Alluvial Fan Research Articles

Possible linkage between Paleolithic site occurrence and past climate change in the central Korean Peninsula

AbstractKorea's Paleolithic sites are primarily located in riverine environments and the margins of alluvial fans. More than 100 Paleolithic excavations have been conducted in the Korean Peninsula, but the relationship between the locations of these sites and past climate change has received little attention. In this study, we investigated this relationship at a Paleolithic site in Wonju city, Korea, that contained two cultural layers and yielded a total of 336 stone artifacts. The lithological units present at the site indicate that the sedimentary environment changed from a riverine sandy channel to an alluvial plain owing to channel migration at the Marine Isotope Stage (MIS) 4. The alluvial plain sediments deposited during MIS 4–2 are characterized by low sand content (<5%) and two soil wedges. Most Paleolithic artifacts were excavated from the upper soil wedge, deposited during MIS 3 under relatively warm and wet conditions associated with global climatic changes (as indicated by sea level or continental ice volume) and the East Asian summer monsoon. The number of Paleolithic cultural layers increases in late MIS 3 in other regions, suggesting that climate conditions are an essential factor in the development of Paleolithic cultural layers.

Targeting the source of fine sediment and associated geochemical elements by using novel fingerprinting methods in proglacial tropical highlands (Cordillera Blanca, Perú)

AbstractIn the Cordillera Blanca, the glaciers delineated by some of the highest peaks in the tropical Peruvian Andes have experienced a fast retreat over the last few decades. At the foot of Artesonraju Peak, the glacier‐fed river conveys fine sediments to Parón Lake, which is enclosed in the proglacial area created by the retreating glaciers of the unique confluence of the Huandoy, Chacraraju, Nevado Caraz and Artesonraju peaks (above 6000 m.a.s.l.). This research addresses the sediment contributions of main glacial landforms to sediment mixtures delivered to the river and lake system (1.6 km2) by applying novel conservativeness and consistency methods for tracer selection and a frequentist unmixing model. A total of 27 surface soil and sediment sources (0–3 cm) were sampled from moraines, alluvial fans and recent colluvium, and 10 composite sediment mixtures, including suspended sediments, were collected to identify the sediment provenance. The unmixing results reveal large variability of the contributing sources related to their predominance and the locations of the mixtures. The largest contributions were from moraines, in percentages varying from 28% to as much as 77%. Alluvial fans contributed between 23% and 47% of the sediments, and colluvium material contributed the least, between 6% and 28%. At the time of sampling, ice melt discharge incising moraines and alluvial fans and eroding riverbanks were the main mechanisms of fine sediment delivery. Runoff over the bare surfaces of recently exposed moraines and the lack of vegetation cover in very active landforms also control sediment mobilization. Overall, highly dynamic changes in this paraglacial environment involve active sediment fluxes accompanying snow and ice melt. Our results indicate that in high tropical mountains, shrinking glaciers expose new surfaces of glacial materials, which deliver fine sediments. Identifying the contributing sources is of interest for water and sediment evaluation and management programs.

Drainage congestion due to road network on the Kosi alluvial Fan, Himalayan Foreland

We use surface soil moisture content as a proxy to assess the effect of drainage congestion due to structural barriers on the alluvial Fan of the Kosi River on the Himalayan Foreland. We used Sentinel-1 satellite images to evaluate the spatial distribution of soil moisture in the proximity of structural barriers (i.e., road network). We applied modified Dubois and a fully connected feed-forward artificial neural network (FC-FF-ANN) models to estimate soil moisture. We observed that the FC-FF-ANN predicts soil moisture more accurately (R = 0.85, RMSE = 0.05 m3/m3, and bias = 0) as compared to the modified Dubois model. Therefore, we have used the soil moisture from the FC-FF-ANN model for further analysis. We identified the road network that traverses on the Kosi Fan horizontally, vertically, and with inclination. We create a buffer of 1 km along either side of the road. Within this, we assessed the spatial distribution of soil moisture. We observed a high concentration of soil moisture near the structural barrier, and decreases gradually as we move farther in either direction across the orientation of the road. The impact of structural barriers on the spatial distribution of soil moisture is prominent in a range between 300 to 750 m within the road buffer. This study is a step towards assessing the effect of structural interventions on drainage congestion and flood inundation.

The formation and sedimentary evolution of the Hutuohe River and its piedmont alluvial fan in the North China Plain

The formation and sedimentary evolution of the Hutuohe River and its piedmont alluvial fan in the North China Plain

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin, Qinghai-Tibet Plateau

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin, Qinghai-Tibet Plateau

Evaluating the effectiveness of heavy liquid density separation in isolating K-feldspar grains using alluvial sediments from the Hajar Mountains, Oman

Heavy liquid density separation is commonly utilised in isolating specific minerals from bulk sediment for luminescence dating. K-feldspars are commonly separated from other minerals by isolating the <2.58 g cm −3 fraction which yields infrared stimulated luminescence (IRSL) signals conducive to dating. However, initial measurements of the IRSL and thermoluminescence (TL) signals from the <2.58 g cm −3 fraction of alluvial fan sediments from the Hajar Mountains, northern Oman, were atypical of K-feldspar luminescence signals reported in the literature. In this study, three different density separates (<2.58 g cm −3 , 2.58–2.54 g cm −3 and <2.565 g cm −3 ) were trialled to attempt to isolate pure K-feldspar samples for dating, to measure K-feldspar IRSL signals which are not contaminated with inputs from other feldspar, quartz and/or heavy mineral signals. The mineralogy of these separates was explored using microscopy, X-ray diffraction and mass spectrometry. We found that despite more refined heavy liquid density separation, the proportions of K-feldspar in these separates had a maximum of 40% by weight, remaining significantly contaminated by other minerals. IRSL and TL signals were atypical of K-feldspar for all density separates and it is likely that there is a contribution of signal from IR-sensitive contaminants, such as muscovite. This highlights the importance of investigating the mineralogy of samples for luminescence dating, especially in regions where little prior work has been undertaken. • K-feldspar fractions remained highly contaminated across the three different density separations applied. • Highlights the need to test the mineralogical purity of samples resulting from standard density separation techniques. • This is particularly important where the signal contributions of IRSL-sensitive contaminants may be relatively greater.

Rates and processes controlling periglacial alluvial fan formation: Implications for martian fans

Abstract Alluvial fans are found across a range of climates and are built from a combination of fluvial and debris flow processes. Correct identification of process is critical to reconstructing the climate and water histories of alluvial fans on Earth and Mars. Theory and data from subaerial Earth fans are often used to estimate paleoflow discharges and sediment fluxes for martian fans; however, most terrestrial work has been conducted on fans that are in hot, dry climates with runoff sourced from rainfall. This differs from the prevailing interpretation that martian fans were sourced from snowmelt under warming periglacial conditions. To characterize processes and rates of periglacial fan formation, we conducted a field-based study of the Black Mountain alluvial fan in the Aklavik Range, Canada. We observed active fluvial bedload transport as well as several small debris flows that had initiated from ice-filled gullies. Following a runoff event of ~0.005 mm/hr to ~0.2 mm/hr across the fan, we estimated sediment fluxes of ~0.04 m3/hr. Under bankfull conditions, we estimated runoff rates between ~0.01 mm/hr to ~14 mm/hr and corresponding sediment fluxes of ~0.3 m3/hr to ~550 m3/hr. This suggests that moderate flow events, well below the maximum runoff production rates suggested for Mars, are capable of entraining and transporting appreciable amounts of sediment by fluvial processes. However, sedimentological and geomorphological observations suggest that ~67% of the fan was deposited fluvially; the remainder was deposited by mass flows. Our results emphasize the need to take care in interpreting martian sedimentary processes and climate from fan surface morphology alone.

Simulation-optimization model for groundwater replenishment from the river: a case study in the Hutuo River alluvial fan, China

AbstractEcological water replenishment (EWR) has been widely implemented for the restoration of the groundwater resources in the North China Plain since 2018, and the Hutuo River is one of the typical rivers. Recovering the groundwater storage capacity while ensuring the safety of the existing land use is essential for groundwater management. To simulate the groundwater response to different recharge schemes, and to determine the optimal recharge strategy that has the maximum amount of water recharged into the aquifers under specific constraints, an optimization framework, which integrates a 3D transient groundwater flow model with a genetic algorithm (GA), was realized in a Python programming environment in this study. The optimization results show that the optimal amount of water recharged into aquifers is 5.36 × 109 m3 from January 2020 to December 2029, and the upper river reaches are the main recharge area, accounting for 67.58% of the total. Compared with constant recharge, optimal results indicate that the total amount of water recharged into aquifers will increase without exceeding the upper limits of the groundwater levels. However, as groundwater exploitation reduces (18.44%), the river's optimal amount of water recharged also decreases (17.23%). Therefore, the developed model can identify the optimal groundwater recharge strategy and eventually facilitate decision-making in the case of EWR.

Geodiversity characterization of the Danxiashan UNESCO Global Geopark of China

The Danxiashan UNESCO Global Geopark (Danxiashan UGGp) is located in Shaoguan, northern Guangdong Province of South China, and was approved as such by the Global Geoparks Network in 2004. It is an ideal site for geodiversity and geoheritage studies as well as a centre for geoeducation owing to its importance in understanding the geodynamics of South China during late Mesozoic and being the most representative danxia landscape (a red beds landscape characterized by well-developed cliffs and developed dominantly on hard conglomerates and sandstones) in the humid subtropical climate of China. The methods of field investigation and literature reviews were applied to document geodiversity characterization of the Danxiashan. The study area is characterized predominately by well-developed Late Cretaceous red beds deposited in alluvial fan and desert environments within a faulted continental basin. The red beds were uplifted during the Himalayan orogenic cycle (ca. 40 Ma to present) and dissected by faulting and jointing to form prominent escarpments and a variety of erosional landforms in tandem with weathering, water erosion and rockfalls. The danxia landscape of Danxiashan is composed of mesas, peaks, cliffs, canyons, rock walls and pillars with dominant bedrock of reddish conglomerates and sandstones. It is designated as the World Heritage ‘China Danxia’ with other five sites in South China owing to its exceptionally beautiful and distinctive landscape as well as diversified geological features and landforms. As one of the earliest and best developed geoparks in China, an assessment and summary of the geodiversity of Danxiashan sets a practical example in formulating long-term strategies in geotourism and geoeducation for geopark development in China and other countries.

Chalcolithic Painted Pottery of the Sialk III Period: Quantifying Stylistic Continuities and Changes on the Northern Central Plateau

ABSTRACT In the last two decades, the Varamin Plain to the southeast of Tehran has been the focus of intensified archaeological work, with surveys and excavations yielding new insights into the region’s settlement history. New material from the dynamic network of Chalcolithic sites on the Jajrud alluvial fan now offers a more solid basis to assess the links between the Varamin Plain and the site of Tappeh Sialk in the Kashan Plain, which still remains a reference point for this period. In this paper, we use painted pottery to examine the dating and relationships of the settlements of Ahmadabad-e Kuzehgaran and Chaltasian on the Varamin Plain to Tappeh Sialk. Based on an in-depth quantitative analysis of motif assemblages at the three sites, we evaluate contemporaneities as well as stylistic similarities and differences. We highlight both shared temporal trends and regional specificities.

Reconstruction of the gross depositional environment evolution in the northern Malay Basin, Malaysia-Thailand joint development area (MTJDA)

This paper provides new insight on the complex interactions between regional tectonic evolution, differential subsidence across the basin, and variation in sediment supply based on a reconstruction of the gross depositional environment in the northern part of Malay Basin. In addition, the variation in sedimentary facies, established from an integrated analysis based on seismic interpretation, well-log analysis, and core evaluation, are used to establish the gross depositional environment for key surfaces within the Oligocene to Miocene succession.The basin fill comprises Oligocene syn-rift and Miocene post-rift successions. The syn-rift successions are Syn-Rift Unconformity (SRU)-Base of Syn-Rift (BSR), and Base Chattian Unconformity (BCU)-Syn-Rift Unconformity (SRU) sequences. Whereas, the post-rift successions represent by Intra-Aquitanian MFS (IAM)-Base Chattian Unconformity (BCU), Intra-Burdigalian MFS (IBM)-Intra-Aquitanian MFS (IAM), Miocene Transgressive-Regressive (MTR)-Intra-Burdigalian MFS (IBM), Intra-Serravalian MFS (ISM)-Miocene Transgressive-Regressive (MTR), and Intra-Tortonian (ITM)-Intra-Serravalian MFS (ISM) sequences.The Oligocene-early Miocene syn-rift succession in the study area is characterized by aggradational stacking patterns, with an indication of retrogradation in individual sand packages for SRU-BSR, and BCU-SRU intervals, whereas an overall aggradational stacking pattern can be observed within the IAM-BCU sequence. The depositional environment of the syn-rift succession is mainly deltaic, fluvial, alluvial fan, shallow and deep lacustrine at the basin center.The early-middle Miocene post-rift succession is characterized by mostly aggradational and fining upwards stacking within the IBM-IAM sequence. This gradually changed to a retrogradational pattern in the MTR-ISM sequence. Depositional environments for this succession consist of an alternation between fluvio-marine and sub-tidal to marine sedimentation. Depositional environments for the overlying late Miocene Intra-Tortonian to Intra-Serravalian (ITM-ISM) was estuarine or tidally-influenced environments comprising fluvial channel, tidal or distributary channel, tidal sand flat, and tidal flat deposition. This interval mainly consists of coarsening upward units that gradually changed to a stacked higher-order fining upwards package. The deeper stratigraphic units are generally more continental (non-marine) in character, but fluvio-tidally influenced marine environments became more dominant in the shallower sequences.

The Hoanh Bo Trough‐a landward keyhole to the syn‐rift Late Eocene–Early Oligocene terrestrial succession of the northern Song Hong Basin (onshore north‐east Vietnam)

Located on the northern Vietnam onshore/offshore transition, the Hoanh Bo Trough is an excellently exposed terrestrial Palaeogene sedimentary sequence that may be treated as an analogue for regional interpretations of the sedimentary and structural evolution of the northern Song Hong Basin. The Hoanh Bo Trough lies to the north of the northern Song Hong Basin and to the west of the Beibuwan Basin, the origin and evolution of which are linked with Palaeogene South China Sea rifting. Field and archival well sedimentological observations were made throughout the Palaeogene succession of the Hoanh Bo Trough, and samples were collected for palynological, petrographical, and geochemical analysis. Based on the coexistence of particular lithofacies, proximal alluvial fan, distal alluvial fan, fluvial alluvial plain with channels, alluvial plain and/or lake margin, and lacustrine facies associations were distinguished. Palynological analyses suggest the sedimentary infill of the Hoanh Bo Trough is of the Late Eocene–Early Oligocene age and was deposited in a very warm tropical/subtropical climate. In turn, geochemical results demonstrate that the deposits have intermediate chemical maturity and were probably reworked from older sedimentary rock sources. Moreover, it is suggested to combine the Dong Ho and Tieu Giao formations and synonymize them as the Dong Ho Formation. The sedimentary pattern, age, climatic conditions, and structural evolution of the Hoanh Bo Trough align well with the rift initiation, rift development, and rift termination tectonic system tracts. Moreover, the Hoanh Bo Trough could be treated as a landward keyhole for the offshore basins: for instance, the Kien An Basin in the northern Song Hong Basin.

Past and present Geomorphological hazard and cultural heritage loss in El Castellar castle scarp (central Ebro Basin, Spain)

The ruins of the Medieval castle and village of El Castellar are located on an abrupt 1.2-km-long scarp of Miocene gypsums, in the central sector of the Ebro depression. The Medieval remains of the main El Castellar castle are perched on a 100 m cliff on the Ebro River. Considering the historical and geoarchaeological relevance of El Castellar settlement, this investigation aimed to study the geomorphological and paleoenvironmental context of the site during and after the settlement and its later evolution, including its current state. Geomorphological data suggest that in Medieval times its constructions were favored by the MCA environmental conditions. During that times, the Ebro River was located in a centered position on its floodplain, and lateral alluvial fans protected the scarp from basal erosion. Later, during the LIA, great climatic flows and recurrent floods changed the river dynamics and promoted the river channel movement against the scarp, destabilizing its foot and generating large landslides and rockfalls, thus promoting its retreat. The village buildings and castle at the top of the scarp were seriously damaged. For several reasons, the area is not easily accessible, but it still contains a relevant archaeological heritage that deserves to be studied and preserved.

Evolution of a stratigraphic model in a fluvial deltaic wedge: implications for groundwater resource protection in an oil and gas-bearing region in the Upper Cretaceous Dunvegan Formation, Northwest Territories, Canada

The Liard Basin, in northwestern Canada, contains one of Canada’s largest natural gas reserves. There are concerns about degradation of Dunvegan Formation groundwater quality, which is the basin's main shallow freshwater aquifer, as a consequence of oil and gas development. Previous lithostratigraphic studies interpreted the Dunvegan as conglomeratic alluvial fans. In this study, newly collected cores and surface resistivity surveys are integrated with legacy hydrocarbon well data and measured sections for improved sedimentary bedrock characterization. Rather than alluvial fans, we interpret the upper Dunvegan as a coarse-sand to gravel bed fluvial system that was likely tributive to incised valleys associated with linked Alberta Basin base-level falls. Correlation of well logs and measured sections suggest the lower Dunvegan comprises a prograding delta complex with off-lapping clinoforms fed by smaller sand-bed rivers that grade into the upper Dunvegan conglomeratic system, which built southeast towards the Cretaceous Western Interior Seaway. This sequence stratigraphic and facies architectural approach is employed to inform the aquifer–aquitard flow system and aid in understanding the 3D groundwater flow system, once hydrogeologic characterisation confirms position and thickness of important hydrogeologic units. Resistivity surveys suggest upper Dunvegan channel-belt facies may be well-connected and laterally extensive, potentially acting as interconnected aquifer units; whereas lower Dunvegan channel belts may be discontinuous, indicating smaller-scale flow units separated by floodplain and marine shale. This revised geologic understanding provides opportunities for determining impacts or resilience from shallow and deep sources of contamination associated with human activities, including oil and gas development, land-use, and (or) climate change.

Alluvial Sedimentary Records in Indian Precambrian Basins: Implications Toward Unique Precambrian Sedimentary Environment?

“Present is the key to the past”—in this all-inclusive uniformitarians’ geological panacea, the Precambrian continental sedimentation system stands out as an odd candidate. The distinctive nature of Precambrian alluvial sedimentation, not analogous to their Phanerozoic counterparts, is highlighted in literature in the absence of rooted vegetation, soil, and an overall greenhouse atmospheric condition. Documentation from Precambrian alluvial deposits around the globe suggests a sedimentation pattern dominated by scree cones, alluvial fans, and braid-plains under the combined effects of aggressive weathering and absence of vegetation; ephemeral braid-plains convincingly outweigh the other alluvial systems in the rock record. It is also surmised that Precambrian fluvial systems, unlike their Phanerozoic-modern analogs, maintained unequivocal ephemeral character across different climatic zones with very less chance of assuming meandering channel planform in absence of buffering effects of rooted plant and adequate mud. Local ponding of muddy sediments, though visualized in some rare cases, was mostly connected with the generation of local paleoslope and unusual riverine hydrology. Recent studies, however, raised a question about the actual paucity of mud, documented meander channel planforms from Precambrian fluvial records, and drew a parallel between the character of the Pre-Silurian alluvial plain on the surface of Earth and meander channel planforms on the Martian surface, interpreted from satellite imagery data. From the collation of data on alluvial deposits from a number of Indian Precambrian basins, augmented by new data from the Bayana basin, a Paleoproterozoic basin in the North Delhi fold belt, the present study attempts to document nuances and intricacies in Precambrian alluvial sedimentation motif that include facies architecture and paleohydrology. From an extensive, though not exhaustive, database, the study intends to claim the establishment of a meander channel-form in Precambrian river systems at a local scale in areas of low discharge and availability of higher silt and mud.

Late Holocene rupture history of the Ash Hill fault, Eastern California Shear Zone, and the potential for seismogenic strain transfer between nearby faults

AbstractUnderstanding how fault systems interact and transfer strain over seismogenic timescales (seconds to ka) requires temporal records of past ruptures along adjacent and intersecting fault networks. Here we document the record of Late Holocene ruptures as recorded in the geomorphology of alluvial deposits along the Ash Hill fault, in the Eastern California Shear Zone (ECSZ). We leverage a multi‐faceted approach to evaluate the relative timing of Ash Hill fault ruptures to those of nearby faults in the ECSZ. We determine the number and timing of Late Holocene earthquakes on the Ash Hill fault using high‐resolution tectono‐geomorphic mapping, a locally calibrated alluvial fan stratigraphy, feldspar luminescence dating, and fault offset analysis from field observations, LiDAR, and drone‐based digital surface elevation models. We find evidence for three surface‐rupturing earthquakes that have occurred since ~4 ka, each with ~1.0 ± 0.2 m of oblique slip per event (Mw ~ 6.9–7.0), and we constrain the timing of these earthquakes by dating deposits that bracket each event. The timing of these three ruptures is similar to the paleoseismic record along the adjacent range‐bounding fault in southern Panamint Valley. Specifically, the two adjacent faults exhibit similar numbers of earthquakes during the Late Holocene, with similar recurrence intervals and rupture timing. These data suggest that it is possible that these two faults have ruptured in the same or closely temporally related events throughout the Late Holocene. Similar spatio‐temporal clustered earthquakes have been recognized in both historic and paleoseismic records in the region, and such behaviour may be common in complexly interlinked fault networks, like those that exist in the ECSZ.

Assessment of Ammonium–N and Nitrate–N Contamination of Shallow Groundwater in a Complex Agricultural Region, Central Western Taiwan

The characteristics of nitrogen contamination of shallow groundwater were evaluated through current status analysis and trend detection of ammonium–N and nitrate–N concentrations under various cropping patterns to assess the effectiveness of rational fertilization in the Choushui River alluvial fan, central Western Taiwan. The influence of cropping patterns on both ammonium–N and nitrate–N contamination associated with redox conditions/dissolved oxygen (DO) in shallow groundwater was also discussed in this study. The analysis revealed that shallow groundwater beneath double rice cropping and rotational cropping regions is still characterized by high ammonium–N concentration despite rational fertilization promotion. However, very few monitoring wells showed an upward trend of ammonium–N/nitrate–N concentrations, indicating that shallow groundwater is not further deteriorated by nitrogen pollution in most parts of the study area. Therefore, the remediation of nitrogen contaminated groundwater will be a long-term process and more effort must be invested. Moreover, the strict redox conditions defined by a single DO threshold value may not account for groundwater nitrogen pollution in the study area. It is difficult to determine the redox conditions and predominant nitrogen pollution patterns of shallow groundwater purely from cropping patterns. Instead, contamination may have resulted from an integrated process governed by several other factors. Tracing the potential sources of nitrogen pollution and establishing a more integral monitoring network should be implemented to formulate a more comprehensive nitrogen pollution control strategy in this area.

Surface water and groundwater interaction in the Kosi River alluvial fan of the Himalayan Foreland.

We report the isotopic composition of the surface water and groundwater of the Kosi River fan on the Himalayan Foreland, India. We have collected 65 water samples from surface water (Kosi River (n = 2), streams (n = 9), waterlogging (n = 29), and canal (n = 4)), and groundwater (n = 21) for δ18O and δ2H analysis during December 2019. We obtained groundwater level data measured at the observation wells from the Central Groundwater Board, India, for 1996 and 2017. The groundwater level varies from 1.0 to 8.1m below ground level (bgl) and from 0.5 to 9.0m bgl during 1996 and 2017, respectively. We have used water table fluctuation approach to estimate the recharge rate. The recharge rate in the Kosi Fan varies from 0.7 to 21.4mm/year from 1996 to 2017. Further, we have used δ18O and δ2H values of water samples to identify the source and the interaction between surface water and groundwater. The δ18O value of groundwater shows a wide variation (from -9.3‰ to -5.6‰) compared to the surface water, i.e., streams (-7.8‰ to -6.4‰) and canals (-6.9‰ to -6.0‰), suggesting mixing in groundwater during recharge processes. Furthermore, we have used a two-component mixing model to assess the fraction contribution from streams and precipitation to groundwater. The estimated fraction contribution from stream water to groundwater ranges from 45 to 83%. We also suggest higher recharge is limited up to the depth of 6m bgl. We suggest precipitation and surface water actively recharge groundwater. We conclude that marked spatial variation in the isotopic composition of groundwater is mainly due to the local recharge sources and interaction between surface water and groundwater.

The Distribution of Soil Carbon and Nitrogen Stocks Among Dominant Geomorphological Terrain Units in Qarlikturvik Valley, Bylot Island, Arctic Canada

AbstractSoils of circumpolar regions store large amounts of carbon (C) and are a crucial part of the global C cycle. Yet, little is known about the distribution of soil C stocks among geomorphological terrain units of glacial valleys in the Arctic. Soil C and nitrogen (N) content for the top 100 cm of the dominant vegetated geomorphological terrain units (i.e., alluvial fans, humid polygons, mesic polygons) at Qarlikturvik Valley, Bylot Island, Canada have been analyzed. Soil C content was greatest in humid low‐center ice‐wedge polygons (82 kg m−2), followed by mesic flat‐center ice‐wedge polygons (40 kg m−2), and alluvial fan area (16 kg m−2), due to prevailing geomorphological processes, differences in vegetation and soil characteristics, as well as permafrost processes. Soil N content was greatest in humid polygons (4 kg m−2), followed by mesic polygons (2 kg m−2), and alluvial fan area (1 kg m−2). Vertically, C and N decreased with increasing depth except for a peak in C at depth in humid polygons, a likely result of past changes in vegetation cover. At Qarlikturvik Valley, which has a size of 121.7 km2, alluvial fans store 0.226 Tg organic C and humid and mesic polygons store 1.643 and 0.218 Tg organic C, respectively in the top 100 cm of soil. Findings like these are important to further constrain pan‐Arctic soil C and N stock estimates and thus climate models.

How Do Vulnerable People in Bangladesh Experience Environmental Stress From Sedimentation in the Haor Wetlands? An Exploratory Study

AbstractThe haor landscape is a wetland ecosystem in northeast Bangladesh, comprising shallow depressions that undergo large changes in water inundation between the monsoon and dry seasons. Sediment is supplied to the haor from rivers originating in the adjacent Shillong Plateau, and can adversely affect these largely arable agricultural lands. The critical adverse effects of changing hydrology and enhanced sedimentation due to anthropogenic change include the reduction of natural water storage capacity, changes in the timing and magnitude of floods, and increasing loss and damage to crops, which consequently affect the livelihoods of wetland dwellers. This study employs a mixed‐methods approach to investigate how sedimentation has affected the livelihoods of the residents and the pressures they experience. Cross‐sectional surveys and interviews were conducted with 180 respondents in Lubar and Pochashul Haors (LPH), Sunamganj District, and allied with an analysis of satellite images that reveals the nature of landscape change over the past 56 years. Our findings confirm that sedimentation has been promoted through both natural processes of alluvial fan progradation and anthropogenic forcings. Enhanced sedimentation threatens the agriculture of the region and affects the livelihood of local inhabitants, leading to other societal issues related to income, education, employment, health, displacement, and sexual harassment. The mixed methods employed herein are essential tools to reveal these effects. In order to reduce the vulnerability of the local population, a transboundary dialog between India and Bangladesh is needed to realize measures to protect wetland resources and achieve progress towards environmental sustainability.