Present geoecological transformations in the Kerch strait ecosystem

This study examined the distribution, structure, and dynamics of bottom communities of macrozoobenthos in the Kerch Strait based on an analysis of literature sources from 1934 and 1955, archival data documenting hydrobiological field investigations of the Southern Research Institute of Marine Fishery and Oceanography (YugNIRO, Kerch) in 1986 and 1989, and results of the joint Russian-Ukrainian benthic survey of the Kerch Strait (47 stations) conducted by the Institute of Geography of RAS and YugNIRO in the summer of 2010. It was found that populations of filter-seston feeding bivalves in the strait ecosystem have degraded over the past 75 years, whereas populations of detritus-feeding polychaetes preferring muddy bottoms have become much more abundant. Researchers identified species of bottom animals and strait areas exhibiting maximum changes. An analysis of the dynamics of bottom sediment structure in the strait based on YugNIRO archival data and the results of a 2008 diving survey conducted by the Institute of Geography of RAS (49 divers) demonstrated that the observed transformations are associated with silting of a considerable part of the strait bottom as a result of both earlier and more recent economic activities, particularly the disposal of dredging grounds from 1960 to 1990 and the construction of the Tuzla Dam in 2003, respectively. However, the character of the fixed transformations does not enable us to identify the specified reasons as the sole causes of the changes; therefore, the authors also consider hypotheses explaining other mechanisms. The authors conclude that further research on geoecological dynamics of the Kerch Strait ecosystem is needed, particularly after the construction of the Crimean Bridge.</jats:p

Concentration of hydrogen sulfide in waters of the Black Sea in the layer of its coexistence with oxygen

About 100 parallel determinations of hydrogen sulfide by the volumetric and photometric methods were made in the layer of coexistence of oxygen with hydrogen sulfide (C layer). Thiosulfates were determined simultaneously. Regardless of locations of the stations, determinations by two methods coincided for the entire range of depths of occurrence of the C layer upper boundary. Within the C layer hydrogen sulfide readings obtained by these two independent methods agreed; thiosulfates were not found by direct measurements. Difference in the readings appears at the lower boundary of the C layer and below it, accompanied by appearance of thiosulfates. It is therefore concluded that it is correct to determine the upper boundary of the C layer by the iodometric method and to use concentration of hydrogen sulfide obtained by this method in the C layer to calculate rate of chemical oxidation of hydrogen sulfide in quasistationary processes