Lowland Basin Research Articles

Spatiotemporal variability of methane over the Amazon from satellite observations

The spatiotemporal variability of the greenhouse gas methane (CH4) in the atmosphere over the Amazon is studied using data from the space-borne measurements of the Atmospheric Infrared Sounder on board NASA’s AQUA satellite for the period 2003–12. The results show a pronounced variability of this gas over the Amazon Basin lowlands region, where wetland areas occur. CH4 has a well-defined seasonal behavior, with a progressive increase of its concentration during the dry season, followed by a decrease during the wet season. Concerning this variability, the present study indicates the important role of ENSO in modulating the variability of CH4 emissions over the northern Amazon, where this association seems to be mostly linked to changes in flooded areas in response to ENSO-related precipitation changes. In this region, a CH4 decrease (increase) is due to the El Nino-related (La Nina-related) dryness (wetness). On the other hand, an increase (decrease) in the biomass burning over the southeastern Amazon during very dry (wet) years explains the increase (decrease) in CH4 emissions in this region. The present analysis identifies the two main areas of the Amazon, its northern and southeastern sectors, with remarkable interannual variations of CH4. This result might be useful for future monitoring of the variations in the concentration of CH4, the second-most important greenhouse gas, in this area.

A new species of Moenkhausia Eigenmann, 1903 (Characiformes, Characidae) from the rio Amazonas basin, Brazil.

Moenkhausia abyss is herein described from the rio Amazonas basin lowlands. The new species can be distinguished from the congeners by presenting the combination of the following characters: a dark blotch located on the upper caudal-fin lobe and the lower lobe hyaline, 25-29 branched anal-fin rays, humeral spot rectangular, vertically oriented, extending horizontally through two or two and a half scales and located over the third to the fifth lateral line scales, five longitudinal scale rows above the lateral line, predorsal scales arranged in a single not interrupted median row and 30-34 perforated lateral line scales. Brief comments on Moenkhausia megalops are provided.

Tangible and Intangible Flood damage evaluation

Flooding and flash floods that cause significant economic and social damage have been widely studied in the last few decades. The European Commission Flood Directive 2007/60 Flood Risk Management Plans require the assessment of potential damage to give an appreciation of the magnitude of the consequences of a flood event and so help stakeholders to use a cost benefit approach to planning flood mitigation measures. This paper evaluates the direct tangible flood damage applying the JRC water depth-damage functions for the European territory to estimate the potential economic damage. Intangible damage is evaluated with the Life Safety Model (LSM) to study the dynamic interactions among people, vehicles, buildings and the flood wave. LSM assesses potential flood damage and allows the development of a Flood Evacuation Plan in case of an emergency, underlining the evacuation routes adopted by people and vehicles. This enables emergency managers to avoid evacuation bottleneck problems and identify areas of potential high mortality. The impact of changes such as road network improvements, the location of safe havens and timing of flood warnings can be assessed in terms of potential loss of life. The developed methodology has been applied on the Sardinian Flood Risk Management Plan pilot basin, the Coghinas river lowland basin.

Catastrophic flooding, palaeolakes, and late Quaternary drainage reorganization in northern Eurasia

ABSTRACTWe review the long history of Russian scientific study of the major late Quaternary palaeodrainages and palaeolakes in northern Eurasia to provide overviews of (1) past research efforts (mainly published in the Russian language) and (2) recent studies that include contributions from those outside of the former Soviet Union region. There are two major groups of catastrophic flooding phenomena and related palaeodrainage and palaeolake systems in this region: (1) those involving large-scale lowland basins and (2) those involving upland intermontane basins. Many of these palaeodrainages and palaeolakes were active during the late Quaternary, though the available age data are inconclusive in regard to more exact timing and synchronicity. These palaeodrainages and palaeolakes in the late Quaternary are strongly linked with climatic change, most notably to ice age. For the megalakes in large-scale basins, spillover events probably occurred because of impoundment by the late Pleistocene Arctic ice sheets. In some cases, gradual transgressions of the megalakes caused by varying climatic conditions could also have contributed to the spillovers. Some of these spillover events may have been catastrophic. Ice-dammed lakes formed when drainage into intermontane basins was impounded by late Pleistocene alpine-type glaciers. The collapses of the glacier dams caused downstream catastrophic flooding, producing a characteristic suite of flood-related landforms. In the Azas Plateau volcanic field, there is evidence for Icelandic-type subglacial flooding.

Wetlands of the Lowland Amazon Basin: Extent, Vegetative Cover, and Dual-season Inundated Area as Mapped with JERS-1 Synthetic Aperture Radar

Wetland extent, vegetation cover, and inundation state were mapped for the first time at moderately high (100 m) resolution for the entire lowland Amazon basin, using mosaics of Japanese Earth Resources Satellite (JERS-1) imagery acquired during low- and high-water seasons in 1995–1996. A wetlands mask was created by segmentation of the mosaics and clustering of the resulting polygons; a rules set was then applied to classify wetland areas into five land cover classes and two flooding classes using dual-season backscattering values. The mapped wetland area of 8.4 × 105 km2 is equivalent to 14 % of the total basin area (5.83 × 106 km2) and 17 % of the lowland basin (5.06 × 106 km2). During high-water season, open water surfaces accounted for 9 % of the wetland area, woody vegetation 77 %, and aquatic macrophytes 14 %. Producer’s accuracy as assessed using high-resolution digital videography was better than 85 % for wetland extent. The mapped flooding extent is representative of average high- and low-flood conditions for latitudes north of 6° S; flooding conditions were less well captured for the southern part of the basin. Global data sets derived from lower-resolution optical sensors capture less than 25 % of the wetland area mapped here.

Recent Structural Evolutions in the Forests of Lowland Basin of Moldova River Between Sadova and Prisaca Dornei

Abstract The considerable expansion of the forests in the mountainous regions of Romania was favored by several factors. The Romanian Carpathians occupy an area of 66300 km², 28% of Romanian territory being represented by mountains of medium height, bordered almost entirely in the boreal forest and nemoral from 400 - 500m at 1600 altitude. The case study indicates that the function and evolution of forest in the basin depression of Câmpulung Moldovenesc took place in conditions of thermal inversions, and the thermal differences caused by the exposition radically opposed to the two main slopes of the valley Moldova. The deforestations in low area of the depression were more intense than in the mountains and were mainly made for new grazing land, and for habitat expansion. Agrarian reforms of 1864 and 1920 affected most forests in the hilly area, especially following the allotment and communal pastures extension deforestation. The reduction of forest areas of Romania continued after the political changes of 1989, due to irrational and sometimes illegal mining, which were practiced amid crumbling forestlands through partial repayment of former private property and the lack of enforcement authority and tolerance massive felling of forests.

Structure and composition of the liana assemblage of a mixed rain forest in the Congo Basin

Background and aims – The Congo Basin lowland forest represents one of the largest tropical forest blocks in the world, but its liana assemblage has never been characterized. We evaluate liana floristics, diversity, and structure in the Ituri Forest, and determine the effects of forest structure and edaphic variation on liana species composition. Methods – Two permanent 10-ha plots (200 × 500 m), 500 m apart, were established in mixed forest. All liana individuals = 2 cm dbh were identified, measured, mapped, and marked. For 20 × 20 m subplots we distinguished terra firme and swamp, and we estimated canopy openness. Key results – The combined 20-ha area contains 15,008 lianas (dbh = 2 cm) representing 195 species, 83 genera, and 34 families. Per hectare, species number averaged 64, mean basal area was 0.71 m2 and mean Fisher's alpha, Shannon index, and Simpson diversity index values were 17.9, 3.1 and 11.4, respectively. Ten dominant plant families represented 69% of total species richness, 92% of liana abundance and 92% of basal area, while ten dominant species accounted for 63% of abundance and 59% of basal area. A single species, Manniophyton fulvum, dominated the liana community (22% of all individuals). Forty-one species (21%) had one individual only. Twiners, zoochorous, light-demanding, and meso- or microphyllous species dominated. Liana abundance increased with abundance of medium-sized and large trees but was, surprisingly, independent of small-tree abundance. Canopy openness, habitat type, and tree size were the most important factors influencing abundance and distribution of liana individuals. Conclusions – The Ituri liana assemblage stands out by showing an extreme one-species dominance. Species floristic composition is, however, generally similar to that in other tropical African forests.

Eolian deposition in the alpine zone of the Uinta Mountains, Utah, USA

Field and laboratory investigations were conducted to determine the origin of a ubiquitous layer of silt that caps soil profiles in the alpine zone of the Uinta Mountains, Utah, USA. Fine sediment isolated from snowbanks was studied to constrain the fraction of this material derived from allochthonous eolian additions. Lake sediments representing deposition over the past few centuries were analyzed to determine whether dust deposition in the Uintas has been a long-term process, and if properties of the modern dust differ from dust which accumulated prior to European settlement. Results indicate that alpine soils have been strongly influenced by long-term eolian deposition. The loess cap in these soil profiles averages 18cm thick, and physical and chemical properties of soil horizons derived from the eolian parent material are significantly different than those of the subsurface horizons derived from in situ produced congelifractate. Fine sediment observed at the surface of snowbanks in the early summer is a mixture of silty exotic eolian material and sandy locally derived sediment. Snowbanks on ridgecrests and on slopes of blocky scree tend to accumulate the maximum amount of exotic dust with the minimum amount of local material. The grain-size distribution, mineralogy, and geochemistry of lake sediments indicate that dust has been accumulating in the Uintas for at least the last few centuries. Modern lake sediments are significantly enriched in elements indicative of upwind mining and agricultural activity, recording an anthropogenic change in dust composition following settlement of the surrounding lowland basins.

Increase in soil erosion after agricultural intensification: Evidence from a lowland basin in France

Changes in agricultural practices impact sediment transfer in catchments and rivers. Long term archives of sediment deposits in agricultural plains of northwestern Europe are rarely available, however, for reconstructing and quantifying erosion and sedimentation rates for the second half of the 20th century. In this context, a multi-parameter analysis was conducted on sedimentary deposits accumulated in a pond created in the 11th century and draining a 24 km2 cultivated catchment in western France. This catchment is representative of cultivated and drained lowland environments where agriculture has intensified during the last 60 years. High resolution seismic profiles and surface sediment samples (n = 74) were used to guide the collection of cores (n = 3) representative of the sequence of sediment accumulated in the pond. The cores were analysed to quantify and characterize the evolution of sediment dynamics in the pond. The first land consolidation period (1954-1960) was characterized by a dominance of allochtonous material input to the pond. This input represents an erosion of 1900 to 2300 t.km−2.yr−1 originating from the catchment. Then, between 1970-1990, the terrigenous input decreased progressively and tended to stabilize. Eutrophication and associated primary production increased in the pond. These processes generated the majority of material accumulated in the pond during this period. Further land consolidation programs conducted in 1992 generated a new increase in soil erosion and sediment input to the reservoir. For the last 10 years, terrigenous input to the pond corresponds to a catchment-wide erosion rate between 90 and 102 t.km−2.yr−1. While a strong decrease is observed, it still represents a 60-fold increase of the sediment flux compared to the pre-intensification period. These large temporal variations of sedimentation rates over a few decades underline the dynamics of sediment transfer and raise questions about the sustainability of soil resources in lowland temperate environments.

Strontium isotope variation and carbonate versus silicate weathering in rivers from across Alaska: Implications for provenance studies

The characterization of strontium (Sr) isotopic (87Sr/86Sr) variation in surface waters of Alaska (AK) has significant implications for provenance studies aiming to track movement patterns of animals. This study presents 87Sr/86Sr ratios, concentrations of Sr, Ca, Mg, Na and K, and selected molar ratios (Sr/Na, Ca/Na, Mg/Na and Ca/Sr) from 61 rivers from across AK to characterize regional patterns in i) 87Sr/86Sr variation and ii) carbonate versus silicate weathering influencing 87Sr/86Sr ratios. 87Sr/86Sr ratios range from 0.70422–0.74041±0.00009. Rivers north of the Denali Fault exhibit more radiogenic and variable 87Sr/86Sr ratios (0.70763 to 0.74041) than rivers to the south (0.70422 to 0.70895), reflecting the tectonic growth of southern AK via accretion of relatively young mafic-rich exotic island arcs along North America's continental margin during the Mesozoic. Within interior AK an east–west gradient exists. Radiogenic 87Sr/86Sr ratios (>0.725) in east-central AK and relatively low ratios (<0.709) in western AK reflect AK's progressive western growth along the ancestral North American miogeocline from the Precambrian to Mesozoic. High relief rivers draining north of the Brooks Range are more radiogenic (>0.711) than lowland rivers (<0.709). Elemental ratios indicate carbonate weathering has the strongest influence on 87Sr/86Sr ratios in high relief watersheds north of the Denali Fault and in watersheds of south-central AK. Elemental and 87Sr/86Sr ratios indicate silicate weathering is important across AK, but is most influential in lowland basins north of the Denali Fault and in southwestern AK. This study illustrates the large Sr isotopic heterogeneity across AK on multiple spatial scales and provides necessary baseline information for provenance studies.

Large-scale analysis of changing frequencies of rain-on-snow events with flood-generation potential

Abstract. In January 2011 a rain-on-snow (RoS) event caused floods in the major river basins in central Europe, i.e. the Rhine, Danube, Weser, Elbe, Oder, and Ems. This event prompted the questions of how to define a RoS event and whether those events have become more frequent. Based on the flood of January 2011 and on other known events of the past, threshold values for potentially flood-generating RoS events were determined. Consequently events with rainfall of at least 3 mm on a snowpack of at least 10 mm snow water equivalent (SWE) and for which the sum of rainfall and snowmelt contains a minimum of 20% snowmelt were analysed. RoS events were estimated for the time period 1950–2011 and for the entire study area based on a temperature index snow model driven with a European-scale gridded data set of daily climate (E-OBS data). Frequencies and magnitudes of the modelled events differ depending on the elevation range. When distinguishing alpine, upland, and lowland basins, we found that upland basins are most influenced by RoS events. Overall, the frequency of rainfall increased during winter, while the frequency of snowfall decreased during spring. A decrease in the frequency of RoS events from April to May has been observed in all upland basins since 1990. In contrast, the results suggest an increasing trend in the magnitude and frequency of RoS days in January and February for most of the lowland and upland basins. These results suggest that the flood hazard from RoS events in the early winter season has increased in the medium-elevation mountain ranges of central Europe, especially in the Rhine, Weser, and Elbe river basins.

High-resolution vegetation history of West Africa during the last 145 ka

The essential characteristics of the vegetation dynamics of tropical Africa remain only partially known. This study assesses the succession of vegetation-types over Central Africa during the last two glacial/interglacial cycles. Analysis of core KZai 02, which contains pollen from the Zaire River watershed (latitudes 9°N–13°S), allows the investigation of long-term patterns of plant ecosystem development and their climatic causes. Core KZai 02 (18.20 m long) was recovered from 6°24.20′S/9°54.10′E in the uppermost axial edifice of the Zaire deep sea fan. The chronology of this sedimentary archive was established using nannofossils and correlations of pollen and total organic carbon signals with the nearby core GeoB1008. The pollen record indicates that: (i) glacials (MIS 6, 4, 2) are marked by the development of afromontane (Podocarpus) forest at high altitudes when central basin lowlands were occupied by Cyperaceae marshes and savannah; (ii) during interglacials (MIS 1, 5) lowland forests were developed, marked by the successive expansion of pioneer, warm-temperate, rain forests, and mangrove indicating sea-level rise; (iii) glacial-interglacial transitions (MIS 6/5, 2/1) display similar vegetation dynamics. The strong evidence of afromontane forest and the opening of the vegetation during glacials suggest a reduced latitudinal distribution of rainfall by the strengthening of the trade wind system. West African monsoon systems were enhanced during interglacials, allowing the progressive development of lowland forests. The development of rain and pioneer forests during glacial Heinrich stadials suggests an enhancement of water availability in tropical Africa associated with these high-latitude events. However, no augmentation of wind activity described by previous studies is evidenced by our pollen record. Similar vegetation successions during glacial/interglacial transitions suggest the diachronous and stepped intervention of CO2 (emphasizing the influence of temperature on plant ecosystems) and water availability.

Bayesian uncertainty assessment of a semi-distributed integrated catchment model of phosphorus transport

Process-based models of nutrient transport are often used as tools for management of eutrophic waters, as decision makers need to judge the potential effects of alternative remediation measures, under current conditions and with future land use and climate change. All modelling exercises entail uncertainty arising from various sources, such as the input data, selection of parameter values and the choice of model itself. Here we perform Bayesian uncertainty assessment of an integrated catchment model of phosphorus (INCA-P). We use an auto-calibration procedure and an algorithm for including parametric uncertainty to simulate phosphorus transport in a Norwegian lowland river basin. Two future scenarios were defined to exemplify the importance of parametric uncertainty in generating predictions. While a worst case scenario yielded a robust prediction of increased loading of phosphorus, a best case scenario only gave rise to a reduction in load with probability 0.78, highlighting the importance of taking parametric uncertainty into account in process-based catchment scale modelling of possible remediation scenarios. Estimates of uncertainty can be included in information provided to decision makers, thus making a stronger scientific basis for sound decisions to manage water resources.

The influence of large-scale climatic patterns on precipitation, temperature, and discharge in Czech river basins

Abstract The present study focuses on the possible influence of large-scale climatic patterns on precipitation, temperature, and discharge in two distinct river basins in the Czech Republic. The first one is a flat lowland basin of the Cidlina River and the second one represents a more mountainous type of climate (the Blanice River). The large-scale climatic patterns used comprise monthly averages of teleconnection patterns, sea level pressure values, and two geopotential heights (850 hPa and 500 hPa). The correlations for corresponding months and also up to a three months lead time were investigated. The relations concerning the corresponding months proved to be most reliable in the winter period of the year. The behaviour of both selected river basins with respect to these predictors is rather similar in character. However, higher values of correlation coefficients are reached in the case of the Cidlina River basin. Considering the prediction abilities with a certain lead time, the results seem to be more promising for the winter and spring periods in both basins. In the Cidlina River basin, they are likely to be beneficial also for the late summer and autumn period.

Aquatic community structure across an Andes‐to‐Amazon fluvial gradient

AbstractAimLittle is known about factors affecting the elevational and longitudinal zonation of tropical Andean stream communities. We investigated epilithon, macroinvertebrate and fish assemblages along a 4100‐m elevational–longitudinal gradient in an Andean headwater of the Amazon Basin. We interpret our results within the context of environmental factors, emphasizing temperature, as well as ecological theory relating shifts in metazoan functional feeding groups to shifts in basal resources along the fluvial continuum.LocationArazá‐Inambari‐Madre de Dios watershed, south‐eastern Peru.MethodsWe sampled water physicochemistry, epilithon and macroinvertebrate diversity and abundance, and fish diversity at 18 main‐stem and 14 tributary sites from high puna grasslands (4300 m a.s.l.) to Amazon Basin lowlands (200 m a.s.l.).ResultsWater physicochemical parameters and the taxonomic and ecological structure of invertebrate and fish assemblages displayed mostly nonlinear responses to elevation: water temperature and percentage of macroinvertebrate taxa identified as leaf shredders had U‐shaped responses; dissolved oxygen and percentage of macroinvertebrate taxa identified as grazers had hump‐shaped responses. Epilithon richness increased slightly with elevation whereas macroinvertebrate and fish richness decreased.Main conclusionsElevational gradients in physicochemical parameters are insufficient to explain abrupt and nonlinear shifts in community taxonomic and functional structure. Rather, trophic interactions, including predation and longitudinal turnover in basal food resources, seem to exert a stronger influence on the distributions of Andean aquatic organisms. A steep elevational decline in relative taxonomic diversity of leaf‐shredding (versus algae‐grazing) insects supports the hypothesis that temperature affects the functional composition of insect assemblages via its influence on microbial decomposition rates. This relationship, and the distributions of several insect and fish species across narrow elevational bands, suggests that Andean stream communities may be sensitive to global warming. Placer mining and road building impacts have already altered stream community structure, including the absence of many benthic species from low‐elevation habitats.

The influence of connectivity in forest patches, and riparian vegetation width on stream macroinvertebrate fauna

We assessed two dimensions of stream connectivity: longitudinal (between forest patches along the stream) and lateral (riparian vegetation), using macroinvertebrate assemblages as bioindicators. Sites representing different land-uses were sampled in a lowland basin that holds a mosaic of protected areas. Land-use analysis, forest successional stages and riparian zone widths were calculated by the GIS analysis. Macroinvertebrate fauna was strongly affected by land-use. We observed a continuous decrease in the number of sensitive species, %Shredders and IBE-IOC biotic index from the upstream protected area to highly deforested sites, increasing again where the stream crosses a Biological Reserve. When analysing buffer strips, we found aquatic fauna responding to land-use alterations beyond the 30 m riparian corridor (60 m and 100 m wide). We discussed the longitudinal connectivity between forest patches and the riparian vegetation buffer strips necessary to hold high macroinvertebrate diversity. We recommend actions for the increase/maintenance of biodiversity in this and other lowland basins.

CO2 Geological Storage in the Province of Québec, Canada Capacity Evaluation of the St. Lawrence Lowlands basin

The evaluation of the storage capacity of the St. Lawrence Lowlands basin was performed in the Province of Québec (Eastern Canada). The Covey Hill and Cairnside formations have global porosities of 5% and 3%, which is enough to be considered in the basin-scale storage capacity evaluation. The efficiency factors used in the capacity calculation are defined in the Carbon Sequestration Atlas of the United States and Canada and range from 0.51% to 5.4% in clastic sedimentary units. Two 3D geological models of the basin were used to represent the potential reservoir units at the basin-scale: uniform and faulted basin. This allowed calculating the volume of the potential reservoirs and comparing the capacity of a large-scale uniform basin with a faulted basin compartmentalized by the existing normal faults.

Responses of aquatic macrophyte assemblages to nutrient enrichment in a lowland river basin of western Greece

In Greece, as in many other Mediterranean countries, there is a lack of information enabling the use of aquatic macrophytes as biological indicators of the water trophic status. This research aimed to investigate the trophic preferences of the aquatic macrophyte assemblages encountered in selected standing water bodies of a lowland river basin of western Greece. It also aimed to assess the response of the macrophyte species that occur in the studied water bodies to different nutrient concentrations. A total of 56 macrophyte species were identified. TWINSPAN analysis distinguished four main vegetation groups potentially related to three trophic types. The Trophic Ranking Score developed in the UK was applied in order to investigate the trend in aquatic macrophytes in response to the different trophic conditions. The results indicated that TRSUK was not in accordance to the water trophic indices. After the addition of 14 new species and the re-scoring of the plants from the UK list, the re-calculation of TRS enabled a better classification of the trophic status convergent with the information from the water trophic indices. The current study constitutes a reference document providing basic information, and must be improved by updating the plant list with new data from other sites.

Discovery of the largest lungless tetrapod, Atretochoana eiselti (Taylor, 1968) (Amphibia: Gymnophiona: Typhlonectidae), in its natural habitat in Brazilian Amazonia

We report the occurrence of the limbless and lungless tetrapod, Atretochoana eiselti, in two widely separated Brazilian Amazonian lowland localities, one (Mosqueiro island and Baía de Marajó, Belém) near the mouth of the Amazon river and another (Cachoeira Santo Antônio) near the border between Brazil and Bolivia in the Madeira river. It is shown that this species is not an inhabitant of cool, oxygen rich and fast running water in elevated localities as supposed until now, but on the contrary occurs in warm (24-30 °C), turbid, fast running water in the lowland Brazilian Amazon basin. We describe the probable habitat and three freshly preserved specimens (one male, two females) and compare them to the only two specimens known; some data are provided about the biology of this species, that seems to have a wide distribution in Brazilian Amazonia and possibly also occurs in other countries, like Bolivia.

How important is it to integrate riverine suspended sediment chemical composition with depth? Clues from Amazon River depth-profiles

The vertical variability in mineralogical, chemical and isotopic compositions observed in large river suspended sediments calls for a depth-integration of this variability to accurately determine riverine geochemical fluxes. In this paper, we present a method to determine depth-integrated chemical particulate fluxes of large rivers, based on river sampling along depth-profiles, and applied to the Amazon Basin lowland tributaries. The suspended particulate matter (SPM) concentration data from depth-profiles is modeled for a number of individual grain size fractions using the Rouse model, which allows to predict the grain size distribution of suspended sediment throughout the whole river cross-section. Then, using (1) the relationship between grain size distribution and the Al/Si ratio (2) relationships between the Al/Si ratio and the chemical concentrations, the chemical composition of river sediment is predicted throughout the river cross-section, and integrated to yield the depth-integrated chemical particulate flux for a number of chemical elements (e.g. Si, Al, Fe, Na, REEs, …). For elements such as Al, Fe, REEs, Th, the depth-integrated flux is around twice as high as the one calculated from river surface sample characteristics. For Na and Si, the depth-integrated flux is three times higher than the “surface” estimate, due to the enrichment of albite and quartz at the bottom of the river. Depth-integrated 87Sr/ 86Sr composition of suspended sediment, also predictable using this method, differs by more than 10 −3 from the surface sample composition. Finally, potential implications of depth-integrated estimates of Amazon sediment chemistry are explored. Depth-integration of particulate 87Sr/ 86Sr isotopic ratios is necessary for a reliable use of Sr isotopes as a provenance tracer. The concept of steady-state weathering of a large river basin is revisited using depth-integrated sediment composition. This analysis shows that, in the Amazon Basin river, the previously observed discrepancy between (1) weathering intensities of channel surface sediment and (2) silicate-derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities. This observation confirms that most large rivers basins are not eroding at steady-state.