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- Köhler, S.J., et al.
(författare)
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Climate's control of intra-annual and interannual variability of total organic carbon concentration and flux in two contrasting boreal landscape elements
- 2008
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 113:G3
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Tidskriftsartikel (refereegranskat)abstract
- [1] Large spatial and temporal variations in stream total organic carbon (TOC) concentration and export occurred during an 11-year observation period (1993-2003) in a boreal headwater catchment. TOC flux and concentration patterns from mire- and forest-dominated subcatchments differed ( mean annual flux 8.2 g m(-2)a(-1) versus 5.8 g m(-2) a(-1)). Temporal variations in stream TOC concentrations in both landscape types were primarily driven by variations in streamflow, with the mire stream generally diluting by half with increased runoff during spring flood and TOC from the forested landscape increasing during runoff peaks irrespective of season. Average TOC concentration in the mire stream in the snow-free season increased with increased seasonal precipitation from around 20 to 40 mg L-1 but then dropped to around 35 mg L-1 during very wet years. Average snow-free season TOC concentration at the forested site remained stable when summer precipitation was below average but then increased from 10 to around 25 mg L-1 during exceptionally wet years. For both the forested subcatchment and the whole catchment, TOC concentrations increased during the warm summer months during wet years, but no such increase occurred during dry years. Interannual variations in TOC flux were primarily driven by variations during the snow-free period. Wet years decreased the relative TOC export from the mire and favored the relative export of TOC from areas dominated by forest, an observation that also held true on a larger scale when similar landscape types were considered. Predicted climate change in rainfall and temperature patterns will affect the amount and character of TOC exported downstream from boreal landscapes with a mix of forest and mire.
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- Köhler, S. J., et al.
(författare)
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Dynamics of stream water TOC concentrations in a boreal headwater catchment : Controlling factors and implications for climate scenarios
- 2009
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 373:1-2, s. 44-56
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Tidskriftsartikel (refereegranskat)abstract
- Two different but complementary modelling approaches for reproducing the observed dynamics of total organic carbon (TOC) in a boreal stream are presented. One is based on a regression analysis, while the other is based on riparian soil conditions using a convolution of flow and concentration. Both approaches are relatively simple to establish and help to identify gaps in the process understanding of the TOC transport from soils to catchments runoff. The largest part of the temporal variation of stream TOC concentrations (4-46 mg L-1) in a forested headwater stream in the boreal zone in northern Sweden may be described using a four-parameter regression equation that has runoff and transformed air temperature as sole input variables. Runoff is assumed to be a proxy for soil wetness conditions and changing flow pathways which in turn caused most of the stream TOC variation. Temperature explained a significant part of the observed inter-annual variability. Long-term riparian hydrochemistry in soil solutions within 4 m of the stream also captures a surprisingly large part of the observed variation of stream TOC and highlights the importance of riparian soils. The riparian zone was used to reproduce stream TOC with the help of a convolution model based on flow and average riparian chemistry as input variables. There is a significant effect of wetting of the riparian soil that translates into a memory effect for subsequent episodes and thus contributes to controlling stream TOC concentrations. Situations with high flow introduce a large amount of variability into stream water TOC that may be related to memory effects, rapid groundwater fluctuations and other processes not identified so far. Two different climate scenarios for the region based on the IPCC scenarios were applied to the regression equation to test what effect the expected increase in precipitation and temperature and resulting changes in runoff would have on stream TOC concentrations assuming that the soil conditions remain unchanged. Both scenarios resulted in a mean increase of stream TOC concentrations of between 1.5 and 2.5 mg L-1 during the snow free season, which amounts to approximately 15% more TOC export compared to present conditions. Wetter and warmer conditions in the late autumn led to a difference of monthly average TOC of up to 5 mg L-1, suggesting that stream TOC may be particularly susceptible to climate variability during this season.
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