Low Snow Cover Research Articles

The dilemma of where to nest: influence of spring snow cover, food proximity and predator abundance on reproductive success of an arctic-breeding migratory herbivore is dependent on nesting habitat choice

Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice.

The effect of winter drought on evaporation from a high‐elevation wetland

AbstractThe surface energy balance of a high‐elevation groundwater‐fed wetland (High Creek Fen) in central Colorado was measured from 9 June 2000 through 18 January 2005. In agreement with observations and predictions for decreased winter snow cover in the region, the low snow cover in 2001–2002 allowed for an examination of the impact of winter drought on the wetland. During years with an average snowpack, summer evaporation far exceeded precipitation. Despite near‐normal summer precipitation following a winter drought, the summertime surface energy balance was affected with decreased latent heat fluxes and increased sensible heat fluxes. The leaf area index and the fraction of photosynthetic radiation absorbed were reduced following the winter drought. A shift in the primary controls on evaporation occurred as the surface's response to vapor pressure deficits and soil moisture increased following the winter drought. The earlier snowmelt coupled with earlier increase in soil temperature and moisture following winter drought did not increase evaporation, since vegetation was not yet developed, and evaporation from soil water was low during the early spring period.

Topographic controls on alpine treeline patterns on Changbai Mountain, China

The control mechanisms of topography on alpine treeline pattern are critical to understanding treeline dynamics and future changes. These mechanisms have not been understood quite well enough because of increasing human disturbance and low data resolution. In this study, the relationship between the treeline pattern and topography was analyzed based on high spatial resolution remote sensing data and a digital elevation model in an area in Changbai Mountain with little human disturbance. Future treeline patterns were also predicted. The results showed that (a) aspects with high solar radiation and low snow cover have a high coverage rate of trees, (b) the peak coverage rate of trees switches from low slopes (<5°) to medium slopes (5°~25°) as the elevation rises because of the extreme environment, (c) the coverage rate of trees is a function that depends on environmental factors controlled by topography, (d) the future treeline pattern is controlled by new temperature mechanisms, new environmental factors and the reallocation effect of topography. Our research implies that topography controls the treeline pattern and changes in the treeline pattern associated with global warming, due to the effect of global warming on environmental factors. This study may well explain the causes of heterogeneous changes in the treeline pattern in the horizontal direction as well as differences in treeline response to climate warming.

First-Light Imagery from Suomi NPP VIIRS

The Suomi National Polar-Orbiting Partnership (NPP) satellite was launched on 28 October 2011, heralding the next generation of operational U.S. polar-orbiting satellites. It carries the Visible– Infrared Imaging Radiometer Suite (VIIRS), a 22-band visible/infrared sensor that combines many of the best aspects of the NOAA Advanced Very High Resolution Radiometer (AVHRR), the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS), and the National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. VIIRS has nearly all the capabilities of MODIS, but offers a wider swath width (3,000 versus 2,330 km) and much higher spatial resolution at swath edge. VIIRS also has a day/night band (DNB) that is sensitive to very low levels of visible light at night such as those produced by moonlight reflecting off low clouds, fog, dust, ash plumes, and snow cover. In addition, VIIRS detects light emissions from cities, ships, oil flares, and lightning flashes. NPP crosses the equator at about 0130 and 1330 local time, with VIIRS covering the entire Earth twice daily. Future members of the Joint Polar Satellite System (JPSS) constellation will also carry VIIRS. This paper presents dramatic early examples of multispectral VIIRS imagery capabilities and demonstrates basic applications of that imagery for a wide range of operational users, such as for fire detection, monitoring ice break up in rivers, and visualizing dust plumes over bright surfaces. VIIRS imagery, both single and multiband, as well as the day/night band, is shown to exceed both requirements and expectations.

Isotopic investigation of runoff generation in a glacierized catchment in northern Sweden

In this study, summer rainfall contributions to streamflow were quantified in the sub-arctic, 30% glacierized Tarfala (21.7 km2) catchment in northern Sweden for two non-consecutive summer sampling seasons (2004 and 2011). We used two-component hydrograph separation along with isotope ratios (δ18O and δD) of rainwater and daily streamwater samplings to estimate relative fraction and uncertainties (because of laboratory instrumentation, temporal variability and spatial gradients) of source water contributions. We hypothesized that the glacier influence on how rainfall becomes runoff is temporally variable and largely dependent on a combination of the timing of decreasing snow cover on glaciers and the relative moisture storage condition within the catchment. The results indicate that the majority of storm runoff was dominated by pre-event water. However, the average event water contribution during storm events differed slightly between both years with 11% reached in 2004 and 22% in 2011. Event water contributions to runoff generally increased over 2011 the sampling season in both the main stream of Tarfala catchment and in the two pro-glacial streams that drain Storglaciaren (the largest glacier in Tarfala catchment covering 2.9 km2). We credit both the inter-annual and intra-annual differences in event water contributions to large rainfall events late in the summer melt season, low glacier snow cover and elevated soil moisture due to large antecedent precipitation. Together amplification of these two mechanisms under a warming climate might influence the timing and magnitude of floods, the sediment budget and nutrient cycling in glacierized catchments. Copyright © 2012 John Wiley & Sons, Ltd.

Detection and stratification approaches for aerial surveys of deer in prairie–parklands

Context For management decisions that require accurate and precise estimates of large mammal population numbers, aerial surveys are considered reliable despite their cost. However, aerial surveys may still suffer from underestimation because of undetected animals and low precision as a result of inefficient sampling designs. Aims We assess detection of two species of deer in prairie-parkland communities of western Canada and evaluate a suite of survey design features for improving the accuracy and precision of population estimates from aerial surveys. Methods Modelling detection of deer was based on 100 sightability trials involving 54 radio-collared white-tailed and 46 mule deer. We used empirical survey data to simulate surveys under three alternative stratification approaches, schemes for grouping strata, and allocations of survey effort and compared the precision and accuracy of the resulting population estimates. Key results We observed deer in 83 of the 100 trials, with detection decreasing with small group size, reduced deer activity, low snow cover, high forest cover and observer fatigue. Survey precision and accuracy were highest when stratification was based on natural breaks, calculated via Jenks optimisation, in the values of resource-selection function (RSF), although improvement was less pronounced for estimates of mule deer abundance. Optimal or equal allocation of sampling effort among strata outperformed proportional allocation of sampling effort. Use of RSF for stratification reduced the coefficient of variation (CV) in estimates of deer numbers from 38% to 23% for white-tailed deer and from 33% to 27% for mule deer compared with past approaches. Conclusions Stratification based on RSF values improved precision of deer surveys the most; however, using even simple measures related to habitat selection can improve population estimates. Where deer are highly aggregated, reliably recording all variables needed to implement sightability models can prove problematic; however, survey detection adjustments are nevertheless important to account for the relatively small, but still significant, proportion of missed animals in open prairie–parkland environments. Implications Field experiments to assess aerial survey design are impractical because of cost. We illustrate how simulated surveys using empirical data can be useful to evaluate alternative survey designs to improve population estimates in a region when high accuracy or precision are needed to address management questions or to calibrate more cost-effective approaches.

Variation in hippocampal morphology along an environmental gradient: controlling for the effects of day length

Environmental conditions may create increased demands for memory, which in turn may affect specific brain regions responsible for memory function. This may occur either via phenotypic plasticity or selection for individuals with enhanced cognitive abilities. For food-caching animals, in particular, spatial memory appears to be important because it may have a direct effect on fitness via their ability to accurately retrieve food caches. Our previous studies have shown that caching animals living in more harsh environments (characterized by low temperatures, high snow cover and short day lengths) possess more neurons within a larger hippocampus (Hp), a part of the brain involved in spatial memory. However, the relative role of each of these environmental features in the relationship is unknown. Here, we dissociate the effects of one theoretically important factor (day length) within the environmental severity/Hp relationship by examining food-caching birds (black-capped chickadee, Poecile atricapillus) selected at locations along the same latitude, but with very different climatic regimes. There was a significant difference in Hp attributes among populations along the same latitude with very different climatic features. Birds from the climatically mild location had significantly smaller Hp volumes and fewer Hp neurons than birds from the more harsh populations, even though all populations experienced similar day lengths. These results suggest that variables such as temperature and snow cover seem to be important even without the compounding effect of reduced day length at higher latitudes and suggest that low temperature and snow cover alone may be sufficient to generate high demands for memory and the hippocampus. Our data further confirmed that the association between harsh environment and the hippocampus in food-caching animals is robust across a large geographical area and across years.

Bio-optical properties of Antarctic pack ice in the early austral spring

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3–10 mg Chl a m −2) spanning the range of general sea-ice microalgal microhabitats (e.g., bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2–0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first-year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest—with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms—perhaps suggesting UVR may be influencing the structure of some parts of the sea-ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, bio-physical interactions operating within the Antarctic pack ice ecosystem.

High-altitude vegetation of the Western Carpathians — a syntaxonomical review

This paper presents a survey of high-altitude plant communities which occur in the Western Carpathians with an enumeration of the characteristic, transgressive and differential species of the individual alliances, orders and classes. It describes the tall-herb vegetation (Mulgedio-Aconitetea) and communities of the subalpine shrubs (Betulo carpaticae-Alnetea viridis), the montane and alpine calcareous swards (Elyno-Seslerietea), the wind-exposed cryophilous swards on ridge edges with low snow cover (Carici rupestris-Kobresietea bellardii), the chionophilous communities of snow beds and snow fields (Salicetea herbaceae), the arctic-boreal dwarf-shrub heathlands (Loiseleurio-Vaccinietea), the alpine acidophilous grasslands (Caricetea curvulae) and the high-mountain mat-grass swards of the alliance Nardion strictae (Nardetea strictae).

Trophic niche comparison of American mink and Eurasian otter under different winter conditions

No abstract available

Deep supercooling, vitrification and limited survival to –100°C in the Alaskan beetleCucujus clavipes puniceus(Coleoptera: Cucujidae) larvae

Larvae of the freeze-avoiding beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) in Alaska have mean supercooling points in winter of -35 to -42 degrees C, with the lowest supercooling point recorded for an individual of -58 degrees C. We previously noted that some larvae did not freeze when cooled to -80 degrees C, and we speculated that these larvae vitrified. Here we present evidence through differential scanning calorimetry that C. c. puniceus larvae transition into a glass-like state at temperatures<-58 degrees C and can avoid freezing to at least -150 degrees C. This novel finding adds vitrification to the list of insect overwintering strategies. While overwintering beneath the bark of fallen trees, C. c. puniceus larvae may experience low ambient temperatures of around -40 degrees C (and lower) when microhabitat is un-insulated because of low snow cover. Decreasing temperatures in winter are correlated with loss of body water from summer high levels near 2.0 to winter lows near 0.4 mg mg(-1) dry mass and concomitant increases in glycerol concentrations (4-6 mol l(-1)) and thermal hysteresis. Finally, we provide direct evidence that Cucujus from Wiseman, Alaska, survive temperatures to -100 degrees C.

Influence of environmental factors on the development of bottom ice protist communities during the winter–spring transition

Seasonal changes in the abundance and taxonomic composition of bottom ice protists (i.e. diatoms, flagellates, and dinoflagellates) were assessed in the first-year landfast ice of Franklin Bay (Canadian Beaufort Sea) from 24 February to 20 June 2004. On each sampling day, bottom sea- ice protists were collected at sites of high (>10 cm) and low (<10 cm) snow cover. The net observed growth rates of diatoms and nanoflagellates were significantly higher during the pre-bloom (24 Feb- ruary to 25 March) than the bloom (ca. 3 April to 23 May) period under low snow cover but were not different under high snow cover. In contrast, dinoflagellates showed relatively constant net observed growth rate before and during the bloom period under both snow covers. These results indicate that the 3 protist groups responded differently to changes in the light regime during the growth period. The decline of the protist community after the bloom period was related to a combination of factors including nitrogen deficiency and melting processes. Prior to the bloom, flagellated cells, likely het- erotrophic, dominated numerically under high snow cover, whereas autotrophic protists, especially solitary diatoms, prevailed under low snow cover. During the bloom period, colonial diatoms such as Nitzschia frigida, N. promare, Navicula sp. 6, N. pelagica, and Fragilariopsis cylindrus dominated the bottom ice community irrespective of snow depth, although abundances were higher under low snow cover. The arborescent colonial N. frigida, a key species of landfast ice across circumarctic regions, was the most abundant bottom ice algal diatom throughout the entire season. During the post-bloom period, colonial and solitary diatoms declined more rapidly than nanoflagellates, suggesting that nanoflagellates, presumably heterotrophic, were better adapted to melting sea-ice conditions. Our results demonstrated that the availability of nitrate in the surface water limits the accumulation of algal biomass in the bottom horizon of Arctic landfast ice during the vernal growth season.

Metapopulation Biology: Microtus richardsoni in the Rocky Mountain Front Range of Alberta

Populations of the Water Vole (Microtus richardsoni) occur along headwater streamlets at timberline in the Rocky Mountain front ranges of Alberta. At the 2000-m contour riparian distances between potential habitat patches ranged from 749 to 24,651 m, whereas overland distances ranged from 157 to 5104 m. Reproduction is restricted to a snow-free (May–August) period of 60 to 112 d in which females typically produce 1 to 2 litters of 2 to 10 young. Based on home range overlaps, the mating system appears to be polygynous. Over 4 habitat patches and 9 patch-seasons, reproduction was dominated by overwintered adults and began with effective populations (Ne) of 9.2 (4.1 males and 6.8 females) occupying 3- to 4-ha patches of mesic vegetation. Territorial behavior opposes recruitment into these breeding populations. Few males have an opportunity to breed in their natal colony in their 1st summer, but 5% of 1st-litter female young (50% known to be philopatric) may do so. Young of subsequent litters, including any born to 1st-litter females, are unlikely to breed in the season of their birth. Episodes of predation may facilitate settlement and breeding of philopatric young of the year, or “floaters” of unknown origin. In a typical colony, breeding generated a mean surplus above replacement (potential emigrants) of 8 males and 6 females. Disappearance rates of overwintered adults (the number of voles present in 1 trapping session and not in the next divided by the number of intervening days) remained low until August. Disappearance of the 1st cohort of young averaged 1.8%/d for females and 3.7 %/d for males. Young persisting into September in their natal colonies were the most likely to be present in the following spring. The socially determined window for recruitment appears limited to late summer and early fall. Winter trapping indicated that low temperatures and heavy snow cover inhibit movement between habitat patches during the winter months. The limited genetic analysis available indicates that variation is maintained in local gene pools despite restriction to small isolated habitat patches, small effective population sizes, and territorial behavior. Conservation concerns may arise due to the habitat specificity of M. richardsoni and the constraints on population dynamics and gene flow imposed by the small size and isolation of habitat patches and the harshness of the subalpine environment.

Climatic effects on the breeding phenology and reproductive success of an arctic‐nesting goose species

AbstractClimate warming is pronounced in the Arctic and migratory birds are expected to be among the most affected species. We examined the effects of local and regional climatic variations on the breeding phenology and reproductive success of greater snow geese (Chen caerulescens atlantica), a migratory species nesting in the Canadian Arctic. We used a long‐term dataset based on the monitoring of 5447 nests and the measurements of 19 234 goslings over 16 years (1989–2004) on Bylot Island. About 50% of variation in the reproductive phenology of individuals was explained by spring climatic factors. High mean temperatures and, to a lesser extent, low snow cover in spring were associated with an increase in nest density and early egg‐laying and hatching dates. High temperature in spring and high early summer rainfall were positively related to nesting success. These effects may result from a reduction in egg predation rate when the density of nesting geese is high and when increased water availability allows females to stay close to their nest during incubation recesses. Summer brood loss and production of young at the end of the summer increased when values of the summer Arctic Oscillation (AO) index were either very positive (low temperatures) or very negative (high temperatures), indicating that these components of the breeding success were most influenced by the regional summer climate. Gosling mass and size near fledging were reduced in years with high spring temperatures. This effect is likely due to a reduced availability of high quality food in years with early spring, either due to food depletion resulting from high brood density or a mismatch between hatching date of goslings and the timing of the peak of plant quality. Our analysis suggests that climate warming should advance the reproductive phenology of geese, but that high spring temperatures and extreme values of the summer AO index may decrease their reproductive success up to fledging.

Changes in extreme nival conditions in Poland during the second half of the 20th century

The two main objectives of this study are: 1. to assess the scale of extreme nival conditions in Poland; 2. to provide a fragmentary, regional verification of the IPCC thesis of the increasing frequency of extreme atmospheric phenomena during recent decades, by the estimation of extreme nival conditions tendencies in the second half of the 20 th century. The daily data of snow cover depth in 12 meteorological stations in Poland, for the period 1954-2001, were analysed. A winter season with extreme nival conditions is the season, when the snow cover duration value and/or the maximum seasonal snow cover depth value, was of the empirical probability of 90 % (a season of extremely long duration and/or thick snow cover). A slight negative, usually statistically insignificant, trend was found for characteristics concerning extremely abundant snow cover, i.e.: the seasonal number of days with snow cover of a considerable depth; the 90th percentile value of the daily snow cover depth for the period from December 1 to February 28; the seasonal maximum of a 24-hour increase in the snow cover depth (except for northern Poland); the seasonal number of days with a 24-hour increase in the snow cover depth of > 10 cm. At the same time, since the 1970's the scarce snow cover (i.e. of the empirical probability < 10 %) has been observed much more frequently than before. The above mentioned IPCC thesis has been confirmed towards the extremely low snow cover values in Poland.

Winter–spring dynamics in sea-ice carbon cycling in the coastal Arctic Ocean

An understanding of microbial interactions in first-year sea ice on Arctic shelves is essential for identifying potential responses of the Arctic Ocean carbon cycle to changing sea-ice conditions. This study assessed dissolved and particulate organic carbon (DOC, POC), exopolymeric substances (EPS), chlorophyll a, bacteria and protists, in a seasonal (24 February to 20 June 2004) investigation of first-year sea ice and associated surface waters on the Mackenzie Shelf. The dynamics of and relationships between different sea-ice carbon pools were investigated for the periods prior to, during and following the sea-ice-algal bloom, under high and low snow cover. A predominantly heterotrophic sea-ice community was observed prior to the ice-algal bloom under high snow cover only. However, the heterotrophic community persisted throughout the study with bacteria accounting for, on average, 44% of the non-diatom particulate carbon biomass overall the study period. There was an extensive accumulation of sea-ice organic carbon following the onset of the ice-algal bloom, with diatoms driving seasonal and spatial trends in particulate sea-ice biomass. DOC and EPS were also significant sea-ice carbon contributors such that sea-ice DOC concentrations were higher than, or equivalent to, sea-ice-algal carbon concentrations prior to and following the algal bloom, respectively. Sea-ice-algal carbon, DOC and EPS-carbon concentrations were significantly interrelated under high and low snow cover during the algal bloom ( r values ≥ 0.74, p < 0.01). These relationships suggest that algae are primarily responsible for the large pools of DOC and EPS-carbon and that similar stressors and/or processes could be involved in regulating their release. This study demonstrates that DOC can play a major role in organic carbon cycling on Arctic shelves.

Impact of snow conditions on selected periglacial landforms in the eastern part of the Krkonoše Mountains

The paper deals with the influence of snow conditions on periglacial landforms. The research was carried out on four study sites in the summit parts of the Krkonoše Mountains with occurrence of recently active periglacial landforms (solifluction lobes, ploughing blocks, peat hummocks and sorted circles). Depth and duration of snow cover were measured there two years. Regularities in snow distribution were evaluated and compared with the position of selected periglacial landforms. The results prove that there is a close relationship between the low snow cover and occurrence of sorted circles and that the distribution of peat hummocks has not any connection with snow cover. Relationships between solifluction lobes and ploughing blocks and snow were rather ambiguous.

Estimation of the Impact of Global Warming on Snow Depth in Japan by the Pseudo-Global-Warming Method

A series of numerical experiments were conducted in order to investigate the impact of global warming on snow amount in Japan during early winter. After confirming the accuracy of hindcast simulations for a High-Snow-Cover (HSC) year and a Low-Snow-Cover (LSC) year, dynamical downscaling experiments were conducted in order to make future projections using the Pseudo-Global-Warming method. The precipitation, snow depth, and surface air temperature of the hindcast simulations show good agreement with the AMeDAS station data. At the end of December, the decreasing ratios of snow water are more significant in areas with an altitude of less than 1,500 m. The increase in the air temperature is one of the major factors influencing the decrease in snow water since the present mean air temperature in most of these areas is near 0°C even in winter. On the other hand, the change in the mean areal precipitation due to global warming is less than 15% in both years.

Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 50:25-38 (2007) - DOI: https://doi.org/10.3354/ame01155 Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition Andrea Riedel1,2,*, Christine Michel2, Michel Gosselin1 1Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Fisheries and Oceans Canada, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada *Email: andrea.niemi@dfo-mpo.gc.ca ABSTRACT: Heterotrophic bacterial dynamics were assessed in the sea ice and surface waters on the Mackenzie Shelf (Beaufort Sea), from 5 March to 3 May 2004. On 11 occasions, heterotrophic protist bacterivory was assessed from the disappearance of fluorescently labeled bacteria (FLB) in sea-ice samples collected from areas of high and low snow cover. Concurrently, sea-ice and surface water samples were analyzed for dissolved organic carbon (DOC), exopolymeric substances (EPS) and chlorophyll a concentrations, and protist and bacterial abundances. Total bacterial abundances were significantly higher in the sea ice than in surface waters. However, DOC concentrations and abundances of large (≥0.7 µm) bacteria were not significantly higher in the sea ice as compared to surface waters. This suggests that DOC was being released from the sea ice, potentially supporting the growth of large-sized bacteria at the ice–water interface. Heterotrophic protist (HP) bacterivory averaged 57% d–1 of large-sized bacterial abundances in the sea ice with ingestion rates averaging 768 and 441 bacteria HP–1 d–1, under high and low snow cover, respectively. High concentrations of EPS during the sea-ice algal bloom may have interfered with the grazing activities of heterotrophic protists as indicated by the significant negative correlations between ingestion rates and EPS-carbon concentrations under high (τ = –0.57, p < 0.05) and low (τ = –0.56, p < 0.05) snow cover. Bacterivory satisfied heterotrophic protist carbon requirements prior to, but not during, the sea-ice algal bloom, under high and low snow cover. EPS may have been an additional carbon source for the heterotrophs, especially during the sea-ice algal bloom period. This study provides evidence of an active heterotrophic microbial food web in first-year sea ice, prior to and during the sea-ice algal bloom. This study also highlights the significance of DOC and EPS as integral components of the microbial food web within the sea ice and surface waters of Arctic shelves. KEY WORDS: Bacteria · FLB · Grazing · DOC · EPS · Sea ice · Arctic Full text in pdf format PreviousNextCite this article as: Riedel A, Michel C, Gosselin M (2007) Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition. Aquat Microb Ecol 50:25-38. https://doi.org/10.3354/ame01155 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 50, No. 1. Online publication date: December 12, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

Effect of Climatic Fluctuations on Post-Fire Regeneration of Two Jack Pine and Red Pine Populations during the Twentieth Century

The age structure of two mixed red pine (Pinus resinosa Ait.) and jack pine (Pinus banksiana Lamb.) forests located at Lac Duparquet, northwestern Québec, were correlated with mean annual temperature and total precipitation recorded at Iroquois Falls for the period between 1913 and 1986. The age structures of both pine species showed a common pattern of regeneration characterized by low regeneration before 1930, an important regeneration peak starting around the 1930s, a dip in the age structure around 1950, a second, though less important, regeneration peak in the 1960s, and an important drop, especially for red pine, after 1970. In general, high regeneration rates were positively correlated with precipitation and negatively with temperature, suggesting that pine recruitment is negatively affected by low snow cover and/or drought. The absence of correlation with temperature suggests that the red pine northern limit may be controlled more by a change in the fire regime than by increasing temperature.