Landscape elements and river chemistry as affected by river regulation – a 3-D perspective

Abstract

Abstract. We tested the hypothesis whether individual land classes within a river catchment contribute equally to river loading with dissolved constituents or whether some land classes act as "hot spots" to river loading and if so, are these land classes especially affected by hydrological alterations. The amount of land covered by forests and wetlands and the average soil depth (throughout this paper soil refers to everything overlying bedrock i.e. regolith) of a river catchment explain 58-93% of the variability in total organic carbon (TOC) and dissolved silicate (DSi) concentrations for 22 river catchments in Northern Sweden. For the heavily regulated Luleälven, with 7 studied sub-catchments, only 3% of the headwater areas have been inundated by reservoirs, some 10% of the soils and aggregated forest and wetland areas have been lost due to damming and further hydrological alteration such as bypassing entire sub-catchments by headrace tunnels. However, looking at individual forest classes, our estimates indicate that some 37% of the deciduous forests have been inundated by the four major reservoirs built in the Luleälven headwaters. These deciduous forest and wetlands formerly growing on top of alluvial deposits along the river corridors forming the riparian zone play a vital role in loading river water with dissolved constituents, especially DSi. A digital elevation model draped with land classes and soil depths which highlights that topography of various land classes acting as hot spots is critical in determining water residence time in soils and biogeochemical fluxes. Thus, headwater areas of the Luleälven appear to be most sensitive to hydrological alterations due to the thin soil cover (on average 2.7-4.5 m) and only patchy appearance of forest and wetlands that were significantly perturbed. Hydrological alterCorrespondence to: E. Smedberg (erik@mbox.su.se) ations of these relatively small headwater areas significantly impacts downstream flux of dissolved constituents and their delivery to receiving water bodies.

Modelling hyporheic processes for regulated rivers under transient hydrological and hydrogeological conditions

“…A first approximation of the distance of influence based on an analytical solution (Sawyer et al, 2009) assumed negligible riverbed resistance and is therefore questionable in the present case (e.g. Singh, 2004). This estimate of the maximum extent (180 m for a 1-month fluctuation period) was further tested using the numerical model.…”

“…Low hydraulic conductivity of the riverbed and daily varying river discharge have resulted in depleted hyporheic exchange flows across the river-aquifer interface (Siergieiev et al, 2014a). Deteriorated river water quality as a result of regulation (Smedberg et al, 2009;Siergieiev et al, 2014b) may partly depend on suppression of hyporheic processes due to regulation (Valett et al, 1996). Improved understanding of the major hydrogeological controls of hyporheic exchange has legacy effects on understanding geochemical fluxes between surface water and groundwater (Fritz and Arntzen, 2007) and can provide a platform for implementation of environmental flows and improved management and ecological status of regulated rivers.…”

Soil frost effects on streamflow recessions in a subarctic catchment

“…These (sub)alpine areas predominantly consist of heath and small shrub vegetation or exposed rock and thin soils. In the valleys, the soil development is estimated to be between 1.7 and 5.3 m, with regolith depths up to 30 m (Smedberg, Humborg, Jakobsson, & Mörth, 2009).…”

Subsurface release and transport of dissolved carbon in a discontinuous permafrost region

“…While there is no detailed soil characterization available for the Abiskojokken catchment, the median depth of the till-dominated unconsolidated sediments has been estimated to range between 5 m for deciduous forest to about 7 m for herbaceous vegetation in this region (Smedberg et al, 2009), and regional studies of nearby Kärkevagge show typically coarseloamy soils with 5 % clay with a slightly acidic soil pH (Darmody et al, 2000). The subalpine birch forest (Betula pubescens tortuosa) in the Abisko valley generally reaches 650 m a.s.l., and up to 700 m a.s.l.…”