Environmental evaluation of geochemical changes in bottom sediments of Ustia headwater

Abstract

Any changes to anthropogenic impact within the watersheds involving the transformation of ecosystem relationships cause irreversible changes in the structure and composition of sediments. The objective of the research was to analytically compare the results of the study on heavy metals in Ustia River sediments with the use of various methods for determining environmental geochemical changes in headwaters due to human transformation of the basin between 1994 and 2015. Ustia River experienced the highest anthropogenic impact during 1968–1994. Starting from 1968 and up to the present time the wastewater volume disposed to the river is more than 25 m3 per day. Despite the downturn in the national economy since the mid 90-ies of the 20th century, the negative impact on the environment of surface water area does not stop. The environmental evaluation of the bottom sediments of Ustia River was held basing on the results of spectral analysis of air-dried samples of silt fraction from the selected samples. The researcher analysed the content of heavy metals which emission takes place within the river basin as a result of runoff generated by chemical and woodworking industries, transport, wastewater and agricultural use of the territory, particularly Pb, Mn, Co, Cu, Zn and Cd. For the first time, researchers have figured out that for the past twenty years there has been no improvement in the overall ecological state of the Ustia River bottom sediments. The human impacts on the hydro-ecosystem, assessed according to the content of heavy metals, have moderated only in the river section near the headstream. The author views this fact as a consequence of reduced chemicals’ usage (i.e. fertilizers, pesticides, compost, sewage and animal waste) on the cultivated land in this part of the basin. The remaining sections of riverbed have experienced deterioration of the bottom sediments; it is particularly notable with regard to the content of such elements as Mn, Cu, Zn and Pb within the urban areas. The increase of the concentrations of metals in the sediments near Basiv Kut Dam Lake in 2015, compared with the relevant data for 1994, can serve as the evidence that the negative impact on hydro-ecosystem has intensified. In both observation periods the bottom sediments of the upper part of the river has demonstrated extremely high content of Mn. Hence, in 1994 it markedly declined in the central section of the stream, and in 2015 it appeared in significant concentrations in the sediments along the channel. It is obvious that in this case there are geochemical features of the basin; however the situation in 2015 indicates a change in the state of bottom sediments with regard to the content of Mn under the influence of anthropogenic factors. The analysis of the geochemical changes in bottom sediments of Ustia headwater from 1994 until 2015 show that the concentrations of such elements as Cu, Zn, Pb, Co and Cd in the bottom sediments according to 2015 data turned out to be higher compared to 1994, excluding the upper part of the river. Nevertheless the geochemical anomalies of Mn contents noticed along the channel are also the case in this situation. The level of anthropogenic impact, measured in terms of total pollution index for the concentration of heavy metals in bottom sediments in both observation periods appeared to be «weak» or «slightly increased» if there were toxic elements. Hence, if in 1994 there was a high risk of pollution of bottom sediments with such elements as zinc, lead and copper both in case of the relative background values and hygiene criteria (maximum allowable concentrations in soil), in 2015 cobalt also appeared among such elements. The level of contamination of sediments according to international contamination classes mainly shows «significant» and «increased» impact on different parts of the river for the Mn content (5–6 grades) in both observation periods; the Cu and Zn content vary from «low» to «moderate» in 1994 (1–3 grades) and from «low» to «substantial» in 2015 (2–4 grades); the Pb content is «poor» (grade 1) in 1994 and «moderate» in 2015; Co and Cd content describes human impact on hydro-ecosystem as «weak» in both periods (0–1 grades). The assessment methods used by the researcher allowed tracking various aspects of heavy metal pollution in the bottom sediments. Furthermore, they help discovering that nowadays the sediments of Ustia River play the role of anthropogeny outcome battery against the geochemical anomalies of individual elements.