Abstract
Abstract. Groundwater flowing from hillslopes through riparian (near-stream) soils often undergoes chemical transformations that can substantially influence stream water chemistry. We used landscape analysis to predict total organic carbon (TOC) concentration profiles and groundwater levels measured in the riparian zone (RZ) of a 67 km2 catchment in Sweden. TOC exported laterally from 13 riparian soil profiles was then estimated based on the riparian flow–concentration integration model (RIM). Much of the observed spatial variability of riparian TOC concentrations in this system could be predicted from groundwater levels and the topographic wetness index (TWI). Organic riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. These TOC fluxes were subject to considerable temporal variations caused by a combination of variable flow conditions and changing soil water TOC concentrations. Mineral riparian gley soils, on the other hand, were related to rather small TOC export rates and were characterized by relatively time-invariant TOC concentration profiles. Organic and mineral soils in RZs constitute a heterogeneous landscape mosaic that potentially controls much of the spatial variability of stream water TOC. We developed an empirical regression model based on the TWI to move beyond the plot scale and to predict spatially variable riparian TOC concentration profiles for RZs underlain by glacial till.
Highlights
Being located directly adjacent to streams, the riparian zone (RZ) is the last strip of land in contact with groundwater before it discharges into the stream network or into the hyporheic zone
In this study we investigated the spatiotemporal variability of groundwater levels, soil water total organic carbon (TOC) concentrations, and TOC export rates from the RZ of a boreal catchment in Sweden
For this simple model to be scalable to entire stream networks, much of the considerable spatial variability in stream TOC would need to derive from variability in lateral exports from different types of RZs and wetlands along the stream networks
Summary
Being located directly adjacent to streams, the riparian zone (RZ) is the last strip of land in contact with groundwater before it discharges into the stream network or into the hyporheic zone. The RZ often distinguishes itself from the surrounding landscape by characteristic hydromorphic features including different soils (Hill, 1990) and vegetation (Jansson et al, 2007). These hydromorphic features have normally evolved over long periods of time ranging from several years to millennia. Understanding RZ functioning is important for understanding long-term and short-term effects of upslope hydrological controls (Vidon and Smith, 2007) on riparian vegetation and soils, which in turn can chemically modulate hydrological fluxes from upslope areas
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