Riparian zone control on base cation concentration in boreal streams

[摘要] Riparian zones (RZ) are a major factor controlling water chemistry in foreststreams. Base cations' (BC) concentrations, fluxes, and cycling in the RZmerit attention because a changing climate and increased forest harvestingcould have negative consequences, including re-acidification, for borealsurface waters. We present a two-year study of BC and silica (Si)flow-weighted concentrations from 13 RZ and 14 streams in different landscapeelements of a boreal catchment in northern Sweden. The spatial variation inBC and Si dynamics in both RZ and streams was explained by differences inlandscape element type, with highest concentrations in silty sediments andlowest concentrations in peat-dominated wetland areas. Temporal stability inBC and Si concentrations in riparian soil water, remarkably stable Mg/Caratios, and homogeneous mineralogy suggest that patterns found in the RZ area result of a distinct mineralogical upslope signal in groundwater. Streamwater Mg/Ca ratios indicate that the signal is subsequently maintained in thestreams. Flow-weighted concentrations of Ca, Mg, and Na in headwater streamswere represented by the corresponding concentrations in the RZ, which wereestimated using the Riparian Flow-Concentration Integration Model (RIM)approach. Stream and RZ flow-weighted concentrations differed for K and Si,suggesting a stronger biogeochemical influence on these elements, including Krecirculation by vegetation and retention of Si within the RZ. Potentialincreases in groundwater levels linked to forest harvesting or changes inprecipitation regimes would tend to reduce BC concentrations from RZ tostreams, potentially leading to episodic acidification.

[学科分类] 地球化学与岩石