Methane in the water and bottom sediments of the mouth area of the Severnaya Dvina River during the winter time

The spatial distribution of methane in the water and bottom sediments of the mouth area of the Severnaya Dvina River shows quite a similar character during the ice-cover and summer periods. It is characterized by the increase of the gas content from the head of the mouth area towards the delta with maximum values at the sites subjected to permanent anthropogenous impact. The difference consists in the higher level of the methane content in the bottom sediments during the winter period. At the same time, the excess of the winter to summer concentrations in the water was registered only at the stations within the impact area of the sources of anthropogenous contamination. As in the summer, the bottom sediments have a prevailing role in the formation of the level of the methane content in the water of the mouth area. The linear dependence between the concentrations of the total hydrogen sulfide and methane in the surface layer of the riverine sediments is probably caused by the parallel and nonconcurrent proceeding of the generation of these gases, which are controlled by the bacterial communities being not inhibitory to each other.     

Field Simulation of Cadmium Pollution of a Freshwater Body

An experiment in mesocosms installed in a fish-rearing pond was used to adequately simulate the character of self-purification, migration, and the redistribution of cadmium and its chemical forms in major components of a freshwater ecosystem, into which this chemical is imported in concentrations far in excess of its MAC. The major portion of the imported cadmium was found to be removed from the water mass within a few days, mostly, as a component of particulate matter settling onto the bed, including dead plankton remains, as ion-exchange cadmium forms adsorbed by suspension (37%), and as forms associated with ferromanganese oxides (41%). The rate of cadmium removal from the water mass is determined both by the amount of particulate matter settling onto the bed and the efficiency of cadmium sorption by it, depending on the acid–alkaline and redox conditions in the water body.     

Dynamics,Cxtent, and Causes of Underflooding of Populated Localities in the Southern Rostov Oblast

Underflooding of different extent was recorded in 133 populated localities in southern Rostov oblast, among which 4 such localities are always partly underflooded, and 77 localities suffer underflooding during spring floods and freshets. Minimal estimates show that the area of the territories underflooded every year and only in wet years is 282 km² or 19% of the total built-up area in the southern Rostov oblast. Technogenic factors were found to dominate as the causes of underflooding in the majority of the populated localities. However, natural or slightly disturbed subsoil water regime is typical of the built-up territories in the southern Rostov oblast, where it implies annual periodicity of level variations with a peak in spring and a minimum in autumn.     

Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river

Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of topography on wind speed over a coastal dune and blowout system at Jockey's Ridge,NC, USA

This study examines the spatial distribution of wind speed across a coastal dune system located at Jockey's Ridge State Park, North Carolina. The study area consists of a trough blowout through a foredune ridge, and the landforms that have developed behind the foredune. Wind speed and direction were measured simultaneously with single sensors placed at a fixed height in 13 locations across the blowout/dune complex. Fractional wind speed‐up is computed for sampling stations using data from a mast located on the beach as the reference. Results show that wind speeds were generally accelerated across the study site. The highest speeds were recorded on the foredune ridges adjacent to the blowout. Wind was accelerated through the center of the blowout throat and along the downwind lateral wall. Further into the blowout, at the base of the ramp to the depositional lobe, higher wind speeds shifted to the upwind lateral wall and continued to accelerate up the ramp as air exited to the rear. Significant variations in the wind speed‐up pattern were associated with different wind approach angles, with greater speed‐up occurring when the winds were aligned normal to the dune system. The speed‐up decreased as the angle of approach became increasingly oblique to the ridge. The patterns of wind speed‐up across the site point to the influence of topography on airflow. To quantify the relationship, measures of several topographic variables were obtained along sample transects running upwind from each sample station along flow lines representing different wind approach angles. Examination of correlation coefficients between wind speed‐up and topographic variables suggests that for groups of stations with similar topographic characteristics, 30–50% of the variations in speed‐up may be explained by the upwind topographic variability. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of the Grain Size Composition of Bottom Sediments in Lake Baikal on the Distribution of Methane and Sulfide Sulfur

Lithology and Mineral Resources - Based on the study of separate areas of Lake Baikal (depth from 14 to 250 m), influence of the grain size composition of bottom sediments on the distribution of...     

1997年回归与港深管理线

保持香港繁荣与稳定的重要性已在１９８４年的中英联合声明中得到保证。在１９９７年７月之后，香港将回归祖国而成为中国的特别行政区，并且实行“一国两制”５０年不变，从而保持香港现有的繁荣。本文旨在探讨港深管理线在香港成为特别行政区后对保持香港的繁荣和稳定 和香港于１９９７年回归后这条管理线及其接壤地区的规划问题。     

South Atlantic circulation in a world ocean model

The circulation in the South Atlantic Ocean has been simulated within a global ocean general circulation model. Preliminary analysis of the modelled ocean circulation in the region indicates a rather close agreement of the simulated upper ocean flows with conventional notions of the large-scale geostrophic currents in the region. The modelled South Atlantic Ocean witnesses the return flow and export of North Atlantic Deep Water (NADW) at its northern boundary, the inflow of a rather barotropic Antarctic Circumpolar Current (ACC) through the Drake Passage, and the inflow of warm saline Agulhas water around the Cape of Good Hope. The Agulhas leakage amounts to 8.7 Sv, within recent estimates of the mass transport shed westward at the Agulhas retroflection. Topographic steering of the ACC dominates the structure of flow in the circumpolar ocean. The Benguela Current is seen to be fed by a mixture of saline Indian Ocean water (originating from the Agulhas Current) and fresher Subantarctic surface water (originating in the ACC). The Benguela Current is seen to modify its flow and fate with depth; near the surface it flows north-westwards bifurcating most of its transport northward into the North Atlantic Ocean (for ultimate replacement of North Atlantic surface waters lost to the NADW conveyor). Deeper in the water column, more of the Benguela Current is destined to return with the Brazil Current, though northward flows are still generated where the Benguela Current extension encounters the coast of South America. At intermediate levels, these northward currents trace the flow of Antarctic Intermediate Water (AAIW) equatorward, though even more AAIW is seen to recirculate poleward in the subtropical gyre. In spite of the model’s rather coarse resolution, some subtle features of the Brazil-Malvinas Confluence are simulated rather well, including the latitude at which the two currents meet. Conceptual diagrams of the recirculation and interocean exchange of thermocline, intermediate and deep waters are constructed from an analysis of flows bound between isothermal and isobaric surfaces. This analysis shows how the return path of NADW is partitioned between a cold water route through the Drake Passage (6.5 Sv), a warm water route involving the Agulhas Current sheeding thermocline water westward (2.5 Sv), and a recirculation of intermediate water originating in the Indian Ocean (1.6 Sv).     

Methane in Water and Bottom Sediments of Lake Baikal

Water Resources - The distribution of methane concentration measured in 2014 and 2015 in different parts of Lake Baikal has been analyzed. In the period of expedition studies, methane concentration...