Estuarine Ecosystems and Their Place in Natural River Mouth Complexes of the Arctic: A Case Study of the Yenisei Mouth Area

Abstract

The estuarine ecosystem is characterized by the mixing of seawater and freshwater with a resulting salinity of 0.5 to 22–26‰, which is preserved for no less than 2–3 weeks, and by the presence of specific brackish water species. The distinguishing features of Arctic estuarine ecosystems are a sharp thermohaline stratification of the waters and, as a consequence, a difference in the boundaries of the brackish water biota distribution near the bottom and in the pelagic zone. Note that only the bottom estuarine biocenoses are characteristic of the river mouth area. The most important factor in the Arctic estuarine ecosystems is the longitudinal migrations of the halocline, especially seasonal ones. The coincidence of the borders of distribution of the true brackish water species with the borders of hydrological and morphological regions of the Yenisei River estuary defined according to long-term observations is noteworthy. Given the relative similarity of the Arctic estuarine ecosystems in their physical, chemical, and biotic components associated with the latitudinal uniformity of the mouths, we assume the presence of this correlation in other estuarine areas as well. In this case, a single survey of the benthos may give the same result as multiyear series of hydrological observations in the regionalization of an estuarine ecosystem.