Ecohydrogeological characteristics of spring waters in rural areas (northeast of Moscow region)

Anthropogenic impact on aquifers leads to variations of groundwaters chemical content. This study is determined to describe current geochemical characteristics of springs in Shelkovo district in order to assess the quality of the water that is used for drinking purposes by residents.

The geological structure of the territory includes Devonian, Upper Carboniferous, Upper Jurassic and Lower Cretaceous terrigenous-carbonate rocks, overlapped by thin Quaternary sandy deposits. Surface sediments are permeable to polluted runoff waters, which can increase the vulnerability of groundwater and reduce its quality.

This research presents the obtained results of water parameters (COD, pH, electrical conductivity), the content of major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺, HCO₃^-, Cl^-, SO₄^2-, NO₃^-)  for 12 springs. The spring waters are slightly mineralized (M=0.1-0.5 g/l), pH values vary from 5.5 to 7.5.  The total hardness is 0.63-5.7 mg-eq/l. The composition of the water is variable. Springs could be divided by the content of major anions: the dominance of HCO₃^- which is due to natural causes. In some cases the presence of Cl^- and SO₄^2- because of the use of fertilizers and deicing reagents in urban territories. 

The concentration of major ions was compared to maximum permissible concentrations in drinking water (by WHO standards). It was noted to slightly exceed the limit for nitrate ion as well as for chemical oxygen demand.  Some waters had a pH indicator lower than the standard range.

Comparison of the ratios Cl^-/(Cl^-+Na⁺) and Na⁺/(Na⁺+Cl^-) to total dissolved salt was applied in order to figure out the mechanism of spring waters forming (Gibbs, 1970). The results showed that chemical composition is primarily controlled by rock weathering. The ratio relationships between equivalent content Cl^-/Na⁺, HCO₃^-/Na⁺, Ca²⁺/Na⁺ indicate the type of rocks as a silicate (Gaillardet, 1999). The effect of human impact on groundwaters used to be assessed by comparing the equivalent ratios Cl^-/Na⁺ and NO₃^-/Na⁺ (Zhang et al, 2024). The calculations performed summarised anthropogenic impact, including agronomic activities. Significantly connections between various major ions were pointed out due to correlation analysis: as well as fertilizer components and pesticides, anti-icing reagents for roads in winter season and household chemicals from sewers were detected. 

The studied waters were formed by dissolving silicate rocks by atmospheric precipitation. As it was figured out by a significant role of chloride and sulfur ions, and presence of nitrogen-ions, the area of springs' feeding is located in permeable contaminated quaternary sediments. But despite anthropogenic impact, the chemical composition of springs correspond to WHO standards for drinking waters.

References

Gaillardet J., Dupre B., Louvat P., Allegre C.J. Global silicate weathering and CO₂ consumption rates deduced from the chemistry of large rivers // Chemical geology – 1999. – Т. 159. – №. 1-4. – С. 3-30.

Gibbs R. J. Mechanisms controlling world water chemistry //Science. – 1970. – Т. 170. – №. 3962. – С. 1088-1090. 

Zhang, H., Wang, Z., Wang, X. et al. Hydrochemical characterization and health risk assessment of different types of water bodies in Fenghuang Mountain Area, Northeast China. Environ Geochem Health 46, 292 (2024)