Historical variations in autochthonous and allochthonous sediment supplies to the largest freshwater lake in Central India

Lacustrine sediment preserves high-resolution biogeochemical records of past variations in watershed processes controlling lake sedimentation. The current study explores historical variations in autochthonous and allochthonous sediment supplies to a large tropical freshwater lake system (Upper Lake, Bhopal) protected under the international Ramsar Convention of 2002 against anthropogenic pressures. For this purpose, multi-proxy biogeochemical data are presented for organic matter (total organic carbon, total nitrogen, phosphorous, and loss on ignition [LOI] at 550 °C), carbonate (LOI at 950 °C), lithic sediment (aluminum, titanium, iron, calcium, magnesium, sodium, potassium, manganese, zirconium, niobium, hafnium, tantalum, thorium, uranium, and rare earth elements), and anthropogenic inputs (lead) measured in a 38 cm long sediment core retrieved from the lake. In addition to the lacustrine sediment core, the samples of catchment bedrock, surface soils, major stream sediment, and eolian dust collected from the lake periphery also are analyzed. The systematic biogeochemical excursions in the upper core section (top ～8 cm) indicate increased anthropogenic inputs, watershed denudation by agricultural activities, artificially reduced fluvial sediment supply, relatively increased dust inputs and lake eutrophication in the last few decades. The current study underscores the roles of anthropogenic land-use and wetland conservation practices in the rapid alteration of autochthonous and allochthonous sediment supplies to open aquatic ecosystems. Further, rising lake eutrophication levels despite a managed reduction in allochthonous sediment supplies seem challenging to control due to dissolved nutrient supply from urban sewage discharge and runoff from agricultural land in the watershed.     

Assessment of Metal Contamination in Surface Sediments of Jiaozhou Bay,Qingdao, China

An assessment of metal contamination in surface sediments of the Jiaozhou Bay, Qingdao, one of the rapidly developing coastal economic zones in China, is provided. Sediments were collected from 10 stations and a total of 15 heavy metals were analyzed. Concentrations of metals show significant variability and range from 210 to 620 ppm for Ti, 2.7 to 23 ppm for Ni, 4.2 to 28 ppm for Cu, 5.2 to 18 ppm for Pb, 12 to 58 ppm for Zn, 0.03 to 0.11 ppm for Cd, 5 to 51 ppm for Cr, 1.5 to 9.9 ppm for Co, 5.3 to 19 ppm for As, 12 to 32 ppm for Se, and 19 to 97 ppm for Sr. Based on concentration relationships and enrichment factor (EF) analyses, the results indicate that sediment grain size and organic matter played important roles in controlling the distribution of the heavy metals in surface sediments of the Jiaozhou Bay. The study shows that the sediment of the Jiaozhou Bay has been contaminated by heavy metals to various degrees, with prominent arsenic contributing the most to the contamination. The analysis suggests that the major sources of metal contamination in the Jiaozhou Bay are land‐based anthropogenic ones, such as discharge of industrial waste water and municipal sewage and run‐off. Notably, the elevated heavy metal concentrations of the Jiaozhou Bay sediments could have a significant impact on the bay's ecosystem. With the rapid economic development and urbanization around the Jiaozhou Bay, coastal management and pollution control should focus on these contaminant sources, as well as provide ongoing monitoring studies of heavy metal contamination within the bay.     

Spatial variability of metals in the inter-tidal sediments of the Medway Estuary,Kent, UK

Concentrations of major and trace metals were determined in eight sediment cores collected from the inter-tidal zone of the Medway Estuary, Kent, UK. Metal associations and potential sources have been investigated using principal component analysis. These data provide the first detailed geochemical survey of recent sediments in the Medway Estuary. Metal concentrations in surface sediments lie in the mid to lower range for UK estuarine sediments indicating that the Medway receives low but appreciable contaminant inputs. Vertical metal distributions reveal variable redox zonation across the estuary and historically elevated anthropogenic inputs. Peak concentrations of Cu, Pb and Zn can be traced laterally across the estuary and their positions indicate periods of past erosion and/or non-deposition. However, low rates of sediment accumulation do not allow these sub surface maxima to be used as accurate geochemical marker horizons. The salt marshes and inter-tidal mud flats in the Medway Estuary are experiencing erosion, however the erosion of historically contaminated sediments is unlikely to re-release significant amounts of heavy metals to the estuarine system.     

Heavy metal release by peat erosion in the Peak District,southern Pennines,UK

Upper North Grain (UNG) is a heavily eroding blanket peat catchment in the Peak District, southern Pennines, UK. Concentrations of lead in the near‐surface peat layer at UNG are in excess of 1000 mg kg⁻¹. For peatland environments, these lead concentrations are some of the highest globally. High concentrations of industrially derived, atmospherically transported magnetic spherules are also stored in the near‐surface peat layer. Samples of suspended sediment taken during a storm event that occurred on 1 November 2002 at UNG, and of the potential catchment sources for suspended sediments, were analysed for lead content and the environmental magnetic properties of anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM). At the beginning of the storm event, there is a peak in both suspended sediment and associated lead concentration. SIRM/ARM values for suspended sediment samples throughout the storm reveal that the initial ‘lead flush’ is associated with a specific sediment source, namely that of organic sediment eroded from the upper peat layer. Using the magnetic ‘fingerprinting’ approach to discrimination of sediment sources, this study reveals that erosion of the upper peat layer at UNG is releasing high concentrations of industrially derived lead (and, by inference, other toxic heavy metals associated with industrial particulates) into the fluvial systems of the southern Pennines. Climate‐change scenarios for the UK, involving higher summer temperatures and stormier winters, may result in an increased flux both of sediment‐associated and dissolved heavy metals from eroding peatland catchments in the southern Pennines, adversely affecting the quality of sediment and water entering reservoirs of the region. Copyright © 2005 John Wiley & Sons, Ltd.     

Heavy metals in the hydrological cycle: Trends and explanation

This paper reviews the major sources and transport characteristics of heavy metals in the hydrological cycle. It is demonstrated that heavy metal releases to the environment have changed from 19th and early 20th century production-related activities to consumption-oriented factors in more recent times. The relative roles of particle size, sorption and desorption processes, partitioning and the chemical speciation of heavy metals on fine sediments are identified to understand the likely fate of heavy metals released into fluvial systems. It is argued that the spatial and temporal distribution of heavy metals in the river corridor depends not only on an understanding of metal solubility and speciation, but also on an understanding of sediment dynamics which control, for example, floodplain alluviation and the accumulation of metals in the bottom sediments of contaminated rivers, lakes and reservoirs. Existing long- and short-term records are examined to identify the current state of knowledge about the factors which affect heavy metal releases into aquatic environments. With limited exceptions, it is shown that few long-term studies of trends in heavy metal transport are available although, for some major rivers, limited data on trends in metal concentration exists. Palaeolimnological reconstruction techniques, based on an analysis of lake and reservoir sediments, are identified as a possible means of supplementing monitored records of heavy metal transport. Although numerous studies have suggested that trends in atmospheric contamination, mining and urbanization may be identified in the bottom sediment record, other research has shown that the radionuclide-based chronology and the heavy metal distribution within the sediment are more likely to be a function of post-depositional remobilization than the history of metal loading to the basin. Despite these limitations, it is shown that the incorporation of reservoir bottom sediment analysis into a heavy metal research programme, based in river corridors of Midland England, provides an opportunity to identify and quantify the relative contribution of point and non-point contributions to the heavy metal budget and to relate trends in metal contamination to specific periods of catchment disturbance.     

Heavy metals mobility in harbour contaminated sediments: the case of Port-en-Bessin

Metallic contaminants associated with sediments showed various behaviours depending on physicochemical conditions. A contaminated sediment core from a harbour in the Bay of Seine was sampled to derive information about metal solubilization from anoxic sediment. In these anaerobic surroundings, physicochemical processes depended on the organic matter cycle, on vertical variation of redox conditions and on precipitation conditions of iron and manganese. In the studied core, anoxic conditions were developed at -15 cm depth. A three-step sequential extraction procedure, modified from the BCR method (now the SM&T), was applied to the anoxic sediment in order to evaluate the potential mobility of fixed metals. Zinc was the most labile metal, recovered in the first extraction stages, and was associated with the non-residual fraction of sediment. Lead was the least labile metal, with up to 70% associated with the residual fraction of the sediment. Copper was associated with organic matter, and its mobility was controlled by the concentration and degradation of the organic fraction. Discharge of organic-rich dredged sediments at sea results in degradation of contained organic matter and may affect the environmental impact of these metals significantly. These results therefore help to improve the waste management of such contaminated sediments.     

Hydrocarbon contamination of coastal sediments from the Sfax area (Tunisia), Mediterranean Sea

The coastal area off the city of Sfax (730,000 inhabitants), well-known for fisheries and industrial activities, receives high inputs of organic matter mostly anthropogenic. Eighteen stations were selected in the vicinity of the direct discharge of industrial sewage effluents in the sea in order to study the spatial distribution of the organic contamination. Surface sediments sampled in the shallow shelf were analysed for hydrocarbons by Fourier transform infrared spectroscopy, gas chromatography and gas chromatography/mass spectrometry. Total hydrocarbon distributions revealed high contamination as compared to other coastal Mediterranean sites, with an average concentration of 1865 ppm/dry weight sediment. Gas chromatographic distribution patterns, values of unresolved mixture/n-alkane ratio and distributions of steranes and hopanes confirmed a petroleum contamination of the Arabian light crude oil type. Biogenic compounds were also identified with a series of short-chain carbon-numbered n-alkenes in the carbon range 16-24.     

The role of vegetation in the retention of fine sediment and associated metal contaminants in London's rivers

Many urban rivers receive significant inputs of metal‐contaminated sediments from their catchments. Restoration of urban rivers often creates increased slack water areas and in‐channel vegetation growth where these metal‐contaminated sediments may accumulate. Quantifying the accumulation and retention of these sediments by in‐channel vegetation in urban rivers is of importance in terms of the planning and management of urban river restoration schemes and compliance with the Water Framework Directive. This paper investigates sediment properties at four sites across three rivers within Greater London to assess the degree to which contaminated sediments are being retained. Within paired restored and unrestored reaches at each site, four different bed sediment patch types (exposed unvegetated gravel, sand, and silt/clay (termed ‘fine’) sediments, and in‐channel vegetated sediments) were sampled and analysed for a range of metals and sediment characteristics. Many samples were found to exceed Environment Agency guidelines for copper (Cu), lead (Pb) and zinc (Zn) and Dutch Intervention Values for Cu and Zn. At all sites, sediments accumulating around in‐channel vegetation were similar in calibre and composition to exposed unvegetated fine sediments. Both bed sediment types contained high concentrations of pseudo‐total and acetic acid extractable metal concentrations, potentially due to elevated organic matter and silt/clay content, as these are important sorbtion phases for metals. This implies that the changed sediment supply and hydraulic conditions associated with river restoration may lead to enhanced retention of contaminated fine sediments, particularly around emergent plants, frequently leading to the development of submerged and emergent landforms and potential river channel adjustments. High pseudo‐total metal concentrations were also found in gravel bed sediments, probably associated with iron (Fe) and manganese (Mn) oxyhydroxides and discrete anthropogenic metal‐rich particles. These results highlight the importance of understanding the potential effects of urban river restoration upon sediment availability and channel hydraulics and consequent impacts upon sediment contaminant dynamics and storage. Copyright © 2014 John Wiley & Sons, Ltd.     

The role of the sediment budget in understanding debris flow susceptibility

This study proposes a sediment‐budget model to predict the temporal variation of debris volume stored in a debris‐flow prone watershed. The sediment‐budget is dominated by shallow landslides and debris outflow. The basin topography and the debris volume stored in the source area of the debris‐flow prone watershed help evaluating its debris‐flow susceptibility. The susceptibility model is applied to the Tungshih area of central western Taiwan. The importance of the debris volume in predicting debris‐flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model. The high prediction rate (0·874) for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows. This model is then used to evaluate the temporal evolution of the debris‐flow susceptibility index. The analysis results show that the numbers of watershed which are classified as a debris‐flow group correspond well to storage of sediment at different time periods. These numbers are 10 before the occurrence of Chi‐Chi earthquake, 13 after the occurrence of Chi‐Chi earthquake, 16 after the occurrence of landslides induced by Typhoon Mindulle (Typhoon M), and 14 after the occurrence of debris flows induced by Typhoon M. It indicates that the occurrence of 7·6 Chi‐Chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons. Copyright © 2009 John Wiley & Sons, Ltd.     

Heavy metals in the Bombay harbour area

Bombay harbour is one of the major sinks, on the western peninsula of the Indian subcontinent, receiving anthropogenic pollutants including heavy metals, radionuclides and hydrocarbons in addition to sewage. To evaluate possible impacts of a few heavy metals on the harbour ecosystem, the distribution patterns of Zn, Mn, Cu, Fe, Co, Ni, Cd, Cr, Pb and Sr in water, sediment and two benthic species, the blood clam Anadara granosa and gobiid mudskipper Boleophthalmus boddaerti were studied over the period 1976–1980. The present levels of the ten elements in biotic and abiotic matrices were found to be far below those that are known to affect adversely the life and quality of benthic communities. Furthermore, the concentrations of these elements in various compartments neither revealed any systematic temporal or spatial fluctuations nor reflected the substantial incease in the total budget over the past 8–12 years. Also these levels were within the range reported in the nearshore and oceanic environs along the west coast. In view of this, the poor growth and high percentage mortality observed in the clam Anadara granosa fished from the Sewri clam bed compared to that of the stock harvested from the Trombay region in the harbour may well be due to anoxic conditions caused by organic pollutants present in the domestic sewage and industrial wastes released in the vicinity of the Sewri clam bed.     

Metal contamination of sediments associated with deepwater ocean sewage outfalls, Sydney, Australia

The New South Wales Environment Protection Authority has recently completed a programme to evaluate the impact on near-shore shelf sediments, following the commissioning of three new deepwater sewage outfalls off Sydney, Australia. These outfalls discharge a total of around 1300 ML day⁻¹ of primary treated sewage derived from domestic and industrial sources. The study compared three locations that were close to the outfalls (likely impacted) and three locations far from the outfalls (likely non-impacted). Four zones were sampled within each location to provide estimates of spatial variability. Three samples of surface sediment were collected from each zone at six monthly intervals over a three year period which encompassed the commissioning of the outfalls. The results of the study suggest that, associated with the commissioning of the three deepwater outfalls, there has not been a significant effect on the concentration of trace metals in the sediments surrounding the outfalls. The concentrations of trace metals in the whole sediment generally were close to the world-wide background levels quoted in the literature, and generally reflected the distribution pattern of the sedimentary fines (< 62.5 mm). When compared to a number of sediment quality guidelines, the concentrations of trace metals were found to be below a level considered to have the potential to cause biological effects or (in the case of As, Ni, Cr) at a level that could be tolerated by the majority of benthic organisms.     

Organic carbon fluxes from the upper Yangtze basin: an example of the Longchuanjiang River,China

To investigate the effects of anthropogenic activity, namely, land use change and reservoir construction, on particulate organic carbon (POC) transport, we collected monthly water samples during September 2007 to August 2009 from the Longchuanjiang River to understand seasonal variations in the concentrations of organic carbon species and their sources and the yield of organic and inorganic carbon from the catchment in the Upper Yangtze basin. The contents of riverine POC, total organic carbon and total suspended sediment (TSS) changed synchronously with water discharge, whereas the contents of dissolved organic carbon had a small variation. The POC concentration in the suspended sediment decreased non‐linearly with increasing TSS concentration. Higher molar C/N ratio of particulate organic matter (average 77) revealed that POC was dominated by terrestrially derived organic matter in the high flows and urban wastewaters in the low flows. The TSS transported by this river was 2.7 × 10⁵ t/yr in 2008. The specific fluxes of total organic carbon and dissolved inorganic carbon (DIC) were 5.6 and 6 t/km²/yr, respectively, with more than 90% in the high flow period. A high carbon yield in the catchment of the upper Yangtze was due to human‐induced land use alterations and urban wastes. Consistent with most rivers in the monsoon climate regions, the dissolved organic carbon–POC ratio of the export flux was low (0.41). Twenty‐two percent (0.9 t/km²/yr) of POC out of 4 t/km²/yr was from autochthonous production and 78% (3.1 t/km²/yr) from allochthonous production. The annual sediment load and hence the organic carbon flux have been affected by environmental alterations of physical, chemical and hydrological conditions in the past 50 years, demonstrating the impacts of human disturbances on the global and local carbon cycling. Finally, we addressed that organic carbon flux should be reassessed using adequate samples (i.e. at least two times in low‐flow month, four times in high‐flow month and one time per day during the flood period), daily water discharge and sediment loads and appropriate estimate method. Copyright © 2011 John Wiley & Sons, Ltd.     

Spatial and temporal variations of heavy metal contamination in sediments of a mangrove swamp in Hong Kong

Spatial and temporal variations of heavy metal contamination in sediments of a small mangrove stand in Hong Kong were examined by laying two transects perpendicular across the shore. Surface sediment samples were taken along the two transects running landward to seaward at intervals of 5 or 10 m during December 1989, and March, July and September 1990. Total concentrations of Cu, Zn, Mn and Pb did not show any specific trend along each transect, although the maximum concentration of heavy metals tended to occur at the landward edge. There was a high level of variability among locations within each transect; for instance, the Cu concentrations fluctuated from 1 to 42 μg g⁻¹. Certain sites contained exceptionally high levels of total metals. Total concentrations of Cu, Zn, Mn and Pb as high as 42, 150, 640 and 650 μg g⁻¹, respectively, were recorded, implying contaminated sediment. A comparison of the two transects indicated that the sediments of Transect B seemed to contain higher total Zn but lower Cu and Mn concentrations than those of Transect A. Most of the heavy metals accumulated in the sediments were not extractable with ammonium acetate and no Cu or Pb was detected in these extracts. The concentrations of extractable Zn and Mn were low, less than 10% of the total metal concentration in the sediment, and appeared to decrease from the landward to seaward samples. For both total and extractable metals, there were significant seasonal fluctuations for both transects, but no specific trends could be identified. These spatial and temporal variations suggest that the scale and representativeness of sampling require careful planning, and a single sample might not give a satisfactory evaluation of the levels of heavy metal contamination in mangrove ecosystems.     

The spatial and temporal distribution of heavy metals in sediments of Victoria Harbour, Hong Kong

Victoria Harbour has received substantial loadings of pollutants from industrial and municipal wastewater discharged since the 1950s. Inputs of contaminants have declined dramatically during the last two decades as a result of better controls at the source and improved wastewater treatment facilities. To assess the spatial and temporal changes of metal contaminants in sediments in Victoria Harbour, core and grab sediments were collected. The central harbour areas were generally contaminated with heavy metals. The spatial distribution of trace metals can probably be attributed to the proximity of major urban and industrial discharge points, and to the effect of tidal flushing in the harbour. In the sediment cores, the highest concentrations of trace metals were observed to have accumulated during the 1950s-1980s, corresponding with the period of rapid urban and industrial development in Hong Kong. From the late 1980s, there has been a major decline in the concentrations of trace metals, due to a reduction in industrial activities and to the enactment of wastewater pollution controls in the territory. The Pb isotopic compositions of the sediments revealed the anthropogenic inputs of Pb to the harbour. The (206)Pb/(207)Pb ratios varied from 1.154 to 1.190, which were lower than those of background geological materials in Hong Kong ((206)Pb/(207)Pb: 1.201-1.279). The data also indicated that the Pb in the harbour sediments most likely originated from mixed sources, including the leaded gasoline used in the past and other anthropogenic sources.     

Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment,southern United Kingdom

Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub‐catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time‐integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub‐catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub‐catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02–27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub‐catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub‐catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15–20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley & Sons, Ltd.     

The dynamics of sediment‐associated contaminants over a transition from drought to multiple flood events in a lowland UK catchment

Fine sediment in suspended form, recently deposited overbank and in temporary storage on or in channel beds, was collected in the Nene basin during a period of drought through to a period of four high flows. The sediment was analysed for arsenic, copper, lead, phosphorus and zinc concentrations with the aim of investigating their sources, movement, temporary storage and potential for environmental harm. Copper, lead and zinc probably originated from urban street dusts, phosphorus (originally in dissolved form) from sewage effluent and arsenic from natural soils developed over ironstone. There was little difference in the metal or arsenic concentrations in the sediment under different flow conditions; instead, proximity to pollutant sources appeared to control their concentrations. Phosphorus in tributary sub‐catchments probably adsorbed to sediment during periods of low flow but these sediments were flushed away during high flows and replaced by sediment with lower concentrations. However, concentrations of all pollutants in overbank sediments along the Nene's main channel were not reduced in successive flood events, suggesting no first flush effect. Only phosphorus accumulated on sediment at concentrations exceeding those of its catchment‐based sources (e.g. street dusts, channel banks and catchment soils). This scavenging of aqueous phosphate by sediment explained the difference in behaviour between phosphorus, arsenic and heavy metals. The surface area and organic matter content were shown to have a small effect on contaminant concentrations. Street dust contaminants only exceeded predicted effect levels in close proximity to urban areas, suggesting a small potential for harm to the aquatic environment. Arsenic concentrations exceeded predicted effect levels in most sediment samples. However, it has been shown to be largely non‐bioavailable in previously published research on the Nene, limiting its potential for significant environmental harm. Phosphorus concentrations in river sediments are high in comparison to the soils in the catchment and in comparison with sediment–P concentrations in other published lowland catchment studies, indicating a large potential for eutrophication should the Phosphorus be, or become, bioavailable. Copyright © 2015 John Wiley & Sons, Ltd.     

Peatland restoration: controls on sediment production and reductions in carbon and pollutant export

Peatlands are an important store of soil carbon, and play a vital role in global carbon cycling, and when located in close proximity to urban and industrial areas, can also act as sinks of atmospherically deposited heavy metals. Large areas of the UK's blanket peat are significantly degraded and actively eroding which negatively impacts carbon and pollutant storage. The restoration of eroding UK peatlands is a major conservation concern, and over the last decade measures have been taken to try to control erosion and restore large areas of degraded peat. This study utilizes a sediment source fingerprinting approach to assess the effect of restoration practices on sediment production, and carbon and pollutant export in the Peak District National Park, southern Pennines (UK). Suspended sediment was collected using time integrated mass flux samplers (TIMS), deployed across three field areas which represent the surface conditions exhibited through an erosion–restoration cycle: (i) intact; (ii) actively eroding; and (iii) recently re‐vegetated. Anthropogenic pollutants stored near the peat's surface have allowed material mobilized by sheet erosion to be distinguished from sediment eroded from gully walls. Re‐vegetation of eroding gully systems is most effective at stabilizing interfluve surfaces, switching the locus of sediment production from contaminated surface peat to relatively ‘clean’ gully walls. The stabilization of eroding surfaces reduces particulate organic carbon (POC) and lead (Pb) fluxes by two orders of magnitude, to levels comparable with those of an intact peatland, thus maintaining this important carbon and pollutant store. The re‐vegetation of gully floors also plays a key role in decoupling eroding surfaces from the fluvial system, and further reducing the flux of material. These findings indicate that the restoration practices have been effective over a relatively short timescale, and will help target and refine future restoration initiatives. Copyright © 2014 John Wiley & Sons, Ltd.     

Heavy metals in surface sediments from nine estuaries along the coast of Bohai Bay,Northern China

Concentrations of heavy metals in river water and sediment were investigated in nine estuaries along the coast of Bohai Bay, Northern China. Multivariate statistical techniques such as principal component analysis and cluster analysis, in combination with metal concentration analysis and correlation analysis, were used to identify the possible sources of the metals and the pollution pattern in nine estuaries along the coast of Bohai Bay. The environmental risks of metals, evaluated by sediment quality guidelines and background values, revealed Hg contamination in the estuaries. However, levels of Cd in estuarine sediments were low, and they were less than those levels in river sediments, partly due to the high mobility and dilution of river or seawater. Cd did not contribute to sediment deposits in estuaries. High organic matter from effluents from large municipal sewage treatment plants was predominantly responsible for restricting Hg mobility from the river to Bohai Bay.     

Contemporary glacigenic inputs to the dust cycle

The importance of glacigenic dust in the Earth's system during glacial periods is widely acknowledged. Under contemporary conditions, the world's largest dust sources are in low‐lying, hot, arid regions and this is where most aeolian research is focused. However the processes of dust production and emissions are still operating in cold climate regions, particularly in proglacial areas. This paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle. It focuses on how elements in the glacial and aeolian geomorphic sub‐systems interact to determine the magnitude, frequency and timing of aeolian dust emissions, and on feedback mechanisms between the systems. Where they have been measured, dust emission intensity and deposition rates in glacierised catchments are very high, in some cases far exceeding those in lower latitudes, however, few studies span long time scales. The impact of future glacier retreat on the balance between sediment supply, availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered. This balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths, which promote dust emissions, and patterns and rates of soil development and vegetation succession on recently‐deglaciated terrain which protect sediments from deflation. Retreat of the Antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non‐glacigenic sources in the southern hemisphere. Copyright © 2012 John Wiley & Sons, Ltd.     

The dynamic effects of sediment availability on the relationship between wind speed and dust concentration

Where sediment supply is unlimited, previous research suggests that a strong, positive relationship between wind speed and dust concentration exists at the event scale. This relationship can break down if sediment availability is limited or changes during an event. This paper explores the dynamic effects of sediment availability on the relationship between wind speed and dust concentration using data from nine high‐latitude dust events recorded in Iceland. Of these events, six showed a strong positive relationship between wind speed and dust concentration. For the remainder, the relationship breaks down periodically during the event due to changing surface moisture conditions and atmospheric humidity. Results suggest a need to understand how spatial and temporal changes in humidity, surface soil moisture, soil texture and threshold velocity interact and control sediment availability for dust emissions in all environments, including at high latitudes. Copyright © 2018 John Wiley & Sons, Ltd.