High spatial resolution remote sensing models for landscape-scale CO₂ exchange in the Canadian Arctic

Figures & data

Figure 1. IKONOS multispectral data for the study sites: (a) Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut (collected in 2004); and (b) Sanagak Lake (SL), Boothia Peninsula, Nunavut (collected in 2001). IKONOS images are displayed as color infrared composites: Bands 4 (near infrared), 3 (red), and 2 (green)

Table 1. Classification summary for dry, mesic, and wet vegetation types at the Cape Bounty Arctic Watershed Observatory (CBAWO) and Sanagak Lake (SL)

	CBAWO			SL
Ecosystem	Dry P. radicatum and till tundra	Mesic Nostoc tundra	Wet sedge tundra	Dry Dryas spp. and till tundra	Mesic Dryas spp. tundra	Wet sedge tundra
Soil moisture (%)	17.1	37.3	123.9	17.2	41.2	123.3
Percent vegetation cover (%)	50.2	101.7	154.0	30.4	80.4	144.8
Bryophyte cover (%)	11.6	57.7	88.0	8.8	1.3	59.7
Graminoid cover (%)	0.0	21.8	71.4	0.5	16.8	38.1
Shrub cover (%)	4.3	0.0	2.9	25.0	57.9	32.1
Lichen cover (%)	11.4	9.0	1.6	1.0	1.1	1.4
Forb cover (%)	0.7	4.1	0.8	0.3	1.2	0.0
Biomass (g m^−2)	348.5	1,477.3	1,561.6	298.2	521.7	825.6
Cover (%)	26.9	89.9	141.0	41.0	87.0	131.3
Primary cover	Till	Nostoc commune	Sphagnum spp.	Till	Dryas spp.	Sphagnum spp.
Secondary cover	Mosses	Mosses	Eriophorum spp.	Dryas spp.	Carex spp.	Eriophorum spp.
Indicator species	P. radicatum	Nostoc commune	Eriophorum spp.	n/a	Dryas spp.	Eriophorum spp.
Bioclimatic class (Walker et al. 2005)	P1	G1	W1	P1	G2	W1

Notes.P1 –  prostrate dwarf shrub and herb tundra; G1 – rush/grass, forb, cryptogam tundra; G2 – graminoid, prostrate dwarf shrub, forb tundra; W1 – sedge/grass, moss wetland.

Table 2. p Value results from two-way repeated measures analysis of variance (ANOVA) testing the effect of site (Cape Bounty Arctic Watershed Observatory versus Sanagak Lake), vegetation type (dry tundra versus mesic tundra versus wet tundra), and time on gross ecosystem exchange (GEE), ecosystem respiration (ER), and net ecosystem exchange (NEE). Numbers within the brackets signify degrees of freedom between and within groups respectively

Flux	Site(1,7)	Veg.(2,7)	Site × Veg.(2,7)	Time(3,21)	Time × Site(3,21)	Time × Veg.(6,21)
GEE	0.65	0.004	0.32	0.06	0.22	0.89
ER	0.89	0.097	0.63	0.22	0.02	0.73
NEE	0.86	0.078	0.36	0.27	0.77	0.50

Figure 2. Mean daytime carbon dioxide (CO₂) exchange rates for the Cape Bounty Arctic Watershed Observatory (CBAWO): (a) dry tundra (DT), (b) mesic tundra (MT), (c) wet tundra (WT); and Sanagak Lake (SL): (d) DT, (e) MT, and (f) WT. Positive CO₂ exchange rates indicate CO₂ loss to the atmosphere, whereas negative signed values indicate CO₂ gain to the vegetation type. Error bars represent standard error of the mean

Table 3. Averaged carbon dioxide (CO₂) flux rates for the duration of the study period (mmol CO₂ m^-2 s^-1) with standard error in parentheses (by vegetation type and geographic location)

	GEE		ER		NEE
Vegetation type	CBAWO	SL	CBAWO	SL	CBAWO	SL
DT	–0.58 (±0.11)	0.02 (±0.14)	0.03 (±0.08)	0.66 (±0.14)	0.74 (±0.05)	0.64 (±0.09)
MT	–1.09 (±0.13)	–1.27 (±0.13)	0.15 (±0.11)	–0.24 (±0.12)	1.25 (±0.08)	1.04 (±0.06)
WT	–2.15 (±0.14)	–1.51 (±0.15)	–0.87 (±0.12)	–0.21 (±0.15)	1.29 (±0.09)	1.31 (±0.06)

Notes. Dry tundra (DT), mesic tundra (MT), wet tundra (WT), gross ecosystem exchange (GEE), ecosystem respiration (ER), net ecosystem exchange (NEE), Cape Bounty Arctic Watershed Observatory (CBAWO), Sanagak Lake (SL).

Figure 3. Interpolated total daily carbon dioxide (CO2) exchange rates for dry tundra (DT), mesic tundra (MT) and wet tundra (WT) at the Cape Bounty Arctic Watershed Observatory (CBAWO) and Sanagak Lake (SL) during the study period

Table 4. Multiple linear regression analysis for plot-level daily averaged carbon dioxide (CO₂) exchange rates in relation to averaged environmental variables (p < .05)

Site	Flux	Type	Predictor	Slope	R^2 adjusted	RMSE	F	p Value	df
CBAWO	GEE	DT	Air temperature	0.65	0.595	0.10	15.69	.003	1, 9
	ER	DT	Air temperature	−0.45	0.542	0.08	12.81	.006	1, 9
		MT	Soil moisture, air temperature	4.02	0.651	0.06	9.38	.010	2, 7
	NEE	MT	Photosynthetically active radiation (PAR)	2.84	0.331	0.12	5.46	.048	1, 8
SL	ER	DT	Soil temperature (10 cm)	0.24	0.996	0.00	729.49	.001	1, 2
		MT	Air temperature	0.42	0.212	0.07	4.77	.048	1, 13
		WT	Soil temperature (10 cm)	0.42	0.676	0.04	19.77	.002	1, 8
	NEE	MT	Soil temperature (10 cm)	−1.23	0.259	0.09	5.890	.030	1, 13

Notes. Dry tundra (DT), mesic tundra (MT), wet tundra (WT), gross ecosystem exchange (GEE), ecosystem respiration (ER), net ecosystem exchange (NEE), Cape Bounty Arctic Watershed Observatory (CBAWO), Sanagak Lake (SL)

Table 5. Bivariate linear regression $\left(Y={\beta }_0+{\beta }_{1}X+\mathrm{E}\right)$ and analysis of covariance (ANCOVA) results for carbon dioxide (CO₂) exchange components gross ecosystem exchange (GEE), ecosystem respiration (ER), and net ecosystem exchange (NEE) with the normalized difference vegetation index (NDVI) for the Cape Bounty Arctic Watershed Observatory (CBAWO) and Sanagak Lake (SL)

						ANCOVA
CO2 flux (Y)	Site	Slope (${\beta }_1$)	Intercept (${\beta }_0$)	R^2	RMSE	Slope (p value)	Intercept (p value)
GEE	CBAWO	−8.41	0.04	0.64	0.23	.695	.528
	SL	−7.72	0.15	0.72	0.14
	Combined	−8.15	0.10	0.65	0.48
	Validation	−7.85	0.15	0.48	0.96	.932	.748
	Combined	−8.05	0.13	0.54	0.70
ER	CBAWO	3.97	0.58	0.66	0.06	.391	.199
	SL	4.07	0.38	0.94	0.02
	Combined	4.03	0.49	0.70	0.21
	Validation	3.81	0.43	0.75	0.26	.847	.337
	Combined	3.97	0.46	0.73	0.23
NEE	CBAWO	−4.28	0.57	0.33	0.14	.485	.916
	SL	−3.25	0.36	0.48	0.08
	Combined	−3.87	0.48	0.35	0.42
	Validation	−3.85	0.54	0.26	0.75	.994	.815
	Combined	−3.91	0.51	0.30	0.57

Figure 4. Combined bivariate linear regressions for carbon dioxide (CO₂) exchange rates: gross ecosystem exchange (GEE), ecosystem respiration (ER), and net ecosystem exchange (NEE)

Table 6. Normalized difference vegetation index (NDVI) model-based carbon dioxide (CO₂) exchange rates for the Cape Bounty Arctic Watershed Observatory (CBAWO) and Sanagak Lake (SL)

Site	Area (km^2)	Flux	Mg CO2 day^−1	SMAPE estimate (%)
CBAWO	80.74	GEE	−141.16	27.2
		ER	244.77	6.4
		NEE	64.19	57.6
SL	74.32	GEE	−338.14	27.2
		ER	305.77	6.4
		NEE	−36.76	57.6

Notes. Gross ecosystem exchange (GEE), ecosystem respiration (ER), net ecosystem exchange (NEE), Symmetric mean absolute percentage error (SMAPE).

Figure 5. One-to-one comparisons of actual calibration values and normalized difference vegetation index (NDVI) modeled values for gross ecosystem exchange (GEE), ecosystem respiration (ER), and net ecosystem exchange (NEE)

Figure 6. Spatially-explicit models of (a) gross ecosystem exchange (GEE) and (b) ecosystem respiration (ER) for the Cape Bounty Arctic Watershed Observatory (CBAWO) (left) and Sanagak Lake (SL) (right). White indicates no flux data

Walker, D. A., M. K. Raynolds, F. J. A. Daniels, E. Einarsson, A. Elvebakk, W. A. Gould, A. E. Katenin, S. S. Kholod, C. J. Markon, E. S. Melnikov, et al. 2005. The circumpolar arctic vegetation map. Journal of Vegetation Science 16:267–82. doi:https://doi.org/10.1111/j.1654-1103.2005.tb02365.x.

 Web of Science ®Google Scholar