The use of heavy metal concentrations and dendrochronology in the reconstruction of sediment accumulation, Ma a Panew River Valley, southern Poland

Heavy metal concentrations were investigated in overbank sediments of the Mala Panew River, southern Poland. Samples were collected from seven vertical profiles located within channel infills of a 20th century floodplain at three sites, each up to 50 m wide. In each profile, 15–24 samples were collected and analysed for Ba, Cd, Cu, Pb, and Zn. Sequential extraction of these elements was carried out in the 0.063-mm fraction of selected samples. Additionally, the age of the oldest trees growing close to the profiles has been used to estimate the initiation of sediment accumulation there. Ba, Cu, and Pb, which occur mostly in less mobile, moderately reducible, and residual fractions, were used for sediment dating. Zn and Cd, which in 50–75% occur in the mobile exchangeable fraction, were not suitable for dating. Correlation of Ba, Cu, and Pb concentrations in vertical profiles with changes in the load of effluents discharged to the river showed abrupt changes in the thickness of the strongly polluted sediments across the floodplains. A comparison of the relative changes between heavy metal peaks in sediments of similar age in the different profiles suggests a variable rate of downward metal migration. In general, none of the heavy metals investigated seems to have been mobilised within the stratigraphic layers above the water table. In layers located at stratigraphically lower levels, the Zn and Cd peaks seem to migrate several centimetres to several decimetres down in the profile. In profiles inundated for several weeks every year, Zn and Cd, as well as the relatively less mobile Ba, Cu, and Pb, have migrated downward by several decimetres. The investigation shows that frequent fluctuations of the water table have blurred the original depositional metal patterns of metal concentrations within a period of less than 40 years.     

Evidence for variations in cryogenic extraction deuterium biases of plant xylem water across foundational northeastern US trees

Measurements of oxygen and hydrogen isotopes in plant xylem water (²H, ¹⁸O) have helped to redefine conceptual and numerical models of the hydrological cycle and understand how plants compete for subsurface water. Recent experiments have shown that Cryogenic Vacuum Extraction (CVE) of plant xylem water can result in a δ²H bias. We tested if CVE δ²H-biases varied significantly across seven foundational northeastern US forest trees with a series of tree core rehydration experiments. Our analysis demonstrated that CVE δ²H-biases were well predicted by sample gravimetric water content and varied significantly with tree species identity. We show that species-level δ²H-bias corrections can result in substantially different understandings of plant water uptake and transpiration versus uncorrected data or generic bias corrections. This research demonstrates an urgent need for the critical evaluation of CVE for plant water extraction. In the absence of a stronger understanding of CVE δ²H-biases, we recommend that xylem water δ²H observations should not be used in plant water uptake studies.     

Flood‐plain responses to contemporary climate change in small High‐Arctic basins (Svalbard,Norway)

Changes in the supply of water and sediment to high‐latitude rivers related to contemporary climate change and glacier fluctuations largely determine the activity of fluvial processes. This study reconstructs fluvial dynamics since the end of the Little Ice Age (LIA) in two small, partially glaciated basins in the southern part of Spitsbergen, Svalbard Archipelago. We use a combination of aerial photograph interpretation, field mapping and dendrochronological analysis. Sequences of abandoned channels and glacifluvial terraces are distinctly visible in middle and lower parts of the Brattegg and Arie basins in this area. The advance of glaciers during the LIA in the upper part of the basins led to the development of a braiding pattern and to channel aggradation corresponding to the highest glacifluvial levels. The decreasing activity of these braidplains occurred at the turn of the 19th and 20th centuries, immediately prior to a significant incision period. A second generation of braided channels developed during the first half of the 20th century. Ice‐marginal lake development, less input of fine‐grained sediment to the river channel, and fast incision began from the second half of the 20th century onward. During the last two decades, the main fluvial response to the climatic warming has been contraction of flow within a narrower channel and the abandonment of braidplains. The increased lateral erosion and rate of downcutting and the formation of the most downstream reaches of the modern valley bottom occurred in the 1980s and 1990s. This process was intensified under flood conditions generated by extreme rainfall events. These micro‐scale (small partially glaciated basins) observations concerning the changes of the activity of fluvial processes since the end of LIA may be helpful for the reconstruction of past fluvial changes over longer time scales.     

塔克拉玛干沙漠南缘典型绿洲ET0模型适用性评价及修正

ET₀模型在不同地区具有不同的适用性,而对极端干旱的塔克拉玛干沙漠南缘绿洲的ET₀模型的适用性研究较为稀缺。利用2006—2014年生长季（4—10月）策勒气象站逐日气象资料,以自动称重式蒸渗仪实测数据为标准,采用最大绝对误差（MAE）、均方根误差（RMSE）、模型效率（EF）和一致性指数（d）4个指标,在日、月时间尺度上评价了6种常用ET₀模型在策勒绿洲的适用性,并使用回归修正法和比例修正法分别修正了这6种模型。结果表明：（1）日、月时间尺度上,Hargreaves-Samani（H-S）模型高估程度较大,其余模型均不同程度低估,拟合度由高到低依次为FAO-56PM、Jensen-Haise（J-H）、Priestley-Taylor（P-T）、Makkink、Turc、H-S。（2）所有ET₀模型月值变化趋势与蒸渗仪实测值基本一致,除FAO-56PM和Turc模型计算的ET₀月值在6月达到峰值外,其余模型均在7月达到峰值,在生长季尺度所有模型ET₀月值与蒸渗仪实测值呈显著相关。（3）日、月时间尺度上,回归修正法和比例修正法修正后的ET₀模型计算结果与蒸渗仪实测值均呈极显著相关,回归修正法优于比例修正法。（4）相关性分析表明,对策勒绿洲ET₀影响由高到低的气象因子依次为T_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{n}}>T_{\mathrm{m}\mathrm{i}\mathrm{n}}>P>T_{\mathrm{m}\mathrm{a}\mathrm{x}}>R_s>U_{\mathrm{2}}>R{H}_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{n}}。     

Snow accumulation, melt, mass loss, and the near-surface ice temperature structure of Irenebreen, Svalbard

This study examines the mass balance, accumulation, melt, and near-surface ice thermal structure of Irenebreen, a 4.1 km² glacier located in northwest Spitsbergen, Svalbard. Traditional glaciological mass balance measurements by stake readings and snow surveying have been conducted annually at the glacier since 2002, yielding a mean annual net mass balance of −65 cm w.e. for the period 2002–2009. In 2009, the annual mass balance of Irenebreen was −63 cm w.e. despite above-average snow accumulation in winter. The near-surface ice temperature in the accumulation area was investigated with automatic borehole thermistors. The mean annual surface ice temperatures (September–August) of the accumulation area were −3.7 °C at 1 m depth and −3.3 °C at 10 m depth. Irenebreen is potentially polythermal, with cold ice and a temperate surface layer during summer. This temperate surface layer is influenced by seasonal changes in temperature. In winter, the temperature of all the ice is below the melting point and temperate layers are probably present in basal sections of the glacier. This supposition is supported by the presence of icings in the forefield of Irenebreen.     

Longitudinal asymmetry of craters' density distributions on the icy satellites

Crater's density distribution versus satellitographical longitude was searched for seven icy satellites: two of Jupiter (Ganymede and Callisto) and five of Saturn (Mimas, Tethys, Dione, Rhea and Iapetus). Craters were classified according to their size. Four bins of the craters' diameter were used. Density distributions were found in the longitudinal sectors of the near-equatorial stripes that circumscribe the satellites. The size distributions (R-plots) were done independently for each of the eight longitudinal sectors of the satellites. Searching for the leading/trailing (apex/antapex) and the near-side/far-side asymmetry was done. It was found that the crater density is longitudinally asymmetric for all seven satellites being studied. However, the apex–antapex asymmetry is much less pronounced than predicted by theory of Zahnle et al. (2003), for impacts on the satellites by ecliptic comets. We conclude that the impact craters observed on the considered satellites are mostly originated from planetocentric swarm of debris. In that case longitudinal asymmetry is not expected, as stated by Horedt and Neukum, 1984a, Horedt and Neukum, 1984b. However, cratering longitudinal asymmetry that we observe for Mimas perfectly agrees with calculations of Alvarellos et al. (2005). It is very likely that important part of craters on Mimas were formed due to impacts of ejecta originated from crater Herschel.     

Where will widening occur in an outwash braidplain? A new approach to detecting controls on fluvial lateral erosion in a glacierized catchment (north-western Spitsbergen,Svalbard)

The dynamics of fluvial system evolution depend on fluvial processes and their driving forces associated with climatic variations, which affect changes in the morphology of river channels and floodplains. Neither channel slope and morphology, nor the properties of fluvial sediment have previously been considered as determinants of active braidplain widening on outwash plains (formed from valley/alpine glaciers and confined by pre-existing topography) in the High Arctic region and in the forefields of retreating glaciers. Factors determining widening of braidplain activity of the Waldemar River outwash (north-western Spitsbergen, Svalbard) were analysed on the basis of geomorphological, sedimentological, glaciological and meteorological research, and indicate significant multiple correlations between meltwater discharge, precipitation, braidplain width, morphology of the braided channel and the textural features of braidplain deposits. The capability of multivariate adaptive regression splines to detect these relationships was described, and threshold values were identified. The results indicate that the rate of active braidplain widening is proportional to the meltwater outflow in proglacial rivers, which can decrease despite a growing rate of glacial ablation. A proposed model enables us to predict zones of braidplain prone to widening activity in the High Arctic (humid) outwash fans and plains as well as fans developed in arid intermountain basins. The necessary conditions to activate braidplain widening processes were (1) spatial changes in the outwash feeding system due to glacier terminus retreat and (2) crossing the thresholds in passive factors (S and d₅₀) controlling lateral erosion intensity. As a result, the braidplain reached a new dynamic equilibrium, in which high-magnitude–low-frequency extreme meltwater discharges were of particular importance in terms of braidplain dynamics and are the dominant controls on the pattern of distributary channels.     

Changes in The Dynamics And Thermal Regime of The Permafrost and Active Layer of The High Arctic Coastal Area in North‐West Spitsbergen,Svalbard

In this paper changes in the active layer of the high arctic coastal area in north‐west Spitsbergen, Svalbard are described. Analysis includes both the ground thawing depth and its near‐surface thermal structure. The study was conducted on the Kaffiøyra Plain (Svalbard) at several fixed sites, which represent places typical of the region: a sandy beach, a tundra plain and a moraine ridge. The results show that in recent years, at two measurement points a significantly deeper thawing was observed. In 1996–2012 on the beach and on the moraine the trend of active layer thickness change was +1.3 cm yr^?1 and +2.5 cm yr^?1, respectively. Generally, in the years 2008–2012 the mean thickness of the active layer in the Kaffiøyra region increased by 3% to 6%. Even at the spatially close sites, within similar environments, there are significant differences in the thickness of the active layer. Measurements show that significant changes also occurred in the thawed ground temperature. Mean values of the observed near‐surface temperature in recent years (2007–2011) were higher by more than 1.0°C, in comparison to the mean in the late 1970s.     

Dating of small gully formation and establishing erosion rates in old gullies under forest by means of anatomical changes in exposed tree roots (Southern Poland)

Small gullies occur in forested gully systems on the undulating loess plateau in southern Poland. The old gully hillslopes are mainly covered with 200-year old beech trees in contrast with the surface of the summit plateau, which is cultivated agricultural land. Beech roots are exposed in the gullies through erosion. Wood vessels in the root tree rings divide into early wood and late wood and, after the roots are exposed, start to make fewer vessels. These anatomical changes in root tree rings allow us to date erosion episodes.Small gullies form in a different manner on the valley floor and on hillslopes. In valley bottoms, erosion features are often formed at some distance from one another, and in time small gullies combine to form a single, longer one. Depending on local conditions, such as the hillslope profile, hillslopes may exhibit headward erosion or may be eroded downwards. Hilllope gullies may be transformed into side valleys as a result of gradual widening and deepening.Dating the exposure of roots indicates that small gullies had already formed in the valley system by 1949. Intensive gully erosion was recorded between 1984 and 2002, during intense precipitation in 1984 and, of particular note, during the extraordinary flood of 1997 which affected all of Central Europe. The mean rate of small gully erosion in the old gully system studied is 0.63 m/year. On hillslopes the mean gully erosion rate is 0.21–0.52 m/year, and on the valley bottoms 0.18–1.98 m/year. High bottom erosion rates resulted from the emergence of long gullies during the erosion episodes in 1984 and 1997. Sheet flow in valley floors intensifies at times of heavy rainfall which causes long gullies to form.Taking into account the fact that conditions favoured erosion, the rate at which the old gullies under forest were transformed should be considered slow. New side gullies form slowly within the valley and it appears that if erosion progressed at the rate observed, new side valleys would take a few hundred years to form.     

Coupling between landslides and eroding stream channels reconstructed from spruce tree rings (examples from the Carpathians and Sudetes – Central Europe)

The analysis of the positive feedback between landslides and erosion requires determination of the precise temporal and spatial relations between events of colluvium delivery and fluvial erosion. In our study we use decennial datasets on the occurrence of landsliding and erosion achieved through dendrochronological methods. Four sites covering areas of landslide slopes and adjacent valley floors with stream channels were studied. Landsliding on slopes was dated from the tree‐ring eccentricity developed in stems tilted due to bedrock instability. Erosion in channels was dated using the wood anatomy of roots exposed by erosion of the soil cover. Analysis of the temporal relations between dated landsliding, erosion and precipitation record has revealed that two types of repeating sequences can be observed: (1) rainfall → landsliding → erosion; (2) rainfall → erosion → landsliding. These sequences are an indication of the occurrence of slope‐channel positive feedback in the sites studied. In the first type, landsliding triggered by rainfall delivers colluvia into the valley floor and causes its narrowing, which in turn causes increased erosion. In the second type erosion triggered by rainfall disturbs the slope equilibrium and causes landsliding. Landsliding and erosion, once triggered by precipitation, can occur alternately in years with average precipitation and reinforce one another. Bidirectional coupling between landsliding and channel erosion was shown notably through the effects of channel shifting and forced sinuosity and by increased erosion of the slopes opposite the active landslides. Observations also suggest that the repetition of sequences described over longer periods of time can lead to a general widening of the valley floor at the expense of slopes and to a gradual change of the valley cross‐profile from narrow, V‐shaped into a wide flat‐bottomed. Thus landsliding–erosion coupling/positive feedback was recognized as an important factor shaping hillslope–valley topography of the mid‐mountain areas studied. Copyright © 2014 John Wiley & Sons, Ltd.