Using Water Stable Isotopes and Cross-Correlation Analysis to Characterize Infiltration of Precipitation through Unsaturated Zone at the Velika Gorica Site of Zagreb Aquifer

Determination of Nitrate Migration and Distribution through Eutric Cambisols in an Area without Anthropogenic Sources of Nitrate (Velika Gorica Well Field, Croatia)

“…Soil water content generally shows lower variability at greater soil depths [69,86], which is in line with the findings of this study. Given that soil tends to become dry and lose moisture during rainless and dry periods [87], the lowest soil moisture was observed for July, August, and September because those months were periods with precipitation below monthly average precipitation for this area.…”

“…From Table S1, S1). Furthermore, smaller values of d-excess in the shallowest soil horizon in the summer months of 2021 (July and August) suggest influence of evaporation, which is consistent with the previous research where it was shown that in most cases evaporation fractionation is limited to the shallowest 0.3 m of soil [85], and which has also been observed in the A soil horizon within the previous research done at the study site [69].…”

“…D-excess ranges from 3.75 to 13.97‰ and shows smaller variability in the 3BC and C soil horizon (TableS1). Furthermore, smaller values of d-excess in the shallowest soil horizon in the summer months of 2021 (July and August) suggest influence of evaporation, which is consistent with the previous research where it was shown that in most cases evaporation fractionation is limited to the shallowest 0.3 m of soil[85], and which has also been observed in the A soil horizon within the previous research done at the study site[69].Concerning the chemical composition of soil water, the F − and Cl − mean concentrations range from 0.11 to 0.32 mg/L and from 1.55 to 3.51 mg/L, respectively. The Cl − concentrations were higher in the colder months compared to the warmer months.…”

“…NO 3 − concentrations are reduced during warmer months, particularly in the first three soil horizons, likely due to assimilation of NO 3 − through plants and denitrification process [11]. Considering that the pedological profile is situated in an area without potential anthropogenic sources of nitrate and that C soil horizon probably cannot retain the most of precipitation that infiltrates [69], which corresponds to different isotopic signature of precipitation and absence of variation in isotopic composition of soil water in C soil horizon within this research (Figure 4b), the examination of variation of the NO 3 − /Cl − molar ratios in relation to Cl − concentrations could be critical for the definition of nitrates produced by soil N nitrification. As shown in Figure 5, the highest values of molar ratios are observed in the C soil horizon with an average of 2.5 and minimum of 0.9 while the highest molar ratio in all other soil horizons is 0.8.…”

“…Despite research conducted in the selected area, there has been no specific focus on investigating the distribution of nitrates through Eutric Cambisols and related geochemical processes. The primary focus of research within the soil and the unsaturated part of the Zagreb aquifer has been on establishing the relationship between permeability and physicochemical properties [66], determining the sorption characteristics of potentially toxic metals [67], evaluating soil water origin [68], and conducting soil water monitoring of multiple soil horizons in Eutric Cambisols at the Velika Gorica site [69].…”