Seasonal mortality rates of Oithona similis (Cyclopoida) in a large Arctic fjord

Instantaneous mortality rates of the common planktonic copepod Oithona similis were investigated for the first time in Kola Bay, a region of the Barents Sea that is influenced by freshwater discharge. The rates were estimated in different seasons (December, May, September 2005 and July 2006). A vertical life table approach (VLT) was used to assess mortality. The total abundance of O. similis (copepodites IV and V, and adults) was highest in autumn and lowest in winter. The maximum mortality of O. similis for the stage pair copepodite IV–copepodite V (0.005 ± 0.001 day^?1) occurred in December 2005, while the highest mortality rates for the pairs copepodite VM–adult male (0.453 ± 0.026 day^?1) and copepodite VF–adult female (0.228 ± 0.006 day^?1) occurred in summer 2006. Simple regression analyses showed that the total abundance of each stage and the mortality rates were positively significantly correlated with water temperature. The mortality rates for the stage pairs copepodite VM–adult male and copepodite VF–adult female were positively significantly correlated with chlorophyll a concentration. The abundance and mortality rate of O. similis in each season was determined by life cycle factors, and possibly by the dynamics of its food resources and potential predators.     

Quantitative estimates of recent environmental changes in the Canadian High Arctic inferred from diatoms in lake and pond sediments

Diatoms were examined in three lacustrine sediment records from Alert, northern Ellesmere Island, and from Isachsen, Ellef Ringnes Island. Diatom assemblages changed markedly since the mid-19th century following relatively stable community composition that spanned centuries to millennia. Three different assemblages, primarily composed of Fragilaria pinnata, Diadesmis spp., or Pinnularia spp., dominated the pre-1850 period at the three sites, but were replaced with different, more diverse assemblages in recent sediments. These species shifts occurred in the mid- to late-19th century in the Isachsen sites, and in the mid- to late-20th century in our Alert site. This difference in timing appears to be a result of the different sensitivities of lakes and ponds to environmental change, rather than of site-specific chemical properties. Reconstructions of pH using diatom inference models indicated increases from 0.5 to 0.8 pH units at these sites over this period of assemblage change. The diatom-inferred pH record from Alert showed agreement with measured climate data from Alert over the last 30 years. These marked community changes suggest that these sensitive high arctic sites have recently crossed important ecological thresholds due to environmental change, most likely related to recent warming.     

Seasonal changes in hydrochemical and microbiological indices of Soda Lake Beloye (Western Transbaikalia)

We report results from a hydrochemical and microbiological investigation of Soda Lake Beloye characterized by high pH values (8.30–9.21). It is shown that the water of the lake under investigation is dominated by magnesium, chlorine and hydrocarbonate ions. A study is made of the numbers of different physiological groups of destructive bacteria, the most numerous of which are saprophytic bacteria (up to 10 mil. cells/mm).     

Seasonal and spatial changes in the zooplankton community of Kongsfjorden, Svalbard

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m⁻³) was much lower than in the summer and autumn (410–10 560 individuals m⁻³). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.     

Aspects of growth in Arctic cod, Boreogadus saida (Lepechin 1773)

In June 1986- 42 young Arctic cod were caught in ice-covered waters of the Barents sea with dip-nets by scuba divers. From August to June 1987 the fish were kept at -PC and fed on frozen shrimp ( Pandalus borealis ). Length and weight were measured monthly. A fast weight increment of about 0.7% per day was observed in the autumn (Sept.-Nov.). In the winter (Jan.-Feb), the growth rate declined to 0.05% per day. However, daily food intake only decreased by 50% during these winter months. Since the fish were exposed to constant illumination in the aquarium, this growth experiment indicates that something else than light has a significant influence on growth in Arctic cod.     

Microseismicity and faulting geometry in the Gulf of Corinth (Greece)

During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al . (1985 ) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 ( Rigo et al . 1996 ), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes ( Hatzfeld et al . 1996 ; Bernard et al . 1997 ) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).     

Changes in diatom assemblages in Lake C2 (Ellesmere Island, Arctic Canada): response to basin isolation from the sea and to other environmental changes

Diatoms preserved in the sediments of Lake C2 (82°50 N, 76°00 W), a high arctic meromictic lake, track changes in the lake's salinity which have occurred as the basin was isolated from the sea. An assemblage dominated by marine taxa, such as Chaetoceros species, Nitzschia cylindrus and Diploneis spp., was replaced by a Cyclotella kuetzingiana var. planetophora dominated freshwater flora. A brief brackish period separates the two assemblages. Relatively little floristic change occurred within either the marine or freshwater periods, indicating rather stable environmental conditions, except that rheophilous diatoms fluctuated in relative abundance during the lacustrine phase, perhaps tracking past changes in discharge from inflowing streams. These may reflect periods of warmer, wetter environmental conditions.This is the eighth in a series of papers published in this issue on the Taconite Lakes Project. These papers were collected by Dr R. S. Bradley.     

Periglacial landscape evolution and environmental changes of Arctic lowland areas for the last 60 000 years (western Laptev Sea coast, Cape Mamontov Klyk)

Non-glaciated Arctic lowlands in north-east Siberia were subjected to extensive landscape and environmental changes during the Late Quaternary. Coastal cliffs along the Arctic shelf seas expose terrestrial archives containing numerous palaeoenvironmental indicators (e.g., pollen, plant macro-fossils and mammal fossils) preserved in the permafrost. The presented sedimentological (grain size, magnetic susceptibility and biogeochemical parameters), cryolithological, geochronological (radiocarbon, accelerator mass spectrometry and infrared-stimulated luminescence), heavy mineral and palaeoecological records from Cape Mamontov Klyk record the environmental dynamics of an Arctic shelf lowland east of the Taymyr Peninsula, and thus, near the eastern edge of the Eurasian ice sheet, over the last 60 Ky. This region is also considered to be the westernmost part of Beringia, the non-glaciated landmass that lay between the Eurasian and the Laurentian ice caps during the Late Pleistocene. Several units and subunits of sand deposits, peat–sand alternations, ice-rich palaeocryosol sequences (Ice Complex) and peaty fillings of thermokarst depressions and valleys were presented. The recorded proxy data sets reflect cold stadial climate conditions between 60 and 50 Kya, moderate inderstadial conditions between 50 and 25 Kya and cold stadial conditions from 25 to 15 Kya. The Late Pleistocene to Holocene transition, including the Allerød warm period, the early to middle Holocene thermal optimum and the late Holocene cooling, are also recorded. Three phases of landscape dynamic (fluvial/alluvial, irregular slope run-off and thermokarst) were presented in a schematic model, and were subsequently correlated with the supraregional environmental history between the Early Weichselian and the Holocene.     

Abundance,biomass and composition of spring ice algal and phytoplankton communities of the Laptev Sea(Arctic)

<正> Abundance,biomass and composition of the ice algal and phytoplank-ton communities were investigated in the southeastern Laptev Sea in spring 1999.Diatoms dominated the algal communities and pennate diatoms dominated the dia-tom population.12 dominant algal species occurred within sea ice and underlyingwater column,including Fragilariopsis oceanica,F.cylindrus,Nitzschiafrigida,N.promare,Achnanthes taeniata,Nitzschia neofrigida,Naviculapelagica,N.vanhoef fenii,N.septentrionalis,Melosira arctica,Clindrothecaclosterium and Pyrarnimonas sp.The algal abundance of bottom 10 cm sea icevaried between 14.6 and 1562.2×10~4 ceils l~(-1)with an average of 639.0×10~4cells l~(-1),and the algal biomass ranged from 7.89 to 2093.5μg C l~(-1)with an av-erage of 886.9μg C l~(-1),which were generally one order of magnitude higherthan those of sub-bottom ice and two orders of magnitude higher than those ofunderlying surface water.The integrated algal abundance and biomass of lower-most 20 cm ice column were averagely 7.7 and 12.2 times as those of upper 20 mwater column,respectively,suggesting that the ice algae might play an importantrole in maintaining the coastal marine ecosystem before the thawing of sea ice.Icealgae influenced the phytoplankton community of the underlying water column.However,the“seeding”of ice algae for phytoplankton bloom was negligible be-cause of the iow phytoplankton biomass within the underlying water column.     

Mine water-induced gradients in sediment metals and arcellacean assemblages in a boreal freshwater bay (Petkellahti, Finland)

Sediment chemistry and arcellacean community composition were analyzed to study the ecological effects of copper mine-derived acidic and metal-rich waters in a freshwater bay in eastern Finland. To track spatial and temporal changes in the bay, 32 mine-impacted (top) and pre-impact (bottom) samples were analyzed from 16 short sediment cores taken along a transect extending from the pollution source. In addition, short cores from the impacted and reference sites were studied. Recent sediments displayed a geochemical gradient from the inner bay, where mine water is discharged, to the outer bay. Inner bay sites were enriched with C, S, and Fe, whereas Mn was depleted, but has precipitated in the outer bay. Among the heavy metals, Cu, Al, Zn, and Ni concentrations had increased in the inner and mid bay, while Co and Cd concentrations had increased at mid-bay sites. The change from the natural to mine-impacted condition was also seen in faunal gradients. According to ordination and distance measures, the greatest changes in species composition occurred in the inner bay, with fairly small changes in the outer bay. Numerical methods suggested that metals (Cu, Pb, Al, Zn, Cr), redox-sensitive elements (Fe, Mn), organic carbon and nutrients could be related to changes in arcellacean assemblages. Geochemical changes in the impacted core started at ~20 cm with increases in S alternating with peaks in Cr and Mg. Heavy metal concentrations increased markedly at 10 cm, after the active mining period, suggesting the beginning of acid mine drainage. Geochemical changes at ~20 cm were already apparent in the arcellacean assemblages, but the most notable change coincided with the geochemical shift at 10 cm, with signs of decreased pH. Numerical methods suggest that mining-related metals Co, Cu, Zn and Ni co-vary with arcellaceans, but Al appears to behave independently with respect to the species data.     

Landscape evolution and geodynamic controls in the Gulf of Cadiz (Huelva coast, SW Spain) during the Late Quaternary

The coastal evolution of the El Abalario area (Huelva, southern Spain) during the Late Pleistocene and Holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence (OSL) dating. New data come from the analysis of soft sediment deformation, palaeosols, geomorphological mapping, and published seismic surveys on the onshore and offshore Gulf of Cadiz.The present structure of El Abalario dome resulted from the complex interaction of littoral-catchment processes and sea-level changes upon an emergent coastal plain, conditioned by the upwarping of the underlying Pliocene–Pleistocene prograding deltaic sequence. Upwarping is probably related to escape of over-pressurized fluids, accompanied by dewatering, prior to (?) and during OIS (Oxygen Isotopic Stage) 5. Continued upwarping produced the large NW–SE gravitational fault of Torre del Loro (TLF) in the southwestern flank of the dome, roughly parallel to the present coastline during OIS 5–OIS 4. The resulting escarpment favoured the accumulation of aeolian sand dunes (units U1, U2, and U3) from OIS 5 to early OIS 1. Unit U1 (OIS 5) ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions. Unit U2 accumulated mainly during OIS 4 and OIS 3 with prevailing W/E winds. The supersurface between U2 and U3 records a part of OIS 2, with relative low sea level. Sedimentation of unit U3 took place during the Last Deglaciation (radiocarbon and OSL ages) with prevailing W/SW winds, under a temperate moist climate, that became more arid towards the top (Holocene). A major supersurface with an iron crust-like layer (SsFe) developed during the Holocene Climatic Optimum (OIS 1) under wetter and more temperate conditions than before, fossilizing the TLF. The supersurface is covered by younger aeolian dunes (U4, U5, U6, and U7) transported by W–SW winds since the Late Neolithic–Chalcolithic cultural period (5.0 ky cal BP).     

Tracking Holocene environmental changes in an alpine lake sediment core: application of regional diatom calibration, geochemistry, and pollen

Diatom abundances in the surface sediment samples of 41 mountain lakes in the central Austrian Alps (Niedere Tauern) were related to environmental variables using multi-variate techniques. Canonical correspondence analysis (CCA) revealed that the pH, date of autumn mixing (A _mix), mean August water temperature (T _Aug), dissolved organic carbon (DOC), and relative water depth (Z _rel) made significant contributions to explain the diatom assemblage variation in the lakes of the training set. A weighted averaging partial least square regression and calibration model was used to establish Di-pH (R ² _boot= 0.72, RMSEP_boot= 0.131), and a thermistor measurements-based PLS model for A _mix (R ² _boot= 0.71, RMSEP_boot= 0.006 log₁₀ Julian days). The latter showed a better prediction than T _Aug, and was used in terms of climate change. These transfer functions, together with analyses of loss on ignition (LOI), the total carbon/nitrogen (C/N)-ratios, and selected pollen, were applied to an early to mid-Holocene (11.5–4 cal. ky BP) sediment core section from an Austrian Alpine treeline lake on crystalline bedrock. Additionally, passive sample scores in the CCA of the diatom training set were used to show trends in the variables DOC and Z _rel. During the early Holocene, diatoms indicative of increased pH, extended warm summers, and low water levels dominated. Between 10.2 and 7.6 cal. ky BP it was followed by diatom assemblages that indicated an increase in lake water depth and an earlier A _mix. The multi-proxy data suggest that the A _mix decline is the result of a series of snow-rich summer cool and wet climate fluctuations, which were divided by climate warming at ∼9 cal. ky BP. Increased A _mix, LOI and DOC, and the correspondent decline in the C/N-ratios, show subsequent climate warming between 7.3 and 6 cal. ky BP. The long-term trend in Di-pH indicates the impact of catchment-related processes during the early-Holocene, that were superimposed by climate.     

西双版纳橡胶林土壤呼吸季节变化及其影响因子

橡胶(Hevea brasiliensis)林是热带地区重要的经济林,其土壤碳排放除受温度、湿度等非生物因子影响外,还受到橡胶林独特物候特征的影响.为探讨橡胶林土壤呼吸季节变化与生物、非生物因子的关系,本实验再西双版纳橡胶林内设去除凋落物(NL)和对照(CK)两种处理,自2005-08到2006-08,用IRGA法测定土壤呼吸速率(SR),同时测定温、湿度因子;记录橡胶林的物候节律;每月中旬测定叶面积指数;进行为期一年的细根生长和分解试验.结果表明:1)两种处理SR有明显的季节变化,且趋势相同,即雨季(CK:14.10 mg CO2·m-2·min-1;NL:13.00 mg CO2·m-2·min-1)＞干热季(CK:9.91 mg CO2·m-2·min-1;NL:9.70 mg CO2·m-2·min-1)＞雾凉季(CK:10.87 mg CO2·m-2·min-1;NL:10.33 mg CO2·m-2·min-1);2)通过温度、湿度与SR的相关分析和回归方程模拟,表明两处理各季节SR与温度因子、湿度因子相关关系不同;影响SR的主导因子在雨季为湿度因子,雾凉季是温度因子,干热季SR受到温、湿度因子的双重制约.3)在雨季,凋落物对土壤呼吸影响显著(p=0.036),在干热季和雾凉季影响不显著(p=0.701,p=0.308);4)细根生长试验和LAI的测定结果表明两处理的土壤呼吸速率季节变化与橡胶树生长节律基本一致,生长旺盛期(雨季,5～10月)＞生长减缓期(雾凉季,11～12月)＞生长恢复期(干热季,3～4月)＞相对休眠期(雾凉季,1～2月);5)通过主成分分析,土壤呼吸源的季节变化是影响橡胶林土壤呼吸的第一主成分,方差贡献率为65.98%,第二主成分是地上部分光合产物的输入,方差贡献率为34.02%.两成分可完全解释土壤呼吸的季节变化.故橡胶林的SR季节变化是温度因子、湿度因子及橡胶树生长季相变化协同作用的结果.     

Adsorption-desorption of phosphate and its availability in the sediment of a saline lake (Fuente de Piedra,southern Spain)

Seasonal changes of soluble reactive phosphorus concentrations in sediments of Fuente de Piedra, a saline lake, have been observed and linked to salinity changes. Phosphate availability in sediments was studied in the laboratory under different salinities, from 10 to 70 g L⁻¹. Changes in adsorption of dissolved phosphate appear to be controlled by salinity variations. The adsorption coefficient increases with salinity and the amount of phosphorus adsorbed ranged between 10 and 30 per cent of the total. Salinity-modulated adsorption is proposed as the primary mechanism explaining the seasonal dynamics of phosphorus in this saline lake and its effects on progressive eutrophication.     

The detection of Rhizosolenia (Bacillariophyceae) in sediment of Ontario lakes and implications for paleoecology

The detection of the freshwater genus Rhizosolenia (Bacillariophyceae) remains in sediments is affected by the oxidants used in the digestion procedures. The Rhizosolenia counts decrease from 30% H₂O₂>50% HNO₃>50% chromic acid>100% HNO₃>100% H₂SO₄. Rhizosolenia is mostly found in Ontario lakes with summer average pH ranging from 5.6 to 8.3, Gran alkalinity from 0.2 to 120 mg L^–1 as CaCO₃ and water colour from 4 to 105 Hazen units. Large Rhizosolenia populations are generally found in clear lakes, neutral pH and low alkalinity.     

Variability of sediment diatom assemblages in an upland,wind-stressed lake (Loch Fleet,Galloway, S.W. Scotland)

The variability of diatom distribution in an acidified, upland wind-stressed lake (Loch Fleet, Galloway, S. W. Scotland) was assessed by analysis of 28 surface sediment samples and 11 cores. Correspondence analysis (CA) and cluster analysis were used to illustrate the variability of the surface sediment and core samples. There was reasonable uniformity of taxa in most of the surface sediment samples, although 7 samples, as indicated by both CA and cluster analyses were atypical. Most cores recorded clearly the acidification of the lake, although percentages of individual taxa varied up to 20% between cores. Two cores had old, preacidification diatom assemblages (of indeterminate age) close to the sediment surface. These old sediments were probably the source of the re-worked diatoms found in the atypical surface sediment assemblages. Diatom trends, as CA ordinations and pH profiles, were less variable than the surface sediment assemblages. It is argued that non-uniform sediment accumulation rates and diatom deposition cause variability in surface sediment diatom samples. This variability may be reduced in core profiles by homogenization during further resuspension/deposition cycles and burial. Cores, and the associated time component they offer, may be useful in assessing the variability of surface sediment assemblages.     

Erosion rates and sediment budgets in vineyards at 1-m resolution based on stock unearthing (Burgundy, France)

A new and simple method is developed to efficiently quantify erosion and deposition rates based on stock unearthing measurements. This is applicable to spatial scales ranging from plot to hillslopes, and to time scales ranging from single hydrologic events to centennial scales. The method is applied to a plot area on vineyard hillslopes in Burgundy (Monthélie, France), with measurement of 4328 vine plants. A sediment budget established at the plot scale shows a mean soil lowering of 3.44 ± 1 cm over 20 years, involving a minimal erosion rate of 1.7 ± 0.5 mm yr^− 1. Locally, erosion rates can reach up to 8.2 ± 0.5 mm yr^− 1.This approach allows the sediment redistribution to be mapped and analyzed at 1-m resolution. It provides novel insights into the characterization of erosion patterns on pluri-decennial scales and into the analysis of spatial distribution of erosion processes on cultivated hillslopes.     

Use of remotely sensed data in mapping underwater landscapes of Srednyaya Bay (Peter the Great Gulf,Sea of Japan)

We examine the selection criteria for satellite images and methods of processing them in the process of mapping underwater landscapes using remotely sensed data, discuss the interpretation principles and algorithms as well as some issues related to the support of observations with field material. It is shown that a detailed landscape mapping of shallow marine waters by methods of visual and automated interpretation requires multispectral superhigh spatial resolution images. Results of investigations made on underwater profiles by using lightweight diving outfits were employed to describe seven types of underwater landscapes, and echo sounder measurements were used in constructing the digital elevation model for the bottom of Srednyaya Bay. It is established that the regions for which it was possible to carry out a reliable interpretation of data from the IKONOS-2 spacecraft are in the range of depths between 0 and 10 m and make up about three-fourths of the area of the bay bottom. Ten facies were identified and put on the map, for each of which we determined the area, the range of depths and the mean depth of propagation. Remotely sensed data were used to assess the contribution (in the spatial structure of the geosystem) of algal vegetation on the littoral; the eelgrass fields were ranked according to the degree of projective cover. As a result of a clustering according to the similarity of spectral attributes, we identified ten groups of pixels of the image analyzed. An analysis is made of the agreement between the distribution of facies identified by expert interpretation and results of an automated classification of pixels, and the contours of landscape units were updated. The conclusion is drawn regarding integration of the computer-aided and visual approaches to interpretation of remotely sensed data for shallow marine waters leading to a “hybrid” express method of mapping landscapes of shallow marine waters.