Geospatial Analysis of Alaskan Lakes Indicates Wetland Fraction and Surface Water Area Are Useful Predictors of Methane Ebullition

Figures & data

Figure 1. Remotely sensed wintertime methane ebullition flux (g CH₄ m⁻²yr⁻¹) for 5,143 Alaskan lakes as estimated by Engram, Walter Anthony, and Meyer (2020) for five study regions: (A) Atqasuk, (B) Barrow Peninsula, (C) Fairbanks, (D) Seward Peninsula, and (E) Toolik.

Table 1. Study site characteristics and ebullitive fluxes

Region	Lake types	Permafrost	MAAT (˚C)	n	M lake area ± SD (km^2)	M ebullitive flux (mg m^−2 d^−1 lake^−1)	Total ebullitive flux (mg m^−2 d^−1)
Atqasuk	Thermokarst (non-yedoma)	Continuous	−9.8	2,397	0.15 ± 0.47	1.32 ± 2.29	3,160
Barrow	Thermokarst (non-yedoma)	Continuous	−10.3	1,448	0.33 ± 2.02	3.62 ± 3.17	5,239
Fairbanks	Thermokarst (yedoma), anthropogenic gravel pit, Tanana River floodplain	Discontinuous	−4.0	178	0.04 ± 0.07	17.3 ± 24.0	3,085
Seward	Thermokarst (yedoma)	Continuous	−6.5	629	0.08 ± 0.21	10.9 ± 10.1	6,884
Toolik	Glacial	Continuous	−9.0	491	0.05 ± 0.11	5.50 ± 6.95	2,702

Note: MAAT = mean annual air temperature.

Table 2. Selected representative variables with sources, variable descriptions, shorthand variable names, data formats, and spatial resolutions

Source	Variable description	Variable name	Data format	Resolution	n
Engram, Walter Anthony, and Meyer (2020)	Region (Atqasuk, Barrow, Fairbanks, Seward, or Toolik)	Region	Categorical	0.005 km^2	5,143
	Methane ebullition flux (mg m^−2 d^−1)	MassFlxCH4	Vector	0.005 km^2	5,143
	Lake area (km^2)	AreaSqkm
Derived from Engram, Walter Anthony, and Meyer (2020)	Lake perimeter (km)	Perimeter	Tabular	0.005 km^2	5,143
Messager et al. (2016)	Lake depth (m)	Depth_avg	Vector	0.1 km^2	1,224
Pastick et al. (2015)	Mean permafrost probability within 1 m of the surface	Pfrst_mean	Raster	30 m	5,143
J. A. Wang et al. (2019)	Fraction of combined wetland class (LWF) in lake and surrounding wetlands within 100 m of lake	lbf_100n	Raster	30 m	5,139
Thornton et al. (2020)	Average winter temperature (˚C)	Tavg_W	Raster	1 km	5,141
Poggio et al. (2021)	Soil organic carbon content in the fine earth fraction (dg/kg)	SOC	Raster	250 m	5,130
C. Kuhn and Butman (2021)	Mean Landsat growing season surface reflectance (Rs) in the green wavelengths	Greenness	Tabular	0.1 km^2	1,061

Note. An expanded version of this table presenting all compiled variables is available in the Supplemental Materials (Table S.2).

Figure 2. Schematic for lake wetland fraction (LWF) calculation. (A) Engram, Walter Anthony, and Meyer (2020) vector lake outline with a 100-m buffer and J. A. Wang et al. (2019) water class. (B) 100-m buffer and J. A. Wang et al. (2019) water, littoral, bog, and fen classes. (C) 100-m buffer and J. A. Wang et al. (2019) water and combined wetlands classes. The two classes within the buffer in (C) are used to calculate LWF.

Table 3. Best performing individual linear regression models for representative variables from each data set, ordered by adjusted R², which accounts for the number of observations (n)

Variable	Adjusted R^2	n	p value
Region	0.320	5,143	< 0.001
Lake wetland fraction	0.211	5,132	< 0.001
Lake area	0.201	5,143	< 0.001
Lake perimeter	0.176	5,143	< 0.001
Average winter temperature	0.157	5,141	< 0.001
Soil organic carbon	0.059	5,129	0.001
Permafrost	0.038	5,143	< 0.001
Lake depth	0.029	1,224	< 0.001
Lake greenness	0.016	1,061	< 0.001

Table 4. Multiple linear regression model results ordered by adjusted R² including the additional test model with region

Equation	Adjusted R^2	AIC	n
Lake area + LWF + Average winter temperature	0.325	3,765.0	5,130
Lake area + LWF + Permafrost	0.237	4,397.0	5,132
Lake area + LWF + SOC	0.227	4,434.0	5,118
Lake area + LWF	0.226	4,467.0	5,132
Lake area + LWF + Lake depth	0.086	767.2	1,224
Lake area + LWF + Lake greenness	0.037	554.1	1,061
(Lake area + LWF + Average winter temperature): Region	0.481	2,430.0	5,130

Note. LWF = lake wetland fraction; SOC = soil organic carbon. Both adjusted R² and Akaike’s information criterion (AIC) are measures of model quality used for model selection. Adjusted R² considers the number of observations (n) but AIC does not; a higher adjusted R² and lower AIC indicates a better model. All variables are log-transformed.

Figure 3. Methane ebullitive flux versus (A) lake wetland fraction, and (B) lake area with corresponding individual regression models.

Figure 4. Observed linear relationship between lake area and lake wetland fraction.

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