Study of the role of natural and anthropogenic factors in the formation of water quality in small rivers on the example of the Veletma river in the Nizhny Novgorod region

Small rivers of Central Russia often experience a high anthropogenic pressure, and at the same time their study and measures taken to preserve them are incomparably more modest than for large rivers. On the example of the Veletma river in the Nizhny Novgorod region, the factors affecting the formation of the water quality of the small river are considered. The ecological and geographical characteristics of the Veletma river are given. It is shown that the current methodology for assessing the water quality of large rivers by the Specific Combinatorial Water Pollution Index does not allow to determine what is the contribution of anthropogenic pressure to the deterioration of water quality, and what is the contribution of natural factors. Studies of a number of physical and chemical characteristics of the waters of the Veletma river have shown that on a short section of the river, which is less than 400 m, there are significant changes in the physical and chemical composition of water, reaching 45-95%. Such significant changes are associated on the one hand with the influence of the treatment facilities of the city of Navashino, and on the other hand, with the special location of the lake Zelenoe in the path of the river. Satellite images of the Veletma's confluence with the lake Zelenoe show the plume. It is suggested that the lake is characterized by the same processes that take place in the confluence of large and medium-sized rivers into the seas and lakes, called marginal filter, in which not only suspended but also dissolved impurities are retained. This fact is confirmed by laboratory studies.