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Linking major and trace element concentrations in a headwater stream to DOC release and hydrologic conditions in a bog and peaty riparian zone

Broder, Tanja, Biester, Harald
Applied geochemistry 2017 v.87 pp. 188-201
aluminum, arsenic, barium, cadmium, calcium, cobalt, dust, geochemistry, groundwater, iron, lead, magnesium, manganese, nitrates, organic horizons, organic matter, organic soils, peat, peatlands, pollution, principal component analysis, riparian areas, streams, strontium, sulfates, variance, watersheds, weathering, zinc
In the organic-rich environments of peatlands and peaty riparian zones, dissolved organic matter (DOM) can act as a carrier for major and trace elements. However, the mobilization and export patterns of elements from these systems are largely unknown. This study elucidates the annual and short-term event-based dynamics of major and trace element concentrations in a headwater stream draining an ombrotrophic peatland and a peaty riparian zone. Elements are expected to exhibit specific export patterns depending on their biogeochemical reactivity and source area. We hypothesize that most elements are released during organic matter decomposition and are co-transported with DOM in the bog catchment, whereas in the riparian zone, other element pools, such as shallow groundwater, also play a major role.Most of the variance in the data, as revealed by Principal Component Analysis, integrated the DOM concentration pattern (element loadings > 0.8: Al, Ca, Fe, Mg, Mn, Zn, Li, Co, As, Sr, Cd, Pb, and DOC). Ca, Mg and Sr were also found to load on this principal component, suggesting that the main control on element mobilization is not DOM, but rather similar source areas and mobilization processes. The DOM-related export was driven by plant uptake, plant decomposition and the bog water level in terms of hydrologic connectivity. The differences between the bog and the riparian zone were mainly driven by different hydrologic conditions and additional elemental sources, such as mineral weathering. The export patterns of Rb, Cs, K, NO3⁻ and SO4²⁻ were predominantly controlled by the season and plant uptake, and they were particularly exported by a surficial fast flow path. In addition to other elements, Ga, Y and Ba were enriched in the upper peat and organic soil layer, likely due to anthropogenic pollution. The specific export pattern of these latter elements indicates their predominant mobilization by the dissolution of dust particles and their subsequent mobilization by coupling to DOM.