Eu anomalies in soils and soil water from a boreal hillslope transect – a tracer for Holocene lanthanide transport?
2019
Abstract Concentrations of
lanthanides(La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu) were measured in soils and
soil waterfrom a hillslope
transectin the Krycklan catchment in northern Sweden.
Soil waterwas collected at different depths and at different distances from the draining stream – from the uphill
Podzolto the peaty
riparian zone– throughout the course of a year. Combined with soil profiles from the same sites this provided a comprehensive dataset to study the fractionation and transport of
lanthanidesfrom boreal forest soils to streams. The
soil waterwas characterised by high concentrations of
lanthanidesin the
riparian zone, more than an order of magnitude higher than in the uphill mineral soil, and when normalised against local unweathered till the
soil waterexhibited distinctly negative Eu anomalies, particularly in deeper soil layers. The soil samples displayed both positive and negative Eu anomalies, but positive Eu anomalies were primarily associated with strongly weathered soils, whereas negative soil Eu anomalies were observed in organic soils at depths were large amounts of
lanthanidesare transported towards the stream. Since reduction of Eu seems unlikely to occur in this
transect, we propose that the Eu anomalies in soils and
soil waterare caused by the partial occurrence of Eu in more weathering-resistant minerals than the other
lanthanides. Based on the collected data and the hydrological and biogeochemical understanding of the studied
transectwe therefore propose a conceptual model for how Eu anomalies arise and how they can be used to interpret the Holocene transport and accumulation of
lanthanidesin soils. The results suggest that Eu anomalies have the potential to become a powerful tracer for studying weathering and soil development.
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