stress for initial movement of non-cohesive sediment particles under a steady-uniform stream flow on a combined lateral (across the flow direction) and longitudinal (streamwise direction) sloping bed is presented. The aim of this paper is to ascertain that the critical bed shear-stress on a combined lateral and longitudinal sloping bed is adequately represented by the product of critical bed shear-stress ratios for lateral and longitudinal sloping beds. Experiments were carried out with closed-conduit flow, in two ducts having a semicircular invert section, with three sizes of sediments. In laboratory flumes, the uniform flow is a difficult – if not impossible – proposition for a steeply sloping channel, and is impossible to obtain in an adversely sloping channel. To avoid this problem, the experiments were conducted with a closed-conduit flow. The critical bed shear-stresses for experimental runs were estimated from side-wall correction. The experimental data agree satisfactorily with the results obtained from the proposed formula.
Statistical downscaling and scenario construction of precipitation in Scania, southern Sweden
Authors: Linderson Maj-Lena , Achberger Christine , Chen Deliang
Published: May 2018

Statistical downscaling models for precipitation in Scania, southern Sweden, have been developed and applied to calculate the changes in the future Scanian precipitation climate due to projected changes in the atmospheric composition. The models are based on multiple linear regression, linking large-scale predictors at monthly time resolution to regional statistics of daily precipitation on a monthly basis. To account for spatial precipitation variability within the area, the precipitation statistics were derived for different regions in Scania. The final downscaling models, developed for different regions and seasons, use atmospheric circulation, large-scale humidity and precipitation as predictors. Among the precipitation statistics examined, only the models for estimating the mean precipitation and the frequency of wet days were skilful. Based on the Canadian Global Circulation Model 1 (CGCM1), a future scenario of these two statistics was created. The downscaled scenario shows a significant increase of the annual mean precipitation by about 10% and a slight decrease in the frequency of wet days, indicating an increase in the precipitation amounts as well as in the precipitation intensity. The main increase of precipitation amounts and intensity occur during winter, while the summer precipitation amounts decrease slightly. The seasonal changes found in precipitation are likely attributed to changes in the westerly flow of the atmospheric circulation.
Modeling arctic snow distribution and melt at the 1 km grid scale*
Authors: Woo Ming-ko , Young Kathy L.
Published: May 2018

Snow accumulation, re-distribution and melt are important hydrological considerations in the Arctic. This study presents a model of the late-winter snow cover and the ensuing snowmelt in a High Arctic environment at a scale of 1 km. Indexing is used to spread the snow data from a lowland weather station to various terrain units over a 16×13 km2 target area east of Resolute, Cornwallis Island, Canada. Meteorological variables measured at this base station are spatially extended by field derived empirical relationships for the computation of melt at various terrain units using the energy balance approach. These melt rates are weighted by the fractional coverage of various terrain unit within each 1×1 km2 cell. The snow distribution pattern is obtained daily and model performance was tested by comparing observed and computed dates of melt and the radiation balance over snow. The simulated snow pattern compared favourably with the snow cover imaged by LANDSAT. Daily changes in the probability distribution of snow water equivalent over the target area was examined and snow depletion curves were derived. They describe sub-grid variability over an area and our results point to several assumptions that should be scrutinized in sub-grid parameterization of snow distribution.
Evaluating snowmelt runoff generation in a discontinuous permafrost catchment using stable isotope, hydrochemical and hydrometric data
Authors: Carey S.K. , Quinton W.L.
Published: May 2018

Research on snowmelt runoff generation in discontinuous permafrost subarctic catchments has highlighted the role of: (i) permafrost in restricting deep percolation and sustaining near-surface water tables and (ii) the surface organic layer in rapidly conveying water to the stream. Conceptual models of runoff generation have largely been derived from hydrometric data, with isotope and hydrochemical data having only limited application in delineating sources and pathways of water. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, Canada, snowmelt runoff generation processes were studied during 2002 using a mixed methods approach. Snowmelt timing varied between basin slopes, with south-facing exposures melting prior to permafrost-underlain north-facing slopes. The streamflow freshet period begain after 90% of snow had melted on the south-facing slope and coincided with the main melt period on the north-facing slope, indicating that contributing areas were largely defined by permafrost distribution. Stable isotope (δ18O) and hydrochemical parameters (dissolved organic carbon, specific conductivity, pH) suggest that, at the beginning of the melt period, meltwater infiltrates soil pores and resides in temporary storage. As melt progresses and bare ground appears, thawing of soils and continued meltwater delivery to the slopes allows rapid drainage of this meltwater through surface organic layers. As melt continues, soil thawing progresses and pre-event water mixes with melt water to impart streamflow with a gradually decreasing meltwater contribution. By the end of the melt period, the majority of water reaching the stream is displaced water that has resided in the catchment prior to melt. For the entire study period, approximately 21% of freshet was supplied by the snowpack, and the remaining majority was pre-melt water stored in the catchment slopes over-winter and displaced during melt. Hydrochemical data support hydrometric observations indicating the dominant flow pathway linking the slopes and the stream is through the organic horizon on permafrost-underlain slopes.
Variation of runoff and nitrogen leaching in a small agricultural catchment in southern Finland
Authors: Granlund Kirsti
Published: May 2018

Long term monitoring data from 1981–2000 was used to study nitrogen (N) losses from a small (15.4 km2) agricultural catchment in southern Finland. The annual loads of total N, NO3-N and NH4-N varied considerably during the study period. The mean total N load was 820 kg km−2 yr−1. More than half of the annual N load was in the form of NO3-N, while the relative contribution of NH4-N was low, which is common in Finnish agricultural fine-textured soils. The measured annual N loads were highly dependent on runoff. The highest annual N load (1310 kg km−2) was observed in 1984, in accordance with the highest annual runoff (616 mm). Due to mild weather conditions during the winters since 1989, the relative proportion of winter runoff was higher than earlier. So far, no decrease could be seen in annual N loads, even though most of the farmers are participating in the Finnish Agri-Environmental Programme established in 1995. However, the amount of NH4-N load seems to have remained very low (less than 50 kg km−2 yr−1) in Savijoki since 1995, which may reflect changes in agricultural practices and a decrease in N deposition.
Hydrology, geochemistry and Sr isotopes in solids and solutes of the meltwater from Mittivakkat Gletscher, SE Greenland
Authors: Hagedorn Birgit , Hasholt Bent
Published: May 2018

This study was initiated to investigate elemental fractionation and Sr isotope systematics associated with glacial erosion by direct comparison of particulate and dissolved load in glacial runoff. Discharge measurements along with chemical and Sr isotope investigations were carried out at the Mittivakkat Gletscher (Glacier), Ammassalik Ø, Southeast Greenland. Major bedrock types are the Ammassalik Intrusive Complex (AIC) of mafic composition and garnet–granite gneiss (GGG) of acidic composition. Mechanical denudation rates (1 mm a−1) reflected in the major outflow are in the range of temperate valley glaciers in Norway. Chemical denudation rates (32 t km−2 a−1) and estimated rates of CO2 drawdown by silicate weathering (720–100 kgC km−2 a−1) are low compared to global mean and match values measured for High Arctic glaciers on Svalbard. The contrast in chemical and Sr isotope composition of bedrock makes Sr isotope ratios a powerful tool for determining source areas of solid and dissolved load. High Ca/K ratios in water compared to suspended particulate matter (SPM) indicate faster dissolution of Ca minerals. By contrast, in GGG bedrock, where biotite and K-feldspar are abundant, Sr isotope ratios in solutes are higher than in SPM, supporting preferential release of 87Sr from a K-mineral lattice.
Preferential water flow in a glacial till soil
Authors: Jansson Christer , Espeby Bengt , Jansson Per-Erik
Published: May 2018

Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in glacial till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a till slope (7–10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in glacial till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.
Evapotranspiration from a riparian fen wetland
Authors: Andersen H.E. , Hansen S. , Jensen H. E.
Published: May 2018

Evapotranspiration rates were measured in a riparian fen wetland dominated by vascular vegetation and surrounded by open agricultural areas and forests. The wetland is situated on a floodplain in central Denmark. Measurements were taken throughout the growing season (April–September) of 1999.

Evapotranspiration rates were higher than those published for most other wetland types, with an average of 3.6 mm d−1 during the growing season and a peak rate of 5.6 mm d−1. Daily average evapotranspiration was 110% of Penman's potential open water evaporation.

Evapotranspiration was the dominant sink in the energy balance of the wetland studied. During the day, evapotranspiration accounted for 82% of the available radiant energy, Rn. Due to the presence of deposited fine-grained sediments, soil-water availability was kept high at all times which resulted in moderate canopy resistances, rc (overall mean =32 s m−1). Evapotranspiration was controlled by a combination of driving forces: Rn, saturation vapour pressure deficit, D, and rc.

It is hypothesized that the results presented in this study are conditioned by the proximity of the wetland to drier upland areas. During periods with high evaporative demand and low precipitation, warm, dry air is formed over the upland areas and wetland evapotranspiration rates are enhanced by local advection. Indicative evidence for the hypothesis is presented. Although the absolute magnitude of the results reported is only directly relevant to similar sites in Denmark, the processes and controls described are considered to be representative of riparian wetlands subjected to frequent flooding and/or with a high groundwater table, with vascular vegetation, and which are narrow corridors in open agricultural landscapes.
Distribution of snow cover over Northern Eurasia
Authors: Kitaev Lev , Førland Eirik , Razuvaev Vjacheslav , Tveito Ole Einar , Krueger Olaf
Published: May 2018

Based on observation data the spatial variability and long-term trends of snow depth, snow water equivalent and number of days with snow coverage ≥50% for Northern Eurasia are estimated. The significance of continental snow cover variability over Northern Eurasia is illustrated by comparison with snow cover variability of the northern part of North America (Canada). The fundamental scientific problem of our investigations is revealing spatial and temporal changes of snow cover under the present climate conditions. The snow cover depends on a climate on the one hand and appreciably defines a hydrological regime on the other hand and, thus, the snow cover is a good indicator of changes in the condition of an environment. In this case the condition of the snow cover of the Northern hemisphere on an example of Northern Eurasia within the boundaries of the NIS and the northern part of North America within the boundaries of Canada is investigated. The novelty of the work, in particular, consists in the attraction to the analysis of a lot of long-term data on the snow cover of two continents. As a result the general regularity of spatial heterogeneity and the long-term variability of snow stocks were revealed.
Expected changes in water resources availability and water quality with respect to climate change in the Elbe River basin (Germany)
Authors: Krysanova Valentina , Hattermann Fred , Habeck Anja
Published: May 2018

Reliable modelling of climate–water interactions at the river basin and regional scale requires development of advanced modelling approaches at scales relevant for assessing the potential effects of climate change on the hydrological cycle. These approaches should represent the atmospheric, surface and subsurface hydrological processes and take into account their characteristic temporal and spatial scales of occurrence. The paper presents a climate change impact assessment performed for the Elbe River basin in Germany (about 100 000 km2). The method used for the study combines:

(a) a statistical downscaling method driven by GCM-predicted temperature trend for producing climate scenarios, and

(b) a simulation technique based on an ecohydrological semi-distributed river basin model, which was thoroughly validated in advance.

The overall result of the climate impact study for the basin is that the mean water discharge and the mean groundwater recharge in the Elbe basin will be most likely decreased under the expected climate change and diffuse source pollution will be diminished. Our study confirms that the uncertainty in hydrological and water quality responses to changing climate is generally higher than the uncertainty in climate input. The method is transferable to other basins in the temperate zone.
Variability of radiosonde-observed precipitable water in the Baltic region*
Authors: Jakobson E. , Ohvril H. , Okulov O. , Laulainen N.
Published: May 2018

The total mass of columnar water vapour (precipitable water, W) is an important parameter of atmospheric thermodynamic and radiative models. In this work more than 60 000 radiosonde observations from 17 aerological stations in the Baltic region over 14 years, 1989–2002, were used to examine the variability of precipitable water. A table of monthly and annual means of W for the stations is given. Seasonal means of W are expressed as linear functions of the geographical latitude degree. A linear formula is also derived for parametrisation of precipitable water as a function of two parameters – geographical latitude and surface water vapour pressure.
Determination of the drainage basin characteristics using vector GIS
Authors: Apaydin H. , Ozturk F. , Merdun H. , Aziz N.M.
Published: May 2018

Detailed geomorphologic characteristics need to be compiled for performing hydrologic modeling of a basin. Basin form and hydrologic characteristics are to be related so the basin form must also be represented by quantitative descriptors. The typical morphologic characteristics used in hydrological analyses are basin area, perimeter, mainstream length, total stream length, contour length, basin shape (form factor, circularity ratio, compactness ratio, basin elongation), slope, drainage density, relief (maximum relief, relief ratio, relative relief), effective basin width, and median elevation. The objective of this study is to propose an algorithm to automatically calculate basin characteristics using vector GIS. The results produced by the algorithm were compared to the manual method and the two methods were found statistically similar.
A large cholera outbreak in Kano City, Nigeria: the importance of hand washing with soap and the danger of street-vended water
Authors: Hutin Yvan , Luby Stephen , Paquet Christophe
Published: May 2018

The aim of this study was to identify the risk factors for cholera during an outbreak in Nigeria. Cases were defined as recent onset of acute diarrhoea with dehydration in a patient hospitalised at the Infectious Diseases Hospital in Kano City. Meningitis patients admitted concurrently at the same hospital were recruited as unmatched controls. Data were collected on age, sex, place of residence, hygienic practices, and on food and water consumption. A total of 5600 cholera cases and 340 cholera deaths were reported between December 1995 and May 1996 (attack rate=86.3 per 100,000 population) in the state of Kano. Compared to the 77 controls, the 102 cases were more likely to have drunk street-vended water (age-adjusted odds ratio (AAOR)=3.2; 95% confidence interval (CI): 1.4–7.1) and less likely to have drunk tap water in their homes (AAOR=0.2; 95% CI: 0.1–0.7) or to have washed hands with soap prior to eating food (AAOR=0.2; 95% CI: 0.1–0.6). While no data suggested that the municipal water supply was contaminated, safe water systems and hand hygiene practices might have prevented a high proportion of cases if implemented early during this outbreak.
Evaluation of a new water treatment for point-of-use household applications to remove microorganisms and arsenic from drinking water
Authors: Souter Philip F. , Cruickshank Graeme D. , Tankerville Melanie Z. , Keswick Bruce H. , Ellis Brian D. , Langworthy Don E. , Metz Kathy A. , Appleby Martin R. , Hamilton Nicola , Jones Amanda L. , Perry John D.
Published: May 2018

Contamination of drinking water by microorganisms and arsenic represents a major human health hazard in many parts of the world. An estimated 3.4 million deaths a year are attributable to waterborne diseases. Arsenic poisoning from contaminated water sources is causing a major health emergency in some countries such as Bangladesh where 35 to 77 million people are at risk.The World Health Organization (WHO) has recently recognized point-of-use water treatment as an effective means of reducing illness in developing country households. A new point-of-use water treatment system that is based on flocculation, sedimentation and disinfection was evaluated for the removal of bacterial, viral and parasitic pathogens as well as arsenic from drinking water to estimate its potential for use in developing countries.Tests were conducted with United States Environmental Protection Agency (EPA)-model and field- sample waters from developing countries. Samples were seeded with known numbers of organisms, treated with the combined flocculation/disinfection product, and assayed for survivors using standard assay techniques appropriate for the organism.Results indicated that this treatment system reduced the levels from 108/l to undetectable (<1) of 14 types of representative waterborne bacterial pathogens including Salmonella typhi and Vibrio cholerae. No Escherichia coli were detected post-treatment in 320 field water samples collected from five developing countries. In addition, the water treatment system reduced polio and rotavirus titres by greater than 4-log values. Cyrptosporidium parvum and Giardia lamblia inocula were reduced by greater than 3-log values following use of this water treatment system. Arsenic, added to laboratory test waters, was reduced by 99.8%, and naturally occurring arsenic in field samples from highly contaminated Bangladeshi wells was reduced by 99.5% to mean levels of 1.2 µg/l.This water treatment system has demonstrated the potential to provide improved drinking water to households in developing countries by removing microbial and arsenic contaminants.
The effect of container-biofilm on the microbiological quality of water used from plastic household containers
Authors: Jagals P. , Jagals C. , Bokako T. C.
Published: May 2018

Studies in Southern Africa have shown that even when microbiologically safe water is supplied to developing communities at communal standpipes, contamination by high numbers of pathogenic microorganisms may occur during the processes of fetching water from the supply source and storage during use at home, rendering such waters unsafe for human consumption. This study investigated the occurrence of biofilm in PVC storage containers as one possible reason for this deterioration, using heterotrophic bacteria and total coliform counts as well as turbidity as indicators. A second objective was to determine whether biofilm in water-storage containers could contribute to hazardous microbiological contamination indicated by Escherichia coli and Clostridium perfringens. Results indicated that increased microbiological contamination is associated with biofilm. The biofilm harbours heterotrophic bacteria, total coliforms and C. perfringens. E. coli could not be associated directly with the levels of biofilm in containers but rather appears to be introduced intermittently from the ambient domestic environment. When dislodged with the biofilm, these bacteria contributed substantially to the deterioration of the microbiological quality of supplied water stored in plastic containers.
Phenotypic library-based microbial source tracking methods: Efficacy in the California collaborative study
Authors: Harwood Valerie J. , Wiggins Bruce , Hagedorn Charles , Ellender R. D. , Gooch Jan , Kern James , Samadpour Mansour , Chapman Annie C. H. , Robinson Brian J. , Thompson Brian C.
Published: May 2018

As part of a larger microbial source tracking (MST) study, several laboratories used library-based, phenotypic subtyping techniques to analyse fecal samples from known sources (human, sewage, cattle, dogs and gulls) and blinded water samples that were contaminated with the fecal sources. The methods used included antibiotic resistance analysis (ARA) of fecal streptococci, enterococci, fecal coliforms and E. coli; multiple antibiotic resistance (MAR) and Kirby-Bauer antibiotic susceptibility testing of E. coli; and carbon source utilization for fecal streptococci and E. coli. Libraries comprising phenotypic patterns of indicator bacteria isolated from known fecal sources were used to predict the sources of isolates from water samples that had been seeded with fecal material from the same sources as those used to create the libraries. The accuracy of fecal source identification in the water samples was assessed both with and without a cut-off termed the minimum detectable percentage (MDP). The libraries (∼300 isolates) were not large enough to avoid the artefact of source-independent grouping, but some important conclusions could still be drawn. Use of a MDP decreased the percentage of false-positive source identifications, and had little effect on the high percentage of true-positives in the most accurate libraries. In general, the methods were more prone to false-positive than to false-negative errors. The most accurate method, with a true-positive rate of 100% and a false-positive rate of 39% when analysed with a MDP, was ARA of fecal streptococci. The internal accuracy of the libraries did not correlate with the accuracy of source prediction in water samples, showing that one should not rely solely on parameters such as the average rate of correct classification of a library to indicate its predictive capabilities.
A comparative study of culture-independent, library-independent genotypic methods of fecal source tracking
Authors: Field Katharine G. , Chern Eunice C. , Dick Linda K. , Fuhrman Jed , Griffith John , Holden Patricia A. , LaMontagne Michael G. , Olson Betty , Simonich Michael T.
Published: May 2018

Culture-independent fecal source tracking methods have many potential advantages over library-dependent, isolate-culture methods, but they have been subjected to limited testing. The purpose of this study was to compare culture-independent, library-independent methods of fecal source tracking. Five laboratories analysed identical sets of aqueous samples that contained one or more of the following sources: sewage, human feces, dog feces, cattle feces and gull feces. Two investigators used methods based on PCR amplification of Bacteroidetes marker genes and both successfully discriminated between samples that did or did not contain human fecal material. One of these investigators was also able to identify the remaining sources, except for gull, with a low rate of false positives. A method based on E. coli toxin genes successfully identified samples containing sewage and cattle feces, but missed some samples with human feces because of low marker prevalence in individual human fecal samples. Researchers who used community terminal restriction fragment length polymorphism (T-RFLP) were limited by the amount of DNA recovered from samples, but they correctly identified human and cattle fecal contamination when sufficient DNA was obtained. Culture independent methods show considerable promise; further research is needed to develop markers for additional fecal sources and to understand the correlation of these source-tracking indicators to measures of human and environmental health.
Assessment of statistical methods used in library-based approaches to microbial source tracking
Authors: Ritter Kerry J. , Carruthers Ethan , Carson C. Andrew , Ellender R. D. , Harwood Valerie J. , Kingsley Kyle , Nakatsu Cindy , Sadowsky Michael , Shear Brian , West Brian , Whitlock John E. , Wiggins Bruce A. , Wilbur Jayson D.
Published: May 2018

Several commonly used statistical methods for fingerprint identification in microbial source tracking (MST) were examined to assess the effectiveness of pattern-matching algorithms to correctly identify sources. Although numerous statistical methods have been employed for source identification, no widespread consensus exists as to which is most appropriate. A large-scale comparison of several MST methods, using identical fecal sources, presented a unique opportunity to assess the utility of several popular statistical methods. These included discriminant analysis, nearest neighbour analysis, maximum similarity and average similarity, along with several measures of distance or similarity. Threshold criteria for excluding uncertain or poorly matched isolates from final analysis were also examined for their ability to reduce false positives and increase prediction success. Six independent libraries used in the study were constructed from indicator bacteria isolated from fecal materials of humans, seagulls, cows and dogs. Three of these libraries were constructed using the rep-PCR technique and three relied on antibiotic resistance analysis (ARA). Five of the libraries were constructed using Escherichia coli and one using Enterococcus spp. (ARA). Overall, the outcome of this study suggests a high degree of variability across statistical methods. Despite large differences in correct classification rates among the statistical methods, no single statistical approach emerged as superior. Thresholds failed to consistently increase rates of correct classification and improvement was often associated with substantial effective sample size reduction. Recommendations are provided to aid in selecting appropriate analyses for these types of data.
Fate of Salmonella following application of swine manure to tile-drained clay loam soil
Authors: Malik Yashpal S. , Randall Gyles W. , Goyal Sagar M.
Published: May 2018

Land application of animal manure is an important means of utilization of nitrogen and phosphorus. However, the presence of pathogens in manure and their occasional leaching into subsurface water has become a topic of concern during the past few years. This study was undertaken to determine the extent to which Salmonella anatum may leach through tile-drained clay loam soil on which swine manure has been applied. For this purpose, swine manure was experimentally contaminated with S. anatum and applied to three tile-drained plots in winter of 2001 while another three plots served as negative controls. Following rainfall events in the spring of 2002 the tiles started to flow and leachate samples of subsurface water were collected at various time intervals and tested for S. anatum. Salmonella anatum was not found to leach into the subsurface drainage water indicating that it was either retained in the upper layers of soil or did not survive over winter. The leaching of faecal coliforms and coliphages was also tested. Faecal coliforms and coliphages were detected in the subsurface water from both manure and control plots, indicating the ability of the tile drainage system to transport these organisms to groundwater as the water percolates through the soil. Additional temporal studies over a longer time period are needed to determine the survival and leaching of pathogens and indicators into subsurface water.
Ferrates (iron(VI) and iron(V)): Environmentally friendly oxidants and disinfectants
Authors: Sharma Virender K. , Kazama Futaba , Jiangyong Hu , Ray Ajay K.
Published: May 2018

Iron(VI) and iron(V), known as ferrates, are powerful oxidants and their reactions with pollutants are typically fast with the formation of non-toxic by-products. Oxidations performed by Fe(VI) and Fe(V) show pH dependence; faster rates are observed at lower pH. Fe(VI) shows excellent disinfectant properties and can inactivate a wide variety of microorganisms at low Fe(VI) doses. Fe(VI) also possesses efficient coagulation properties and enhanced coagulation can also be achieved using Fe(VI) as a preoxidant. The reactivity of Fe(V) with pollutants is approximately 3–5 orders of magnitude faster than that of Fe(VI). Fe(V) can thus be used to oxidize pollutants and inactivate microorganisms that have resistance to Fe(VI). The final product of Fe(VI) and Fe(V) reduction is Fe(III), a non-toxic compound. Moreover, treatments by Fe(VI) do not give any mutagenic/carcinogenic by-products, which make ferrates environmentally friendly ions. This paper reviews the potential role of iron(VI) and iron(V) as oxidants and disinfectants in water and wastewater treatment processes. Examples are given to demonstrate the multifunctional properties of ferrates to purify water and wastewater
Occurrence and correlations between coliphages and anthropogenic viruses in the Massachusetts Bay using enrichment and ICC-nPCR
Authors: Ballester Nicola A. , Fontaine Justin H. , Margolin Aaron B.
Published: May 2018

We evaluated a two-step enrichment procedure to detect coliphages and an integrated cell culture-nested polymerase chain reaction (ICC-nPCR) to detect human astrovirus, enteroviruses, rotavirus and adenovirus type 40 and 41 in marine water samples collected by the Massachusetts Water Resource Authority (MWRA). MWRA has been monitoring its receiving waters for coliphages, anthropogenic viruses and indicator bacteria in order to evaluate the impact of Boston's Deer Island Sewage Treatment Plant discharge. Coliphages and enteric viruses were originally assayed using single agar overlay and most probable number cell culture (MPN) methods, respectively. Reanalysis of these samples for enteric viruses by ICC-nPCR demonstrated that 46% were positive for at least one virus compared with 23% with the MPN method. Use of the enrichment method showed a 47% increase in the detection of male specific and somatic coliphages compared with the single agar overlay method. Correlations between the presence of coliphages, enteric viruses and indicator bacteria were based on proximity to the treatment plant discharge, seasonal variations and site levels. The presence of enteric viruses was significantly correlated to coliphages but not to indicator bacteria. Preliminary comparative results demonstrate that effective and efficient monitoring of anthropogenic contamination can be achieved using these more sensitive and specific techniques.