Human impact in the form of reservoir construction and river regulation downstream of reservoirs, is causing irreversible alterations to hillslope and river channel connectivity in river catchments. This disruption in the dynamic equilibrium of the river is attributed to sediment accumulation upstream of the reservoir's dam, limited sediment outflow from the reservoir, and increased downcutting downstream of the dam. Consequently, these alterations necessitate further human interference in natural environmental processes through the construction of various river engineering structures designed to reduce the intensity of downcutting. The purpose of the present study was to assess the impact of a small mountain reservoir and additional river regulation structures on the Wapienica River in southern Poland, focusing on the structural and functional connectivity of the river channel in terms of sediment transfer. This assessment was based on erosion and connectivity modeling, as well as field mapping. A high-resolution digital elevation model (HRDEM) was examined in the study along with survey data on suspended sediment accumulation sites along the river. The study utilized open-source tools, including SedInConnect for connectivity index (IC) calculation, and the Soil and Water Assessment Tool (SWAT) for ArcGIS software. It was found that the Wapienica reservoir permanently retains the floating material, making the likelihood of this material flowing out of the reservoir minimal. Within the reverse delta of the reservoir, the entire load of bottom material (sand) is also retained. Thicker bottom material (gravel, boulders) is deposited in the riverbed within the delta, leading to the shallowing of the bed upstream of the delta. These processes disrupt longitudinal connectivity. Six connectivity zones have been identified within the catchment. The first four are situated in the southern part of the catchment: strong connectivity, reduction, concrete channel, and damage area. The remaining two, situated in the northern part are: artificial channel and drainage channels. Each of the six zones is characterized by different sediments and river processes. It was demonstrated that a more detailed and more probably connectivity pattern for hillslopes and river channels may be obtained through the use of several tools and parameters at the same time (i.e., fieldwork, SWAT, IC).

Soil erosion is an important driver of land and ecological degradation, with hydraulic erosion in particular leading to widespread impacts and damage. As an important concept and indicator for characterizing the potential and pathways of sediment production and transportation within watersheds or on slopes, sediment connectivity has gained global attention and thus been analysed since its proposal in 2003. Sediment connectivity has become an effective metric for analysing the sources, processes, and potentials of soil erosion and sediment yield (SY) in watersheds, and it has been considered a popular research topic in the field of soil erosion over the past decade. Considering the lack of up-to-date systematic reviews of conceptual connotations, characterization indicators for sediment connectivity, and quantitative relationships between these indicators and erosion and SY, a bibliometric analysis of sediment connectivity was conducted via the CiteSpace tool, which is based on the Web of Science (WOS), Scopus (Elsevier) and China National Knowledge Infrastructure (CNKI) databases. In this research, the current state, popular topics, and trends in relevant studies were identified, and the conceptual connotations, influencing factors, and indicator algorithms of sediment connectivity and their quantitative relationships with soil erosion and SY were summarized. Furthermore, the contents and directions to be strengthened and improved in the future were determined. The results indicated that over the past 21 years, sediment connectivity has been analysed in 123 countries or regions. Researches have focused primarily on related concepts, indicators, scales, and influencing factors. This concept has been widely applied in various practices such as soil and water resource regulation, land use optimization, and soil erosion control. In previous studies, several linear (SY = a center dot IC + b) and exponential (SY = a center dot eb center dot IC) increasing relationships between sediment connectivity indicators (such as the index of connectivity (IC)) and SY at the slope or watershed scale have been established, facilitating the development of research on prediction and attribution analysis for the identification of sediment sources and changes. There is a consensus on what sediment connectivity is to date, but a unified and complete system has not been yet formed for sediment connectivity and several of its derived concepts. The Index of Connectivity (IC), as the primary means for quantitatively characterizing the status and distribution of sediment connectivity, has led to the creation of more than 20 different algorithms, whereas the included parameters mainly reflect the internal factors influencing topography and land use/cover. The effects of climatic factors and human activities have not been fully considered in previous studies, which has led to relatively backwards researching on functional connectivity indicators. Hence, the classification systems and theoretical frameworks for a series of concepts must be further refined on the basis of sediment connectivity, such as the objective openness, scale dependence, comprehensive impact, and distribution heterogeneity. Moreover, the amount of research on the influences of external drivers and the coupled effects of different factors on indicators of sediment connectivity should be increased. Nevertheless, it is still necessary to explore certain aspects, such as the parameter combinations and normalization methods of the upslope and downslope components of the IC algorithm, and to continuously improve the explanation of the dynamic changes in sediment while considering both hydrological connections along flow paths and off-site impacts on underlying surface variations. Moreover, there is a need to increase the spatiotemporal scale of research on sediment connectivity, explore its feedback mechanisms and close quantitative relationships with soil erosion and SY, focus on the integrated application of different indicators (methods), and validate and results via multisource information to promote relevant applications. The obtained results provide valuable reference for the refinement of theories and methods for sediment connectivity and enhance its support of studies of soil erosion and SY in watersheds.

This study investigates the impact of fabric anisotropy on the directional filtration mechanisms in granular filters, which arise from inherent particle shape variations and different preparation methods. Using the discrete element method, diverse filter samples underwent extensive numerical filtration tests in different directions. Subsequently, the pore space of these samples was analysed using an extraction algorithm. The results highlight the significant influence of particle shapes and preparation methods on intensifying anisotropy, which in turn remarkably affects directional filtration properties. Analysis of the pore space reveals variations in pore connectivity across different directions, explaining the observed differences in retention coefficients. This study emphasises the need for a comprehensive approach that accounts for constriction size, number, and connectivity to yield precise results. It contributes valuable insights into the role of anisotropy in granular materials, sheds light on complex directional filtration mechanisms, and advances related applications.

In many soil processes, including solute and gas dynamics, the architecture of intra-aggregate pores is a crucial component. Soil management practices and wetting-drying (W-D) cycles, the latter having a significant impact on pore aggregation, are two key factors that shape pore structure. This study examines the effects of W-D cycles on the architecture of intra-aggregate pores under three different soil management systems: no-tillage (NT), minimum tillage (MT), and conventional tillage (CT). The soil samples were subjected to 0 and 12 W-D cycles, and the resulting pore structures were scanned using X-ray micro-computed tomography, generating reconstructed 3D volumetric data. The data analyses were conducted in terms of multifractal spectra, normalized Shannon entropy, lacunarity, porosity, anisotropy, connectivity, and tortuosity. The multifractal parameters of capacity, correlation, and information dimensions showed mean values of approximately 2.77, 2.75, and 2.75 when considering the different management practices and W-D cycles; 3D lacunarity decreased mainly for the smallest boxes between 0 and 12 W-D cycles for CT and NT, with the opposite behavior for MT. The normalized 3D Shannon entropy showed differences of less than 2% before and after the W-D cycles for MT and NT, with differences of 5% for CT. The imaged porosity showed reductions of approximately 50% after 12 W-D cycles for CT and NT. Generally, the largest pores (>0.1 mm3) contributed the most to porosity for all management practices before and after W-D cycles. Anisotropy increased by 9% and 2% for MT and CT after the cycles and decreased by 23% for NT. Pore connectivity showed a downward trend after 12 W-D cycles for CT and NT. Regarding the pore shape, the greatest contribution to porosity and number of pores was due to triaxial-shaped pores for both 0 and 12 W-D cycles for all management practices. The results demonstrate that, within the resolution limits of the microtomography analysis, pore architecture remained resilient to changes, despite some observable trends in specific parameters.

This study proposes a new approach for analyzing images of the internal structure of soil (microtomograms) and modeling key hydrophysical functions based on the tomographic characteristics of the pore space. The approach is based on constructing a series of closed shells (alpha-shapes) around the studied three-dimensional of the tomogram. These shells are capable of penetrating into the pores of the object with a diameter greater than a specified value. The dependence of the internal volume of the shells on the minimum pore size is analyzed. The algorithm of alpha-shapes construction simulates the process of drying pores connected to the surface and allows for analyzing the anisotropy of pore connectivity by limiting the permeability of a part of the object's surface. The constructed alpha-shapes model the surface of the liquid phase, and the maximum curvature of the surface corresponds to the capillary pressure. The approach is applied to analyze samples of the soil microprofile of a crusty solonetz with a contrasting pore space structure. The microhorizons of the solonetz demonstrate pronounced closed porosity and anisotropy of pore connectivity. The approach allows for the assessment of connectivity and anisotropy of pores, the water retention curve (WRC) without considering soil shrinkage. The results were compared with typical known WRCs of solonetzic soil horizons in soils of Russia. A comparison of WRC models obtained based on 2D and 3D images was conducted. The method was also tested on tomograms of samples of aeolian laminated sandstone, for which both tomograms and direct WRC measurements were simultaneously available.

The traditional view of Na+ as harmful and Ca2+ as beneficial doesn't always apply in multi-cationic soil solutions. Initially, adding Ca2+ promotes Na+ leaching, reducing salinity, but excess Ca2+ becomes counterproductive. As Na+ leaches, the soil's Ca2+-Na+-Mg2+ mix shifts to Ca2+-K2+-Mg2+, Ca2+'s function changes, even causing the opposite effect. To investigate the complex mechanism of Ca2+ to Na+-Mg2+ and K+-Mg2+, we conducted an indoor soil column experiment using saline water (4 dS m(-1)) with different cation compositions [Na+-Ca2+-Mg2+ (NCM), Na+-Mg2+ (NM), K+-Ca2+-Mg2+ (KCM), K+-Mg2+ (KM)] and deionized water as the control (CK). The results showed that NM exhibited the highest crack volume, while KM had the greatest macropore volume, with NM having approximately 15 % more crack volume than KM. Notably, only NM displayed a more pronounced inclination towards pore anisotropy value of 0 when compared to CK. NCM and KCM had higher pore anisotropy values than NM and KM. KM and KCM had more cracks angled ranging from 45-90 degrees than NM and NCM. KCM notably decreased transitional macropores 0.05) observed in widths < 2.5 mm between KCM and KM. NM displayed the shallowest macropore distribution and the highest variability in macropore length among all treatments. Only NCM showed significantly reduced variability in both macropore length and width compared to CK. In summary, Ca2+ exhibited distinct action patterns on K+-Mg2+ and Na+-Mg2+. For specific soil types and cationic compositions, Ca2+ may not fully exert its amendment effects. However, Ca2+'s effect is soil-specific, necessitating comprehensive studies across varied soil types.

On the Arctic Coastal Plain (ACP) in northern Alaska (USA), permafrost and abundant surface-water storage define watershed hydrological processes. In the last decades, the ACP landscape experienced extreme climate events and increased lake water withdrawal (LWW) for infrastructure construction, primarily ice roads and industrial operations. However, their potential (combined) effects on streamflow are relatively underexplored. Here, we applied the process-based, spatially distributed hydrological and thermal Water Balance Simulation Model (10 m spatial resolution) to the 30 km(2) Crea Creek watershed located on the ACP. The impacts of documented seasonal climate extremes and LWW were evaluated on seasonal runoff (May-August), including minimum 7-day mean flow (MQ7), the recovery time of MQ7 to pre-perturbation conditions, and the duration of streamflow conditions that prevents fish passage. Low-rainfall scenarios (21% of normal, one to three summers in a row) caused a larger reduction in MQ7 (-56% to -69%) than LWW alone (-44% to -58%). Decadal-long consecutive LWW under average climate conditions resulted in a new equilibrium in low flow and seasonal runoff after 3 years that included a disconnected stream network, a reduced watershed contributing area (54% of total watershed area), and limited fish passage of 20 days (vs. 6 days under control conditions) throughout summer. Our results highlight that, even under current average climatic conditions, LWW is not offset by same-year snowmelt as currently assumed in land management regulations. Effective land management would therefore benefit from considering the combined impact of climate change and industrial LWWs.

Climate change in Arctic landscapes may increase freeze-thaw frequency within the active layer as well as newly thawed permafrost. Freeze-thaw is a highly disruptive process that can deform soil pores and alter the architecture of the soil pore network with varied impacts to water transport and retention, redox conditions, and microbial activity. Our objective was to investigate how freeze-thaw cycles impacted the pore network of newly thawed permafrost aggregates to improve understanding of what type of transformations can be expected from warming Arctic landscapes. We measured the impact of freeze-thaw on pore morphology, pore throat diameter distribution, and pore connectivity with X-ray computed tomography (XCT) using six permafrost aggregates with sizes of 2.5 cm3 from a mineral soil horizon (Bw; 28-50 cm depths) in Toolik, Alaska. Freeze-thaw cycles were performed using a laboratory incubation consisting of five freeze-thaw cycles (-10 C to 20 C) over five weeks. Our findings indicated decreasing spatial connectivity of the pore network across all aggregates with higher frequencies of singly connected pores following freeze-thaw. Water-filled pores that were connected to the pore network decreased in volume while the overall connected pore volumetric fraction was not affected. Shifts in the pore throat diameter distribution were mostly observed in pore throats ranges of 100 mu m or less with no corresponding changes to the pore shape factor of pore throats. Responses of the pore network to freeze-thaw varied by aggregate, suggesting that initial pore morphology may play a role in driving freeze-thaw response. Our research suggests that freeze-thaw alters the microenvironment of permafrost aggregates during the incipient stage of deformation following permafrost thaw, impacting soil properties and function in Arctic landscapes undergoing transition.

Under a warming climate, permafrost degradation has resulted in profound hydrogeological consequences. Here, we mainly review 240 recent relevant papers. Permafrost degradation has boosted groundwater storage and discharge to surface runoffs through improving hydraulic connectivity and reactivation of groundwater flow systems, resulting in reduced summer peaks, delayed autumn flow peaks, flattened annual hydrographs, and deepening and elongating flow paths. As a result of permafrost degradation, lowlands underlain by more continuous, colder, and thicker permafrost are getting wetter and uplands and mountain slopes, drier. However, additional contribution of melting ground ice to groundwater and stream-flows seems limited in most permafrost basins. As a result of permafrost degradation, the permafrost table and supra-permafrost water table are lowering; subaerial supra-permafrost taliks are forming; taliks are connecting and expanding; thermokarst activities are intensifying. These processes may profoundly impact on ecosystem structures and functions, terrestrial processes, surface and subsurface coupled flow systems, engineered infrastructures, and socioeconomic development. During the last 20 years, substantial and rapid progress has been made in many aspects in cryo-hydrogeology. However, these studies are still inadequate in desired spatiotemporal resolutions, multi-source data assimilation and integration, as well as cryo-hydrogeological modeling, particularly over rugged terrains in ice-rich, warm (>-1 degrees C) permafrost zones. Future research should be prioritized to the following aspects. First, we should better understand the concordant changes in processes, mechanisms, and trends for terrestrial processes, hydrometeorology, geocryology, hydrogeology, and ecohydrology in warm and thin permafrost regions. Second, we should aim towards revealing the physical and chemical mechanisms for the coupled processes of heat transfer and moisture migration in the vadose zone and expanding supra-permafrost taliks, towards the coupling of the hydrothermal dynamics of supra-, intra- and sub-permafrost waters, as well as that of water-resource changes and of hydrochemical and biogeochemical mechanisms for the coupled movements of solutes and pollutants in surface and subsurface waters as induced by warming and thawing permafrost. Third, we urgently need to establish and improve coupled predictive distributed cryo-hydrogeology models with optimized parameterization. In addition, we should also emphasize automatically, intelligently, and systematically monitoring, predicting, evaluating, and adapting to hydrogeological impacts from degrading permafrost at desired spatiotemporal scales. Systematic, in-depth, and predictive studies on and abilities for the hydrogeological impacts from degrading permafrost can greatly advance geocryology, cryo-hydrogeology, and cryo-ecohydrology and help better manage water, ecosystems, and land resources in permafrost regions in an adaptive and sustainable manner.

Climate change in the Arctic leads to permafrost degradation and to associated changes in freshwater geochemistry. There is a limited understanding of how disturbances such as active layer detachments or retrogressive thaw slumps impact water quality on a catchment scale. This study investigates how permafrost degradation affects concentrations of dissolved organic carbon (DOC), total dissolved solids (TDS), suspended sediment, and stable water isotopes in adjacent Low Arctic watersheds. We incorporated data on disturbance between 1952 and 2015, as well as sporadic runoff and geochemistry data of streams nearby. Our results show that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66% in all six catchments. The spatial variability of hydrochemical parameters is linked to catchment properties and not necessarily reflected at the outflow. Degrading ice-wedge polygons were found to increase DOC concentrations upstream in Ice Creek West, whereas hydrologically connected disturbances were linked to increases in TDS and suspended sediment. Although we found a great spatial variability of hydrochemical concentrations along the paired watershed, there was a linear relationship between catchment size and daily DOC, total dissolved nitrogen, and TDS fluxes for all six streams. Suspended sediment flux on the contrary did not show a clear relationship as one hydrologically connected retrogressive thaw slump impacted the overall flux in one of the streams. Understanding the spatial variability of water quality will help to model the lateral geochemical fluxes from Arctic catchments. Plain Language Summary One effect climate change has in the Arctic is the thawing of permafrost. Permafrost is defined as ground that remains below 0 degrees C for at least two consecutive years. The low temperatures in the High North lead to very slow decomposition rates of organic material from plants and animals. A lot of this material has accumulated over thousands of years. As air temperatures in the Arctic are rising, permafrost is thawing. This is also termed permafrost degradation. It can occur in two forms: (1) The gradual deeper thawing of permafrost is called thermal perturbation. It might lead to a subsidence (sinking) of the ground, because water that was previously frozen runs off. (2) Thawing of the ground may lead to a destabilization of the ground and connected landslides. This is termed physical or surface disturbance. These two forms of permafrost degradation have an impact on the water quality of rivers flowing through the terrain. In this study, we investigated the impacts of permafrost degradation on stream hydrochemistry on Herschel Island, Yukon Territory, Canada. We identified active physical disturbances in the past using aerial photographs from 1952 and 1970 and satellites images from 2011 and 2015. This was done for the areas from which rainwater flows into the same river (catchment area) of six streams named Water Creek, Beach Creek, Fox Creek, Ice Creek West, Ice Creek East, and Eastern Gully. In 2016, we collected water samples along two neighboring streams (Ice Creek West and Ice Creek East) to compare the impacts of local physical disturbances on the hydrochemistry. In these two streams, we also measured water flow (discharge) during the monitoring season. We further collected samples at the outflow of the other four streams nearby. Water samples were analyzed in the laboratory for different chemical properties that help us to understand the influence of permafrost degradation. For the six streams, we found that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66%. We were able to link permafrost degradation to changes in chemical water composition within the two neighboring streams. It is important that disturbances are hydrologically connected to impact concentrations of inorganic compounds (total dissolved solids) and mud (suspended sediment) in the streams. Essentially, this means that water needs to flow through these disturbances to mobilize the material and influence the concentration in the stream. Taking all studied streams together, the overall flux of dissolved organic carbon, total dissolved solids, and total dissolved nitrogen (i.e., the amount of chemical compound [in kg] transported away in every liter of river water) depends on catchment size. The larger the catchment, the more of this material is transported away. This relationship could not be confirmed for suspended sediment, because a hydrologically connected retrogressive thaw slump heavily impacted the flux in one of the streams. This study is important because the river water ultimately drains into the Arctic Ocean and might change the water quality there. This may have consequences for the animals and plants living in the ocean. We need to understand the influence of permafrost degradation on stream water quality to assess future changes of the Arctic Ocean. Key Points Between 1952 and 2015, the total disturbed area decreased by 41%, and the number of disturbances increased by 66% Hydrological connectivity of permafrost disturbances is essential to impact suspended sediment and solute concentrations in the stream There is a linear relationship between catchment size and daily flux of dissolved organic carbon, total dissolved nitrogen, and solutes