| 1. |
- Bouksila, Fethi, et al.
(författare)
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Estimating soil salinity over a shallow saline water table in semiarid Tunisia
- 2010
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Ingår i: Open Hydrology Journal. - : Bentham Science Publishers Ltd.. - 1874-3781. ; 4, s. 91-101
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Rapid and reliable observations of soil electrical conductivity are essential in order to maintain sustainable irrigated agriculture. Direct measurement of the electrical conductivity of saturated soil paste (ECe), however, is tedious andtime consuming. Therefore, there are needs to find efficient indirect methods to predict the soil salinity from other readily available observations. In this paper we explore the application of multiple linear regression (MLR) and artificial neural networks (ANN) to predict ECe variation from easily measured soil and groundwater properties under highly complex and heterogeneous field conditions in semiarid Tunisia. We compare two methods for dividing the data set into training and validation sub-sets; a statistical (SD) and a random data set division (RD), and their effect on model performance. The input variables were chosen from the plot coordinates, groundwater table properties (depth, electrical conductivity, piezometric level), and soil particle size at 5 depths. The results obtained with ANN and MLR indicate that the statistical properties of data in the training and validation sets need to be taken into account to ensure that optimal model performance is achieved. The SD can be considered as a solution to resolve the problem of over-fitting a model when using ANN. For the SD, the determination coefficient (R 2 ) when using an ANN model varied from 0.85 to 0.88 and the root mean square error from 1.23 to 1.80 dS m -1 . Because of the complexity of the field soil salinity process and the spatial variability of the data, this clearly indicates the potential to use ANN models to predict ECe.
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| 2. |
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| 3. |
- Hamed Abd El Mageed, Yasser, et al.
(författare)
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Spatial variability of soil water content and salinity in a semi-arid agricultural field
- 2014
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Ingår i: Vatten: tidskrift för vattenvård /Journal of Water Management and research. - 0042-2886. ; , s. 151-157
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- One technique for collecting rainwater and prevent soil erosion applied on large areas in Tunisia involves theuse of soil ridges (1–1.5 m high). These contour ridges are constructed parallel to topographical isolines. Theeffects of the contour ridges on the soil water content (θ) distribution, bulk soil salinity σa, and soil water salin-ity (σw) were investigated in the catchment of El-Gouazine in central Tunisia. In total 258 measuring pointswere obtained in an 80 m x 120 m area. Spatial maps of σw, σa, and θ displayed essentially a random variationand no apparent pattern within the sampling area. A geostatistical analysis, however, displayed spatial correla-tion for all variables. A variational analysis displayed small measurement errors as compared to small-scale vari-ation in the soil. A potential risk with soil ridges could be salt accumulation just upstream the ridges, however,no such effect could be observed in the studied area.
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| 4. |
- Haridy, Sahar, et al.
(författare)
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Mapping of non-aqueous phase liquids using time domain reflectometry
- 2011
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Ingår i: Vatten: tidskrift för vattenvård /Journal of Water Management and research. - 0042-2886. ; , s. 123-130
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Ett tvådimensionellt transportförsök utfördes i en behållare (45 cm x 54 cm x 20 cm) fylld med fin sand. En färgad icke vattenlöslig vätska (LNAPL) spreds över en rektangulär yta, 5 x 20 cm, på försöksytan. Spridningen gjordes i fyra omgångar på olika sätt; med konstant flöde, konstant nivå och varierande nivå. Fyrtiotvå tidsdo män reflektometri (TDR) prober användes för att följa LNAPL transporten. Förutom TDR proberna följdes också transporten av LNAPL med en digital kamera som tog bilder av den transparanta framsidan på behålla ren. Resultaten visar att TDR mätningarna kunde detektera transporten av LNAPL. Felet i mätningarna var 0.01 m3 m–3 för vattenhaltsmätningen och 0.045 m3 m–3 för LNAPL-mätningen. Resultaten visar att TDR är en lovande metod för att följa utbredningen av LNAPL i marken.
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| 5. |
- Kargas, George, et al.
(författare)
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Prediction of soil solution electrical conductivity by the permittivity corrected linear model using a dielectric sensor
- 2017
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Ingår i: Journal of Irrigation and Drainage Engineering. - 0733-9437. ; 143:8
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the electrical conductivity of the soil solution (σp) was predicted using a linear model in which the bulk soilelectrical conductivity (σb) effect on the apparent dielectric permittivity (εs) was considered. The performance of the proposed model wasevaluated by measurements with a dielectric sensor (the WET sensor) in four porous media at four different levels of electrical conductivity ofthe moistening KCl solution (σw). It was found that the relationship between the square root of the permittivity (εs) and soil volumetric watercontent (θ) was dependent on soil type, which is consistent with the low operating frequency of the sensor. Establishing a soil specific θm-√εsrelationship substantially increased the θ measurement accuracy compared to the factory calibration. It was shown that the new approach forthe σp prediction gave reasonably accurate results in sands irrespective of the σp values. For the finer porous media, it improved the predictionof σp only for the higher salinity levels, but the σp values appear to be underestimated. The relationship between the corrected dielectricpermittivity εR and σb is strongly linear for σw and σb values up to 6 and 1.7 dS · m-1, respectively.
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| 6. |
- Olsson, Jonas, et al.
(författare)
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Nonlinear and scaling spatial properties of soil geochemical element contents
- 2001
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Ingår i: Water Resources Research. - 0043-1397. ; 37:4, s. 1031-1042
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Tidskriftsartikel (refereegranskat)abstract
- The present study aimed at investigating whether a nonlinear and scaling approach is suitable for statistically characterizing the spatial variability of soil geochemical element contents at field conditions. Spatial distributions of 20 soil geochemical elements' contents in an agricultural field soil were investigated. Two indicators of nonlinear scaling were employed, empirical probability distribution functions (pdfs) and structure functions. For the pdfs, a trend was discovered with major elements naturally occurring in the soil being hyperbolic and minor trace elements being close to Gaussian. Further, fertilizer management was found to modify the behavior of related elements. The structure functions were generally nonscaling for major elements and scaling for minor elements, however, without any noticeable effect of fertilizer application. The scaling was of both monoaffine and multiaffine type. This suggests that the random cascade models recently used within geophysics may be useful also for geochemical element variability in soil.
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| 7. |
- Pollet, Marc, et al.
(författare)
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A long-lasting taxonomic problem in European Sympycnus resolved, with the description of a new species and data on habitat preferences
- 2015
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Ingår i: Zootaxa. - : Magnolia Press. - 1175-5334 .- 1175-5326. ; 4032:1, s. 81-102
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Tidskriftsartikel (refereegranskat)abstract
- Type specimens of Sympycnus pulicarius, S. annulipes, S. cinerellus and S. desoutteri were examined to clear up a long-lasting taxonomic confusion. Our study revealed that they represent, together with S. pygmaeus and S. annulipes var. brunnitibialis, a single species, with S. pulicarius as the senior subjective synonym, which is redescribed in this paper. Lectotypes were designated for Dolichopus pulicarius, Porphyrops annulipes, Chrysotus cinerellus and Sympycnus desoutteri. The postpedicel in this species shows substantial variation in shape and size, but the presence of a posteroventral bristle on the mid tibia is more reliable and the particular chaetotaxy and relative lengths of the tarsomeres of the male hind tarsus are entirely consistent. Both latter features separate S. pulicarius from another species, S. septentrionalis sp. nov., that is described here. Ecological data on both species were examined. An analysis of Malaise trap and white pan trap samples collected in Belgium revealed that S. pulicarius is most common in the western part of Flanders, and most abundant in open grassy habitats. In contrast to S. pulicarius, which is widespread over Europe, S. septentrionalis sp. nov. seems confined to northern Europe, where it exhibits a similar habitat preference.
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| 8. |
- Sivakumar, Bellie, et al.
(författare)
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Monthly runoff prediction using phase-space reconstruction
- 2001
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 46:3, s. 377-387
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear prediction method, developed based on the ideas gained from deterministic chaos theory, is employed: (a) to predict monthly runoff; and (b) to detect the possible presence of chaos in runoff dynamics. The method first reconstructs the single-dimensional (or variable) runoff series in a multi-dimensional phase space to represent its dynamics, and then uses a local polynomial approach to make predictions. Monthly runoff series observed at the Coaracy Nunes/Araguari River basin in northern Brazil is studied. The predictions are found to be in close agreement with the observed runoff, with high correlation coefficient and coefficient of efficiency values, indicating the suitability of the nonlinear prediction method for predicting the runoff dynamics. The results also reveal the presence of low-dimensional chaos in the runoff dynamics, when an inverse approach is adopted for identification, as: (a) an optimal embedding dimension exists, and (b) the prediction accuracy decreases with an increase in prediction lead lime.
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| 9. |
- Söderberg, Stefan, et al.
(författare)
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Hydrologiska aspekter på de höga europeiska elpriserna i augusti 2022
- 2022
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Ingår i: Vatten: tidskrift för vattenvård /Journal of Water Management and research. - 0042-2886. ; 78:4, s. 213-224
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electricity prices in Sweden and Europe during 2022 have reached very high levels. The main reason for this being the war in Ukraine, which has led to a decreased availability for gas. During summer, the electricity prices reached extreme levels when meteorological and hydrological factors worsened the situation on the electricity market. The highest daily electricity price on the Nordic market was reached August 30, when it was 462 €/MWh. In the present article we review how hydrological factors affected the electricity price in August 2022; drought, low water flow and high water temperature in European rivers.
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