Increased Sediment Loads Research Articles

Assessment of temporal and spatial variations of water quality parameters in the Zarafshan River basin

AbstractRiver ecosystems in Central Asia face significant stress from environmental changes and pollution. This study assesses temporal and spatial variations in water quality parameters within the Zarafshan River Basin using retrospective data and field measurements. Water quality indicators, including electrical conductivity (EC), total suspended solids (TSS), ammonium nitrogen (N‐NH4), nitrite nitrogen (N‐NO2), nitrate nitrogen (N‐NO3), temperature (T), chemical oxygen demand (COD), dissolved oxygen (DO), and discharge, were analyzed using the Pearson's correlation coefficient and ANOVA, with the Mann–Kendall (MK) test detecting trends over time. Obtained results indicate significant seasonal effects with elevated TSS during summer, increasing sediment load and changing aquatic habitats. The strong inverse correlation (–0.89) between DO and N‐NH4 signifies ecological challenges particularly in low DO concentrations during summer (3.25 mg L–1). Long‐term analysis identifies Navoiazot chemical factory as a major pollution hotspot. Spatial analyses based on extended sampling have revealed the Siab and Dargom canals and Samarkand City as major pollution sources of elevated N‐NO2 and COD, respectively. Trends at various gauging stations (MK‐test) show increasing EC (τ = 0.72) and N‐NH4 (τ = 0.46) levels, with decreasing TSS, N‐NO3, T, and COD levels over time. Recommendations include targeted measures to reduce pollution at the Navoiazot factory and downstream, introducing sustainable agriculture practices, increasing public awareness for environmental conservation, and improving urban wastewater treatment to meet water quality requirements for different users.

Quantification of Bed Load Transport in the Northern Part of the Central Plateau of Morocco: Case of Wadi Skhirate

Rivers play a vital role in our ecosystems, providing fresh water, supporting rich biodiversity, and contributing to human well-being. However, in the face of climate change and intensive human activities, the sediment load in rivers can reach critical levels, presenting a complex set of challenges that require immediate action. The increased sediment load can alter aquatic habitats, clog channels, reduce reservoir storage capacity, and increase the risk of flooding. These direct threats entail high costs in terms of material and ecological damage, loss of life, and expenditure on rebuilding damaged infrastructure. The quantification of bedload in watercourses is therefore crucial for maintaining water and soil resources, safeguarding riparian communities, and preserving ecological balance. The study reports the findings of a three-year monitoring of the bed load of Skhirate Wadi, a river that drains a part of the western Moroccan Meseta. The study used the colorimetric monitoring method, which quantifies the volumes of coarse sediment that were transported by monitoring topographic variations in the riverbed and measuring the distances covered by the sediment. The study showed the sediment was found to move around seven times annually on average. However, the frequency and magnitude of floods and the size of particles affect the variation in this displacement. It also showed sediments travel an average distance ranging from 649 to 883 meters per year, and that the average specific bedload at the watershed scale is 30 m3/ Km2/ year. Relationships between flood peaks mobilized sediment volumes, and average particle distances are established and discussed. These results are fundamental to understanding of coarse sediment transfer processes in the small rivers of the central plateau. They are also essential for assessing the impact on the aquatic ecosystem, on downstream dams, and on the various existing road and hydro-agricultural infrastructures. This assessment will enable the implementation of appropriate management strategies to anticipate changes and plan the planning of the river and its watershed.

The effect of sedimentation on spore settlement and recruitment of the endemic Arctic kelp, Laminaria solidungula (Phaeophyceae).

Environmental changes associated with rapid climate change in the Arctic, such as the increased rates of sedimentation from climatic or anthropogenic sources, can enhance the impact of abiotic stressors on coastal ecosystems. High sedimentation rates can be detrimental to nearshore kelp abundance and distribution, possibly due to increased mortality at the spore settlement stage. Spore settlement and viability of the Arctic kelp Laminaria solidungula were examined through a series of lab-based sedimentation experiments. Spores were exposed to increasing sediment loads in three experimental designs simulating different sedimentation scenarios: sediment deposition above settled spores, settlement of spores on sediment-covered substrate, and simultaneous suspension of spores and sediments during settlement. Spore settlement was recorded upon completion of each experiment, and gametophyte abundance was assessed following a growth period with sediments removed to examine short-term spore viability via a gametophyte-to-settled-spore ratio. In all three types of sediment exposure, the addition of sediments caused a 30%-40% reduction in spore settlement relative to a no-sediment control. Spore settlement decreased significantly between the low and high sediment treatments when spores were settled onto sediment-covered substrates. In all experiments, increasing amounts of sediment had no significant effect on spore viability, indicating that spores that had settled under different short-term sediment conditions were viable. Our results indicate that depending on spore-sediment interaction type, higher rates of sedimentation resulting from increased sediment loading could affect L. solidungula spore settlement success with potential impacts on the long-term persistence of a diverse and productive benthic habitat.

Linking marsh sustainability to event-based sedimentary processes: Impulsive river floods initiated lateral erosion of deltaic marshes

Salt marshes providing valuable services in buffering flooding risks are regarded as cost-effective coastal defense solutions. Given that eroding marsh cliffs will threaten the sustainability of these protective functions, there is a need for mechanistic understanding of cliff formation. Based on short-term field measurements together with satellite-derived dataset and a morphodynamic model, we determined the response of marsh lateral dynamics to event-based sedimentary processes in the Yellow River Delta, China. It was found that the Eastern Marsh with a cliff of ∼1.2 m in height significantly differed from the gentle Western Marsh in accretion pattern and lateral dynamics. Attributed to an artificial flood lasting ∼20 days in 2022, the Eastern Marsh platform experienced average vertical accretion of 23.3 mm, ∼5 times higher than the Western Marsh barely impacted by fluvial sediment supply. Although the accretion pattern ensured the overall vertical adaptability, Eastern Marsh has translated from a phase of rapid expansion to lateral retreat of ∼60 m/yr since 2018, whereas Western Marsh was relatively stable in recent decade. With a validated delta-marsh model, we showed that the observed disparities were attributed to different marsh edge morphodynamic responses to river flood sediment supplies. When Spartina alterniflora initially colonized, the Eastern Marsh platform was lower and the trapping efficiency could rise by ∼3 times than the present. Integrating with ten-fold increases in sediment loads, it was estimated that the large artificial floods in 2018 could contribute to a vertical growth approximating 30 cm at Eastern Marsh. Such episodic but rapid marsh accretion played a crucial role in initiating the development of marsh cliff. Driven by positive feedbacks between platform elevations and cumulative wave thrust, a series of event-based marsh sedimentation will promote long-term marsh loss caused by lateral retreat at sediment-starved systems. This study provides insights in predicting marsh sustainability and long-term evolutions under episodic sedimentary events.

Inter‐ and intra‐annual fluctuations and attribution analysis of runoff and sediment transport in the middle and lower Yangtze River

AbstractAssessing the changing regimes of runoff and sediment load in rivers, as well as analysing their underlying causes, is essential for maintaining the ecological integrity of rivers and promoting the sustainable development of water resources. Current methods of attribution analysis focus on accounting for the effects of climate change and human activities on inter‐annual variability in streamflow and sediment. However, the contribution of individual drivers to intra‐annual hydrologic variability is often overlooked. The study analysed the inter‐ and intra‐annual fluctuations in runoff and sediment load in the middle and lower Yangtze River using a water‐sediment variation attribution model, the Extreme Gradient Boosting algorithm, and the Multiple‐Factor Attribution method. The results showed that human activities were responsible for over 70% of the inter‐ and intra‐annual fluctuation in runoff and sediment load in the Yichang, Hankou, and Datong sections. Additionally, it was found that human activities were the main contributor to the reduction in both runoff and sediment load in all sections. Closer to the Yangtze estuary, human influence on intra‐annual fluctuation of runoff decreases while climate change influence increases, and human influence on both inter‐ and intra‐annual fluctuation of sediment load becomes less significant. The sensitivity of annual runoff to precipitation is greater than that of air temperature and evaporation in the Yichang, Hankou, and Datong sections. An increase of 10% in precipitation from baseline values leads to a corresponding increase of 3.13%, 2.24%, and 3.91% in runoff for the Yichang, Hankou, and Datong sections. The annual sediment load is more sensitive to changes in runoff than to precipitation, air temperature, and evaporation in each section. A 10% increase in runoff from the baseline value leads to an annual sediment load increase of 20.36%, 10.11%, and 8.78% at Yichang, Hankou, and Datong, respectively. This study provides a theoretical basis and guidance for decision‐making to protect and sustainably develop the water and sediment resources in the Yangtze River Basin.

Hydrological response to land use land cover and climate variability, and simulation of sediment export and water yield in the catchment Kotri Sindh Pakistan using Soil and Water Assessment tool model.

The water availability concerns have been increasing due to significant impacts of land use land cover change, and climate variability. In terms of developing countries, it is one of the biggest challenges to overcome and manage sustainability in the present and future. This study aims to evaluate the change in hydrological components and simulation of sediment yield and water yield on the large-scale basin of Kotri barrage with a change in runoff due to a change in land use land cover. This study has been done on the watershed as well as the sub-watershed level to have an accurate estimation and simulation by finding the response of hydrological components toward its natural and human-induced factors using the Soil and Water Assessment tool with high-resolution geospatial-temporal inputs over the Kotri catchment. The sediment and water yield were quantified using 42 years of simulation (1981-2022) on the sub-basin level, projected to land use land cover 1990, 2000, 2010, and 2022. The increase in deforestation, agriculture, and settlement areas resulted increase in sediment load in the catchment. The sub-basins 14, 11, 12, and 13, with a high elevation and slope and with less vegetation showed higher sediment load and water yield than the sub-basins with gentle slope and with high natural vegetation cover. The sub-basins 10, 4, and 1 showed high water yield availability compared to basins 2, 3, 5, 6, 7, 8, 9. This may be the result of vegetation differences. However, contained less sediment load than basins 14, 11, 12, and 13. The main objective was to quantify the significant changes affecting catchment and sub-catchment areas, to have a better understanding of the management plan regarding land use land cover. The simulated data was further projected to prediction using machine algorithms (autoregressive integrated moving average) model for precipitation prediction, and (seasonal autoregressive integrated moving average with exogenous factors) model to predict the sediment yield and water yield in the catchment to 2060.

Assessing the stability of the reservoir rim in moraine deposits for a mega RCC dam

<abstract> <p>Diamer Basha Dam is an under-construction, 272-meter-high, roller compacted concrete (RCC) dam on the Indus River in Pakistan. Once constructed, it will be the world's highest RCC gravity dam with a 105-kilometer-long reservoir. Most of the reservoir lies in unstable moraine deposits with steep slopes. Events like saturation during reservoir filling, alternate wetting, drawdown during reservoir operation, or a seismic event could trigger a large mass movement of these slopes into the reservoir to disrupt the dam functionality. This work identified the 15 most vulnerable slide areas using digital slope maps, elevation maps, and satellite imagery. Deterministic slope stability analysis was carried out on the identified sections under various stages of reservoir operation for static and seismic loading, using pseudo-static and dynamic analysis approaches. Probabilistic analysis was then performed using Monte Carlo simulation. The findings showed that most moraine deposits would collapse under reservoir filling, rapid drawdown, or seismic activity. Following the assessments, landslide susceptibility maps were generated, and an assessment of potential impacts, including the generation of dynamic waves, reservoir blockage, increased sediment loads, and reduced reservoir storage capacity, was also performed.</p> </abstract>

A Half-Century of Human Impact on Nan River Runoff and Sediment Load Supplied to the Chao Phraya River

The construction of large dams in the upper tributary basin of the Chao Phraya River (CPR) has been linked to a significant decrease in sediment load in the CPR system, estimated between 75–85%. This study, utilizing historical and recent river flow and sediment data from 1922 to 2019, examines the impact of three major dams constructed in the Nan River basin (the Sirikit, Naresuan, and Khwae Noi dams) on river runoff and sediment loads in the CPR. The investigation employed the Mann–Kendall (MK) test and the double mass curve (DMC) for analysis. Findings indicate that the Nan River is a major contributor to the CPR, accounting for around 40% of the runoff and 57% of the total sediment load (TSL). The Naresuan diversion dam’s water regulation was found to significantly reduce annual runoff and TSL downstream of the dam. Despite an initial increase in sediment load at the CPR headwater (C.2) post the construction of the Sirikit dam, attributed to expanded irrigation downstream and channel improvements in the lower Nan River, the operation of the three dams eventually led to a 31% reduction in sediment load at C.2 compared to pre-construction levels.

A strategy for modelling sediment distribution along slope lengths of an ephemeral gully through the simulated scouring experiments

Accurately describing the soil erosion process is crucial for improving the accuracy of existing simulation models of ephemeral gully erosion. However, a laboratory experimental strategy for simulating sediment distribution along slope lengths of an ephemeral gully is lacking. This limitation greatly hinders the development of simulation models for ephemeral gully erosion. In this study, we constructed six soil flumes with 12 m in length, 0.1 m in width, and 0.5 m in depth, which were filled with cultivated loess soils. Four flow rates (5.33, 10.67, 21.33, and 42.67 × 10−3 m3 s−1 m−1), four slope gradients (5°, 10°, 15°, and 20°), and six gully lengths (2, 4, 6, 8, 10 and 12 m) were adopted to perform a series of laboratory scouring experiments. The measured sediment concentrations at the outlet ranged from 23.39 kg m−3 to 534.60 kg m−3. The trend of exponential increase in sediment concentrations along slope lengths of an ephemeral gully was similar to that observed in a rill. According to the fitting equation, the maximum sediment concentrations (Ae) ranged from 358.05 kg m−3 to 910.88 kg m−3. The attenuation coefficients (Be) indicated the rate of increase in sediment load with slope length, which ranged from 0.042 m−1 to 0.185 m−1. By combining the measured sediment loads along the slope length (8 m) with the sediment transport capacity, the sediment distribution along slope lengths of an ephemeral gully could be accurately quantified. Moreover, the results confirmed that a flume with a short slope length (4/6 m) could effectively determine the sediment distribution along slope lengths at gentle slope of 5° and 10°. However, a minimum length of 8 m was advisable at steep slope of 15° and 20°. In summary, our experimental strategy provides an efficient method for determining the sediment distribution along slope lengths of an ephemeral gully.

Ecophysiological and behavioural response of juveniles of the Chilean cold-water coral Caryophyllia (Caryophyllia) huinayensis to increasing sediment loads

Chilean Patagonia is a hotspot of biodiversity, harbouring cold-water corals (CWCs) that populate steep walls and overhangs of fjords and channels. Through anthropogenic activities such as deforestation, roadworks, aquafarming and increased landslide frequency, sediment input increases in the fjord region. While the absence of CWCs on moderately steep slopes has been suggested to reflect high vulnerability to sedimentation, experimental evidence has been lacking. Here, we investigated the sensitivity of CWCs to sediment stress, using juvenile Caryophyllia (Caryophyllia) huinayensis as a model. A 12-week aquarium experiment was conducted with three sediment loads: the average natural sediment concentration in Comau Fjord, 100- and 1000-fold higher sediment levels, expected from gravel road use and coastal erosion. Changes in coral mass and calyx dimensions, polyp expansion, tissue retraction and respiration were measured. For CWCs exposed to two and three order of magnitude higher sediment concentrations, 32% and 80% of the animals experienced a decrease in tissue cover, respectively, along with a decrease in respiration rate of 34% and 66%. Under the highest concentration corals showed reduced polyp expansion and a significantly reduced growth of ~ 95% compared to corals at natural concentration. The results show that C.huinayensis is affected by high sediment loads. As human activities that increase sedimentation steadily intensify, coastal planners need to consider detrimental effects on CWCs.

Experimental riparian forest gaps and increased sediment loads modify stream metabolic patterns and biofilm composition

AbstractForest management operations greatly influence stream habitats. Canopy clearing and subsequent canopy development during succession, site preparation, and ditching alter the light environment, and increase sediment inputs and nutrient exports from upland and riparian soils to streams. These physicochemical changes affect aquatic biofilms and metabolic rates, and in this study, we tested their individual and combined effects. We used 12 artificial streamside channels, together with a field survey of nine streams in and around clear‐cuts, to assess the effects of shading, substrate composition, and nutrient addition on biofilm biomass and composition, as well as metabolic rates. We found that biofilm biomass and gross primary production (GPP) were light limited in channels under 70% canopy shading. Nitrate additions at this shading level only marginally increased autotrophic biomass, while the rates of respiration increased 10‐fold when carbon was added. Open (unshaded) channels had three times higher rates of GPP compared with channels with 70% shading, and autotrophic biomass was twice as high, largely caused by the colonization of filamentous green algae. These changes to biofilm biomass, composition, and GPP were caused by differences in light alone, as temperature was not affected by the shading treatment. Notably, higher rates of GPP led to no positive effect on net ecosystem production. Further, fine‐grained substrates negatively affected GPP as compared with stone substrates in the experimental channels. In the surveyed streams, the negative effects of fine‐grained substrates exceeded the positive influence of light on biofilm biomass. Altogether, our results highlight the need for riparian management that protects headwaters from unwanted stressors by focusing on preventing sediment erosion and carbon transport in clear‐cuts, while providing variable shade conditions in second‐growth forests.

Illustrating land cover change associated with erosion management of the Little Blue River, Kansas, USA

AbstractErosion is a concern due to environmental degradation, loss of valuable cropland, increased sediment loads in aquatic systems, and reduced reservoir capacity. To manage erosion, riparian forest buffers and bendway weirs were installed in the Little Blue River, Kansas, during years 2002–2010. To illustrate land cover changes associated with management for upland and streambank erosion, indicated through terrestrial land gains, particularly of permanent tree cover relative to short‐lived crop cover, we digitized 1 m orthoimagery. For the pretreatment interval of 1991–2002, we digitized streambank edges to approximate change in river area. Due to river dynamics, for the 2002 and 2014 interval before and after treatment, we used land ownership parcels as fixed locations to assess changes in land area and land classes for 24 treated and 24 untreated parcels, each parcel group totaling 1575 ha. We appraised two extents of the unified streambank for both years and all land in parcels rather than isolating the river from the surrounding watershed. During 1991 to 2002, treated land parcels lost terrestrial land, whereas untreated land parcels gained land. During 2002–2014, treated land had greater river and crop cover, and less tree cover than untreated land. For the entire extent, with similar trends for the unified streambank extent, by 2014, treated parcels gained 27.3 ha of terrestrial land compared to 4.6 ha gained by untreated parcels. Gains occurred in tree cover and losses in river water and sediments cover. In treated parcels crop cover decreased, whereas in untreated parcels crop cover increased. Streamflows decreased over time, likely contributing to streambank stability. Despite lack of documented cost‐share agreements, in untreated parcels, landowners managed land by increasing tree cover to protect soil from erosion. All measurements were consistent with erosion followed by management for erosion through terrestrial land gains of tree cover.

Hysteresis and streamflow-sediment relations across the pre-to-post dam construction continuum in a highly regulated transboundary Himalayan River basin

Worldwide more than 16 million reservoirs of dams have trapped 65 Gt of fluvial sediment each year, affecting river ecosystems and human livelihoods. It is important to understand the effect of dam construction and possible shifts in hydrologic regimes. This study aims to create a conceptual framework to explore the interdependent streamflow and suspended sediment load (SSL-Q) shifts across the natural-to-post dam construction continuum in a transboundary Himalayan river basin. We study the sediment supply, erosivity, and hysteresis for sediment provenance and transportation to answer whether the changing patterns of the SSL-Q relationships can explain the cascading effects from natural to operational dam phases during the monsoon and non-monsoon seasons. Results indicate the disruptive effect of dam construction on increasing sediment loads. Such effect contrasts with the sediment trapping in the post-construction stage, which is exacerbated during the non-monsoon season. However, during the monsoon season, dam-released sediment-starved streamflow leads to increased erosion in the basin. Natural and dam-construction hysteresis evidenced an anticlockwise and clockwise figure-eight pattern with variability in SSL-Q scattering, respectively. The regime shift responds to the underlying processes that the natural sediment regime shifted to sediment-surplus and sediment-deficit conditions during the construction and post-construction phases, respectively. In the post-construction phase, the relationship between streamflow and SSL-Q creates a quasi-linear hysteresis pattern, implying that the dam-controlled discharge altered the carrying capacity in the basin. These patterns can help build resilience in systems affected by the increase in dam construction and the inherent hydropower demand.

Modelling impacts of climate change and anthropogenic activities on inflows and sediment loads of wetlands: case study of the Anzali wetland

Understanding the effects of climate change and anthropogenic activities on the hydrogeomorpholgical parameters in wetlands ecosystems is vital for designing effective environmental protection and control protocols for these natural capitals. This study develops methodological approach to model the streamflow and sediment inputs to wetlands under the combined effects of climate and land use / land cover (LULC) changes using the Soil and Water Assessment Tool (SWAT). The precipitation and temperature data from General Circulation Models (GCMs) for different Shared Socio-economic Pathway (SSP) scenarios (i.e., SSP1-2.6, SSP2-4.5, and SSP5-8.5) are downscaled and bias-corrected with Euclidean distance method and quantile delta mapping (QDM) for the case of the Anzali wetland watershed (AWW) in Iran. The Land Change Modeler (LCM) is adopted to project the future LULC at the AWW. The results indicate that the precipitation and air temperature across the AWW will decrease and increase, respectively, under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios. Streamflow and sediment loads will reduce under the sole influence of SSP2-4.5 and SSP5-8.5 climate scenarios. An increase in sediment load and inflow was observed under the combined effects of climate and LULC changes, this is mainly due to the projected increased deforestation and urbanization across the AWW. The findings suggest that the densely vegetated regions, mainly located in the zones with steep slope, significantly prevents large sediment load and high streamflow input to the AWW. Under the combined effects of the climate and LULC changes, by 2100, the projected total sediment input to the wetland will reach 22.66, 20.83, and 19.93 million tons under SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios, respectively. The results highlight that without any robust environmental interventions, the large sediment inputs will significantly degrade the Anzali wetland ecosystem and partly-fill the wetland basin, resulting in resigning the wetland from the Montreux record list and the Ramsar Convention on Wetlands of International Importance.

The Impact of Land-Use and Climate Change on Water and Sediment Yields in Batanghari Watershed, Sumatra, Indonesia

The Batanghari River flows from the province of West Sumatra into the West Coast of Jambi, with the main river extending up to 870 km. Also, the Batanghari watershed Land use changes have shown a decreasing forest cover and an increasing agricultural area. Therefore, this study aims to calculate the impact of land use and climate change on water and sediment yield using Soil and Water Assessment Tools (SWAT) hydrological modeling. Land-use change analysis was performed with projections in 2040 while, near future and future climate projections under Representative Concentration Pathway (R.C.P.) 4.5 and 8.5 were used for global climate change scenarios. The results show a changing pattern of growing agricultural area and decreasing forest area in 1990, 1997, 2005, 2015, and 2040. SWAT hydrological model used for the simulation was calibrated automatically with SWAT-CUP and the results were validated on good criteria. The sensitivity analysis results showed that effective hydraulic conductivity in main channel alluvium (CH_K2) and Base flow alfa factor (Alfa_BF) formed the most sensitive parameters for discharge. Furthermore, the model simulation showed an increase in surface runoff and a decrease in lateral flow and base flow due to land-use changes, which increased sediment loading over time. The impact of climate change on water and sediment yield increased the average flow discharge ratio, resulting in more frequent droughts and floods events.

Characteristics of runoff and sediment load during flood events in the Upper Yangtze River, China

Understanding the change in sediment load at a flood-event scale helps to enhance channel regulation and optimize reservoir operation. This is particularly true in the Upper Yangtze River basin where a few flood events contribute most of the annual sediment load. This paper collected field data from representative hydrological stations and applied statistical analysis to investigate the change in runoff and sediment load during flood events in the Upper Yangtze River, including both the mainstream (Jinsha River) and its major tributaries (Min, Tuo, Jialing, and Wu Rivers). The results show that flood events contribute more sediment load than runoff volume to the annual statistics. A general decreasing trend occurs in sediment load in all river basins, which is closely related to soil conservation efforts and dam construction. The series of sediment load modulus of each stations present abrupt change. The variations in sediment load modulus in low flow are more significantly than those in high flow at different abrupt-change period, indicating high flows during flood event have been found to still carry the same amount of sediment as their predecessors in the Upper Yangtze River. An “abnormal” increase in sediment load in recent years (2013–2020) has been observed at the Fushun station in Tuo River, and three factors, i.e., earthquake, high-intensity rainstorm and local scouring, were identified to be responsible for such increase. The findings of our study are helpful for better management of basin-scale sediment resources and regulation of reservoirs in the Upper Yangtze River.

Coral Record of Increased Soil Erosion Since East and Southeast Asia Economic Boom

AbstractSoil erosion in East and Southeast Asia is believed to have increased significantly since the regional economic boom of the 1970s–1980s. However, limited records of soil erosion make it difficult to understand and indeed verify such changes. Here we present two new monthly resolved Ba/Ca records from Porites coral skeletons from southern Taiwan and central Vietnam, supplemented with some sporadic monthly and annually resolved coral δ138/134Ba data. Our records span the 1980s to the 2000s and suggest that there were intervals of elevated seawater Ba concentrations (Basw) during the intervals 1987–1995 in southern Taiwan and 1992–2001 in central Vietnam. In combination with evidence for insignificant changes in regional seawater δ138/134Ba values, model simulations, and other published coral Ba/Ca records from Lanyu (offshore southeast Taiwan) and Hainan, we infer that the intervals of high Basw values are linked to soil erosion associated with land use changes and socioeconomic developments. The increased sediment loads are also likely responsible for the recent degradation of regional coral reefs. Our study provides new insights into regional soil erosion histories, which may prove useful for guiding soil conservation and sustainable land management.

Climate change impacts on erosion and suspended sediment loads in New Zealand

Soil is a critical resource that provides many ecosystem services and is highly valued by indigenous cultures as key for supporting essential human needs. Land degradation processes such as erosion are depleting soil resources while increased sediment loads impact downstream receiving environments, with compounding effects due to land use and climate change. Models are required to estimate the magnitude and extent of climate impacts on soil erosion and sediment loads at national scale for policymakers and catchment managers to assess the future effectiveness and feasibility of policies and mitigation plans, and to prioritise mitigation efforts. Commonly used soil erosion and sediment load models are often unable to represent the diversity of erosion processes and the future trajectory of their hydroclimatic drivers at such scales. We present a modelling framework that estimates suspended sediment load contributions from three predominant erosion processes: mass movement, surficial erosion, and streambank erosion within their respective spatial erosion domains by differencing models of surficial erosion and total load within the domains. We estimate how catchment suspended sediment loads may change under future climate using change factors derived from the main hydroclimatic driver of each erosion process. Applying this framework at national scale for Aotearoa New Zealand, we demonstrate a disproportionate increase in mass movement erosion expected in soft-rock hill country, with <1–28 % of North Island watersheds and <1–8 % of South Island watersheds estimated to experience a 100 % increase in sediment yield by end-century, primarily driven by the impact of increasing storm magnitude-frequency on mass movement erosion. This results in regional increases in sediment load delivered to the coast ranging from 1 to 233 %. Our results highlight the need for policymakers and catchment managers to recognise spatial variations in the response of erosion processes and catchment loads to climate change when developing policy and prioritising mitigation efforts, as combating future erosion may require different methods to those used in contemporary management to achieve catchment objectives.

Verification of the detachment-transport coupling relationship of rill erosion using colluvium material in steep nonerodible slopes.

The detachment-transport coupling equation by Foster and Meyer is a classical equation that describes the relationship between detachment and transport. The equation quantifies the relationship between sediment loads and soil detachment rates, deepens the understanding of soil erosion and provides a reliable basis for the establishment of an erosion model. However, the applicability of this equation to slopes with gradients greater than 47% is limited. In this work, the detachment-transport coupling relationship is investigated using the colluvium material of Benggang. A nonerodible rill flume 4 m long and 0.12 m wide was adopted. The slope gradient ranged from 27% to 70%, the unit flow discharge ranged from 0.56 × 10-3 to 3.33 × 10-3 m2 s-1, and the sediment transport capacity (Tc ) was measured under each slope and discharge combination. The sediment was inputted into the flume according to the predetermined sediment addition rate (from 0% to 100% of Tc ), and the detachment rate (Dr ) under each combination of the slope and discharge was measured. Dr linearly decreased with increasing sediment loads, which is consistent with the detachment-transport coupling equation by Foster and Meyer. The linear equations can predict the detachment capacity (Dc ) and Tc well (Nash-Sutcliffe efficiency coefficient (NSE) = 0.98 for Dc , and NSE = 0.99 for Tc ). The detachment-transport coupling equation can adequately predict the Dr (NSE = 0.89). However, its applicability to slopes of <47% (NSE: 0.92-0.96) was greater than that to slopes of ≥47% (NSE: 0.81-0.89), and the predicted Dr under Tc levels of 20% and 40% were higher than the measured values, while the predicted value under a Tc level of 80% was lower than the measured value. In summary, the detachment-transport coupling equation by Foster and Meyer can accurately reflect the negative feedback relationship between detachments and transports along steep-slope fixed beds and is suitable for colluvial deposit research. The results provide a basis for the construction of steep-slope colluvial deposit erosion models. In the future, the study of the hydrodynamic characteristics of sediment transport processes should be strengthened to clarify the detachment-transport effect of flows through hydrodynamics.

Design and functionality of sedimentation areas – Targeted lowering of floodplains to improve the habitat quality and flood safety by removing high loads of fine sediments

In many rivers of the Bohemian Massif in Northern Upper Austria, an increase in sediment loads can be observed, which has a negative impact on food safety and the habitat quality for aquatic organisms. To protect endangered species, measures must be taken to preserve natural aquatic habitats. Nature-based measures are well suited for improving the sediment balance of streams. Sediment deposition can be forced through the targeted lowering of a riparian plain. On these so-called sedimentation areas, sand and fine sediments in particular are removed from the watercourse. This locally improves the composition and morphology of the riverbed and restores important structures for aquatic organisms. The present work deals with the implementation of nine sedimentation areas and the verification of their functionality. The implementation of sedimentation areas requires technical requirements and the involvement of property owners, operators and authorities. To investigate the sediment budget, the removals from the sedimentation areas were documented. For the evaluation of the riverbed structure, surveys of the substrate composition and the morphology were carried out in several transects. The results show that even on small sedimentation areas significant amounts of sand and fine sediments are deposited. Furthermore sedimentation areas locally lead to an improvement of habitat conditions in the watercourse and can thus contribute to the conservation of endangered species. As the positive effects of sedimentation areas are locally limited, for far-reaching effects the implementation of several sedimentation areas in a watercourse section is required.