Landscape types and pH control organic matter mediated mobilization of Al, Fe, U and La in boreal catchments
2014 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 135, 190-202 p.Article in journal (Refereed) Published
In this study we present data from a seven-year time series from 15 nested streams within a 68 km(2) catchment, covering a pH gradient of almost three units. We demonstrate that the two landscape types, forest and wetlands, control the relative mobilization of Al and Fe in this boreal landscape. The La/U ratio is almost constant across the whole catchment despite large variations in pH, Al/Fe and TOC, whereas U and La mobilization increases with increasing contribution of deeper soils and groundwater further downstream. High Al/TOC ratios in the forested catchments suggest that Al originates from the underlying mineral soils, and low Al/TOC ratios derive from wetlands where Al is retained. We observe a competition effect on the binding to TOC between Al and La and also that the relationship between TOC, Al and La changes from the smaller (0.05-2 km(2)) catchments to larger (3-68 km(2)) downstream locations. As pH increase downstream, Al and Fe are gradually removed from the aqueous phase by precipitation of particulate gibbsite-like phases and ferrihydrite. This selective removal of Al and Fe from TOC binding sites results in higher La, and U concentrations downstream. Observed element patterns (U, La) and the range of upper continental crust normalized (La/Nd)(UCC) and (La/Yb)(UCC) in the near stream, riparian zone were very similar to the observed ratios across the whole catchment. The rising (La/Nd)(UCC) over (La/Yb)(UCC) may be due to a selective removal of REE binding to ferrihydrate in the riparian soil, the result of two distinctly different end-members but most probably not due to the in-stream precipitation of ferrihydrate or gibbsite-like phases.
Place, publisher, year, edition, pages
2014. Vol. 135, 190-202 p.
IdentifiersURN: urn:nbn:se:uu:diva-227242DOI: 10.1016/j.gca.2014.03.033ISI: 000335656900009OAI: oai:DiVA.org:uu-227242DiVA: diva2:731761