Dominant Sediment Source Research Articles

Evaluation of suspended-sediment sources in the Yeongsan River using Cs-137 after major human impacts

Large direct human impacts on the Yeongsan River resulting from the construction of two large weirs on the main stream, and dredging of almost all sections of the main river has occurred in the past 5 years. Subsequent to these human impacts, some problems related to the sediment budget, such as channel changes, have occurred. To evaluate the dominant source of suspended sediment in the Yeongsan River, three time-integrated suspended-sediment samplers were installed in the upper and middle Yeongsan River (YS-S1, -S2, and -S3), and we obtained suspended-sediment samples every month. Potential sources of the suspended sediment were sampled using a soil scraper on the forest floor and channel bank. Source fingerprinting was conducted using 137Cs, which exhibits distinguishable characteristics of surface and subsurface (bank) materials. Probability distribution functions fit to the detected values of 137Cs at the forest floor and channel bank were derived. The relative contributions of forest floor and bank materials to suspended sediment in the Yeongsan River were calculated using Monte Carlo simulation and a simple mixing model, and the results indicated that the dominant source of suspended sediment was bank materials. Dredging a riverbed and constructing river-crossing facilities can affect the channel in many ways, but it remains unclear from this study how much the human impacts influenced channel erosion due to the absence of pre-interference data. However, this study may contribute to planning prevention measures for sediment problems induced by human impacts in the Yeongsan River catchment. Additionally, to reduce the uncertainty and limitations of the 137Cs methodology, a multi-fingerprinting approach using geochemical analysis, various radionuclides, and so forth is needed for better spatial and temporal evaluation of the sediment sources.

Coastal erosion as a major sediment supplier to continental shelves: example from the abandoned Old Huanghe (Yellow River) delta

The Old Huanghe (Yellow River) delta in Jiangsu Province, China, has suffered intense erosion since the river mouth changed from the Yellow Sea to the Bohai Sea in 1855, and this erosion has since been the dominant sediment source to the Yellow Sea and East China Sea. To analyze the topographic and bathymetric changes to the Old Huanghe delta area and derive a regional sediment budget, we extracted shoreline positions and bathymetry from charts and maps published since 1875 and georectified these data into a common coordinate system, combining them with extensive single-beam bathymetric survey data acquired between 2002 and 2008 off Jiangsu Province. The results show continuous seabed erosion throughout the 20th century, consisting of the retreat of shoreface morphology in the nearshore zone (mostly <15-m depth) and deepening of the flat seabed offshore (15 to ~20m). Off the abandoned river mouth of the Old Huanghe, historically persistent sandbanks disappeared and other recent sandbanks shrank. Sediment yielded by coastal erosion from depths of <20m has amounted to >790 Mt annually on average for the last 100 years. Of this very large amount of sediment, ~25% is deposited on the offshore slope in the western Yellow Sea, another 20–25% is deposited along the south Jiangsu coast as far as the Changjiang (Yangtze) river delta, and the rest is transported southeastward along the mud belt that crosses the central Yellow Sea to south of Cheju Island in the East China Sea. This amount is an order of magnitude larger than the sediment supply from the modern Huanghe River to the Yellow Sea and also greatly exceeds the present sediment discharge of the Changjiang River.

Using in situ cosmogenic 10Be to identify the source of sediment leaving Greenland

ABSTRACTWe use the concentration of in situ 10Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland's sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized (n = 19) and non‐glacerized terrain (n = 10), from channels where sediment from glacerized and non‐glacerized terrain is mixed (n = 28), from Holocene glacial‐fluvial terraces (n = 4), and from one sand dune. In situ 10Be concentrations in sediment range from 1600 to 34 000 atoms g‐1. The concentration of in situ 10Be in sediment sourced from non‐glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ 10Be concentration in bedrock (n = 5) and boulder (n = 6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5 ka.The isotope concentration in sediment sourced from non‐glacerized terrain is higher than in sediment sourced from glacerized terrain because the non‐glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of 10Be that probably accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of 10Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Differences between the source contribution of bed material and suspended sediments in a mountainous agricultural catchment of western Iran

Soil erosion is intense in semi-arid regions of Iran and causes a decline in dam reservoir capacities and losing fertile soils from agricultural areas. Effective control of sediment delivery to the water storage requires an understanding of the sediment sources. To investigate the spatial provenance of suspended and bed material sediments in the Taleghani catchment, western Iran, eleven geochemical tracers were used to distinguish sediment sources. In total, 44 source samples were collected from the surface soil of three land use sources and the sub-soil of channel banks together with eight suspended samples in different flood events, and eleven bed material samples from different river stream sites were collected. Two mixing models (i.e., the Collins and Hughes mixing models) were applied to compute the contribution of different sources to both river bed and suspended sediments. The results of more accurate mixing model, the Hughes model based on goodness of fit test, indicated that channel-derived sediments dominate (average ~71.5%) the sediment sources contributing to bed materials. In addition, temporal variability of sources when suspended load was applied as the sediment input in mixing models showed that crop fields were the dominant source of sediment in flood events with high sediment concentrations. However, in flood events with less sediment concentrations, channel banks reach to higher apportionment.

Modeling soil erosion and river sediment yield for an intermountain drainage basin of the Central Apennines, Italy

The overall aim of this research was to investigate the spatial patterns of the soil erosion risk. We focused on accelerated soil erosion processes in an Italian central Apennine intermountain watershed using modeling techniques implemented in a GIS environment. Our thorough literature review revealed a gap in research on soil erosion processes in such forested, intermountain watersheds. To gain a better understanding of the soil erosion processes in such landscapes, we proposed an integrated modeling approach applying a RUSLE model and a Turbidity Unit Index. The model outcomes were validated through measurements of lake sediment deposition. Our findings indicate a potential high soil erosion risk. With 1.33Mt−1yr−1 of annual sediment yield, corresponding to an area-specific sediment yield of 32.35tha−1yr−1, the Turano drainage basin belongs to the Italian basins with the highest sediment discharge. The outcomes of the RUSLE model showed that, despite the diverse forms of forests that cover about 62% of the drainage basin area, sizable plots of the investigated area are prone to soil erosion. The validation of the model outcomes revealed that the TU Index model performed significantly better than the RUSLE model with regard to sediment yield prediction. Accordingly, we found that even though rill and interrill processes reach very alarming values (RUSLE), they are not the dominant sediment source within the Turano watershed. Other geomorphological processes contributing to the watershed sediment yield – for instance, megarill, gully, bank and channel erosion and re-entrainment of landslide sediments – were very active in the study area. If both models are used in a combined approach, the amount of river load (TU Index) as well as the relative spatial distribution of rill and interrill erosion processes (RUSLE) can be described with sufficient precision.

Simulating the impact of watershed management for surface water quality protection: A case study on reducing inorganic nitrogen load at a watershed scale

The management and control of non-point source pollutants (NPSPs) has been an increasing concern throughout the world. Controlling NPSP is critical to achieve the goals for improving surface water quality. This study used the Soil and Water Assessment Tool (SWAT) model to compare the effects of different kinds of watershed management measures on the transport of sediments and nutrients (ammonium nitrogen and nitrate nitrogen) in one of the main tributaries of the Xiangjiang River, the Zhengshui River. Our results confirmed that agricultural areas were the dominant sources of nutrients and sediment in the watershed and that a filter strip can significantly mitigate surface water pollution by intercepting and absorbing nutrients. We hypothesized five management plans to improve water quality for achieving the standard set by the National Twelfth Five-Year Plan (NTFYP). These plans were assessed according to their effects, economic cost efficiency and social impacts. The results showed that all five plans can successfully meet the goal of the NTFYP to reduce pollutant loads at the outlet of the watershed by more than 10%; and the results showed that plan that focused on critical source areas (CSAs) did not show its superiority as previous studies had theoretically suggested when the economic and social impacts were considered. Meanwhile, plans which considered economic factors and cost effectiveness would be more feasible and suitable as their cost efficiency were 10% and 30% higher than that of CSA plans for NO3− and NH4+, respectively, and their social impacts were much lower than other plans. Moreover, regression analysis further revealed the main characteristics of subbasin controlling the treatments efficiency of the inorganic nitrogen. Our study highlights the significance of combining theory with actual practice and would facilitate the selection and implement of more effective and reasonable measures to improve water quality.

Hysteresis effects of suspended sediment transport in relation to geomorphic conditions and dominant sediment sources in medium and large rivers of the Russian Arctic

Preliminary analysis of long-term hydrological data shows that sediment dynamics of Russian Arctic rivers is largely affected by hysteresis effects in relation of water discharge to suspended sediment concentration (SSC). The role of large-scale geomorphic and geocryological conditions in sediment transport is still relatively understudied. This research aims to assess the links between hydrogeomorphology and regularities of sediment formation and movement in Russian Arctic rivers. A dataset containing information on measured water discharges and SSC for 27 gauges on 16 medium and large rivers of the Russian Arctic was used in this research. Clockwise hysteresis is typical during spring events, while in summer counterclockwise and ‘figure eight’ curves are widely observed. The results show that the form of the rating curve can be attributed to the dominant sediment source, dominant channel pattern and, to certain extent, to the cross-section position within the river basin. Seasonality in hysteresis effects reflects the role frozen ground dynamic plays in sediment flux formation. Thus, reaction of permafrost landscapes on the widely observed climate shift should lead to significant changes in sediment transfer systems.

Channel–floodplain connectivity during an extreme flood event: implications for sediment erosion, deposition, and delivery

ABSTRACTThe term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies. However, considerable confusion remains regarding its definition and quantification, especially as it relates to fluvial systems. This confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately. Extreme flood events provide a useful framework to assess variability in connectivity, particularly the connection between channels and floodplains. The catastrophic flood of January 2011 in the Lockyer valley, southeast Queensland, Australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes. High resolution aerial photographs and multi‐temporal LiDAR digital elevation models (DEMs), coupled with hydrological modeling, are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls. Longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel–floodplain connectivity. The major control on connectivity was significant non‐linear changes in channel capacity due to the presence of notable macrochannels which contained a &gt; 3000 average recurrence interval (ARI) event at mid‐catchment locations. The spatial pattern of hydrological connectivity was not straight‐forward in spite of bankfull discharges for selected reaches exceeding 5600 m3s–1. Data indicate that the main channel boundary was the dominant source of sediment while the floodplains, where inundated, were the dominant sinks. Spatial variability in channel–floodplain hydrological connectivity leads to dis‐connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains. Consideration of such variability for even the most extreme flood events, highlights the need to carefully consider non‐linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative ‘connectivity index’. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Subsoil erosion dominates the supply of fine sediment to rivers draining into Princess Charlotte Bay, Australia

The Laura–Normanby River (catchment area: 24,350 km2), which drains into Princess Charlotte Bay, has been identified in previous studies as the third largest contributor of sediment to the Great Barrier Reef World Heritage Area. These catchment scale modelling studies also identified surface soil erosion as supplying >80% of the sediment. Here we use activity concentrations of the fallout radionuclides 137Cs and 210Pbex to test the hypothesis that surface soil erosion dominates the supply of fine (<10 μm) sediment in the river systems draining into Princess Charlotte Bay. Our results contradict these previous studies, and are consistent with channel and gully erosion being the dominant source of fine sediment in this catchment. The hypothesis that surface soil erosion dominates the supply of fine sediment to Princess Charlotte Bay is rejected. River sediment samples were collected using both time-integrated samplers and sediment drape deposits. We show that there is no detectable difference in 137Cs and 210Pbex activity concentrations between samples collected using these two methods. Two methods were also used to collect samples to characterise 137Cs and 210Pbex concentrations in sediment derived from surface soil erosion; sampling of surface-wash deposits and deployment of surface runoff traps that collected samples during rain events. While there was no difference in the 137Cs activity concentrations for samples collected using these two methods, 210Pbex activity concentrations were significantly higher in the samples collected using the runoff traps. The higher 210Pbex concentrations are shown to be correlated with loss-on-ignition (r2 = 0.79) and therefore are likely to be related to higher organic concentrations in the runoff trap samples. As a result of these differences we use a three end member mixing model (channel/gully, hillslope surface-wash and hillslope runoff traps) to determine the relative contribution from surface soil erosion. Probability distributions for 137Cs and 210Pbex concentrations were determined for each of the end members, with these distributions then used to estimate the surface soil contribution to each of the collected river sediment samples. The mean estimate of contribution of surface derived sediment for all river samples (n = 70) is 16 ± 2%. This study reinforces the importance of testing model predictions before they are used to target investment in remedial action and adds to the body of evidence that the primary source of sediment delivered to tropical river systems is derived from subsoil erosion.

A sediment budget for a small semiarid watershed in southeastern Arizona, USA

A sediment budget was developed for a 43.7ha and a nested 3.7ha semiarid, shrub dominated watershed based on hydrologic, geomorphic, erosion, and sediment data collected from 1963 through 2006 on the USDA-ARS Walnut Gulch Experimental Watershed in the southwestern US. Sediment budgets based on such extensive and intensive field campaigns over several decades are rare. The sediment budget was balanced with a high degree of confidence because the study watershed is controlled by an earth dam at the outlet. Although the channel network is well developed and incising in the steeper reaches of the watershed, hillslopes are the dominant source of sediment, contributing 85% of the overall total sediment yield. Erosion and sediment redistribution were driven by highly variable rainfall and runoff during July, August, and September. Sediment transfers are influenced by channel abstractions and the presence of the outlet dam, which created conditions for deposition in the pond approach reach. Although earth dams are ubiquitous throughout the southwestern US, and they can provide a measure of outlet sediment yield, these outlet measurements may be insufficient to interpret temporal and spatial variability in watershed sediment dynamics. Identification of dominant processes and sediment sources is critical for determining management actions that will improve rangeland conditions.

Importance of bank erosion for sediment input, storage and export at the catchment scale

The importance of bank erosion was quantified during three periods (October 2006–April 2007, May 2007–April 2008 and May 2008–April 2009) in the 486 km2 catchment area of River Odense, Denmark. A catchment sediment budget was established including other sediment sources such as tile drains and surface runoff, in-channel and overbank sinks and storage and the resulting bed load and suspended sediment load exported from the catchment. Bank erosion and sedimentation were measured using ca. 3,000 erosion pins established in 180 pin plots, each consisting of three vertical lines of pins. Thirty-six representative reaches, each with a length of 100 m, were selected by a stratified random procedure in GIS. Bed load and suspended sediment export from the catchment were measured using a bed load sampler and from continuous measurements of turbidity at the outlet gauging station. The gross sediment input from bank erosion during the three study periods amounted to 21,100–25,200 t in the River Odense catchment, which is considerably higher than the estimated input of sediment from tile drains and surface runoff, which amounted to 220–500 t and 0–100 t, respectively. The measured bed load (20–490 t) was five to 60 times lower than the suspended sediment export from the catchment (1,240–2,620 t) during the three study periods, with the largest difference occurring in the driest year. Sediment sinks and storage were of high importance for the catchment sediment budget as the measured in-channel storage of sediment on stream banks was as high as 16,200–20,100 t, and the overbank sediment sink was estimated at 360–3,100 t. Bank erosion was the dominant sediment source (90–94 %) in the River Odense catchment during the three study years. In-channel and overbank sediment sinks and storage dominated the sediment budget as 79–94 % of the sediment input from all sources was not exported from the catchment during the three study years. Such a large attenuation of sediment in river channels and on floodplains is extremely important for fluvial habitats and ecology. Moreover, it has strong implications for attempts to document changes in sediment export following implementation of mitigation measures.

Detrital zircon geochronology and sandstone provenance of basement Waipapa Terrane (Triassic–Cretaceous) and Cretaceous cover rocks (Northland Allochthon and Houhora Complex) in northern North Island, New Zealand

AbstractDetrital zircon U–Pb ages are reported for 14 sandstones of mainly Cretaceous age from the Northland Allochthon, Houhora Complex and Waipapa Terrane of northern North Island, New Zealand. Results from the Waipapa Terrane samples, selected from sequences in the Bay of Plenty, Coromandel Peninsula and Great Barrier Island, show that deposition continued into late Early Cretaceous time and, as in the Torlesse Composite Terrane, finally waned at c. 110–114 Ma. Upper Lower Cretaceous and Upper Cretaceous sedimentary successions in the Houhora Complex and Northland Allochthon have dominant sediment sources derived from local, contemporary volcanism, with a minor older contribution from the Murihiku Terrane to the west. As in eastern North Island, upper Upper Cretaceous sandstones lack major Albian magmatic components and their sources are solely in the Murihiku Terrane, and possibly the Western Province. We propose a Cretaceous palaeogeographic model that invokes a recently extinct orogen and a partially submerged continental borderland, dissected by rivers supplying submarine fans.

Streambank erosion in two watersheds of the Central Claypan Region of Missouri, United States

This study was undertaken to assess the importance of streambank erosion to the total in-stream sediment of two agricultural watersheds within the Central Claypan Areas. The objective of this research was to determine the effect of stream order, adjacent land use, and season on streambank erosion rates. Thirty-four study sites were established in 2007 and 2008 within Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Missouri. At each site, field assessments of severely to very severely eroding bank length were determined along 300 to 400 m (984 to 1,312 ft) stream reaches. A factorial experimental design was implemented with four land uses (crop, forest, pasture, and riparian forest), three seasons, and three stream orders (1st, 2nd, and 3rd). Each treatment was replicated three times for each stream order, except for the cropped 3rd order treatment as only one suitable treatment site could be found. Streambank erosion was measured using erosion pins, which were installed in randomly assigned plots that included at least 20% of the eroded bank length within each site. The effect of different seasons was assessed by measuring the length of the exposed pins three times per year (March, July, and November). The bulk density and carbon and nitrogen content of bank material were also determined. Sediment loss rates showed that season and the three-way interaction between season, land use, and stream order were highly significant. Erosion rates were consistently higher in the winter months than spring/summer and fall seasons; however, the significant three-way interaction precluded a simple interpretation of the seasonal effect. Soil nutrient concentration data showed that forest sites had significantly lower C and N concentrations than other land uses. At the watershed scale, bank sediment accounted for 79% to 96% of the total in-stream sediment and 21% to 24% of the total N exported from the study area. These results indicate that streambanks are the dominant source of sediment and a significant source of N in these streams. Therefore, improved management of riparian areas to decrease streambank erosion would result in significant water quality improvement in streams of the Central Claypan Areas in northeastern Missouri.

Determining the effects of wildfire on sediment sources using 137Cs and unsupported 210Pb: the role of landscape disturbances and driving forces

Purpose Wildfires represent one of the major natural disturbances within forested landscapes and have potential implications for the quality and function of downstream aquatic ecosystems. This study aimed to determine if a wildfire in a mountainous, forested watershed in British Columbia, Canada, caused a change in the dominant sediment source in the immediate 1–2 years following the wildfire, and if the sediment sources changed over the medium term (3–7 years) as the landscape recovered.

Using sediment tracing to assess processes and spatial patterns of erosion in grazed rangelands, Burdekin River basin, Australia

Identifying how agricultural practices can be changed to reduce sediment loss requires knowledge of the erosion processes and spatial areas contributing to end of catchment sediment loads. The Burdekin River basin in northeast Australia is a priority for such knowledge because of its large size (130,000km2), ongoing public investment in changing agricultural practices, and because sediment exports are known to affect the health of a significant aquatic ecosystem, the Great Barrier Reef (GBR). This study applied sediment tracing techniques within the Burdekin River basin to identify the contributions of surface versus subsurface soil, and spatial areas to fine sediment export. Tracer properties included fallout radionuclides and geochemistry. The contributions of each sediment source to river sediment were identified with 95% confidence intervals using a Monte-Carlo numerical mixing model. Between 77% and 89% of fine sediment loss in the study area was derived from subsurface soil sources. High-resolution monitoring of river suspended sediment concentrations indicated that sediment sources were in close proximity to the drainage network, since concentrations were higher on the rising limb than the falling limb of large hydrographs. Gully erosion is likely to be the dominant subsurface soil erosion process, although channel bank erosion and hillslope rilling cannot be discounted. The results contrast with previous sediment budget spatial modelling, which predicted that hillslope erosion was the dominant sediment source in the area, thus demonstrating the need to independently verify modelling predictions where input datasets are poor. The contribution of surface soil to river sediment was generally similar between catchments which were currently grazed and two catchments where livestock grazing ceased 7 years ago. Concurrent increases in vegetation cover in the non-grazed catchments indicate that surface erosion rates had declined, suggesting that subsurface soil erosion rates had also declined by a similar amount. The estimated contributions of spatial source areas within the large study catchments had narrower confidence intervals when source areas were defined using sediment from geologically distinct river tributaries, rather than using soil sampled from geological units in the catchment, since tributary sediment had less-variable geochemistry than catchment soil. Programs to reduce fine sediment losses from the Burdekin River basin should primarily focus on reducing sub-surface soil erosion proximal to the basin's drainage network. Understanding the biophysical processes of pollutant generation is important to help guide on-ground activities to improve water quality.

The dominant erosion processes supplying fine sediment to three major rivers in tropical Australia, the Daly (NT), Mitchell (Qld) and Flinders (Qld) Rivers

The tropics of northern Australia have received relatively little attention with regard to the impact of soil erosion on the many large river systems that are an important part of Australia's water resource, especially given the high potential for erosion when long dry seasons are followed by intense wet season rain. Here we use 137Cs concentrations to determine the erosion processes supplying sediment to two major northern Australian Rivers; the Daly River (Northern Territory), and the Mitchell River (Queensland). We also present data from five sediment samples collected from a 100km reach of the Cloncurry River, a major tributary of the Flinders River (Queensland). Concentrations of 137Cs in the surface soil and subsurface (channel banks and gully) samples were used to derive ‘best fit’ probability density functions describing their distributions. These modelled distributions are then used to estimate the relative contribution of these two components to the river sediments. Our results are consistent with channel and gully erosion being the dominant source of sediment, with more than 90% of sediment transported along the main stem of these rivers originating from subsoil. We summarize the findings of similar studies on tropical Australian rivers and conclude that the primary source of sediment delivered to these systems is gully and channel bank erosion. Previously, as a result of catchment scale modelling, sheet-wash and rill erosion was considered to be the major sediment source in these rivers. Identifying the relative importance of sediment sources, as shown in this paper, will provide valuable information for land management planning in the region. This study also reinforces the importance of testing model predictions before they are used to target investment in remedial action.

Sediment modelling with fine temporal and spatial resolution for a hilly catchment

The suitability of the physically based model SHETRAN for simulating sediment generation and delivery with a high degree of spatial (20 m) and temporal (sub-hourly) resolution was assessed through application of the model to a 167-km2 catchment leading to an estuary in New Zealand. By subdividing the catchment and conducting calculations on a computer cluster for a 6-month hydrology initialisation period, it was possible to simulate a large rainfall event and its antecedent conditions in 24 h of computation time. The model was calibrated satisfactorily to catchment outlet flow and sediment flux for a large rainfall event in two subcatchments (~2 km2). Validation for a separate subcatchment was successful for flow (Nash–Sutcliff efficiency of 0.84) with a factor 2.1 over-prediction for sediment load. Validation for sediment at full catchment scale using parameters from the subcatchment scale was good for flow but poor for sediment, with gross under-estimation of the dominant stream sources of sediment. After recalibration at catchment scale, validation for a separate event gave good results for flow (Nash–Sutcliff efficiency of 0.93) and sediment load within a factor of two of measurements. An exploratory spatially explicit landslide model was added to SHETRAN, but it was not possible to test this fully because no landslides were observed in the study period. Application to climate change highlighted the non-linear response to extreme rainfall. However, full exploration of land use and climate change and the evaluation of uncertainty were severely constrained by computational limitations. Subdivision of the catchment with separate stream routing is suggested as a way forward to overcome these limitations. Copyright © 2011 John Wiley & Sons, Ltd.

Geochemical characteristics and provenance implication of rare earth elements in surface sediments from bays along Guangdong Coast, Southeast China

A systematic study of the granulometric properties and the occurrence and distribution of rare earth elements (REE) within surface sediments from ten bays situated along the coast of Southeast China has facilitated a more rigorous understanding of constraints on sediment provenance in the area. The results show that REE concentrations are similar within a single bay, but vary considerably (133.58–251.77 mg/kg) among the bays. The chondrite-normalized distribution patterns show the typical enrichment of light REEs (LREEs: La–Eu) relative to heavy REEs (HREEs: Gd–Lu), and an apparent depletion of Eu, which is diagnostic of a terrigenous sediment source. Obvious enrichments of the middle REEs (MREEs: Sm–Ho) in the PAAS-normalized (Post-Archean Australian Shale) distribution patterns of these bay sediments are similar to results reported from large rivers in China. Comparing the REE composition of the bay sediments with those of adjoining fluvial sediments and with the bedrock of the surrounding drainage basins, the latter are indicated as the dominant sediment source. The uniform REE distribution patterns, and MREE enrichments, prove that the sediments are derived from the material transported by the streams and rivers that discharge into the bays.

Fingerprinting Suspended Sediment Sources in the Nukabira River, Northern Japan

Geological setting is crucial to the occurrence of slope failure and landslides, resulting in prolonged suspended sediment runoff; in this sense, local geology can affect the magnitude of suspended sediment yield. To clarify the suspended sediment sources in a watershed with various geological units, hydrological monitoring and fingerprinting techniques using natural radionuclides were conducted during a heavy rainfall event in August 2010 in the Nukabira River watershed, a tributary of the Saru River, in northern Japan. A GIS analysis for slope failure and landslide areas was also conducted to investigate the distribution of potential suspended sediment sources. During the rainfall event, the dominant sources of suspended sediment were found to be areas consisting of metamorphic rock (31%), sedimentary rock (30%), and accretionary sedimentary rock (24%). The highest sediment yield was found in metamorphic rock, which is consistent with the dense distribution of slope failure and landslides identified by the GIS analysis. Active landslides can introduce a significant amount of sediment from the hillslope to the stream channel, providing a source of fine sediment. In the area of the accretionary basalt block, there was an inconsistency between the sediment yield and the density of slope failure and landslides, perhaps attributable to the lack of a fine particle fraction in the sediment deposited on the bare slope along the stream channel and riverbed due to the resistance of bed rock to slaking and weathering. These results indicate that natural radionuclides can be used in order to elucidate the suspended sediment sources and sediment yield of various geological units within a watershed.

Sediment fingerprinting as an environmental forensics tool explaining cyanobacteria blooms in lakes

Cyanobacteria (blue-green algae) blooms in water bodies present serious public health issues with attendant economic and ecological impacts. Llyn Tegid (Lake Bala) is an important conservation and amenity asset within Snowdonia National Park, Wales which since the mid-1990s has experienced multiple toxic cyanobacteria blooms threatening the ecology and tourism-dependent local economy. Multiple working hypotheses explain the emergence of this problem, including climate change, land management linked to increased nutrient flux, hydromorphological alterations or changing trophic structure - any of which may operate individually or cumulatively to impair lake function. This paper reports the findings of a sediment fingerprinting study using dated lake cores to explore the linkages between catchment and lake management practices and the emergence of the algal blooms problem. Since 1900 AD lake bed sedimentation rates have varied from 0.06 to 1.07 g cm −2 yr −1, with a pronounced acceleration since the early 1980s. Geochemical analysis revealed increases in the concentrations of total phosphorus (TP), calcium and heavy metals such as zinc and lead consistent with eutrophication and a rising pollution burden, particularly since the late 1970s. An uncertainty-inclusive sediment fingerprinting approach was used to apportion the relative fluxes from the major catchment land cover types of improved pasture, rough grazing, forestry and channel banks. This showed improved pasture and channel banks are the dominant diffuse sources of sediment in the catchment, though forestry sources were important historically. Conversion of rough grazing to improved grassland, coupled with intensified land management and year-round livestock grazing, is concluded to provide the principal source of rising TP levels. Lake Habitat Survey and particle size analysis of lake cores demonstrate the hydromorphological impact of the River Dee Regulation Scheme, which controls water level and periodically diverts flow into Llyn Tegid from the adjacent Afon Tryweryn catchment. This hydromorphological impact has also been most pronounced since the late 1970s. It is concluded that an integrated approach combining land management to reduce agricultural runoff allied to improved water level regulation enabling recovery of littoral macrophytes offers the greatest chance halting the on-going cyanobacteria issue in Llyn Tegid.