A comparative analysis of the spatial distribution of salinity and biomass of nekton and nektobenthos in the estuaries of the large plain river Razdolnaya and the mountain river Sukhodol (the Sea of Japan)

Abstract

This paper discusses the two estuaries of the large flat river Razdolnaya and the mountain river Sukhodol (the Sea of Japan). The data of hydrological surveys on these estuaries are presented and the distribution zones of waters of different salinity are shown. The graphs of changes in the biomass of some hydrobionts along the river are given. The studies have shown that water with a salinity of 5% penetrates the Razdolnaya River up to the main channel for 15 km. In the Sukhodol River, it happens that almost the entire estuary is occupied by salt water, and fresh water is traced in a layer of water no more than 0,5 m thick, no closer than 500 m to the mouth of the river. In the Razdolnaya River, there is a tendency for the growth of hydrobiont catches from the outer estuary to the inner one (from the sea to the river) to maximum values at a distance of 5 km from the mouth, followed by a gradual descent upstream. In the Sukhodol River, the specific biomass gradually decreases from the top of the river to a minimum of 0,4 km from the mouth with a sharp increase in the area of the mouth itself (the mouth of the lagoon and the sea coast) and the subsequent smooth decrease. The specific biomass of hydrobionts in the inner estuaries of the Razdolnaya and Sukhodol rivers was 6,7 and 4,0 g/m respectively.