Krycklan Catchment Research Articles

Local‐ and network‐scale influence of peatlands on boreal catchment response to rainfall events

AbstractBoreal catchments are composed of different land covers, such as forests, peatlands and lakes, which differ in their runoff response to rainfall events. Understanding the individual and combined responses to rainfall events of these different land cover types is crucial for predicting potential impacts of future climate conditions on boreal water cycling. A common assumption is that peatlands attenuate peak flows, which is used as a motivation to restore drained boreal wetlands. However, it remains unclear how and to what extent peatlands can affect peak flow response. Only a few previous studies have looked at the hydrologic dynamics of peatlands in response to specific rainfall events across a wide range of nested sub‐catchments with varying peatland cover. In this study, we use nine years of hourly hydrometric data from 14 catchments within the Krycklan Catchment Study in northern Sweden to examine how peatlands contribute to flood attenuation at both local and stream network scales. Our analysis at the local scale demonstrated that during large events with low antecedent wetness conditions, peatland‐dominated catchment exhibited more muted responses compared to the similar‐sized forest‐dominated catchment. However, during events with high antecedent wetness conditions, the peatland‐dominated catchment exhibited flood magnitudes similar to the forest‐dominated catchment, although the elevated flow condition at the peatland‐dominated catchment persisted for longer periods. Finally, our analysis revealed no significant influence of peatlands on the attenuation or amplification of floods at the stream network scale.

Shallow-groundwater-level time series and a groundwater chemistry survey from a boreal headwater catchment, Krycklan, Sweden

Abstract. Shallow groundwater can respond quickly to precipitation and is the main contributor to streamflow in most catchments in humid, temperate climates. Therefore, it is important to have high-spatiotemporal-resolution data on groundwater levels and groundwater chemistry to test spatially distributed hydrological models. However, currently, there are few datasets on groundwater levels with a high spatiotemporal resolution because of the large effort required to collect these data. To better understand shallow groundwater dynamics in a boreal headwater catchment, we installed a network of groundwater wells in two areas in the Krycklan catchment in northern Sweden for a small headwater catchment (3.5 ha; 54 wells) and a hillslope (1 ha; 21 wells). The average well depth was 274 cm (range of 70–581 cm). We recorded the groundwater-level variation at 10–30 min intervals between 18 July 2018–1 November 2020. Manual water-level measurements (0–26 per well) during the summers of 2018 and 2019 were used to confirm and re-calibrate the automatic water-level measurements. The groundwater-level data for each well was carefully processed using six data quality labels. The absolute and relative positions of the wells were measured with a high-precision GPS and terrestrial laser scanner to determine differences in absolute groundwater levels and calculate groundwater gradients. During the summer of 2019, all wells with sufficient water were sampled once and analyzed for electrical conductivity, pH, absorbance, and anion and cation concentrations, as well as the stable isotopes of hydrogen and oxygen. The data are available at https://doi.org/10.5880/fidgeo.2022.020 (Erdbrügger et al., 2022). This combined hydrometric and hydrochemical dataset can be useful for testing models that simulate groundwater dynamics and evaluating metrics that describe subsurface hydrological connectivity.

Analysing gap dynamics in forest canopies with landscape metrics based on multi-temporal airborne laser scanning surveys – A pilot study

For a long time gaps or openings in the forest canopy have been of considerable interest to forest ecologists and to forest managers. In the context of disturbances induced by climate change, canopy gap dynamics are of particular interest, since they can indicate imminent damage to forest resources and irreversible trends such as forest decline. Here, statistical significance is crucial for establishing whether any imminent large-scale threat to the sustainability of forest resources exists. In order to be able to assess significance, we applied the Boolean model, a null or reference model from random set statistics. The Boolean model served as a theoretical benchmark for testing the significance of the observed trends in forest canopy gap dynamics. As a pilot study we analysed airborne laser scan (ALS) data collected in the Krycklan catchment area (Northern Sweden) in 2006 and 2015. The data were analysed using eight different landscape metrics. Despite the moderate resolution of our ALS data the landscape metrics have proved to be useful tools for monitoring canopy gap dynamics of forest ecosystems. The Boolean model has been successful in ascertaining statistical significance and the model parameters indicated important trends. In the Krycklan catchment area, there was no significant trend of canopy gap dynamics indicating any harmful development between 2006 and 2015. On the contrary, we found evidence for gaps closing in and gap locations becoming more random whilst the canopy cover increased between the two survey years.

Convergence of Groundwater Discharge through the Hyporheic Zone of Streams.

Significant attention has been given to hyporheic water fluxes induced by hydromorphologic processes in streambeds and the effects they have on stream ecology. However, the impact of hyporheic fluxes on regional groundwater flow discharge zones as well as the interaction of these flows are much less investigated. The groundwater-hyporheic interactive flow not only governs solute mass and heat transport in streams but also controls the retention of solute and contamination following the discharge of deep groundwater, such as naturally occurring solutes and leakage from geological waste disposal facilities. Here, we applied a physically based modeling approach combined with extensive hydrologic, geologic and geographical data to investigate the effect of hyporheic flow on groundwater discharge in the Krycklan catchment, located in a boreal landscape in Sweden. Regional groundwater modeling was conducted using COMSOL Multiphysics by considering geologic heterogeneity and infiltration constraint of the groundwater circulation intensity. Moreover, the hyporheic flow was analyzed using an exact spectral solution accounting for the fluctuating streambed topography and superimposed with the regional groundwater flow. By comparing the discharge flow fields with and without consideration of hyporheic flows, we found that the divergence of the discharge was substantially enhanced and the distribution of the travel times of groundwater was significantly shifted toward shorter times due to the presence of hyporheic flow. Particularly important is that the groundwater flow paths contract near the streambed interface due to the hyporheic flow, which leads to a phenomenon that we name "fragmentation" of coherent areas of groundwater upwelling in pinhole-shaped stream tubes.

Groundwater travel times predict DOC in streams and riparian soils across a heterogeneous boreal landscape

Dissolved organic carbon (DOC) in surface waters is an important component of the boreal landscape carbon budget and a critical variable in water quality. A dominant terrestrial DOC source in the boreal landscape is the riparian zone. These near stream areas play a key role in regulating DOC transport between land and aquatic ecosystems. The groundwater dynamics at this interface have been considered a major controlling variable for DOC export to streams. This study focuses on the regulating role of groundwater levels and mean travel times (MTT) on riparian DOC concentrations and, subsequently, stream DOC. This is done by comparing them as explanatory variables to capture the spatial and intra-annual variability of the stream and riparian groundwater DOC. We used a physically based 3D hydrological model, Mike SHE, to simulate DOC concentrations of the riparian zones for 14 sub-catchments within the Krycklan catchment (Sweden). The model concept assumes that DOC concentrations will be higher in groundwater moving through shallow flow paths. In the model, this can be linked to the position of the groundwater table at a point of observation or the travel time, which will generally be shorter for water that has travelled through shallow and more conductive soil layers. We compared the results with both observed stream and groundwater concentrations. The analysis revealed that the correlation between modelled and observed annual averages of stream DOC increased from r = 0.08 to r = 0.87 by using MTT instead of groundwater level. MTT also better captured the observed spatial variability in riparian DOC concentrations and more successfully represented seasonal variability of stream DOC. We, therefore, suggest that MTT is a better predictor than groundwater level for riparian DOC concentration because it can capture a greater variety of catchment heterogeneities, such as variation in soil properties, catchment size, and input from deep groundwater sources.

Use of stable Mg isotope ratios in identifying the base cation sources of stream water in the boreal Krycklan catchment (Sweden)

The knowledge of the sources of base cations in stream water is a prerequisite to assess potential effects of changing environmental conditions such as changing rainfall, weathering or groundwater flows on cation export with stream water. This study use stable Mg isotopes to identify potential sources in the well-studied catchment of Krycklan located on gneissic bedrock covered by quaternary sediments in Sweden. Samples were collected from open filed rain, throughfall, stream, soil, rock and litterfall. The δ26Mg values of these samples was determined and the contributions of different sources to Mg fluxes in the stream were determined from the variation of the Mg isotope and Sr / Mg ratios.The results show an overall variation of 1.10‰ between all samples. In addition, Magnesium isotope ratios varied little in the streamwater and in soil solution, except during snowmelt periods during which a large portion of the annual runoff occurs. Magnesium in the streamwater is explained as a mixture of three pools (open field rain, soil solution and groundwater) with the latter two influenced by catchment processes. Outside the snowmelt period, Mg in streamwater mainly derived from the groundwater, assumed to be mineral weathering signature in this catchment, with a contribution ranging from 12 to 63% to Mg fluxes. Open field rain dominates Mg fluxes in streamwater during spring flood (0 to 78%) and may contribute significantly during larger summer and autumn rainfall events. Soil solution input to streamwater range from 16 to 59% of Mg fluxes in streamwater. Our results demonstrate that δ26Mg values together with Mg concentrations and Sr/Mg ratios can be used to constrain the Mg sources of stream water and quantify weathering release rates.

An improved dual-baseline PolInSAR method for forest height inversion

P-band PolInSAR technique has been validated to be a useful tool for forest height inversion. Aiming at the residual ground scattering contribution and temporal decorrelation in repeat-pass interferometry that affect the inversion accuracy, we proposed a dual-baseline method based on the RVoG + VTD model. This method is firstly applied to E-SAR P-band data acquired over the Krycklan Catchment, Sweden with mixed forests, and the influence of ground scattering contribution and temporal decorrelation related to vertical wavenumber kz and height hv are theoretically and experimentally explored by comparing the traditional three-stage inversion method, the fixed extinction method and the proposed method. The experimental results show that the traditional three-stage inversion method has a overall serious overestimation for the whole study area, resulting in a R2 of ca. 0.4 and RMSE of ca. 7 m. Compared with the three-stage inversion method, the fixed extinction method improves the overestimation in the near range but has little effect in the far range. After introducing the RVoG + VTD model, both the overestimation in the near and far range are improved. In general, the study area is affected by both the influence of ground scattering contribution and temporal decorrelation. The overestimation in the near range (with kz larger than ca. 0.1 rad/m) is mainly caused by ground scattering contribution while for the far range (with kz smaller than ca. 0.06 rad/m) temporal decorrelation is the dominated reason. The simulation experiment further reveals the relationship between the influence of ground scattering contribution, temporal decorrelation and kz. Simulative results also show that ground scattering contribution has a greater influence for a large kz while temporal decorrelation generally brings overestimation, and has a greater impact for a small kz inversely. The proposed method simultaneously reduces the effects of ground scattering contribution and temporal decorrelation, and produces the highest accuracy with R2 reaching to ca. 0.6 and RMSE reducing to ca. 3.48 m, further demonstrating its validity for forest height inversion.

Forest Height Estimation from a Robust TomoSAR Method in the Case of Small Tomographic Aperture with Airborne Dataset at L-Band

Forest height is an essential input parameter for forest biomass estimation, ecological modeling, and the carbon cycle. Tomographic synthetic aperture radar (TomoSAR), as a three-dimensional imaging technique, has already been successfully used in forest areas to retrieve the forest height. The nonparametric iterative adaptive approach (IAA) has been recently introduced in TomoSAR, achieving a good compromise between high resolution and computing efficiency. However, the performance of the IAA algorithm is significantly degraded in the case of a small tomographic aperture. To overcome this shortcoming, this paper proposes the robust IAA (RIAA) algorithm for SAR tomography. The proposed approach follows the framework of the IAA algorithm, but also considers the noise term in the covariance matrix estimation. By doing so, the condition number of the covariance matrix can be prevented from being too large, improving the robustness of the forest height estimation with the IAA algorithm. A set of simulated experiments was carried out, and the results validated the superiority of the RIAA estimator in the case of a small tomographic aperture. Moreover, a number of fully polarimetric L-band airborne tomographic SAR images acquired from the ESA BioSAR 2008 campaign over the Krycklan Catchment, Northern Sweden, were collected for test purposes. The results showed that the RIAA algorithm performed better in reconstructing the vertical structure of the forest than the IAA algorithm in areas with a small tomographic aperture. Finally, the forest height was estimated by both the RIAA and IAA TomoSAR methods, and the estimation accuracy of the RIAA algorithm was 2.01 m, which is more accurate than the IAA algorithm with 3.25 m.

How catchment characteristics influence hydrological pathways and travel times in a boreal landscape

Abstract. Understanding travel times and hydrological pathways of rain and snowmelt water transported through the landscape to recipient surface waters is critical in many hydrological and biogeochemical investigations. In this study, a particle-tracking model approach in Mike SHE was used to investigate the pathway and its associated travel time of water in 14 partly nested, long-term monitored boreal sub-catchments of the Krycklan catchment (0.12–68 km2). This region is characterized by long and snow-rich winters with little groundwater recharge and highly dynamic runoff during spring snowmelt. The geometric mean of the annual travel time distribution (MTTgeo) for the studied sub-catchments varied from 0.8 to 2.7 years. The variations were related to the different landscape types and their varying hydrological responses during different seasons. Winter MTTgeo ranged from 1.2 to 7.7 years, while spring MTTgeo varied from 0.5 to 1.9 years. The modelled variation in annual and seasonal MTTgeo and the fraction of young water (<3 months) was supported by extensive observations of both δ18O and base cation concentrations in the different streams. The travel time of water to streams was positively correlated with the area coverage of low-conductive silty sediments (r=0.90, P<0.0001). Catchments with mixed soil–landscape settings typically displayed larger variability in seasonal MTTgeo, as contrasting hydrological responses between different soil types (e.g. peat in mires, till and silty sediments) are integrated. The areal coverage of mires was especially important for the young water contribution in spring (r=0.96, P<0.0001). The main factor for this was attributed to extensive soil frost in mires, causing considerable overland flow during the snowmelt period. However, this lower groundwater recharge during snowmelt caused mire-dominated catchments to have longer stream runoff MTTgeo than comparable forest catchments in winter. Boreal landscapes are sensitive to climate change, and our results suggest that changes in seasonality are likely to cause contrasting responses in different catchments depending on the dominating landscape type.

Northern landscapes in transition: Evidence, approach and ways forward using the Krycklan Catchment Study

AbstractImproving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long‐term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem‐atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere‐atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi‐spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi‐, trans‐, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long‐term monitoring, shorter‐term research projects, and large‐scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.

Partitioning growing season water balance within a forested boreal catchment using sap flux, eddy covariance, and a process-based model

Abstract. Although it is well known that evapotranspiration (ET) represents an important water flux at local to global scales, few studies have quantified the magnitude and relative importance of ET and its individual flux components in high-latitude forests. In this study, we combined empirical sapflux, throughfall, and eddy-covariance measurements with estimates from a process-based model to partition the water balance in a northern boreal forested catchment. This study was conducted within the Krycklan catchment, which has a rich history of hydrological measurements, thereby providing us with the unique opportunity to compare the absolute and relative magnitudes of ET and its flux components to other water balance components. During the growing season, ET represented ca. 85 % of the incoming precipitation. Both empirical results and model estimates suggested that tree transpiration (T) and evaporation of intercepted water from the tree canopy (IC) represented 43 % and 31 % of ET, respectively, and together were equal to ca. 70 % of incoming precipitation during the growing season. Understory evapotranspiration (ETu) was less important than T and IC during most of the study period, except for late autumn, when ETu was the largest ET flux component. Overall, our study highlights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes.

Policy change implications for forest water protection in Sweden over the last 50\xa0years

Improving water quality has become an important environmental issue, spurred in part by the Water Framework Directive. However, the relationship of policy change with forest water protection measures is relatively unknown. We analyzed how policy and practice have developed in Sweden using 50 years of historic data from the Krycklan Catchment Study, focusing on riparian buffers. Corresponding to legislation, education and voluntary measures emphasizing stream protection, two step changes occurred; between the 1970s–1980s, buffers increased by 67%, then by 100% between 1990s and 2000s. By 2013, just 50% of the stream length affected by forestry was protected and the application has varied by stream size; small streams lacked a buffer approximately 65% of the time, while 90% of large streams had buffers. The doubling of buffer implementation from the 1990s–2000s corresponded to the adoption of a number of environmental protection policies in the 1990s that all came into effect during this period.

Detecting Cultural Remains in Boreal Forests in Sweden Using Airborne Laser Scanning Data of Different Resolutions

ABSTRACTAirborne laser scanning (ALS) is increasingly being used to detect cultural remains in forest landscapes. Boreal forests are challenging, however, since most ancient land use was carried out without major permanent ground disturbances. If this challenge can be met, there is a large potential for surveys through existing nation-wide laser-scanning programs, although their resolutions tend to be low. In this study, we compare the performance of low-resolution (LR) and high-resolution (HR) ALS data in the Krycklan catchment in northern Sweden, an area where ancient land use was small-scale and diverse. About three times as many cultural remains were detected in the HR data set, but the LR set was satisfactory for distinct structures. We analyze how LR data sets can be enhanced at ground-point classification and terrain-model generation and conclude that ALS data have a large potential for the detection and protection of cultural remains in the boreal forest.

Eu anomalies in soils and soil water from a boreal hillslope transect – A tracer for Holocene lanthanide transport?

Concentrations of lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Lu) were measured in soils and soil water from a hillslope transect in the Krycklan catchment in northern Sweden. Soil water was collected at different depths and at different distances from the draining stream – from the uphill Podzol to the peaty riparian zone – throughout the course of a year. Combined with soil profiles from the same sites this provided a comprehensive dataset to study the fractionation and transport of lanthanides from boreal forest soils to streams. The soil water was characterised by high concentrations of lanthanides in the riparian zone, more than an order of magnitude higher than in the uphill mineral soil, and when normalised against local unweathered till the soil water exhibited distinctly negative Eu anomalies, particularly in deeper soil layers. The soil samples displayed both positive and negative Eu anomalies, but positive Eu anomalies were primarily associated with strongly weathered soils, whereas negative soil Eu anomalies were observed in organic soils at depths were large amounts of lanthanides are transported towards the stream. Since reduction of Eu seems unlikely to occur in this transect, we propose that the Eu anomalies in soils and soil water are caused by the partial occurrence of Eu in more weathering-resistant minerals than the other lanthanides. Based on the collected data and the hydrological and biogeochemical understanding of the studied transect we therefore propose a conceptual model for how Eu anomalies arise and how they can be used to interpret the Holocene transport and accumulation of lanthanides in soils. The results suggest that Eu anomalies have the potential to become a powerful tracer for studying weathering and soil development.

Seasonal trends of legacy and alternative flame retardants in river water in a boreal catchment.

Boreal forests store large amounts of atmospherically deposited (semi-)persistent organic pollutants (POPs). The terrestrial POPs may be exported to streams and rivers through processes that are heavily impacted by seasonality. In this screening study, concentrations of 4 legacy and 45 alternative flame retardants (FRs) were determined in the dissolved and particulate phase in streams within a relatively pristine boreal catchment in northern Europe (Krycklan Catchment Study; 3 sites) and in rivers more impacted by human activities further downstream towards the Baltic Sea (3 sites). The sampling included the main hydrological seasons (snow-free, snow-covered, and spring flood) and was conducted during two consecutive years (2014-2016). Of the 49 analyzed FRs, 11 alternative halogenated FRs (HFRs), 13 alternative organophosphorus FRs (OPFRs), and 4 legacy polybrominated diphenyl ethers (PBDEs) were detected in at least one sample. The average bulk (dissolved + particulate) concentrations of ∑FRs (including all sites) were highest for ∑HFRs (38 ± 70 ng L-1), followed by the ∑OPFRs (3.9 ± 4.9 ng L-1) and the ∑PBDEs (0.0040 ± 0.016 ng L-1). Bulk concentrations of HFRs, OPFRs, and PBDEs were highly variable with season and sampling location, e.g., during spring flood, bulk concentrations were up to 600 times, 3.7 times, and 4.9 times higher for HFRs, OPFRs and PBDEs, respectively, than during periods of lower flow. Bulk concentrations of ∑OPFRs, were elevated at all sites ~6 days before the actual start of the spring flood in 2015, suggesting that hydrophobicity fractionation had occurred within the snowpack. Similar to previous studies of other POPs in the same headwater catchment, there was a general trend that levels of ∑FRs were higher at the mire site than at the forested site. Annual fluxes of FRs were found to be ~15 times higher downstream the city of Umeå compared to at the outlet of the pristine catchment. This study should be regarded as a screening study considering the large number of diverse FRs analyzed and variability in the results.

Forest Above-Ground Biomass Estimation Using Single-Baseline Polarization Coherence Tomography with P-Band PolInSAR Data

Forest above ground biomass (AGB) extraction using Synthetic Aperture Radar (SAR) images has been widely used in global carbon cycle research. Classical AGB inversion methods using SAR images are mainly based on backscattering coefficients. The polarization coherence tomography (PCT) technology which can generate vertical profiles of forest relative reflectivity, has the potential to improve the accuracy of biomass inversion. The relationship between vertical profiles and forest AGB is modeled by some parameters defined based on geometric characteristics of the relative reflectivity distribution curve. But these parameters are defined without physical characteristics. Among these parameters, tomographic height (TomoH) is considered as the most important one. However, TomoH only corresponds to the highest volume relative reflectivity, which is lower than the actual forest height, affecting the accuracy of forest height and AGB inversion. In this paper, we introduce a new parameter, the canopy height (Hac), for AGB inversion by analyzing the vertical backscatter power loss. Then, we construct an inversion model based on the combination of the new parameter (Hac) and other parameters from the tomographic profile. The P-band polarimetric SAR datasets of the European Space Agency (ESA) BioSAR 2008 campaign acquired over Krycklan Catchment are selected for the verification experiment at two different flight directions. The results show that Hac performs better in estimating forest height and AGB than TomoH does. The inversion root mean square error (RMSE) of the proposed method is 18.325 t ha−1, and the result of using TomoH is 21.126 t ha−1.

Groundwater-surface water interactions across scales in a boreal landscape investigated using a numerical modelling approach

Groundwater and surface-water interactions are regulated by catchment characteristics and complex inter- and intra-annual variations in climatic conditions that are not yet fully understood. Our objective was to investigate the influence of catchment characteristics and freeze-thaw processes on surface and groundwater interactions in a boreal landscape, the Krycklan catchment in Sweden. We used a numerical modelling approach and sub-catchment evaluation method to identify and evaluate fundamental catchment characteristics and processes. The model reproduced observed stream discharge patterns of the 14 sub-catchments and the dynamics of the 15 groundwater wells with an average accumulated discharge error of 1% (15% standard deviation) and an average groundwater-level mean error of 0.1 m (0.23 m standard deviation). We show how peatland characteristics dampen the effect of intense rain, and how soil freeze-thaw processes regulate surface and groundwater partitioning during snowmelt. With these results, we demonstrate the importance of defining, understanding and quantifying the role of landscape heterogeneity and sub-catchment characteristics for accurately representing catchment hydrological functioning.

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

Catchment science plays a critical role in the protection of water resources in the face of ongoing changes in climate, long‐range transport of air pollutants, and land use. Addressing these challenges, however, requires improved understanding of how, when, and where changes in water quantity and quality occur within river networks. To reach these goals, we must recognize how different catchment features are organized to regulate surface chemistry at multiple scales, from processes controlling headwaters, to the downstream mixing of water from multiple landscape sources and deep aquifers. Here we synthesize 30‐years of hydrological and biogeochemical research from the Krycklan catchment study (KCS) in northern Sweden to demonstrate the benefits of coupling long‐term monitoring with multi‐scale research to advance our understanding of catchment functioning across space and time. We show that the regulation of hydrological and biogeochemical patterns in the KCS can be decomposed into four, hierarchically structured landscape features that include: (1) transmissivity and reactivity of dominant source layers within riparian soils, (2) spatial arrangement of groundwater input zones that govern water and solute fluxes at reach‐ to segment‐scales, (3) landscape scale heterogeneity (forests, mires, and lakes) that generates unique biogeochemical signals downstream, and (4) broad‐scale mixing of surface streams with deep groundwater contributions. While this set of features are perhaps specific to the study region, analogous hierarchical controls are likely to be widespread. Resolving these scale dependent processes is important for predicting how, when, and where different environmental changes may influence patterns of surface water chemistry within river networks. WIREs Water 2018, 5:e1265. doi: 10.1002/wat2.1265This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water and Environmental Change Science of Water > Methods

Identifying and assessing the potential hydrological function of past artificial forest drainage

Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km2 Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178–327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25–50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.

From soil water to surface water – how the riparian zone controls element transport from a boreal forest to a stream

Abstract. Boreal headwaters are often lined by strips of highly organic soils, which are the last terrestrial environment to leave an imprint on discharging groundwater before it enters a stream. Because these riparian soils are so different from the Podzol soils that dominate much of the boreal landscape, they are known to have a major impact on the biogeochemistry of important elements such as C, N, P and Fe and the transfer of these elements from terrestrial to aquatic ecosystems. For most elements, however, the role of the riparian zone has remained unclear, although it should be expected that the mobility of many elements is affected by changes in, for example, pH, redox potential and concentration of organic carbon as they are transported through the riparian zone. Therefore, soil water and groundwater was sampled at different depths along a 22 m hillslope transect in the Krycklan catchment in northern Sweden using soil lysimeters and analysed for 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 sulfate and total organic carbon (TOC). The results showed that the concentrations of most investigated elements increased substantially (up to 60 times) as the water flowed from the uphill mineral soils and into the riparian zone, largely as a result of higher TOC concentrations. The stream water concentrations of these elements were typically somewhat lower than in the riparian zone, but still considerably higher than in the uphill mineral soils, which suggests that riparian soils have a decisive impact on the water quality of boreal streams. The degree of enrichment in the riparian zone for different elements could be linked to the affinity for organic matter, indicating that the pattern with strongly elevated concentrations in riparian soils is typical for organophilic substances. One likely explanation is that the solubility of many organophilic elements increases as a result of the higher concentrations of TOC in the riparian zone. Elements with low or modest affinity for organic matter (e.g. Na, Cl, K, Mg and Ca) occurred in similar or lower concentrations in the riparian zone. Despite the elevated concentrations of many elements in riparian soil water and groundwater, no increase in the concentrations in biota could be observed (bilberry leaves and spruce shoots).