Microscopic and chemical studies of metal particulates in tree bark and attic dust : evidence for historical atmospheric smelter emissions, Humberside, UK.

Tree barks and attic dusts were examined as historical archives of smelter emissions, with the aim of elucidating the pathways of pollution associated with a plume of Sn and Pb contamination in top soils, found close to the former Capper Pass smelter, Humberside, UK. Samples were collected from three villages within the area of the contamination plume. Scanning Electron Microscopy (SEM) and bulk chemical analyses were used to assess particle type, number and deposition patterns. SEM analysis of dusts and bark revealed that Sn and Pb particles were present in samples from all three villages along with copper, zinc and iron particles. These were almost entirely <10 m in diameter and occurred mostly as oxides, frequently forming clusters of sub-micron crystals. Samples further from the smelter contained considerably fewer particles. We present images of smelter derived Sn particles. Chemical assays of the barks and attic dusts demonstrated that concentrations of Sn, Pb, Cu, As, Sb and Cd diminished with increasing distance from the source. Strong positive correlations were found between Sn and Pb, As, Sb and Cd in the attic dusts. Enrichment Factors (EF) were calculated for these trace elements based on topsoil element concentrations obtained from the soil survey of the study area. Decreases in these trace element concentrations and EF values with distance away from the smelter are consistent with trends found in the soil survey for Sn and Pb and are typical of deposition patterns around smelter stacks. The study demonstrates that tree bark and attic dusts can be effective archives of metal particulates deposited from large static emission sources

Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K.

Alluvial soils are reservoirs of metal contaminants such as Pb that originate from many different sources and are integrated temporally and spatially through erosional and depositional processes. In this study the source, lability and solubility of Pb was examined in a range of alluvial soils from the middle and lower River Trent and its tributary the River Dove using Pb isotope apportionment and isotopic dilution. All samples were collected within 10 m of the river bank to represent the soil that is most likely to be remobilised during bank erosion. Paired samples were taken from the topsoil (0-15 cm) and subsoil (35-50 cm) to assess differences with depth. Lead concentrations in soil ranged from 43 to 1282 mg/kg. The lability of soil Pb varied between 9-56% of total metal concentration whilst Pb concentrations in pore water varied between 0.2 and 6.5 µg/L. There was little difference in the % Pb lability between paired top and sub soils, possibly because soil characteristics such as pH, iron oxides and clay content were generally similar; a result of the recycling of eroded and deposited soils within the river system. Soil pH was found to be negatively correlated with % Pb lability. Source apportionment using 206Pb/207Pb and 208Pb/207Pb ratios showed that the isotopic ratios of Pb in the total, labile and solution pools fitted along a mixing line between Broken Hill Type (‘BHT’) Pb, used as an additive in UK petrol, and the local coal/Sourthern Pennine ore Pb. Various anomalies were found in the Pb isotopes of the bankside alluvial soils which were explained by point source pollution. Statistically significant differences were found between (i) the isotopic composition of Pb in the total soil pool and the labile/solution pools and (ii) the isotopic composition of Pb in the labile and solution pools, suggesting an enrichment of recent non-Pennine sources of Pb entering the soils in the labile and solution pools

Characterising changes in fluorescence properties of dissolved organic matter and links to N cycling in agricultural floodplains

Sand and gravel aquifer systems are common features below and adjacent to river networks and are important in providing a hydrological link between terrestrial and aquatic ecosystems. They are often used for intensive agriculture and therefore provide a conduit for the transport of nutrients to aquatic systems. Understanding the biogeochemical cycles of C and N in such systems is essential in efforts to improve water quality, with a major link being the transfer and properties of DOM which drives microbial processing of nutrients. In this work undertaken in the Trent Valley, U.K., the differences in dissolved organic matter (DOM) properties in the soil, aquifer ground water and river water are examined using excitation–emission matrix fluorescence spectroscopy (EEM), in addition to chemical analysis. In the aquifer system studied the water table is ∼1.5 m below the land surface, suggesting that DOM and nutrient transfer would occur between the soil and groundwater. Nitrate levels in the ground water were ∼50 mg L−1 NO3-N. Soil DOM properties were measured in KCl extracts used to extract inorganic and organic N so that further information could be obtained regarding possible sources and properties of the DON and the biodegradability of the DOC pool. Within the soils tested, fulvic-like properties and the humification index (HI) were significantly (P < 0.05) higher in sandy soils suggesting that microbial accessibility to organic matter was greater. The applicability of assessing DOM characteristics in the different matrices were assessed and quantitative or qualitative comparisons made. Properties of DOM in both the soils and aquifer waters all showed a typical terrestrial source with principal component analysis (PCA) showing strong correlations between DOC, fulvic-like properties, the HI and tryptophan-like properties. A major finding was that the HI was generally higher in the groundwater, suggesting continued processing of DOM within the aquifer whilst qualitative comparisons showed the groundwater possessed a higher fluorescence index (FI). Whilst DON and the tyrosine-like proteins were correlated in the soil, the tryptophan-like proteins were strongly correlated to fulvic-like substances in both the soil and groundwater. This suggested that phenolic compounds were also being identified in this part of the EEM matrix, emphasising the need for additional compound analysis to fully understand the nature of DOM in these systems

Understanding the controls on sediment-P interactions and dynamics along a non-tidal river system in a rural–urban catchment: the River Nene

The release of Phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘Good Ecological Status’ under the EU Water Framework Directive (WFD). To identify the contribution of sediment-P to river systems, an understanding of the factors that influence its distribution within the entire non-tidal system is required. Thus the aims of this work were to examine the (i) total (PTotal) and labile (PLabile) concentrations in sediment, (ii) the sequestration processes and (iii) the interactions between sediment P and the river water in the six non-tidal water bodies of the River Nene, U.K. Collection of sediments followed a long period of flooding and high stream flow. In each water body, five cores were extracted and homogenised for analysis with an additional core being taken and sampled by depth increments. Comparing the distribution of sediment particle size and PTotal data with soil catchment geochemical survey data, large increases in PTotal were identified in sediments from water body 4–6, where median concentrations of PTotal in the sediment (3603 mg kg−1) were up to double those of the catchment soils. A large proportion of this increase may be related to in-stream sorption of P, particularly from sewage treatment facilities where the catchment becomes more urbanised after water body 3. A linear correlation (r = 0.8) between soluble reactive phosphate (SRP) and Boron in the sampled river waters was found suggesting increased STW input in water bodies 4–6. PLabile concentrations in homogenised cores were up to 100 mg kg−1 PO4–P (generally < 2% of PTotal) and showed a general increase with distance from the headwaters. A general increase in Equilibrium Phosphate Concentrations (EPC0) from an average of 0.9–∼1.7 μm L−1 was found between water bodies 1–3 and 4–6. Fixation within oxalate extractable phases (Al, Fe and Mn) accounted for ∼90% of P binding in water bodies 4–6, but only between 31 and 74% in water bodies 1–3. Statistical models predicting PTotal (R2 = 0.78), oxalate extractable P (R2 = 0.78) and Olsen P (R2 = 0.73) concentrations in river sediments identified Mn oxy-hydroxides (MnOx) as a strong predictive variable along with the location within the river system. It is suggested that MnOx within model predictions is identifying a pool of mixed Fe–Mn oxy-hydroxides (MnOx–FeOOH) or Fe oxy-hydroxide (FeOOH) from the wider FeOxalate pool that are particularly effective at sorbing and fixing P. The findings demonstrate how sediment and P may accumulate along a 100 km non-tidal river system, the extent to which a range of processes can fix P within mineral phases and how natural flooding processes may flush sediment from the river channel. The processes identified in this study are likely to be applicable to similar river systems over their non-tidal water bodies in eastern England

Using 206/207Pb isotope ratios to estimate phosphorus sources in historical sediments of a lowland river system

Purpose Engineering and dredging strategies to manage sediment, along with river-scouring, can reveal older sediments. These present a unique opportunity to assess past sources of phosphorus (P) inputs into river sediments. We used the sediment concentrations of P, lead (Pb) and 206/207Pb isotopes to produce ‘first-order’ estimates of the source (diffuse agricultural or sewage treatment) of phosphorus. Materials and methods Sediment cores (n = 30) were collected from the length of the non-tidal River Nene, a lowland river in eastern England. Cores were analysed for sediment elemental concentrations and Pb isotopes. Principal component analysis and linear regression modelling were used to assess the relationships between P, Pb and Pb isotopes. Monte-Carlo simulations and boot-strapping were undertaken to estimate, with 95% confidence intervals, the source of P in these sediments. Results and discussion Analysis of the relationships between PTotal, PbTotal and 206/207Pb isotope ratios suggested that sediments were deposited largely prior to the phasing out of tetra-ethyl Pb (PbBHT) from petrol. Regression models showed positive correlations between PTotal and PbTotal (R2 = 0.85). Principal component analysis suggested a strong sewage treatment signal for Pb and P enrichment. In the rural upper three water bodies, little sewage treatment work (STW)-derived P was found in the sediment, a consequence of limited STW input and greater sediment transport. In the more urbanised water bodies 4–6, ‘first-order estimates’ of STW P suggest that median concentrations were 30–40% of PTotal. Conclusions The strong relationships between Pb and P concentrations in river water provided the opportunity to use 206/207Pb isotope ratios to calculate ‘first-order’ estimates of the proportion of P released from STWs in the historical sediment. Understanding the sources of historical sediment P can be used to assess the success of current sediment management strategies and to base further mitigation measures. Results suggest that whilst much recent sediment P is removed, the legacy sediment remains to contribute P to the water body. Thus, options regarding the practical removal of these sediments and the extent to which this would improve water P status need to be assessed and balanced against options such as further decreasing soil P or STW P stripping

Implications of short-range spatial variation of soil bulk density for adequate field-sampling protocols: methodology and results from two contrasting soils

Soil bulk density (BD) is measured during soil monitoring. Because it is spatially variable, an appropriate sampling protocol is required. This paper shows how information on short-range variability can be used to quantify uncertainty of estimates of mean BD and soil organic carbon on a volumetric basis (SOCv) at a sampling site with different sampling intensities. We report results from two contrasting study areas, with mineral soil and with peat. More sites should be investigated to develop robust protocols for national-scale monitoring, but these results illustrate the methodology. A 20 × 20-m2 monitoring site was considered and sampling protocols were evaluated under geostatistical models of our two study areas. At sites with local soil variability comparable to our mineral soil, sampling at 16 points (4 × 4 square grid of interval 5 m) would achieve a root mean square error (RMSE) of the sample mean value of both BD and SOCv of less than 5% of the mean (topsoil and subsoil). Pedotransfer functions (PTFs) gave predictions of mean soil BD at a sample site, comparable to our study area on mineral soil, with similar precision to a single direct measurement of BD. On peat soils comparable to our second study area, the mean BD for the monitoring site at depth 0–50 cm would be estimated with RMSE to be less than 5% of the mean with a sample of 16 cores, but at greater depths this criterion cannot be achieved with 25 cores or fewer

How the composition of sandstone matrices affects rates of soil formation

Soils deliver multiple ecosystem services and their long-term sustainability is fundamentally controlled by the rates at which they form and erode. Our knowledge and understanding of soil formation is not commensurate with that of soil erosion, in part due to the difficulty of measuring the former. However, developments in cosmogenic radionuclide accumulation models have enabled soil scientists to more accurately constrain the rates at which soils form from bedrock. To date, all three major rock types – igneous, sedimentary and metamorphic lithologies – have been examined in such work. Soil formation rates have been measured and compared between these rock types, but the impact of rock characteristics on soil formation rates, such as rock matrices and mineralogy, have seldom been explored. In this UK-based study, we used cosmogenic radionuclide analysis to investigate whether the lithological variability of sandstone governs pedogenesis. Soil formation rates were measured on two arable hillslopes at Woburn and Hilton, which are underlain by different types of arenite sandstone. Rates were faster at Woburn, and we suggest that this is due to the fact that the Woburn sandstone formation is less cemented that that at Hilton. Similarly, rates at Woburn and Hilton were found to be faster than those measured at two other sandstone-based sites in the UK, and faster than those compiled in a global inventory of cosmogenic studies on sandstone-based soils. We suggest that the cementing agents present in matrix-abundant wackes studied previously may afford these sandstones greater structural integrity and resistance to weathering. This work points to the importance of factoring bedrock matrices into our understanding of soil formation rates, and the biogeochemical cycles these underpi

Predicting trace metal solubility and fractionation in urban soils from isotopic exchangeability

Metal-salt amended soils (MA, n = 23), and historically-contaminated urban soils from two English cities (Urban, n = 50), were investigated to assess the effects of soil properties and contaminant source on metal lability and solubility. A stable isotope dilution method, with and without a resin purification step, was used to measure the lability of Cd, Cu, Ni, Pb and Zn. For all five metals in MA soils, lability (%E-values) could be reasonably well predicted from soil pH value with a simple logistic equation. However, there was evidence of continuing time-dependent fixation of Cd and Zn in the MA soils, following more than a decade of storage under air-dried conditions, mainly in high pH soils. All five metals in MA soils remained much more labile than in Urban soils, strongly indicating an effect of contaminant source on metal lability in the latter. Metal solubility was predicted for both sets of soil by the geochemical speciation model WHAM-VII, using E-values as an input variable. For soils with low metal solution concentrations, over-estimation of Cd, Ni and Zn solubility was associated with binding to the Fe oxide fraction while accurate prediction of Cu solubility was dependent on humic acid content. Lead solubility was most poorly described, especially in the Urban soils. Generally, slightly poorer estimation of metal solubility was observed in Urban soils, possibly due to a greater incidence of high pH values. The use of isotopically exchangeable metal to predict solubility is appropriate both for historically contaminated soils and where amendment with soluble forms of metal is used, as in toxicological trials. However, the major limitation to predicting solubility may lie with the accuracy of model input variables such as humic acid and Fe oxide contents where there is often a reliance on relatively crude analytical estimations of these variables

Environmental factors influencing pipe failures

This report details work carried out under NERC grants NE/M008339/1 and NE/NO13026/1 which were collaborations between the British Geological Survey and Yorkshire Water, with an additional knowledge transfer component involving Scottish Water and Dŵr Cymru Welsh Water. The work examines whether models developed using environmental, topographical and geohazard information could complement existing management tools, and increase the understanding as to how pipe networks of different materials interact with their broader environment. This can be seen as a first step in identifying ways in which greater resilience could be built into pipe networks