| 1. |
- 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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| 2. |
- Haei, Mahsa, 1981-, et al.
(författare)
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Cold winter soils enhance dissolved organic carbon concentrations in soil and stream water
- 2010
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Ingår i: Geophysical Research Letters. - : American Geophysical Union. - 0094-8276 .- 1944-8007. ; 37, s. L08501-
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of dissolved organic carbon ([DOC]) have increased in lakes, streams and rivers across a large part of the northern hemisphere and raised an animated scientific debate about the underlying mechanisms. The lack of consensus about the role of climate in controlling the DOC trends highlights the need for understanding the regulation of surface water DOC. We found that longer and colder winters result in higher [DOC] in a boreal headwater stream during the subsequent snowmelt. In addition, prolonged soil frost increases the spring and summer [DOC] in the riparian soil water, which is a major contributor of stream water DOC in the studied area. We conclude that winter climatic conditions can play a substantial role in controlling stream [DOC] in ways not previously understood. These findings are especially important for northern latitude regions expected to be most affected by climate change. Citation: Haei, M., M. G. Oquist, I. Buffam, A. angstrom gren, P. Blomkvist, K. Bishop, M. Ottosson Lofvenius, and H. Laudon (2010), Cold winter soils enhance dissolved organic carbon concentrations in soil and st ream water, Geophys. Res. Lett., 37, L08501, doi: 10.1029/2010GL042821.
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| 3. |
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| 4. |
- Karlsen, Reinert, 1983-, et al.
(författare)
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The role of landscape properties, storage and evapotranspiration on variability in streamflow recessions in a boreal catchment
- 2019
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Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 0022-1694 .- 1879-2707. ; 570, s. 315-328
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Tidskriftsartikel (refereegranskat)abstract
- Streamflow recession analysis provides valuable insights into catchment functioning that can be related to runoff generation, storage retention and baseflow dynamics. As an integrated characteristic, recession analysis is particularly useful in catchment comparison studies to help explain drivers of spatial and temporal variability in hydrological behavior. Here, five years of hourly streamflow data from 14, partly nested, catchments within a 68 km(2) boreal forest landscape in Northern Sweden were used to explore spatiotemporal variation in hydrological processes through recession analysis. The aim of this study was to better understand spatial variation in runoff generation and storage-discharge dynamics across the landscape, as well as the relation to landscape properties. Due to high collinearity between variables, partial least square regression was used to quantify the associations between recession characteristics and catchment properties, as well as to identify key variables controlling recession behavior. We analyzed recession characteristics using both an aggregated approach including all recession data and individual recession events. The analyses based on individual recession events, indicated that catchment topography, quantified by indices such as mean slope or elevation above the stream network, is a primary control on the recession behavior during relatively high flows, whereas catchment area gains importance when flows are relatively low. The proportion of sediment and deep soils also controlled recession behavior. Furthermore, we found that recession characteristics are influenced by both evapotranspiration (ET) and proxies of antecedent catchment storage, but that the patterns were different depending on catchment properties. ET was less influential in catchments with deeper soils and larger catchment area. Shifts in recession rates were primarily related to variation in storage, with faster streamflow recessions occurring during periods with low storage. The results demonstrate the influence of catchment properties on recession behavior, and we found great value in analyzing individual recession events for an increased understanding of spatial and temporal recession characteristics. When recession properties were lumped together, the relationships to catchment characteristics were obscured. This indicates the value of more detailed analyses, at least under the strongly seasonal hydroclimatic conditions of this site.
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| 5. |
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| 6. |
- Oni, Stephen, et al.
(författare)
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Long-term patterns in dissolved organic carbon, major elements and trace metals in boreal headwater catchments: trends, mechanisms and heterogeneity
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 2315-2330
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Tidskriftsartikel (refereegranskat)abstract
- The boreal landscape is a complex, spatio-temporally varying mosaic of forest and mire landscape elements that control surface water hydrology and chemistry. Here, we assess long-term water quality time series from three nested headwater streams draining upland forest (C2), peat/mire (C4) and mixed (C7) (forest and mire) catchments. Acid deposition in this region is low and is further declining. Temporal trends in weather and runoff (1981-2008), dissolved organic carbon concentration [DOC] (1993-2010) and other water quality parameters (1987-2011) were assessed. There was no significant annual trend in precipitation or runoff. However, runoff increased in March and declined in May. This suggested an earlier snowmelt regime in recent years. Significant monotonic increasing trends in air temperature and length of growing season suggested a decrease in snowfall and less spring runoff. Stream [DOC] was positively correlated with some trace metals (copper, iron and zinc) and negatively with several other chemical parameters (e. g. sulfate, conductivity, calcium). Both sulfate and conductivity showed declining trends, while a significant increase was observed in pH during winter and spring. Calcium and magnesium showed monotonic decreasing trends. The declining trajectories of stream base cation and sulfate concentrations during other times of the year were not accompanied by changes in pH and alkalinity. These results indicate subtle effects of recovery from acidification. Water temperature increased significantly both annually and in most months. A simultaneous monotonic increase in iron (Fe) and [DOC] in autumn suggests co-transport of Fe-DOC in the form of organometallic complexes. monotonic increase in UV absorbance in most months without co-occurring changes in DOC trend suggests a shift in DOC quality to a more humic-rich type. The observed increase in soil solution [DOC] and subtle trends in stream [DOC] suggest that climate rather than recovery from acidification is the dominant driver of DOC trends in the Svartberget catchment.
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| 7. |
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| 8. |
- Öquist, Mats, et al.
(författare)
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The full annual carbon balance of boreal forestsis highly sensitive to precipitation
- 2014
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Ingår i: Environmental Science and Technology Letters. - : American Chemical Society (ACS). - 2328-8930. ; 1:7, s. 315-319
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Tidskriftsartikel (refereegranskat)abstract
- The boreal forest carbon balance is predicted to be particularly sensitive to climate change. Carbon balance estimates of these biomes stem mainly from eddy-covariance measurements of net ecosystem exchange (NEE). However, a full net ecosystem carbon balance (NECB) must include the lateral carbon export (LCE) through discharge. We show that annual LCE at a boreal forest site ranged from 4 to 28%, averaging 11% (standard deviation of 8%), of annual NEE over 13 years. Annual LCE and NEE are strongly anticorrelated; years with weak NEE coincide with high LCE. The decreased NEE in response to increased precipitation is caused by a reduction in the amount of incoming radiation caused by clouds. If our finding is also valid for other sites, it implies that increased precipitation at high latitudes may shift forest NECB in large areas of the boreal biome. Our results call for future analysis of this dual effect of precipitation on NEE and LCE.
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