Production and hydrochemical characteristics of ice,under-ice water and sediments in the Razdolnaya River estuary (Amursky Bay,Sea of Japan) during the ice cover period

Production and hydrochemical characteristics of ice, under-ice water, and sediments in the Razdol’naya River estuary (Sea of Japan) were studied during the ice cover periods of the years 2007 and 2008. In 2007, snow cover was absent until mid-February and PAR levels under ice were sufficient for the development of phytoplankton. The chlorophyll a content in ice, under-ice water, and surface sediments was high, while nutrient levels were decreased. After a snowfall, the chlorophyll content in ice and under-ice water decreased sharply. In winter 2008, snow cover was formed immediately after freeze-up; therefore, PAR levels in the ice and under-ice water were significantly reduced. The chlorophyll content was lower, but nutrient levels were higher than in 2007. In both winter seasons, the greatest portion of chlorophyll (up to 85%) was contained in surface sediments. Diatoms were dominant in ice and under-ice water. In the absence of snow, primary production at the end of ice cover period may reach 1 g cal/(m² day). With snow cover present, this index was markedly reduced.     

Plankton ecology in an ice-covered bay of Lake Michigan: utilization of a winter phytoplankton bloom by reproducing copepods

Plankton ecology was examined during the 1986 winter in Grand Traverse Bay, a 190 m deep, fjordlike bay on Lake Michigan. Before ice cover, algal concentration was low and uniformly distributed with depth, as it is in open Lake Michigan. During ice cover (February and March), a bloom of a typical winter-spring phytoplankton community developed in the upper 40 m, resulting in a 4 to 7-fold increase in feeding rate of adult Diaptomus spp. High algal concentration and zooplankton feeding persisted after ice melt (April). During and after ice cover, lipid concentrations of Diaptomus dropped rapidly from 34% of dry weight to 17 % because of egg production. High incident photosynthetically active radiation (PAR), high (45–50%) PAR transmittance of the ice due to little snow on the ice, and water column stability were probably responsible for the bloom. High ice transparency may be a common feature of large lakes and bays, where strong winds blow snow cover off the ice, or at low latitudes where snowmelt due to occasional rains and warm temperature is common. Winter reproducing calanoid copepods use these blooms to increase their reproductive output.     

Long-term trends in water temperature and ice cover in the subalpine lake, Øvre Heimdalsvatn,and nearby lakes and rivers

Long-term data series of ice cover on lakes and river temperatures from the mountain areas of Norway are lacking. The present study analyses the last four decades of ice data from the subalpine lake, Øvre Heimdalsvatn, and water temperature data from its outlet river, Hinøgla. These data are compared to water temperature data from three neighbouring, quite different locations, the glacier-fed rivers Leirungsåi and Sjoa, and the alpine lake, Bessvatn. The study also examines the air temperature/river temperature relationships, and the air temperature/ice freeze-up and break-up dates. During the months of July, August and September, the water temperature in Hinøgla was well correlated to the air temperature, but the correlation was poor in the remaining months due to the ice cover and snow conditions. A significant temperature increase of 2–3°C has been observed in Hinøgla in the months August–October since 1984. There were only minor changes in the duration of the ice cover season during the last 40 years, but a delay of 9 days was found in the freeze-up date and a delay of 6 days in the break-up date, although the latter was not significant.     

Spectral downwelling irradiance in an Antarctic lake

Summary Spectral downwelling irradiance (400–700 nm) was determined in the ice-covered Lake Hoare located in the dry valleys near McMurdo Sound, Antarctica. Full waveband PAR beneath the ice was <44E·m^-2·s^-1 or <3% of surface downwelling irradiance. Maximum light transmission just beneath the 2.6–4 m ice cover, which contained sediments and air bubbles, occurred between 400–500 nm. In the water column below, attenuation of light by phytoplankton in the 400–500 nm region and between 656–671 nm suggested absorption of light by algal pigments.     

The timing of sea ice formation and exposure to photosynthetically active radiation along the Western Antarctic Peninsula

Understanding the flow of solar energy into ecosystems is fundamental to understanding ecosystem productivity and dynamics. To gain a better understanding of this fundamental process in the Antarctic winter sea ice, we produced a model that estimates the time-integrated exposure of seasonal Antarctic sea ice to PAR through the use of remotely sensed sea ice concentrations, sea ice movement and spatially distributed PAR calculations that account for cloud cover and have applied this model over the past three decades. The resulting spatially distributed estimates of sea ice exposure to PAR by mid-winter are evaluated in context of changes in the timing of sea ice formation that have been documented along the Western Antarctic Peninsula (WAP) region and its potential effects on the variation (seasonal and inter-annual) in the accumulation of sea ice algae in this region. The analysis shows the ice pack is likely to have large inter-annual variations (10–100 fold) in productivity throughout the autumn to winter transition in the sea ice along the WAP. Moreover, the pack ice is likely to have spatial structure in regards to biological processes that cannot be determined from analysis of sea ice concentration information alone. The resulting inter-annual variations in winter processes are likely to affect the dynamics of Antarctic krill (Euphausia superba).     

Perennially ice-covered Lake Hoare,Antarctica: physical environment,biology and sedimentation

Lake Hoare (77° 38 S, 162° 53 E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3–5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30–60 years. Therefore, the lake environment responds to changes on a 10–100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.     

Water temperatures and ice cover in lakes of the Tatra Mountains

In 2000 and 2001, miniature thermistors with integrated data loggers were employed to measure lake surface water temperatures (LSWTs) and temperature profiles in high-altitude mountain lakes lying between 1580 and 2145 m a.s.l. on both the Slovak and Polish sides of the Tatra Mountains. This allowed the annual cycle of water temperatures and ice cover in these lakes to be described quantitatively, and their dependence on lake altitude above sea level to be investigated. LSWTs in the Tatra Mountains are found to decrease approximately linearly with increasing altitude from late spring to autumn. LSWT in summer can be modelled well in terms of exponentially smoothed ambient air temperature. Although the timing of ice-off is dependent on altitude, the timing of ice-on is not; the dependence of the duration of ice cover on altitude is therefore wholly due to the altitudinal dependence of the timing of ice-off. The temperature profile measurements allow quantitative characterization of summer and winter stagnation, and spring and autumn turnover.     

Large geographical differences in the sensitivity of ice‐covered lakes and rivers in the Northern Hemisphere to temperature changes

Based on a unique dataset of more than 50 000 observations of ice phenology from 1213 lakes and 236 rivers in 12 different countries, we show that interannual variations in the timing of ice‐on and ice‐off on lakes and rivers are not equally pronounced over the entire Northern Hemisphere, but increase strongly towards geographical regions that experience only short periods during which the air temperature falls below 0 °C. We explain our observations by interannual fluctuation patterns of air temperature and suggest that lake and river ecosystems in such geographical regions are particularly vulnerable to global warming, as high interannual variability is known to have important ramifications for ecosystem structure and functioning. We estimate that the standard deviation of the duration of ice cover, viewed as a measure of interannual variability, exceeds 25 days for lakes and rivers located on 7% of the land area of the Northern Hemisphere. Such high variability might be an early warning signal for a critical transition from strictly dimictic, ice‐covered systems to monomictic, open‐water systems. Using the Global Lake and Wetland Database, we suggest that 3.7% of the world's lakes larger than 0.1 km² are at high risk of becoming open‐water systems in the near future, which will have immediate consequences for global biogeochemical cycles.     

Lung collapse among aquatic reptiles and amphibians during long-term diving

Numerous aquatic reptiles and amphibians that typically breathe both air and water can remain fully aerobic in normoxic (aerated) water by taking up oxygen from the water via extrapulmonary avenues. Nevertheless, if air access is available, these animals do breathe air, however infrequently. We suggest that such air breathing does not serve an immediate gas exchange function under these conditions, nor is it necessarily related to buoyancy requirements, but serves to keep lungs inflated that would otherwise collapse during prolonged submergence. We also suggest that lung deflation is routine in hibernating aquatic reptiles and amphibians in the northern portions of their ranges, where ice cover prevents surfacing for extended periods.     

The ice cover on small and large lakes: scaling analysis and mathematical modelling

Lake ice cover is described by its thickness, temperature, stratigraphy and overlying snow layer. When the ratio of ice thickness to lake size is above ～10^?5, the ice cover is stable; otherwise, mechanical forcing breaks the ice cover, and ice drifting takes place with lead-opening and ridging. This transition enables a convenient distinction to be made between small and large lakes. The evolution of the ice cover on small lakes is solved by a wholly thermodynamic model, but a coupled mechanical–thermodynamic model is needed for large lakes. The latter indicates a wide distribution of ice thickness, and frazil ice may be formed in openings. Ecological conditions in large lakes differ markedly from those in small lakes because vertical mixing and oxygen renewal may take place during the ice season, and the euphotic zone penetrates well into the water column in thin ice regions. Mesoscale sea ice models are applicable to large lakes with only minor tuning of the key parameters. These model systems are presented and analysed using Lake Peipsi as an example. As the climate changes, the transition size between small and large lake ice cover will change.     

Annual primary production of phytoplankton in Lake Verkhneye,Schirmacher Oasis,Antarctica

Algal carbon 14 fixation, photosynthetically active radiation (PAR), temperature and nutrients were measured from March 1976 to January 1977 and from November 1983 to February 1984 in a small freshwater lake. As a consequence of the minute meltwater input, the PAR extinction coefficient was very low ranging between 0.04 and 0.12m^–1 throughout the year. Low extinction combined with the transparent and mostly snowless ice cover resulted in high noon PAR intensities of 640–2340 Em^–2s^–1 in the lake from November to January. As a result of the small annual total phosphorus loading (0.01 mmol m^–3 of lake), phosphate concentration in the main water mass did not exceed 0.03 mmol m^–3 during most of the growing season. Phytoplankton assimilation rates were very low with a minimum of 0.03 mgC (mgChl a)^–1 h^–1 in December. The annual net primary production was 0.58 gCm^–2, the lowest value on record. These low levels were due to photoinhibition and phosphorus limitation.     

Microbiota within the perennial ice cover of Lake Vida, Antarctica

Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.     

Removal of snow cover inhibits spring growth of Arctic ice algae through physiological and behavioral effects

The snow cover of Arctic sea ice has recently decreased, and climate models forecast that this will continue and even increase in future. We therefore tested the effect of snow cover on the optical properties of sea ice and the biomass, photobiology, and species composition of sea ice algae at Kangerlussuaq, West Greenland, during March 2011, using a snow-clearance experiment. Sea ice algae in areas cleared of snow was compared with control areas, using imaging variable fluorescence of photosystem II in intact, unthawed ice sections. The study coincided with the onset of spring growth of ice algae, mainly an increase in two pennate diatoms (Achnanthes taeniata and Navicula directa), as temperature increased and ice thickness and brine volume stabilized. The increase in biomass was accompanied by an increase in minimum variable fluorescence (F _o) and the maximum quantum yield of PSII (F _v /F _m) and filling of brine channels with fluorescing cells. In contrast, in the minus snow area, PAR transmittance increased sixfold and there was an exponential decrease in chl-a and no increase in F _o, and the area of fluorescing biomass declined to become undetectable. This study suggests that the onset of the spring bloom is predominantly due to temperature effects on brine channel volume, and that the algal decline after snow removal was primarily due to emigration rather than photodamage.     

Effects of ice cover on the diel behaviour and ventilation rate of juvenile brown trout

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A method of collecting water samples from immediately below an ice cover

A plexiglas box with cellular neoprene gaskets in two opposite faces which can be frozen in situ in a developing ice cover on a lake is described along with a water sampling system using evacuated glass tubes (Vacutainers) and blood collecting needles. This system allows collecting of water samples from directly beneath the ice without disturbing the ice cover. The box may be removed in an ice block at the end of the sampling period.     

Weak trends in ice phenology of Estonian large lakes despite significant warming trends

We studied changes in air temperature (AT) in Tartu, Estonia, since 1866; ice phenology in two Estonian large lakes since the 1920s; and daily surface water temperatures (SWT) in these lakes since the 1940s. The Mann–Kendall test showed increasing AT trends in all seasons with biggest changes in spring. The strongest increase in SWT occurred in April and August. The temperature increase has accelerated since 1961. Despite significant trends in the seasonal AT and SWT of Estonian large lakes, trends in ice phenology were weak or absent, implying that the processes governing ice phenology are more complex than those governing lake SWT. Greater snowfall was associated with later ice breakup, longer duration of ice cover, and greater ice thickness, while the relationship between winter rainfall and these ice parameters was the opposite. In the deeper Lake Peipsi, ice-on occurred later and ice-off earlier than in the shallower Võrtsjärv. The dates of both ice-on and ice-off responded more sensitively to AT in the case of Peipsi than in the case of Võrtsjärv. An increase of the average November–March AT by 2°C would presumably halve the ice cover duration in Peipsi but shorten it only by about 20% in Võrtsjärv.     

THE EFFECTS OF ULTRAVIOLET‐B RADIATION ON ANTARCTIC SEA‐ICE ALGAE1

The impacts of ultraviolet‐B radiation (UVB) on polar sea‐ice algal communities have not yet been demonstrated. We assess the impacts of UV on these communities using both laboratory experiments on algal isolates and by modification of the in situ spectral distribution of the under‐ice irradiance. In the latter experiment, filters were attached to the upper surface of the ice so that the algae were exposed in situ to treatments of ambient levels of PAR and UV radiation, ambient radiation minus UVB, and ambient radiation minus all UV. After 16 d, significant increases in chl a and cell numbers were recorded for all treatments, but there were no significant differences among the different treatments. Bottom‐ice algae exposed in vitro were considerably less tolerant to UVB than those in situ, but this tolerance improved when algae were retained within a solid block of ice. In addition, algae extracted from brine channels in the upper meter of sea ice and exposed to PAR and UVB in the laboratory were much more tolerant of high UVB doses than were any bottom‐ice isolates. This finding indicates that brine algae may be better adapted to high PAR and UVB than are bottom‐ice algae. The data indicate that the impact of increased levels of UVB resulting from springtime ozone depletion on Antarctic bottom‐ice communities is likely to be minimal. These algae are likely protected by strong UVB attenuation by the overlying ice and snow, by other inorganic and organic substances in the ice matrix, and by algal cells closer to the surface.     

PRESENCE OF ALGAE IN FRESHWATER ICE COVER OF FLUVIAL LAC SAINT‐PIERRE (ST. LAWRENCE RIVER,CANADA)1

Winter ice cover is a fundamental feature of north temperate aquatic systems and is associated with the least productive months of the year. Here we describe a previously unknown freshwater habitat for algal and microbial communities in the ice cover of the freshwater St. Lawrence River, Quebec, Canada. Sampling performed during winter 2005 revealed the presence of viable algal cells, such as Aulacoseira islandica (O. Müll.) Simonsen (Bacillariophyceae), and microbial assemblage growing in the ice and at the ice–water interface. Vertical channels (1–5 mm wide) containing algae were also observed. Concentrations of chl a ranged between 0.5 and 169 μg · L^?1 of melted ice, with maximal concentrations found in the lower part of the ice cores. These algae have the potential to survive when ice breakup occurs and reproduce rapidly in spring/summer conditions. Freshwater ice algae can thus contribute to in situ primary production, biodiversity, and annual carbon budget in various habitats of riverine communities.     

Effects of ice cover on the behavioural patterns of aquatic-mating male bearded seals

We used vocalizations to examine the behaviour of male bearded seals, Erignathus barbatus, in relation to ice cover over 2 consecutive years. Site fidelity varied between males. Territorial males returned to the same display locations in successive years, whereas roaming males returned to the study area but not to specific display locations. Males did not vocalize under the land-fast-ice edge and were therefore limited by access to areas of drift ice and open water for the purpose of displaying. Between-year fluctuations in ice cover restricted the number of displaying males during the early part of the mating season in April. Decreased ice cover during May resulted in more males displaying, but the number of males declined in June irrespective of the continued decline in ice cover. Roaming males were not heard when the ice cover was more than 60%, whereas territorial males were present during all ice conditions. Yearly fluctuations in ice cover may alter the long-term mating success of individuals and predictably available display areas may be preferred to areas that are more likely to be enclosed by fast-ice in some years.     

华北山区侧柏冠层气孔导度特征及其对环境因子的响应

冠层气孔导度(g_s)是衡量冠层-大气界面水汽通量的重要生物学常数,研究其特征及对环境因子的响应,能为开展森林冠层水汽交换过程的机理性研究提供理论依据.于2014年利用SF-L热扩散式探针测定了侧柏的树干液流密度(J_s),同步监测光合有效辐射(PAR)、饱和水汽压差(VPD)、气温(T)等环境因子,计算侧柏的冠层气孔导度特征并分析其对各环境因子的响应.结果表明: 侧柏液流密度的日变化总体呈双峰曲线,生长季高于非生长季,且胸径越大液流密度越大;冠层气孔导度日变化与单位叶面积冠层蒸腾(E_L)趋势相近,均呈双峰曲线,生长季的冠层气孔导度和蒸腾较非生长季略高.侧柏冠层气孔导度与空气温度呈抛物线关系,在10 ℃左右冠层气孔导度达到峰谷;光合有效辐射以400 μmol·m^-2·s^-1为界,小于该阈值两者呈正相关关系,大于该阈值则冠层气孔导度受其影响较小;与饱和水汽压差呈负对数函数关系,随饱和水汽压差增大而逐渐降低.较高的空气温度和光合有效辐射、较低的饱和水汽压差有利于侧柏形成较大的冠层气孔导度,进而促进冠层蒸腾.