Hydrometeorological behaviour of pine and larch forests in eastern Siberia

Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (R_n ? G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded R_n ? G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day^?1. The contributions of understory evapotranspiration (E_u) and overstory transpiration (E_o) to the evapotranspiration of the entire ecosystem (E_t) were both from 25 to 50% throughout the period analysed. These results suggest that E_u plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to ?26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd.     

Shear-wave polarizations in the Peter the First Range indicating crack-induced anisotropy in a thrust-fault regime

Summary. Three-component seismograms of small local earthquakes recorded in the Peter the First Range of mountains near Garm, Tadzhikistan SSR, display shear-wave splitting similar to that previously observed near the North Anatolian Fault in Turkey. The Peter the First Range is in a region of compressional tectonics, whereas the North Anatolian Fault is a comparatively simple strike-slip fault. Detailed analysis of the Turkish records suggests that the splitting is diagnostic of crack-induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression. Preliminary examination of paper records from Garm shows that most shear waves arriving within the shear-wave window display shear-wave splitting, and that the polarizations of leading shear-waves are consistently aligned in a NE/SW direction. The area is complicated and the tectonics are not well-understood, but the NE/SW direction is approximately perpendicular to the compressional axis in many of the fault-plane mechanisms of the earthquakes. These earthquakes are usually at depths between 5 and 12 km, although there are some deeper events nearby.
Parallel shear-wave polarizations, such as those observed, are expected to indicate the strike of nearly vertical parallel microcracks, which would be aligned parallel to the direction of maximum compression. Thus the shear-wave polarizations in the Peter the First Range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place.     

Statistical estimation of the threshold of toxic effects

A method of the statistical estimation of the threshold of “no effect” and “100% effect” levels of a test compound has been suggested. The experimental data of this method concern the survival of organisms exposed to a range of concentration of toxic chemicals.     

Aerodynamic Scaling for Estimating the Mean Height of Dense Canopies

We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h _a as the most effective means of resolving the representative canopy height for all forests. We determined h _a by simple linear regression between zero-plane displacement d and roughness length z ₀, without the need for stand inventory data. The applicability of h _a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h _a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z ₀ was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h _a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h _a was also verified using data from several previous studies.     

Regime shift in the ecosystem of the eastern Gulf of Finland caused by the invasion of the polychaete Marenzelleria arctia

The changes in the concentrations of the mineral nitrogen (nitrates and nitrites) and phosphorus and in the state of the planktic communities in the eastern Gulf of Finland following a large-scale invasion of the polychaete Marenzelleria arctia were analyzed. The bioirrigation and bioturbation of the bottom deposits by polychaetes resulted in a dramatic increase in the nitrogen/phosphorus ratio in the waters of the gulf, thus leading to cascade changes in the plankton. As a result of the decrease in the abundance of colonial nitrogen-fixing cyanobacteria, which cause “blooming” in surface waters, the total biomass of the phytoplankton and chlorophyll a concentration decreased. Because of the disappearance of large colonies of cyanobacteria and the surge of small algae, the food supply for the zooplankton improved and its biomass increased. According to our calculations, the amount of phosphorus deposited in the bottom sediments as a result of the polychaete activity markedly exceeded the external phosphorus load on the Gulf of Finland from the Russian coast. We conclude that the invasion of Marenzelleria arctia resulted in the cardinal reconstruction of the entire ecosystem of the eastern Gulf of Finland.     

Factors controlling diurnal variation in the isotopic composition of atmospheric water vapour observed in the taiga,eastern Siberia

Deciduous forest covers vast areas of permafrost under severe dry climate in eastern Siberia. Understanding the water cycle in this forest ecosystem is quite important for climate projection. In this study, diurnal variations in isotopic compositions of atmospheric water vapour were observed in eastern Siberia with isotope analyses of precipitation, sap water of larch trees, soil water, and water in surface organic layer during the late summer periods of 2006, 2007, and 2008. In these years, the soil moisture content was considerably high due to unusually large amounts of summer rainfall and winter snowfall. The observed sap water δ¹⁸O ranged from ?17.9‰ to ?13.3‰, which was close to that of summer precipitation and soil water in the shallow layer, and represents that of transpired water vapour. On sunny days, as the air temperature and mixing ratio rose from predawn to morning, the atmospheric water vapour δ¹⁸O increased by 1‰ to 5‰ and then decreased by about 2‰ from morning to afternoon with the mixing ratio. On cloudy days, by contrast, the afternoon decrease in δ¹⁸O and the mixing ratio was not observed. These results show that water vapour that transpired from plants, with higher δ¹⁸O than the atmospheric water vapour, contributes to the increase in δ¹⁸O in the morning, whereas water vapour in the free atmosphere, with lower δ¹⁸O, contributes to the decrease in the afternoon on sunny days. The observed results reveal the significance of transpired water vapour, with relatively high δ¹⁸O, in the water cycle on a short diurnal time scale and confirm the importance of the recycling of precipitation through transpiration in continental forest environments such as the eastern Siberian taiga. Copyright © 2012 John Wiley & Sons, Ltd.     

The Central Aldan gold-uranium ore magmatogenic system,Aldan-Stanovoy shield,Russia

The Central Aldan ore district (CAOD) is considered as an integral ore-forming magmatogenic system (IOMS) consisting of ore-forming systems of different ranks. The epicenter of the IOMS is occupied by the main (head) magma conduit expressed at the present erosion level as the Western El’kon magmatic area. The systematic radial position of the main ore-bearing zones relative to the IOMS’s epicenter is considered as an indication of their relation to the head magma conduit. There are daughter ore forming systems of the first order (the El’kon (EOS), Kuranakh (KOS), and Tommot (TOS)), as well as ore systems of higher orders. Ore zoning distinctly observed in the EOS and KOS and outlined in the TOS consists of the change of the gold or molybdenum (EOS) mineralization for gold-uranium mineralization toward the head of the magma conduit. The ore objects are derivatives of magmatic reservoirs (chambers) located at different levels of the staged magmatogenic system. The gold and uranium mineralization is mainly related to the pervasive potassic metasomatism. The CAOD is considered as a superproductive area promising for revealing new large ore deposits and recommended as a priority object for large scale gold and uranium exploration.