From soil water to surface water – how the riparian zone controls the transport of major and trace elements from a boreal forest to a stream

Abstract

<p><strong>Abstract.</strong> The riparian zone is the narrow strip of land, which lines lakes and watercourses. In the boreal region the riparian zone of headwaters often tends to be -wetland-like with high concentrations of organic matter, low pH and more or less reducing conditions. This means that riparian soils in many respects are different from the podzols and other types of mineral soils that dominate the boreal landscape. In this study a large number of major and trace elements (Al, As, B, Ba, Ca, Cd, Cl, Co, Cr, Cs, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Si, Sr, Th, Ti, U, V, Zn, Zr) and other parameters such as sulphate, total organic carbon (TOC) and pH were analysed in groundwater and soil water in a boreal hillslope. The objective was to investigate how the chemistry changes as the groundwater passes through the riparian zone and enters the stream.<br><br> Most of the investigated elements displayed substantially higher (up to 60 times) concentrations in the riparian soils than in the uphill mineral soils. There were also examples of nearly uniform concentrations throughout the transect (e.g. Na and Si), but in only a few cases were lower concentrations observed in the riparian zone (e.g. K, Mg and Ca). The degree of enrichment in the riparian soils could be linked to the affinity for organic matter, indicating that the pattern with strongly elevated concentrations in riparian soils is typical for organophilic elements. However, the elevated concentrations of many elements in the riparian zone could not be linked to increased uptake in biota (bilberry leaves and spruce shoots). In summary, the results confirmed that the riparian zone plays a central role for regulating the stream water quality and the transfer of a wide range of elements from terrestrial to aquatic ecosystems. Hence, riparian soils are essential for understanding the fate of nutrients, pollutants and other substances in the boreal landscape.</p>

How landscape organization and scale shape catchment hydrology and biogeochemistry: insights from a long‐term catchment study

“…Specifically, as groundwater moves from uphill mineral soils, through the riparian zone with large stores of soil organic matter, major biogeochemical transformations occur within meters of the stream. Most notably, these changes include dramatic reductions in pH and increases in DOC along this flowpath . In the KCS, the dominant source layer framework has been applied successfully to describe the riparian zone/stream interaction for a wide range of solutes and compounds, including DOC, lead (Pb), base cations (BC), selenium (Se), dissolved carbon dioxide (CO 2 ), and ammonium (NH 4 + ).…”

“…Although important advances in our understanding of the role of the boreal riparian zones have been made in recent years, much work remains to fully appreciate how the dominant source layer regulates stream chemistry . One puzzle that still needs to be resolved is how organic rich riparian soils can remain such an important supplier for so many natural and anthropogenic metals and organic compounds, when concentrations of these solutes are often up to 100 times lower in the upland soils that often serve as the original source . We do know that, at the present rate of DOC export, the riparian organic carbon pool can continue to sustain several hundred years of losses without any new organic carbon production .…”

Co‐occurrence of browning and oligotrophication in a boreal stream network

“…Finally, wetter conditions during the non‐growing season could elevate water tables, activating shallower layers of riparian soils and thereby promoting geochemical processes that remove DIP. Specifically, these upper soil horizons are more organic rich and acidic (Ledesma et al 2018), and in some cases also have higher concentrations of aluminum (Al) and iron (Fe) (Lidman et al 2017). Activating more surficial soil pathways could therefore enhance phosphate sorption (Giesler et al 2005) and thereby reduce mobilization to streams.…”

Application of a standard risk assessment scheme to a North Africa contaminated site (Sfax, Tunisia) -Tier 1

“…individually and then integrating all the LoEs. Hence, and regarding the ChemLoE, total concentrations of metals were used to calculate the multi substances (or elements) potentially affected fraction of species (msPAF) using the log-logistic concentration addition (CA) model(De Zwart and Posthuma, 2005;Lidman et al, 2016). This procedure was performed aftercorrecting total concentrations of metals for background concentrations (based on the REF soil) and calculating the toxic pressure or the potentially affected fraction of species (PAF) for each metal individually according to following equations: substances taken into account in the risk estimation HCp -Hazard concentration for a given percentage of species TMC -pseudo-total metal concentration β -constant value for each metal J o u r n a l P r e -p r o o f…”