Peculiarities of mercury distribution,migration, and transformation in the estuarine area of the Northern Dvina River

The mercury concentration levels in the water of aquatic ecosystem of the Northern Dvina River delta are defined. The interrelations of mercury concentrations with physicochemical parameters of the water body, namely with pH, Eh, temperature, salinity, oxygen and organic matter content are studied. The dominant forms of mercury migration and its presence in the water are revealed. Regularities of changes and spatial variability of the mercury concentrations in the estuarine area of the river, peculiarities of mercury compound migration and transformation in the barrier zone of the Northern Dvina River-Dvina Bay of the White Sea are studied.     

Bottom sediments and their role in surface water pollution with mercury (with a special reference to the Northern Dvina River Mouth and the Dvina Bay of the White Sea)

Mercury content in bottom estuarine sediments of the Northern Dvina River and the Dvina Bay of the White Sea is studied. Major regularities of the behavior of the metal and its compounds in bottom sediments of the water area are defined. The role of lithological composition, pH and Eh of the environment, the presence of hydrogen sulfide for determining the content and forms of the mercury presence in the bottom sediments of the region are studied. The sediments related to technogenic formations are specified. The paths and forms of mercury coming from bottom sediments to the near-bottom water level are detected, and the methylmercury content in the sediments is calculated.     

The Kolyma River mouth area under present conditions of anthropogenic impact

The variability is under consideration of the hydrological and ecological state of the water environment of the Kolyma River mouth area. Its hydrological regime and variability of the component composition of the water environment are described. The anthropogenic load is estimated of the inflow of dissolved chemical substances to the Kolyma River mouth area. The hydrobiocenosis structure is studied from qualitative and quantitative indicators of the level of the phyto- and zooplankton development in the mouth area. The hydrobiocenosis state and structure indicate that the ecosystem of the Kolyma River mouth area is functioning under conditions of moderate pollution of the water environment and the depression effect of the biocenosis development is periodically pronounced.     

Influx of dissolved chemical substances to the Ob-Taz estuarine area

The results of calculation and analysis of a long-term spatial variability in volumes of the influx of a wide spectrum of dissolved chemical substances to the Ob-Taz estuarine area are under consideration. It is shown that physical transport of mineral nitrogen and phosphorus, silicic acid, petroleum hydrocarbons, phenols, heavy metal compounds down the rivers flowing into the Ob-Taz estuarine area dominates over the processes of their chemical-biological transformation. Therefore, a substantial amount of these compounds enters the estuarine ecosystems, which leads to a substantial transformation of the component composition of their water environment and a greater extent of its pollution. The latter predetermines a possible transition of the Ob-Taz estuarine area state from equilibrium into crisis, and in occasional years, even into critical state.     

Chemical runoff of the Selenga River under conditions of low water content

Changes in chemical runoff of the main tributary of Lake Baikal, the Selenga River, observed since the mid-1990s, and determinant factors of these changes are under consideration. The estimates derived are indicative of a 20–40% reduction in the annual removal of dissolved substances because of a decrease in the water runoff of the river due to climate oscillations. The decreased inflow to Lake Baikal of mineral substances, especially silicon, nitrogen, and phosphorus, can lead to disturbance of production processes in Lake Baikal.     

Estimation of possible climatic changes of river runoff in the Northern Dvina River basin in the 21st century

Presented is a method of studying possible climate-driven changes of river runoff characteristics, according to which the atmosphere-ocean general circulation models are used for computing the climate system impact, whereas the response of a watershed to given disturbance is estimated using the model of runoff formation in a river basin. The study is carried out for the Northern Dvina River basin. Estimates of possible changes (relative to the reference period) by the middle and late 21st century of such water regime characteristics as mean annual and maximum water discharge, as well as mean discharge values for the spring, summer-fall and winter seasons, are presented.     

Assessment of groundwater impact on water quality in the built-up areas at the Lower Don

The impact is assessed that the groundwater flow from the built-up areas on the left bank of the Don River in the Rostov oblast produces on the chemical composition and quality of surface water in the lower river reaches. It is demonstrated that the total average annual groundwater flow from the built-up areas on the left river bank is very small and equals 0.002 km3/year on average or 0.01% of the average annual water flow in the estuarine outlet. Despite the rather high degree of contamination of groundwater and the high content of principal ions, this causes the insignificant impact of groundwater runoff on water quality in the Lower Don. The average total mass of substances that annually come from the left-bank urbanized areas in the groundwater flow is about 4.9 x 10³ t or 0.04% of total mass of substances transported by the Don River to the Taganrog Bay.     

The role of different links of the river net in forming winter river runoff

Results of investigations of the winter river runoff formation in the Northern Dvina River basin (without the Vychegda River basin) are under consideration. The peculiarities of the winter runoff formation are revealed from the analysis of the conditions of the runoff reduction in different parts of the river basin. A regulatory effect of the upper links of the river net on the lower links is established.     

The circulation and residence time of the strait of Georgia using a simple mixing‐box approach

Abstract

New observations in the Strait of Georgia, British Columbia, Canada show that temperature and dissolved oxygen have a pronounced seasonal cycle, with a spatially varying phase. Phase lags in oscillating systems arise due to internal time scales which can be interpreted in fluid systems as residence times. Exploiting phase we construct a quantitative and internally consistent circulation scheme for this body of water after dividing it into four regions: the Fraser River plume, the surface waters down to 50 m, the intermediate waters down to 200 m, and the deep water. In this scheme the intermediate water, the largest region by volume, is continually renewed, and its characteristics change in response to continuous changes in the characteristics of source waters. The dependence of the estuarine circulation on variations in fresh inflow is weak. The deep water is volumetrically less important, but seasonal changes in the density of oceanic source waters can produce a variation in the overall circulation by driving an additional inflow which leads to both deep renewal and increased upwelling. In turn, this increased upwelling results in lower surface temperatures than might otherwise be expected. Intermediate water residence times are about 160 days. Deep water is renewed once per year in summer and is affected only by vertical diffusion during the rest of the year. Surface water residence times for the entire Strait are a few months at most, but the Fraser River plume has a freshwater residence time of approximately 1 day. In addition, we find that the residence time of oceanic source waters in the Strait is 1.7 years due to a substantial recirculation in Haro Strait. Other consequences of this scheme are consistent with independent estimates of horizontal transports, air‐sea heat fluxes, subsurface oxygen (O₂) utilization, and primary production. Finally, analysis of the spatial phase variations suggests that the intermediate inflow enters the Strait as a boundary current along the slopes of the Fraser delta.     

Monitoring of the ice jamming process in rivers using spatiotemporal plots of the water levels

A methodology of plotting of the water levels along a river and its using for (1) finding places where ice jamming is possible, (2) estimation of the maximum levels caused by jams, and (3) estimation of risks of flooding in ungauged river sections is presented. For the Northern Dvina River case study, isolines of the 2003 river flood levels are plotted for the entire river length and places of possible jams are defined by using the proposed approach.     

Long-term and intraannual changes in run-off and water levels in the Volga River delta

Data of the State Observation Network on the water run-off for the whole observation period and on water levels in the delta of the Volga River for the period of regulated run-off regime (1961–2006) are analyzed. Periods of various water content are revealed and the current tendency of long-term run-off changes is established with the help of difference-integral curve of recovered natural annual run-off. Periods of various degree of man’s impact on the run-off, entering the delta of the Volga River, are marked out. The role of irretrievable anthropogenic loss and the influence of run-off regulation on its intraannual distribution are assessed. Regularities of seasonal and long-term water level changes in the delta of the Volga River are revealed. The run-off regulation effect on the intraannual distribution of water levels is assessed. The influence of the water divider on the redistribution of the run-off and water levels in the delta is shown. The effect of the current increase in the Caspian Sea level on the penetration of the backwater into the delta of the Volga River is revealed.     

Winter severity effects on the nonuniformity of winter flow formation in a river basin

Results of studying winter flow formation in the Northern Dvina and Lovat?? river basins are presented. Substantial effect of temperature factor on water exchange between upper and lower parts of a river basin is established.     

Freezing types and winter runoff of small rivers

Investigations carried out in the Northern Dvina River basin revealed that the decrease in the ice thickness on small rivers is of significant importance in the increase in the water content of rivers in winter in recent decades. This process resulted in the improvement of the channel capacity as a result of the decrease in the ice formation intensity on the rivers and of the increase in the fraction of ground waters participating in the winter river runoff formation. It is proposed to consider the initial winter ice conditions as a separate important factor of this process as they define the types of river freezing influencing on the winter river runoff formation as well.     

Elevational Dependence of Projected Hydrologic Changes in the San Francisco Estuary and Watershed

California's primary hydrologic system, the San Francisco Estuary and its upstream watershed, is vulnerable to the regional hydrologic consequences of projected global climate change. Previous work has shown that a projected warming would result in a reduction of snowpack storage leading to higher winter and lower spring-summer streamflows and increased spring-summer salinities in the estuary. The present work shows that these hydrologic changes exhibit a strong dependence on elevation, with the greatest loss of snowpack volume in the 1300–2700 m elevation range. Exploiting hydrologic and estuarine modeling capabilities to trace water as it moves through the system reveals that the shift of water in mid-elevations of the Sacramento river basin from snowmelt to rainfall runoff is the dominant cause of projected changes in estuarine inflows and salinity. Additionally, although spring-summer losses of estuarine inflows are balanced by winter gains, the losses have a stronger influence on salinity since longer spring-summer residence times allow the inflow changes to accumulate in the estuary. The changes in inflows sourced in the Sacramento River basin in approximately the 1300–2200 m elevation range thereby lead to a net increase in estuarine salinity under the projected warming. Such changes would impact ecosystems throughout the watershed and threaten to contaminate much of California's freshwater supply.     

1997、1998年长江上游地区水汽输送及其与径流量之间关系的对比分析

该文利用1997、1998年7~8月的探空资料, 计算了围绕长江上游地区四周925~200 hPa之间的水汽通量及每日的水汽输送净量.通过水汽输送净量的候、旬资料, 讨论了长江上游地区水汽输送净量与径流量之间的关系, 发现这两者之间有显著的相关性, 其平均相关系数为0.871.另外, 对比分析了这一地区1997与1998年水汽输送与大气环流形势的关系.其结果表明:由于特殊的大气环流背景, 导致了长江上游地区这两年水汽输送的主要方向差异很大.     

Evapotranspiration in the basins of the Northern Dvina and the Western Dvina rivers and its variability

Considered is a possibility of using the previously developed method for estimating the evapotranspiration from the river basin based on the observations at the network of water- and soil-evaporation stations and on the data on the land use dynamics for the Northern Dvina and Western Dvina river catchments. It is demonstrated that the method enables to obtain rather realistic and reliable estimates both of evapotranspiration over the basin and of the contribution of different landscapes to its value. The value of evapotranspiration and its interannual variability depend not only on the trends in the fluctuations of evaporation from the water surface and the land surface, but also on the changes in landscape characteristics. The present paper is a continuation of the papers dealing with the study of the basins of the Volga and Don rivers started under V.S. Golubev’s leadership and participation.     

Assessment of water quality in the rivers of northern European Russia by using oxygen demand indices

Analysis of the probability curves of multiyear organic content data and water colour indices of the rivers located in the northern part of European Russia (the Northern Dvina, Pechora, Onega, and Mezen) allowed revealing seasonal patterns of hydrochemical indices. Water quality for different seasons was assessed. Regional estimates of hydrochemical indices and water quality were obtained. Relations between oxygen demand indices, water colour indices, and water content of those rivers were considered.     

Hydrochemical and Hydrological Conditions in the Ural River Lower Reaches and in the Caspian Sea Mouth Region at the Beginning of the Spring Flood

The study presents data of hydrophysical observations and the results of studying the chemical composition of water and suspended particulate matter obtained in April of 2016 and 2017 during the complex studies in the Ural River lower reaches and in the Caspian Sea region adjoining the river mouth. It is revealed that the chemical composition of river runoff varied greatly not only from year to year but also within the period of field studies that may be explained by the water inflow from different parts of the river catchment during the spring flood.     

影响黄河下游断流的气象因素分析

分析了影响黄河下游断流的气象因素 ,结果表明 :降雨量减少造成产流量减少是影响黄河下游断流的重要原因 ;气温升高 ,蒸发量增大 ,造成农业灌溉等用水增加 ,加剧了黄河水资源的供需矛盾 ;而各区间耗水量的增加 ,使进入下游河道的水量减少是断流的主要原因     

Formation factors and forecast of ice dams on rivers of the north of the European territory of Russia

Regional peculiarities of ice dams’ formation process on large rivers of the north of the European territory of Russia are considered. Methodology and methods of ice-clogging floods’ forecasting at stretches with the risk of ice dams of the Northern Dvina, Sukhona, Vaga, Pechora, and Mezen’ rivers are described. Method of forecasting of the flood characteristic, which has not been forecasted before at ice dams, the duration of high water levels’ stand, is proposed. The possibility to plan ice-dam prevention activities on the base of hydrological forecasting is shown.