Large Fluvial Systems Research Articles

Enhancing the freshness of particulate organic carbon through the regulation of dam and river-lake interactions

The composition and fluxes of organic carbon transported by river systems are important for the terrestrial carbon cycle in terms of source to sink, and the impacts of dam regulation on large rivers are well documented. However, complex river–lake interactions and extreme weather events still hinder a comprehensive understanding of the transformation of riverine carbon within the large river basin. This study investigated particulate organic matter during the 2012 flood in the Changjiang Basin (CJB) and collected suspended particles from the mainstream of the CJB, Dongting and Poyang lakes. The amount, grain size, particulate organic carbon (POC) content, chlorophyll a (Chl-a), and lignin phenols of samples were measured. The results indicate that soil is the primary source of POC in lake-unaffected stations (46.9%–86.9%), while lake-affected stations exhibit significant contributions from phytoplankton (41.4%–78%). Notable alterations in the composition of terrestrial organic carbon occur during its transfer from soil to the river and from the upper to the lower reaches. Comparing the POC characteristics in the Changjiang across various years and hydrological conditions reveals that the characterization of POC in the Changjiang during flooding is mainly influenced by the dams. Another notable finding is that Dongting and Poyang lakes intercepted sediment and transported algae-rich organic matter to the mainstream. This process potentially converts the middle reaches of the Changjiang into a carbon source. River-lake interactions are complex and affected by lake morphology and flooding events. This study enhances our understanding of biogeochemical processes in dam-regulated rivers under extreme weather conditions, and emphasizes the importance of river–lake interactions for the transformation and transportation of riverine organic carbon in large fluvial system.

Quantification of the provenance contribution and sedimentary mixing effect of sediments in the Yellow River Basin, China

Quantifying the source contributions of sediments in large fluvial systems with active wind erosion problems has crucial implications for understanding morphological evolution and ecological progression in the Earth system. Much effort have been focused on characterizing sediments of the Yellow River, but quantitation of the sediment source proportions at the basin-wide scale is lacking. To this end, the research aims to quantitatively elucidate the potential source contributions of sediments in the Yellow River based on geochemical characteristics and sediment fingerprinting technique, in order to identify sedimentary mixing effect and propose sustainable development strategies. In total, samples of four source groups (n = 107) and target floodplain sediments (n = 61) were collected and tested for elemental composition, grain size, magnetic susceptibility, and quartz grain microtextures. The results indicated that the optimal tracer combination was determined as P, Zn, and Ca. The average contributions of the “Tibetan Plateau”, “Sandy deserts-Loess Plateau”, “Loess Plateau”, and “Loess Plateau-Qinling Mountains” source groups to the target sediments were 23.0 %, 21.5 %, 31.6 %, and 23.9 %, respectively. The accuracy of source apportionments was supported by the goodness of fit (GOF) and virtual mixtures tests. Meanwhile, large amounts of debris from surrounding mountains was transported to the Loess Plateau through fluvial processes and ultimately mixed with aeolian deposits, leading to sedimentary mixing effect. To maintain water balance and minimize erosion risk, the drought-resistant perennial planting and moderate grazing were recommended. The findings are instrumental in promoting soil and water conservation and disclosing fluvial and aeolian interaction on a global scale.

Analysis of the fluvial stratigraphic response to the Paleocene–Eocene Thermal Maximum in the Bighorn Basin, U.S.A.

ABSTRACT Geological deposits can reveal how environments of the past have responded to climate change, enabling important insights into how environments may respond to our current anthropogenically induced warming. The Paleocene–Eocene Thermal Maximum (PETM) occurred ca. 56 Ma and was a short-lived (approximately 200,000 years) global warming event (5–8°C rise). The PETM has been investigated at several terrestrial and marine localities across the globe. However, many studies are based on single successions, with very few sites being placed within a well-defined spatial and temporal context and with comparisons limited to deposits that lie immediately above and below the event. Due to the inherent variability of sedimentary systems, it is imperative that the appropriate context is provided to fully understand the impacts of climate change on landscapes and subsequent deposits. This study examines 28 locations, totaling over 4 km of recorded stratigraphy, within a newly defined quantified sedimentary basin context (Bighorn Basin, USA) to evaluate variability of fluvial response to the PETM. We show that channel-body and story thicknesses across the PETM are not statistically significantly different from deposits outside the climate event, implying that there is not a consistent sedimentary response to the climate event across the basin. Based on our large dataset we calculate that precipitation would have had to double for statistically significant changes in deposit thickness to be generated. We discuss how climatic signals may be lost due to the self-organization, spatial–temporal varied response and preservation potential in large fluvial systems. This study gives a new quantified perspective to climate events in the geologic record.

Late Oligocene Formation of the Pearl River Triggered by the Opening of the South China Sea

AbstractThe Pearl River is one of the largest rivers entering the South China Sea, yet its initiation time remains debated, a topic we address using Pb isotopes in detrital K‐feldspar. Based on these Pb data, Eocene and Early Oligocene sandstones from the northern South China Sea are interpreted to have been supplied with sediment by proximal rivers draining the Cathaysia Block. In contrast, the Late Oligocene and Miocene sandstones are mainly derived from the western Pearl tributaries (e.g., Hongshui River), suggesting that the Pearl River had formed by the Late Oligocene. Detrital zircon data from the Beibuwan Basin previously suggested that the western tributaries flowed into this basin before being captured by the paleo‐Pearl River. These lines of evidence suggest that progressive headward erosion of the eastern Pearl River and late Oligocene integration of this large fluvial system can be linked to contemporaneous sea‐floor spreading of the South China Sea.

Channel morphology as a key factor to hydrological and sedimentological patterns in the largest fluvial ria lake of Amazonia

Amazon ria lakes are geomorphological features still poorly known despite their great magnitude and uniqueness. The Tapajós ria comprises one of the largest natural channels in the world, measuring impressive 20 km in width in its lower reach. Important data on longitudinal distribution of matter and energy has been collected in the last decades, but far less attention has been given to its transversal variation. In this paper we analyze grain size and major element concentration of bottom sediment on Tapajós ria lake, sampled along transversal profiles, in order to investigate the importance of channel morphology on data interpretation and to better describe fluvial dynamics. Geomorphological analyses of the channel Digital Elevation Model (DEM) coupled with remote sensing products allowed us to describe depositional features along the ria. We observed that novel patterns might emerge when transversal distribution is considered. Our results also support that local drainages and processes such as marginal scarp retreat may have an important role on the ria infilling. This approach has the potential to be applied to other large fluvial systems in the world helping to increase our understanding of the processes that shape their morphology.

Oxidation of petrogenic organic carbon in a large river-dominated estuary

Riverine export of petrogenic organic carbon (OCpetro) from continents to coastal oceans is a dynamic component of the global carbon budget and affects the long-term atmospheric carbon reservoir. In large fluvial systems, oxidation of OCpetro during transit releases a large flux of carbon dioxide to the atmosphere, influencing climate changes; however, the transport and fate of OCpetro and their controls along the fluvial–marine transition remain poorly constrained. Here, we combined Raman spectral, radiocarbon activity (F14C), mineralogical, and sedimentological techniques with multiple geochemical analyses to characterize the dynamics of OCpetro in the water column and sediment particles from the Yangtze River channel–estuary–shelf continuum systems.Our data show that much of the OCpetro present in suspended sediment (POCpetro) exported by the Yangtze River is “labile” fractions (mostly disordered materials) that can be degraded or lost during transport across the estuarine continuum, whereas the OCpetro deposited in seabed sediment are characterized by highly recalcitrant, unreactive, and graphitic carbon phases. As discrete “free” particles, coarse plant debris (>63 μm) with ages of several thousand years observed in the proximal delta of the Yangtze River exhibit nearly identical characteristics of disordered materials, and the presence of aged vascular plant detritus (carbon-rich and 14C-depleted materials) may lead to an overestimate of OCpetro in marine sediments. Using a Bayesian endmember mixing approach, a binary mixing model, and the ratio of fraction modern carbon (F14C) to Al/OC, we found a large decrease in POCpetro concentration and loading from the suspended sediments to seabed sediments, suggesting a loss of mineral-bound OCpetro fraction during sediment transport through the estuary and deposition on the shelf. We estimated that, on average, 46 ± 35 % of the POCpetro initially present in suspended sediments delivered to the Yangtze River Estuary during a flood event was primarily oxidized at the sediment–water interface, leaving the most graphitic carbon components transported laterally and efficiently reburied in shelf sediments. We found that during estuarine mixing, flocculation process-induced microaggregates may provide transient physical protection for POCpetro in the form of inclusions/aggregates with carbonate minerals; however, when POCpetro is physically and chemically separated from its mineral matrix via disaggregation and dissolution, it may be easily oxidized by microbial activity. In contrast, OC-phyllosilicates interactions exert a first-order control on the preservation of OCpetro in marine sediments. Our findings suggest that the importance of POCpetro oxidation and loss in carbon cycling and budget assessments of estuaries may be underestimated.

Cage transplant experiment shows weak transport effect on relative abundance of fish community composition as revealed by eDNA metabarcoding

Protection of freshwater fish diversity is a global conservation priority in face of its alarming decline in the last decades. A crucial step to protect freshwater fish diversity is the production of prompt and precise evaluation of community composition and spatial distribution. Metabarcoding of environmental DNA (eDNA metabarcoding) generally surpasses traditional methods for documenting diversity and community composition in aquatic environments. Nevertheless, empirical evidence evaluating how eDNA transportation in water affect community composition and structure via eDNA metabarcoding data remains scarce. Using a brown trout (Salmo trutta) cage transplant experiment in the St. Lawrence River (Canada), a large fluvial system, we tested the detection and relative abundance of species’ eDNA along 15 sampling locations. We detected brown trout eDNA in five localities up to 5,000 m from the cage, but only one sampling location situated 10 m downstream and in the direct line of the cage was affected at the community composition level. This locality showed a relative abundance of brown trout eDNA of 13.1%, while the four others showed a relative abundance under 1.0%. K-means cluster analysis confirmed the impact of brown trout eDNA on community composition by separating this locality from all others. Based on species loading of a redundancy analysis, we showed that this different k-means group was associated with the high relative abundance of brown trout. No evidence of transport effect of brown trout eDNA on fish community composition was observed in any other sampling locations. Together, our results support the view that eDNA metabarcoding can be both a conveyor belt of biodiversity information and a precise tool to study the composition and structure of fish communities in river.

Stratigraphic reconstruction of the lower–middle Miocene Goto Group, Nagasaki Prefecture, Japan

AbstractThe Goto Islands are located at the westernmost tip of the Japan archipelago, and preserve a lower–middle Miocene sedimentary sequence deposited during rifting of the continental margin and opening of the Sea of Japan. The stratigraphy of the Goto Group and new K–Ar, fission‐track, and U–Pb age data were used to determine the initial conditions of rifting in southwest Japan. The thickness of the Goto Group is 2000–3000 m. The lower unit (ca. 22–17.6 Ma) consists of thick, greenish, volcaniclastic rocks with basaltic volcanic material, representing the initial stages of continental rifting. The middle unit (ca. −17.6 Ma) consists of alternating sandstones and shales deposited in lacustrine and meandering fluvial environments in a syn‐rift sedimentary basin during a period of volcanic activity. The upper unit (ca. 17.6–16.8 Ma) consists of thick sandstones of fluvial–deltaic facies that were deposited during rapid subsidence at the continental margin. This unit was deposited by a large fluvial system that flowed into the Sea of Japan. These sequences contain relatively cooler to warmer flora (Daijima‐type) and record the warm period of the Miocene Climatic Optimum. The Goto felsic volcanic rocks (16.8 ~ 15.4 Ma) unconformably overlie the Goto Group, and granitic magmatism (ca. 16–14.5 Ma) occurred after sedimentation of the Goto Group. The widespread lacustrine, meandering–braided fluvial, and vast deltaic systems of the Goto Group, and felsic volcanism, were formed due to rapid subsidence that produced a horst‐and‐graben basin during the early stages of rifting of a volcanic arc along the eastern margin of Eurasia. These events occurred from 22.0 to 16.8 Ma before and during the formation of the Sea of Japan.

Potentially toxic elements in surface soils of the Lower Don floodplain and the Taganrog Bay coast: sources, spatial distribution and pollution assessment.

The pollution of floodplain, deltaic and adjacent coastal soils in large fluvial systems, considered an urgent environmental problem, as well as potentially toxic elements in such environments, can negatively affect aquatic ecosystems, as well as pose significant risks to human health. This paper is devoted to the geochemistry of potentially toxic elements in soils of the Lower Don basin, which is one of the largest and most anthropogenically transformed water bodies in Southern Russia, as well as the adjacent areas of the Taganrog Bay coast. The median element concentrations in the soils of the study area were consistent with the world soil average and the contents of elements in background soils. Comparative assessment of the spatial distributions as well as the results of Pearson's correlations, cluster analysis and principal component analysis showed that Cr, Ni, Cu and Zn are predominantly of natural origin; Mn and As are of mixed sources; and Cd and Pb are predominantly of anthropogenic origin. The geochemical anomalies of elements were associated with the impact of local anthropogenic sources. Geochemical background values for Cr, Mn, Ni, Cu, Zn, As, Cd and Pb in the soils of the Lower Don and the Taganrog Bay coast determined using the 'median + 2 median absolute deviations' approach are presented. The highest values of the integrated pollution indices were observed in floodplain soils of small rivers.

Lake-islands: A distinct morphology of river systems

Islands are important morphologies in multichannel fluvial systems for maintaining secondary channels, increasing flow efficiency in the widest stretches, and hosting important ecological environments. This study presents a hitherto unclassified, distinct type of fluvial island that occurs in large rivers: the lake-island. We analyzed islands from large rivers, particularly from South American rivers, the Negro (Amazon Basin) and Paraná (La Plata Basin) Rivers. Satellite images were used for identification and morphometric analysis, while morphometric indices were used to compare island morphologies. Sedimentary facies analysis and dating were also conducted to characterize the island deposits. Lake-islands are differentiated from typical fluvial islands by their lenticular morphology, and frontal and lateral levees that protect and isolate the lake or allow it to be partially connected to the channel. Lake-island morphology can be elongated or circular, based on their morphometric indices and their relationship with channel width. Lake-island lengths varied from hundreds of meters to tens of kilometers. They are formed by in-channel deposition on preexisting sand bars or fluvial islands. Their sedimentary characteristics are relatively simple and comprise basal sandy facies capped by finer-grained deposits. The permanence of lake-islands depends on the flow regime and sedimentary load of the fluvial system. The lake-island's age ranges from 101 to 103 years. A comprehensive understanding of the formation processes and dynamics of lake-islands is of fundamental importance in the management of large fluvial systems, and studies of fluvial ecology.

Paleogene Sedimentary Records of the Paleo‐Jinshajiang (Upper Yangtze) in the Jianchuan Basin, Yunnan, SW China

AbstractCenozoic surface uplift of Tibetan Plateau has driven the birth and reorganization of large river systems in Asia. The development of the Yangtze River, closely linked to plateau uplift, has important implications for the regional tectonic‐geomorphology processes, but is still under debate. The key scientific question is whether the Upper Yangtze (upper Jinshajiang) once flowed southeast to the South China Sea. In this study, we carried out provenance analysis on Paleogene sedimentary rocks in the Jianchuan Basin, composed of the Baoxiangsi, Jinsichang, and Shuanghe formations. We compared them with similar deposits in other regional basins, as well as with potential sources. Heavy‐mineral and geochemical data show that sediments from the Jinsichang formation are more mature compared with those from the Shuanghe and Baoxiangsi formations. The Jinsichang formation represents the products of a large fluvial system, whereas the Baoxiangsi formation is mainly dominated by local sources. The Shuanghe formation contains material from both distant sources and locally eroded materials. Detrital zircon U‐Pb age patterns from the Jianchuan Basin are similar to those in sediments in the Gonjo, Simao, and Chuxiong basins, and show great similarity with the modern Jinshajiang River. Statistical analysis of the zircon ages suggests that the Songpan‐Ganzi terrane was the primary source for all sediments, while the Yangtze Craton and northern Qiangtang terrane constitute secondary sources. Taken together these data confirm that a paleo‐Jinshajiang flowed south toward to the South China Sea from the SE Tibetan Plateau in the late Eocene, constraining the age of formation of the First Bend.

Fluvial aggradation and incision in the Brazilian tropical semi-arid: Climate-controlled landscape evolution of the São Francisco River

Large rivers are dynamic systems whose evolution depends on both internal and external forcing, particularly tectonics, sea level, and climate. Associating fluvial responses to a specific driver is a complex task that has been debated for a long time. Thus, rivers that flow exclusively under tectonically stable areas and without direct influence of relative sea level changes are suitable targets to understand how large fluvial systems responded to past climate changes. The São Francisco River is one of the largest cratonic rivers across South America, and its late Quaternary sedimentary deposits record the fluvial landscape evolution in a thousand-year timescale. The São Francisco River flows northward over different climate zones, with its upper course in a semi-humid setting, but with most of its watershed under semi-arid conditions. To understand the controls on sediment erosion, transport, and storage from uplands to lowlands, we investigated a 200-km section of the medium course of the São Francisco River in northeast Brazil. Several geomorphological zones were characterized, mapped, and dated by optically stimulated luminescence (OSL). Two zones are represented by degraded terraces with lakes, but no preserved alluvial features: (zone 1) high-level terrace (87.7 ± 12.7 ka) and (zone 2) low-level terrace (65.5 ± 5.3 to 39.3 ± 4.3 ka). Three zones comprise the active confined aggradational plain, with features such as scroll bars and abandoned channels: (zone 3) older meander belt (18.1 ± 1.6 ka); (zone 4) young meander belt (15.5 ± 1.5 to 9.5 ± 1.0 ka), and (zone 5) modern channel belt (0.4 ± 0.1 to 0.3 ± 0.1 ka). Zone 6 comprises an eolian dune field composed of parabolic dunes with two phases of active sedimentation (45.1 ± 5.2 to 25.5 ± 4.4 ka and 14.3 ± 2.6 to 5.2 ± 1.4 ka). Sediment deposition ages allowed the recognition of at least four phases of fluvial aggradation (⁓90 ka; ⁓66 to 39 ka; ⁓18 to 9 ka and ⁓0.3 ka to recent), three phases of incision (⁓85 to 66 ka; ⁓39 to 18 ka and ⁓9 to 1 ka), and two phases of dune field stabilization (⁓25 to 15 ka and ⁓5 ka to recent). Development of the eolian dune fields occurred during drier conditions, when the inland activity of trade winds reworked sediments deposited on the fluvial plain. We interpret the incision events as having been set in motion by an increase of fluvial discharge in the upper catchment area, produced by rainfall intensification due to activity of the South Atlantic Convergence Zone (SACZ). The aggradation and incision phases on the São Francisco River during the last 100 ka are therefore likely controlled by multi-millennial precipitation changes, possibly related to precession cycles. The events of high sedimentation rate in the São Francisco river mouth are partially correlated with incision phases in its middle course. This suggests that sedimentation in plains of large plateau rivers can be decoupled from the coastal area.

A physical and chemical sedimentary record of Laramide tectonic shifts in the Cretaceous-Paleogene San Juan Basin, New Mexico, USA

Fluvial siliciclastic rocks bracketing the Cretaceous-Paleogene (K-Pg) boundary in the San Juan Basin, New Mexico (USA), provide records of regional fluvial and tectonic evolution during the Laramide orogeny. Petrographic analyses of sandstones from the Upper Cretaceous Fruitland Formation and Kirtland Formation and the Paleocene Ojo Alamo Sandstone and Nacimiento Formation show that the rivers depositing these sediments were sourced in areas where unroofing of crystalline basement rocks took place, introducing an increasing proportion of immature detrital grains into the fluvial system through time. After the Cretaceous-Paleogene boundary, rivers deposited an increasing amount of microcline and orthoclase feldspar relative to plagioclase feldspar, suggesting a growing source in unique crystalline basement rocks. Geochemical analyses show significant differences between Al- and K-poor Upper Cretaceous sandstones and Al- and K-rich lower Paleocene sandstones in the San Juan Basin. The high proportion of sand-sized material in the Ojo Alamo Sandstone suggests that it was deposited in a basin with a low ratio of sediment supply to accommodation. However, magnetostratigraphic age constraints suggest it had a relatively high sedimentation and/or subsidence rate of as much as 0.38 m/k.y. The sediment supply must have been high in order to deposit a basin-wide coarse sand-dominated package, suggesting rapid creation of topographic relief in the San Juan uplift, the proposed source area of the Ojo Alamo fluvial system. The observed sedimentary architecture and age constraints of the Ojo Alamo Sandstone, including kilometers-wide sand bodies and limited overbank mudstones throughout most of the outcrop area, are difficult to reconcile with accepted models of aggradation and avulsion in large fluvial systems, but available age and lithologic data make difficult a complete understanding of Paleocene San Juan Basin fluvial systems and basin evolution. Here, we present new lithologic, petrographic, and thickness data from San Juan Basin K-Pg fluvial siliciclastic units and interpretations of their origins.

Heavy and light marker minerals around the East African Rift System (EARS) with special reference to the evolution of Zanzibar Island, Tanzania

Mineral assemblages encompassing heavy (HM), light (LM) and clay minerals (CM) can be used as marker minerals for geodynamic and weathering processes. The highly diverse lithology of the Precambrian basement rocks around and the rift-related magmatic rocks of the East African Rift system (EARS) form an ideal platform to use sediment-mineralogical techniques to study the origin of the Island of Zanzibar, Tanzania, during the Quaternary. Four reference mineral associations have been defined: (1) Precambrian basement rocks (Tanzania Craton + Proterozoic rim), (2) Mesozoic rocks (magmatic rocks of the rift-and-graben system), (3) Cenozoic rocks (magmatic rocks of the rift system), (4) Quaternary placers, duricrusts and soils which form a transition zone between bedrock and the depocenter under study. Detrital grains of pyroxene and amphibole s.s.s. and autochthonous kaolinite group minerals in context with Fe–Al oxide/hydrates play a leading role for the geodynamic and geomorphological-mineralogical correlation of Zanzibar with mainland Tanzania. During the Holocene HM are likely to have been introduced into the beach sands from a magmatic submarine source and assigned Zanzibar to the marginal facies of the EARS, while a central island ridge blanketed by an argillaceous duricrust zone denotes a HM barrier towards mainland Tanzania. The difference between the mineral assemblage along the east coast of Zanzibar and the mineral assemblage of the mainland fed by the large fluvial drainage systems argues for a local magmatic HM source.

Life in the “dead heart” of Australia: The geohistory of the Australian deserts and its impact on genetic diversity of arid zone lizards

AbstractAimThe Australian deserts are home to a remarkable diversity of taxa that might appear to have evolved in the absence of topographic and physical barriers to dispersal. In fact this is a biogeographical illusion, as the dunefields of the modern arid zone obscure the fossil landscapes of the wet desert that existed for much of the Cenozoic. As the geohistory of Australia's arid zone is not widely understood by biologists, we review its geological development and contemporary landscapes in an accessible way, and describe eight biogeographical hypotheses centred on how geomorphology, evolutionary history and contemporary ecological factors interact to shape diversification patterns in the desert lowlands.LocationAustralia.TaxonLizards.MethodsWe review the arid zone landscapes before and after the development of the vast dunefields. As lizards represent a significant component of genetic studies that sample widely across the arid biome, we focus on this taxonomic group to establish emerging patterns.ResultsRecent geological work suggests that the dunefields never formed extensive mobile landscapes such as in the Sahara, but rather were a mosaic of vegetated and stable dune surfaces with scattered bare, mobile patches. Large fluvial systems in the eastern arid zone during the Pleistocene also are at odds with the general perception of an arid landscape during this time. Incorporating this geohistorical insight, understanding where landscape heterogeneity is greatest within the arid zone, and where relative homogeneity might facilitate connectivity and gene flow, are at the heart of our biogeographic hypotheses.Main conclusionsPatterns are emerging that reflect the underlying influence of geomorphological processes on the genetic structure of Australian desert taxa. Quantifying finer‐scale edaphic complexity across the arid zone, widespread genetic sampling from disparate taxonomic groups, and a more detailed understanding of species ecology and life history will greatly improve our understanding of the ecological and historical drivers of diversity gradients in the Australian deserts.

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

We study cross-sections on the Detailed Geological Map of Poland (SMGP) to find a geologic and geomorphic pattern under river valleys in Poland. The pattern was found in 20 reaches of the largest Polish rivers (Odra, Warta, Vistula, Narew, and Bug) located in the European Lowland, in the landscape of old (Pleistocene, Saalian) glacial high plains extending between the Last Glacial Maximum (LGM) moraines on the North and the Upland on the South. The Upland was slightly folded and up-faulted during Alpine orogeny together with the thrust of Carpathian nappes and the uplift of Tatra Mts. and Sudetes. The found pattern is an alluvial river with broad Holocene floodplain and the channel developed atop the protrusion of bedrock (Jurassic, Cretaceous limestones, marlstones, sandstones) or non-alluvial, cohesive, overconsolidated sediments resistant to erosion (glacial tills, lacustrine or “ice-dammed lake” clays) of Cenozoic (Paleogene, Neogene, Quaternary—Elsterian). We regard the sub-alluvial protrusion as the limit of river incision and scour. It cannot be determined why the river flows atop these protrusions, in opposition to “differential erosion”, a geomorphology principle. We assume it is evidence of geological flood control. We propose an environmental and geomorphological framework for the hydrotechnical design of instream river training.

Diversity of macrophytes in the Amazon deforestation arc: information on their distribution, life-forms and habits

Abstract The Amazon possesses the largest fluvial system on the planet, harboring a diverse biota. Still, many species remain undescribed, because of the Amazon’s immense scale and complexity, and because many habitats are now increasingly under pressure from anthropogenic activities. Macrophytes are important to physical and biological processes in aquatic ecosystems but remain poorly studied in Northern Brazil. The objective of this study was to provide a checklist of macrophyte species that occur in municipalities that form part of the Arc of Deforestation, Pará state, Brazil, bringing information on their habits and life-forms. We sampled 36 sites at three types of aquatic ecosystems (streams, ponds and lakes). In total, we recorded 50 species, 38 genera and 24 families. Most species were amphibious or emergent. Degraded streams have environmental characteristics similar to lentic habitats, which could provide more suitable habitats for macrophytes that otherwise would not occur in lotic habitats, thus explaining the higher diversity in these ecosystems. Macrophyte diversity in this region follows similar patterns to other Brazilian regions. This study contributes to the assessment of aquatic macrophytes in the Amazon, especially in more degraded regions, such as the Amazon deforestation arc.

Aeolian sand dunes alongside the Yarlung River in southern Tibet: A provenance perspective

The potential interactions between aeolian and fluvial systems are critical in understanding environmental change. Whether aeolian products originated from the river depends on the river characteristics and wind regimes. In southern Tibet, aeolian sand dunes are widespread along the Yarlung River, and thus provide an ideal example to explore the relationships between large fluvial systems and aeolian products. Although previous studies postulated that those aeolian products were originated from the Yarlung River, few empirical data actually exist to support this idea. We analysed the spatial pattern, sand transportation directions, and granulometric characteristics of the sand dunes to evaluate the potential influence of the Yarlung River on the aeolian processes. Comparison of the dune field distribution against channel width and longitudinal profile of the Yarlung River shows that sand dunes are clustered at the wide and flat segments of the river. Analyses of >4,600 sand dune orientations using Google Earth imagery show that the dunes located at the southern and northern sides of the Yarlung River demonstrate opposite sand transportation directions that generally point against the river. This suggests that the sand grains probably originated from the river. Grain size distributions from dune samples show unimodal or unimodal‐like patterns. This means that each sand dune field was dominantly fed by a simple transportation process rather than by compound processes from smaller‐level fluvial systems, which in turn implies that the Yarlung River was the most possible candidate for the provenance of these aeolian deposits. This study provides new constraints to demonstrate that the Yarlung River provides both accommodation space and sorted fluvial sand for the aeolian sand dunes along the river.

Integrating Petrography, X-Ray Fluorescence, and U-Pb Detrital Zircon Geochronology to Interpret Provenance of the Mississippian Hartselle Sandstone, USA

The Chesterian (Mississippian) Hartselle Sandstone is a tar sand exposed in the Black Warrior Basin and southern Appalachian fold belt in northern Mississippi and Alabama. Previous studies disagree about the delivery direction and relative contributions of sediment from the cratonic interior, the Appalachians, and the Ouachitas. The goal of this research is to investigate lateral trends in sedimentary and geochemical properties to provide new details about the provenance of the Hartselle. Samples were collected along a west-to-east transect and analyzed using petrography, X-ray fluorescence (XRF) geochemistry, and U-Pb detrital zircon (DZ) geochronology. Point counting indicated a major cratonic interior source with a minor recycled orogen signal. Sillimanite in the easternmost sample narrows down the potential Appalachian sources to areas of high-grade metamorphism. Petrographic observations suggest both western and eastern sources. The XRF results showed high concentrations of Ti and Mo in the westernmost sample, suggestive of a nearby terrigenous source. All of the samples had similar U-Pb DZ age distributions except for the easternmost sample, which had statistically higher proportions of Paleozoic- and Archean-aged grains (Kolmogorov-Smirnov test: p < .02). For the first time, Eoarchean and Paleoarchean grains were found in the Hartselle, indicating a likely sediment source from the Minnesota River Valley gneisses of the Superior Craton prior to Grenvillian overprinting. Based on integration of all data, we conclude that a large fluvial system draining the continental interior provided a substantial volume of sediment from the northwest. At the same time, a more dispersed drainage basin associated with the Appalachian front contributed recycled orogenic material from the northeast.

Caged fish experiment and hydrodynamic bidimensional modeling highlight the importance to consider 2D dispersion in fluvial environmental DNA studies

AbstractThe analysis of environmental DNA (eDNA) is a powerful tool to increase the efficiency of species detection and monitoring in aquatic ecosystems. Yet, several points remain to be clarified in order to estimate with better precision the distribution and abundance of targeted species, such as the dispersion and dilution of eDNA in large lotic systems. This study aimed to document the dispersion patterns of eDNA in the St. Lawrence River, the largest fluvial system in eastern North America. Caged Brown trout (Salmo trutta) were placed in two different water masses present in this part of the river, the Ottawa River, and water from the outlet of the Laurentian Great Lakes. eDNA detection of the caged fish was performed for two days following cage removal at 53 sampling stations located at 500 upstream, and 10, 100, 500, 1,000, and 5,000 m downstream from the cages. Quantitative PCR analysis using a Brown trout specific assay revealed a positive detection only at downstream stations and up to 5,000 m. To further investigate patterns of dispersion, the relative concentrations of eDNA were predicted using a bidimensional hydrodynamic model, calibrated for downstream advection and lateral mixing of particles (i.e., quantification of 2D dispersion). The detection and the quantities of eDNA obtained by qPCR analyses were compared with the model predictions. Our model which predicts a low lateral mixing and a downstream flow in direct line from the eDNA source best fits the results. We discuss how such studies can improve our capacity to produce more precise estimates of species abundance and distribution in order to better interpret eDNA signals in large lotic systems.