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| 2. |
- Cienciala, Emil, et al.
(författare)
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The effect of a north-facing forest edge on tree water use in a boreal Scots pine stand
- 2002
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Ingår i: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 32:4, s. 693-702
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Tidskriftsartikel (refereegranskat)abstract
- Tree water use and growth increment were studied in a north-facing forest edge of a 70 year old mono-specific stand of Scots pine (Pinus sylvestris) trees growing on poor sandy soils in the northern boreal zone of Sweden. The forest edge in this study bordered a clear-cut established two decades ago. There were differences in water use and growth increment during the growing season between trees growing at the forest edge and trees growing in the forest interior. These differences were likely related to soil conditions, such as access to soil moisture, soil temperature and soil frost conditions, whereas an effect of above ground microclimate was not found. The estimated tree water use and growth increment over one growing season tended to be larger for trees at the edge zone relative to those from the interior. The variability of the measured tree water fluxes was high, especially for the edge zone trees. There were also structural differences between the two groups of trees, most notably in the radial profile of conductive xylem, in tree height and in green crown length, but these differences were on the limits of statistical significance. The estimated seasonal transpiration was low, about 70 mm when estimated exclusively for trees from the forest interior and 107 mm when estimated exclusively for trees at the forest edge. This illustrates the likely magnitude of water use enhancement due to the conditions specific to forest edge.
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| 5. |
- Mellander, Per-Erik, et al.
(författare)
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The influence of soil temperature on transpiration: : a plot scale manipulation in a young Scots pine stand
- 2004
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 195:1-2, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Classic studies have stressed the importance of forest management for soil frost and the dynamics of soil warming during spring. But, we know very little about the potential loss of forest production due to cold soils. Liquid soil water may not be available to trees due to cold soil conditions, thus reducing transpiration and photosynthesis. We believe that these effects need to be quantified in order to keep silvicultural practices from inadvertently reducing forest growth through effects on soil temperature. In order to test this hypothesis it is important to know more about water uptake in the field by trees in cold environments. The snow cover was manipulated on plots in a young stand of Pinus sylvestris L. to create plots with different timings of soil warming. Soil profile temperature and liquid water content, as well as snow and frost depths, were measured together with tree physiological parameters such as sap flow, stomatal conductance and needle water potential. The study has confirmed the importance of the soil temperature for tree water uptake when soil warming was delayed beyond the start of growing season as defined by air temperature. The absence of frost (and hence the presence of liquid water) was not sufficient to enable water uptake. It was rather elevation of soil temperature above zero in the upper soil layers that was required for substantial water uptake, in combination with other site factors. Below ca. +8 °C, soil temperature was a factor in the restriction of transpiration, explained by a lower stomatal conductance and likely decreased root permeability. The effect of a certain soil temperature was not the same at different times due to its interaction with aboveground factors such as air temperature and day-length. The effect of low soil temperature increased with the persistence of low temperatures after the start of the growing season. The timings of soil warming induced by our study were within the spatial and inter-annual variation of soil warming in this region. Thus, we conclude that influences of forest management on soil temperature can affect the transpiration deficit during spring, with potential implications for forest productivity
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| 6. |
- Munthe, John, et al.
(författare)
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New concepts and methods for effect-based strategies on transboundary air pollution. Synthesis Report, April 2002
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report was prepared in connection with the scientific evaluation of the ASTA programme in May, 2002. It consists of a comprehensive summary of the approaches and results from the different ASTA sub programmes. ASTA is presently in its fourth and last year of the first phase. The report is not intended to give a full description of all relevant aspects of the problem of transboundary air pollution but rather discuss some crucial problems and their possible scientific solutions. After the preparation and submission of this report, ASTA has been positively evaluated and will continue into its second phase. The evaluation reports as well as a letter of intent for the second phase of the ASTA programme are available on the ASTA web page (http://asta.ivl.se). Further information of the programme is also available at the web page. For those who wish to receive more information of the programme, there is a list of contact persons at the end of the report. Many of the ASTA phase 1 activities are currently in a state of intense evaluation and reporting and additional scientific results as well as synthesises and assessments will be prepared during the remainder of 2002.
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| 7. |
- Nyberg, Lars, et al.
(författare)
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Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations
- 2001
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087. ; 15:6, s. 909-926
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Tidskriftsartikel (refereegranskat)abstract
- To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage.
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| 8. |
- Seibert, Jan, et al.
(författare)
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Groundwater dynamics along a hillslope : A test of the steady state hypothesis
- 2003
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 39:1, s. 1014-
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Tidskriftsartikel (refereegranskat)abstract
- [1] Appropriate conceptual simplifications and assumptions are a central issue for hydrological modeling, especially when those models serve as the foundation for more complex hydrochemical or ecological models. A common and often unexamined assumption in conceptual modeling is that the relation between groundwater levels and runoff can be described as a succession of steady state conditions. This results in a single-valued, monotonic function between the groundwater levels and runoff. Consequently, the simulated rise and fall in groundwater levels always follow the dynamics of runoff. We tested this assumption with an analysis of detailed groundwater level data along two opposing hillslopes along a stream reach in a Swedish till catchment at Svartberget. Groundwater levels in areas close to the stream followed the dynamics of the runoff. The correlation between groundwater level and runoff decreased markedly for wells farther than approximately 40 m from the stream. The levels were often independent of streamflow: Upslope area groundwater could be rising when riparian groundwater and runoff were falling, and vice versa. There was a high degree of correlation between groundwater levels at similar distances from the stream. The median Spearman rank correlation between wells within 35 m from the stream was 0.86 and for wells located more than 60 m from the stream was 0.96. This indicated that there is a common hydrological pattern even in the upslope area that can be identified and modeled. Despite the widespread acceptance of the steady state assumption previously in this and other study catchments, our study shows that it is not valid for the investigated hillslope site. If the divergence from steady state, with potential ramifications for other processes such as runoff chemistry, is common, then it will be worthwhile to reconsider the appropriate range of applicability for the steady state hypothesis, and the alternatives to that hypothesis.
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| 9. |
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| 10. |
- Seibert, J., et al.
(författare)
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Simulating interactions between saturated and unsaturated storage in a conceptual runoff model
- 2003
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 17:2, s. 379-390
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing demand for modelling the fluxes of chemical constituents at the catchment scale. Conceptual runoff models provide a basis for such modelling tasks provided that they capture the essential hydrological processes. However, most conceptual models do not fully address interactions between unsaturated and saturated storage. This can lead to unrealistic simulations for watersheds with shallow groundwater, where a large part of the soil volume can contribute to both the unsaturated and the saturated storage, depending on groundwater levels. Adding a small amount of water to the saturated storage will cause a significant amount of water stored in the unsaturated zone to change its status to ‘saturated’. The maximum volume of the unsaturated storage also decreases with rising groundwater levels, i.e. increasing saturated storage. In this study, a new model concept was proposed in which special emphasis was put on the interaction between saturated and unsaturated storage. The total storage was divided into two compartments, representing saturated and unsaturated storage, with a boundary moving up and down in response to the water budget of the compartments. Groundwater dynamics show a distinct pattern along the hillslope studied. Groundwater levels in an area close to the stream had dynamics similar to runoff, whereas levels further upslope responded to rainfall with a delay. To represent these differences in the model, the hillslope was subdivided into a riparian and an upslope reservoir. The performance of the new model was compared with that of simpler model variants without spatial differentiation and with or without the new formulation allowing for interactions between unsaturated and saturated storage. The new model approach provided the best results for simulating both runoff and groundwater dynamics. The subdivision of the hillslope accounted for most of the performance increase. To test the model structure further, 18O concentrations in the stream were simulated and compared with measured values.
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