| 1. |
- Jonsson, K., et al.
(författare)
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Hyporheic exchange of reactive and conservative solutes in streams - tracer methodology and model interpretation
- 2003
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 278:04-jan, s. 153-171
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Tidskriftsartikel (refereegranskat)abstract
- A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (H-3 and Cr-51(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was similar to 85 times longer for chromium than for tritium (i.e. similar to 45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
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| 2. |
- Jonsson, Karin, et al.
(författare)
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Hyporheic Exchange of Reactive and Conservative Solutes in Streams - Tracer Methodology and Model Interpretation
- 2003
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Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 278:1-4, s. 153-171
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Tidskriftsartikel (refereegranskat)abstract
- A transient storage model is evaluated using results from a tracer experiment, where a conservative and a reactive tracer (3H and 51Cr(III)) were injected simultaneously and monitored in stream water and bed sediment. About 76% of the chromium was lost from the stream water on the reach 30 km downstream of the injection point directly after the passage of the pulse in the flowing water. The bed sediment hosted the main part of the retained chromium. The time to washout 75% of the maximum solute uptake in the sediment was ∼85 times longer for chromium than for tritium (i.e. ∼45 days). It was possible to describe the sediment-water exchange with a diffusive flux formulation that could be evaluated using tritium breakthrough curves in the stream water or the tritium inventory breakthrough curves in the sediment. This experiment revealed further that observations of chromium concentrations in the sediment were essential for the quantifying of sorption properties, as it was not possible to catch accurately the time scale of sorption within the duration of the breakthrough curves in the stream water. There was a clear need for a rate-limited description of the sorption of chromium in the sediment. We found that a first-order kinetic description of the sorption process could acceptably describe the breakthrough curves in both the stream water and the bed sediment.
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| 3. |
- Stålnacke, P., et al.
(författare)
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Trends in nutrient concentrations in Latvian rivers and the response to the dramatic change in agriculture
- 2003
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Ingår i: Journal of Hydrology. - 0022-1694 .- 1879-2707. ; 283:1-4, s. 184-205
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, the use of fertilisers in the Baltic countries (Estonia, Latvia, and Lithuania) has decreased at an unprecedented rate. The import of mineral fertilisers and feed stuff became almost non-existent, and extensive slaughtering of livestock reduced the amount of manure. In Latvia, the purchase of mineral fertilisers decreased by a factor of 15 between 1987 and 1996 and the number of livestock decreased with a factor of almost 4 during the same time period. Such abrupt and comprehensive changes in land use have never before occurred in the history of modern European agriculture. Here, the impact that this dramatic reduction has had on concentrations of nutrients in Latvian rivers is examined. To discern temporal changes, statistical analyses were undertaken on time series of nutrient concentrations and relationships between concentrations and runoff at 12 sampling sites in ten Latvian rivers covering drainage areas from 334 to 64,000 km2. Considering the study period 1987-1998, only four of the 12 sites showed statistically significant downward trends (one-sided test at the 5% level) in the dissolved inorganic nitrogen (DIN = NO3-N + NO2-N + NH4-N) data. There are probably two main explanations for the weak DIN trends. Firstly, long water-transit times in the soilwater and groundwater may have caused substantial time lag between changes in input and output of nitrate in the studied catchments. Secondly, the loss of DIN might have been dominated by mineralisation of large pools of organic nitrogen that have accumulated over several years. These inferences are supported by (i) a hydrograph recession analysis and (ii) indications of DIN transformation processes, presumably denitrification, in smaller streams and channels, based on measurements in small agricultural catchments (1-4 km2) in Estonia and Latvia. Formal testing of trends in phosphorus data revealed that marked drops occurred in riverine concentrations at six sites in 1987-1998. A joint analysis of concentration time series for all sampling sites for 1987-1998 showed weak statistical significance for downward trends in NH4-N, NO 3-N, and DIN (p ? 0.04) and substantial significance for PO 4-P (p < 0.01). Thus, the extensive decrease in agricultural intensity that began in the early 1990s has led to only a slow and limited (especially regarding nitrogen) response in Latvian rivers. The difference noted between nitrogen and phosphorus also suggests that factors other than reduced fertiliser application influenced the inertia of the water quality response. Our findings, along with those obtained in similar studies, show that large cuts in nutrient inputs do not necessarily cause an immediate response, particularly in medium-sized and large catchment areas.
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| 4. |
- Laudon, Hjalmar, et al.
(författare)
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Episodic acidification in northern Sweden: a regional assessment of the anthropogenic component
- 2004
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 297:1-4, s. 162-173
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Tidskriftsartikel (refereegranskat)abstract
- Spring flood is the period in boreal ecosystems that is most sensitive to acid deposition since as much as half of the year's precipitation melts and enters streams or the soil in the space of a few weeks. The ‘Episode Project‘ in northern Sweden found a consistent relationship between the SO42− concentration of snow and the anthropogenic component of acid neutralization capacity (ANC) decline during spring flood. This correlation creates the possibility for a regional prediction of the severity of anthropogenic episodic acidification during spring flood episodes using SO42− deposition data together with chemical data from 1240 lakes selected to be representative of northern Sweden. The regional assessment found that in 1998, ca 6% of the region was seriously affected by anthropogenic acidification during spring flood. The results from this study have important implications for both the national liming strategy and international negotiations to further reduce emissions of air pollutants in Europe.
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| 5. |
- Persson, Magnus, et al.
(författare)
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Estimating soil solution electrical conductivity from time domain reflectometry measurements using neural networks
- 2003
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Ingår i: Journal of Hydrology. - 0022-1694. ; 273:1-4, s. 249-256
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Tidskriftsartikel (refereegranskat)abstract
- Time domain reflectometry (TDR) is a widely used method for measuring the dielectric constant (K-a) and bulk electrical conductivity (sigma(a)) in soils. The TDR measured sigma(a) and K-a can be used to calculate the soil solution electrical conductivity, sigma(w.) The sigma(w), in turn, can be related to the concentration of an ionic tracer. Several models of the sigma(w)-sigma(a)-K-a relationship can be found in the literature. Most of these models require extensive calibration experiments in order to obtaining best-fit parameters. In this paper, we attempt to model the sigma(w)-sigma(a)-K-a relationship using neural networks (NN). We used TDR measured K-a and sigma(a) along with five different soil physical parameters (sand, silt, clay, and organic matter content and bulk density) measured in nine different soil types using three different sigma(w) levels in each soil type. In total, 2953 K-a and sigma(a) measurements were obtained. The NN estimated sigma(w) was found to have a root mean square error (RMSE) of 0.05-0.13 dS m(-1) for the nine different soil types whereas the RMSE of two traditional sigma(w)-sigma(a)-K-a models was 0.12-0.87 dS m(-1). Furthermore, the traditional models exhibited larger errors for low sigma(a) and K-a, whereas the NN estimated sigma(w) did not show any trend in the errors. A sensitivity analysis showed that the NN model was more sensitive to small changes in sigma(a) compared to K-a. Of the five soil physical parameters, the silt and clay content affected the sigma(w)-sigma(a)-K-a relationship the most. The results presented shows that using NN, the sigma(w)-sigma(a)-K-a relationship can be predicted using soil physical parameters without need for elaborate soil specific calibration experiments. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 6. |
- Persson, Magnus, et al.
(författare)
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Modeling plot scale dye penetration by a diffusion limited aggregation (DLA) model
- 2001
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Ingår i: Journal of Hydrology. - 0022-1694. ; 250:1-4, s. 98-105
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Tidskriftsartikel (refereegranskat)abstract
- Solute transport in the unsaturated zone often occurs in preferential How paths. There are several reasons for this, e.g., water repellency, the occurrence of fissures and cracks, animal borrows, decomposed root threads etc. The resulting How patterns often display a fractal resemblance which is difficult to predict using conventional transport models. A way to preserve the fractal property of observed data is to use the diffusion limited aggregation (DLA) model concept. In the present paper we use dye infiltration data to further develop the DLA model concept as applied to solute movement in soils. The DLA model is first calibrated against detailed field observations of dye infiltration. The model is shown to give a good description of observed mean and variance of dye penetration. After this, the calibrated model is verified against independent data from a nearby plot. The model is shown to reproduce observed dye patterns in a satisfactory way also at the verification plot.
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| 7. |
- Sander, Mikkel, et al.
(författare)
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The relationship between annual varve thickness and maximum annual discharge (1909-1971)
- 2002
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Ingår i: Journal of Hydrology. - 0022-1694. ; 263:1-4, s. 23-35
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Tidskriftsartikel (refereegranskat)abstract
- Annually laminated (varved) sediments from the River Angermanalven, mid-central Sweden, have been used to construct an annual 2000-year long record of varve thickness. Maximum daily annual discharge and mean varve thickness for the years 1909-1971 are significantly correlated (r = 0.87). A relationship between maximum daily annual discharge for the observed period (1909-1971) and varve thickness was determined. The return time of two exceptionally thick varves in the 2000-year long record at the years 658 and 492 AD were estimated and their likelihood estimated based on a Gumbel frequency analysis. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 8. |
- Öhrström, Pernilla, et al.
(författare)
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Field-scale variation of preferential flow as indicated from dye coverage
- 2002
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Ingår i: Journal of Hydrology. - 0022-1694. ; 257:1-4, s. 164-173
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Tidskriftsartikel (refereegranskat)abstract
- Field investigations were performed in semiarid Tunisia to investigate spatial variability of preferential pathways in catchment- and plot-scales. A rainfall simulator with dye was used to simulate effects of a 20-year rainstorm. After infiltration into six one-meter square plots, vertical 2.5-cm thick soil sections were excavated, and dye penetrations were photographed, The results show that different catchment physiographic areas (nose, slope, and hollow) displayed significantly different responses to the infiltrating dye. Nose and hollow areas exhibited larger susceptibility to preferential flow. Here. infiltrated dye was transported to greater depths. Slopes had fewer deep cracks and fissures. The dye distribution within each plot was also investigated. The variability of the dye patterns increased with scale. Cross-correlations and power spectrum analyses indicated that the preferential pathways were randomly distributed. The power-law behavior of the dye patterns' spectral density suggested scale invariance and the possibility of random cascade modeling. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 9. |
- Nasri, S, et al.
(författare)
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Use of a geomorphological transfer function to model design floods in small hillside catchments in semiarid Tunisia
- 2004
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 287:1-4, s. 197-213
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Tidskriftsartikel (refereegranskat)abstract
- In the beginning of the 1990s, the Tunisian Ministry of Agriculture launched an ambitious program for constructing small hillside reservoirs in the northern and-central region of the country. At present, more than 720 reservoirs have been created. They consist of small compacted earth dams supplied with a, horizontal overflow weir. Due to lack of hydrological data and the area's extreme floods, however, it is very difficult to design the overflow weirs. Also, catchments are very sensitive to erosion and the reservoirs are rapidly silted up. Consequently, prediction of flood volumes for important rainfall events becomes crucial. Few hydrological observations, however, exist for the catchment areas. For this purpose a geomorphological model methodology is presented to predict shape and volume of hydrographs for important floods. This model is built around a production function that defines the net storm rainfall (portion of rainfall during a storm which reaches a stream channel as direct runoff) from the total rainfall (observed rainfall in the catchment) and a transfer function based on the most complete possible definition of the surface drainage system. Observed rainfall during 5-min time steps was used in the model. The model runoff generation is based on surface drainage characteristics which can be easily extracted from maps. The model was applied to two representative experimental catchments in central Tunisia. The conceptual rainfall-runoff model based on surface topography and drainage. network was seen to reproduce observed runoff satisfactory. The calibrated model was used to estimate runoff from 5, 10, 20, and 50 year rainfall return periods regarding runoff volume, maximum runoff, as well as the general shape of the runoff hydrograph. Practical conclusions to design hill reservoirs and to extrapolate results using this model methodology for ungauged small catchments in semiarid Tunisia are made. (C) 2004 Elsevier B.V. All rights reserved.
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| 10. |
- Öhrström, Pernilla, et al.
(författare)
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Characterizing unsaturated solute transport by simultaneous use of dye and bromide
- 2004
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 289:1-4, s. 23-35
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Tidskriftsartikel (refereegranskat)abstract
- Variability in solute transport properties in the unsaturated zone is of growing concern due to environmental hazards. By combining dye and salt tracers, a detailed description of the solute transport can be made in both time and space. In this paper, qualitative and quantitative effects of preferential flow were investigated in a sandy loam. The experimental site was equipped with 64 TDR probes. The plot was irrigated with pure water for 12 days to achieve steady state conditions. Then the plot was irrigated with a solution containing a dye tracer and KBr over three days. During the experiment, bromide concentration and soil moisture were measured hourly by the TDR probes. On the day following the last day of irrigation, a trench was dug and 14 vertical slices were excavated and photographed. A Sigma Probe (SP) was used to investigate the bromide concentration in an individual finger. The SP is a new dielectric measuring technique that gives readings of soil solution electrical conductivity. The dye photographs provided visualization of finger flow. Horizontal flow was evident in the E horizon at 0.3-0.4 m depth. Also the bromide concentration was elevated at these depths. The occurrences of high bromide as measured by the SP concentration corresponded fairly well to the dye patterns. The visible lower limit of dye stained soil corresponded to a bromide concentration of 0.10. A comparison between the bromide and dye penetration showed that the retardation factor of the dye as compared to bromide was 1.5. This is within the range reported by other authors and shows that the SP can be a useful tool to investigate the retardation of dyes as compared to bromide. (C) 2003 Elsevier B.V. All rights reserved.
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