Dissolved organic carbon (DOC) runoff into the Kara Sea with Ob and Yenisei river water was calculated. The estimates showed that DOC runoff with Yenisei water (3.67 × 106 tC/year) is less than that with Ob water (4.06 × 106 tC/year), which is due to differences in the structure of the drainage basins and estuaries of these rivers. All previous published estimates show the opposite. The lack of DOC content data during the Yenisei’s maximum flood prevents accurate calculation of DOC runoff with its water, but its maximum and minimum values can be estimated (3.11–4.18 × 106 tC/year).

The article presents the results of generalizing the data of 20 years of research in the river–sea transition zone of the Northern Dvina River and White Sea (marginal filter zone), in which sedimentation and biogeochemical transformation of riverine sedimentary material lead to significant losses on its way to the open area of the sea. For the first time, based on a large amount of material, the average-weighted (in terms of runoff) quantities of the so-called “pure” discharge of suspended particulate matter and dissolved and suspended particulate Fe and Mn were obtained. These are discharges of these substances closest to reality with account for losses in the marginal filter zone depending on the season. It was determined that on average in a year from the total volumes transported by river waters to the boundary with the sea, only about 40% of suspended sediments, 50% of total iron, and almost 60% of total manganese reach its open areas. Precisely these volumes should be taken into account in computing the geochemical balance and in ecological research in the sea.

The results of continuous four-year-long investigations (from May 2015 to April 2019) of the elemental composition of water and suspended matter in the Northern Dvina River are given. Water was sampled every month at two sites in the lower reaches of the river. More than 50 major and trace elements are determined in water filtered through Nuclepore filters and in suspended matter on the filters. The methods of inductively coupled plasma mass spectrometry and atomic absorption spectrophotometry were used. In contrast to most similar publications previously, the mean concentrations of elements weighted to water discharge (dissolved forms) and to suspended matter discharge (suspended forms) are obtained, which enables us to consider them as the closest to reality. Comparison with the mean concentrations in world rivers shows that the Corg and Fe concentrations in the water of the Northern Dvina River exceed them by 3–5 times. This is related to natural factors, primarily to specific features of the catchment basin (widely spread bogs). The presence or absence of correlation between trace elements and organoferric colloids significantly affects their concentration. The content of elements in the suspended matter of the river is similar to the mean global level, except for Corg and P. We calculate the discharges of dissolved and suspended elements for every year of research and the mean for the four-year period.

The results of four years of continuous investigations (from May 2015 through April 2019) of the elemental composition of the water of the Northern Dvina River are presented; the water sampling was performed monthly year around at two sites in the lower reaches. More than 50 major and trace elements were determined in filtered water (0.45-µm membrane filter) and in suspended matter on filters, as well as Corg on GF/F glass fiber filters. The ICP MS and AAS methods were applied. The most important outcome is that the average weighted concentrations of elements in the water discharge (dissolved forms) and in suspended matter discharge (suspended form) were obtained in contrast to most similar previous publications; the average weighted concentrations allowed us to consider these results to be the most close to real. The Corg and Fe concentrations in waters of the Northern Dvina River are three- to fivefold higher compared to the average concentrations of these elements in the rivers of the world. This has a natural explanation, which includes the features of the watershed basin (widespread distribution of wetlands). The presence or absence of a correlation between elements and organoferric colloids significantly determines their concentration. The average content of elements in riverine suspended matter is very similar to the global levels, except for organic carbon and P. The annual element discharge for every year of study and the four-year average for two forms of matter (dissolved and suspended) were calculated.

The paper presents new data on concentrations and fluxes of organic carbon, iron, and manganese in waters of the mouth area of the Northern Dvina River. The work was conducted within the project "Northern Dvina River Marginal Filter Observatory" from May 2015 to May 2019 with monthly collection of water samples. Systematic determinations of the concentrations of the main carrier elements of many trace elements in dissolved and particulate forms were used to establish the average weighted of C-org, Fe, and Mn concentrations. The results of 4 years of systematic investigations established the main regularities of seasonal variations of dissolved and particulate forms of element concentrations and the relationships between. Significant variations were observed not only between concentrations but also between fluxes of elements in both forms. However, more than half the annual fluxes of all elements in all years studied was transported to the sea in the spring flood period. The results also demonstrated significant variations between element concentrations and their fluxes in different years. This is unsurprising, since even during the 4 years of investigations, the difference between water runoff and SPM fluxes in different years was up to, respectively, 1.4 and 2.6 times.

The paper presents the first results of a study of seasonal variations in the grain size distribution and mineral compositions of suspended particulate matter (SPM) of the Northern Dvina River. The SPM samples were collected every month during 2016–2017 at the outlet of the Kuznetchiha arm to Dvina Bay of the White Sea. The grain size fractions were separated by Petelin’s water-mechanical method with retention of fractions for subsequent analyses using an electron microscope, energy-dispersion microanalyzer, and X-ray difractometer. The results demonstrated that the pelitic and subcolloidal fractions predominated in the grain size distribution of river SPM, with subordinate coarser fractions. Seasonal variations in the SPM concentration and the total amount of detrital and clay minerals are influenced by river water discharge and achieved a maximum in high water periods (spring flood and partly at the end of summer–autumn heavy rains). The subcolloidal fraction in the March sample stands out in the fine fraction distribution. Its share in this sample was the highest among these fractions throughout the year. The reason is probably related to the highest content of fine dispersed detrital minerals in the fraction. The question of why this is encountered only in March remains open.

Atomic absorption determinations of a group of heavy metals (Cu, Zn, Ni, Co, Cr, Pb, Fe, Mn) in 190 samples of surface bottom sediments of the Middle and Southern Caspian Sea that were sampled by crab in middle of XX century (the collection of G.N. Baturin) and in 30 samples of recent sampling by grab also (2012–2015) were carried out. The aim of the investigations was to construct the schematic maps of heavy metal distribution in bottom sediments of both parts of the Caspian Sea on the materials of a half of century prescription that may serve as a base for comparison with the data of recent researches in frameworks of the program “The Caspian Sea System” under leadership of academic A.P.Lisitzin from 2012 till present time. The comparison between chemical composition of old and new sediment samples was realized, their similarities and divergences were revealed and probable reasons of divergences were presented. The maps of distribution of several metals (Fe, Mn, Co, Cr) are submitted together with necessary for interpretation maps of CaCO3, Corg and some other. It was shown that the structure of maps for all metals investigated was very similar because all these metals had concern to the group of iron.

Abstract—The duplicate samples of the Amazon River suspended matter (SM) collected during the 9th cruise of R/V Professor Shtokman were studied using modern analytical techniques. Waters of the Amazon basin are subdivided into three main types differing in SM content and chemical composition: white (turbid yellow waters of the Amazon River and Madeira tributary), clear (transparent waters of the large Xingu, Tapajós, Trombetas, and Tocantins tributaries) and black (waters with strong coffee color, high content of dissolved organics, and elevated acidity, Riu Negro). The specific features of SM from different parts of the river basin have been established. The contents and relationships of major and trace elements in the SM vary within wide ranges, but in general the bulk composition of the SM is close to the average composition of river SM and clay rocks, except for some samples from clear waters. The SM of the white and clear waters (blackwater samples unfortunately have not been preserved) are enriched in mercury. Literature data indicate that artisanal gold mining with the use of mercury (amalgamation method) has been carried out for many years in the Amazon Basin, i.e., the SM enrichment in mercury is related to the anthropogenic factor. At the same time, significant (up to two orders of magnitude) enrichment of SM of the clear water Xingu and Tokantins rivers, the Amazon tributaries, in tin, zink, lead, and to lesser extent, in copper, cadmium, silver, and some other metals give grounds to suggest ore mineralization in these regions.

In the present chapter, the results of detailed investigations of the river discharge into the White Sea are considered. The White Sea is an inland sea of Russian western Arctic territory that appears as the sub-Arctic sea. This sea may serve as a good example for case studies of the Arctic seas. Significant river discharge to this relatively small sea plays very important role in all the processes in it. It’s evident that the detailed knowledge is needed both on the volumes of water and suspended matter fluxes, and also about the chemical composition of water and grain-size, mineralogical, and chemical composition of suspended particulate matter (SPM), that are formed on the extensive area of the basin. During 2000–2010 year, we carried out about 40 different expeditions, for the first time in the lower reaches of the biggest river in the White Sea basin, in the Severnaya Dvina River, and in the whole sea in the frameworks of the program “The White Sea System.” Results of these expeditions allowed to obtain absolutely new materials for investigations of biogeochemical processes in the rivers and in the sea. These unique data, in particular about the concentrations of organic carbon and many major and trace elements in river and estuarine waters and SPM and the forms of their existence including the colloidal one, are presented here.

The decrease in Aral Sea area, which started in the 1960s, caused considerable changes in the hydrological, chemical, and biological structure of sea water. Regular observations of Aral water chemistry ceased in the early 1990s. There were no observations of the concentrations of biogenic element compounds in water (the so-called “first-day analyses”). During expeditions of the Institute of Oceanology, RAS, in September 2012 and October 2013, integrated hydrochemical observations were carried out, including measuring the concentrations of biogenic element compounds, dissolved oxygen, hydrogen sulfide, and carbonate equilibrium components. An objective of this study was to develop methods of hydrochemical studies under high water salinity (mineralization). In addition to the standard hydrochemical complex, water samples were taken to determine total water mineralization and the concentration of dissolved and suspended metal forms. The results of these studies are given.

The paper presents the results of lithological, mineralogical, and geochemical studies of bottom sediments in the central part of the South Caspian Basin. A complex of analytical methods was used to identify authigenic minerals from groups of sulfates, carbonates, and sulfides; study their forms of crystals and aggregates and their composition; and determine the distribution pattern in bottom sediments. The lithological and geochemical data were used to identify the characteristic property of authigenic mineral formation processes in the central part of the South Caspian Basin under hydrogen sulfide contamination conditions.

The geochemical study of the suspended matter in the waters of the Amazon River and its tributaries revealed that the chemical composition of this material ranges widely; however, generally, it is similar to the average composition of the suspended matter in the rivers and clayey sedimentary rocks around the world. Against this background, an essential regional Hg enrichment due to the anthropogenic factor is distinguished. The suspensions from the so-called clear waters from the tributaries of the Amazon River—Xingu and Trombetas—demonstrate the local enrichment in Pb, Sn, Zn, and organic carbon indicating the ore mineralization of the drainage basin, and points to the presence of metal-organic complexes.