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, δ26Mg, δ44Ca 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 δ26 Mg and 87Sr/86Sr ratios, and silicate sediments often have higher δ26Mg and 87Sr/86Sr ratios than runoff at the study site. Mixing of these two sources, if confirmed, could reconcile the flux and isotope data.

• Klíčová slova
• Calcium, Forest catchment, Isotopes, Magnesium, Nutrient imbalances, Strontium,
• MeSH
• ekosystém MeSH
• hořčík * analýza   MeSH
• izotopy stroncia analýza   MeSH
• izotopy MeSH
• kationty MeSH
• monitorování životního prostředí MeSH
• uhličitany MeSH
• vápník * analýza   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• hořčík * MeSH
• izotopy stroncia MeSH
• izotopy MeSH
• kationty MeSH
• uhličitany MeSH
• vápník * MeSH

Magnesium isotope ratios (26Mg/24Mg) can provide insights into the origin of Mg pools and fluxes in catchments where Mg sources have distinct isotope compositions, and the direction and magnitude of Mg isotope fractionations are known. Variability in Mg isotope compositions was investigated in three small, spruce-forested catchments in the Czech Republic (Central Europe) situated along an industrial pollution gradient. The following combinations of catchment characteristics were selected for the study: low-Mg bedrock + low Mg deposition (site LYS, underlain by leucogranite); high-Mg bedrock + low Mg deposition (site PLB, underlain by serpentinite), and low-Mg bedrock + high Mg deposition (site UDL, underlain by orthogneiss). UDL, affected by spruce die-back due to acid rain, was the only investigated site where dolomite was applied to mitigate forest decline. The δ26Mg values of 10 catchment compartments were determined on pooled subsamples. At LYS, a wide range of δ26Mg values was observed across the compartments, from -3.38 ‰ (bedrock) to -2.88 ‰ (soil), -1.48% (open-area precipitation), -1.34 ‰ (throughfall), -1.19 ‰ (soil water), -0.99 ‰ (xylem), -0.95 ‰ (needles), -0.82 ‰ (bark), -0.76 ‰ (fine roots), and -0.76 ‰ (runoff). The δ26Mg values at UDL spanned 1.32 ‰ and were thus less variable, compared to LYS. Magnesium at PLB was isotopically relatively homogeneous. The δ26Mg systematics was consistent with geogenic control of runoff Mg at PLB. Mainly atmospheric/biological control of runoff Mg was indicated at UDL, and possibly also at LYS. Our sites did not exhibit the combination of low-δ26Mg runoff and high-δ26Mg weathering products (secondary clay minerals) reported from several previously studied sites. Six years after the end of liming at UDL, Mg derived from dolomite was isotopically undetectable in runoff.

• MeSH
• chemické látky znečišťující vodu chemie   MeSH
• hořčík chemie   izolace a purifikace   MeSH
• izotopy chemie   MeSH
• kyselý déšť MeSH
• látky znečišťující půdu chemie   izolace a purifikace   MeSH
• lidé MeSH
• monitorování životního prostředí * MeSH
• půda chemie   MeSH
• stromy chemie   MeSH
• uhličitan vápenatý chemie   MeSH
• znečištění životního prostředí prevence a kontrola   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Česká republika epidemiologie   MeSH
• Evropa MeSH
• Názvy látek
• calcium magnesium carbonate MeSH Prohlížeč
• chemické látky znečišťující vodu MeSH
• hořčík MeSH
• izotopy MeSH
• kyselý déšť MeSH
• látky znečišťující půdu MeSH
• půda MeSH
• uhličitan vápenatý MeSH