Bioindication of the suitability of bottom sediments of the Don River in agriculture

Introduction. Bottom sediments are rich in organic compounds, but due to their accumulation at the bottom of the reservoir, water quality deteriorates. Dredging is one of the methods of cleaning water bodies, during which the resulting soil is unloaded along the banks with possible subsequent transportation to solid waste landfills. This method of waste disposal is not rational, since the qualitative composition of some sludge allows it being used as fertilizer in agriculture. Materials and methods. Contamination of bottom sediments of the lower Don River with polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) was studied to assess their potential use as fertilizers in agriculture. Sediments were analyzed for pH, humus content, HMs, PAHs, and phytotoxicity. For this purpose, samples of bottom sediments were taken in the Tsimlyansk Reservoir and the lower reaches of the Don River and its tributary, the Aksai River. Winter wheat of the Bumba ES variety was chosen as a test object. To assess the phytotoxicity of bottom sediments, there were used foreign standards for the quality of bottom sediments and background regional values of soils in the Rostov region. Results. Studies have shown that the deposits are of an organomineral nature, with a high content of silicon, calcium, and magnesium. The pH values varied between the neutral and slightly alkaline ranges. In the sediments, all HMs are within acceptable limits, and only zinc and strontium have increased contents, with the highest concentrations found in the middle part of the Tsimlyansk Reservoir. PAHs level varied significantly, with the highest levels observed in the lower reaches of the river. The sediments showed varying degrees of phytotoxicity, with all samples showing a decrease in root length. Limitations. The limitations of the study are due to the fact that the changes and additions made to the sanitary and epidemiological requirements for various types of soils and bottom sediments are not exhaustive and can be revised as standards for new substances appear, data on the toxicity and danger of standardized compounds. Conclusion. The conducted ecological assessment of the state of bottom sediments of the Don River, based on calculations of the total pollution coefficient, indicates a low level of pollution of the studied objects, which allows their using in agriculture.