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Spatial variation of dissolved organic carbon along streams in Swedish boreal catchments
Örebro University, Department of Natural Sciences.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

Denna avhandling behandlar den småskaliga rumsliga variationen av löst organiskt kol (DOC, engelsk term: dissolved organic carbon), dess koncentration, masstransport och karaktär, i bäckar inom två barrskogsbeklädda avrinningsområden (delavrinningsområden 0,01-78 km²). Provtagningen gjordes uppströms och nedströms varje bäckförgrening under sommarbasflöde. Koncentrationen av DOC varierade inom en tiopotens (4-66 mg/l), liksom flera andra kemiska parametrar. Vid riksinventeringen av vattendrag för 2000 i norra Sverige noterades en snarlik spännvidd. Enligt Naturvårdverkets bedömningsgrunder för sjöar och vattendrag återfanns alla tillståndsklasser för DOC och pH, samt mänsklig påverkansgrad till försurningen inom de två studerade områdena. Den specifika avrinningen (flöde per areaenhet) varierade kraftigt i källflödena och inverkade på deras bidrag till kemin nedströms. Vattenkemin och specifika avrinningen var stabila i delavrinningsområden större än 15 km². Det kan vara nödvändigt att provta så stora områden om generella värden för landskapet önskas, men källflödenas kemi kommer då inte att kunna karakteriseras, ehuru källflödena utgör den största delen av bäcksträckan och det akvatiska ekosystemet.

Nedströms är DOC-koncentrationen, och många andra kemiska parametrar, lika med summan av bidragen från källflödena och nedströms utspädning av inflödande vatten. Tillkommer gör processer inom bäcken och vattnets utbyte med botten/grundvatten (den hyporheiska zonen), men även DOC-förluster/transformationer vid vissa bäckförgreningar och sjöar. Ovanstående resonemang förklarade bäckvattenkemins minskande variation och vanligen lägre DOC-koncentrationer nedströms i ett landskapsperspektiv. Längs bäcksträckorna observerades ingen generell minskning av DOC-koncentration eller ändring av dess karaktär. Skillnaden i DOC-koncentration och relaterade parametrar mellan källflöden och nedströms styrdes i hög grad av vilka landskapselement (myrar, sjöar och skogsmark) som vattnet hade passerat innan det hamnade i bäckarna, samt samspelseffekter med den specifik avrinningen och platserna med DOC-förlust. Prognoser med multivariata modeller baserade på kartinformation testades men kunde inte förutsäga det rumsliga mönstret eller DOC-koncentrationen med erforderlig precision.

Lämpliga rutiner inom miljöövervakningen för att övervaka den rumsliga variationen av kemin i ytvatten saknas alltjämt. Vid planering av terrestra och akvatiska skötselåtgärder bör man beakta bäckvattnets naturliga kemiska variation.

Abstract [en]

This thesis quantifies the small-scale spatial variation of dissolved organic carbon (DOC) concentrations, fluxes and character in two boreal catchments (subcatchments 0.01-78 km²) using ”snapshots” of summer base flow where samples were taken upstream and downstream from every node in the stream network. An order of magnitude variation was found in DOC-concentrations, and many other chemical parameters. The range was similar to that found in all of northern Sweden by the national stream survey in 2000. According to the official assessment tools used in Sweden, the entire range of environmental status for DOC, pH and human acidification influence existed within these two study catchments. A large variability in specific discharge had a major impact on the contribution of headwaters to downstream chemistry. The water chemistry parameters were relatively stable at catchment areas greater than 15 km². Sampling at that scale may be adequate if generalised values for the landscape are desired. However the chemistry of headwaters, where much of the stream length and aquatic ecosystem is found would not be characterized.

Downstream DOC-concentrations, as well as many other chemical parameters, are the sum of headwater inputs, in combination with progressive downstream dilution by inflowing water with its own DOC-concentration and character. Superimposed upon this are in-stream and hyporheic processes, as well as discrete loci of DOC loss/transformation at lakes and stream junctions. At the landscape scale, this results in a decreased downstream variation in stream water chemistry and often, but not necessarily, lower average DOC-concentrations. Along stream reaches there was not a loss of DOC-concentration or a consistent change in character. While the importance of in-stream/hyporheic processes that consistently alter DOC-concentrations along the channel network cannot be ruled out, the differences between headwater and downstream DOC-concentrations and related parameters depend largely on the mosaic of landscape elements (mires, lakes and forest soil) contributing water to the channel network, combined with patterns of specific discharge and discrete loci of DOC loss. Assessment would be facilitated by map information that could predict spatial patterns. Multivariate models using maps, however, did not give satisfactory predictions.

Appropriate procedures for dealing with spatial variation in the environmental assessment of surface waters are not yet established. An awareness of stream water chemistry’s natural spatial variability should be considered when planning aquatic and terrestrial management.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek , 2005. , 41 p.
Series
Örebro Studies in Environmental Science, ISSN 1650-6278 ; 6
Keyword [en]
Physical geography and sedimentology, spatial variation of stream water chemistry
Keyword [sv]
Naturgeografi och sedimentologi
National Category
Physical Geography
Research subject
Enviromental Science
Identifiers
URN: urn:nbn:se:oru:diva-116ISBN: 91-7668-437-7 (print)OAI: oai:DiVA.org:oru-116DiVA: diva2:134721
Public defence
2005-05-27, Hörsal P 2, Prismahuset, Örebro universitet, Fakultetsgatan 1, Örebro, 10:00
Opponent
Supervisors
Available from: 2005-05-04 Created: 2005-05-04 Last updated: 2011-06-01Bibliographically approved
List of papers
1. Spatial variation of streamwater chemistry in two Swedish boreal catchments: implications for environmental assessment
Open this publication in new window or tab >>Spatial variation of streamwater chemistry in two Swedish boreal catchments: implications for environmental assessment
2005 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 39, no 6, 1463-1469 p.Article in journal (Refereed) Published
Abstract [en]

To evaluate the scale-dependent spatial variability of water chemistry within two Swedish boreal catchments (subcatchment areas 0.01-78 km2), samples were taken at every junction in the stream network during June 2000 and August 2002. The values of most chemical constituents spanned more than an order of magnitude, and the range was similar to that found in all of Northern Sweden by the national stream survey in 2000. According to the official assessment tools used in Sweden, the entire range of environmental status (for pH, absorbance, alkalinity, dissolved organic carbon (DOC)) and human acidification influence existed within these two study catchments. The water chemistry parameters were relatively stable at catchment areas greater than 15 km2. Sampling at that scale may be adequate if generalized values for the landscape are desired. However the chemistry of headwaters, where much of the stream length and aquatic ecosystem is found would not be characterized. Map parameters correlated to the variability in a key chemical parameter, DOC, but the best predictive map parameters differed markedly between catchments. This study highlights the importance of accounting for headwater spatial variability in environmental assessments of running waters, even in relatively pristine areas. The nature of drainage networks with many headwaters and progressively fewer downstream watercourses makes this a considerable challenge.

National Category
Natural Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2827 (URN)10.1021/es040045q (DOI)
Available from: 2005-05-04 Created: 2005-05-04 Last updated: 2011-06-01Bibliographically approved
2. Spatial variation in concentrations and fluxes of dissolved organic carbon in a catchment network of boreal streams in northern Sweden
Open this publication in new window or tab >>Spatial variation in concentrations and fluxes of dissolved organic carbon in a catchment network of boreal streams in northern Sweden
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences Natural Sciences
Research subject
Chemistry; Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2828 (URN)
Available from: 2005-05-04 Created: 2005-05-04 Last updated: 2016-12-14Bibliographically approved
3. Landscape scale patterns in the character of dissolved organic carbon in a boreal stream network
Open this publication in new window or tab >>Landscape scale patterns in the character of dissolved organic carbon in a boreal stream network
Show others...
(English)Manuscript (Other academic)
National Category
Natural Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2829 (URN)
Available from: 2005-05-04 Created: 2005-05-04 Last updated: 2016-12-14Bibliographically approved
4. Modelling dissolved organic carbon concentration in Swedish boreal watercourses using map information
Open this publication in new window or tab >>Modelling dissolved organic carbon concentration in Swedish boreal watercourses using map information
Show others...
(English)Manuscript (Other academic)
National Category
Natural Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-2830 (URN)
Available from: 2005-05-04 Created: 2005-05-04 Last updated: 2016-12-14Bibliographically approved

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