Impact of dredging on the environmental state of a small river with considering the composition of bottom sediments

Abstract

Reports on the environmental impact assessment of planned activities aimed at restoring the hydrological regime and sanitation of rivers do not always pay attention to in-depth analysis of the physicochemical composition of bottom sediments. The silt deposits have proven to be a good ameliorant for agricultural lands, provided they are of satisfactory quality. Bottom sediments, especially their fine alluvial fraction, accumulate various compounds and trace elements, including heavy metals. Analysis of the content of iron Fe, manganese Mn, cobalt Co, chromium Cr and determination of the integrated level of contamination of bottom sediments did not reveal their toxic contamination in the area of the village Kleshnivka and the village Petrykivka. Determination of "geoaccumulation indices" by G.M. Mueller allowed to classify the sediments of the Chaplinka River as unpolluted, and the man-caused load on the hydroecosystem as low. In compliance with the recommendations on the content of Mn grades in the soil cover of the obtained fifth Igeoclass, which provides heavy pollution and significant man-caused load on the hydroecosystem. To characterize the processes occurring in the hydroecosystem of the Chaplynka River, the bottom accumulation coefficient was calculated. The assessment of the ecological status of hydroecosystems revealed an overwhelming ecological emergency. There is a significant threat of deposits of iron Fe, manganese Mn in bottom sediments. Despite the low risk of contamination of bottom sediments with chromium Cr, the risk will increase due to the rather variable chemical composition of surface waters, and hence the possibility of an ecological crisis for the hydroecosystem. The sanitary condition of a small river could be improved by restoring its hydrological regime. The decrease in the efficiency of dredging works is related to the regulation of the regulation of the riverbed. In the vast majority of cases, hydraulic structures are not provided for or do not correspond to the current level regime of watercourses. After clearing the river bed, there is a danger of their secondary silting, due to the abandonment of part of the temporary dumps on the banks within the water protection zones without fixing.