Acidic Tundra Research Articles

Characterizing soil organic matter quality in arctic soil by cover type and depth

In the past 30 years, the arctic climate has warmed appreciably. Mounting evidence suggests that climate warming is being amplified at the earth's polar regions. A warmer Arctic could lead to the gradual loss of circumpolar permafrost. Northern soils are estimated to contain 25–33% of the world's soil carbon, much of which is frozen in permafrost as poorly decomposed plant remains. A warming and thawing of northern permafrost would result in an increase in soil organic matter (SOM) exposed to decomposition. Carbon dioxide (CO 2) or methane (CH 4) released from decomposing SOM would likely result in a positive feedback to climate warming. The rate that SOM decomposes in soil depends on many variables, including temperature, soil moisture, nutrient availability, pH, oxidation–reduction potential, and chemical composition of the SOM. This paper addresses the effect of regional scale ecosystem differences on SOM composition and the potential for CO 2 to be respired from these soils under SOM-limiting conditions. In previous research, an empirical model was developed to predict CO 2 flux from arctic soils based on specific compounds in the SOM. The model was built using an incubation designed to create SOM-limiting conditions and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) analysis of SOM. SOM-limiting conditions were defined as the state in which microbial respiration was limited only by the SOM quality. That is, during the incubation, ample nutrients were available to microorganisms, the pH was neutral, and the system was kept aerobic, mixed, and at 20 °C. SOM that was rapidly mineralized was defined as being of high quality. SOM that was slowly mineralized was defined as being of low quality. With an understanding of SOM quality in different soil types, one can better understand the relative potential for different soils to contribute to atmospheric CO 2 in a warmer, drier arctic environment. In the research described herein, soils from across the Western and Northern Alaska transects were analyzed to determine if SOM quality could be tied to cover class, a parameter that can be remotely sensed. In nearly all cases, SOM quality under similar cover classes was of similar quality regardless of its geographic origin. The clearest trend observed was that SOM quality was highest in soil under moist acidic tundra, followed by tussock tundra and tundra/shrub transitions, shrubs, and nonacidic tundra, respectively.

Responses of moist non‐acidic arctic tundra to altered environment: productivity, biomass, and species richness

In arctic Alaska, researchers have manipulated air temperature, light availability, and soil nutrient availability in several tundra communities over the past two decades. These communities responded quite differently to the same manipulations, and species responded individualistically within communities and among sites. For example, moist acidic tundra is primarily nitrogen (N)‐limited, whereas wet sedge tundra is primarily phosphorus (P)‐limited, and the magnitude of growth responses varies across sites within communities. Here we report results of four years of manipulated nutrients (N and/or P) and/or air temperature in an understudied, diverse plant community, moist non‐acidic tussock tundra, in northern Alaska. Our goals were to determine which factors limit above‐ground net primary productivity (ANPP) and biomass, how community composition changes may affect ecosystem attributes, and to compare these results with those from other communities to determine their generality.Although relative abundance of functional groups shifted in several treatments, the only significant change in community‐level ANPP and biomass occurred in plots that received both N and P, driven by an increase in graminoid biomass and production resulting from a positive effect of adding N. There was no difference in community biomass among any other treatments; however, some growth forms and individual species did respond. After four years no one species has come to dominate the treatment plots and species richness has not changed. These results are similar to studies in dry heath, wet sedge, and moist acidic tundra where community biomass had the greatest response to both N and P and warming results were more subtle. Unlike in moist acidic tundra where shrub biomass increased markedly with fertilization, our results suggest that in non‐acidic tundra carbon sequestration in plant biomass will not increase substantially under increased soil nutrient conditions because of the lack of overstory shrub species.

Carbon and Nitrogen Cycling in Soils from Acidic and Nonacidic Tundra with Different Glacial Histories in Northern Alaska

Moist acidic and nonacidic tundra are two of the most common vegetation types of the tundra in the northern foothills of the Brooks Range, Alaska, and they differ considerably in vegetation, soil nutrient availability, and soil pH. Both occur on mesic, gentle slopes, but acidic tundra is more common on older glacial surfaces whereas nonacidic tundra is more common on younger surfaces. Although much prior research has focused on moist acidic tundra, nonacidic tundra is still relatively unstudied. We compared rates of soil carbon (C) and nitrogen (N) cycling and their response to warming and changes in moisture in moist acidic tundra on Itkillik I glacial drift (50,000 –120,000 years old, pH 3– 4) and moist nonacidic tundra on Itkillik II glacial drift (11,500 – 60,000 year old, pH 6 –7). We hypothesized that rates of soil C and N cycling would be faster at the nonacidic site because it has a more favorable pH for microbial activity and higher-quality organic matter inputs arising from its greater herbaceous plant production relative to the acidic site. However, in contrast to our hypothesis, in situ soil respiration, as well as respiration, dissolved organic C production, and net N mineralization in laboratory incubations, was greater for soils from the acidic site. Nevertheless, the sites responded similarly to manipulations of temperature and moisture, exhibiting exponential increases in respiration with warming between 4°C and 15°C but surprisingly little sensitivity to changes in moisture between 300% and 700%. Slower soil organic matter decomposition at the nonacidic site likely results from the stabilization of soil organic matter by high concentrations of calcium.

Spatial characteristics of AVHRR‐NDVI along latitudinal transects in northern Alaska

Abstract. Two‐weekly AVHRR images were used to examine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental variables for moist acidic tundra (MAT) and moist non‐acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5‐yr time series (1995–1999) of two‐weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homogeneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non‐linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP‐NDVI), average growing season NDVI (GS‐NDVI), and early June NDVI (EJ‐NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p<0.01) relations between NDVI (AP‐NDVI, GS‐NDVI and EJ‐NDVI) and total summer warmth (TSW) and elevation in the region. EJ‐NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant.

Spatial characteristics of AVHRR-NDVI along latitudinal transects in northern Alaska

Two-weekly AVHRR images were used to exam- ine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental vari- ables for moist acidic tundra (MAT) and moist non-acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5-yr time series (1995-1999) of two-weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homo- geneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non-linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP-NDVI), average growing season NDVI (GS-NDVI), and early June NDVI (EJ-NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p < 0.01) relations between NDVI (AP-NDVI, GS-NDVI and EJ-NDVI) and total summer warmth (TSW) and elevation in the region. EJ-NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant.

Responses of an arctic landscape to Lateglacial and early Holocene climatic changes: the importance of moisture

Many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes, and their sensitivities to climate change are poorly understood. Stratigraphic records of land–surface processes and vegetation change in the Arctic Foothills of northern Alaska reveal how tundra landscapes responded to climatic changes between 13,000 and 8000 14C yr BP. Peat deposition began and shrub vegetation became widespread ca. 12,500 14C yr BP, probably in response to the advent of warmer and wetter climate. Increased slope erosion caused rapid alluviation in valleys, and Populus trees spread northward along braided floodplains before 11,000 14C yr BP. Lake levels fell and streams incised their floodplains during the Younger Dryas (YD) (11,000–10,000 14C yr BP). A hiatus in records of Populus suggest that its geographic range contracted, and pollen records of other species suggest a cooler and drier climate during this interval. Basal peats dating to the YD are rare, suggesting that rates of paludification slowed. Immediately after 10,000 14C yr BP, lake levels rose, streams aggraded rapidly again, intense solifluction occurred, and Populus re-invaded the area. Moist acidic tundra vegetation was widespread by 8500 14C yr BP along with wet, organic-rich soils. Most of these landscape-scale effects of climatic change involved changes in moisture. Although low temperature is the most conspicuous feature of arctic climate, shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions.

Soils of the Barrow region, Alaska1

Soils have been studied near Barrow, Alaska for nearly 50 years. Since 1995 we have described, sampled, and characterized 26 pedons in the Barrow region, primarily within the Barrow Experimental Observatory, as part of a legacy soils database. The soils occur on land cover types that range from dry to wet acidic tundra. Cryoturba‐tion is the dominant process that affects most of the soils, but other processes include paludization, gleization, melanization, base‐cation leaching, and anthrosolization. In general, the soils have high levels of total organic carbon, total N, and silt. The cation‐exchange capacity is high but is dominated by exchangeable acidity. Twelve soil subgroups were recognized in the region, of which four were classified as Turbels, four as Orthels, and four as Histels. There is considerable spatial variability in the soils due to the presence of low‐, flat‐, and high‐centered frost polygons. The thaw‐lake cycle is of special importance in the Barrow region.

Calcium-rich tundra, wildlife, and the “Mammoth Steppe”

Moist calcareous tundra has many ecosystem properties analogous to those of the hypothesized “Mammoth Steppe” or steppe tundra of glacial Beringia, and today it is an important range land for arctic wildlife. Moist calcium-rich tundras are associated with moderately drained fine-grained arctic soils with relatively high soil pH. Compared to tussock tundra, moist calcareous tundra has 10 times the extractable Ca in the active layer, half the organic layer thickness, and 30% deeper active layers. The vegetation is less shrubby than that of tussock tundra, has twice the vascular-plant species richness, greater habitat diversity at multiple scales, and contains plants with fewer antiherbivory chemicals and more nutrients (particularly calcium). It has some properties that are unlike the hypothesized steppe tundras, including abundant sedges and a mossy understory. Moist calcium-rich tundra is common north of the acidic shrubby southern tundras and south of the sparsely vegetated polar deserts. Successionally, this tundra type occurs between the present-day dry calcareous dune vegetation and tussock tundra. Thus, at least conceptually, moist calcareous tundra is intermediate between the steppe tundra and tussock tundra and provides insights regarding the transitions from cold arid Beringian ecosystems to present-day moist acidic tundra.

Landsat MSS-derived land-cover map of northern Alaska: Extrapolation methods and a comparison with photo-interpreted and AVHRR-derived maps

Vegetation maps of Arctic areas are needed for a variety of tundra ecosystem and climate change studies and for extrapolating from relatively small, well-known sites to broader regions. We made a preliminary land-cover map of northern Alaska by extrapolating a Landsat Multi-Spectral Scanner (MSS) derived classification of the Kuparuk River Region (KRR) to all of northern Alaska. We used a 26-scene mosaic that was previously made by the EROS Data Center, and a K-means unsupervised classification algorithm to produce eight broad land-cover categories. The northern Alaska-MSS map (NA-MSS) has the following land-cover categories and respective percentage coverage within the 200000km2 Arctic Slope: Dry Prostrate-shrub Tundra and Barrens, 8%; Moist Graminoid, Prostrate-shrub Tundra, 22%; Moist Tussock-graminoid, Dwarf-shrub Tundra, 4%; Moist Dwarf-shrub, Tussock-graminoid, Tundra, 28%; Moist Lowshrub Tundra and other Shrublands, 19%; Wet Graminoid Tundra, 9%; Water, 6%; Clouds and ice, <1%; Shadows, 4%. Ancillary data were used to improve the classification for a region of sandy tundra not encountered in the KRR and to separate shadows in the mountains from water and wetlands elsewhere. The NA-MSS map helps to define the distribution of a recently described moist nonacidic (calcareous) tundra and areas of shrublands that are of broad interest to the tundra- and climate-change modelling communities. A boundary separating moist acidic tundra from moist nonacidic tundra stretches across all of northern Alaska (about 850km). Shrub-dominated tundra is prevalent in the southern and western (warmer, wetter) portions of the map. We created difference maps for comparing the northern Alaska-MSS (NA-MSS) map to the Major Ecosystems of Alaska (MEA) map and a map derived from a time series of Advanced Very High Resolution Radiometer images (NA-AVHRR). Compared to the other maps, the NA-MSS map provides more detailed information for moist tundra areas and shows more shrub-dominated vegetation with different spatial distributions than the other two maps. An accuracy assessment of the map will be performed in 1999.

The character and bioactivity of dissolved organic matter at thaw and in the spring runoff waters of the arctic tundra North Slope, Alaska

The brief spring thaw period in the arctic is an important time when carbon is transferred from terrestrial to aquatic systems as melting snow and soil waters run off into the streams, lakes, and ocean. Measurements were made of the quantity and quality of dissolved organic carbon (DOC) in thawing soil and runoff waters in the foothills region of the Kuparuk River basin of arctic Alaska, during the thaw of May 1996. Incubations were performed using DOC and soil cores at the time of thaw from the surface layers of two major tundra types of the region, nonacidic and acidic tundra. Results indicated that there are major changes in both the quantity and quality of DOC as soil waters thaw and move to the streams and lakes. DOC concentrations were found to be reduced up to 90% as soil waters thawed and became free‐flowing soil waters with leachates from thawed soil cores averaging 116 mg DOC/L at thaw and soil waters averaging 20 mg DOC/L. Stream and inlet to Toolik Lake DOC concentrations averaged 12 and 10 mg DOC/L respectively indicating further dilution of DOC. Quality differences elucidated by XAD‐8/4 resin fractionation of DOC were observed for waters at various points in the ecosystem. The hydrophilic neutral fraction (HIN) accounted for 71% of the DOC in waters of thawing soil cores, but was only 23% in flowing waters of soils, and 9–20% in stream waters. A 14 day 4°C incubation of DOC from thawing soil core waters reduced DOC an average of 39%, with 80% of that reduction occurring in the HIN fraction. Soil waters and stream waters were similar in DOC fraction composition, and fulvic acid fractions were dominant. Initial 14 day DOC respiration rates with high HIN waters were 10 mg CO2‐C/g DOC/d, and reduced to 1.2–1.7 mg CO2‐C/g DOC/d after 34 days incubation. Respiration rates of thawed cores ranged from 0.12 to 0.06 and 0.03 mg CO2‐C/g C/d for nonacidic and acidic cores, respectively.

Characteristics of cryogenic soils along a latitudinal transect in arctic Alaska

The morphological, chemical, and physical properties of arctic tundra soils were examined along a 200‐km latitudinal gradient in northern Alaska which includes two major physiographic provinces; the Arctic Coastal Plain and the Arctic Foothills. Annual air temperature and precipitation increase along the gradient from north to south. Soils on the Arctic Coastal Plain support wet, nonacidic tundra vegetation and have high carbonate contents. Soil on the Arctic Foothills support moist, nonacidic tundra in the northern part and moist acidic tundra in the southern part. Most arctic tundra soils are characterized by medium texture, poor drainage, and high organic matter content. From north to south along the transect, the base saturation of the active layer decreases and exchangeable aluminum increases from north to south. Most soils have strongly developed cryogenic features, including warped and broken horizons, ice lenses, thin platy structure, and organic matter frost‐churned into the ice‐rich upper permafrost horizons.

Energy and trace-gas fluxes across a soil pH boundary in the Arctic

Studies and models of trace-gas flux in the Arctic consider temperature and moisture to be the dominant controls over land–atmosphere exchange1,2, with little attention having been paid to the effects of different substrates. Likewise, current Arctic vegetation maps for models of vegetation change recognize one or two tundra types3,4 and do not portray the extensive regions with different soils within the Arctic. Here we show that rapid changes to ecosystem processes (such as photosynthesis and respiration) that are related to changes in climate and land usage will be superimposed upon and modulated by differences in substrate pH. A sharp soil pH boundary along the northern front of the Arctic Foothills in Alaska separates non-acidic (pH > 6.5) ecosystems to the north from predominantly acidic (pH < 5.5) ecosystems to the south. Moist non-acidic tundra has greater heat flux, deeper summer thaw (active layer), is less of a carbon sink, and is a smaller source of methane than moist acidic tundra.

Soils and Cryoturbation in Moist Nonacidic and Acidic Tundra in the Kuparuk River Basin, Arctic Alaska, U.S.A.

We compared 22 pedons derived from silty materials in moist nonacidic tundra (MNT) and moist acidic tundra (MAT) in the arctic foothills of the 9200-km2 Kuparuk River basin in northern Alaska. Soils in MNT have thinner organic horizons, a significantly thicker active layer, and greater cryoturbation than soils in MAT. The quantities of clay and organic-plus-inorganic C in the upper 100 cm are comparable; however, soils in MNT have significantly greater amounts of extractable Ca, Mg, and sum of base cations and significantly lower amounts of exchangeable acidity and Al than soils in MAT. Tissues from forbs, sedges, and woody shrubs in MNT have two to three times as much Ca as the same or similar species in MAT. The area of nonsorted circles was significantly greater in MNT (9.6%) than in MAT (0.9%). Although the existence of nonacidic tundra in the Arctic has been known for some time, its origin and distribution have not been fully explained. Our data link soil and vegetation properties and indicate that cryoturbation plays an important role in maintaining MNT in arctic Alaska.

Soils and Cryoturbation in Moist Nonacidic and Acidic Tundra in the Kuparuk River Basin, Arctic Alaska, U.S.A.

We compared 22 pedons derived from silty materials in moist nonacidic tundra (MNT) and moist acidic tundra (MAT) in the arctic foothills of the 9200-km2 Kuparuk River basin in northern Alaska. Soils in MNT have thinner organic horizons, a significantly thicker active layer, and greater cryoturbation than soils in MAT. The quantities of clay and organic-plus-inorganic C in the upper 100 cm are comparable; however, soils in MNT have significantly greater amounts of extractable Ca, Mg, and sum of base cations and significantly lower amounts of exchangeable acidity and Al than soils in MAT. Tissues from forbs, sedges, and woody shrubs in MNT have two to three times as much Ca as the same or similar species in MAT. The area of nonsorted circles was significantly greater in MNT (9.6%) than in MAT (0.9%). Although the existence of nonacidic tundra in the Arctic has been known for some time, its origin and distribution have not been fully explained. Our data link soil and vegetation properties and indicate that cryoturbation plays an important role in maintaining MNT in arctic Alaska.

Satellite-derived vegetation index and cover type maps for estimating carbon dioxide flux for arctic tundra regions

The spatial variability and co-variability of two different types of remote sensing derivatives that portray vegetation and geomorphic patterns are analyzed in the context of estimating regional-scale CO 2 flux from land surfaces in the arctic tundra. For a study area encompassing the Kuparuk River watershed of the North Slope of Alaska, we compare satellite-derived maps of the normalized difference vegetation index (NDVI) generated at two different spatial resolutions to a map of vegetation types derived by image classification of data from the Landsat multispectral scanner (MSS). Mean values of NDVI for each cover type stratum are unique (with the exception of moist acidic tundra and shrubland types). Based on analysis of semi-variograms generated for SPOT-NDVI data, most of the vegetation cover and landform features of this arctic tundra landscape have spatial dimensions of less than 1 km. Thaw lakes on the coastal plain and glacial depositional landforms, such as moraines in the foothills, seem to be the largest features, with vegetation units having dimensions no larger than 700 m. Frequency distributions of NDVI and vegetation types extracted for sampling transects flown by an aircraft sensing CO 2 flux, relative to distributions for the entire Kuparuk River watershed, suggest a slight sampling bias towards greater cover of mesic wet sedge tundra and thaw lakes and associated lower NDVI values. The regional pattern of NDVI for the North Slope of Alaska corresponds primarily to differences between the two major physiographic provinces of this region.

The use of solid peroxides to stimulate growth of aerobic microbes in tundra

Solid peroxides and peroxyhydrates degrade into a basic salt, water, and molecular oxygen when in contact with biologically active soils. Column reactors were used to quantify the extent to which three solid peroxides would stimulate growth of aerobic, heterotrophic bacteria and fungi in contaminated tundra soil. Soils in contact with a peroxide compound were incubated in column reactors at field moisture conditions at either 12 or 25°C with no mixing. After 1200-h incubations, localized concentrations of bacteria and fungi were at least 2 orders of magnitude greater in soil amended with sodium carbonate peroxyhydrate than in soil containing either calcium peroxide or magnesium peroxide. Only in soil containing sodium carbonate peroxyhydrate did microbes grow to an appreciably higher concentration than in control soil, which contained no peroxide. Stimulation of both bacterial and fungal growth occurred primarily at distances of less than 5 cm from the peroxide, suggesting that under static moisture conditions, only localized microbial growth can be expected in acidic tundra soils.

EFFECTS OF ROADSIDE DISTURBANCE ON SUBSTRATE AND VEGETATION PROPERTIES IN ARCTIC TUNDRA

Tundra adjacent to the gravel Dalton Highway in northern Alaska was examined for effects of 15 yr of chronic road and road dust disturbance. Road effects at a nonacidic site (soil pH ≥ 5.0) and an acidic site (soil pH < 5.0) were compared to examine differential susceptibility. Overall, effects on vegetation were more pronounced in acidic tundra. Initial substrate pH appears to control the degree of response to disturbance by road and calcareous road dust. Soil at the acidic site is normally pH 4.0, whereas in the disturbed area next to the road soil pH was as high as 7.3 ± 0.07 (at 2 m from the road edge). Soils next to the road had lower nutrient levels, altered organic horizon depth, higher bulk density, and lower moisture. Effects on snowpack include both increased drifting in the lee of the road and earlier meltout near the road due to dust-induced change in albedo. Permafrost thaw was deeper next to the road at both sites, and potentially could affect road structure detrimentally. Vegetation biomass of most taxa was reduced near the road at both sites. Total aboveground biomass of nonacidic tundra ranged from 330.0 ± 34.72 g/m2 (mean ± 1 se) at 2 m from the road to 690.7 ± 94.52 g/m2 at 100 m away from the road. Total biomass of acidic tundra ranged from 150.5 ± 16.60 g/m2 at 5 m from the road to 743.1 ± 168.98 g/m2 at 100 m from the road. Species richness in acidic tundra next to the road was less than half of that at 100 m away from the road. Community composition was altered most noticeably in acidic tundra. The moss Tomentypnum nitens, dominant in nonacidic arctic tussock tundra, was nearly equally abundant at all distances from the road at the nonacidic tundra site, whereas Sphagnum mosses, dominant in acidic low arctic tussock tundra, were virtually eliminated near the road at the acidic tundra site. Salix lanata was more abundant next to the road at the nonacidic site. Ordinations indicate that variation in vegetation cover is explained by distance from the road. Knowledge of differential effects of road construction and use, including the long-term effects of hydrological alterations and dust mobilization on local corridors, is key information for planning development in areas of arctic tundra. Planned placement of roads in the future should consider the impact of such changes to sensitive (acidic) tundra areas in the Arctic.

Effects of Roadside Disturbance on Substrate and Vegetation Properties in Arctic Tundra

Tundra adjacent to the gravel Dalton Highway in northern Alaska was examined for effects of 15 yr of chronic road and road dust disturbance. Road effects at a nonacidic site (soil pH ≥ 5.0) and an acidic site (soil pH < 5.0) were compared to examine differential susceptibility. Overall, effects on vegetation were more pronounced in acidic tundra. Initial substrate pH appears to control the degree of response to disturbance by road and calcareous road dust. Soil at the acidic site is normally pH 4.0, whereas in the disturbed area next to the road soil pH was as high as 7.3 ± 0.07 (at 2 m from the road edge). Soils next to the road had lower nutrient levels, altered organic horizon depth, higher bulk density, and lower moisture. Effects on snowpack include both increased drifting in the lee of the road and earlier meltout near the road due to dust-induced change in albedo. Permafrost thaw was deeper next to the road at both sites, and potentially could affect road structure detrimentally. Vegetation biomass of most taxa was reduced near the road at both sites. Total aboveground biomass of nonacidic tundra ranged from 330.0 ± 34.72 g/m2 (mean ± 1 se) at 2 m from the road to 690.7 ± 94.52 g/m2 at 100 m away from the road. Total biomass of acidic tundra ranged from 150.5 ± 16.60 g/m2 at 5 m from the road to 743.1 ± 168.98 g/m2 at 100 m from the road. Species richness in acidic tundra next to the road was less than half of that at 100 m away from the road. Community composition was altered most noticeably in acidic tundra. The moss Tomentypnum nitens, dominant in nonacidic arctic tussock tundra, was nearly equally abundant at all distances from the road at the nonacidic tundra site, whereas Sphagnum mosses, dominant in acidic low arctic tussock tundra, were virtually eliminated near the road at the acidic tundra site. Salix lanata was more abundant next to the road at the nonacidic site. Ordinations indicate that variation in vegetation cover is explained by distance from the road. Knowledge of differential effects of road construction and use, including the long-term effects of hydrological alterations and dust mobilization on local corridors, is key information for planning development in areas of arctic tundra. Planned placement of roads in the future should consider the impact of such changes to sensitive (acidic) tundra areas in the Arctic.

NDVI, biomass, and landscape evolution of glaciated terrain in northern Alaska

AbstractThe patterns of the normalized difference vegetation index (NDVI) on three glacial surfaces of different ages in the vicinity of Toolik Lake, Alaska, were examined. NDVI was derived from SPOT multispectral digital data, and the images were stratified according to boundaries on glacial geology and vegetation maps. Ground-level measurements of NDVI from common vegetation types were also collected, using a portable spectrometer. Late Pleistocene glacial surfaces have lower image-NDVI than older Middle Pleistocene surfaces, and the mean NDVI is correlated with approximate time since deglaciation. The trends are related to differences in NDVI associated with vegetation growing on mineral vs peaty substrates. Nonacidic mineral substrates are more common on the younger landscapes, and acidic peaty soils are more common on the older surfaces. The field-NDVIs of acidic dry, moist, and wet tundra are consistently higher than those of corresponding nonacidic tundra types. These same trends are seen when the SPOT NDVI image is stratified according to vegetation boundaries appearing on two detailed vegetation maps in the region. Above-ground biomass of moist and wet acidic tundra is significantly greater than corresponding nonacidic types. Vegetation species composition was examined along two transects on the oldest and youngest glacial surfaces. Shrub cover is the most important factor affecting the spectral signatures and biomass. Older surfaces have greater cover of shrub-rich tussock tundra and shrub-filled water tracks, and the younger surfaces have more dry, well-drained sites with low biomass and relatively barren nonsorted circles and stripes. These trends are related to paludification and modification of the terrain by geomorphic and geochemical processes. Similar patterns of spectral reflectance have been noted in association with a variety of large-scale natural disturbances in northern Alaska. However, extrapolation of these results to much broader regions of the circumpolar Arctic will require the use of sensors covering larger areas, such as the AVHRR aboard the NOAA satellites.

Extreme metal and acid tolerance ofEuglena mutabilis and an associated yeast from Smoking Hills, Northwest Territories, and their apparent mutualism

In isolates ofEuglena mutabilis and an associated yeast from strongly acidic tundra ponds (pH 1.8-2.0) at the Smoking Hills, North West Territories (N.W.T.), and in isolates from acidic ponds in the Yukon, a remarkable degree of tolerance to a number of toxic elements and to very low pH has been found. Growth was used as a measure of tolerance. The tolerances to both low pH and to elevated metal concentrations were markedly enhanced when both organisms were present together. This mutualism occurred even betweenE. mutabilis from one field location and a yeast from another. In every field collection we made ofEuglena, the yeast was also found. The tolerances to metals are 10-100 times higher than the highest reported previously for algae, and include tolerance to some metals not elevated in the ponds from which isolations were made. Reciprocal combinations of algal-yeast partners suggest a generalized benefit of association and an increased benefit for co-selected pairs from a specific site. This algal-yeast association may be a major factor in allowing colonization of these extreme acid habitats, paralleling the cyanobacteria-bacterial associations of extremely alkaline waters.