Noatak National Preserve Research Articles

‘LandsatTS': an R package to facilitate retrieval, cleaning, cross‐calibration, and phenological modeling of Landsat time series data

The Landsat satellites provide decades of near‐global surface reflectance measurements that are increasingly used to assess interannual changes in terrestrial ecosystem function. These assessments often rely on spectral indices related to vegetation greenness and productivity (e.g. Normalized Difference Vegetation Index, NDVI). Nevertheless, multiple factors impede multi‐decadal assessments of spectral indices using Landsat satellite data, including ease of data access and cleaning, as well as lingering issues with cross‐sensor calibration and challenges with irregular timing of cloud‐free acquisitions. To help address these problems, we developed the ‘LandsatTS' package for R. This software package facilitates sample‐based time series analysis of surface reflectance and spectral indices derived from Landsat sensors. The package includes functions that enable the extraction of the full Landsat 5, 7, and 8 records from Collection 2 for point sample locations or small study regions using Google Earth Engine accessed directly from R. Moreover, the package includes functions for 1) rigorous data cleaning, 2) cross‐sensor calibration, 3) phenological modeling, and 4) time series analysis. For an example application, we show how ‘LandsatTS' can be used to assess changes in annual maximum vegetation greenness from 2000 to 2022 across the Noatak National Preserve in northern Alaska, USA. Overall, this software provides a suite of functions to enable broader use of Landsat satellite data for assessing and monitoring terrestrial ecosystem function during recent decades across local to global geographic extents.

Human-caused climate change in United States national parks and solutions for the future

Author(s): Gonzalez, Patrick | Abstract: Human-caused climate change has exposed the US national park area to more severe increases in heat and aridity than the country as a whole and caused widespread impacts on ecosystems and resources. Reducing carbon dioxide emissions from cars, power plants, and other human sources would reduce future risks. Since 1895, annual average temperature of the area of the 419 national parks has increased at a rate of 1.0 ± 0.2oC (1.8 ± 0.4oF) per century, double the rate of the US as a whole, while precipitation has declined significantly on 12% of national park area, compared with 3% of the US. This occurs because extensive areas of national parks are located in extreme environments. Scientific research in national parks has detected numerous changes that analyses have attributed primarily to human-caused climate change. These include a doubling of the area burned by wildfire across the western US, including Yosemite National Park, melting of glaciers in Glacier Bay National Park, a doubling of tree mortality across the western US, including Sequoia National Park, a loss of bird species from Death Valley National Park, a shift of trees onto tundra in Noatak National Preserve, sea level rise of 42 cm (17 in.) near the Statue of Liberty National Monument, and other impacts. Without emissions reductions, climate change could increase temperatures across the national parks, up to 9oC (16oF) by 2100 in parks in Alaska. This could melt all glaciers from Glacier National Park, raise sea level enough to inundate half of Everglades National Park, dissolve coral reefs in Virgin Islands National Park through ocean acidification, and damage many other natural and cultural resources. Adaptation measures, including conservation of refugia in Joshua Tree National Park and raising heat-resistant local corals in Biscayne National Park, can strengthen ecosystem integrity. Yet, reducing greenhouse gas emissions from human activities is the only solution that prevents the pollution that causes climate change. Energy conservation and efficiency improvements, renewable energy, public transit, and other actions could lower projected heating by two-thirds, reducing risks to our national parks.

Changes in vegetation cover and snowmelt timing in the Noatak National Preserve of Northwestern Alaska estimated from MODIS and Landsat satellite image analysis

ABSTRACT Trends and transitions in the growing season Normalized Difference Vegetation Index (NDVI) from the MODerate resolution Imaging Spectroradiometer (MODIS) satellite sensor at 250-m resolution were analyzed for the period from 2000 to 2018 to understand recent patterns of vegetation change in ecosystems of the Noatak National Preserve in northwestern Alaska. Statistical analysis of changes in the NDVI time series was conducted using the “Breaks for Additive Seasonal and Trend” method (BFAST). This structural change analysis indicated that at least one NDVI abrupt change breakpoint was detected in 25% of the MODIS pixels covering the NOAT. All of the large wildfires mapped by Landsat burn severity classifications within the NOAT since the year 2000 coincided with multiple negative NDVI breakpoints. Results showed that six large drainage basins, all within the Eli River and Kugururok River systems of the western NOAT, had significant correlations between early spring snowmelt and annual area burned. Later-than-average snowmelt dates were strongly associated with a high number of abrupt shifts in greenness cover detected by BFAST. Negative (browning) NDVI trends in the de-seasonalized residuals were detected as significant (p < 0.05) at 15% of the total MODIS 250-m pixel coverage of the NOAT.

Automated detection of thermoerosion in permafrost ecosystems using temporally dense Landsat image stacks

Anthropogenic climate change has been linked to the degradation of permafrost across northern ecosystems, with notable implications for regional to global carbon dynamics. However, our understanding of the spatial distribution, temporal trends, and seasonal timing of episodic landscape deformation events triggered by permafrost degradation is hampered by the limited spatial and temporal coverage of high-resolution optical, RADAR, LIDAR, and hyperspectral remote sensing products. Here we present an automated approach for detecting permafrost degradation (thermoerosion), using meso-scale high-frequency remote sensing products (i.e., Landsat image archive). This approach was developed, tested, and applied in the ice-rich lowlands of the Noatak National Preserve (NOAT; 12,369 km2) in northwestern Alaska. We identified thermoerosion (TE) by capturing the spectral signal associated with episodic sediment plumes in adjacent water bodies following TE. We characterized and extracted this episodic turbidity signal within lakes during the snow-free period (June 15–October 1) for 1986–2016 (continuous data limited to 1999–2016), using the cloud-based geospatial parallel processing platform, Google Earth Engine™. Thermoerosional detection accuracy was calculated using seven consecutive years of sub-meter high-resolution imagery (2009–2015) covering 798 (~33%) of the 2456 lakes in the NOAT lowlands. Our automated TE detection algorithm had an overall accuracy and kappa coefficient of 86% and 0.47 ± 0.043, indicating that episodic sediment pulses had a “moderate agreement” with landscape deformation associated with permafrost degradation. We estimate that lake shoreline erosion, thaw slumps, catastrophic lake drainage, and gully formation accounted for 62, 23, 13, and 2%, respectively, of active TE across the NOAT lowlands. TE was identified in ~5% of all lakes annually in the lowlands between 1999 and 2016, with a wide range of inter-annual variation (ranging from 0.2% in 2001 to 22% in 2004). Inter-annual variability in TE occurrence and spatial patterns of TE probability were correlated with annual snow cover duration and snow persistence, respectively, suggesting that earlier snowmelt accelerates permafrost degradation (e.g. TE) in this region. This work improves our ability to detect and attribute change in permafrost degradation across space and time.

Effects of environmental features and sport hunting on caribou migration in northwestern Alaska

BackgroundUngulate movements are influenced by a variety of biotic and abiotic factors, which may affect connectivity between key resource areas and seasonal ranges. In northwestern Alaska, one important question regarding human impacts on ungulate movement involves caribou (Rangifer tarandus) response to autumn hunting and related aircraft activity. While concerns have been voiced by local hunters about the influence of transporter aircraft and non-local sport hunters, there has been little quantitative analysis of the effects of hunter activity on caribou movement. We utilized a novel spatial dataset of commercial aircraft landing locations and sport hunter camps in and around Noatak National Preserve to analyze resource selection of caribou in autumn for non-local hunting activity and environmental features. We combined step selection functions with randomized shortest paths to investigate whether terrain ruggedness, river width, land cover, and hunting activity (in the form of aircraft landings and sport hunter camps) facilitated or impeded caribou movement. By varying a parameter in the randomized shortest path models, we also explored the tradeoff between exploration and exploitation in movement behavior exhibited by traveling caribou.ResultsWe found that caribou avoided rugged terrain and areas with more river, forest, and tall shrubs while selecting for areas dominated by tussock tundra and dwarf shrubs. Migration of caribou through Noatak does not appear to be inhibited by sport hunting activity, though this does not preclude the possibility of temporary effects altering availability of caribou for individual hunters. Caribou exhibited exploratory movement, following predictions of a random walk model. This behavior may facilitate the location of remaining patches of high-quality forage prior to the onset of winter, especially during mild autumns.ConclusionsUnderstanding animal movement behavior is fundamental to protecting critical areas of connectivity and to informing management decisions. Our study identifies migratory connectivity and hotspots of potential conflict among user groups, enabling development of policies that balance human access with species conservation.

Charcoal reflectance suggests heating duration and fuel moisture affected burn severity in four Alaskan tundra wildfires

Wildfires are anticipated to increase in frequency and extent in the Arctic tundra. In the unprecedented 2010 fire season, 37 tundra fires burned 435 km2 of the Noatak National Preserve, Alaska. We sampled sixteen soil monoliths from four of these burned areas, which based on microsite burn severity assessments ranged from scorched to moderate–high. Surface charcoals were later studied using reflectance microscopy, as charcoal reflectance may semiquantitatively indicate the duration of heating experienced by a given fuel. Here, the combination of high fuel moisture contents and rapid consumption of fine tussock fuels likely resulted in short fire residence times across the four burned areas, giving an overall low median charcoal reflectance for the entire assemblage (0.82%Romedian). The low charcoal reflectances of the ground fuels provide further evidence for limited heat transference to the organic soil (bryophytes, 0.57 ± 0.17%Romedian; duff and litter, 0.83 ± 0.33%Romedian). The range of observed microsite burn severities is therefore likely attributable to localised variations in above- and ground fuel moisture contents resulting in heterogeneously burned fuels. Consequently, charcoal reflectance is able to provide additional information about current fire behaviour that may improve our understanding of tussock–shrub tundra fires in the future.

Development of Methods for Detection and Monitoring of Fire Disturbance in the Alaskan Tundra Using a Two-Decade Long Record of Synthetic Aperture Radar Satellite Images

Using the extensive archive of historical ERS-1 and -2 synthetic aperture radar (SAR) images, this analysis demonstrates that fire disturbance can be effectively detected and monitored in high northern latitudes using radar technology. A total of 392 SAR images from May to August spanning 1992–2010 were analyzed from three study fires in the Alaskan tundra. The investigated fires included the 2007 Anaktuvuk River Fire and the 1993 DCKN178 Fire on the North Slope of Alaska and the 1999 Uvgoon Creek Fire in the Noatak National Preserve. A 3 dB difference was found between burned and unburned tundra, with the best time for burned area detection being as late in the growing season as possible before frozen ground conditions develop. This corresponds to mid-August for the study fires. In contrast to electro-optical studies from the same region, measures of landscape recovery as detected by the SAR were on the order of four to five years instead of one.

Microbial biogeography of arctic streams: exploring influences of lithology and habitat.

Terminal restriction fragment length polymorphism and 16S rRNA gene sequencing were used to explore the community composition of bacterial communities in biofilms on sediments (epipssamon) and rocks (epilithon) in stream reaches that drain watersheds with contrasting lithologies in the Noatak National Preserve, Alaska. Bacterial community composition varied primarily by stream habitat and secondarily by lithology. Positive correlations were detected between bacterial community structure and nutrients, base cations, and dissolved organic carbon. Our results showed significant differences at the stream habitat, between epipssamon and epilithon bacterial communities, which we expected. Our results also showed significant differences at the landscape scale that could be related to different lithologies and associated stream biogeochemistry. These results provide insight into the bacterial community composition of little known and pristine arctic stream ecosystems and illustrate how differences in the lithology, soils, and vegetation community of the terrestrial environment interact to influence stream bacterial taxonomic richness and composition.

Variability of tundra fire regimes in Arctic Alaska: millennial-scale patterns and ecological implications

Tundra fires have important ecological impacts on vegetation, wildlife, permafrost, and carbon cycling, but the pattern and controls of historic tundra fire regimes are poorly understood. We use sediment records from four lakes to develop a 2000-yr fire and vegetation history in a highly flammable tundra region and compare this history with previously published fire records to examine spatial and temporal variability of tundra burning across Arctic Alaska. The four sites span a modern climatic gradient in the Noatak National Preserve, from warmer, drier down-valley locations to cooler, generally moister up-valley locations. Modern vegetation varies from herb- to shrub-dominated tundra from down- to up-valley sites, and pollen data suggest that this spatial pattern in vegetation persisted over the past two millennia. Peaks in macroscopic charcoal accumulation provide estimates of fire-event return intervals (FRIs), which did not vary significantly at millennial time scales but did vary across space. Down-valley sites burned relatively frequently over the past two millennia, with median FRIs of 150 years (95% CI 101–150) and FRI distributions statistically similar to those from ancient shrub tundra and modern boreal forest. At up-valley sites FRIs were significantly longer than those at down-valley sites, with a median FRI of 218 years (95% CI 128–285). These differences likely reflect the cooler growing-season temperatures and lower evaporative demand at up-valley sites, but local-scale variability in vegetation may have also shaped tundra fire regimes. Comparisons with other long-term fire records in Alaska reveal that the tundra biome can sustain a wide range of burning, with individual FRIs from as low as 30 years to more than 5000 years. These records together indicate that frequent tundra burning has occurred under a range of climatic and vegetation scenarios. The variety of tundra fire histories within Alaska suggests that the ecological impacts of tundra burning likewise vary widely, with important implications for wildlife-habitat maintenance and for the responses of tundra biophysical and biogeochemical processes to climatic change.

Environmental Controls on Needle Gas Exchange and Growth of White Spruce (Picea glauca) on a Riverside Terrace near the Arctic Treeline

Recent studies have revealed positive and negative trends in the radial growth of treeline white spruce (Picea glauca) as temperatures have warmed in recent decades. Investigators have speculated that negative growth trends reflect the increasing importance of temperature-induced drought stress, yet direct observations of drought-induced stomatal closure have not been made in white spruce near the Arctic treeline. In this study, we measured needle gas exchange, a variety of needle traits, and branch growth in contrasting growing seasons on a riverside terrace near the Arctic treeline in Noatak National Preserve, northwest Alaska. Needle gas exchange was limited by cold soils (<7 °C), nighttime frosts, large vapor pressure deficits (VPD) and/or low soil water contents during the majority of our midday measurements. Near optimal conditions for needle gas exchange were consistently found in late August, when soils were relatively warm, air temperatures were moderate, and the VPD was relatively small. Defoliation during a two-year bud moth infestation (Zeiraphera spp.) substantially reduced branch growth, obscured potential relationships between needle gas exchange and growth, and revealed the importance of whole canopy gas exchange measurements. Results of our study show there is a very narrow window of environmental conditions for near optimal needle gas exchange in white spruce near the Arctic treeline. Although we identified many abiotic constraints on needle gas exchange, a single biological factor likely had the greatest effect on annual branch growth.

Microtopographic Control of Treeline Advance in Noatak National Preserve, Northwest Alaska

Arctic treeline positions are of fundamental importance to the function of high latitude landscapes, as regulators of surface energy exchange and carbon cycling. Most studies aimed at explaining current and predicting future treeline positions have examined growth trends in mature treeline trees, but treeline advance requires seed production, germination, seedling establishment, and recruitment of new trees beyond the treeline and these processes may not be well correlated with growth of mature trees. Tussock tundra is a widespread, microtopographically complex vegetation type, covering vast areas of northern Alaska and Siberia. We examined a site where the white spruce (Picea glauca) treeline has recently advanced into tussock tundra and asked if white spruce seedlings (~36-cm tall) occurred in tussocks, inter-tussocks, and frost boils disproportionate to the abundance of these habitats in the treeline ecotone. We found that seedlings disproportionately occurred in tussocks and frost boils. Seedlings found in tussocks and frost boils also showed greater branch growth than those in inter-tussocks. Tussocks and frost boils had higher soil temperatures than inter-tussocks. Tussocks had higher N, P, and K availability, whereas frost boils had greater secondary and micronutrient availability. The disproportionate occurrence of seedlings in tussocks and frost boils can likely be explained by the combination of warmer soils and greater nutrient availability. It is also possible that low competition for primary nutrients contributes to the success of seedlings in frost boils. Results of the study highlight the importance of biotic and abiotic facilitation as mediators of treeline advance in a changing Arctic.

Macrolichen communities in relation to soils and vegetation in the Noatak National Preserve, Alaska

Macrolichen community structure and its relation to environment in the Noatak National Preserve, Alaska, is described using a two-way stratified random sample. We found 201 macrolichen taxa. Two primary gradients in lichen species composition were related to substrate pH and vegetation physiognomy, grading from forests to high alpine communities. Site characteristics associated with the first community gradient are soil moisture and exposure. Both ends of this gradient, including protected forests and densely shrubby sites at one end and exposed, high elevation alpine sites at the other end, are relatively dry and well-drained. The mid-region of this gradient consists of mesic, lowland tundra habitats. The second gradient, related to substrate pH, is driven by the presence of Sphagnum moss contrasting with calcareous soils and bedrock. Combining these two gradients of lichen community composition, we found six groups of plots using two-way cluster analysis. Further, division of macrolichen species occurring in five or more plots yielded seven species groups, based on a combination of environmental factors and species distribution characteristics. This snapshot of macrolichen communities in Arctic Alaska serves as an important baseline for future comparisons to environments altered by changing climate and land use.

Subsistence and Seasonality at a Late Prehistoric House Pit in Northwest Alaska

In this report, I examine a house from a Late Prehistoric village site near the confluence of Maiyumerak Creek and the Noatak River in the Noatak National Preserve, Alaska. In 2006, several thousand artifacts and over 100,000 faunal remains were excavated from this approximately 500-year-old house. Faunal remains and subsistencerelated artifacts associated with the living fl oor of the house were analyzed to assess diet and seasonal occupation. I also address how this house fits into previously proposed Late Prehistoric land- and resource-use models. The dietary reconstruction shows that both classes of data (artifacts and fauna) indicate a primary reliance upon terrestrial mammal resources, a secondary reliance upon bird and fi sh resources, and a limited reliance upon marine mammal resources. Th e seasonal analysis of the house indicates a late summer, fall, and/or winter occupation (July through February). The seasonal occupation, radiocarbon dates and evidence of coastal contact at this site illustrate current difficulties with testing hypothesized periods of coastal abandonment during this time period. Finally, this case illustrates that for any region and time period studies related to patterns of human settlement need to be comprehensive and incorporate multiple lines of evidence and large, robust region-specifi c data sets.

Macrolichen diversity in Noatak National Preserve, Alaska

We sampled macrolichens in Noatak National Preserve to help address the need to document lichen biodiversity in Arctic ecosystems and to initiate regional-scale monitoring in the face of climate change and air pollution. We used a stratified random sample to allow unbiased park-wide diversity estimates, along with an intensive sample in a limited area. The purpose of the intensive sample was to allow us to calculate a correction from diversity estimates based on a single person in a time-constrained method to a value that more closely approximates the “true” diversity of a plot. Our 88, 0.38-ha plots averaged 26 species of macrolichens in the sample, while our best estimate of the true average was 42 species per plot. Our raw estimate of gamma diversity (park-wide macrolichen species richness) was 209 species, with jackknife estimates adjusting this to 255 or 290 species, depending on the estimator. Overall beta diversity was rather high at 7.1, reflecting the considerable variation in lichen communities among topographic positions, rock chemistry, substrate pH, climate, and vegetation. The richest lichen communities were in conifer forests, low birch/ericaceous vegetation, dwarf shrub, and talus lichen cover. Sparse vegetation was the cover type with lowest lichen species richness, reflecting the frequency of bare rock in that cover type. The herbaceous cover type was the most heterogeneous in lichen communities, having a high gamma diversity, high beta diversity, but averaging rather low alpha diversity. Several notable species are among the 364 taxa reported here. Leucocarpia biatorella is reported as new to the American Arctic. Cladonia libifera and C. jacutica are newly reported for North America. A second location for Rhizocarpon cumulatum beyond the type locality was found. The range of Parmelia squarrosa is extended ca. 1500 km north of coastal southeast Alaska. The high landscape-level diversity and high beta diversity in Noatak National Preserve provide a rich biotic tapestry for detecting future changes in macrolichen communities.

Biogeochemistry of a Treeline Watershed, Northwestern Alaska

Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800-ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze-thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO3-) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.

Expansion of forest stands into tundra in the Noatak National Preserve, northwest Alaska

Temperatures across the northern regions of North America have been increasing for 150 years, and forests have responded to this increase. In the Noatak National Preserve in Alaska, white spruce (Picea glauca [Moench] Voss) forests reach their northern limit, occurring primarily on well-drained sites and as gallery forests along streams. Rolling plateaus of tundra separate the white spruce forests into disjunct stands. We examined patterns of tree age, tree growth, and tree encroachment into tundra ecosystems in six stands along the Agashashok River. Warming over the past 150 years appears to have increased tree growth and resulted in forest expansion into adjacent tundra ecosystems. The forest/tundra ecotone shifted by about 80 to 100 m into the tundra in the past 200 years, as evidenced by declining maximum tree age with distance towards the tundra. The decadal-scale pattern of tree establishment at the farthest extent of trees into the tundra (the tundra-forest ecotone) correlated with the detrended growth index for trees within the forests; climate conditions that led to higher tree growth appeared to foster tree establishment in the tundra. This recent forest expansion has occurred across topographic boundaries, from well-drained soils on slopes onto poorly drained, flatter areas of tundra. Further expansion of the forests may be limited by more severe wind exposure and poor drainage that make the majority of tundra less suitable for trees.

Ecosystem development on terraces along the Kugururok River, northwest Alaska

:Riverside terraces along the Kugururok River in the Noatak National Preserve provided an opportunity to study primary succession, considering general trends that apply across all terraces, and unique events that influence individual terraces. The 30-year-old willow/poplar (Salix spp., Populus balsamifera L.) terrace had no trees taller than 1.5 m; the abundant spruce trees were not tall enough to emerge from the canopy height of the willows and poplars, and moose (Alces alces [Clinton]) browsing limited the canopy height of these plants. The 75-year-old poplar/spruce (Picea glauca [Moench] Voss) terrace had a high density of poplars (> 1000/ha) and low density of spruce (125/ha); heavy browsing by moose reduced the density of poplar by about one-half. The removal of the poplar by moose in this stand resulted in sustained increases in growth of individual spruce trees. The 100-year-old younger spruce/poplar terrace had about twice as many spruce trees (1250/ha) as poplar trees (500/ha), and the spruce trees were larger on average than the poplar trees. In the 220+ year-old older spruce/poplar type, only a few poplars remained (about 25/ha), and the number of spruce trees (600/ha) was only half that of the younger stage, either from lower initial spruce density on this terrace, or increased mortality of spruce. The 240+ year-old spruce type was a second-generation forest, characterized by a high density (1950/ha) of small spruce trees, some of which were tilted, indicating discontinuous permafrost. Plant litterfall mass showed no strong trend with terrace age, although N content of litterfall appeared to decline by about 1/3 in the spruce-dominated stages. Fungal biomass increased with ecosystem age, whereas bacterial biomass and microfauna declined. We found no evidence of declining soil N supply in older stages, but fertilization experiments would be needed to determine if N limitation of productivity changed with ecosystem development. We conclude that the general successional trend of increased spruce dominance is robust for this location, but that unique events play important roles in determining tree densities and the timing of the shift in dominance from poplar to spruce. The arrival of moose in the 1970s accelerated dominance by spruce on young terraces.

Soil nitrogen availability in some arctic ecosystems in northwest Alaska: Responses to temperature and moisture

AbstractWe explored patterns in soil nitrogen (N) availability in five ecosystems in the Noatak National Preserve in northwestern Alaska, and the potential response of N availability to changes in soil moisture and temperature. Nitrogen availability appeared to be highest in an ecosystem dominated by Alnus crispa (Ait.) Pursh, and lowest in ecosystems dominated by willows or by cotton grass tussocks. All soils responded strongly to changes in moisture; repeated watering during 30-day incubations raised net N mineralization rates by 1.5 to 3.0 fold. Net N mineralization at 12°C was 5 to 10 fold greater than at 5°C. The responses of net mineralization rates derived from strong effects of treatments on both microbial mineralization (release) of N, and microbial immobilization (uptake) of N. For example, incubation of soils from the alder site at 12°C slightly increased gross mineralization of N, more than doubled microbial immobilization of N, reduced gross nitrate production by more than 80%, and more than ...

Ecosystem monitoring at global baseline sites

Integrated ecosystem and pollutant monitoring is being conducted at prototype global baseline sites in remote areas of the Noatak National Preserve, Alaska, the Wind River Mountains, Wyoming, and Torres del Paine National Park, Chile. A systems approach has been used in the design of these projects. This approach includes: (1) evaluation of source-receptor relationships, (2) multimedia (i.e., air, water, soil, biota) monitoring of key contaminant pathways within the environment, (3) the use of selected ecosystem parameters to detect anthropogenic influence, and (4) the application of a systems conceptual framework as a heuristic tool.Initial short-term studies of air quality (e.g. SO2, NO2) plus trace metal concentrations in mosses generally indicate pristine conditions at all three of the above sites as expected although trace metals in mosses were higher at the Wyoming site. Selected ecosystem parameters for both terrestrial (e.g. litter decomposition) and aquatic (e.g. shredders, a macroinvertebrate functional feeding group) habitats at the Wyoming site reflected baseline conditions when compared to other studies.Plans also are being made to use U.S. Department of Energy Research Parks for global change monitoring. This will involve cross-site analyses of existing ecological databases and the design of a future monitoring network based on a systems approach as outlined in this paper.