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Eutrophication effects on greenhouse gas fluxes from shallow-lake mesocosms override those of climate warming.

https://arctichealth.org/en/permalink/ahliterature275430
Source
Glob Chang Biol. 2015 Dec;21(12):4449-63
Publication Type
Article
Date
Dec-2015
Author
Thomas A Davidson
Joachim Audet
Jens-Christian Svenning
Torben L Lauridsen
Martin Søndergaard
Frank Landkildehus
Søren E Larsen
Erik Jeppesen
Source
Glob Chang Biol. 2015 Dec;21(12):4449-63
Date
Dec-2015
Language
English
Publication Type
Article
Keywords
Air Pollutants - analysis
Carbon Dioxide - analysis
Climate change
Denmark
Eutrophication
Greenhouse Effect
Lakes - analysis
Methane - analysis
Temperature
Abstract
Fresh waters make a disproportionately large contribution to greenhouse gas (GHG) emissions, with shallow lakes being particular hot spots. Given their global prevalence, how GHG fluxes from shallow lakes are altered by climate change may have profound implications for the global carbon cycle. Empirical evidence for the temperature dependence of the processes controlling GHG production in natural systems is largely based on the correlation between seasonal temperature variation and seasonal change in GHG fluxes. However, ecosystem-level GHG fluxes could be influenced by factors, which while varying seasonally with temperature are actually either indirectly related (e.g. primary producer biomass) or largely unrelated to temperature, for instance nutrient loading. Here, we present results from the longest running shallow-lake mesocosm experiment which demonstrate that nutrient concentrations override temperature as a control of both the total and individual GHG flux. Furthermore, testing for temperature treatment effects at low and high nutrient levels separately showed only one, rather weak, positive effect of temperature (CH4 flux at high nutrients). In contrast, at low nutrients, the CO2 efflux was lower in the elevated temperature treatments, with no significant effect on CH4 or N2 O fluxes. Further analysis identified possible indirect effects of temperature treatment. For example, at low nutrient levels, increased macrophyte abundance was associated with significantly reduced fluxes of both CH4 and CO2 for both total annual flux and monthly observation data. As macrophyte abundance was positively related to temperature treatment, this suggests the possibility of indirect temperature effects, via macrophyte abundance, on CH4 and CO2 flux. These findings indicate that fluxes of GHGs from shallow lakes may be controlled more by factors indirectly related to temperature, in this case nutrient concentration and the abundance of primary producers. Thus, at ecosystem scale, response to climate change may not follow predictions based on the temperature dependence of metabolic processes.
PubMed ID
26258771 View in PubMed
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Forest streams are important sources for nitrous oxide emissions.

https://arctichealth.org/en/permalink/ahliterature309222
Source
Glob Chang Biol. 2020 02; 26(2):629-641
Publication Type
Journal Article
Date
02-2020
Author
Joachim Audet
David Bastviken
Mirco Bundschuh
Ishi Buffam
Alexander Feckler
Leif Klemedtsson
Hjalmar Laudon
Stefan Löfgren
Sivakiruthika Natchimuthu
Mats Öquist
Mike Peacock
Marcus B Wallin
Author Affiliation
Department of Bioscience, Aarhus University, Silkeborg, Denmark.
Source
Glob Chang Biol. 2020 02; 26(2):629-641
Date
02-2020
Language
English
Publication Type
Journal Article
Keywords
Fertilizers
Forests
Nitrous Oxide
Soil
Sweden
Abstract
Streams and river networks are increasingly recognized as significant sources for the greenhouse gas nitrous oxide (N2 O). N2 O is a transformation product of nitrogenous compounds in soil, sediment and water. Agricultural areas are considered a particular hotspot for emissions because of the large input of nitrogen (N) fertilizers applied on arable land. However, there is little information on N2 O emissions from forest streams although they constitute a major part of the total stream network globally. Here, we compiled N2 O concentration data from low-order streams (~1,000 observations from 172 stream sites) covering a large geographical gradient in Sweden from the temperate to the boreal zone and representing catchments with various degrees of agriculture and forest coverage. Our results showed that agricultural and forest streams had comparable N2 O concentrations of 1.6 ± 2.1 and 1.3 ± 1.8 µg N/L, respectively (mean ± SD) despite higher total N (TN) concentrations in agricultural streams (1,520 ± 1,640 vs. 780 ± 600 µg N/L). Although clear patterns linking N2 O concentrations and environmental variables were difficult to discern, the percent saturation of N2 O in the streams was positively correlated with stream concentration of TN and negatively correlated with pH. We speculate that the apparent contradiction between lower TN concentration but similar N2 O concentrations in forest streams than in agricultural streams is due to the low pH (
PubMed ID
31465582 View in PubMed
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