Sediment Retention Research Articles

Forest ecosystem services of water-related filtration and regulation, a multi-source assessment and economic valuation in Mangla watershed

ABSTRACT Watershed forests offer crucial ecosystem services for hydrological systems. This study provides comprehensive insights into sediment retention within the Mangla watershed. We analyzed spatial layers from Sentinel-2 imagery, land use data, weather, soil properties, and terrain characteristics to identify soil erosion and sediment delivery hotspots. Using the Integrated Valuation of Environmental Services and Tradeoffs-sediment delivery ratio (InVEST-SDR) model, we quantified sediment exported to the downstream Mangla Dam. The InVEST-sediment retention (InVEST-SR) model estimated the sediment retention capacity of various land cover types. Our findings show that forests retained 20,300.70 tons of sediment in 2017 and 29,887.60 tons in 2021, making them the primary source of sediment retention. The economic value of this ecosystem service was approximately USD 2.59 trillion for 973,168.51 ha of forest in 2017 and USD 4.02 trillion for 1,023,927 ha in 2021. Understanding the dynamics and economic value of this forest ecosystem service at a large watershed scale provides essential insights for decision-making and conservation efforts aimed at protecting water resources and ecological integrity.

Wood jam characteristics influence but do not fully explain wood jam morphologic functions

In-stream wood jams alter their surrounding channel morphology, thus setting riverscape morphology and ecosystem function. While wood jams clearly scour pools, retain sediment, and influence bank erosion, there is a lack of observational evidence of how wood jam characteristics themselves control morphologic effects. Here, I analyzed field observations of hundreds of wood jams to test the hypothesis that wood jam characteristics can predict local morphologic effects such as sediment retention, bar forcing, and pool scour. I found mixed support for this hypothesis: While jam characteristics such as porosity, channel blockage ratio, thalweg occupation, and having rootwads and multiple trunks significantly predicted morphologic effect occurrence and magnitude, they only explained a small portion of the variance in those morphologic effects. While wood jam characteristics are relevant in controlling their overall morphologic functions, those functions are both inherently variable and likely affected by numerous other factors, such as reach-scale topography, the sediment transport capacity to supply ratio, and interactions with surrounding wood and vegetation. Wood function restoration may be more effective if it targets reach-scale objectives across dynamic wood jam assemblages, instead of individual jams.

Mapping and Identification of Ecosystem Services Hotspots in the Brazilian Pampa Biome.

The intensification and expansion of changes in land use and land cover (LULC) can reduce the availability and quality of natural habitats and ecosystem services (ES). These changes have generated environmental damage in different parts of the world, especially in biomes more susceptible to modifications, such as the Pampa biome in the extreme south of Brazil. The Pampa biome has been neglected by environmental protection laws, despite its broad ecosystem and social importance. In this study, we used InVEST models to map and quantify five ES provided (i.e., water supply, carbon stock, groundwater stock, sediment retention and habitat quality) by 14 watersheds distributed in the Brazilian Pampa biome as well as determine ES hotspots by summing the areas with high provision of ES. We identified low availability of water supply and groundwater stock in practically the entire study area. High sediment retention and carbon stock were reported in areas with the presence of native vegetation. In addition, despite the large degraded areas, we observed high habitat quality associated with native vegetation in all studied watersheds. The hotspots varied spatially in the study area according to the proposed scenarios, the supply and the overlap of ES. Scenario 1 (>50% of ES) presented a larger area of high provision of ES. In contrast, scenario 2 (>75% of ES) presented smaller patches of areas with high provision of ES distributed across different watershed. We observed that large territorial extensions with high and medium provision of ES are vulnerable to the negative effects of LULC. Our study presented scenarios that indicate areas of high provision of ES, contributing to a more practical application, being a simplified and useful tool that can assist conservation and sustainable policies.

Estimation of the soil erosion and sediment trapping using Gerlach troughs in different Land Uses in Luangprabang Province

This study aims to study sediment loss in different areas by collecting data from the Reservoir and Gerlach troughs in the Luangprabang Province, Laos The implementation of this experiment was a selection of study areas to install soil sediment retention tools (Gerlach trough) according to 6 treatments such as T1: No teak+Ruzi grass; T2: No teak + Fallow; T3: Teak with low understory density + Natural regrowth; T4: Teak with low understory density + Ruzi grass; T5: Teak with high understory density+ Natural regrowth; T6: Teak with high understory density+ mixed fodder cover (Ruzi and Napier grass). In 3 replicates/treatments by RCBD design, a total of 18 instruments will be installed by installing them in a row on both sides of the soil, to trap the soil sediment that flows with the water, then there will be a collection of samples that can be collected, and then filter the soil sediment and dry it at a temperature of 105 degrees, for a period of 48 hours and calculate the amount of soil sediment loss in the area. Results found that the highest soil loss (sediment) was in the area planted teak with low understory density + Natural regrowth (T3) followed by the area planted teak with low understory density + Ruzi grass, (T4), and the lowest soil loss was in the area no teak+Ruzi grass (T1) and the area no teak + fallow (T2). While the highest surface water runoff was in the area planted teak with low understory density + Natural regrowth (T3) and the area planted teak with low understory density + Ruzi grass, (T4). On the other hand, factors that are related to surface water runoff and soil sediment loss such as percentage of land cover density, slope of the land, and residue or humus on the land were found that the area no teak with planted Ruzi grass and the area no teak with fallow (natural growth) had lowest rate of surface water runoff and lowest soil sediment loss compared to other areas. It can be concluded that the land cover factor has an important role in helping to reduce surface water runoff and help prevent soil sediments from being lost to runoff in agricultural land and upland cultivation.

Quantifying Ecosystem Services to Maximize Co-Benefits under Market-Based Conservation Solutions in the Edisto River Basin, South Carolina

As climate change intensifies, the need to conserve ecosystem services and our natural resources increases. Nature-based solutions projects that focus on sequestering carbon can also have significant impacts on the ecosystem services in the project area. Herein, we describe a method to quantify ecosystem services via the Integrated Valuation of Ecosystem Services and Tradeoffs (Version 3.14) model. We use those quantitative methods to show where carbon projects and other restoration projects could increase certain ecosystem services through best practices. Using the Edisto River Basin in South Carolina as a study site, we developed a spatial additionality model that shows where water retention, carbon, and sediment retention can be improved. InVEST modeling showed high levels of sediment export and water yield, with 0.12 tons/acre of sediment exported and 256.3 cm/acre of water yielded downstream on average. The model indicates that over 70,000 acres comprised of parcels greater than 20 contiguous acres could implement management to increase ecosystem service provisioning. This model output shows spatially where best management practices can be implemented to achieve positive outcomes and where carbon projects could be implemented to derive additional co-benefits. Furthermore, it can be used as a tool for measurement and verification as data is updated.

Comparing the Sources of Sediment Retained by Beaver Dams and Beaver Dam Analogs

AbstractBeavers modify riverine systems by building dams that alter downstream fluxes of water and sediment. Where beavers have been lost and stream channels degraded, beaver dam analogs (BDAs) are being used to mimic the effects of beaver engineering. Central to the success of these structures in accelerating stream recovery is creating similar ecosystem responses as beaver dams including sediment retention. Unknown is the relative importance of beaver actions versus erosion in the catchment in generating the retained sediment. This study tested the viability of sediment fingerprinting to determine the source of sediment retained by beaver dams and BDAs in a watershed in Alberta, Canada. Concentrations of 29 elements were measured as potential tracers from known sediment sources: upland, terrace, stream bank, and beaver canal. Virtual mixture tests, used to compare the computed source estimates with known source mixtures, revealed that sediment fingerprinting is a robust method for identifying sources of sediment retained by beaver ponds and BDAs. The un‐mixing model results indicate that on average 56% of the sediment retained by the beaver dams originated from terraces, 23% from uplands, and 13% from beaver canals. About 89% of sediment retained by the BDAs originated from eroding stream banks. We conclude that the geomorphic effects of beavers and their dams are more diverse, resulting in more diverse sources of sediment retained by their dams. This differentiates beaver dams from BDAs. The study has implications for informing management practices that involve beavers and beaver mimicry.

Study on the Performance Evaluation Method and Application of Drainage Nonwoven Geotextile in the Yellow River Sediment Filling Reclamation Area

Technical challenges associated with drainage and filling efficacy confront the Yellow River sediment filling reclamation, a novel approach to reclaiming coal-mined subsided lands. This study proposes an improved geotextile performance evaluation method to address the shortcomings of current geotextile screening methodologies in the drainage of the Yellow River sediment. This method comprehensively considers essential characteristics under working conditions, such as permeability, soil conservation, and blockage prevention properties, including indicators such as the permeability coefficient and sediment retention rate of geotextiles under pressure. Indoor flume filling and drainage experiments were implemented to verify the efficacy of geotextile drainage. The improved method identified thermal-bonded nonwoven geotextiles of 200 and 250 g·m−2 as having the highest comprehensive evaluation scores. The experimental results showed that these geotextiles significantly improved their drainage efficiency and better met the specific requirements of the Yellow River sediment filling reclamation. Traditional screening methods may be unsuitable for sediment drainage conditions, necessitating sediment interception and rapid drainage due to the streaming water–sediment mixture. Therefore, the newly established performance evaluation method is more appropriate for the specific requirements. It is recommended that a simple vibrating device be installed to maintain 20 vibrations per minute to keep drainage channels clear and provide stable drainage performance in engineering applications.

Evaluation and Optimization of Landscape Spatial Patterns and Ecosystem Services in the Northern Agro-Pastoral Ecotone, China

The alteration of landscape spatial patterns (LSPs) and ecosystem services (ESs) in watersheds can have detrimental effects on the local environment and community. However, a comprehensive understanding of the current state of LSPs and ESs in watersheds around Winter Olympic venues in China is limited. Here, we assessed current LSPs and ESs and developed optimization strategies for the Xigou watershed around Winter Olympic venues in the northern agro-pastoral ecotone of China. The results indicated that the main land use type was grassland in the Xigou watershed, and landscape types were relatively homogenous. All three ESs (water yield, sediment retention, and carbon storage) generally improved from 2004 to 2020. For ESs, there was the lowest total volume of water yield in 2004 (637.44 × 104 m3). But sediment retention (10.54 × 106 t, 18.13 × 106 t, 13.28 × 106 t, and 16.85 × 106 t) had an upward, then downward, then upward trend before and after ERP. Carbon storage grew steadily. Correlation analysis suggested that the three ESs were closely related to the landscape spatial indices of average patch area (AREA_MN), contagion index (CONTAG), and Shannon’s evenness index (SHEI). AREA_MN, CONTAG, and SHEI in the eastern part of the study area promoted sediment retention and carbon storage, while in the southwestern part of the study area, they inhibited water yield and sediment retention. The results suggest that improving sediment retention by optimizing land use and cover change (LUCC) and LSPs is the main approach to further enhance ESs in the study area. Our study suggests that the inclusion of multiple landscape pattern indices can provide a more comprehensive representation of regional ecosystem service.

Wave attenuation by Cystoseira sensu lato in two shallow Mediterranean coastal waters

Coastal protection from erosion is an important ecosystem service provided by marine vegetation. Seaweeds and seagrasses can attenuate wave action in coastal areas and increase sediment retention. Here we investigated for the first time the effects of erect Cystoseira sensu lato forests in attenuating the wave energy in two Mediterranean shallow areas (Greece and Tunisia). The hydrodynamic effects were measured using the dissolution rate of gypsum cones (fd) r. Experiments were carried out in Greece, on the species Ericaria barbatula, and in Tunisia on the species E. brachycarpa and Cystoseira crinitophylla. Wave attenuation was directly related to percent cover of these macroalgal forests under different spatial and temporal conditions. On average, Cystoseira s.l. forests with 100 % cover reduced the wave action by 38 % more than the control (0 % cover). This study shows that Cystoseira s.l. forests under specific conditions play a key role for protecting the Mediterranean coasts from erosion, and can present a nature-based solution as an alternative to unsustainable and costly artificial constructions.

Assessing sediment dynamics and retention services in the vulnerable mountain ecosystem of the Indian Himalayas.

Sediment loss and export pose significant global environmental issues, profoundly affecting water quality, soil fertility, and ecosystem stability, particularly in vulnerable mountain ecosystems like the Indian Himalayas. The present study used remote sensing data and the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) sediment delivery ratio (SDR) model to analyze spatial-temporal variations in soil loss (SL), sediment export (SE), and sediment retention (SR) capabilities in the South Shimla watershed, Himachal Pradesh, India, from 1993 to 2023. The findings showed significant changes in land use and land cover (LULC): evergreen forest and scrub land decreased sharply by 11.53% and 36.43%, respectively, while agricultural areas and built-up areas increased notably by 71.16% and 215.76%, respectively. Despite a decline of 19.18% in SL and 24.43% in SE, sediment loss and export varied across the study area, highlighting the heterogeneous nature of sediment dynamics. The overall retention capacity increased by 2.59%, with scrub forests playing a critical role in SR, while built-up areas showed the lowest retention. Northern and central sub-watersheds (SWs) experienced a significant decrease in retention capacity (from - 1.92 to - 11.6%), whereas those in the southern and eastern regions saw an increase in SR (from 3.69 to 28.24%). These results underscore the complex interactions between LULC changes, sediment dynamics, and retention services, highlighting the importance of preserving natural ecosystems and informing policy for landscape-based conservation and development planning in the vulnerable Himalayan region.

The Late Holocene evolution of the Adra Delta subaqueous system (Northern Alboran Sea): Seismic-stratigraphic and geomorphic evidence of millennial scale climatic and anthropic effects

The formation and development of a small Mediterranean deltaic system are investigated through a primary seismic stratigraphic interpretation of a high-resolution seismic profile network, combined with multiple bathymetric data (including multibeam bathymetric imagery) and collated with shallow sediment cores collected with a vibro-corer device.The submarine delta of the Adra River is divided into a basal patchy seismic unit and five wedge-shaped younger seismic units that are related to the Holocene highstand stabilization. Limited age control indicates that the two uppermost seismic units are very recent, most likely related to a dearth of fluvial fluxes led by channel deviations and by sediment retention. The formation of the three older seismic units is correlated to three humid periods during the Middle Holocene, Late Holocene and Little Ice Age, under a general context of progressive aridification of southeastern Iberia.The stacking patterns and spatial distribution of individual seismic units document a history of episodic progradation of successive prodeltaic lobes, with a long-term evolution mediated by climatically-induced changes in the river basin and more recent anthropogenic interventions. Overall, the subaqueous deltaic system registers the complete modification of a deltaic system that evolves from a fluvial-dominated delta to recent wave-dominated wedges. In between, the deltaic system exhibits a progressive asymmetric character, due to the instauration of Atlantic waters on the shelf and their subsequent eastward redistribution. The Adra deltaic system is proposed as an outstanding example of a small deltaic system that reacts almost immediately to the complex interaction between natural changes in the system and anthropogenic interventions in the drainage basin.

Modeling Ecosystem Regulation Services and Performing Cost–Benefit Analysis for Climate Change Mitigation through Nature-Based Solutions Using InVEST Models

Climate change and land degradation menace ecosystem sustainability. This study assessed the effectiveness of integrating nature-based solutions (NBSs); soil and water conservation techniques, agroforestry, and reforestation, to mitigate these impacts. Focusing on carbon storage and sediment retention at the watershed level (Sidi Barrak), the InVEST model quantified changes from 1990 to 2050 under the Business as Usual (BAU) and management scenarios. The results showed a significant decrease in sediment retention and carbon storage from 19.25 to 15.5 t ha−1year−1 and from 1.72 to 1.61 t ha−1year−1, respectively, between 1990 and 2021. By 2050, BAU scenario projections demonstrate a 28% decrease in sediment retention and a 16% drop in carbon storage under Representative Concentration Pathways (RCP) 4.5. The Management scenarios indicate substantial improvements, with carbon storage increasing by 77% and sediment retention by 87% when all strategies were combined. The economic valuation, performed through the application of the cost–benefit analysis, shows positive net benefit values (NPVs) for the different NBS management scenarios. The combined management scenario, which includes soil and water conservation techniques, agroforestry, and reforestation under the same scenario, presents the highest total NPV with 11.4 M€ (2%, 2050), an average of 130 €/ha (2%, 2050), and an opportunity cost of 1.7 M€ compared to BAU. Such results may orient decision-making by providing solid arguments toward ecosystem resilience and climate change mitigation.

Effects of salinity on nitrogen reduction pathways in estuarine wetland sediments

Denitrification, anammox, and DNRA are three important nitrogen (N) reduction pathways in estuarine sediments. Although salinity is an important variables controlling microbial growth and activities, knowledge about the effects of changing salinity on those three processes in estuarine and coastal wetland sediments are not well understood. Herein, we performed a 60-d microcosms experiment with different salinities (0, 5, 15, 25 and 35 ‰) to explore the vital role of salinity in controlling N-loss and N retention in estuarine wetland sediments. The results showed that sediment organic matter, sulfide, and nitrate (NO3−) were profoundly decreased with increasing salinity, while sediment ammonium (NH4+) and ferrous (Fe2+) varied in reverse patterns. Meanwhile, N-loss and N retention rates and associated gene abundances were differentially inhibited with increasing salinity, while the contributions of denitrification, anammox, and DNRA to total nitrate reduction were apparently unaffected. Moreover, denitrification rate was the most sensitive to salinity, and then followed by DNRA, while anammox was the weakest among these three processes. In other words, anammox bacteria showed a wide range of salinity tolerance, while both denitrification and DNRA reflected a relatively limited dynamic range of it. Our findings could provide insights into temporal interactive effects of salinity on sediment physico-chemical properties, N reduction rates and associated gene abundances. Our findings can improve understanding of the effects of saltwater incursion on the N fate and N balance in estuarine and coastal sediments.

A multi‐site and hypothesis‐driven approach to identify controls on the bedload transport regime of an anthropised gravel‐bed river

AbstractUnderstanding the effects of human disturbance on the bedload transport regime of anthropised rivers is a topic of growing importance, as such information is of interest for adequate river diagnosis, correct implementation of restoration measures and appropriate design of post‐action monitoring programs. However, such assessments are complex, especially in sites where multiple factors simultaneously influence the bedload transport regime, so that it is difficult to establish simple causal relationships between human disturbances and changes in the sediment transport regime, notably on bedload. To overcome this, there is a need for rigorous hypothesis‐driven approaches to assess the isolated effects of each driver. With this in mind, we have characterised the dynamics of bedload transport in the Upper Garonne (Central Pyrenees, Spain‐France), a river impacted by sediment retention, flow diversion and mining that influence its morphological conditions and transport regime. We assessed the effects of (1) surface grain size distribution, (2) river morphology, (3) sediment supply and (4) flow diversion on the bedload transport regime. Four sites with different degrees of river anthropisation were selected. After defining hypotheses on the most likely bedload transport conditions for each site, we proposed a set of discriminating criteria to test these hypotheses, based on temporal within‐site and spatial between‐site comparisons of coarse particle tracking measurements over four years. The results of this research showed that the hydrosedimentary regime of the Garonne is controlled by a complex combination of drivers such as valley physiography, which exerts a first‐order control on differences in reach‐scale bedforms and bedload dynamics; and human disturbances which contribute to a reduction in sediment supply through changes in land cover and hydropower dams, or to changes in hydrology (i.e., flow competence) due to water diversion and abstraction.

Calculating the Volume of the Sediment Wedge in Retention Check Dams by Using Most Appropriate Models in Jammu and Kashmir\'s Budgam District

Abstract: Though their efficacy is currently under question, check dams are crucial for sediment retention globally. To estimate the retained sediment fast, readily, and with a suitable degree of approximation, 10 geometric models are proposed in this study together with their field technique and equations. The models were used to calculate the volume of trapped silt and compare them with other commonly used techniques on a sample of check dams in the Budgam district of Jammu and Kashmir based on the valley's form. Compared to topographic methods, our geometric method produced lesser volumes, but it produced larger volumes than basic methods. As a result, this approach minimizes fieldwork, computations, and expense when used as a preliminary approximation to estimate the sediment trapped by check dams and tiny silted dams. Additionally, compared to the outdated, basic procedures, it enables the selection of a higher precision and better match to the sediment wedge shape.

Optimizing coastal protection: Nature-based engineering for longitudinal drift reversal and erosion reduction

Traditional hard engineering solutions have shown weaknesses in mitigating erosion processes in vulnerable coastal areas, contributing in some cases to their aggravation, which makes it necessary to study innovative nature-based engineering solutions. This research deals with an in-depth analysis of hydro-morphodynamic modelling results for optimizing the geometry of maritime structures under longitudinal drift reversal conditions by mimicking and manipulating natural processes to promote wave energy dissipation and sediment retention through wave deformation due to obstacle interposition. The solutions draw inspiration from the full-scale observation data of two examples of longitudinal drift reversal. Additionally, numerical simulations were developed for predicting wave climate near the Iberian Peninsula shoreline under different scenarios. Hydrodynamics and morphodynamics modelling results are discussed based on the impact of a specific storm, considering different characteristics of protection structures, followed by parametric sensitivity analysis and comparative studies performed with an optimized solution. Results indicated this solution contributed to sediment accumulation downdrift near the shoreline, as there is no interruption of the longitudinal drift compared to traditional protection structures. At the alignment, the structure also improved nearshore sediment accretion, reduced areas of erosion relative to a no-structure scenario and exhibited behaviour akin to an emerged structure with its crest level. Compared to wholly submerged structures, it becomes a relevant coastal protection alternative, as it guarantees excellent protection on the adjacent coastal zone by safeguarding against tidal variations induced by storm surges and mean sea level rise due to climate change. Furthermore, there is a positive effect to help promote biodiversity whenever the structure is located in an intertidal zone. Despite the enormous computational effort required in the hydro-morphodynamic modelling process, this study shows that it is possible to create innovative engineering coastal solutions to induce longitudinal drift reversal and reduce erosion near the shoreline.

Human-made small reservoirs alter dryland hydrological connectivity

Our research shed light on the distribution, number, and impact of small reservoirs (SRs) on rural dryland water availability and hydrology. We measured the storage capacity, relationship to environmental variables, and effects on the hydrology of all SRs (1225) found within a Sonoran Desert basin. SRs were predominantly associated with Tertiary conglomerates and Quaternary alluvium and were less common in extrusive rocks. A higher concentration of reservoirs was observed in woodlands and thornscrub, with fewer SRs in desertscrub than anticipated by chance. The average size of these small reservoirs was 5205 m2. All SRs reached full storage capacity during the rainy season, but only 20 % retained water throughout the year. Furthermore, our analysis revealed a significant impact on basin connectivity, with only 41 % of superficial drainage being connected. Notably, two large dams were found to disconnect 26 % of the basin. Despite their relatively small watershed footprint, SRs were found to be responsible for disconnecting 33 % of the total basin area. The magnitude of rainfall events played a crucial role in connectivity dynamics. Low-magnitude rainfall events led to sediment retention in SRs, reducing connectivity, while moderate events increased connectivity by repeatedly filling SRs. High-magnitude events reshaped channels, transported sediments, and enhanced overall connectivity. The concentration of SRs in the upper reaches of the basin coincides with higher stocking rates. SRs, are relatively recent additions to desert landscapes, impacting ecological dynamics. Their construction and use fragment an already disjointed basin, thereby restricting water retention by larger dams. These findings emphasize the intricate relationship between SRs, rainfall occurrences, and the overall connectivity of the basin. We underline that documenting the cumulative effects of SRs yields valuable insights for managing water resources in arid ecosystems.

Enhancing Water Ecosystem Services Using Environmental Zoning in Land Use Planning

Land use and land cover (LULC) changes alter the structure and functioning of natural ecosystems, impacting the potential and flow of ecosystem services. Ecological restoration projects aiming to enhance native vegetation have proven effective in mitigating the impacts of LULC changes on ecosystem services. A key element in implementing these projects has been identifying priority areas for restoration, considering that resources allocated to such projects are often limited. This study proposes a novel methodological framework to identify priority areas for restoration and guide LULC planning to increase the provision of water ecosystem services (WESs) in a watershed in southeastern Brazil. To do so, we combined biophysical models and multicriteria analysis to identify priority areas for ecological restoration, propose environmental zoning for the study area, and quantify the effects of LULC changes and of a planned LULC scenario (implemented environmental zoning) on WES indicators. Previous LULC changes, from 1985 to 2019, have resulted in a nearly 20% increase in annual surface runoff, a 50% increase in sediment export, a 22% increase in total nitrogen (TN) export, and a 53% increase in total phosphorus (TP) export. Simultaneously, they reduced the provision of WESs (baseflow −27%, TN retention −10%, and TP retention −16%), except for sediment retention, which increased by 35% during the analyzed period. The planned LULC scenario successfully increased the provision of WESs while reducing surface runoff and nutrient and sediment exports. The methodology employed in this study proved to be effective in guiding LULC planning for improving WES. The obtained results provide a scientific foundation for guiding the implementation of WES conservation policies in the studied watershed. This method is perceived to be applicable to other watersheds.

A conceptual model on the influence of logjam formation on longitudinal and lateral sediment dynamics in forested streams

Large wood (LW) and log jams have important implications for sediment dynamics within river systems. Although many case studies explore this topic, far fewer synthesize these results at the reach and basin scales. In this paper, we present a conceptual model that relates valley setting and landscape history of forested, mountain streams to spatiotemporal patterns of sediment storage and transport via the formation and decay processes of logjams. This conceptual model explores the function of logjams as sediment transport moderators, significantly influencing sediment retention, channel morphology, and lateral and longitudinal connectivity. Detailed wood inventories, channel topographic surveys, and channel morphology from four case studies are used to illustrate the range of channel responses to logjam formation, evolution, and decay in different valley contexts. Valley setting is shown to influence logjam formation and dynamics by determining the mechanisms and timing of sediment and wood recruitment. In steep and narrow (and thus coupled, confined) reaches, colluvial processes are the dominant mechanisms of wood and sediment delivery, and logjams grow vertically as sediment is stored in a wedge behind the jam (longitudinal disconnectivity). In contrast, in unconfined reaches (decoupled hillslopes), wood and sediment recruitment occurs primarily through fluvial processes, and logjams grow laterally as the channel shifts across the valley bottom. These logjams have long lifespans, often over a century, and gradually release sediment as the logjam decomposes. Sediment deposits stabilized by riparian vegetation behind these structures may persist long after logjam decay. This conceptual model is a testable framework and practical tool that offers insight into wood-sediment interaction mechanisms within steep, forested basins.

A Quantitative Provenance Analysis (QPA) Approach to Quantify Controls on Sediment Generation and Sediment Flux in the Upper Reaches of the Magdalena River (Colombia): 1. Natural and Anthropic Controls on the Sand Fraction

AbstractThis study investigates the upper Magdalena river basin (Colombia), which is characterized by tectonic activity, tropical climate, heterogeneous lithological assemblages, and anthropic influence. It aims to comprehend factors controlling sediment generation, flux, and composition by incorporating petrographic data from 27 recent fluvial samples along with geochemistry, geomorphological parameters, historical precipitation, land cover, landsliding and suspended sediment load data. The analysis shows mismatches between sand composition and drainage lithology distribution. A new set of endmember mixing models is presented, quantifying the impacts of erodibility, sand generation potential (related to lithology), and sediment connectivity between hillslopes and river outlets (related to geomorphology). Results show enhanced sediment generation from sedimentary rocks (up to 40%) due to high erodibility, and decreased sediment flux from low‐ to medium‐grade metamorphic rocks (up to 60%) due to controlling morphometric parameters. Overrepresentation of plutonic and high‐grade metamorphic rocks and underrepresentation of volcanic rocks (up to 100%) are controlled by mineralogical and textural parameters. Enhanced landsliding activity in areas with volcanic activity occasionally overshadows basin‐wide compositional trends driven by morphological and lithological characteristics, as it controls rare overrepresentation of volcanic and low‐grade metamorphic detritus in the sand fraction. Sediment retention by hydroelectric dams significantly decreases suspended sediment flux by 30%, while deforestation plays a minor role in sediment flux. This study underscores the importance of coupling sediment generation, geomorphology and the distribution of stochastic events related to seismic activity in any sediment production‐focused study and for developing numerical models in Quantitative Provenance Analysis (QPA).