Sediment Production Research Articles

Synthesis on the Impact of Land Cover Conversion towards Water Quantity and Quality

This research intends to establish a policy on watershed management based on the land use recommendation and an analysis of land cover conversion to per-urban location towards water quality and discharge which many sub-watersheds in Indonesia are in critical condition due to the frequent event of flooding, drought, and landslide. It is further worsened by the changes of land cover in the watershed that causes to increase in surface runoff which also affects the water quality in the watershed. Watershed condition can be restored by management if the correct implementation and regulation is effective. Out of 458 watersheds in Indonesia, 60 of them were very critical, 222 were critical, and the remaining 176 were in endangered condition. One of the critical watersheds is Ciliwung watershed. Furthermore, public participation is a key in managing watershed. The methodology consists of collecting the primary data as a benchmark for simulation by using SWAT; the regression model is used for covering the water quality while the water discharge analysis is performed through hydrological simulation. Then socio-economic survey is conducted to evaluate public willingness and capacity to participate in the watershed management. The result of simulation shows that sediment and nitrate is positively affected by water discharge while phosphate is negatively affected by it. The conversion of forest into agriculture significantly increases the nitrate and sediment production in while phosphate is not really affected. Meanwhile, in the watershed overall, surface runoff, nitrate, and phosphate are increasing drastically. The result of survey shows that most people that are living in the watershed do not have the funding or yard to participate in the watershed management. This result is a recommendation which reduces the agriculture land use by 10% and allocating it for water management.

Mangroves increased the mercury methylation potential in the sediment by producing organic matters and altering microbial methylators community.

Mangrove ecosystem has attracted global attention as a hotspot for mercury (Hg) methylation. Although numerous biotic and abiotic parameters have been reported to influence methylmercury (MeHg) production in sediments, the key factors determining the elevated MeHg levels in mangrove wetlands have not been well addressed. In this study, Hg levels in the sediments from different habitats (mudflats, mangrove fringe, and mangrove interior) in the Futian mangrove wetland were investigated, aiming to characterize the predominant factors affecting the MeHg production and distinguish the key microbial taxa responsible for Hg methylation. MeHg concentrations in the sediments from the mangrove interior (1.03±0.34ngg-1 dw) were significantly higher than those in mudflats (0.26±0.08ngg-1 dw) and mangrove fringe (0.45±0.10ngg-1 dw). Mangrove vegetation also promoted the accumulation of organic matters in sediments, which stimulated the growth of methylators, ultimately leading to an elevated MeHg level in the sediment. The data from 16S sequencing and random forest analysis further indicated that the increased abundances of Desulfococcus and Desulfosarcina, which belong to complete-oxidizing microbes with acetyl-CoA pathway and are favored by mangrove vegetation, were the primary contributors to MeHg production. Besides, syntrophic partners of methylators (e.g. Syntrophus) also play a considerable role in MeHg production. The present findings provide a deep understanding of Hg-methylation in mangrove wetlands, and offers valuable insights into of the interactions between mangrove plants and soil microbiome in the presence of Hg contamination.

Lithiation-driven cascade dissolution coprecipitation of sulfide superionic conductors

We present a Li2S-free and cost-effective wet chemistry method for the preparation of sulfide solid electrolytes (SSEs), which addresses a major challenge in the commercialization of all-solid-state batteries (ASSBs). Our method universally synthesizes various electrolytes, including LixMS4 (M = P, Sb, or Si) and Li6PS5X (X = Cl, Br, or I). It particularly produces Li6PS5Cl of high quality (5.7 mS cm−1 of ionic conductivity at 25°C) at a material cost of one-tenth of previously reported methods. The synthesis process, featuring a cascade-dissolution-coprecipitation mechanism, is investigated using analytical techniques for soluble intermediates and sediment products. The Li6PS5Cl-based pellet ASSBs with a LiNi0.8Mn0.1Co0.1O2 cathode and a Li-In anode provide high initial capacity (190 mAh g−1 at a 0.1C rate, 55°C) and hold a capacity retention of > 80% after 1,000 cycles at a 2.0C rate. Additionally, a 0.7 Ah pouch cell with a silver/carbon anode exhibits a remarkable energy density (352.8 Wh kg−1 at 45°C). This solvent-based and Li2S-free synthetic process proposes a cost-effective pathway toward sustainable mass production for synthesizing SSEs.

Drivers of high rates of carbon burial in a riverine-influenced freshwater marsh in the Long Point Walsingham Priority Place of southern Ontario

Reported rates of soil organic carbon (SOC) accumulation in wetlands are markedly higher over recent versus longer timescales, caused by SOC losses through decomposition, paleoenvironmental changes, and recent increases in sedimentation or biomass production. Explaining changes in SOC sequestration rates and determining the time horizon over which high rates are sustained are both critical for accurately measuring the potential for wetland conservation as a natural climate solution. Here, we present analyses on a 4-m core from a riverine-influenced marsh in Big Creek watershed, southern Ontario, to track changes in SOC accumulation regimes. Since wetland initiation ∼5700 years ago, mean long-term (pre-industrial) rates of SOC accumulation were 24 g C m−2 year−1, and recent rates up to four times higher. We demonstrate that elevated recent rates of SOC accumulation are largely explained by more labile carbon in surficial soils, and are sustained for less than a century before transitioning to slower burial rates of predominantly recalcitrant organic matter. However, there are exceptions to this trend, such as when labile SOC was buried intermittently during Holocene Lake Erie highstands. Our research underscores the importance of organic matter type and hydroclimatic context in predicting long-term potential for marsh soils to stabilize atmospheric carbon.

Quantification of soil losses using RUSLE model in the Boumlal watershed (Central Rif, Morocco)

This contribution estimates soil losses in the Boumlal watershed by applying the Revised Universal Soil Loss Equation (RUSLE) and using GIS and remote sensing. This model incorporates five essential factors in water erosion: rainfall erosivity (R), soil erodibility (K), slope length (LS), cover management (C), and erosion control practice (P). The overlay of these parameters makes it possible to produce the synthetic map of annual soil losses (t/ha/year) and identify the most vulnerable areas to water erosion. The results indicate that Boumlal watershed is characterized by high sediment production. Indeed, more than 40% of the watershed produces a considerable amount of sediment exceeding 50 t/ha/year, with soil losses reaching over 200 t/ha/year in some parts of the study area. However, areas with low erosion rates represent approximately 33% of the total watershed area. The extent of water erosion and the high soil loss values are linked to the study area's vulnerability and inadequate anthropogenic interventions. Water erosion in this watershed directly affects soil quality, agricultural land productivity, arable land area, and the siltation of downstream reservoirs.

Do ice-dam rupture events leave a distinctive signature in proglacial lake sediments?

Abstract Lake sediment provides a valuable record of past environmental change. However, the controls on sedimentation in proglacial lakes and their relation to glacier retreat remain poorly understood. In this study we analyze glaciolacustrine sediment production and deposition in Canal de los Témpanos, Lago Argentino, Argentine Patagonia. We associate temporal changes in the sedimentologic and geochemical characteristics analyzed from Lago Argentino cores with Late Holocene fluctuations of the Perito Moreno and Ameghino glaciers. We show that the dominant sediment source at our study site switched from Ameghino to Perito Moreno Glacier after the recession of Ameghino Glacier and the formation of the marginal ice-contact lake into which it currently calves. Spectacular ice-dam rupture events generated by Perito Moreno Glacier redistribute large volumes of water through the lake system but do not leave a significant sedimentary signature. Our results demonstrate that a detailed analysis of sedimentologic, petrophysical, and geochemical changes in lake cores can provide insight into regional glacial dynamics and sedimentary processes even in complex systems with multiple competing glacial sources and that changing glacier geometries during retreat can provide insights into the provenience of the sediments.

A simple approach to quantifying whole‐lake methane ebullition and sedimentary methane production, and its application to the Canadian Lake Pulse dataset

AbstractAquatic sediments represent a key component for understanding CH4 dynamics and emission to the atmosphere. Once produced in the sediments, CH4 is released either by diffusion at the sediment–water interface or by bubbling out to the atmosphere when total gas pressure in the sediment exceeds local ambient pressure due to high CH4 production. Although bubbling is one of the dominant CH4 emission pathways in lakes, direct measurements of this flux are hampered by its high spatiotemporal variability and methodological limitations. Here, we develop a conceptual approach to quantify CH4 production in lake sediments and particularly its release as bubbles based on simple measurements of bubble gas content and depth. Its main assumptions were empirically tested using > 200 long‐term bubble trap deployments collected from 4 temperate lakes. We then applied the developed methodology to a suite of 408 Canadian lakes to produce the first standardized large‐scale assessment of lakes CH4 ebullitive flux during summer. Our results show that lake sediments produced CH4 at a median rate of 3.3 mmol m−2 d−1 (ranged from 0.2 to 11.8 mmol m−2 d−1), releasing 33% via ebullition to the atmosphere. These rates are remarkably similar in magnitude to other regional estimates in the literature. Moreover, our approach revealed that catchment slope was an important determinant of both the lake‐wide ebullitive fluxes and the fraction of sediment CH4 production released as bubbles.

Impacts of LULC and climate change on runoff and sediment production for the Puyango-Tumbes basin (Ecuador-Peru)

Climate change will cause alterations in the hydrological cycle, a topic of great relevance to the scientific community due to its impacts on water resources. Investigating changes in hydrological characteristics at the watershed level in the context of climate change is fundamental for developing mitigation and adaptation strategies against extreme hydrological events. This study aimed to analyze the impacts of climate change on flow and sediment production in the Puyango-Tumbes watershed. Projected climate data from CMIP6 were used, corrected through a bias adjustment process to minimize discrepancies between model data and historical observations, ensuring a more accurate representation of climate behavior. The analysis combined two representative climate change scenarios (SSP2-4.5 and SSP5-8.5) with two land use and land cover (LULC) scenarios: (a) an optimistic scenario with reduced anthropogenic effects (LULC_1985) and (b) a pessimistic scenario reflecting future impacts (LULC_2015). The SWAT model estimated future flow and sediment production for two periods (2035-2065 and 2070-2100), following model calibration and validation against the reference period 1981-2015 at three hydrometric stations: Pindo, Puyango, and El Tigre, located in Ecuador and Peru. The simulations revealed a significant increase in sediment generation under the pessimistic scenario SSP5-8.5, followed by SSP2-4.5, while lower sediment yields were observed in the optimistic scenarios. Even in the best-case scenario (optimistic SSP2-4.5), sediment yields remained substantially higher than the reference conditions. Additionally, higher flows were anticipated in some scenarios, with the El Tigre station in the lower watershed being the most affected area. These findings underscore the high probability of more frequent flooding events due to increased sediment yields and flow variability. The results highlight the urgent need for implementing adaptation measures, such as improved land use management and hydrological infrastructure, to enhance social resilience and mitigate the impacts of climate change in the watershed.

A Holistic Approach for Coastal–Watershed Management on Tourist Islands: A Case Study from Petra–Molyvos Coast, Lesvos Island (Greece)

Shoreline configurations are a complex outcome of the dynamic interplay between natural forces and human actions. This interaction shapes unique coastal morphologies and affects sediment transport and erosion patterns along the coastline. Meanwhile, ephemeral river systems play a vital role in shaping coastlines and maintaining ecosystem sustainability, especially in island settings. In this context, the present study seeks to develop a holistic approach that views coast and watershed systems as a continuum, aiming to investigate their relationships in an island environment, while accounting for human interventions in the river regime. For this task, the empirical USLE method was employed to quantify sediment production and transport from the catchment area to the coast, while hydraulic simulations using HEC-RAS were conducted to assess sediment retention within flood-affected areas. Moreover, coastal vulnerability to erosion was evaluated by applying the InVEST CVI model in order to identify areas at risk from environmental threats. The coastal zone of Petra–Molyvos, Lesvos, Greece, was selected as the study area due to ongoing erosion issues, with particular emphasis on its interaction with the Petra stream as a result of significant human intervention at its mouth. According to the study’s findings, the examined coastal zone is highly vulnerable to combined erosion from wind and waves, while the river’s mouth receives only a small amount of sediment from water fluxes. Evidently, this leads to an increase in beach retreat phenomena, while highlighting the necessity for integrated coastal–watershed management.

Spatial Assessment of Soil Erosion Risk Using RUSLE and GIS in Dhumuga Watershed, Ambo, Ethiopia

Soil erosion has become a critical problem leading to land degradation and environmental risks globally. To grasp the rates of soil loss and identify the main factors driving these issues, it is vital to examine the specific impacts of soil erosion across different locations. Therefore, between 2021 and 2023, a research initiative was undertaken to assess, rank, identify, and map sections of the watershed that are particularly susceptible to soil erosion. The RUSLE components for factors R, K, L, S, C, and P were integrated using the ArcGIS 10.4.1 spatial analyst's raster calculator tool to calculate and create maps that illustrate the risk and intensity of soil erosion in the Dhumuga watershed. The Dhumuga watershed was categorized into five groups based on average annual soil loss: 0–5 ton/ha<sup>-1</sup> year<sup>-1</sup> (very slight), 5–10 ton/ha<sup>-1</sup> year<sup>-1</sup> (slight), 10–20 ton/ha<sup>-1</sup> year<sup>-1</sup> (moderate), 20–50 ton/ha<sup>-1</sup> year<sup>-1</sup> (high), and > 50 ton/ha-1 year-1 (very high). The assessment of soil erosion severity was influenced by factors such as rainfall, soil type, DEM, land use, and land cover, employing the GIS-based RUSLE equation. The spatial risk of soil erosion was sorted into five categories based on severity, with 11.58% of the area categorized as very high risk (>50 ton ha<sup>-1</sup> year<sup>-1</sup>), and 54.2% in the very low to low-risk category. On average, the watershed yielded an annual sediment production of up to 13.94 tons/ha/year, which is within an acceptable range. Considering these research findings, GIS-based analyses can be utilized to pinpoint areas at risk of soil erosion and identify vulnerable zones, offering crucial insights for future soil conservation and model enhancement.

Sequence stratigraphic framework of carbonates in mixed siliciclastic–carbonate sequences: local versus external controls in a tectonically active basin (Lorca Basin, Miocene, SE Spain)

ABSTRACT The sequence stratigraphic framework of initiation and growth of carbonates in environments impacted by siliciclastic inputs is highly variable because of the biogenic nature of the sedimentary production and its sensitivity to environmental conditions. Using panorama interpretations, logging, and characterization of benthic communities, the mixed carbonate–siliciclastic sedimentary succession of the Neogene Lorca Basin (SE Spain) has been studied to decipher the role of local and global controlling parameters on the sequence stratigraphic framework of carbonate production. Three different carbonate depositional models are distinguished: 1) retrogradational homoclinal ramps (type 1) dominated by heterozoan communities that developed lateral to alluvial fans, 2) progradational flat-topped coral platforms (type 2) with Porites and Tarbellastraea coral carpets with a coeval retrogradational pattern on basin margins, and 3) retrogradational narrow siliciclastic-rich coral platforms (type 3) with Tarbellastraea buildups intercalated with deltaic deposits. Onset of carbonate production systematically occurred during transgressions controlled by eustasy and was locally enhanced by extensional tectonics. In steep margins located in the vicinity of major marginal faults, transgressions were characterized by high terrigenous inputs, and only heterozoan-dominated ramps (type 1) developed. The flooding of these steep and tectonically active margins characterized by small drainage basins and immature, locally sourced alluvial systems led to lower terrigenous fluxes and the growth of coral flat-topped platforms (type 2) during subsequent highstands. Away from main marginal faults, deltaic environments were sourced by large drainage basins. They were characterized by a flat topography that permitted the occurrence of a shallow photic zone subject to low and irregular terrigenous inputs up to the distal part of the depositional profile during transgressions. In this deltaic configuration, the growth of narrow siliciclastic-rich coral platforms (type 3) were favored. On these platforms, coral buildups were regularly buried by terrigenous inputs during highstands. In the Lorca Basin, the dimensions of siliciclastic systems and the size of their drainage basins also directly impacted the sequence stratigraphic framework of carbonates intercalated in terrigenous units. This study illustrates the marked variability in: 1) the different types of carbonate depositional profiles and 2) the timing of these carbonates in a mixed carbonate–siliciclastic system because of the size, maturity, and location of siliciclastic systems, local tectonics, inherited topography, and global sea-level fluctuations.

Physicochemical perturbation increases nitrous oxide production from denitrification in soils and sediments

Abstract. Atmospheric concentrations of nitrous oxide (N2O), a potent greenhouse gas that is also responsible for significant stratospheric ozone depletion, have increased in response to the intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Microbial denitrification in soils and sediments is a major source of N2O, produced as an intermediate during the reduction of oxidized forms of nitrogen to dinitrogen gas (N2). Substrate availability (nitrate and organic matter) and environmental factors such as oxygen levels, temperature, moisture, and pH influence rates of denitrification and N2O production. Here we describe the role of physicochemical perturbation (defined here as a change from the ambient environmental conditions) in influencing rates of denitrification and N2O production. Changes in salinity, temperature, moisture, pH, and zinc in agricultural soils induced a short-term perturbation response characterized by lower rates of total denitrification and higher rates of net N2O production. The ratio of N2O to total denitrification (N2O : DNF) increased strongly with physicochemical perturbation. A salinity press experiment on tidal freshwater marsh soils revealed that increased N2O production was likely driven by transcriptional inhibition of the nitrous oxide reductase (nos) gene and that the microbial community adapted to altered salinity over a relatively short time frame (within 1 month). Perturbation appeared to confer resilience to subsequent disturbance, and denitrifiers from an environment without salinity fluctuations (tidal freshwater estuarine sediments) demonstrated a stronger N2O perturbation response than denitrifiers from environments with more variable salinity (oligohaline and mesohaline estuarine sediments), suggesting that the denitrifying community from physicochemically stable environments may have a stronger perturbation response. These findings provide a framework for improving our understanding of the dynamic nature of N2O production in soils and sediments, in which changes in physical and/or chemical conditions initiate a short-term perturbation response that promotes N2O production that moderates over time and with subsequent physicochemical perturbation.

3D CFD-DEM modeling of sand production and reservoir compaction in gas hydrate-bearing sediments with gravel packing well completion

Sand production is one of the bottlenecks restricting the safe, efficient, and controllable production of hydrates. Enhancing the understanding of mesoscopic sand production responses is essential for sand production risk management. Yet, existing mesoscopic sand production models inadequately capture the effects of hydrate cementation, resulting in an incomplete assessment of the mechanical impacts of hydrates on sand production. Herein, we developed a new three-dimensional model for sand production in gas hydrate-bearing sediments (GHBSs) with gravel packing well completion, utilizing the coupled computational fluid dynamics and discrete element method (CFD-DEM). The model considers the coupled interactions of mechanical weakening and permeability variation in GHBSs caused by hydrate cementation reduction. Simulations are analyzed to clarify the responses of sand production and reservoir compaction under the coupled mechanical, hydraulic, and sand control completion in GHBSs during depressurization. The high fluid flow rate induced by a high production pressure differential can promote sand production and reservoir compaction. Additionally, the high effective stress and high hydrate dissociation rate induced by a high production pressure differential are beneficial for initial sand production, but they can also prematurely lead to gravel packing layer obstruction, inhibiting the final sand production. This also results in a dual impact on compaction deformation, enhancing it through compaction while decelerating it by inhibiting sand production. This work provides a viable simulation idea and preliminary insights into the mechanism of sand production from GHBSs.

Uranium-series isotopes as tracers of physical and chemical weathering in glacial sediments from Taylor Valley, Antarctica

The McMurdo Dry Valleys of Antarctica formed by extensive glacial erosion, yet currently exhibit hyperarid polar conditions canonically associated with limited chemical and physical weathering. Efficient chemical weathering occurs when moisture is available, and polythermal subglacial conditions may accommodate ongoing mechanical weathering and valley incision. Taylor Valley, one of the MDV, hosts several Pleistocene glacial drift deposits that record prior expansions of Taylor Glacier and sediment redistribution, if not sediment production. We present U-series isotopics of fine-grained sediments from these drifts to assess the timescales of physical weathering and subsequent chemical alteration. The isotopes 238U, 234U, and 230Th are sensitive to both chemical and physical fractionation processes in sedimentary systems, including the physical fractionation of daughter isotopes by energetic recoil following radioactive decay. By comparing U-series isotopic measurements with models of U-series response to chemical weathering and physical fractionation processes, we show that Pleistocene drift sediments record histories of significant chemical alteration. However, fine-grained sediments entrained in the basal ice of Taylor Glacier record only minor chemical alteration and U-series fractionation, indicating comparatively recent sediment comminution and active incision of upper Taylor Valley by Taylor Glacier over the Pleistocene. In addition, the results of this study emphasize the utility of U-series isotopes as tracers of chemical and physical weathering in sedimentary and pedogenic systems, with particular sensitivity to radionuclide implantation by α-recoil from high-U authigenic phases into lower-U detrital phases. This process has occurred extensively in >200 ka drifts but to a lesser degree in younger deposits. U-series α-recoil implantation is an important physicochemical process with chronometric implications in other hyperarid and saline sedimentary systems, including analogous Martian environments.

Hydrological Dynamics in Response to Vegetation Restoration in a Typical Wind–Water Erosion Crisscross Catchment

ABSTRACTThe intricate climate and surface composition of the wind‐water erosion crisscross region create a distinctive environment for erosion and sediment production. However, research on the hydrological characteristics and responses to vegetation restoration in this area is limited. This study focuses on a representative catchment (3253 km2) in the northern Loess Plateau of China, examining the streamflow and sediment transport dynamics before (P1: 1977–1988) and after (P2: 2006–2017) vegetation restoration. Our results show that streamflow is relatively evenly distributed throughout the year, while sediment transport is highly concentrated over a few days during the wet season. Flood events account for the majority of sediment yield, contributing over 70% in both periods, with hyperconcentrated flows (SSCp ≥ 300 kg m−3) being particularly significant. Vegetation restoration has resulted in an 85% reduction in annual sediment yield and an 89% decrease in the frequency of hyperconcentrated flood events. Despite these reductions, hyperconcentrated floods remain the dominant sediment transport mechanism, with just 9.7% of events in P2 responsible for nearly half of the sediment transported. Analyses of effective sediment transport discharge and sediment rating curves indicate a higher discharge threshold for hyperconcentrated floods post‐vegetation restoration, leading to a greater sediment transport magnitude in P2. Hysteresis analysis shows a predominant counter‐clockwise pattern in both periods, driven by abundant sediment sources and the high transport capacity of hyperconcentrated floods. Vegetation restoration has reduced the availability of sediment for transport, resulting in more linear relationships and decreased complexity in hysteresis patterns. Under future scenarios of intensified climate extremes, this region remains at high risk of erosion and sediment yield.

Nationwide occurrence and prioritization of tire additives and their transformation products in lake sediments of China

As a group of emerging contaminants of global concern, tire additives and their transformation products (TATPs) are causing a severe threat to aquatic ecosystems, particularly the highly lethal effects of N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine quinone (6PPD-Q) on certain fish species. Yet, the contamination status of TATPs in the lake ecosystems remains largely uncharacterized. This study conducted the first nationwide monitoring of the distribution characteristics of TATPs in 208 lake sediments collected from five lake regions across China. All the 13 TATPs were identified in lake sediments, with the total levels varying between 1.4 and 1355 ng/g, and 4-hydroxydiphenylamine (4-OH-PPD) as the most dominant. The total levels of TATPs decreased in the following order: Yunnan-Guizhou Plateau > Inner Mongolia-Xinjiang Region, Eastern Plain > Qinghai-Tibet Plateau, and Northeast Plain (p < 0.05). The geographical distribution of TATPs in lake sediments was significantly driven by total organic carbon content, temperature, and population density. N,N’-di-2-naphthyl-p-phenylenediamine, 6PPD-Q, N,N′-diphenyl-p-phenylenediamine, and 4-OH-PPD belonged to high-priority contaminants. Our study emphasizes that emerging pollutant TATPs place significant pressure on lake ecosystems and deserve urgent attention.

Effects of Rainfall Variability and Land Cover Type on Soil Organic Carbon Loss in a Hilly Red Soil Region of Southern China

Rainfall intensity (RI) and land cover type are two important factors that affect soil erosion and thus the transfer and loss of soil organic carbon (SOC). However, the in situ quantitative monitoring of SOC loss under natural rainfall and various land cover types restored on eroded lands has not been thoroughly examined. In order to further study the effects of rainfall changes and vegetation types on SOC loss in the red soil region of Southern China, the Jiangxi Eco-Science Park of Soil and Water Conservation in De’an County, Jiangxi Province, was taken as the research object. Considering natural rainfall and based on the long-term field in situ monitoring of rainfall and runoff and sediment data, we studied the effects of three land cover types (bare land, orchards, and grass cover) on surface runoff, sediment production, and SOC loss in relation to 1 hour of RI during natural rainfall in the red soil region of Southern China during rainy seasons of 2020 and 2021 (March to August). Compared with bare land plots, the orchard and grass cover plots had surface runoff reductions of 67% and 98%, respectively, and sediment reductions of 79% and 99% over the two rainy seasons, respectively. With an increasing RI over 1 hour, total SOC loss increased for each of the three land cover types. More SOC loss was associated with sediments, and the enrichment ratio of SOC in the sediments (ERoc) decreased significantly. The ERoc values decreased in the following order: bare land (1.23) &gt; orchard (1.08) &gt; grass cover (0.81). Bare land exhibited the highest proportion of SOC associated with sediment in the total SOC loss (Ps), at 68.69%, followed by the orchard plots, at 55.02%, and then the grass cover plots at 49.24%. With the transfer of land cover type from bare land to orchard and to grass cover (decreased soil loss intensity, SLI), more SOC was lost associated with runoff in the form of dissolved organic carbon (DOC); the values of ERoc and organic carbon loss intensity (CLI) also decreased significantly. These findings are crucial to improving our understanding of the regulatory mechanisms of rainfall changes and land cover types on SOC loss during soil erosion.

Study on the Sand Reduction Effect of Slope Vegetation Combination in Loess Areas

Slope erosion in the Loess Plateau region has long been a concern, and vegetation plays an important role in slowing down erosion and controlling sedimentation. However, a single vegetation model shows some limitations when facing complex natural conditions and variable rainfall events. Therefore, this study investigated the influence mechanism of vegetation configuration on slope sand production at different slopes through theoretical analyses and indoor experiments. The results of the study showed that certain factors, such as vegetation configuration mode, flow rate, runoff power, runoff velocity, and runoff shear, are closely related to slope runoff sand production. The specific findings are as follows: (1) Under the condition of slope gradient of 2°, the sand reduction effect of the rigid–flexible single-row staggered configuration is the most significant, and the sediment production is reduced by 29.89%. (2) With the increase in the slope gradient and flow rate, the sand production on the slope surface rises significantly, and when the slope gradient is increased from 2° to 6°, the average sand production is increased from 1.43 kg to 2.51 kg.(3) The erosion reduction effects of different vegetation configurations were in the order of rigid–flexible single-row staggered combination &gt; flexible vegetation single combination &gt; rigid–flexible double-row staggered combination &gt; rigid vegetation single combination &gt; upstream rigid downstream flexible combination &gt; bare slope. This study provides a theoretical basis for optimizing the vegetation configuration for effective sand reduction and provides an important reference for the sustainable development of the Yellow River Basin.

Effects of Different Land Uses and Slope on Runoff and Soil Loss on the Loess Plateau of China

ABSTRACTThe Loess Plateau has one of the most serious areas of soil erosion in China; therefore, studying the effect of soil and water conservation measures on the erosion of loess soil slopes is important for land management and agricultural development. This study is based on 5 years of field runoff observations and rainfall data from 2015 to 2019. Correlation and regression analyses were used to study the runoff and sediment production of loess soil and its relationship with rainfall, slope and land use. The results show that &gt; 80% of the erosive rainfall occurs mainly in July to August in the area. Runoff and soil loss from the plots differed substantially, depending on land use, soil conservation measures and slope degree. Bare plots experienced the highest soil loss rate of over 27 t/ha with higher runoff depth, followed by cultivated plots (4.55 t/ha), grass plots (0.43 t/ha), shrub plots (0.35 t/ha) and forest plots (0.13 t/ha). Among the four soil and water conservation measures, the runoff and sediment reduction benefits of forest and shrub plots were the highest. The runoff reduction benefit fluctuated at approximately 0.8, and the benefit of sediment reduction was ≈1. The overall performance was forest &gt; shrubland &gt; grassland &gt; cultivated land &gt; bare land, and the benefits of sediment reduction were greater than those of runoff reduction. Forests had the highest soil retention capacity on slopes from 5° to 25°, and forests on gentle slopes had the best water storage capacity. Shrub plots had the best water storage capacity when they were on steep slopes. Rainfall erosion forces were significantly and positively correlated (p &lt; 0.01) with runoff depth and soil loss, making it the most significant rainfall indicator of sediment production. Under the same rainfall conditions, soil and water conservation measures are still required on bare slopes, land use is the main control factor for slope sediment production, and appropriate land use can greatly reduce the threat of slopes in terms of soil erosion. This study shows that soil and water conservation measures are imperative to prevent runoff and soil loss, especially for bare land without any measures; on steep slopes, a vegetation combination primarily featuring shrubs is expected to achieve greater benefits in reducing runoff and sediment. This study can provide a scientific basis for the management of vegetation measures and the implementation of soil and water conservation measures on loess soil slopes.

Mapping N2O production pathways in estuarine and coastal sediments through coupled 15N tracing and N2O isotopocules analysis

Estuarine and coastal zones are important sources of atmospheric nitrous oxide (N2O). Previous studies have explored the overarching roles of nitrification and denitrification in N2O production from these critical zones, yet the specific productions of various pathways within these processes remain elusive. Using dual 15N tracers (15NH4+ and 15NO3-) coupled with N2O isotopocules analysis, we quantified the contributions of multiple nitrification (both autotrophic and heterotrophic) and denitrification (bacterial, fungal, and chemical) pathways to N2O production in estuarine and coastal sediments. Furthermore, we leveraged microecology theory to dissect the biogeochemical mechanisms that govern the spatiotemporal dynamics of these pathways. Results showed that denitrification was the dominant process, accounting for over 70 % of N2O production. The remainder was attributed to autotrophic nitrification (5.80–23.92 %) and heterotrophic nitrification (1.07–7.10 %). Isotopocules analyses further showed that fungal denitrification was the primary source at freshwater sites (40.47–49.99 %), whereas bacterial denitrification prevailed at high-salinity sites (51.37–52.55 %). Moreover, these processes displayed contrasting spatial variability along the estuarine salinity gradient. Mechanistic investigation informed by microecology theory demonstrated that distinct assembly processes governed bacterial and fungal communities across this gradient, resulting in divergent ecological adaptation strategies of bacterial and fungal denitrifiers and, consequently, the contrasting contribution patterns of bacterial and fungal denitrification. Collectively, our work presents a comprehensive and refined picture of N2O sources and dynamics, offering essential insights for improving predictive models and formulating effective mitigation strategies targeting N2O emissions from estuarine and coastal zones.