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Seasonal variation and landscape regulation of dissolved organic carbon concentrations and character in Swedish boreal streams
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The seasonal variation and landscape regulation of dissolved organic carbon (DOC) concentrations in streams have been studied in two watersheds in the boreal zone. The seasonal variation was found to be highly correlated to variations in runoff. An increase in runoff was always accompanied with an increase in DOC concentration. However, there were indications that the TOC concentration was restricted by the soil TOC pool during snowmelt.

The main factors affecting DOC exports varied between seasons. During winter baseflow the spatial variation in DOC exports was strongly influenced by wetland coverage, during snowmelt the exports were correlated to factors describing the size and location of the catchment, and during the snow-free season they were heavily affected by the proportions of wetlands and forests in the catchments. Small headwaters had the highest terrestrial DOC export, per unit area.

The properties of the DOC changed during spring flood, towards lower molecular weight and more aliphatic compounds. These changes affected the bioavailability of the DOC, which increased during spring flood. There were also differences in the DOC properties between wetlands and forest soils; the forested soils yielded DOC with lower molecular weight (measured as 254 nm/365 nm light absorbance ratios), largely from superficial layers that were activated during high flow events, while wetland soils generally provided a more constant carbon source with higher molecular weight. The majority of the DOC was exported by wetlands, but most of the short-term bioavailable DOC (BP7) was derived from the forests, during the spring flood period, indicating that bacterial production in streams and lakes is likely to be almost entirely based on DOC exported from forested areas during, and some time after, the spring flood event.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap , 2007. , 35 p.
Keyword [en]
DOC, temporal variation, spatial variation, seasonal variation, forested catchment, wetland catchment, catchment characteristics, DOC characteristics, absorbance-ratio, bioavailability.
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:umu:diva-1374ISBN: 978-91-7264-372-7 (print)OAI: oai:DiVA.org:umu-1374DiVA: diva2:140795
Public defence
2007-10-19, KB3A9, KBC, Umeå universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2007-09-28 Created: 2007-09-28 Last updated: 2010-01-08Bibliographically approved
List of papers
1. Seasonal and runoff-related changes in dissolved organic carbon concentrations in the River Öre, Northern Sweden
Open this publication in new window or tab >>Seasonal and runoff-related changes in dissolved organic carbon concentrations in the River Öre, Northern Sweden
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2008 (English)In: Aquatic Sciences, Vol. 70, no 1, 21-29 p.Article in journal (Refereed) Published
Abstract [en]

The impact of runoff on allochthonous organic carbon was studied in the River Öre, Northern Sweden, using extensive TOC (total organic carbon) and runoff measurements. No relationship existed between TOC concentration and runoff on an annual basis. However, positive correlations between TOC concentration and runoff were found when observations were divided into three different seasons (winter, spring and summer/autumn). During these seasons runoff explained 62-70% of the TOC variation. Differences in these seasonal relationships indicated that the TOC concentration was restricted by the soil TOC pool during snowmelt, while the pool of TOC in the soil or its availability never limited the TOC export during the rest of the year. Two sets of data were used, a detailed study over 2 years and a long-term study over 14 years. Both showed similar results which indicated that the seasonal variation in the relationship between TOC and runoff is similar from year to year. The chemical variation usually decreases downstream in large rivers due to mixing of water from different sources. Our study, however, showed a strong correlation between TOC and runoff even in a large river like the River Öre. This result indicated that the general pattern of the TOC concentrations was to a large extent determined by the hydrology and climate conditions.

Identifiers
urn:nbn:se:umu:diva-11460 (URN)doi:10.1007/s00027-007-0943-9 (DOI)
Available from: 2009-01-09 Created: 2009-01-09 Last updated: 2011-01-10Bibliographically approved
2. Importance of seasonality and small streams for the landscape regulation of dissolved organic carbon export
Open this publication in new window or tab >>Importance of seasonality and small streams for the landscape regulation of dissolved organic carbon export
2007 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, Art. No. G03003- p.Article in journal (Refereed) Published
Abstract [en]

The regulation of the spatial and seasonal variation in terrestrial dissolved organic carbon (DOC) exports was studied in a 68 km2 boreal stream system in northern Sweden. A total of 1213 DOC samples were collected in 15 subcatchments over a 3 year period (2003–2005). The mean annual DOC exports from the 15 subcatchments (0.03–21.72 km2) ranged from 14.8 to 99.1 kg ha−1 yr−1. Many catchment characteristics determined the spatial variation in DOC exports. The relative importance of the different catchment characteristics varied greatly between seasons because of differing hydrological conditions. During winter base flow the spatial variation was linked to patterns in wetland coverage. During snowmelt in spring the spatial variation was connected to characteristics describing size and location, i.e., median stream size, silty sediment distribution, stream order, altitude, and proportion of catchment above highest postglacial coastline (HC). During the snow-free season the spatial variation in DOC exports was regulated by the amount of wetlands and forests, particularly forests made up of Norway spruce (Picea abies). Median stream size also influenced the exports during this season. A striking result in this study was the effect of size implying that small headwaters may be the largest contributor to the terrestrial DOC export, per unit area.

Identifiers
urn:nbn:se:umu:diva-6223 (URN)10.1029/2006JG000381 (DOI)
Available from: 2007-12-07 Created: 2007-12-07 Last updated: 2017-12-14Bibliographically approved
3. Dissolved organic carbon characteristics in boreal streams in a forest-wetland gradient during the transition between winter and summer
Open this publication in new window or tab >>Dissolved organic carbon characteristics in boreal streams in a forest-wetland gradient during the transition between winter and summer
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2008 (English)In: Journal of Geophysical Research, Vol. 113, G03031- p.Article in journal (Refereed) Published
Abstract [en]

The character and quantity of dissolved organic carbon (DOC) were studied in nine small boreal streams and adjacent soils during two years, with focus on the spring snowmelt period. The streams cover a forest-wetland gradient, spanning from 0% to 69% wetland coverage. Lower values of the absorbance ratio measured at 254 nm and 365 nm (A254/A365), in both soil plots and streams, indicated that wetland-derived DOC had higher average molecular weight than forest DOC. Higher SUVA254 (DOC specific ultraviolet absorption at 254 nm) in wetland runoff indicated more aromatic DOC from wetlands than forests. During low flow, the stream DOC character was sensitive to the forest-wetland proportion of the catchment, and when wetland coverage exceeded 10%, the streams appeared to be dominated by wetland-derived DOC. During the spring snowmelt period, the character changed to lower molecular weight and more aliphatic DOC, particularly in streams with a high proportion of forest in the catchment. The forested soil solutions had higher A254/A365 in the surface horizons that were hydrologically activated during the high flow events, while wetland soil solution had relatively low A254/A365 at all depths. Consequently forest soils contributed more to stream DOC concentration during snowmelt that during winter low flow.

Identifiers
urn:nbn:se:umu:diva-11415 (URN)doi:10.1029/2007JG000674 (DOI)
Available from: 2009-01-08 Created: 2009-01-08 Last updated: 2011-01-10Bibliographically approved
4. Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods
Open this publication in new window or tab >>Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods
2008 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 53, no 5, 964-972 p.Article in journal (Refereed) Published
Abstract [en]

1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.

2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP7; μg C L-1day-1) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP7 can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.

3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha-1 and was negatively correlated to forest cover (%). However, the export of BP7 carbon was positively correlated to forest cover and varied from about 0.1 kg ha-1 in mire-dominated streams to about 0.2 kg ha-1 in forest-dominated streams.

4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC.

Keyword
bacterial production, bioavailability, dissolved organic carbon, forests, mires
Identifiers
urn:nbn:se:umu:diva-11455 (URN)doi:10.1111/j.1365-2427.2008.01955.x (DOI)
Available from: 2009-01-08 Created: 2009-01-08 Last updated: 2017-12-14Bibliographically approved

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