| 1. |
- Bengtsson, Stefan, et al.
(author)
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Accumulation of wet-deposited radiocaesium and radiostrontium by spring oilseed rape (Brássica napus L.) and spring wheat (Tríticum aestívum L.)
- 2013
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 182, s. 335-342
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Journal article (peer-reviewed)abstract
- The accumulation of 134Cs and 85Sr within different parts of spring oilseed rape and spring wheat plants was investigated, with a particular focus on transfer to seeds after artificial wet deposition at different growth stages during a two-year field trial. In general, the accumulation of radionuclides in plant parts increased when deposition was closer to harvest. The seed of spring oilseed rape had lower concentrations of 85Sr than spring wheat grain. The plants accumulated more 134Cs than 85Sr. We conclude that radionuclides can be transferred into human food chain at all growing stages, especially at the later stages. The variation in transfer factors during the investigation, and in comparison to previous results, implies the estimation of the risks for possible transfer of radionuclides to seeds in the events of future fallout during a growing season is still subjected to considerable uncertainty.
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| 2. |
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| 3. |
- Bengtsson, Stefan, et al.
(author)
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Interception and retention of wet-deposited radiocaesium and radiostrontium on a ley mixture of grass and clover
- 2014
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In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 497-498, s. 412-419
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Journal article (peer-reviewed)abstract
- The aims of this study were to assess the potential radioactive contamination of fodder in the case of accidental radionuclide fallout, and to analyse the relationship between interception and retention of radionuclides as a function of biomass and Leaf Area Index (LAI). The interception and the retention of wet deposited Cs-134 and Sr-85 in ley (a mixture of grass and clover) were measured after artificial wet deposition in a field trial in Uppsala (eastern central Sweden). The field trial had a randomised block design with three replicates. Cs-134 and Sr-85 were deposited at six different growth stages during two growing seasons (2010 and 2011) using a rainfall simulator. The biomass was sampled in the center of each parcel 2 to 3 h after deposition and at later growth stages (1 to 5) during the growing season. The above ground biomass and LAI were measured as well. The interception of radionuclides by the ley was largest at the late growth stages; the spike and tassel/flowering (code 5:6) in the 1st year, and at flowering/initial flowering (code 6:5) in the 2nd year. There was a correlation between radionuclide interception and above ground plant biomass, as well as with LAI, for both radionuclides in both years. The highest activity concentrations of both radionuclides were measured after deposition at the late growth stages and were found to be higher in the 2nd year. The weathering half-lives were shorter at the earlier growth stages than at the later growth stages for both radionuclides. For the magnitude of deposition chosen in our experiment, it can be concluded that the above ground biomass is a good predictor and the LAI a more uncertain predictor of the interception of radiocaesium and radiostrontium by ley grass and clover. (C) 2014 Elsevier B.V. All rights reserved.
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| 4. |
- Bengtsson, Stefan, et al.
(author)
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Interception of wet deposited and transfers of radiocaesiumand radiostrontium by Brássica napus L. and Tríticumaestívum L.
- 2011
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In: Radioprotection. - : EDP Sciences. - 0033-8451 .- 1769-700X. ; 46, s. S475-S478
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Journal article (peer-reviewed)abstract
- The aim of this study is to assess the interception and transfer to edible part of wet deposited 134Cs and 85Sr to spring oilseed rape and spring wheat and the dependency of the intercepted fraction on the development stage e.g. the total plant biomass. The radionuclides, 134Cs and 85Sr, were deposited at six different development stages using a rainfall simulator. The results showed that there was a positive correlation between the interception fraction for 134Cs and 85Sr and the biomass both for spring oilseed rape and spring wheat. The interception fraction and transfer factors were highest at growing stage of senescence (ripening) for both crops
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| 5. |
- Choma, Michal, et al.
(author)
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Recovery of the ectomycorrhizal community after termination of long-term nitrogen fertilisation of a boreal Norway spruce forest
- 2017
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In: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 29, s. 116-122
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Journal article (peer-reviewed)abstract
- © 2016 Elsevier Ltd and British Mycological Society.Ectomycorrhizal fungi (ECM) are a fundamental component of boreal forests promoting tree growth and participating in soil nutrient cycling. Increased nitrogen (N) input is known to largely influence ECM communities but their potential recovery is not well understood. Therefore, we studied the effects of long-term N-fertilisation on ECM communities, and their recovery after termination of N treatment. Fungal ITS sequencing data indicated that N-fertilisation (34 kg N ha-1 y-1) for 46 y decreased the relative abundance of ECM species in the fungal community and suppressed originally dominating medium-distance fringe exploration types adapted to N-limited conditions, while the ECM diversity remained unaffected. In other plots, 23 y after termination of fertilisation at 73 kg N ha-1 y-1 for 23 y, the relative abundance of ECM species shifted closer to, but did not reach, control levels. These observations indicate only slow recovery of ECM community, likely due to a high soil N retention capacity.
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| 6. |
- Gebrehiwot, Solomon Gebreyohannis, et al.
(author)
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Forest cover change over four decades in the Blue Nile Basin, Ethiopia : comparison of three watersheds
- 2014
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In: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 14:1, s. 253-266
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Journal article (peer-reviewed)abstract
- The objective of this study was to quantify forest cover changes in three watersheds (Gilgel Abbay (1,646 km(2)), Birr (980 km(2)), and Upper-Didesa (1,980 km(2)) of the Blue Nile Basin between 1957 and 2001. Four land cover maps were produced for each watershed for 1957/1958, 1975, 1986, and 2000/2001. Nine different types of land cover were identified, five of which were forest cover classes. Between 1957 and 2001, the total forest cover increased in Gilgel Abbay (from 10 to 22 % cover) and decreased in Birr (from 29 to 22 % cover) as well as in Upper-Didesa (from 89 to 45 % cover). The increase in Gilgel Abbay was primarily due to the expansion of eucalyptus plantations. Natural forest cover decreased in all three watersheds. Wooded grassland decreased by two-thirds, dry/moist mixed forests decreased by half, and riverine forests had disappeared by 1975 in Gilgel Abbay and Birr. Major deforestation had already taken place in the northern watersheds, Gilgel Abbay and Birr, before the 1960s and 1970s, while in the southern watershed, Upper-Didesa, much of the deforestation occurred after 1975. The southern watershed still remained by far the most forested watershed in 2001 despite the strong ongoing deforestation. The changes in forest cover could affect natural resource management, greenhouse gas emissions, water resources, and agricultural production including coffee production. The patterns of change are different in the three watersheds. We therefore recommend further studies of the local conditions and drivers of change as the basis for designing effective policy to halt further loss of natural forest, which offers a wealth of ecosystem services.
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| 7. |
- Gebrehiwot, Solomon Gebreyohannis, et al.
(author)
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The long-term hydrology of East Africa's water tower : statistical change detection in the watersheds of the Abbay Basin
- 2014
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In: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 14:1, s. 321-331
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Journal article (peer-reviewed)abstract
- Forty-five years (1960-2004) of hydrological data from 12 watersheds in the Abbay Basin, Ethiopia, were tested for possible trends over the entire time series and differences in medians (step-wise changes) between three sub-periods. The classification of the sub-periods was based on the major political changes in 1975 and 1991. Variables investigated were rainfall (P), total flow (Q(t)), high flow (Q(h)), low flow (Q(1)), low flow index (LFI) and run-off coefficient (C). Data were checked for outliers, errors and homogeneity. Trend was tested after serial and cross-correlation tests. The data for each variable were serially uncorrelated from 1 to 10 lag years. There were five globally significant trends out of 50 test cases and 36 significant step-wise changes out of 180 tests. The majority of the significant changes were watershed specific. Run-off coefficient was the single variable showing a consistently increasing trend and stood for ca. 25 % of the total significant trends and step-wise changes. Half of these changes occurred after 1991. We concluded that despite the land use policy changes in 1975 and 1991, as well as the long-term soil degradation, the hydrological regime was quite stable over the 45-year period, with the exception of an increase in the run-off coefficient in the latter part of the run-off record in some watersheds.
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| 8. |
- Gebrehiwot, Solomon, et al.
(author)
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Hydrological change detection using modeling : Half a century of runoff from four rivers in the Blue Nile Basin
- 2013
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In: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:6, s. 3842-3851
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Journal article (peer-reviewed)abstract
- Land cover changes can have significant impacts on hydrological regime. The objective of this study was to detect possible hydrological changes of four watersheds in the Blue Nile Basin using a model-based method for hydrological change detection. The four watersheds, Birr, Upper-Didesa, Gilgel Abbay, and Koga range in size from 260 to 1800 km(2). The changes were assessed based on model parameters, model residuals, and in the overall function of the watersheds in transferring rainfall into runoff. The entire time series (1960-2004) was divided into three periods based on political and land management policy changes. A conceptual rainfall-runoff model, the HBV (Hydrologiska Byrans Vattenbalansavdelning) model, was used for the analysis, and suitable parameter sets for each period were found based on a Monte Carlo approach. The values of six out of nine parameters changed significantly between the periods. Model residuals also showed significant changes between the three periods in three of the four watersheds. On the other hand, the overall functioning of the watersheds in processing rainfall to runoff changed little. So even though the individual parameters and model residuals were changing, the integrated functioning of the watersheds showed minimal changes. This study demonstrated the value of using different approaches for detecting hydrological change and highlighted the sensitivity of the outcome to the applied modeling and statistical methods.
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| 9. |
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| 10. |
- Gebrehiwot, Solomon, et al.
(author)
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Hydrological characterization of watersheds in the Blue Nile Basin, Ethiopia
- 2011
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 15:1, s. 11-20
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Journal article (peer-reviewed)abstract
- Thirty-two watersheds (31-4350 km(2)), in the Blue Nile Basin, Ethiopia, were hydrologically characterized with data from a study of water and land resources by the US Department of Interior, Bureau of Reclamation (USBR) published in 1964. The USBR document contains data on flow, topography, geology, soil type, and land use for the period 1959 to 1963. The aim of the study was to identify watershed variables best explaining the variation in the hydrological regime, with a special focus on low flows. Moreover, this study aimed to identify variables that may be susceptible to management policies for developing and securing water resources in dry periods. Principal Component Analysis (PCA) and Partial Least Square (PLS) were used to analyze the relationship between five hydrologic response variables (total flow, high flow, low flow, runoff coefficient, low flow index) and 30 potential explanatory watershed variables. The explanatory watershed variables were classified into three groups: land use, climate and topography as well as geology and soil type. Each of the three groups had almost equal influence on the variation in hydrologic variables (R-2 values ranging from 0.3 to 0.4). Specific variables from within each of the three groups of explanatory variables were better in explaining the variation. Low flow and low flow index were positively correlated to land use types woodland, dense wet forest and savannah grassland, whereas grazing land and bush land were negatively correlated. We concluded that extra care for preserving low flow should be taken on tuffs/basalts which comprise 52% of the Blue Nile Basin. Land use management plans should recognize that woodland, dense wet forest and savannah grassland can promote higher low flows, while grazing land diminishes low flows.
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