Methane dynamics in different boreal lake types

Abstract

Abstract. This study explores the variability in concentrations of dissolved CH 4 and annual flux estimates in the pelagic zone in a statistically defined sample of 207 lakes in Finland. The lakes were situated in the boreal zone, in an area where the mean annual air temperature ranges from −2.8 to 5.9 • C. We examined how lake CH 4 dynamics related to regional lake types assessed according to the EU water framework directive. Ten lake types were defined on the basis of water chemistry, color, and size. Lakes were sampled for dissolved CH 4 concentrations four times per year, at four different depths at the deepest point of each lake. We found that CH 4 concentrations and fluxes to the atmosphere tended to be high in nutrient rich calcareous lakes, and that the shallow lakes had the greatest surface water concentrations. Methane concentration in the hypolimnion was related to oxygen and nutrient concentrations, and to lake depth or lake area. The surface water CH 4 concentration was related to the depth or area of lake. Methane concentration close to the bottom can be viewed as proxy of lake status in terms of frequency of anoxia and nutrient levels. The mean pelagic CH 4 release from randomly selected lakes was 49 mmol m −2 a −1 . The sum CH 4 flux (storage and diffusion) correlated with lake depth, area and nutrient content, and CH 4 release was greatest from the shallow nutrient rich and humic lakes. Our results support earlier lake studies regarding the regulating factors and also the magnitude of global emission estimate. These results propose that in boCorrespondence to: S. Juutinen (sjuutine@mtholyoke.edu) real region small lakes have higher CH 4 fluxes per unit area than larger lakes, and that the small lakes have a disproportionate significance regarding to the CH 4 release.

Exceptional summer warming leads to contrasting outcomes for methane cycling in small Arctic lakes of Greenland

“…Methane (CH 4 ) emissions from freshwater environments are expected to increase with warming climates (Juutinen et al, 2009;Yvon-Durocher et al, 2011Tan and Zhuang 2015a, b) but quantitative modeled projections of emissions are poorly constrained (Bastviken et al, 2011;Rasilo et al, 2015;Sepulveda-Jauregui et al, 2015;Tan et al, 2015). Observations of seasonal and annual lake CH 4 dynamics in the Arctic are necessary to define source estimates in models and understand the impact warming may have on greenhouse gas emissions.…”

“…Observations of seasonal and annual lake CH 4 dynamics in the Arctic are necessary to define source estimates in models and understand the impact warming may have on greenhouse gas emissions. Currently, in the Arctic, small lakes (surface area < 10 km 2 ) are abundant (Downing, 2010;Downing et al, 2006) and emit substantially more CH 4 per unit area than larger lakes (Bastviken et al, 2004;Cole et al, 2007;Juutinen et al, 2009;Wik et al, 2016), and seasonal variability in CH 4 emissions are influenced by energy input and organic carbon availability (Tan et al, 2015). However, climate change will lead to variations in heat balance, temperature profiles, and vertical mixing in lakes (Jankowski et al, 2006;MacIntyre et al, 2009;Hinkel et al, 2012;Butcher et al, 2015), causing many variations to both lake structure (Livingstone 2003;Coats et al, 2006) and CH 4 dynamics.…”

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

“…Numerous processes were found to proceed faster in small aquatic systems than in larger ones. Sequestration rates of organic carbon (Downing, 2010;Downing et al, 2008), the concentrations of CH 4 , CO 2 , and dissolved organic carbon (DOC) in the water column (Bastviken et al, 2004;Juutinen et al, 2009;Kelly et al, 2001;Kortelainen et al, 2006;Xenopoulos et al, 2003), and CH 4 and CO 2 emissions from the water to the atmosphere increase with decreasing lake size (Juutinen et al, 2009;Kortelainen et al, 2006;Michmerhuizen et al, 1996;Repo et al, 2007).…”

Environmental Impacts—Lake Ecosystems

“…Increased N-deposition in concert with elevated export of DOM may promote export of N 2 O (Hong et al 2015). For lakes in agricultural systems, increased productivity due to increased nutrient inputs from the catchment may promote the net efflux of CH 4 and N 2 O (Juutinen et al 2009;Hong et al 2015), while the net impact of the CO 2 -balance will also depend on lake morphometry and stratification and so is harder to predict.…”

“…Increased loads of DOM in boreal lakes would also promote anoxia in the deeper water layers, which promotes CH 4 production and its net flux to the atmosphere (Juutinen et al 2009). Increased N-deposition in concert with elevated export of DOM may promote export of N 2 O (Hong et al 2015).…”