Snow Regimes Research Articles

Evidence for nutrient enrichment of high‐elevation lakes in the Sierra Nevada, California

Long‐term measurements (1983–2001) of nutrients and seston in Emerald Lake (Sierra Nevada, California) have revealed ecologically significant patterns. Nitrate, both during spring runoff and during growing seasons, declined from 1983 through 1995. Declining snowmelt nitrate was caused primarily by changes in snow regime induced by the 1987–1992 drought: years with shallow, early melting snowpacks had lower snowmelt nitrate concentrations owing to less labile N production in catchment soils and longer plant growing seasons. However, nitrate declines during growing seasons carried through the wetter years of 1993–2000 and are likely the result of increased P loading to the lake and the release of phytoplankton from P limitation. Contemporaneous with these changes was an increase in algal biomass and a shift from P limitation toward more frequent N limitation of phytoplankton abundance. Particulate carbon concentrations in the late 1990s were two‐ to threefold greater than in the early 1980s. These trends were reflected in a larger set of Sierra Nevada lakes sampled as part of synoptic surveys (n = 28). Between 1985 and 1999, nitrate decreased and total P increased in .>0% of the lakes sampled. Our data suggest that lakes throughout the Sierra Nevada are experiencing measurable eutrophication in response to the atmospheric deposition of nutrients.

Nitrogen mass balances and abiotic controls on N retention and yield in high‐elevation catchments of the Sierra Nevada, California, United States

Interannual variations in nitrogen mass balances for the Emerald Lake watershed (ELW) and six additional headwater basins of the Sierra Nevada of California are described and used to investigate the influence of physical (snow regime, runoff, and precipitation) and chemical (N loading) forcings on the observed variability in annual catchment yield and retention of N. At ELW, annual yield of N varied by a factor of 8 (0.4–3.2 kg ha−1 yr−1) and was a linear function of runoff (R2 = 0.89 and 0.74 for dissolved inorganic nitrogen and dissolved organic nitrogen, respectively). Nitrogen yield increased faster than increases in runoff; that is, ecosystem processes enhanced N losses during years with high runoff and retarded losses during dry years. The timing of snowmelt runoff had a large effect on catchment inorganic N dynamics: nitrate pulses were greater and DIN retention was lower in years with deep, late melting snowpacks. We hypothesize that in the Sierra Nevada, labile N pools in soils are increasingly stocked during years with high snowfall amounts. These findings and modeling studies in high‐elevation watersheds suggest that if current trends toward warmer air temperatures and earlier snowmelt continue, N retention will increase in the Sierra Nevada.

The Representation of Snow in Land Surface Schemes: Results from PILPS 2(d)

Twenty-one land surface schemes (LSSs) performed simulations forced by 18 yr of observed meteorological data from a grassland catchment at Valdai, Russia, as part of the Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS) Phase 2(d). In this paper the authors examine the simulation of snow. In comparison with observations, the models are able to capture the broad features of the snow regime on both an intra- and interannual basis. However, weaknesses in the simulations exist, and early season ablation events are a significant source of model scatter. Over the 18-yr simulation, systematic differences between the models’ snow simulations are evident and reveal specific aspects of snow model parameterization and design as being responsible. Vapor exchange at the snow surface varies widely among the models, ranging from a large net loss to a small net source for the snow season. Snow albedo, fractional snow cover, and their interplay have a large effect on energy available for ablation, with differences among models most evident at low snow depths. The incorporation of the snowpack within an LSS structure affects the method by which snow accesses, as well as utilizes, available energy for ablation. The sensitivity of some models to longwave radiation, the dominant winter radiative flux, is partly due to a stability-induced feedback and the differing abilities of models to exchange turbulent energy with the atmosphere. Results presented in this paper suggest where weaknesses in macroscale snow modeling lie and where both theoretical and observational work should be focused to address these weaknesses.

Hydrologic sensitivity of global rivers to climate change

Climate predictions from four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei). The four climate models (HCCPR-CM2, HCCPR-CM3, MPI-ECHAM4, and DOE-PCM3) all predicted transient climate response to changing greenhouse gas concentrations, and incorporated modern land surface parameterizations. Model-predicted monthly average precipitation and temperature changes were downscaled to the river basin level using model increments (transient minus control) to adjust for GCM bias. The variable infiltration capacity (VIC) macroscale hydrological model (MHM) was used to calculate the corresponding changes in hydrologic fluxes (especially streamflow and evapotranspiration) and moisture storages. Hydrologic model simulations were performed for decades centered on 2025 and 2045. In addition, a sensitivity study was performed in which temperature and precipitation were increased independently by 2 °C and 10%, respectively, during each of four seasons. All GCMs predict a warming for all nine basins, with the greatest warming predicted to occur during the winter months in the highest latitudes. Precipitation generally increases, but the monthly precipitation signal varies more between the models than does temperature. The largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes. This results in part from the greater amount of warming predicted for these regions, but more importantly, because of the important role of snow in the water balance. Because the snow pack integrates the effects of climate change over a period of months, the largest changes occur in early to mid spring when snow melt occurs. The climate change responses are somewhat different for the coldest snow dominated basins than for those with more transitional snow regimes. In the coldest basins, the response to warming is an increase of the spring streamflow peak, whereas for the transitional basins spring runoff decreases. Instead, the transitional basins have large increases in winter streamflows. The hydrological response of most tropical and mid-latitude basins to the warmer and somewhat wetter conditions predicted by the GCMs is a reduction in annual streamflow, although again, considerable disagreement exists among the different GCMs. In contrast, for the high-latitude basins increases in annual flow volume are predicted in most cases.

Hierarchical subdivision of Arctic tundra based on vegetation response to climate, parent material and topography.

Current land-cover classifications used for global modelling portray Arctic tundra as one or two classes. This is insufficient for analysis of climate-vegetation interactions. This paper presents a simple three-level vegetation-map legend system useful for modelling at global, regional, and landscape scales. At the highest level (global scale: 107 -108 km2 ) the Tundra Zone is divided into four subzones based on vegetation response to temperature along the latitudinal temperature gradient from north to south: (1) Cushion-forb, (2) Prostrate Dwarf-shrub, (3) Erect Dwarf-shrub, and (4) Low Shrub subzones. The boundaries follow a modification of Yurtsev's phytogeographic subzones. Parent material and topography are also major considerations at global, regional, and landscape scales. Soil pH is a key variable for many ecosystem responses, and a division into acidic (pH 5.5 or less) and nonacidic soils is used. A conceptual mesotopographic gradient is used to characterize the influence of soil-moisture and snow regimes. The example legend framework focuses on the Northern Alaska floristic subprovince, and could be expanded to other floristic provinces using local expert knowledge and available literature. Dominant plant functional types within each habitat type within the four subzones are also presented. Modellers could include or ignore different levels of resolution depending on the purpose of the model. The approach resolves conflicts in terminology that have previously been encountered between the Russian, North American, and Fennoscandian approaches to Arctic zonation.

Long-term experimental manipulation of winter snow regime and summer temperature in arctic and alpine tundra

Three 60 m long, 2·8 m high snowfences have been erected to study long-term effects of changing winter snow conditions on arctic and alpine tundra. This paper describes the experimental design and short-term effects. Open-top fiberglass warming chambers are placed along the experimental snow gradients and in controls areas outside the fences; each warming plot is paired with an unwarmed plot. The purpose of the experiment is to examine short- and long-term changes to the integrated physical-biological systems under simultaneous changes of winter snow regime and summer temperature, as part of the Long-Term Ecological Research network and the International Tundra Experiment. The sites were at Niwot Ridge, Colorado, a temperate high altitude site in the Colorado Rockies, and Toolik Lake, Alaska, a high-latitude site. Initial results indicate that although experimental designs are essentially identical at the arctic and alpine sites, experimental effects are different. The drift at Niwot Ridge lasts much longer than do the Toolik Lake drifts, so that the Niwot Ridge fence affects both summer and winter conditions, whereas the Toolik Lake fence affects primarily winter conditions. The temperature experiment also differs in effect between the sites. Although the average temperature increase at the two sites is similar (daily increase 1·5 °C at Toolik and 1·9 °C at Niwot Ridge), at Toolik Lake there is only minor diurnal variation, whereas at Niwot Ridge the daytime increases are extreme on sunny days (as much as 7–10 °C), and minimum nighttime temperatures in the chambers are often slightly cooler than ambient (by about 1 °C). The experimental drifts resulted in wintertime increases in temperature and CO2 flux. Temperatures under the deep drifts were much more consistent and warmer than in control areas, and at Niwot Ridge remained very close to 0 °C all winter. These increased temperatures were likely responsible for observed increases in system carbon loss. Initial changes to the aboveground biotic system included an increase in growth in response to both snow and warming, despite a reduced growing season. This is expected to be a transient response that will eventually be replaced by reduced growth. At least one species, Kobresia myosuroides, had almost completely died at Niwot Ridge three years after fence construction, whereas other species were increasing. We expect in both the short- and long-term to see the strongest effects of snow at the Niwot Ridge site, and stronger effects of temperature at Toolik Lake. Copyright © 1999 John Wiley & Sons, Ltd.

Recent paludification of kettle holes on the central isjands of Lake Bienville, northern Quebec, Canada

This paper reports on the paludification of kettle holes formed in a proglacial esker complex at Lake Bienville in northern Quebec. Deep hollows on the central islands of this large subarctic lake (c. 900 kin2), are highly exposed to northeasterly and southwesterly winds over long fetches, and accumulate large amounts of drifting snow (c. 4 m). Modifications in local snow distribution associated with Holocene vegetation and climate changes contributed to an increased water supply in kettle holes. Podzolic soils with light patches in the B horizon are attributed to differential water circulation during thawing in coarse-textured soils with high moisture supply associated with thicker snow. Peat started to form over well-drained podzolic soils after 600 BP, especially c. 200 BP, when suitable conditions for Sphagnum growth established at the front of snowbeds. The recent development of patchy podzolic soils and paludification of kettle holes are interpreted as the result of a combination of bioclimatic events including: (l) the development of a postfire, open-vegetation cover after c. 1500 BP associated with cooler conditions exacerbated by the presence of a large water body; and (2) the shift from a boreal-to a subarctic-like (wind-controlled) snow regime permitting the accumulation of large amounts of snow and late melting.

LANDSCAPE CHANGE FOLLOWING DEFORESTATION AT THE ARCTIC TREE LINE IN QUÉBEC, CANADA

This study examines the influence of fire-induced deforestation in well- drained conifer sites on the development of adjacent, surviving spruce stands in peatlands at the arctic tree line (northern Quebec). Tree-ring and growth-form patterns of cross-dated black spruce (Picea mariana) remains in peat were used to analyze stand responses in two contrasting topographical settings: a moderately protected valley-bottom peatland, and an exposed hilltop peatland. Dense, old-growth spruce populations occupied the studied peat- lands between the 11th and 16th centuries, with stunted and erect spruce dominating the hilltop and the valley sites, respectively. Spruce continued to colonize the peatlands as long as the adjacent well-drained sites were occupied by forest trees able to attenuate the dam- aging effect of winter snow-drifting conditions. The surviving conifer stands exhibited similar growth responses following deforestation of the well-drained sites by wildfire in AD 1567-1568. These responses included dieback of supranival (above snow) stems and death of trees due to drowning in permafrost-induced ponds. The postfire degradation and disappearance of the conifer stands from the peatlands were the ultimate stage of a positive feedback process triggered by a modification of the snow regime at the landscape scale. Deforestation of the well-drained sites led to reduced snow accumulation and enhanced snow-drift exposure, thus inducing permafrost aggradation and drainage impediment in the nearby peatland sites. While the hilltop conifer stand responded immediately to forest exclusion in the nearby sites, ecosystem changes in the valley peatland were delayed until AD 1580-1590, at the beginning of the Little Ice Age. Our results emphasize the sensitivity and connectedness of adjoining ecosystems to fire and frost disturbances in a changing subarctic landscape mosaic.

Radar measurements of melt zones on the Greenland Ice Sheet

Surface‐based microwave radar measurements were performed at a location on the western flank of the Greenland Ice Sheet. Here, firn metamorphosis is dominated by seasonal melt, which leads to marked contrasts in the vertical structure of winter and summer firn. This snow regime is also one of the brightest radar targets on Earth with an average backscatter coefficient of 0 dB at 5.3 GHz and an incidence angle of 25°. By combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter's snow pack. This observation has important implications for monitoring and understanding changes in ice sheet volume using space‐borne microwave sensors.

Long-Term Studies of Snow-Vegetation Interactions

Relationships among vegetation, wind, snow, and temperature regimes may help predict effects of climate change. This paper presents a hierarchic geographic information system (HGIS) which helps examine links between species distributions at the plot level, at the level of landscape patterns of plant communities, and at the level of regional patterns of greeness. Geographically referencing ecological data, mapping techniques, landscape and regional scale mapping, and linking ground-level observations to remotely sensed information are all discussed. Results include discussion of specific plant species-snow relationships, landscape-level patterns of specific plant communities, regional patterns of the normalized difference vegetation index (NDVI), and linking patterns to variations in climate or direct anthropogenic impacts. 50 refs., 12 figs., 3 tabs.

Spatial interrelationships between terrain, snow distribution and vegetation patterns at an arctic foothills site in Alaska

A multidisciplinary approach combining field surveys, aerial photographic techniques, digital terrain modelling, and GIS technology was used to analyze spatial interrelationships at a study site in the northern foothills of the Brooks Range, The sensitivity of snow drifting to topography at the site is pronounced. The drift patterns indicate winter winds are predominantly from the south with a major secondary component from the southwest. These southwest winds are likely in conjunction with storm events. The deepest snow beds are found on the steeper, north‐facing slopes. Snow also has an effect on vegetation that is evident at the scale of mapping (1:6000). Communities dominated by Cassiope tetragona are associated with deeper snow regimes, and may be useful indicators of deeper snow regimes even at much smaller scales because of their unique spectral signatures. The analyses conducted to date demonstrate the power of the GIS for analyzing terrain‐geobotanical interrelationships, which will increase as we add new layers for other variables, and are able to correlate these with satellite data.

Studies of morphological parameters affecting ungulate locomotion in snow

We deal with possible morphological adaption to varied snow conditions by four North American ungulate species. Chest heights and weight loads on track are key parameters in estimating capabilities of species, and of age and sex classes within species, to cope with snow. Methods believed suitable for measuring those parameters in replicable fashion are discussed. Comparative studies of bison (Bison bison), moose (Alces alces), wapiti (Cervus elaphus), and white-tailed deer (Odocoileus virginianus) are described. There are pronounced differences in both parameters between species and between some age and sex classes within species. Chest heights of the three cervids differed by a fixed interval suggesting that differential ability to use varied snow depths may play a role in resource partitioning. Differential winter mortality may be related to sex and age class differences in ability to cope with snow. Morphological differences relate to regional distributions by determining species suitability for survival in varying snow regimes.

MONTHLY CLIMATIC CONTRIBUTION TO THE WINTER INJURY OF ALFALFA

A technique was developed to determine the long-term climatic contribution of each month to the winter injury of alfalfa from the start of growth in May to the end of the dormant period in April the next year. The basic hypothesis was that this contribution is proportional to the number of climatic variables (single or combined) showing a significant difference between the years of higher and lower survival, i.e. to the number of variables affecting survival. The variables were related to soil and air temperatures, soil frost depth, hours of sunshine, and rain and snow regimes. Annual curves of the monthly numbers of significant variables for Swift Current and La Pocatière were similar. Converting the number of significant variables into terms of relative winter injury, the critical months at Swift Current were: May, contributing to winter injury by 12%; October (12%); December (19%); March (11%); and April (22%). At La Pocatière, they were: May (12%); November (15%); January (10%); March (10%); and April (33%). The similarity in the relative importance of various months at both sites indicated that alfalfa survival is more particularly influenced by the climate during certain phases of its life cycle.

The effect of snow cover on the social behavior of bighorn rams and mountain goats

The social behavior of bighorn rams (Ovis canadensis canadensis) and mountain goats (Oreamons americanus) were studied quantitatively under different snow regimes in two winters. It was found that snow cover has little noticeable effect on the intensity of social behavior for mountain sheep during the rutting season. Thick snow cover reduces the total number of social behavior patterns per ram during the postrut; among mountain goats the number of social behavior patterns per individual remains consistently high. The thickness of the snow cover effects circumstantial changes in the function of specific behavior patterns among rams. Under extreme snow conditions, rams begin to exhibit rarely seen aggressive behavior. During deep snow, both species show an increase in overt aggressive behavior and a reduction in dominance displays. Under conditions of low snow and favorable weather rams increasingly engage in clashing, dominance displays, and appeasement behavior and reduce aggressive bulling.

HYDROLOGICAL REGIONS IN SCANDINAVIA AND FINLAND

The rivers of Scandinavia and Finland are studied with regard to regime, regional distribution, and long-term variations in discharge. The regime studies are based on monthly mean coefficients, i.e. the relation between the monthly means and the average annual discharge for a 30-year period. Within the two main areas of nival highland and lowland regime and Atlantic snow and rain regime (Fig. 1), different regime types have been studied (Figs. 2 and 3, tables 2-4). The regional distribution has been estimated with correlation coefficients and relations between means for one year expressed as a percentage of the mean discharge of 1931-60. Some of the correlation coefficients are shown in Table 5. The variations of 30- and 10-year mean discharge in percentage of the mean discharge 1911-60. have been studied by the method of moving averages from the year 1901 (Figs. 4-9). As to the 30-year records there are four regions with different trends, the North Calotte with two parts, the Arctic Sea part and the inland, the Scandinavian high mountain district, Vestland in Norway, and the eastern lowland (Fig. 10). The relations between discharge, precipitation, and temperature are discussed. Based on the results of the studies, mainly those of regional distribution together with other elements such as the situation of drainage areas and runoff values, hydrological regions have been delineated, Fig. 11.