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The influence of soil frost on the quality of dissolved organic carbon in a boreal forest soil: combining field and laboratory experiments
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
2012 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 107, no 1-3, 95-106 p.Article in journal (Refereed) Published
Abstract [en]

Riparian soils exert a major control on stream water dissolved organic carbon (DOC) in northern latitudes. As the winter climate in northern regions is predicted to be particularly affected by climate change, we tested the sensitivity of DOC formation to winter conditions in riparian soils using an 8 year field-scale soil frost manipulation experiment in northern Sweden. In conjunction with the field experiment, we also carried out a laboratory experiment based on three levels of four winter climatic factors: frost intensity, soil water content, frost duration and frequency of freeze–thaw cycles. We evaluated changes in lability of DOC in soil solution from lysimeter samples taken at different depths (10–80 cm) as well as from DOC extracted from soils in the laboratory, using carbon-specific ultraviolet absorbance at 254 nm (sUVA254). In the field, significantly more labile DOC was observed during the spring and summer from upper horizons of frost-exposed soils, when compared to controls. In addition, the amount of labile DOC was positively correlated with frost duration at a soil depth of 10 cm. In the laboratory, frost intensity was the factor that had the greatest positive influence on DOC lability; it also reduced the C:N ratio which may indicate a microbial origin of the DOC. The laboratory experiment also demonstrated significant interactions between some of the applied climatic factors, such as frost intensity interacting with water content. In combination, field and laboratory experiments demonstrate that winter soil conditions have profound effects on DOC-concentration and quality during subsequent seasons.

Place, publisher, year, edition, pages
Springer , 2012. Vol. 107, no 1-3, 95-106 p.
Keyword [en]
Soil frost, sUVA254, Dissolved organic carbon, Water content, Riparian zone, CCF design
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:umu:diva-43398DOI: 10.1007/s10533-010-9534-2ISI: 000298226700007OAI: oai:DiVA.org:umu-43398DiVA: diva2:413431
Note
Published online october 2010Available from: 2011-04-28 Created: 2011-04-28 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Importance of winter climate and soil frost for dissolved organic carbon (DOC) in boreal forest soils and streams: - implications for a changing climate
Open this publication in new window or tab >>Importance of winter climate and soil frost for dissolved organic carbon (DOC) in boreal forest soils and streams: - implications for a changing climate
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dissolved organic carbon (DOC) is a defining feature of surface waters in a large part of the world and it influences a variety of physical, chemical and biological processes in aquatic ecosystems. Riparian soils exert a major control on stream water chemistry in many northern latitude regions and provide a local source of DOC to adjacent streams. As the winter climate in northern regions is predicted to be particularly affected by climate change, it is important to investigate the sensitivity of DOC in riparian soils and the potential implications for adjacent streams’ chemistry in a changing winter climate. The effects of a changing winter climate on riparian soil DOC production and export to streams has received little attention to date, and this is the focus of my thesis.

In this thesis I first evaluate the hydro-climatic drivers of inter-annual variation in spring snowmelt DOC concentrations in two boreal forest streams of northern Sweden. By accounting for the effects of seasonal hydrology, I was able to statistically evaluate the importance of antecedent winter climatic conditions to inter-annual variation in stream DOC concentrations during the spring snow-melt periods. This descriptive work was complemented by a long-term field experiment where snow packs were manipulated to investigate the impacts of soil freezing on the concentration and quality of DOC in soil water. The effect of soil freezing on DOC was further addressed in a multi-factor laboratory experiment on soil samples taken from the riparian zone. The laboratory experiment was designed based on a central composite face-centered (CCF) model which applied three levels of four freezing-related factors: temperature, water content, duration and frequency of freeze-thaw cycles. The responses of soil microbial- activity and composition to the same experimental factors as well as their potential link to frost induced changes in DOC were also tested.

Large inter-annual variations were observed in spring snow-melt DOC concentrations in streams. Lower export of DOC during the preceding seasons and longer, and colder, winters resulted in higher spring snow-melt DOC concentrations. Soil water DOC concentrations and lability were significantly enhanced in the upper soil horizons which experienced extensive soil frost and longer frost duration. In the laboratory experiment, similar responses of soil water DOC were observed in that the higher concentrations and greater lability were found in samples incubated at the lowest temperatures (-12°C). The fungal to bacterial growth ratio also increased in the lower temperature treatments. In addition, fungal growth rate and soil basal respiration responded positively to frost-induced increases in DOC concentration. The frequency of freeze-thaw cycle did not appear to be an influential factor in the laboratory experiment. Several significant interactions of the factors were also detected.

By conducting and integrating field and laboratory experiments I highlight the importance of soil frost regime and winter climatic conditions for regulating DOC in riparian soils and their adjacent streams in areas with seasonally frozen soils. However, in a changing future winter climate, alterations in soil frost should be assessed as the result of changes in air temperature and snow-pack formation and extent, and implications for streams should be investigated with regard to changes in hydrology and export processes in soil-water interface.  

Place, publisher, year, edition, pages
meå: Department of Ecology and Environmental Sciences, Umeå University, 2011. 22 p.
Identifiers
urn:nbn:se:umu:diva-43171 (URN)978-91-7459-219-1 (ISBN)
Public defence
2011-05-20, KBC huset, KB3A9 (lilla hörsalen), Umeå universitet, Umeå, 10:00 (English)
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Available from: 2011-04-29 Created: 2011-04-21 Last updated: 2011-04-28Bibliographically approved

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