| 1. |
- Andersson, Jan-Olov, 1966-
(författare)
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A GIS-based landscape analysis of dissolved organic carbon in boreal headwater streams
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In boreal catchments, stream water chemistry is influenced and controlled by several landscape factors. The influence of spatially distributed variables is in turn dependent on the hydrological scale. Headwater streams have larger variability of water chemistry, and thus together represent a large biodiversity, and therefore need to be monitored in official environmental assessments. One objective of this study was, using Geographical Information Systems (GIS), to analyse co-variation between landscape variables and water chemistry and to determine which of the landscape variables have a major influence on the concentration of dissolved organic carbon (DOC) in headwater streams. Another objective was to find a simple method for predicting sources of DOC, using official map data and publically available GIS applications. Totally 85 headwater catchments (0.1-4 km2) in the county of Värmland, western south Sweden, were used in the study. Water chemistry was analysed for water sampled at low, medium and high flows, and landscape variables were extracted from official map data sources: topographic maps, a digital elevation model (DEM, 50 m grid), and vegetation data. Statistical analyses showed that topography (mean slope and mean topographic wetness index (TWI)) and wetland cover often correlated well with DOC in headwater catchments. Official map data could satisfactorily extract landscape variables (mean slope, mean TWI) that were useful in predicting stream water chemistry (DOC). A high-resolution elevation model, which was generated by interpolation of photogrammetric data, was used to calculate and evaluate two different wetness indices and their ability to predict the occurrence of wetlands in six catchments of different sizes and topography. The SAGA (System for Automated Geoscientific Analyses) wetness index (SWI) gave substantially better results than the TWI. The effects of resolution of DEMs on calculations of the SWI were investigated using 5, 10, 25 and 50 m grids. The results showed that SWI values increased with increasing cell size. The near linear increment of mean values for resolutions 10-50 m suggests a independence of terrain type and catchment size, which supported previous findings that indicated that mean slope and mean wetness index calculated from coarse elevation models may be used for prediction of DOC in headwater streams.
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| 2. |
- Björkvald, Louise, 1973-
(författare)
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Landscape hydrogeochemistry of Fe, Mn, S and trace elements (As, Co, Pb) in a boreal stream network
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transport of elements by streams from headwater regions to the sea is influenced by landscape characteristics. This thesis focuses on the influence of landscape characteristics (e.g. proportion of wetland/forest coverage) on temporal and spatial variations of Fe, Mn, S and trace elements (As, Co, Pb) in streams located in northern Sweden, a boreal region characterized by coniferous forests and peat wetlands.Water samples from a network of 15 streams revealed a different hydrogeochemistry in forested catchments compared to wetland catchments. The temporal variation was dominated by spring flood, when concentrations of Fe, Mn and trace elements increased in forested headwaters. However, in streams of wetland catchments concentrations decreased, but Pb concentrations were higher in comparison to other streams. Both Fe and Pb showed positive correlations with wetland area, while Co correlated with forest coverage. The anthropogenic contribution of As and Pb appear to be larger than the supply from natural sources.During spring flood SO42- decreased in most streams, although concentrations increased in streams of wetland catchments. Concentrations of SO42- were higher in streams of forested catchments than in wetland dominated streams, the former being net exporters of S and the latter net accumulators. Isotope values of stream water SO42- (δ34SSO4) were close to that of precipitation during spring flood, indicating that the major source of S is from deposition. The results show that, although emissions of anthropogenic S have been reduced, there is still a strong influence of past and current S deposition on runoff in this region.In conclusion, wetlands are key areas for the hydrogeochemistry in this boreal landscape. The findings emphasize the importance of understanding stream water chemistry and element cycling from a landscape perspective. This may be important for predicting how boreal regions respond to environmental disturbances such as climate change.
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| 3. |
- Grabs, Thomas, 1980-
(författare)
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Water quality modeling based on landscape analysis: importance of riparian hydrology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several studies in high-latitude catchments have demonstrated the importance of near-stream riparian zones as hydrogeochemical hotspots with a substantial influence on stream chemistry. An adequate representation of the spatial variability of riparian-zone processes and characteristics is the key for modeling spatio-temporal variations of stream-water quality. This thesis contributes to current knowledge by refining landscape-analysis techniques to describe riparian zones and by introducing a conceptual framework to quantify solute exports from riparian zones. The utility of the suggested concepts is evaluated based on an extensive set of hydrometric and chemical data comprising measurements of streamflow, groundwater levels, soil-water chemistry and stream chemistry. Standard routines to analyze digital elevation models that are offered by current geographical information systems have been of very limited use for deriving hydrologically meaningful terrain indices for riparian zones. A model-based approach for hydrological landscape analysis is outlined, which, by explicitly simulating groundwater levels, allows better predictions of saturated areas compared to standard routines. Moreover, a novel algorithm is presented for distinguishing between left and right stream sides, which is a fundamental prerequisite for characterizing riparian zones through landscape analysis. The new algorithm was used to derive terrain indices from a high-resolution LiDAR digital elevation model. By combining these terrain indices with detailed hydrogeochemical measurements from a riparian observatory, it was possible to upscale the measured attributes and to subsequently characterize the variation of total organic-carbon exports from riparian zones in a boreal catchment in Northern Sweden. Riparian zones were recognized as highly heterogeneous landscape elements. Organic-rich riparian zones were found to be hotspots influencing temporal trends in stream-water organic carbon while spatial variations of organic carbon in streams were attributed to the arrangement of organic-poor and organic-rich riparian zones along the streams. These insights were integrated into a parsimonious modeling approach. An analytical solution of the model equations is presented, which provides a physical basis for commonly used power-law streamflow-load relations.
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| 4. |
- Haei, Mahsa, 1981-
(författare)
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Importance of winter climate and soil frost for dissolved organic carbon (DOC) in boreal forest soils and streams : - implications for a changing climate
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dissolved organic carbon (DOC) is a defining feature of surface waters in a large part of the world and it influences a variety of physical, chemical and biological processes in aquatic ecosystems. Riparian soils exert a major control on stream water chemistry in many northern latitude regions and provide a local source of DOC to adjacent streams. As the winter climate in northern regions is predicted to be particularly affected by climate change, it is important to investigate the sensitivity of DOC in riparian soils and the potential implications for adjacent streams’ chemistry in a changing winter climate. The effects of a changing winter climate on riparian soil DOC production and export to streams has received little attention to date, and this is the focus of my thesis. In this thesis I first evaluate the hydro-climatic drivers of inter-annual variation in spring snowmelt DOC concentrations in two boreal forest streams of northern Sweden. By accounting for the effects of seasonal hydrology, I was able to statistically evaluate the importance of antecedent winter climatic conditions to inter-annual variation in stream DOC concentrations during the spring snow-melt periods. This descriptive work was complemented by a long-term field experiment where snow packs were manipulated to investigate the impacts of soil freezing on the concentration and quality of DOC in soil water. The effect of soil freezing on DOC was further addressed in a multi-factor laboratory experiment on soil samples taken from the riparian zone. The laboratory experiment was designed based on a central composite face-centered (CCF) model which applied three levels of four freezing-related factors: temperature, water content, duration and frequency of freeze-thaw cycles. The responses of soil microbial- activity and composition to the same experimental factors as well as their potential link to frost induced changes in DOC were also tested. Large inter-annual variations were observed in spring snow-melt DOC concentrations in streams. Lower export of DOC during the preceding seasons and longer, and colder, winters resulted in higher spring snow-melt DOC concentrations. Soil water DOC concentrations and lability were significantly enhanced in the upper soil horizons which experienced extensive soil frost and longer frost duration. In the laboratory experiment, similar responses of soil water DOC were observed in that the higher concentrations and greater lability were found in samples incubated at the lowest temperatures (-12°C). The fungal to bacterial growth ratio also increased in the lower temperature treatments. In addition, fungal growth rate and soil basal respiration responded positively to frost-induced increases in DOC concentration. The frequency of freeze-thaw cycle did not appear to be an influential factor in the laboratory experiment. Several significant interactions of the factors were also detected. By conducting and integrating field and laboratory experiments I highlight the importance of soil frost regime and winter climatic conditions for regulating DOC in riparian soils and their adjacent streams in areas with seasonally frozen soils. However, in a changing future winter climate, alterations in soil frost should be assessed as the result of changes in air temperature and snow-pack formation and extent, and implications for streams should be investigated with regard to changes in hydrology and export processes in soil-water interface.
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| 5. |
- Kuglerová, Lenka, 1985-
(författare)
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Grow with the flow : Hydrological controls of riparian vegetation in boreal stream networks
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- What drives species diversity across landscapes is one of the most fundamental questions in ecology. Further, understanding the mechanisms underlying species diversity patterns is important not only for forming and challenging ecological theories but also essential for appropriate landscape management and effective nature conservation. This thesis focuses on patterns of vascular plant, moss and liverwort species richness and composition in relation to water flow in boreal-forest catchments, focusing mostly on riparian zones (RZs), that is terrestrial areas bordering streams and rivers. I addressed some of the most essential questions related to the ecology of riparian vegetation including the role of stream network position, groundwater (GW) flow paths, substrate availability, upland perturbations, and stream restoration. I also investigated how riparian soil processes and habitat properties relate to these factors in order to provide a holistic understanding of riparian dynamics. The results showed that the species richness and composition of riparian vascular plants, mosses and liverworts are strongly influenced by position along the stream network, GW discharge, presence of variable substrates in RZs, and by stream restoration. Generally, more species were found downstream in the network, at sites with inputs of upland GW, sites with high diversity of substrates (e.g., open mineral soil, rocks, stones, wood and bark), and along streams restored after channelization. This thesis also describes how riparian habitat properties responded to position in the landscape and human impacts, thus providing mechanistic links between plant species diversity and riparian processes across spatial scales. These ecological insights are further implemented into numerous recommendations for freshwater and upland management in boreal Sweden. Given that streams and rivers connect landscape elements both longitudinally and laterally I argue that management plans should be designed for entire catchments instead of individual river segments. Ignoring the connectivity of streams as well as the high connectivity of riparian areas to uplands via GW flows may result in failure of restoration, mitigation and/or protection actions. Further, during forestry operations more emphasis should be placed on GW discharge areas along streams and rivers, because they represent important ecological and biogeochemical hotspots in the landscape. The riparian buffers left along streams in boreal catchments affected by forestry are presently insufficiently wide and often uniform in width. This threatens the assemblages of species in GW discharge hotspots and the ecosystem services they provide. Overall, this thesis describes a holistic picture of riparian diversity patterns and riparian processes in boreal landscapes, acknowledges and elaborates on current ecological theories, presenting new patterns in biodiversity, and offers management guidelines.
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| 6. |
- Lidman, Fredrik
(författare)
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Radionuclide transport in the boreal landscape : Uranium, thorium and other metals in forests, wetlands and streams
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The boreal landscape is complex mosaic of vast forests, lakes and wetlands. Through the landscape flows a fine network of streams and rivers, carrying dissolved and suspended material from atmospheric deposition and weathering of soils and bedrock to downstream recipients. This thesis investigates the transport of U, Th and other metals in the boreal landscape by comparing a set of catchments with contrasting characteristics, ranging from 0.12-68 km2 in area. Using uranium (234U/238U) and oxygen isotopes (δ18O) it was demonstrated that catchment size has a strong impact on the hydrological pathways and on the mobilisation of uranium. Both tracers also displayed a consistent shift towards more superficial sources and more superficial flow pathways when going from winter baseflow conditions to the spring flood. Large spatiotemporal variability was observed with U fluxes ranging from 1.7 -30 g km-2 a-1. Using a wide set of hydrochemical parameters and landscape characteristics it was demonstrated that wetlands play a decisive role for the biogeochemical cycling of many metals. Comparing normalised fluxes of 13 different elements (Al, Ba, Ca, Cr, Cu, La, Mg, Na, Ni, Si, Sr, U and Y) 73% of the spatial variance could be explained based on the wetland coverage and the affinity for organic matter, the latter of which was quantified using thermodynamic modelling. Hence, it was possible to link the large-scale transport patterns of a wide range of metals to fundamental biogeochemical properties. When restraining the analysis to the smaller streams (<10 km2), the explanatory power increased to 88%. For elements such as Na and Si with low affinity for organic matter the decrease in wetland-dominated catchments corresponded closely to the area of mineral soils that had been replaced by peat, indicating that reduced weathering was the main cause of the decrease. For organophilic metals the decrease in wetland-dominated catchments was even greater, suggesting that there also was an accumulation of these metals in the peat. This was confirmed by investigating the distribution of radionuclides in local mire, which revealed considerable accumulation of uranium and thorium along the edges of the mire. Based on the inventories of uranium and thorium and their distribution in the peat it was concluded that the mire historically had been a sink for these metals and that it most likely will continue to be so for a long time to come. All and all, wetlands were estimated to decrease the fluxes of metals from the boreal forests to downstream lakes and oceans by 20-40%, depending on how strongly they bind to organic matter.
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| 7. |
- Pontér, Simon
(författare)
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Isotope Ratio and Trace Element Measurements Using Inductively Coupled Plasma – Mass Spectrometry : Method Development and Applications in Environmental Forensics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Environmental Forensics is a scientific methodology developed for identifying sources, the timing of release, and transport pathways for potentially hazardous environmental contaminants. It combines a variety of analytical methods with principles derived from disciplines such as chemistry, geology, geochemistry, hydrogeology, and statistics, with the purpose to provide objective scientific and legal conclusions on the source and/or time of a contaminant release. Instrumental development and refining separation schemes have allowed higher quality data to be obtained and played a major role in the recent progress of the field. The use of modern techniques such as inductively coupled plasma sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for trace and ultra-trace element concentrations and isotope ratio measurements provides Environmental Forensics with new opportunities. The work described in the present thesis has been focused on closing knowledge gaps in the field of Environmental Forensics, including analytical method development as well as processes- and source(s)t-tracing using multiple isotopes in environmental studies. Paper I is dedicated to the assessment of performance of double-focusing, sector field mass spectrometry (ICP-SFMS) for determination of analytes (including technology critical elements (TCE)) at ultra-trace levels in complex matrixes, with a special emphasis on the determination of Au, Ag, Ir, Os, Pd, Pt, Re, Rh, Ru, Sb, and Te. Instrumentation development was performed by optimization and testing different configurations of the ICP-SFMS introduction system as well as various sample preparations, pre-concentration, and matrix separation methods. Factors affecting instrumental sensitivity, contamination risks, reagent purity, spectral interferences, matrix effects, and analyte recovery are discussed. Optimized matrix specific methods were applied to a range of reference and control materials (riverine and brackish waters, seawater, whole blood, serum, and urine). Samples included brackish water and seawater from the Laptev Sea, venous blood, tap water, and snow samples collected in Luleå, northern Sweden. In Paper II an analytical procedure was developed, consisting of high pressure/temperature acid digestion using an UltraCLAVE system followed by a one pass, single column matrix separation allowing the first Cr isotope study in epiphytic lichens and mosses, as well as analysis of chromite and soils by ICP-SFMS and MC-ICP-MS. The overall reproducibility of the method, which was found to be ±0.11‰ (2σ), was assessed by replicate preparation and Cr isotope ratio measurements performed by different operators in multiple analytical sessions over a few months. Results indicated no correlation between soil concentrations and isotopic compositions (R2=0.2), while a strong negative correlation (R2=0.7) between Cr concentrations in lichens and mosses and δ53Cr signatures indicates airborne Cr contribution from local anthropogenic source(s) depleted in heavy isotopes. Chromium isotope data obtained for lichens and mosses indicate the potential of using this approach for tracing and quantifying airborne Cr pollution caused by stainless steel foundries. Paper III evaluates heavy metal contamination in brackish water, groundwater, and sediments collected close to a deposit facility at the Rönnskär Cu–Pb–Zn smelter in Skellefteå, northern Sweden. This study investigates the ranges of isotopic compositions of four elements (Cd, Cu, Pb, and Zn) in smelter process materials (ores, products, and waste), as well as in polluted groundwater and sediments of the affected area. The study’s objective was to evaluate the isotope variability of the polluting source and identify possible isotope fractionation between a source and a sink. This study further assesses the viability of using isotopic information to identify the source of the pollutant in various matrices. Isotope composition data were used as a compliment to multi-element screening analysis and multivariate statistical techniques. Expanding the number of elements utilized in isotope tracing empowers our abilities to decipher the source(s) and the extent of environmental exposure from contamination events related to mining and refining operations. Results show clusters of elements with elevated concentrations and significant inter-element correlations that can be traced practically in all matrices tested (from dust samples to sediments), confirming a link between the source and the polluted environmental compartments. Differences in the relative mobility in the environment for different elements (shown in the example of Re and Mo distribution in sediments) may however affect the usefulness of the elemental ratios in reconstructing the extent and timing of pollution events. Among the isotopes evaluated in this study, radiogenic Pb and stable Zn isotope systems offer the most promising source identification in the area close to the smelter. However, temporal variability in the isotopic composition of the source adds complexity for the Pb isotopes. Numerous post-deposition fractionating processes alter the original source ratios for Cu, Zn, and to a lesser extent, Cd. At larger distances from the source, additional fractionation during element migration and dilution of source-specific signatures with background components makes source tracing more challenging. To fully realize the great promise offered by expanding the number of elements utilized in isotope tracing as a powerful way to decipher sources and fate of environmental exposure, a comprehensive evaluation of both source(s) and background variability, as well as post-depositional fractionation, needs to be an integral part of any Environmental Forensics investigation. Paper IV combines uranium (U) and other trace element concentrations with iron and uranium isotope measurements as a proxy to reconstruct historical changes of U release and accumulation in one tailings pond and two lakes (Mettä-Rakkurijärvi and Rakkurijärvi) receiving deep mine waters in northern Sweden, Kiruna. Uranium is deposited in lake sediments downstream of the mine, with elevated U concentrations in the surface sediments exceeding 55 mg kg-1, a >20-fold increase from the pre-industrial years. The distribution of anthropogenic U between the lakes does not follow the distribution of other contaminants reaching the system with mine waters, with a higher relative proportion of U accumulating in sediments of the second lake. Vertical concentration profiles for redox-sensitive elements as well as Fe isotopic composition were used to re-construct past redox-conditions potentially controlling early diagenesis of U in surface sediments. The isotopic signature of U in surface sediments (activity ratio AR=2.5) is far from that of secular equilibrium. These signatures are a function of time and weathering-induced fractionation, used here as a source signature of U originating in the deep groundwater in the mine. Linear regressions of inverse U concentration in water (dissolved, particulate, and total) versus AR reaffirms a simplified mixing situation with two isotopically distinct sources: 1) a natural source (low U concentration, AR 2.64), and 2) an anthropogenic source (high U concentration, AR ≈1.95). After mixing with mine water from the Rakkurijoki system, the AR of receiving Kalix River water decreases from 2.66 to 2.24. Monitoring data on the surface waters demonstrate the effects of the tributary waters of the Rakkurijoki systems as it discharges into the Kalix River, where the U concentration of the river downstream is more than doubled.
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| 8. |
- Serikova, Svetlana, 1989-
(författare)
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Carbon Emissions from Western Siberian Inland Waters
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inland waters (i.e. rivers, streams, lakes, ponds) emit carbon (C) into the atmosphere. The magnitude of global inland water C emission has been estimated to equal the global ocean C sink, thus making inland waters an important component of the global C cycle. Yet, the data used in estimating the magnitude of global inland water C emission lacks measurements of inland water C emissions from permafrost-affected regions in general and from Russia in particular, despite permafrost covering ~25% of the Northern Hemisphere and ~65% of Russia. This lack of data questions the accuracy of the current estimate of global inland water C emission and its predictive power in assessing changes in the global C cycle following permafrost thaw.In this thesis, we conducted detailed measurements of river and lake C emissions across ~1000 km permafrost gradient of Western Siberia (from permafrost-free to continuous permafrost zone) and assessed the magnitude of the total C emission from Western Siberian inland waters. We found that river and lake C emissions varied across the permafrost gradient with river C emissions being greatest in areas where permafrost is actively degrading, and lake C emissions being greatest in areas where permafrost is still intact. We also found that river and lake C emissions are likely driven by different factors with river C emissions being mainly controlled by temperature and hydrological conditions, whereas lake C emissions by sediment respiration and availability of recently thawed organic C. Further, we estimated the total C emission from Western Siberian inland waters to be greater than previously thought and exceeding the C export from this region to the Arctic Ocean. Such finding implies that a major part of the terrestrially-derived C is lost in Western Siberian inland waters, making this region a hotspot for inland water C emission following permafrost thaw. We also showed that apart from C emissions measurements across different inland water types and across the landscape, estimates of inland water surface areas are needed for accurate assessments of the total inland water C emission of any given region. Particularly, water surface areas of streams and ponds as well as inundated floodplains, especially in years of extreme flood events, are important for quantifying the total inland water C emission. Overall, this thesis presents new data related to C emissions from rivers and lakes in an area that undergoes rapid permafrost thaw, and urges to account for all inland water types and their respective water surface areas when attempting to achieve unbiased estimates of the inland water contribution to the atmospheric C budget.
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| 9. |
- Siergieiev, Dmytro
(författare)
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Hydrogeochemical effects of hydropower regulation on river-aquifer continuum in boreal rivers
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydropower infrastructure affects many large rivers worldwide, threatening riverine and coastal ecosystems by fragmenting flow, disturbing landscapes and water retention and altering sedimentation and primary production. This thesis investigated major impacts of hydropower regulation on hydrological and geochemical processes in large boreal rivers. Geochemical river transport, sediment composition and hydrogeochemical functioning of the river-aquifer interface were studied in the regulated Lule River and the unregulated, otherwise similar, Kalix River in Northern Sweden.Regulation halved mean maximum runoff and tripled minimum runoff and winter transport of total organic carbon (TOC), Fe, Si, suspended Mn and P compared with the unregulated river. Summer suspended C/N ratio was 10-20 and <10 in the regulated and unregulated river, respectively, indicating organic matter decay during long residence times in Lule River reservoirs. Suspended P/Fe ratio varied little annually in the regulated river, indicating low abundance of phytoplankton. Sediment cores from the headwater reservoir revealed simultaneous Fe and P sequestration under a Mn-oxyhydroxide layer on the sediment surface. Reservoirs also enhanced diatom production and sedimentation of non-detrital Si, decreasing Si transport to the sea. Retention of total Fe, Si and P was 15%, 7% and 25% of the total river transport, respectively.The river-aquifer interface (hyporheic zone) functioned differently in the two rivers. Daily oscillating discharge in the regulated river and reduced spring peaks caused riverbed colmation, impairing river-aquifer exchange and forming stagnant subsurface areas. The hyporheic zone functioned as a source/sink of Fe, Mn, dissolved OC and NH4 in the regulated/unregulated river. Regulation also altered temporal hydraulic gradients dynamics between river and aquifer favouring solute pulses and presumably causing irregular TOC patterns at the river mouth.Hydrological modelling of river-aquifer interactions indicated that short-term regulation diminished orthogonal fluxes. Prolonged river flow peaks increased bank storage, favouring a release of nutrients and major/trace elements into the river during return flows. Colmation restricted water movement across the river-aquifer interface, increasing residence time and favouring suboxic conditions. Gently sloping river banks (former floodplains) of the regulated river facilitated river water entry to subsurface layers, potentially increasing solute export.Overall, modified river discharge altered river-aquifer spatial and temporal connectivity and interface biogeochemistry. Longitudinal connectivity was disrupted by long-term regulation, while lateral and vertical connectivity and hyporheic exchange were reduced by oscillating river water levels and clogging. These novel findings on post-regulation riverine hydrological pathways and geochemical fluxes can help sustain riverine ecosystems.
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