River Sediments Research Articles

A smart, multi-configuration, and low-cost system for water turbidity monitoring

Measuring the amount of suspended sediment in rivers is important for a better understanding of phenomena like soil erosion or floods. Since such phenomena are not spatially homogeneous, a distributed measurement approach is required to obtain fine-grained and realistic models. We designed and implemented a low-cost, flexible, and smart suspended sediment concentration monitor. The system only uses components that are easy to find and assemble. This, together with the reduced costs, enables the use of multiple instances for distributed monitoring. The system can operate according to different configurations, fixed or mobile, and using a variety of connection technologies, to possibly cover the various necessities that arise from the diverse installation sites. Each measuring unit automatically retrieves its operational parameters, easing the configuration of a possibly large distributed measurement system.

Study on the source identification and migration and transformation characteristics of heavy metal pollution in sediments of Chaohu Lake Tongyang River Basin.

Heavy metal pollution in soil and groundwater is difficult to detect in time because of its long-term accumulation. This poses a severe hazard to the ecosystem security in polluted areas. Considering the Tongyang River Basin of the Chaohu Lake water system as the research object, various pollution evaluation methods, Geographic Information System (GIS) source analysis models, adsorption and desorption experiments, and mathematical models were used. Based on the data of the heavy metal content in the soil and river sediments in the study area, regional heavy metal pollution evaluation, spatial distribution characteristics, source identification, and lake loss analysis were conducted to evaluate the current situation of environmental pollution, pollution sources, and migration and transformation of heavy metals in the basin. The results show that the heavy metals in the soil of the basin are mainly distributed from the southwest to the northeast and the island distribution to the east of Tongyang Town. The Cd, Cu, Zn, and Pb concentrations are higher in the sediment than in the soil. The Unmix analytical model was established. The natural source of heavy metals in the Tongyang River Basin and the composite pollution source of traffic-production and life showed a high correlation. According to the one-dimensional steady-state model, the concentrations of the heavy metals are in the following descending order: Zn, Cr, Pb, Cu, Ni, and Cd. The amounts of these elements entering the lake annually are 1993.04, 1028.1, 372.47, 301.72, 308.80, and 19.46 kg, respectively (a total of 4023.6 kg).

Investigating the Potential of River Sediment Bacteria for Trichloroethylene Bioremediation

Trichloroethylene (TCE) is a prevalent groundwater contaminant detected worldwide, and microbes are sensitive indicators and initial responders to these chemical contaminants causing disturbances to their ecosystem. In this study, microbes isolated from San Marcos River sediment were screened for their TCE degradation potential. Among the twelve isolates (SAN1-12), five isolates demonstrated TCE degradation within 5 days at 25 °C and 40 mg/L of TCE concentration in the following order: SAN8 (87.56%), SAN1 (77.31%), SAN2 (76.58%), SAN3 (49.20%), and SAN7 (3.36%). On increasing the TCE concentration to 80 mg/L, the degradation efficiency of these isolates declined, although SAN8 remained the prominent TCE degrader with 75.67% degradation. The prominent TCE-degrading isolates were identified as Aeromonas sp. SAN1, Bacillus sp. SAN2, Gordonia sp. SAN3, and Bacillus proteolyticus SAN8 using 16S rRNA sequencing. The TCE degradation and cell biomass of Bacillus proteolyticus SAN8 were significantly improved when the incubation temperature was increased from 25 °C to 30 °C. However, both slightly acidic and alkaline pH levels, as well as higher TCE concentrations, lowered the efficacy of TCE degradation. Nevertheless, these conditions led to an increase in bacterial cell biomass.

Cascaded reservoirs promote phosphorus bioavailability of surface sediments in the Upper Mekong River

As a key nutrient for primary productivity in freshwater ecosystems, the effect of upper cascade reservoirs on the downstream phosphorus (P) loading is subject to an ongoing scientific debate in the Mekong River. To investigate the effects of cascade reservoirs on the forms of P and its bioavailability in surface sediment, two rounds of field research were carried out both in a free-flowing river (Nu River) and in the Upper Mekong River (Lancang River) during winter and summer. Results showed that while the P was trapped with sediments and environmental parameters changed significantly, high relative abundance of bioavailable phosphorus (BioP, generally include Fe-bound P, Al-bound P, and Organic P) in sediment was detected in reservoirs and at near the border between China and Myanmar. The increased Bio-P in reservoirs may be caused by sediments sorting, anaerobic surface sediments, appropriate temperature, longer residence time and algae-nutrient positive feedback loops. Accumulated Bio-P in sediments may elevate the phosphorus release to overlying water and exacerbate eutrophication in reservoirs. Considered the intense anthropogenic phosphorus loading, nutrients enrichment risk in the lower Mekong River should receive more attention in further research.

Economic impacts of large dams on downstream brickmaking in developing countries

Large dams have positive and negative impacts, including disrupting brickmaking on the floodplains downstream due to flow regulation and sediment reduction, affecting the supply of essential construction material, notably in developing countries. In this study, we introduce an analytical framework to assess the economywide effects of large dams on downstream brickmaking, focusing on Traditional Fired Clay Brick (TFCB). The framework includes three steps: characterizing the impacts on river flow and sediment load using river system modeling and secondary data, understanding the role of TFCB production in the economy based on survey and economic data, and quantifying the economywide impacts of changes in TFCB production using dynamic computable general equilibrium modeling. We demonstrate the functionality of the approach by conducting a case study of the impacts of the Grand Ethiopian Renaissance Dam (GERD) on the Sudanese economy due to changes in TFCB production by comparing two scenarios: “with GERD” and “no GERD.” Results show that Sudan’s accumulated (2023–2050) discounted (at 0.5% annually) Gross Domestic Product (GDP) at factor cost would decline by US$ 6 billion (−0.38%) due to a reduction in TFCB production. Consumer flexibility regarding brick types and the ability of alternative brick sources to fill the demand gap are key determinants of the impacts.

Axial and transverse river deposits preserved in an Aptian rift basin, Northeastern Brazil: Implications for sandstone reservoir quality

A syn-rift, up to 250 m thick, fluvial sandstone unit of Aptian age (Marizal Formation, Tucano Basin, northeastern Brazil) preserves the deposits of an axial fluvial system and contemporary tributaries. These deposits exhibit characteristic variations in composition, grain size, and paleocurrents, indicating different sources for each system. There is a systematic downstream increase in the tributary contribution to the axial system along the basin axis. This sediment mixture model is established based on extensive paleocurrent data in conjunction with macroscopic, microscopic, and detrital zircon provenance data. The spatial distribution of diagenetic patterns and reservoir permo-porosity properties were compared to the paleogeographic model. The comparison revealed that the increase in lithic fragments brought by a main tributary led to a reduction in intergranular porosity and permeability of axial system deposits downstream, following a change in pebble and sand composition. Our findings highlight that the relative amount of bedload brought by tributaries plays a crucial role in the composition and diagenetic evolution of fluvial reservoirs. Spatial variations in sandstone composition at specific stratigraphic intervals are expected due to the intricate patterns of mixture and preservation of axial and transverse river deposits within fault-bounded basins.

Estimation of the Potential for Soil and Water Conservation Measures in a Typical Basin of the Loess Plateau, China

Abstract: In the context of the large-scale management of the Loess Plateau and efforts to reduce water and sediment in the Yellow River, this study focuses on a typical watershed within the Loess Plateau. The potential for vegetation restoration in the Kuye River Basin is estimated based on the assumption that vegetation cover should be relatively uniform under similar habitat conditions. The potential for terrace restoration is assessed through an analysis of topographic features and soil layer thickness, while the potential for silt dam construction is evaluated by considering various hydrological and geomorphological factors. Based on these assessments, the overall potential for soil erosion control in the watershed is synthesized, providing a comprehensive understanding of target areas for ecological restoration within the Kuye River Basin. The study demonstrates that the areas with the greatest potential for vegetation restoration in the Kuye River Basin are concentrated in the upper and middle reaches of the basin, which are in closer proximity to the river. The total potential for terracing is 1013.85 km2, which is primarily distributed across the river terraces, farmlands, and gentle slopes on both sides of the riverbanks. Additionally, the potential for the construction of check dams is 14,390 units. The target areas for terracing measures in the Kuye River Basin are primarily situated in the middle and lower reaches of the basin, which are in closer proximity to the river. Conversely, the target areas for forest, grass, and check dams, as well as other small watershed integrated management measures, are predominantly located in the hill and gully areas on the eastern and southern sides of the basin. The implementation of the gradual ecological construction of the watershed, based on the aforementioned objectives, will facilitate the protection, improvement, and rational utilization of soil, water, and other natural resources within the watershed.

Fingerprinting to trace sources of suspended solids in the transport of heavy metals in urban stormwater runoff

Suspended solids are an important pollutant in urban stormwater runoff. Past studies have mainly focused on a single transport stage of pollutants, constraining source identification of suspended solids at the catchment scale. Therefore, identifying the sources of suspended solids in stormwater runoff for the formulation of effective pollution mitigation measures is an effective way to manage suspended solids pollution in receiving waters. Sediment source fingerprinting is a widely used technique to trace the sources of river sediments, which can accurately identify the source of sediment through widely used tracers. This study used six heavy metals including Cd, Cr, Ni, Cu, Zn and Pb as tracers to quantify the sources of suspended solids in stormwater runoff from urban catchments. The spatial and temporal distribution characteristics of suspended solids during stormwater transport were investigated. The study results showed that the concentration of suspended solids was the highest in road runoff and sewer flow, especially particles <44 μm. In addition, relatively large rainfall depth, high rainfall intensity and long antecedent dry periods can lead to higher concentrations of suspended solids in roof and road runoff whereas longer rainfall duration can result in more suspended solids in sewer runoff. Sediment source fingerprinting and principal component analysis confirmed that coarse (>105 μm) particles primarily originate from road deposited sediments (63.80%), while fine (<105 μm) particles primarily originate from stormwater grate sediments and soil. The outcomes derived can help to comprehensively understand the sources of suspended solids and provide guidance for the management of urban stormwater particulate pollution, as well as being a technical reference for pollutant source traceability in urban stormwater runoff.

Utility of Certain AI Models in Climate-Induced Disasters

To address the current challenge of climate change at the local and global levels, this article discusses a few important water resources engineering topics, such as estimating the energy dissipation of flowing waters over hilly areas through the provision of regulated stepped channels, predicting the removal of silt deposition in the irrigation canal, and predicting groundwater level. Artificial intelligence (AI) in water resource engineering is now one of the most active study topics. As a result, multiple AI tools such as Random Forest (RF), Random Tree (RT), M5P (M5 model trees), M5Rules, Feed-Forward Neural Networks (FFNNs), Gradient Boosting Machine (GBM), Adaptive Boosting (AdaBoost), and Support Vector Machines kernel-based model (SVM-Pearson VII Universal Kernel, Radial Basis Function) are tested in the present study using various combinations of datasets. However, in various circumstances, including predicting energy dissipation of stepped channels and silt deposition in rivers, AI techniques outperformed the traditional approach in the literature. Out of all the models, the GBM model performed better than other AI tools in both the field of energy dissipation of stepped channels with a coefficient of determination (R2) of 0.998, root mean square error (RMSE) of 0.00182, and mean absolute error (MAE) of 0.0016 and sediment trapping efficiency of vortex tube ejector with an R2 of 0.997, RMSE of 0.769, and MAE of 0.531 during testing. On the other hand, the AI technique could not adequately understand the diversity in groundwater level datasets using field data from various stations. According to the current study, the AI tool works well in some fields of water resource engineering, but it has difficulty in other domains in capturing the diversity of datasets.

Morphological Characteristics of Constrained Meandering Rivers in the Loess Plateau

In the Loess Plateau of China, loess is widely distributed and forms a unique geomorphic feature of the world. Meanwhile, the Yellow River water and sediment regulation system is under construction. Nonetheless, the morphological characteristics of constrained meandering rivers in the Loess Plateau are still unknown due to the difficulty of extracting the sediment-laden water body. An improved method is proposed based on Landsat 8 imagery, which automatically extracts the multi-band spectral relationship of high-sediment-concentration rivers in valleys. This study analyzes the morphological characteristics of constrained meandering rivers in the middle reaches of the Yellow River Basin, including their sinuosity, periodicity, curvature, and skewness based on the deflection points bend segmentation and continuous wavelet transform methods. These characteristics are then compared with those of other constrained meandering rivers and alluvial meandering rivers. The results show that the sinuosity of the constrained river bends is generally low (with an average of 1.55) due to limitations imposed by the riverbanks, which prevent full development. The average dimensionless curvature radius of the constrained rivers is 18.72, lower than that of alluvial rivers. The skewing angle of the constrained river bends typically inclines upstream, with a proportion reaching 59.44%. In constrained river bends, as the sinuosity increases, the proportion of bends skewing upstream initially increases and then gradually decreases. This indicates that constrained river bends can develop similarly to alluvial bends at lower sinuosity but are limited by the mountains on both sides at medium sinuosity. The analysis of river characteristics in regions with different geological structures reveals the effect of geological structures on the formation of constrained rivers in the Loess Plateau. These findings can provide a reference for selecting reservoir dam sites and are important for the dredging engineering layout in the middle reaches of the Loess Plateau. They also offer quantitative explanations for the meandering characteristics of these rivers.

Environmental and human health risk associated with heavy metals in sediment of a tropical river in India

ABSTRACT Heavy metals persist in the sediment and can induce toxicological effects on living organisms. For analysing the risk of heavy metals, geochemical fractionation is beneficial. These geochemical fractions or speciations help to determine the heavy metals availability, mobility, toxicity, enrichment, and various risks. Here, we show how heavy metal contamination of sediment poses risks to both the ecosystem and human beings. We found significant Zn, Co and Cd contamination by analysing the geoaccumulation index. We also observed higher geoaccumulation index values for the pre-monsoon season than the post-monsoon one. Furthermore, pollution load index indicated gradual contamination of heavy metals in the sediments. This study's risk assessment and modified risk assessment codes showed low or no risk, but contamination factors indicated moderate to high risk. Our analysis of the effective range median mean quotient revealed some sampling stations as medium to high-priority sites. Similarly, probable effect level mean quotient designated some sampling stations as medium-low priority sites. We anticipated a moderate to significant mortality effect on the organisms from toxicity unit index values. Potential ecological risk index indicated a very high ecological risk on the Mahananda River. Furthermore, we predicted non-carcinogenic health hazards and carcinogenic health risks in the river's sediment.

Source distribution, ecological risks, and controlling factors of heavy metals in river sediments: Receptor model-based study in a transboundary river basin

In the context of transboundary rivers, which constitute intricate fluvial ecosystems, the persistent threat of heavy metals (HMs) contamination poses significant risks to ecosystem health. In this study, ecotoxicological hazards, governing factors, and the distribution of nine HMs (uranium (U), lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr), manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu)), as well as sediment characteristics (sand, silt, clay, organic matter, and pH) are assessed within the sediment. The current investigation encompasses the analysis of twenty-seven sediment samples, utilizing inductively coupled plasma mass spectrometry, in the transboundary river basin of Bangladesh, specifically the Teesta River. Notably, the findings underscore the predominance of Cd as a contaminant, responsible for 51.85%, 81.84%, and 100% of the geo-accumulation index, contamination factor, and enrichment factor, respectively. The Teesta River emerges as moderately to highly polluted, with cumulative probabilities of 7.4%, 85.2%, and 7.4% denoting "medium", "high", and "priority" pollution levels, respectively. Regions in the upstream and downstream middle sections of the study area exhibit relatively higher pollution levels, particularly in proximity to Kaunia Upazila in the Rangpur district. Ecologically, the potential risk index indicates a low likelihood of ecological impacts at 77.8%, alongside a moderate risk observation of 22.2%. The current results attribute the distribution of these HMs to the pH and organic matter content within the sediment, serving as pivotal factors. To unravel the origins of the HMs, the positive matrix factorization (PMF) model successfully identifies four contributing factors, primarily from geogenic sources. Validation of the PMF model through Spearmen correlation and principal component analysis (PCA) reveals a consistent pattern, affirming its efficacy in this analysis. Within the region, HM sources are identified as originating from anthropogenic activities such as irrigation, industrial discharges, and domestic effluent, in addition to substantial inputs from geogenic sources. Recognizing the transboundary nature of metal pollution, the current study underscores the imperative for continuous and vigilant monitoring, coupled with the implementation of robust management practices. The interplay of both anthropogenic and geogenic factors necessitates a comprehensive approach to effectively and sustainably combat HM contamination.

Fingerprint of Plio–Quaternary detrital zircon geochronology: Implications for sediment provenances and geomorphological evolution of the Yangtze Delta

The Yangtze (Changjiang River) Delta serves as a prominent depocenter for siliciclastic sediments from the Tibetan Plateau and Yangtze Craton, providing essential data on sediment source-to-sink dynamics and geomorphological evolution of large river drainage systems. This study presents the detrital zircon geochronology of Plio–Pleistocene sediments in the Yangtze Delta, alongside the data from modern river sediments, to elucidate provenance evolution since the Pliocene. The zircon geochronology reveals a considerable shift in sediment provenance during the Pliocene–Pleistocene transition. The Pliocene sediments exhibit a straightforward and predominant zircon age spectrum characterized by a typical peak age of 100–200 Ma. This spectrum markedly differs from the modern upper–middle Yangtze River sediments but closely resembles those of local rivers in the lower Yangtze River region. This demonstrates that the Pliocene sediments originated from local mountainous rivers, indicating the paleo-Yangtze River channelization prior to the Quaternary. In contrast, the zircon age spectra of Pleistocene sediments in the present-day delta reveal several dominant age groups ranging from 11.9 ± 1 to 3643 ± 30 Ma, similar to those found in present-day upper–middle Yangtze River sediments. This implies that the Pleistocene sediments were mainly derived from the upper–middle Yangtze River, showing a diversity of source rocks with varying geological ages and origins. The presence of the upper Yangtze River provenance signal, characterized by Cenozoic (<65 Ma) zircons, in early Pleistocene strata (ca. 1.6 Ma) of the delta suggests that the paleo-Yangtze River transported Tibet-sourced sediments into the modern delta area no later than that time. These findings indicate the geomorphological evolution of the Yangtze River Delta from an intermontane basin in the Pliocene to an alluvial–fluvial plain during the Quaternary. This geomorphological and geographic evolution, along with changes in sediment source, directly reflect extensive tectonic subsidence in eastern China since the late Cenozoic.

Riparian vegetation entraps macroplastics along the entire river course: implications for eco-safety activities and mitigation strategies

Macroplastic litter causes detrimental effects on freshwater biota affecting human health. Despite the significant role of rivers in transporting plastic waste, most plastics remain in fluvial ecosystems, accumulating in infrastructure, river sediment, and (riverbank) vegetated areas. However, the entrapment of plastics by riparian vegetation was overlooked, particularly in upper and middle river courses. For the first time, we aimed to quantify the entrapment of plastics by riparian vegetation along the entire river course. Sampling riparian areas in the upper, middle, and lower river courses in central Italy, we found 1,548 macrolitter items, with vegetation entrapping 93.9% of total litter. Riverbank and riparian plastics acted as long-term indicators of river plastics. We emphasized the trapping efficiency at the species level highlighting that the best plastic trapper species were trees, shrubs and reeds (Populus spp., Salix spp., Rubus ulmifolius, Phragmites australis, and Ficus carica), blocking 85.4% of the total macrolitter entrapped by plants. Plastic pieces, bags, bandages, sanitary items, and packaging were among the most trapped types. Furthermore, vegetation in the lower river course exhibited greater plastic entrapment compared to the upper and middle courses, following the fact that all the river courses contribute to plastic pollution. Recognizing the potential of riparian vegetation as a valuable ecosystem service in trapping macroplastics, further research should explore the characteristics and structures of riparian communities involved in this process. By developing eco-safe practices and mitigation strategies based on these findings, we might contribute significantly to managing, conserving, and restoring riverine ecosystems.

Towards a new generation of fluvial facies models for the interpretation of ancient deposits, based on inter‐annual peak discharge variance of modern rivers

ABSTRACTFluvial facies models based on river planform are flawed and not fully fit for purpose. An alternative approach to classifying fluvial deposits is based on river discharge characteristics. A recent paper showed that the co‐efficient of variance of annual peak discharge (CVQp) correlates well with the characteristics of preserved alluvium for a suite of modern rivers. Here, the database of rivers is expanded and augmented, and the utility of this statistic confirmed. For modern rivers, plotting the running‐value of CVQp for a set interval (for example, 30 years) over a longer discharge record shows that the statistic varies both spatially and temporally. The CVQp can rise abruptly at a given location in response to a single flow event if that event is significantly larger than is common in that river. Such abrupt changes in CVQp are superimposed on longer‐term patterns of more gradual change stimulated by environmental factors or anthropogenic effects such as dam construction. If the period of calculation for CVQp is relatively short, ‘anomalous’ events appear more frequently. Sequential studies of modern rivers indicate that such anomalous events have a high probability of being preserved in the alluvial record of the river, and suggest that, over the timeframes of channel filling and abandonment, they may constitute the dominant (characteristic) portion of the record in high CVQp systems. Since flow events with strongly peaked hydrographs (flashy discharges) are more common in high CVQp systems and leave a record dominated by upper flow regime stratification styles, it follows that the alluvial record of high CVQp rivers will be dominated by upper flow regime stratification. In contrast, in lower CVQp systems the occurrence of an event that changes the running CVQp value significantly may form a distinct event deposit, and the temporarily changed CVQp is unrepresentative for the duration of the channel's life. The dominance of upper flow regime stratification, together with decreased preservation of identifiable macroform structure, increased lateral lithological heterogeneity, and in many cases increased preservation of in situ tree fossils in channel deposits of higher CVQp rivers, forms the basis for a series of new facies models for low, moderate, high and very high/ultra‐high CVQp alluvial systems and deposits. The new models can be applied to ancient successions either in combination with traditional, planform‐based models, or not. These models provide information about ancient palaeoenvironmental conditions, and changes in such conditions over time at various scales via stratigraphic investigations.

Research on the relationships between river erosion and sedimentation and energy loss in the Yangtze River Basin of China

River scour and siltation, inherently prolonged and multifaceted phenomena, profoundly impact the hydraulic conductivity and navigational safety of waterways, thereby rendering the precise forecasting of their fluctuations a paramount and unresolved challenge. This study embarks on a novel investigative trajectory by examining energy dissipation in rivers, specifically through the scrutiny of empirical hydrological records. Employing the principles of energy balance theory, this study elucidates the intricate connection between energy losses and sedimentation volumes in the upper reaches of the Yangtze River and at its confluence with the significant tributary, the Jialing River.Our findings diverge from conventional wisdom, revealing that standard metrics of energy loss, encompassing kinetic, potential, and total mechanical energies, along with momentum losses, inadequately characterize the complexity of sediment deposition processes. In contrast, we demonstrate that the loss of suspension power is a more indicative measure of sedimentation quantity. Through meticulous comparisons of various formulations for calculating suspension power, we identified a formula grounded in the concept of minimal available power dissipation in river systems that exhibits superior accuracy in correlating suspension power losses with sedimentation patterns in river sections. This formula's efficacy is further enhanced when considering aggregate suspension power dissipation under the influence of tributary inflows, enabling refined predictions of sedimentation variations along river segments. In conclusion, the insights derived from this meticulous research contribute significantly to the realm of river resource management and the pursuit of sustainable, high-quality aquatic ecosystem development.

Quantitative Analysis of Planform Changes in the Lower Mahaweli River, Sri Lanka

ABSTRACT The development of hydraulic structures has impacted the river discharge and sediment transportation, thus highlighting the river planform changes. Among 103 river catchments in Sri Lanka, the Mahaweli River is the longest river with the largest basin. Many development projects over the years diversely impacted the changes in river masks. However, no study has been conducted to quantify the planform changes in the lower Mahaweli River. Therefore, a comprehensive study was conducted to analyse the river planform changes over 30 years (1991-2021) from Damanewewa to Trincomalee. Freely available remotely sensed satellite data with 30 m resolution were used in the analysis. These images were processed using the QGIS mapping tool and RivMAP toolbox in MATLAB. Major changes were identified at the downstream part of the river and an oxbow lake formation was also observed. The average width for the entire reach (Wra) was identified as 14.83 m and channel width average (Wavg) was noted as 18.09 m. In addition, erosion and accretion rates were calculated, and the cumulative sequence of these rates was increased over the years affecting the change in channel width. Furthermore, the migration rates were also computed with generated river centerline. Highest migration rate reached about 400 m/yr, in the downstream which finally leads to severe meandering. Results revealed that this methodology can be applied to similar river planform analysis. Further, these results showcase the potential importance of analyzing channel stability as well as for water resource management.

Carbon and nitrogen sources in tropical coastal lagoon food webs under variable hydrological conditions

Whilst the impact of continental and marine nutrient sources on the ecological functioning of coastal food webs is well investigated in temperate regions, tropical ecosystems remain less well understood, in particular coastal lagoons. In this study, the sources of carbon and nitrogen in a coastal lagoon system in the southeast of Madagascar are traced using stable isotopes of carbon (δ13C) and nitrogen (δ15N). Three interconnected coastal lagoons with different degree of river influence and eutrophication are investigated. Their food webs are assessed with respect to spatial and seasonal (wet and dry seasons) variations in lagoon water conditions, as well as with respect to the sources of nutrients and organic matters. Results show that river input is the main source of NO3−, and that NO3− supply is significantly higher during the wet season. In contrast, NH4+ is produced internally in the lagoon, and concentrations are higher during the dry season. A lower δ13C value observed in particulate organic matter (POM; proxy of phytoplankton) indicates terrestrial-riverine carbon inputs, which generally have low δ13C values. During the dry season, exceptionally high δ15N values of lagoon POM suggest the uptake of newly produced lagoon water NH4+ and/or the 15N enrichment of lagoon POM pool due to mineralization, resulting in 15N enrichment in consumers. Moreover, δ13C and δ15N values of consumers (fishes and invertebrates) reflect predominantly those of lagoon POM and sediment organic matter (SOM), suggesting that consumers primarily depend on lagoon POM and SOM as sources of carbon and nitrogen. The δ15N values in consumers further indicate that some species feed on more than one trophic level, suggesting flexible foraging strategy of consumers as a function of food source availability. This study demonstrates the roles of both river inflow and sediment in supplying carbon and nitrogen to a coastal lagoon food web, documenting the ecological implications of seasonal variations in lagoon hydrological conditions.

Anatomy of Niger and Benue river sediments from clay to granule: grain-size dependence and provenance budgets, Nigeria

ABSTRACT This study explores in detail the complexity of textural–compositional relationships in fluvial sediments. To this aim, fifteen size fractions (from clay to granule) of three sediment samples characterized by virtually identical size distribution from the Niger and Benue rivers in central Nigeria were separately analyzed by multiple methods (optical microscopy, manual and semi-automated Raman spectroscopy, X-ray diffraction, elemental geochemistry, Nd isotopes). The independent mineralogical and geochemical datasets thus obtained allowed us to investigate processes of sediment generation for five diverse size modes (clay, fine cohesive silt, very coarse frictional silt, very fine sand, coarse sand) derived in different proportions from different sources (wind-blown dust, soils and paleosols, fine-grained and coarse-grained siliciclastic units, igneous and metamorphic bedrocks). Controls on the size distribution of detrital minerals (settling equivalence, size inheritance, weathering, mechanical durability, and chemical durability through multiple sedimentary cycles) were examined, specifically focusing on tectosilicates and on the long-standing petrological problem of feldspar–grain-size relations. Various factors determine the composition of different size modes: kaolinite-dominated clay derives from both deeply weathered soils or paleosols and distant Saharan sources; cohesive silt is largely recycled from mudrocks and soils formed in sedimentary basins. The proportion of detritus derived first-cycle from basement rocks increases from very coarse silt to very fine sand, whereas the coarse-sand mode is quartz-dominated with scarce plagioclase and amphibole and local occurrence of garnet, staurolite, monazite, or xenotime reflecting a combined influence of size inheritance from igneous (pegmatite) and metamorphic sources, mechanical and chemical durability, and recycling from coarse-grained siliciclastic units. Sediment budgets based on mineralogical, geochemical, and geochronological signatures consistently indicate dominance of Benue sediment supply, although the contribution from the Niger mainstem to the Niger Delta is inferred to have been notably greater in the wetter past, before clastic fluxes dropped in response to the aridification of the Sahel.

Tracing of phosphorus in river sediments using the structural equation modeling

ABSTRACT Phosphorus (P) is transported into the water resources mainly due to soil erosion. Using the structural equation modeling, this study investigated the relative contribution of different P-producing sources in the Pasikhan River watershed, south of the Caspian Sea, Northern Iran. For this purpose, 79 surface soil samples and 14 suspended sediments were taken from the potential P sources and the river. These sources included undisturbed and degraded rangelands, forests, rice fields, tea gardens, and gullies. The built-in structural equations in PLS software were used for modeling purposes. The overall model fitting index (goodness of fit (GOF) = 0.591) showed the model's strong forecasting capability. Degraded rangelands, gullies, rice fields, and tea gardens significantly contribute to P in the river sediments. In particular, the highest contribution was related to degraded rangelands and gullies (intensity of the effect = 0.63 and 0.47). Finally, the results showed that gullies' contribution was 28.26% to the P production in river sediments, while the other sources had a relatively equal contribution. In conclusion, this study elucidates that undisturbed rangelands and forests exhibit negligible contributions to phosphorus levels in river sediments. Overall, the results confirmed that structural equation modeling is a robust and efficient approach to identifying P sources.