Frost boils in northern Alaska vary from large, 2–3-m diameter, barren non-sorted circles to completely vegetated hummocks. Summer warmth increases southwards from the coast. Average thaw-layer thickness shows the opposite trend. Frost heave shows no trend along the climate gradient but is affected by soil texture. Heave is greatest on frost boils with fine-grained sediments. Biomass increases from 183 g m � 2 at the coast to 813 g m � 2 in the Arctic Foothills. An aggrading permafrost table is evident in most of the frost-boil soil profiles, indicating that, over time, accumulation of plant biomass leads to reduced thaw-layer thickness. A conceptual model suggests how vegetation affects the morphology of patterned ground forms. In the coldest parts of the High Arctic well-developed frost boils do not form and there is little vegetation on frost boils or the inter-boil areas. In the warmest parts of the Low Arctic, vegetation is usually sufficient to stabilize the frost boil soils. Frost boils play an important role in Arctic ecosystems functions, including the flux of trace gases to the atmosphere, flux of water and nutrients to streams, and the recycling of important nutrients to wildlife populations. Copyright # 2004 John Wiley & Sons, Ltd.

/pdf/frost-boil-ecosystems-complex-interactions-between-landforms-h18snjhctk.pdf

Frost‐boil ecosystems: complex interactions between landforms, soils, vegetation and climate

Arctic tundra environments are thought to be particularly sensitive to changes in climate, whereby alterations in ecosystem functioning are likely to be expressed through shifts in vegetation phenology, species composition, and net ecosystem productivity (NEP). Remote sensing has shown potential as a tool to quantify and monitor biophysical variables over space and through time. This study explores the relationship between the normalized difference vegetation index (NDVI) and percent-vegetation cover in a tundra environment, where variations in soil moisture, exposed soil, and gravel till have significant influence on spectral response, and hence, on the characterization of vegetation communities. IKONOS multispectral data (4 m spatial resolution) and Landsat 7 ETM+ data (30 m spatial resolution) were collected for a study area in the Lord Lindsay River watershed on Boothia Peninsula, Nunavut. In conjunction with image acquisition, percent cover data were collected for twelve 100 m × 100 m study plots to determine vegetation community composition. Strong correlations were found for NDVI values calculated with surface and satellite sensors, across the sample plots. In addition, results suggest that percent cover is highly correlated with the NDVI, thereby indicating strong potential for modeling percent cover variations over the region. These percent cover variations are closely related to moisture regime, particularly in areas of high moisture (e.g., water-tracks). These results are important given that improved mapping of Arctic vegetation and associated biophysical variables is needed to monitor environmental change.

https://journalhosting.ucalgary.ca/index.php/arctic/article/download/63073/47013

Remote Sensing of Arctic Vegetation: Relations between the NDVI, Spatial Resolution and Vegetation Cover on Boothia Peninsula, Nunavut

Measurements of net ecosystem CO 2 exchange (NEE) and energy balance were made using chamber-, tower-, and aircraft-based measurement techniques in Alaskan arctic tundra ecosystems during the 1994-1995 growing seasons (June-August). One of our objectives was to quantify the interrelationships between the NEE and the energy balance measurements made from different sampling techniques. Oualitative and quantitative intercomparisons revealed that on average the correspondence between the mass and energy fluxes measured by these sampling methods was good despite potential spatial and temporal mismatches in sampling scale. Quantitative comparisons using least squares linear regression analyses with the tower-based measurements of NEE as the independent variable indicate that the chamber- and aircraft-based NEE measurements were generally lower relative to the tower-based measurements (slope = 0.76-0.86). Similarly, tower-aircraft comparisons of latent (L e ) and sensible (H) heat exchange indicated that the aircraft-based measurements were lower than the tower-based measurements (slope = 0.72-0.80). Qualitative comparisons, however, indicate that the correspondence among the chamber-, tower-, and aircraft-measured fluxes varied both seasonally and interannually, suggesting the lack of a consistent bias between the sampling techniques. The results suggest that differences observed between the chamber, tower, and aircraft flux measurements were primarily due to the failure to account for the spatial distribution of surface types in the tower and aircraft sampling footprint, problems involved in the comparison of temporal and spatial averages, and temporal (e.g., seasonal and interannual) variance in rates of mass and energy flux for a given point. Other potential sources of variance include the underestimation of nocturnal NEE by the tower-based eddy covariance system, and the periodic occurrence of an elevated CO 2 plume in the atmosphere over the Prudhoe Bay oil field. Even with these potential sources of variation, the results reveal that the various methods give comparable estimates of NEE and energy flux within a range of temporal or spatial variability.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998JD200015

Intercomparison among chamber, tower, and aircraft net CO2 and energy fluxes measured during the Arctic System Science Land-Atmosphere-Ice Interactions (ARCSS-LAII) Flux Study

Summary

Net CO2 flux measurements conducted during the summer and winter of 1994–96 were scaled in space and time to provide estimates of net CO2 exchange during the 1995–96 (9 May 1995–8 May 1996) annual cycle for the Kuparuk River Basin, a 9200 km2 watershed located in NE Alaska. Net CO2 flux was measured using dynamic chambers and eddy covariance in moist-acidic, nonacidic, wet-sedge, and shrub tundra, which comprise 95% of the terrestrial landscape of the Kuparuk Basin. CO2 flux data were used as input to multivariate models that calculated instantaneous and daily rates of gross primary production (GPP) and whole-ecosystem respiration (R) as a function of meteorology and ecosystem development. Net CO2 flux was scaled up to the Kuparuk Basin using a geographical information system (GIS) consisting of a vegetation map, digital terrain map, dynamic temperature and radiation fields, and the models of GPP and R.



Basin-wide estimates of net CO2 exchange for the summer growing season (9 May−5 September 1995) indicate that nonacidic tundra was a net sink of −31.7 ± 21.3 GgC (1 Gg = 109 g), while shrub tundra lost 32.5 ± 6.3 GgC to the atmosphere (negative values denote net ecosystem CO2 uptake). Acidic and wet sedge tundra were in balance, and when integrated for the entire Kuparuk River Basin (including aquatic surfaces), whole basin summer net CO2 exchange was estimated to be in balance (−0.9 ± 50.3 GgC). Autumn to winter (6 September 1995–8 May 1996) estimates of net CO2 flux indicate that acidic, nonacidic, and shrub tundra landforms were all large sources of CO2 to the atmosphere (75.5 ± 8.3, 96.4 ± 11.4, and 43.3 ± 4.7 GgC for acidic, nonacidic, and shrub tundra, respectively). CO2 loss from wet sedge surfaces was not substantially different from zero, but the large losses from the other terrestrial landforms resulted in a whole basin net CO2 loss of 217.2 ± 24.1 GgC during the 1995–96 cold season. When integrated for the 1995–96 annual cycle, acidic (66.4 + 25.25 GgC), nonacidic (64.7 ± 29.2 GgC), and shrub tundra (75.8 ± 8.4 GgC) were substantial net sources of CO2 to the atmosphere, while wet sedge tundra was in balance (0.4 + 0.8 GgC). The Kuparuk River Basin as a whole was estimated to be a net CO2 source of 218.1 ± 60.6 GgC over the 1995–96 annual cycle. Compared to direct measurements of regional net CO2 flux obtained from aircraft-based eddy covariance, the scaling procedure provided realistic estimates of CO2 exchange during the summer growing season. Although winter estimates could not be assessed directly using aircraft measurements of net CO2 exchange, the estimates reported here are comparable to measured values reported in the literature. Thus, we have high confidence in the summer estimates of net CO2 exchange and reasonable confidence in the winter net CO2 flux estimates for terrestrial landforms of the Kuparuk river basin. Although there is larger uncertainty in the aquatic estimates, the small surface area of aquatic surfaces in the Kuparuk river basin (≈ 5%) presumably reduces the potential for this uncertainty to result in large errors in basin-wide CO2 flux estimates.

A scaling approach for quantifying the net CO2 flux of the Kuparuk River Basin, Alaska

Northern ecosystems are a major sink for atmospheric CO2 and contain much of the world's soil organic carbon (SOC) that is potentially reactive to near-term climate change. We introduce a simple terrestrial carbon flux (TCF) model driven by satellite remote sensing inputs from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) to estimate surface (<10-cm depth) SOC stocks, daily respiration, and net ecosystem carbon exchange (NEE). Soil temperature and moisture information from AMSR-E provide environmental constraints to soil heterotrophic respiration (R h), while gross primary production (GPP) information from MODIS provides estimates of the total photosynthesis and autotrophic respiration. The model results were evaluated across a North American network of boreal forest, grassland, and tundra monitoring sites using alternative carbon measures derived from tower CO2 flux measurements and BIOME-BGC model simulations. Root-mean-square-error (rmse) differences between TCF model estimates and tower observations were 1.2, 0.7, and 1.2 g middot C middot m-2 middot day-1 for GPP, ecosystem respiration (Rtot) and NEE, while mean residual differences were 43% of the rmse. Similar accuracies were observed for both TCF and BIOME-BGC model simulations relative to tower results. TCF-model-derived SOC was in general agreement with soil inventory data and indicates that the dominant SOC source for Rh has a mean residence time of less than five years, while R h is approximately 43% and 55% of R tot for respective summer and annual fluxes. An error sensitivity analysis determined that meaningful flux estimates could be derived under prevailing climatic conditions at the study locations, given documented error levels in the remote sensing inputs.

A Satellite Approach to Estimate Land–Atmosphere $\hbox{CO}_{2}$ Exchange for Boreal and Arctic Biomes Using MODIS and AMSR-E

Relating CO 2 fluxes to spectral vegetation indices in tundra landscapes: importance of footprint definition

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Relating CO 2 fluxes to spectral vegetation indices in tundra landscapes: importance of footprint definition