bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen and Phosphorus Fluxes from Finnish Agricultural Areas to the Baltic Sea
Authors: Rekolainen Seppo , Pitkänen Heikki , Bleeker Albert , Felix Sietske
Published: May 2018

Nutrient losses from small drainage basins were compared to the nutrient fluxes in small coastal rivers in order to study the representativeness of the Finnish monitoring network of small basins, especially as regards agricultural loading to the Baltic Sea. Additionally flux estimates from the period 1986-1990 were compared to those of the period 1981-1985 in order detect possible trends. The results suggest that in coastal regions with high proportions of agricultural land and with low lake percentage, the nutrient losses from agricultural areas mostly enter coastal waters with negligible retention in river channels. The net effect of the various processes in the rivers is small because most of the nutrient losses occur in spring, fall or early winter in connection with high water flows and current velocities, short residence times of water and low intensities of biogeochemical processes. Nitrogen losses from agriculture has probably increased during the 1980s due to increased winter flows and increased use of nitrogen fertilizers. The results indicate that nitrogen loading of the southern and south-western coastal waters of Finland has increased as well.
Estimation of Aquifer Parameters by Least-Squares Method under Linear Flow Conditions in Fractured Rocks
Authors: Jat M.L. , Acharya M.S. , Singh J.
Published: May 2018

Pumping and recovery test data in phyllite formations were analysed under linear flow conditions by incorporating modification in the method proposed by Şen (1986). Although the Şen (1986) method is developed for analysis of borewell test data, this method has been used for large-diameter well-test data by taking average inflow rate in the well. The results obtained were compared with Şen's graphical method. Lower values of root mean-square error were obtained by least-squares method. The estimated values of transmissivity and storage coefficient were acceptable at 1 per cent level of significance. An advantage of the least-squares method is the automization, which is lacking in the graphical method utilising curve-matching technique.
Combined Modelling of Groundwater Table and Open Water Level in Raised Mires
Authors: Spieksma J. F. M. , Schouwenaars J. M. , Blankenburg J.
Published: May 2018

Wetlands are mostly characterized by a large proportion of open water and frequent inundation. In most soil water flow models little attention is payed to phenomena related to open water. In this study, limitations of one dimensional soil water flow models in wetlands are identified. A simple model approach for incorporating the relation between open water and groundwater in soil water flow models is introduced. This model concept is implemented in an extended version of the SWATRE model and tested with data from three lowland raised mires (Engbertdijksvenen, Fochteloërveen (The Netherlands) and Leegmoor (Germany)). The model runs are evaluated by comparing measured and calculated groundwater levels. Results show that the runs with the extended SWATRE model (Standard Error of estimate 4.32-10.9 cm) are considerably better than runs with the standard SWATRE model (Standard Error of estimate 17.6-33.2 cm). It is concluded that a modified quasi two-dimensional approach improves the simulation of water table fluctuations in wetlands.
Validation and Intercomparison of Different Updating Procedures for Real-Time Forecasting
Authors: Refsgaard Jens Christian
Published: May 2018

The paper presents a classification and a review of the updating procedures currently used in real-time flood forecasting modelling. On the basis of results from the WMO project ‘Simulated Real-Time Intercomparion of Hydrological Models’, comprising more than 10 commonly used hydrological models and a variety of different updating procedures, an analysis of the relative importance of updating procedures and hydrological simulation models is provided. In particular, an intercomparison is made beteween two models (NAMS11/MIKE11 and NAMKAL) consisting of the same hydrological model (NAM conceptual rainfall-runoff) but containing different routing modules (linear reservoirs versus hydraulic routing) and different updating procedures (error prediction versus state variable updating based on an extended Kalman filter). A main conclusion is that updating procedures significantly improve the performances of hydrological models for short-range forecasting. Furthermore, there are no clear conclusions regarding which type of updating procedure performs the better. However. intercomparison of the NAMS11 and NAMKAL models indicates that the extended Kalman filter is marginally better than an error prediction model in cases where the basic hydrological model simulation is good. Finally, it is concluded that the basic simulation is very essential for accurate forecasts, and that the better the basic simulations are the better the updating routines in general function. This puts emphasis on the importance of thoroughly calibrating and validating the hydrological simulation models before applying them together with updating routines in operational real-time forecasting.
Investigating Catchment Hydrology and Low Flow Characteristics using GIS
Authors: Skop Eli , Loaiciga Hugo A.
Published: May 2018

The most frequent use of Geographic Information Systems (GIS) in hydrology has been in input/output data handling for modeling purposes, as well as in the derivation of flow direction, flow length and slope maps from Digital Elevation Models (DEMs). In turn, these maps have been merged with other maps, such as soils, land use, and vegetation maps to obtain flow velocities, isochrones, and Hydrologic Response Units (HRUs). This study presents examples of GIS applications to 1) create a depression-less DEM from contour lines of terrain elevation 2) interpolate groundwater heads based on head measurements at geo-referenced points, 3) derive topographic catchments based on the DEM and derive groundwater contributing areas to given surface points based on interpolated head values, and 4) estimate streamflow characteristics based on topographic catchments, groundwater contributing areas, and soil maps. Our results indicate the usefulness of GIS applications in spatial hydrologic analysis, interpolation, and prediction.
Arctic Snow Cover Information for Hydrological Investigations at Various Scales
Authors: Woo Ming-ko
Published: May 2018

Routine snow survey and snow gauge data provided by weather stations establish snow-on-the-ground and snowfall time series but they lack a spatial dimension. Of particular importance to arctic hydrology is the end-of-winter snow conditions. For micro-scale investigations of spring breakup, slope runoff generation or gully sediment production, detailed mapping of the late winter snow cover is required. On a meso-scale, terrain exerts the principal control on snow distribution so that for catchment snowmelt and water balance studies, terrain units should be distinguished and the snow water equivalent for various terrain types obtained through ground survey. Regional dispositon of the snowline or early melt zones can be mapped from satellite but ground truthing is necessary if the quantity of snow needs to be known. Passive microwave sensor offers the potential of mapping the snow water equivalent after the signals are calibrated by ground snow data. Spatially distributed but areally integrated rather than point snow data are appropriate for macro-scale hydrological investigations. Field studies carried out in the Canadian Arctic Islands over the past decades provide the database and the experience needed to recommend appropriate methods for acquiring snow cover information compatible with the scale and the subject of enquiry.
FEM-Modelling of Open Stormwater Detention Ponds
Authors: Pettersson Thomas J. R.
Published: May 2018

Stormwater in urban areas is polluted with suspended materials which transport heavy metals and degrade the quality of the receiving waters. Since open detention ponds improve water quality, an investigation of a constructed pilot-scale detention pond was carried out. Measurements of inflow and outflow were performed and two flow-weighted samplers were used to collect representative samples of suspended solids and heavy metals. The particle size distribution was analysed to allow an estimation of the settling of suspended solids. Particle removal from a rain event was defined as two different phases where the first phase occurs during the rain event and the second phase after the event. In this paper only the first phase is considered. A FEM-software package (FIDAP) was used to calculate the three dimensional velocity flow field for one rain event. A sedimentation approach was applied to the flow field where paths were calculated through the detention pond for different particle sizes. The results from four different particle sizes show satisfactory agreement between FEM-calculated and observed particle removal. The results show that FIDAP is a useful tool to predict pollutant removal for open detention ponds with arbitrary geometry.
Fracture Distribution and Occurrence of DNAPL in a Clayey Lodgement Till
Authors: Jakobsen Peter Roll , Klint Knud Erik S.
Published: May 2018

This study examines the spatial fracture network in a clayey lodgement till, and the preferential flow pattern of DNAPL in the till. The study was conducted on a former gasworks site contaminated with coal tar. Fracture analysis was carried out and four fracture systems were recognised. Apart from fractures, burrows and root channels were recorded in the near surface sediments. Field investigation shows that two fracture systems were formed subglacially by loading of a glacier and horizontal shear within the lodgement till. Two other fracture systems were formed subsequently by desiccation and unloading/freeze-thaw processes in the unsaturated zone. Spatial distribution of free-phase DNAPL in the lodgement till is controled by the fracture network. The migration path of the DNAPL through the fracture systems is predominantly vertical in the upper 2 m and horizontal between 2 and 3.5 m. b.s. Below this depth the migration pathway is vertical. DNAPL was visually observed to a depth of 9 m.b.s. within fractures which continued downwards to unknown depth. Upscaling of the fracture properties was performed and a regional fracture model is suggested as a tool in future remidiation.
Determination of Anisotropy of Tills by Means of Azimuthal Resistivity and Conductivity Measurements
Authors: Penttinen Sari , Sutinen Raimo , Hänninen Pekka
Published: May 2018

Anisotropy of glacial tills in Lapland revealed with azimuthal galvanic (Terrameter 300 C) resistivity and inductive (Geonics EM-31) electrical conductivity measurements, which were carried out at four test sites. It was found that the azimuthal electrical conductivity parallelled with the preferred orientation of the till fabric at the top of the soil sequences. The present results indicate that azimuthal resistivity and conductivity are depositional in origon and are attributed to the former ice flow directions. Different coil orientations gave information from different depths and resistivity and conductivity anisotropy varied along with depth.
Impulse Radar Snow Surveys – Influence of Snow Density
Authors: Lundberg A. , Thunehed H. , Bergström J.
Published: May 2018

Snow cover water equivalent (SWE) is of major importance for planning of e.g. hydropower production in areas where a large proportion of the annual precipitation falls as snow. Radar technique can be used to determine SWE from the two-way travel time (twt) of a radar-wave propagation through a snowpack. SWE is usually related to twt through an empirical relationship, SWE = −b + atwt, where the values of a and b are determined by linear regression from simultaneous measurements of SWE (with snow-courses) and twt (with radar technology). In this paper a theoretical relationship between twt and SWE is developed showing the need for introducing the density when relating twt to SWE. Use of different empirical relationships for the real dielectric constant showed that the a-value for dry snow with a density of 350 kg m−3 (a typical value at the end of the accumulation season in the Nordic countries) is 0.040 m ns−1 (twt given in nanoseconds). When the snow density deviates considerably from this value a corrected a-value has to be used. A density of 300 and 400 kg m−3 gives a =0.036 and 0.045 m ns−1 respectively. The b-value should theoretically be zero for measurements at the snow surface, non-zero values are probably due to the use of the direct wave between transmitter and receiver antennas as reference. The theoretically derived equations were confirmed by laboratory and field measurements as well as by measurements taken from literature.
Numerical Modelling of Circulation in Lake Sperillen, Norway
Authors: Olsen N. R. B. , Lysne D. K.
Published: May 2018

A three-dimensional numerical model was used to model water circulation and spatial variation of temperature in Lake Sperillen in Norway. A winter situation was simulated, with thermal stratification and ice cover. The numerical model solved the Navier-Stokes equations on a 3D unstructured non-orthogonal grid with hexahedral cells. The SIMPLE method was used for the pressure coupling and the k-ε model was used to model turbulence, with a modification for density stratification due to the vertical temperature profile. The results were compared with field measurements of the temperature in the lake, indicating the location of the water current. Reasonably good agreement was found.
The Wind Influence on the Jutland Coastal Current Interpreted on the Basis of som Observations
Authors: Jakobsen Flemming
Published: May 2018

The Jutland Coastal Current (JCC) is a freshwater-influenced coastal current localised in the south-eastern part of the North Sea. Its main sources are the Elbe, the Weser, and the Ems, which run into the German Bight, as well as smaller rivers along the Danish west coast. Tides, buoyancy and wind mainly determine the flow field in the Jutland Coastal Current. The Ekman transport in the North Sea far away from land feeds the coastal current along the Jutland coastline within approximately one Rossby radius of the coastline. In this study the influence of the wind on the Jutland Coastal Current (JCC) is investigated on the basis of measurements of wind, salinity, nitrate and current. The wind determines the spatial extent of the current and only during south-southwesterly winds does the JCC flow into the Skagerrak. The major river discharge into the German Bight in 1995 was followed by a decrease in the salinity outside Hirtshals after only 21-45 days in connection with changing southerly and westerly winds. On the 50-hour time-scale the wind determines the gross and residual transport in the JCC as expected from the Ekman transport, together with minor contributions from the buoyancy and tide. The spatial nitrate distributions clearly indicate an inter-annual variation in the nitrate concentrations and thus influence the transport of nitrate.
The Effect of Riverine Nitrate Loads on Winter Concentrations in the Great Belt, Denmark
Authors: Jürgensen Carsten , Tornbjerg Niels Henrik
Published: May 2018

This paper presents a method that models the fraction of the NOx concentrations (nitrate and nitrite) in a marine recipient resulting from riverine runoff from land. The analysis is performed on the surface waters in the Great Belt, Denmark, during winter seasons. The method is based on simulation of two independent NOx fractions: First, the “background” fraction, which results from the oceanographic mixing in the Belt Sea between Kattegat water and Baltic Sea water, and second, the nutrient load from land. The calculation of the background fraction is based on the finding that the Kattegat water has high salinity and high NOx contents whereas the Baltic Sea water has low salinity and low NOx contents. By means of an empirical relation between salinity and NOx a specific salinity measurement in the mixing zone can be related to a “background” NOx concentration. Measurements in the Great Belt show to be higher than the calculated “background” concentrations, which indicates the presence of a second NOx fraction. The second fraction is defined as the difference between the calculated background concentration and the measured NOx concentration. The hypothesis of the present paper is that this second fraction is dominated by the river runoff. Cross correlation analysis between the time series of the river NOx load and the time series of surplus concentration in the Great Belt reveals a time lag between maximum river load and maximum surplus concentration during winter seasons of approx. 1 month. An empirical transfer function has been developed in order to connect the daily NOx river loads with the surplus concentration in the Great Belt. The development of the NOx-concentration in the Great Belt due to river run off is modelled for 8 specific winter periods of 3 months (December - February) between 1988/1989 and 1995/1996.

The model simulates concentrations on a weekly basis and quantifies the NOx-increase during each winter based on the river load data. The analysis indicates that the NOx concentration can be doubled during winters with high runoff, giving rise to an increase of approx. 60 μgN/1 at the end of February. In winters with minimal runoff no significant increase above the background level is found.
Hydrological Response of a Patchy High Arctic Wetland
Authors: Young Kathy L. , Woo Ming-ko
Published: May 2018

High Arctic patchy wetlands are ecological oases in a polar desert environment and are vulnerable to climatic warming. At present, understanding of their responses to external factors (climate and terrain) is limited. This study examines a wetland located in a topographic depression maintained by seasonal snowmelt, ground ice melt and lateral inflows. The wetland is located on Cornwallis Island, Nunavut, Canada. Hydrological, climatological and soil observations were made over several summers with different weather conditions. The summers of 1996 and 1997 were cool and wet but the summer of 1998 was warm and dry. The melt in 1996 was rapid due to rain on snow events and only lasted six days. Deeper snow in 1997 prolonged the melt season to 18 days. A shallow snow-cover in 1998 and early melt depleted the snow by early June. Surface, groundwater and storage fluctuations in the wetland were dictated by snowmelt, rainfall, evaporation loss from the wetland and lateral inputs which in turn were controlled by the melting of the late-lying snow storage in the catchment. Soil factors influence the spatial variations in ground thaw which affects the surface and subsurface flow. Streamflow response of the wetland reflects a nival regime and augmentation of streamflow thoughout the summer season in all three years is supported by multiple water sources: ground ice melt and suprapermafrost water from a large late-lying snowpack. Overall, this study suggests that the survival of some patchy wetlands depends on their interaction with the surrounding basin, with a dependency probably being more important during warm and dry seasons.
Nitrogen Concentrations Simulated with HBV-N: New Response Function and Calibration Strategy
Authors: Pettersson Anna , Arheimer Berit , Johansson Barbro
Published: May 2018

HBV-N is a conceptual process-based model for simulation of transformation and transport of nitrogen on the catchment scale. This paper presents further development with focus on the response function and calibration procedures. Evaluation of the model routines was made in 12 test basins in southern Sweden (without or with only few lakes). Previous versions of HBV-N included a HBV version with a single reservoir in the response function. The presented results show that both nitrogen concentrations and water discharge simulations improved when a second reservoir was introduced. The two-reservoir model was found to be more well-posed for description of residence-times and flow paths. On average, this resulted in an increase in explained variance (R2) for nitrogen concentrations by 0.3.

Multiple-responee split-sample calibration was found to further improve the model performance and reliability. In previous applications HBV-N has been applied by using single-response calibration. However, simultaneous calibration of water discharge and nitrogen improved the R2 for nitrogen concentrations by about 0.1 (range 0.02-0.25), but did not affect the simulation of water discharge. This new calibration strategy forces the hydrological parameters to a new optimum, and reduces the level of uncertainty for both hydrochemical and hydrological modelling.
Inter-Comparison of two Snow Models with Different Complexity using Data from an Alpine Site
Authors: Strasser U. , Etchevers P. , Lejeune Y.
Published: May 2018

This contribution describes the modelization of the snow cover evolution with the two physically based snow models CROCUS and ESCIMO at the Col de Porte station (1,325 m a.s.l., French Alps) for the three subsequent seasons 1994/95–1996/97. CROCUS is a detailed, multi-layer snow model developed for the operational avalanche forecasting system of METEO France, whereas ESCIMO is a one-layer energy and mass balance snow model for hydrological applications. The snow albedo function parameters for ESCIMO are calibrated in 1994/95. In the first verification season (1995/96), the results of the two models show a good correspondence, whereas in the second (1996/97) they differ significantly. For this season a considerable gain in performance of ESCIMO is achieved by recalibration of the snow albedo function parameters.
Runoff Generating Processes in Boreal Forest Environments with Glacial Tills
Authors: Beldring Stein
Published: May 2018

This review describes the processes by which runoff is generated from rain or snowmelt in a boreal forest landscape with a shallow layer of glacial tills overlying a relatively impermeable bedrock. Glacial tills are the main surface deposits in the Nordic countries, and are also of frequent occurrence in other boreal forest environments in the Northern Hemisphere. Soil moisture and groundwater conditions control the partitioning of rain or snowmelt into evapotranspiration, runoff and temporary storage. Groundwater is viewed as the major determinant of runoff generation, both because it is the most important contributor to event flow, and because of its influence on saturation overland flow. A characteristic feature of till deposits is a saturated hydraulic conductivity which decreases rapidly with depth. As a consequence, topography has a significant impact on runoff by controlling movement and storage of water through convergence and divergence of flow. Modeling and field experience point to the idea of a continuum in both spatial and temporal occurrence of saturation overland flow and subsurface flow within individual catchments under different rainfall and snowmelt events and antecedent groundwater and soil moisture conditions. Results from studies using hydrological models with a structure which may be suitable for landscapes with glacial tills are presented.
A Review of Modeling Approaches to Simulate Saline-Upconing under Skimming Wells
Authors: Saeed Muhammad Mazhar , Bruen M. , Asghar M.N.
Published: May 2018

The occurrence of saline water along with fresh water in inland aquifers is due to different reasons. The extraction of fresh water from these aquifers is severely hampered by the underlying saline water. The saline water may rise in the form of a cone under the well bottom if the design and operational parameters for skimming well are not selected carefully. Physically, it is difficult to play with different design and operational scenarios due to economic and time constraints. Analytical and numerical models can help solve this problem. The paper reviews different models to simulate the saline-upconing under different pumping regimes. These models are categorized based on the assumptions of sharp interface and transition zone.
Effect of Potential Warming on Evapotranspiration from Forest Catchments in Karelia
Authors: Karpechko Yury V. , Bondarik Natalia L.
Published: May 2018

The amount of evapotranspiration from a woodland largely depends on the site and stand productivity. The factor largely responsible for the stand productivity (productivity class) of an individual forest type under the climatic conditions of northwest Russia is temperature. If mean annual air temperature rises by 1°C and 2°C the average productivity of a coniferous stand in Karelia will increase by 0.3-0.4 and 0.6-0.8 of the productivity class, respectively. The average estimated increment of annual evapotranspiration from a forest in a sufficiently large catchment area will not exceed 15-20 mm even if the warming up is 2°C.
Seasonal Water Balance of an Alpine Catchment as Evaluated by Different Methods for Spatially Distributed Snowmelt Modelling
Authors: Zappa M. , Pos F. , Strasser U. , Warmerdam P. , Gurtz J.
Published: May 2018

The application of three temperature-index based models and of one energy balance based snowmelt model was investigated. The snow models were integrated in the spatially distributed hydrological model PREVAH. In this study the hydrological simulations of the alpine catchment of the Dischmabach in Switzerland in the period 1982-2000 have been analyzed. The PREVAH model was driven by hourly interpolated meteorological data.

All snowmelt approaches allowed a good simulation of the discharge regime and of the seasonal course of the snowpack. The highest model efficiency was obtained by a radiation based temperature-index approach. A simplified energy balance approach combined with the positive degree-day method showed a very similar performance to the classical positive degree-day approach. The energy balance approach ESCIMO showed a high performance variability from year to year.

The dependency of the seasonal water balance with respect to altitude is also discussed in this report. The quality of the spatially distributed reproduction of periods with positive and negative water balance (snow accumulation and snowmelt) is crucial for the correct simulation of the runoff hydrograph. The analysis shows that runoff maximum in the Dischmabach catchment is caused by a superposition of the main snowmelt season in the areas between 2,100-2,800 m a.s.l. and the period with maximum rainfall.
Estimation of Monthly River Discharge from Danish Catchments
Authors: Müller-Wohlfeil Dirk-I. , Xu Chong-Yu , Iversen Hans Legard
Published: May 2018

To simulate the nutrient loading of Danish coastal waters, river discharge from unmonitored areas must be assessed. In an attempt to identify the most suitable method, for this purpose eight different versions of the three-parameter monthly water balance model “MWB-3” were tested on data from various Danish catchments for the period 1989-97. The model with the highest R2 and the lowest correlation between the model parameters was chosen for subsequent establishment of regression equations between the model parameters and catchment and climate characteristics. The most important explanatory variables of the regressions are soil properties, potential evapotranspiration, groundwater table depth, percentage of wetland area and catchment slope. Mean R2 was 0.82 for the calibration data subset (62 catchments) and 0.79 for the test data subset (22 catchments). Sensitivity tests indicate that the selected model version is more robust for application in catchments dominated by loamy soils than in catchments dominated by sandy soils. Though the MWB-3 model provides a good basis for determining the water balance of Danish catchments at the regional and national levels, modifications and extensions need to be considered for future studies.
Fuzzy awakening in rainfall-runoff modeling
Authors: Şen Zekai , Altunkaynak Abdüsselam
Published: May 2018

Rainfall-runoff relationships are widely used in many engineering hydrologic designs in urban and rural areas. Such relationships are obtained through the application of regression analysis in many studies. Unfortunately, in the classical regression approach to determine rainfall-runoff relationships, internal uncertainties are not taken explicitly into consideration. In this paper, an alternative to the classical regression approach is proposed through fuzzy system modeling. It is concluded that the fuzzy systems approach yields comparatively less relative error than a regression approach and, therefore, it is recommended for use in future. The application is presented for rainfall-runoff records at two sites near Istanbul, Turkey.
Lithuanian karst region rivers' water ecology: hydrochemical and hydrobiological evaluation
Authors: Tumas Rimvydas
Published: May 2018

The Lithuanian karst region covers about 1000 km3 in the northern part of the country. This is the most vulnerable area from a pollution point of view. The structure of the total dissolved solids (TDS) shows that the flow of rivers in the karst region is from hydraulically interconnected aquifers. For the last decade (1991–2000) TDS has varied considerably, from 529 to 732 mg/l. The predominant sources of nitrogen and phosphorus within the headwaters of the monitored rivers were diffuse and agricultural in nature. Downstream from the towns nitrogen and especially phosphorus showed both diffuse and point source signals. Contributions of point sources to the stream pollution by nutrients prevail.

The time series of monthly dissolved oxygen (O2) in the main karst region river – the Musa – shows the existence of multiplicative seasonality. The trend cycle (1991–1999) shows low levels of dissolved oxygen in 1991–1993, with a similar fluctuation in 1994, 1995 and 1996 (due to point pollution from the town of Siauliai) and a gradually improving situation since 1997. The general multiplicative trend of dissolved oxygen in the lower reaches of the Musa river (near the border with Latvia) is decreasing (within the accuracy limits).

The abundance and species of zoo benthos are suitable criteria (biotic index – BI) for evaluation of a river's biological water quality. Zoo benthos demonstrates tolerances that vary among species, the oxygen regime and the pollution with nitrogen. The best living conditions for invertebrates are in the riverhead of the karst region rivers – BI=5.62–6.74 (1991–1999), where pollution with nutrients is caused mostly by agricultural activity. Rare and asynchronous data of biological water quality shows up tendencies that invertebrates prefer less contaminated reaches of rivers.
Seasonal trends in the stable isotopic composition of snow and meltwater runoff in a subarctic catchment at Okstindan, Norway
Authors: Gurney S.D. , Lawrence D.S.L.
Published: May 2018

Seasonal variations in the stable isotopic composition of snow and meltwater were investigated in a sub-arctic, mountainous, but non-glacial, catchment at Okstindan in northern Norway based on analyses of δ18O and δD. Samples were collected during four field periods (August 1998; April 1999; June 1999 and August 1999) at three sites lying on an altitudinal transect (740–970 m a.s.l.). Snowpack data display an increase in the mean values of δ18O (increasing from a mean value of −13.51 to −11.49‰ between April and August), as well as a decrease in variability through the melt period. Comparison with a regional meteoric water line indicates that the slope of the δ18O–δD line for the snowpacks decreases over the same period, dropping from 7.49 to approximately 6.2.This change points to the role of evaporation in snowpack ablation and is confirmed by the vertical profile of deuterium excess. Snowpack seepage data, although limited, also suggest reduced values of δD, as might be associated with local evaporation during meltwater generation. In general, meltwaters were depleted in δ18O relative to the source snowpack at the peak of the melt (June), but later in the year (August) the difference between the two was not statistically significant. The diurnal pattern of isotopic composition indicates that the most depleted meltwaters coincide with the peak in temperature and, hence, meltwater production.
Density effects on salt tracer breakthrough curves from constructed wetland ponds
Authors: Schmid Bernhard H. , Hengl Michael A. , Stephan Ursula
Published: May 2018

Salt tracer experiments are a convenient method to determine travel time distributions in constructed wetland ponds. Typically, these flows are characterized by low Reynolds numbers at times even within the laminar flow regime. In this environment the injection of salt may cause strong density effects, thereby jeopardizing the usefulness of the recorded breakthrough curves. After a tracer experiment has been completed, an indication of potential density stratification in the field may be noticed in the form of surprisingly small recovery rates of a tracer considered as nearly conservative. To provide a tool that permits the intended experiment to be judged at the planning stage already, criteria have been developed that yield approximate maximum concentrations, not to be exceeded if density effects shall be avoided. Laboratory experiments were carried out and the newly derived relationships applied with success. The criteria may in future be useful, too, in the planning of tracer experiments in slowly flowing rivers and streams.
Year-to-year variability of solute flux in meltwaters draining from a highly-glacierised basin
Authors: Collins David N. , MacDonald Oliver G.
Published: May 2018

Electrical conductivity was monitored continuously in the Gornera, which drains the 83% glacierised basin of area 82 km2 containing Gornergletscher, Pennine Alps, Switzerland, during the summer months, in order to provide an indication of meltwater solute content during each of the four years 1979, 1983, 1987 and 1998. Discharge was also recorded between 1970 and 1999. Solute flux, calculated as the product of electrical conductivity and discharge, was used to assess how the year-to-year variability of discharge influences solute transport. Total May through September discharge of the Gornera was in the range −39.1% (1978) to +38.9% (1994) of the 1970–1999 period mean of 118.75×106 m3. The range of variability of July through September electrical conductivity was between −25.0% and +29.1% of the mean of 19.6 μS cm−1 for the four study years. The intra-annual range of total July through September solute flux in the Gornera extended from −22.4% (in 1987, during which, of the four years, discharge for the three months was greatest) to +12.4% (in 1979, when discharge was the lowest) of the four study year means, which represents an average cationic load of ∼25×106 eq. Variability of total solute flux (cv=0.142) was greater than that of total discharge (cv=0.127) in the three month period over the four years. Considerable intra-annual variability of total discharge over the three decades suggests that the total annual solute flux also fluctuated significantly from year to year.
Flow prediction by three back propagation techniques using k-fold partitioning of neural network training data
Authors: Cigizoglu H. Kerem , Kişi Özgür
Published: May 2018

Flow forecasting performance by artificial neural networks (ANNs) is generally considered to be dependent on the data length. In this study k-fold partitioning, a statistical method, was employed in the ANN training stage. The method was found useful in the case of using the conventional feed-forward back propagation algorithm. It was shown that with a data period much shorter than the whole training duration similar flow prediction performance could be obtained. Prediction performance and convergence velocity comparison between three different back propagation algorithms, Levenberg–Marquardt, conjugate gradient and gradient descent was the next concern of the study and the Levenberg–Marquardt technique was found advantageous thanks to its shorter training duration and more satisfactory performance criteria.
Variation in water level under ice-jammed condition – field investigation and experimental study
Authors: Sui Jueyi , Karney Bryan W. , Fang Daxian
Published: May 2018

This paper presents the impacts of frazil ice jams on the variation in water level at the Hequ Reach of the Yellow River in China. Based on both field observations and experimental studies, it is found that both the evolution of frazil ice jams and the associated variation in water level depend upon an interesting interaction between hydraulic variables during the ice-jammed period. In particular, the critical Froude number governing the formation of river ice jams and their upstream propagation is about 0.09. The water level during ice-jammed periods depends not only on the slope of the water surface and the water level under open-water conditions with the same discharge, but also on the length of the ice jam and the ice concentration in the water. Moreover, the field investigations show that the thickness of river ice strongly influences the variation in water level during ice-jammed periods. Empirical relationships are derived to quantify the relationship between the highest water level during ice periods and related physical parameters. To confirm the field results, and to explore the influence of ice discharge on the variation in water level, experimental studies were also conducted. These results confirm that the ice concentration plays a key role in the variation in water level and the jam thickness. Given the complexity of the jamming processes, surprisingly good agreement is observed between field and experimental investigations.
Spatial distribution of near surface soil moisture and its relationship to microtopography in the Alaskan Arctic coastal plain
Authors: Engstrom R. , Hope A. , Kwon H. , Stow D. , Zamolodchikov D.
Published: May 2018

The Arctic coastal plain of Alaska is characterized by marked heterogeneity in microtopography and above ground vegetation productivity at a variety of scales. This heterogeneity may be expected to lead to large variations in near surface soil moisture and have a substantial impact on measured and modeled fluxes of carbon and water. In this study, we hypothesized that microtopography was the primary control over the spatial patterns of near surface soil moisture. Near surface soil moisture measurements were collected in the summers of 2000, 2001, 2002 and 2003 in the fetch of an eddy flux tower (0.5 km2). Results confirmed the expected relationship between intra- and inter-seasonal variations in near surface soil moisture and variations in precipitation. However, over two time periods, near surface soil moisture increased without corresponding measured precipitation inputs and this was attributed to fog and dew, which are difficult to measure, and/or the melting of the active layer. Spatial variations in near surface soil moisture are largely controlled by microtopography in areas characterized by high centered polygons and troughs. In areas without large variations in microtopography, macrotopography, in the form of drained thaw lakes, has a substantial control over near surface soil moisture.
Uncertainty in flood discharges from urban and small rural catchments due to inaccurate head measurement
Authors: Petersen-Øverleir A. , Reitan T.
Published: May 2018

Despite frequent use of estimated flood discharges from urban and small rural catchments, the assessment of uncertainty in instantaneous discharge due to inaccurate head measurements is generally not performed. The present work discusses the impact of inaccurate head measurement on observed instantaneous flood discharge. The sources and sizes of uncertainties in head determination are discussed. A simple uncertainty model is developed in order to quantify the uncertainty in error-corrupted instantaneous and mean discharge. It is shown that uncertainty in mean discharge is less affected by uncorrelated head measurement error, while instantaneous discharges are substantially affected. Practical modelling using data from a Norwegian urban gauging station is undertaken. It is shown that the estimated annual maximum instantaneous flood discharge from this watershed has 95% confidence limits with sizes of 17–19% of the estimated discharge for average head measurement accuracy. Furthermore, it is shown that variability in head determination causes only a minor potential for bias in estimated instantaneous flood population statistics and quantiles.
Artificial neural networks for estimating daily total suspended sediment in natural streams
Authors: Tayfur Gokmen , Guldal Veysel
Published: May 2018

Estimates of sediment loads in natural streams are required for a wide spectrum of water resources engineering problems from optimal reservoir design to water quality in lakes. Suspended sediment constitutes 75–95% of the total load. The nonlinear problem of suspended sediment estimation requires a nonlinear model. An artificial neural network (ANN) model has been developed to predict daily total suspended sediment (TSS) in rivers. The model is constructed as a three-layer feedforward network using the back-propagation algorithm as a training tool. The model predicts TSS rates using precipitation (P) data as input. For network training and testing 240 sets of data sets were used. The model successfully predicted daily TSS loads using the present and past 4 days precipitation data in the input vector with R2=0.91 and MAE=34.22 mg/L. The performance of the model was also tested against the most recently developed non-linear black box model based upon two-dimensional unit sediment graph theory (2D-USGT). The comparison of results revealed that the ANN has a significantly better performance than the 2D-USGT. Investigation results revealed that the ANN model requires a period of more than 75 d of measured P-TSS data for training the model for satisfactory TSS estimation. The statistical parameter range (xmin−xmax) plays a major role for optimal partitioning of data into training and testing sets. Both sets should have comparable values for the range parameter.
Comparison of genotypic-based microbial source tracking methods requiring a host origin database
Authors: Myoda Samuel P. , Carson C. Andrew , Fuhrmann Jeffry J. , Hahm Byoung-Kwon , Hartel Peter G. , Yampara-Iquise Helen , Johnson LeeAnn , Kuntz Robin L. , Nakatsu Cindy H. , Sadowsky Michael J. , Samadpour Mansour
Published: May 2018

Microbial source tracking (MST) results, obtained using identical sample sets and pulsed field gel electrophoresis (PFGE), repetitive element PCR (rep-PCR) and ribotyping techniques were compared. These methods were performed by six investigators in analysis of duplicate, blind sets of water samples spiked with feces from five possible sources (sewage, human, dog, cow and seagull). Investigators were provided with samples of the fecal material used to inoculate the water samples for host origin database construction. All methods correctly identified the dominant source in the majority of the samples. Modifications of some of these methods correctly identified the dominant sources in over 90% of the samples; however, false positive rates were as high as 57%. The high false positive rates appeared to be indirectly proportional to the levels of stringency applied in pattern analysis. All the methods produced useful data but the results highlighted the need to modify and optimize these methods in order to minimize sources of error.
Use of viral pathogens and indicators to differentiate between human and non-human fecal contamination in a microbial source tracking comparison study
Authors: Noble Rachel T. , Allen Steven M. , Blackwood Angelia D. , Chu Weiping , Jiang Sunny C. , Lovelace Greg L. , Sobsey Mark D. , Stewart Jill R. , Wait Douglas A.
Published: May 2018

Assays for the detection and typing of adenoviruses, enteroviruses and F+ specific coliphages were performed on samples created as part of a national microbial source tracking methods comparison study. The samples were created blind to the researchers, and were inoculated with a variety of types of fecal contamination source (human, sewage, dog, seagull and cow) and mixtures of sources. Viral tracer and pathogen assays demonstrated a general ability to discriminate human from non-human fecal contamination. For example, samples inoculated with sewage were correctly identified as containing human fecal contamination because they contained human adenovirus or human enterovirus. In samples containing fecal material from individual humans, human pathogen analysis yielded negative results probably because the stool samples were taken from healthy individuals. False positive rates for the virus-based methods (0–8%) were among the lowest observed during the methods comparison study. It is suggested that virus-based source tracking methods are useful for identification of sewage contamination, and that these methods may also be useful as an indication of the public health risk associated with viral pathogens. Overall, virus-based source tracking methods are an important approach to include in the microbial source tracking ‘toolbox’.
Fluorides in groundwater, soil and infused black tea and the occurrence of dental fluorosis among school children of the Gaza Strip
Authors: Shomar B. , Müller G. , Yahya A. , Askar S. , Sansur R.
Published: May 2018

The purpose of this study was to determine the fluoride levels in water, soil and tea, and to identify the major fluoride minerals in soil that supply water with fluoride ions. Another aim was to study the prevalence of dental fluorosis in permanent dentition of the school children of the Gaza Strip. Monitoring of fluoride levels in 73 groundwater wells and 20 topsoil samples for the last three years revealed a general trend of increasing from north to south of the Gaza Strip. A linear regression analysis found a correlation coefficient of r=0.93 between the fluoride concentrations in groundwater and soil for the same geographic areas. However, the X-ray diffraction technique (XRD) results showed that none of the four major fluoride minerals were detected in the tested soil samples; the PHREEQC model showed that fluorite (CaF2) was the main donating mineral of fluoride ions to groundwater.A high positive correlation was found between fluoride concentrations in groundwater and occurrence of dental fluorosis. Among 353 school children of the five geographic areas of the Gaza Strip the prevalence of dental fluorosis was 60%, and 40% had no signs of fluorosis in their permanent dentitions. The highest occurrence, 94%, was in Khan Yunis, followed by 82% in Rafah, 68% in the middle area, 29% in Gaza and the lowest occurrence of 9% was in the northern area. These percentages were directly proportional to the average content of fluoride in groundwater of each area: 2.6, 0.9, 1.7, 1.2, and 0.7 ppm, respectively. The exception was Rafah where people drank from new groundwater wells that have been dug in the last 10 years.The occurrence of the disease was due to intake of high amounts of fluorides in drinking water, tea and fish. Communication with population indicated a heavy intake of tea starting from a very young age; not uncommonly tea is put in nursing bottles. No significant correlation was found between prevalence figures and gender or age groups. This high prevalence indicates a need to examine other sources of F including diet.