Sizeable net export of base cations from a Carpathian flysch catchment indicates their geogenic origin while the ²⁶Mg/ ²⁴Mg, ⁴⁴Ca/ ⁴⁰Ca and ⁸⁷Sr/ ⁸⁶Sr isotope ratios in runoff are indistinguishable from atmospheric input

Abstract

Nutrient imbalances may negatively affect the health status of forests exposed to multiple stress factors, including drought and bark beetle calamities. We studied the origin of base cations in runoff from a small Carpathian catchment underlain by base-poor flysch turbidites using magnesium (Mg), calcium (Ca) and strontium (Sr) isotope composition of 10 ecosystem compartments. Our objective was to constrain conclusions drawn from long-term hydrochemical monitoring of inputs and outputs. Annual export of Mg, Ca and Sr exceeds 5-to-15 times their atmospheric input. Mass budgets per se thus indicate sizeable net leaching of Mg, Ca and Sr from bedrock sandstones and claystones. Surprisingly, δ ²⁶Mg, δ ⁴⁴Ca and ⁸⁷Sr/ ⁸⁶Sr isotope ratios of runoff were practically identical to those of atmospheric deposition and soil water but significantly different from bedrock isotope ratios. We did not find any carbonates in the studied area as a hypothetical, easily dissolvable source of base cations whose isotope composition might corroborate the predominance of geogenic base cations in the runoff. Marine carbonates typically have lower δ ²⁶ Mg and ⁸⁷Sr/ ⁸⁶Sr ratios, and silicate sediments often have higher δ ²⁶Mg and ⁸⁷Sr/ ⁸⁶Sr ratios than runoff at the study site. Mixing of these two sources, if confirmed, could reconcile the flux and isotope data.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11356-024-32866-1.