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The role of lakes in carbon cycling in boreal catchments

Abstract

Lakes are an important component of ecosystem carbon cycle through both organic carbon sequestration and carbon dioxide and methane emissions, although they cover only a small fraction of the Earth's surface area. Lake sediments are considered to be one of rather permanent sinks of carbon in boreal regions and furthermore, freshwater ecosystems process large amounts of carbon originating from terrestrial sources. These carbon fluxes are highly uncertain especially in the changing climate. The present study provides a large-scale view on carbon sources and fluxes in boreal lakes situated in different landscapes. We present carbon concentrations in water, pools in lake sediments, and carbon gas (CO{sub 2} and CH{sub 4}) fluxes from lakes. The study is based on spatially extensive and randomly selected Nordic Lake Survey (NLS) database with 874 lakes. The large database allows the identification of the various factors (lake size, climate, and catchment land use) determining lake water carbon concentrations, pools and gas fluxes in different types of lakes along a latitudinal gradient from 60 deg N to 69 deg N. Lakes in different landscapes vary in their carbon quantity and quality. Carbon (C) content (total organic and inorganic carbon) in lakes is highest in agriculture and peatland  More>>
Authors:
Publication Date:
Jul 01, 2010
Product Type:
Thesis/Dissertation
Resource Relation:
Other Information: Thesis or Dissertation; TH: Thesis (Ph.D.); 123 refs. Monographs of the Boreal Environment Research 35. The thesis includes also 6 previous publications published elsewhere
Subject:
54 ENVIRONMENTAL SCIENCES; LAKES; LEACHING; SOILS; WATERSHEDS; WETLANDS; PEAT; AGRICULTURE; BOREAL REGIONS; CARBON CYCLE; EMISSION; CARBON DIOXIDE; METHANE
OSTI ID:
1008047
Research Organizations:
Helsinki Univ. (Finland). Dept. of Environmental Sciences, Aquatic sciences
Country of Origin:
Finland
Language:
English
Other Identifying Numbers:
Other: ISBN 978-952-11-3743-3; ISBN 978-952-11-3744-0; TRN: FI1103015
Availability:
Available in fulltext at http://www.environment.fi/download.asp?contentid=117984&lan=en
Submitting Site:
FI
Size:
38 p. pages
Announcement Date:
Mar 14, 2011

Citation Formats

Rantakari, M. The role of lakes in carbon cycling in boreal catchments. Finland: N. p., 2010. Web.
Rantakari, M. The role of lakes in carbon cycling in boreal catchments. Finland.
Rantakari, M. 2010. "The role of lakes in carbon cycling in boreal catchments." Finland.
@misc{etde_1008047,
title = {The role of lakes in carbon cycling in boreal catchments}
author = {Rantakari, M}
abstractNote = {Lakes are an important component of ecosystem carbon cycle through both organic carbon sequestration and carbon dioxide and methane emissions, although they cover only a small fraction of the Earth's surface area. Lake sediments are considered to be one of rather permanent sinks of carbon in boreal regions and furthermore, freshwater ecosystems process large amounts of carbon originating from terrestrial sources. These carbon fluxes are highly uncertain especially in the changing climate. The present study provides a large-scale view on carbon sources and fluxes in boreal lakes situated in different landscapes. We present carbon concentrations in water, pools in lake sediments, and carbon gas (CO{sub 2} and CH{sub 4}) fluxes from lakes. The study is based on spatially extensive and randomly selected Nordic Lake Survey (NLS) database with 874 lakes. The large database allows the identification of the various factors (lake size, climate, and catchment land use) determining lake water carbon concentrations, pools and gas fluxes in different types of lakes along a latitudinal gradient from 60 deg N to 69 deg N. Lakes in different landscapes vary in their carbon quantity and quality. Carbon (C) content (total organic and inorganic carbon) in lakes is highest in agriculture and peatland dominated areas. In peatland rich areas organic carbon dominated in lakes but in agricultural areas both organic and inorganic C concentrations were high. Total inorganic carbon in the lake water was strongly dependent on the bedrock and soil quality in the catchment, especially in areas where human influence in the catchment is low. In inhabited areas both agriculture and habitation in the catchment increase lake TIC concentrations, since in the disturbed soils both weathering and leaching are presumably more efficient than in pristine areas. TOC concentrations in lakes were related to either catchment sources, mainly peatlands, or to retention in the upper watercourses. Retention as a regulator of the TOC concentrations dominated in southern Finland, whereas the peatland sources were important in northern Finland. The homogeneous land use in the north and the restricted catchment sources of TOC contribute to the close relationship between peatlands and the TOC concentrations in the northern lakes. In southern Finland the more favorable climate for degradation and the multiple sources of TOC in the mixed land use highlight the importance of retention.Carbon processing was intensive in the small lakes. Both CO{sub 2} emission and the Holocene C pool in sediments per square meter of the lake area were highest in the smallest lakes. How-ever, because the total area of the small lakes on the areal level is limited, the large lakes are important units in C processing in the landscape. Both CO{sub 2} and CH{sub 4} concentrations and emissions were high in eutrophic lakes. High availability of nutrients and the fresh organic matter enhance degradation in these lakes. Eutrophic lakes are often small and shallow, enabling high contact between the water column and the sediment. At the landscape level, the lakes in agricultural areas are often eutrophic due to fertile soils and fertilization of the catchments, and therefore they also showed the highest CO{sub 2} and CH{sub 4} concentrations. Export from the catchments and in-lake degradation were suggested to be equally important sources of CO{sub 2} and CH{sub 4} in fall when the lake water column was intensively mixed and the transport of sub-stances from the catchment was high due to the rainy season. In the stagnant periods, especially in the winter, in-lake degradation as a gas source was highlighted due to minimal mixing and limited transport of C from the catchment.The strong relationship between the annual CO{sub 2} level of lakes and the annual precipitation suggests that climate change can have a major impact on C cycling in the catchments. Increase in precipitation enhances DOC export from the catchments and leads to increasing greenhouse gas emissions from lakes. The total annual CO{sub 2} emission from Finnish lakes was estimated to be 1400 Gg C a-1. The total lake sediment C pool in Finland was estimated to be 0.62 Pg, giving an annual sink in Finnish lakes of 65 Gg C a-1. (orig.)}
place = {Finland}
year = {2010}
month = {Jul}
}