Changes In Sediment Load Research Articles

Effects of Climate Change and Human Activities on Soil Erosion in the Xihe River Basin, China

Climate change and human activities are the major factors affecting runoff and sediment load. We analyzed the inter-annual variation trends of the annual rainfall, air temperature, runoff and sediment load in the Xihe River Basin from 1969–2015. Pettitt’s test and the Soil and Water Assessment Tool (SWAT) model were used to detect sudden changes in hydro-meteorological variables and simulate the basin hydrological cycle, respectively. According to the simulation results, we explored spatial distribution of soil erosion in the watershed by utilizing ArcGIS10.0, analyzed the average soil erosion modulus by different types of land use, and quantified the contributions of climate change and human activities to runoff and sediment load in changes. The results showed that: (1) From 1969–2015, both rainfall and air temperature increased, and air temperature increased significantly (p < 0.01) at 0.326 °C/10 a (annual). Runoff and sediment load decreased, and sediment load decreased significantly (p < 0.01) at 1.63 × 105 t/10 a. In 1988, air temperature experienced a sudden increased and sediment load decreased. (2) For runoff, R2 and Nash and Sutcliffe efficiency coefficient (Ens) were 0.92 and 0.91 during the calibration period and 0.90 and 0.87 during the validation period, for sediment load, R2 and Ens were 0.60 and 0.55 during the calibration period and 0.70 and 0.69 during the validation period, meeting the model’s applicability requirements. (3) Soil erosion was worse in the upper basin than other regions, and highest in cultivated land. Climate change exacerbates runoff and sediment load with overall contribution to the total change of −26.54% and −8.8%, respectively. Human activities decreased runoff and sediment load with overall contribution to the total change of 126.54% and 108.8% respectively. The variation of runoff and sediment load in the Xihe River Basin is largely caused by human activities.

Changes and Driving Forces of the Water-Sediment Relationship in the Middle Reaches of the Hanjiang River

Riverine sediment transport plays an important role in the global geochemical cycle. With a growing interest in global riverine environmental changes, a better understanding of water-sediment relationship dynamics and their driving forces is crucial for basin management, which is particularly associated with cascade dam construction. In this contribution, a simple and effective sediment load reduction factor analysis is used to attribute the changes in river sediment load to different drivers. The Mann–Kendall (MK) trend test and the double-mass curve (DMC) method were combined to reveal the trends and causes of change in the water-sediment relationship from 1965 to 2015 in the middle reaches of the Hanjiang River. We found that sediment load trend decreased significantly, which was caused by a decrease in water yield (5.05%), and the relative contributions of precipitation decrease (1.66%). Furthermore, only one mutation could be identified in 1974 at Huangzhuang station. Evapotranspiration and vegetation coverage had slight decreasing effects on sediment load. The impact of human activities on the water-sediment relationship has intensified over the past 15 years. We therefore propose the establishment of an integrated basin-wide ecosystem and optimized reservoir operation rule for sustainable water use and sediment regulation.

Response of Sediment Load to Hydrological Change in the Upstream Part of the Lancang-Mekong River over the Past 50 Years

Sediment load and its response to the variations of the hydrological elements are important for the healthy utilization of a river. In this study, the response of sediment load to hydrological change was explored in the upstream part of the Lancang-Mekong River, a major transboundary river originating from the Tibetan Plateau and running through China, over the past 50 years. A sediment rating curve for the Jiuzhou Station was developed based on the available SSC-Q (suspended sediment concentration (SSC) and flow) data and trends in annual precipitation, runoff, peak flow (PF), low flow (LF), maximum water level (MWL), and sediment load were analyzed from 1957 to 2006. The correlation analysis method and Random Forest (RF) were adopted to qualitatively and quantitatively quantify the contribution of each hydrological element to the sediment load change. Results indicated that both the runoff and sediment load showed a significantly upward trend, especially after 1979, at the 95% confidence level. The sediment load had significantly positive correlations with runoff, PF, and MWL at the 99% confidence level, respectively. In particular, the sediment load had the largest significant positive correlation with runoff since 1980. Runoff had the largest variable importance to the sediment load change, followed by PF, MWL, precipitation, and LF. The increasing trend in the sediment load was mainly attributed to the increase of runoff in the upstream part of the Lancang-Mekong River since the mid-1980s.

Runoff and sediment load change and its influencing factors in the Xiaonanchuan River Basin, China

Based on the annual monitoring data of runoff and sediment and the Normalized Difference Vegetation Index (NDVI), the water and sediment change and the vegetation coverage dynamics in the Xiaonanchuan (XNC) River basin were analyzed. The main impacts factors of the water and sediment change were further identified by using the Multiple Linear Regression method. It is found that the runoff was increasing and the sediment was reducing in the XNC River basin during 2000 to 2013. Simultaneously, a significant upward trend was shown in NDVI. It indicates that the vegetation coverage was increasing and the natural ecological environment was improved in the basin. The quantitative analysis results show that the vegetation coverage is the dominant influencing factor of the water and sediment change in the XNC River basin. Therefore, under the condition of recent climate change, ecological restoration is one of the most effective way to prevent water and soil loss in arid area.

A critical evaluation of coral Ba/Ca, Mn/Ca and Y/Ca ratios as indicators of terrestrial input: New data from the Great Barrier Reef, Australia

Coral trace element proxies of terrestrial runoff are widely applied to document and quantify historical changes in river discharge, constituent loads and land disturbance. However, some studies show poor replication between trace element records where cores from multiple coral colonies have been analyzed. Conflicting interpretations also exist on the environmental variable the coral trace element proxy is recording. Indeed, few studies have examined trace element behavior in the estuarine mixing zone that influence the coral records and only limited data on river discharge and constituent loads are available to validate the proxy records of terrestrial runoff. This study examined the behavior of Barium (Ba), Manganese (Mn) and Yttrium (Y) in the Burdekin River estuarine mixing zone, north-eastern Australia during several flood events and investigated the ability of coral Ba/Ca, Mn/Ca and Y/Ca ratios to record the variability of measured Burdekin River discharge and suspended sediment loads along a transect of replicate coral cores (10 cores from 5 locations). The results show limited evidence for Ba desorption from suspended sediments in the estuarine mixing zone while considerable desorption of Mn over a wide salinity mixing gradient was evident. Y showed evidence of removal in the initial mixing zone of the estuary (0–5 PSU) but displayed a relatively flat pattern thereafter indicating that it was not diluted by seawater mixing. The coral trace element records generally showed poor agreement within sites and the Ba/Ca ratios in some corals did not respond to regional river discharge, although coral luminescent lines were present in all cores and were significantly correlated with each other and Burdekin River discharge. While it was difficult to disentangle the influence of Burdekin River discharge and suspended sediment loads on the coral Ba/Ca proxy, several lines of evidence point towards discharge as the major contributor to this proxy in this region. A combination of factors likely influence the coral Ba/Ca ratio including an as yet undetermined physiological mechanism possibly related to crystallography or species, distance of the coral to the river mouth, variability in river discharge (including both annual totals and peaks, and local influences), variability in sediment load, the behavior of trace elements in the estuarine mixing zone, the hydrodynamics of flood plumes in the marine environment and the water depth of the coral. While the coral Mn/Ca and Y/Ca ratios did not respond to Burdekin River discharge events, the considerable desorption of Mn and the elevated Y throughout the estuarine mixing zone shows some promise in their ability to record long-term changes in suspended sediment loading and large terrestrial disturbances. Future studies examining coral records of terrestrial runoff should examine trace element behavior in the river estuarine mixing zone of influence, establish a correlation between the trace element and river discharge (such as luminescent lines) and demonstrate replication between different coral colonies.

Environmental and human impacts on sediment transport of the largest Asian rivers of Russia and China

The paper deals with comparative summary of sediment loads and particulate trace metals (V, Cr, Co, Cu, Zn, Cd, Pb) transport in the largest Asian rivers of Russia and China. Environmental conditions and human interventions in the selected catchments (Lena, Ob, Enisey, Selenga, Kolyma, Amur, Yellow, Yangtze, Pearl) are analyzed with respect to the rate and composition of suspended sediment loads. The paper presents calculations of sediment load changes at the downstream sections of the rivers and new database of the chemical composition of suspended matter which involves all recent studies of the last decade for the sediment geochemistry. The results indicate that fluvial system and its human modifications are the most significant drivers of sediment load. Fluvial erosion in the unconfined channels exerts a significant control on the sediment load changes due to observed permafrost melting. We concluded that construction of reservoirs has the most important influence on land–ocean sediment fluxes in the largest rivers of Asia but plays relatively weak role in heavy metal composition in suspended particulate matter (SPM) due to lowest sedimentation rates of the fine clay particles, which are mostly enriched with heavy metals. The paper also presents novel mapping approaches related to cartographic recognition of the fluvial system and its human modification and sediment transfer processes in the largest Asian rivers of Russia and China, linked with a specific legend. Finally, analysis of uncertainties associated with estimating the SPM composition in the rivers was done with respect to spatial and temporal variability. It was shown that the main error occurs due to incorporation of data only from particular hydrological seasons which usually ignore high flood conditions.

Rainfall erosivity and sediment load over the Poyang Lake Basin under variable climate and human activities since the 1960s

Accelerated soil erosion exerts adverse effects on water and soil resources. Rainfall erosivity reflects soil erosion potential driven by rainfall, which is essential for soil erosive risk assessment. This study investigated the spatiotemporal variation of rainfall erosivity and its impacts on sediment load over the largest freshwater lake basin of China (the Poyang Lake Basin, abbreviate to PYLB). The spatiotemporal variations of rainfall erosivity from 1961 to 2014 based on 57 meteorological stations were detected using the Mann–Kendall test, linear regression, and kriging interpolation method. The sequential t test analysis of regime shift (STARS) was employed to identify the abrupt changes of sediment load, and the modified double mass curve was used to assess the impacts of rainfall erosivity variability on sediment load. It was found that there was significant increase (P < 0.05) in rainfall erosivity in winter due to the significant increase in January over the last 54 years, whereas no trend in year and other seasons. Annual sediment load into the Poyang Lake (PYL) decreased significantly (P < 0.01) between 1961 and 2014, and the change-points were identified in both 1985 and 2003. It was found that take annual rainfall erosivity as the explanatory variables of the double mass curves is more reasonable than annual rainfall and erosive rainfall. The estimation via the modified double mass curve demonstrated that compared with the period before change-point (1961–1984), the changes of rainfall erosivity increased 8.0 and 2.1% of sediment load during 1985–2002 and 2003–2014, respectively. Human activities decreased 50.2 and 69.7% of sediment load during the last two periods, which indicated effects of human activities on sediment load change was much larger than that of rainfall erosivity variability in the PYLB.

Optical Classification of the Coastal Waters of the Northern Indian Ocean

Coastal waters are optically diverse; studying their optical characteristics is an important application of satellite oceanography. In coastal ecosystems of the northern Indian Ocean, optical diversity has been little studied, except for the global analysis by Me´ lin and Vantrepotte (2015). This paper is a contribution towards identification and characterisation of optical classes in the coastal regions of the northern Indian Ocean. The study identified eight optical classes using the monthly climatological datasets of remote sensing reflectance for the 1998-2013 period from the Ocean Colour Climate Change Initiative (OC-CCI, www.oceancolour.org). The optical classification we adopted uses the fuzzy logic method, based on Moore et al. (2009). The seasonal variations of the eight resultant optical classes of the coastal waters of the northern Indian Ocean were explored. From the mean reflectance spectral signals obtained, it appears that classes 1 to 6 belong to Case-1 waters and classes 7 and 8 correspond to Case-2 waters. Classes 1 to 2 appear in deeper oligotrophic waters; classes 3 to 6 are present in intermediate depths; classes 7 and 8 are mostly found within inshore eutrophic regions with high chlorophyll concentrations, sediments from river plumes and land runoffs. The optical variability between seasons (the summer and winter monsoon and the intermonsoon seasons) are influenced by variations in physical forcing, such as surface winds, ocean currents, precipitation and sediment influx from rivers and land runoff. Optical diversity index ranged from around 0.3 to 1.36. High diversity indices ranging between 1 and 1.36 were found in areas dominated by classes 1 to 4, whereas low diversity indices 0.3 occurred in areas where classes 7 and 8 dominated. The variations in the dominant optical classes are shown to be related to changes in chlorophyll concentration and suspended sediment load, as indicated by remote sensing reflectance at 670 nm. On the other hand, optical diversity appears to be high in zones of transition between dominant optical classes. Keywords: Coastal ecosystems, Satellite Ocean colour, Classification, Remote sensing reflectance, ecosystem management.

Hidden in plain sight: species richness and habitat characterisation of sublittoral pebble beds

Sublittoral pebble beds are generally considered to be impoverished, but the physical and biological characteristics of these habitats are poorly known. We characterised nineteen pebble bed sites in the Maltese Islands, providing detailed habitat data for Mediterranean sublittoral pebble beds for the first time. Nearly 40,000 individuals belonging to 332 taxa were recorded in all, with total richness estimated to reach 440 taxa; molluscs, crustaceans and polychaetes were the most diverse faunal groups. This high diversity is likely due to the structural complexity of the pebble beds, which had a vertically stratified arrangement of sediment particles that is likely maintained through periodic physical disturbance. Variation in the biotic assemblage from site to site was correlated with changes in the quantity of sand and silt, with the area of the pebble bed, with water depth, and with the thickness of the pebble layer. This indicates that pebble-bed macrofaunal assemblages are sensitive to changes in hydrodynamic conditions and sediment loading, to alterations to the stratification of the pebble beds, and to fragmentation of the habitat patches. These results contradict assertions that sublittoral pebble beds are impoverished, instead showing that they can be highly diverse habitats supporting biotic assemblages that respond to a complex set of environmental variables. The present findings enable better understanding of the ecological importance of pebble beds and of the potential impacts of anthropogenic disturbance, enabling more informed decisions for habitat conservation and management.

Possible Sediment Mixing and the Disparity between Field Measurements and Paleolimnological Inferences in Shallow Iowa Lakes in the Midwestern United States

Field measurements of water quality in Iowa lakes contradict paleolimnological studies that used 210Pb dating techniques in 33 lakes to infer accelerating eutrophication and sediment accumulation in recent decades. We tested this hypothesis by analyzing a series of water quality measurements taken in 24 of these lakes during the period 1972–2010. There was little change in the trophic state variables. Total phosphorus and algal chlorophylls did not increase, and Secchi depths did not decrease with no evidence that the lakes had become more eutrophic. Changes in daily sediment loads in the Raccoon River also did not match the paleolimnological inferred rates of soil erosion for the period 1905–2005, and an independent estimate of soil erosion rates showed a decline of 40% in the 1977 to 2012 period rather than an increase. We hypothesized that sediment mixing by benthivorous fish could be responsible for violating the basic assumption of 210Pb sediment dating that the sediments are not disturbed once they are laid down. We developed a mathematical model that demonstrated that sediment mixing could lead to false inferences about sediment dates and sediment burial rates. This study raises the possibility that sediment mixing in Iowa lakes and similar shallow, eutrophic lakes with benthivorous fish may cause significant sediment mixing that can compromise dating using 210Pb dating of sediment cores.

Variability and Trend Detection in the Sediment Load of the Upper Indus River

Water reservoirs planned or constructed to meet the burgeoning energy and irrigation demands in Pakistan face a significant loss of storage capacity due to heavy sediment load from the upper Indus basin (UIB). Given their importance and the huge investment, assessments of current UIB sediment load and possible future changes are crucial for informed decisions on planning of optimal dams’ operation and ensuring their prolonged lifespan. In this regard, the daily suspended sediment loads (SSLs) and their changes are analyzed for the meltwater-dominated zone up to the Partab Bridge and the whole UIB up to Besham Qila, which is additionally influenced by monsoonal rainfall. The gaps between intermittent suspended sediment concentration (SSC) samples are filled by wavelet neural networks (WA-ANNs) using discharges for each site. The temporal dynamics of SSLs and discharges are analyzed using a suite of three non-parametric trend tests while the slope is identified using Sen’s slope estimator. We found disproportional spatio-temporal trends between SSLs and discharges caused primarily by intra-annual shifts in flows, which can lead to increased trap efficiency in planned reservoirs, especially upstream of Besham Qila. Moreover, a discernible increase in SSLs recorded at Partab Bridge during summer is being deposited downstream in the river channel. This is due to a decrease in river transport capacity in the monsoonal zone. These findings will not only help to identify these morphological problems, but also accurately anticipate the spatio-temporal changes in the sediment budget of the upper Indus River. Our results will help improve reservoir operational rules and sediment management strategies for existing and 30,000-MW planned dams in the UIB.

Impact assessment of projected climate change on diffuse phosphorous loss in Xin'anjiang catchment, China.

Diffuse nutrient loss is a serious threat to water security and has severely deteriorated water quality throughout the world. Xin'anjiang catchment, as a main drinking water source for Hangzhou City, has been a national concern for water environment protection with payment for watershed services construction. Detection of diffuse phosphorous (DP) pollution dynamics under climate change is significant for sustainable water quality management. In this study, the impact of projected climate change on DP load was analyzed using SWAT to simulate the future changes of diffuse components (carriers: water discharge and sediment; nutrient: DP) at both station and sub-catchment scales under three climate change scenarios (RCP2.6, RCP4.5, and RCP8.5). Results showed that wetting and warming years were expected with increasing tendencies of both precipitation and temperature in the two future periods (2020s: 2021~2030, 2030s: 2031~2040) except in the 2020s in the RCP2.6 scenario, and the annual average increasing ratios of precipitation and temperature reached - 1.79~3.79% and 0.48~1.27°C, respectively, comparing with those in the baseline (2000s: 2001~2010). Climate change evidently altered annual and monthly average water discharge and sediment load, while it has a remarkable impact on the timing and monthly value of DP load at station scale. DP load tended to increase in the non-flood season at Yuliang due to strengthened nutrient flushing from rice land into rivers with increasing precipitation and enhanced phosphorous cycle in soil layers with increasing temperature, while it tended to decrease in the flood season at Yuliang and in most months at Tunxi due to restricted phosphorous reaction with reduced dissolved oxygen content and enhanced dilution effect. Spatial variability existed in the changes of sediment load and DP load at sub-catchment scale due to climate change. DP load tended to decrease in most sub-catchments and was the most remarkable in the RCP8.5 scenario (2020s, - 9.00~2.63%; 2030s, - 11.16~7.89%), followed by RCP2.6 (2020s, - 10.00~2.90%; 2030s, - 9.00~6.63%) and RCP4.5 (2020s, - 6.81~5.49%, 2030s, - 10.00~9.09%) scenarios. Decreasing of DP load mainly aggregated in the western and eastern mountainous regions, while it tended to increase in the northern and middle regions. This study was expected to provide insights into diffuse nutrient loss control and management in Xin'anjiang catchment, and scientific references for the implementation of water environmental protection in China.

Land use change uncertainty impacts on streamflow and sediment projections in areas undergoing rapid development: A case study in the Mekong Basin

AbstractQuantitative understanding of potential changes in streamflow and sediment load is complicated by uncertainty related to land use change projections, which is characterized by a high uncertainty in terms of demand (quantity) and location of changes (spatial distribution). We simulate the Sesan, Srepok, and Sekong Rivers (3S), the most important tributaries of the lower Mekong River, with the Soil and Water Assessment Tool (SWAT) to investigate the implications of conversion of forest to agricultural lands. Multiple land use transitions in the 3S basin are projected using the Land Change Modeler. The uncertainty in land use projection was addressed using an ensemble forecasting approach for 2060, combining (a) three land demand scenarios, (b) two transition potential modeling approaches (i.e., approach to create maps of the likelihood for areas to transition from one land use type to another), and (c) retaining or not protected areas. Land demand leads to the greatest uncertainty in land use change projections. Transition potential modeling approaches do not make much difference in the total change, but can result in spatial variations of change. Retaining protected areas can contribute significantly to uncertainty in land use change projections. Decrease in annual streamflow of the 3S basin varied from 3% to 21%, and changes in annual sediment outflux from the basin ranged from −8% to 249% for simulated scenarios. Land use demand uncertainty results in the highest streamflow and sediment load changes and can thus have major consequences for water and sediment management strategies in areas undergoing rapid development.

Quantifying the Contribution of Sediment Load to Soil Detachment Rate by Sediment‐Laden Rill Flow

Core Ideas A standardization‐based method was adopted to quantify the contribution rate. The experiment was specifically designed to isolate the effect of sediment load on detachment rate. The negative contribution of sediment load on detachment rate was almost one‐third of the total. This study aimed at rill erosion of loessial soil. Sediment load changes with downslope distance during rill erosion process, and thus quantifying the potential contribution of sediment load on soil detachment rate is essential to accurately model the rill erosion process. A standardization‐based method was adopted to quantify the contribution for the first time, and the rill flume with a soil‐feeding hopper was specifically designed to insulate the effect of sediment load on detachment rate. Loessial soil was quantitatively fed into rill flow to produce different sediment loads. Seven flow discharges were combined with six slopes. Soil detachment rate was measured for each combination under five sediment loads (10, 25, 50, 75, and 90% of the sediment transport capacity, respectively). The results showed that soil detachment rate by sediment‐laden rill flow decreased linearly with the increase in sediment load. Stream power is the best hydrodynamic parameter in relation to the detachment rate under different sediment loads compared with shear stress and unit stream power. The comprehensive response relationship of soil detachment rate to sediment load and stream power is a binary linear equation (R2 = 0.9482). The contribution rate of sediment load to soil detachment rate is 30.43% and that of stream power is 64.39%. The negative effect of sediment load on soil detachment rate accounts for almost one‐third of the total contribution. It is important to draw sediment load as a negative factor into process‐based rill erosion model. This study can provide a feasible way for researchers to quantify the contribution rate of factors and can help to understand rill erosion process sufficiently.

Glacial conditioning of stream position and flooding in the braid plain of the Exit Glacier foreland, Alaska

Flow spilling out of an active braid plain often signals the onset of channel migration or avulsion to previously occupied areas. In a recently deglaciated environment, distinguishing between shifts in active braid plain location, considered reversible by fluvial processes at short timescales, and more permanent glacier-conditioned changes in stream position can be critical to understanding flood hazards. Between 2009 and 2014, increased spilling from the Exit Creek braid plain in Kenai Fjords National Park, Alaska, repeatedly overtopped the only access road to the popular Exit Glacier visitor facilities and trails. To understand the likely cause of road flooding, we consider recent processes and the interplay between glacier and fluvial system dynamics since the maximum advance of the Little Ice Age, around 1815. Patterns of temperature and precipitation, the variables that drive high streamflow via snowmelt, glacier meltwater runoff, and rainfall, could not fully explain the timing of road floods. Comparison of high-resolution topographic data between 2008 and 2012 showed a strong pattern of braid plain aggradation along 3km of glacier foreland, not unexpected at the base of mountainous glaciers and likely an impetus for channel migration. Historically, a dynamic zone follows the retreating glacier in which channel positions shift rapidly in response to changes in the glacier margin and fresh morainal deposits. This period of paraglacial adjustment lasts one to several decades at Exit Glacier. Subsequently, as moraine breaches consolidate and lock the channel into position, and as the stream regains the lower-elevation valley center, upper-elevation surfaces are abandoned as terraces inaccessible by fluvial processes for timescales of decades to centuries. Where not constrained by these terraces and moraines, the channel is free to migrate, which in this aggradational setting generates an alluvial fan at the breach of the final prominent moraine. The position of this fan is glacially conditioned but the process of migration of the braided channels across it is not. This broad perspective on channel controls identifies incipient avulsion into the roadside forest as part of a long-term fan-building process independent from changes in streamflow or sediment load.

Dynamic linear models to explore time‐varying suspended sediment‐discharge rating curves

AbstractThis study presents a new method to examine long‐term dynamics in sediment yield using time‐varying sediment‐discharge rating curves. Dynamic linear models (DLMs) are introduced as a time series filter that can assess how the relationship between streamflow and sediment concentration or load changes over time in response to a wide variety of natural and anthropogenic watershed disturbances or long‐term changes. The filter operates by updating parameter values using a recursive Bayesian design that responds to 1 day‐ahead forecast errors while also accounting for observational noise. The estimated time series of rating curve parameters can then be used to diagnose multiscale (daily‐decadal) variability in sediment yield after accounting for fluctuations in streamflow. The technique is applied in a case study examining changes in turbidity load, a proxy for sediment load, in the Esopus Creek watershed, part of the New York City drinking water supply system. The results show that turbidity load exhibits a complex array of variability across time scales. The DLM highlights flood event‐driven positive hysteresis, where turbidity load remained elevated for months after large flood events, as a major component of dynamic behavior in the rating curve relationship. The DLM also produces more accurate 1 day‐ahead loading forecasts compared to other static and time‐varying rating curve methods. The results suggest that DLMs provide a useful tool for diagnosing changes in sediment‐discharge relationships over time and may help identify variability in sediment concentrations and loads that can be used to inform dynamic water quality management.

A review of source tracking techniques for fine sediment within a catchment.

Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments.

Comparison of the Suspended Sediment Dynamics in Two Loess Plateau Catchments, China

AbstractChanges in runoff and sediment loads are of great importance for the management of river basins and the implementation of soil and water conservation measures. This study compared the suspended sediment dynamics in the Huangfuchuan and Yanhe catchments on the Loess Plateau. Both annual runoff and sediment load displayed significant reductions from 1955 to 2012. The decreasing rates were −0·88 mm a−1 and −2·72 Mg ha−1 a−1 in the Huangfuchuan catchment, respectively, and ‐0.31 mm a−1 and −1·20 Mg ha−1 a−1 in the Yanhe catchment. A total of 183 and 195 events, respectively, were selected to assess the suspended sediment dynamics in both catchments during the periods of 1971–1989 and 2006–2012. The results showed a good linear relationship between the sediment yield and runoff depth in both catchments from 1971 to 1989 and a relatively worse relationship in the Yanhe catchment from 2006 to 2012. The magnitude and frequency of the hyper‐concentrated sediment flow obviously decreased in the 2000s compared with that between 1971 and 1989. A hysteresis analysis suggested that complex and counter‐clockwise loops were the dominant patterns. Various soil and water conservation measures (e.g., afforestation, grassing, terraces, and check dams) played a critical role in runoff and sediment load changes in both catchments. The two catchments showed obvious heterogeneities in runoff and sediment yield because of different lithologies, soil types, and vegetation. The results of this study provide valuable information on suspended sediment dynamics and could be used to improve soil erosion control measures on the Loess Plateau. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Quantifying anthropogenic and climatic impacts on sediment load in the sediment-rich region of the Chinese Loess Plateau by coupling a hydrological model and ANN

The sediment load on the Chinese Loess Plateau has decreased sharply in recent years. Therefore, it is critical to determine the effects of anthropogenic and climatic factors on the reduction in sediment load. The Huangfuchuan River is the primary tributary in the sediment-rich region of the Loess Plateau in China. This study identified a significant reduction in the sediment load in the Huangfuchuan River basin. The accumulative anomaly method was used to determine the change in annual sediment load from 1960 to 2010. The mean annual sediment load in the Huangfuchuan River was 0.564 × 108 t from 1960 to 1979 (Period I), and it decreased to 0.379 × 108 t between 1980 and 1996 (Period II) and to 0.100 × 108 t between 1997 and 2010 (Period III). Instead of conventional ways, a method that coupled a dynamic water balance model and a back-propagation artificial neural network was employed to separate the contributions of climate variability and human activities on the reduction in sediment load. The results showed that compared to the sediment load in Period I, human activities were responsible for 64.32 and 71.55% of the reductions in sediment load in Periods II and III, respectively, while climatic effects accounted for 35.68 and 28.45% of the reductions in Periods II and III, respectively. The construction of check dams was the main human activity that resulted in the sediment reduction between Periods I and II and accounted for 35.51% of the decrease. Vegetation restoration due to the implementation of the “Grain-to-Green” program was the dominant cause of the reduction in sediment between Periods II and III and caused more than 40.00% of the decrease. The increase of water consumption by humans also contributed the reduction in sediment between Periods II and III in the Huangfuchuan River basin.

Mapping of coastal landforms and volumetric change analysis in the south west coast of Kanyakumari, South India using remote sensing and GIS techniques

The coastal landforms along the south west coast of Kanyakumari have undergone remarkable change in terms of shape and disposition due to both natural and anthropogenic interference. An attempt is made here to map the coastal landforms along the coast using remote sensing and GIS techniques. Spatial data sources, such as, topographical map published by Survey of India, Landsat ETM+ (30m) image, IKONOS image (0.82m), SRTM and ASTER DEM datasets have been comprehensively analyzed for extracting coastal landforms. Change detection methods, such as, (i) topographical change detection, (ii) cross-shore profile analysis, (iii) Geomorphic Change Detection (GCD) using DEM of Difference (DoD) were adopted for assessment of volumetric changes of coastal landforms for the period between 2000 and 2011. The GCD analysis uses ASTER and SRTM DEM datasets by resampling them into common scale (pixel size) using pixel-by-pixel based Wavelet Transform and Pan-Sharpening techniques in ERDAS Imagine software. Volumetric changes of coastal landforms were validated with data derived from GPS-based field survey. Coastal landform units were mapped based on process of their evolution such as beach landforms including sandy beach, cusp, berm, scarp, beach terrace, upland, rockyshore, cliffs, wave-cut notches and wave-cut platforms; and the fluvial landforms. Comprising of alluvial plain, flood plains, and other shallow marshes in estuaries. The topographical change analysis reveals that the beach landforms have reduced their elevation ranging from 1 to 3m probably due to sediment removal or flattening. Analysis of cross-shore profiles for twelve locations indicate varying degrees of loss or gain of coastal landforms. For example, the K3-K3′ profile across the Kovalam coast has shown significant erosion (−0.26 to −0.76m) of the sandy beaches resulting in the formation of beach cusps and beach scarps within a distance of 300m from the shoreline. The volumetric change of sediment load estimated based on DoD model depict a loss of 241.69m3/km2 for 62.82km2 of the area and land gain of 6.96m3/km2 for 202.80km2 of the area during 2000–2011. However, an area of 26.38km2 unchanged by maintaining equilibrium in sediment budgeting along the coastal stretch. The study apart from providing insight into the decadal change of coastal settings also supplements a database on the vulnerability of the coast, which would help the coastal managers in future.