Critical loads for soils and waters in a selected Scottish catchment

In the UK, critical loads have been mapped for both soils and freshwaters and the maps indicate that discrepancies may occur between these two receptors over sensitive areas of the UK. Freshwater critical load maps were prepared by calculating the Henriksen critical load for the most sensitive water body in each 10 km grid square. Critical loads for soils were calculated according to the mineralogy and associated soil properties of the dominant soil at a 1 km resolution. To examine the differences between the soil and freshwater data sets it is necessary to calculate critical loads at a smaller scale using the catchment as the focus for study. This was done by selecting a catchment on granitic parent material in the North of Scotland. Data on water chemistry, collected on a weekly basis, was used to calculate temporal variations in critical loads for freshwaters using the Henriksen method. Soil sampling across the catchment was conducted on a grid based system to provide estimates of spatial variability in sensitivity. Profile characteristics and soil chemical data obtained from detailed soil sampling programmes were used in the PROFILE model to determine the spatial variation in critical loads for soils. In general, the results show that the critical loads for soils tend to be lower than those for freshwater. The spatial variation in the soil critical load tends to be small whilst the temporal variation in critical load for freshwaters is large. In order to account for these differences it is important to identify the key processes within the catchment which play a major role in controlling streamwater chemistry. This procedure improves the relationship between critical loads for soils and waters.     

Total copper contents of Scottish soils

The distribution of the total copper contents of 4179 samples from 946 Scottish soil profiles is reported and the relation of copper content to some other soil variables is examined. The frequency distribution of copper contents is found to be approximately lognormal. The derived mean for the full set of data is 10 mg/kg and the normal range 0.93–110 mg/kg. The copper contents of basic and intermediate igneous rocks exceed those of acidic rocks by a factor of about 5 and among sedimentary rocks copper contents are higher in argillaceous than in arenaceous types. The general trend is for copper to increase with increasing depth and ash content and to decrease with increasing sand content. On the basis of total copper content the risk of copper deficiency is assessed to be high in 26 soil associations in Scotland and moderate in a further 10. Naturally occurring copper toxicity is unlikely to be encountered.     

Extractable copper concentrations in Scottish soils

The distribution of ethylenediaminetetraacetic acid (EDTA)-extractable Cu concentration levels in 3653 samples from 725 Scottish soil profiles is reported. The derived mean for the full set of data is 0.86 mg kg^?1 and the normal range 0.08–9.8 mg kg^?1. The relation of extractable Cu concentration to that of total Cu and to some other soil variables is also examined. Extractable Cu contents decrease with increasing depth over the first 50 cm and are almost constant below this. The correlation between total and extractable copper (r=+ 0.453) is statistically highly significant (P<0.001). The extractability (i.e. the percentage of total Cu extractable by EDTA) has also been considered in relation to the other soil variables. Extractability is inversely related to ash content though the relationship is not linear. Extractability is enhanced under conditions of impeded drainage but there is no indication that it is related to clay or sand contents. Approximately 18% of the arable topsoil samples contain levels of extractable Cu which are inadequate to supply the nutritional requirements of cereal crops and approximately 79% contain levels inadequate to support herbage with a Cu content sufficient to supply the requirements of grazing cattle.     

Extractable lead concentrations in Scottish soils

The distribution of acetic acid-extractable lead concentration levels in 3764 samples from 751 Scottish soil profiles is reported. The relation of extractable lead concentration to that of total lead and to some other soil variables is also examined.Because the frequency distribution of concentration levels is approximately lognormal, a logarithmic transformation of the data has been performed to provide a more satisfactory means of describing the distribution. The derived mean for the full set of data is 0.24 mg/kg and the normal range 0.016?3.4 mg/kg.Total lead concentration was found to be the dominant factor in determining the level of extractable lead in these soils and it was concluded that it would be more meaningful to consider the extractability of lead (i.e., the percentage of total lead extractable by acetic acid) rather than the absolute level of extractable lead in relation to the various other soil variables which are of interest in this connection.There is evidence that extractability is enhanced under conditions of impeded drainage but none to indicate that it is related to clay or ash content.Extractable lead was found to be generally higher in surface horizons than at depth thus reflecting the pattern of variation exhibited by total lead concentration. Extractability of lead shows little evidence of variation with depth.     

Evidence for acidification of sensitive Scottish soils by atmospheric deposition

The Scottish soils most sensitive to acidification from acid deposition are peats and those derived from quartzite or Devonian and Torridonian sandstones. It is shown that the surface horizons of Calluna moorland podzols derived from these mineral parent materials behave in a similar way to peats, in that their pH depends upon cation exchange equilibria between H⁺ and Ca²⁺. The pH is therefore related, as might be expected from the ratio law, to the ratio [H⁺]:[Ca²⁺], and this relationship may be used to predict the effect of emission reductions or increases upon these soils.     

Critical loads of acid deposition on Scottish soils

The impact of acid deposition, attributable to sulphur and nitrogen pollutants, on the soils of Scotland has been analysed using a critical loads approach. The critical load of a soil (as an indicator of ecological damage) is calculated from the soil parent material controlling weathering and soil development. Using existing soil survey information national maps for critical loads of acidity and the sulphur fraction are presented for soils under natural and semi-natural ecosystems. The results show that highly sensitive soils, that is those derived from quartzite and granite are limited in occurrence. However, there are large areas of sensitive soils predominantly to the north and west of the Midland Valley and in the Southern Uplands, in receipt of acid deposition in excess of their critical load. Enhanced soil acidification should be widespread in these areas and consequently the ecosystems which they support will be adversely affected. The least sensitive soils, overlying limestone or marl, are restricted in occurrence and are confined to the major deposits of marine alluvium. The results of the analysis may be used to help policy makers derive emission abatement strategies in the context of the European Sulphur protocol renewal in 1993. In Scotland the maps may be used to aid the planning of large scale afforestation.     

Nitrous oxide production and denitrification in Scottish arable soils

Nitrous oxide (N₂O) emissions and concentrations in the soil atmosphere were measured at a number of sites of differing soil type in south-east Scotland between 1985 and 1988. Concentrations followed log-normal distributions and were significantly affected by soil type, tillage treatment, and nitrate application rate. The shape of the profiles suggested significant consumption in the upper 5 cm, making calculations of emission rates using Fick's Law unsatisfactory. Emission rates measured using closed flux chambers were at least one order of magnitude smaller from heavier-textured arable soils than from lighter ones. Denitrification fluxes measured by field application of the acetylene inhibition technique were lowest in a clay loam, and highest in an alluvial sandy loam; this was attributed to a failure to achieve a satisfactory distribution of acetylene in the heavier soil. Denitrification rates in soil cores generally exceeded measured surface fluxes; incubation at decreased oxygen concentrations typical of those measured in the field produced a further significant increase. Core incubation should be used as an alternative to in situ field measurement only if the oxygen concentration in the incubation vessels is adjusted to mimic that in the field; otherwise denitrification rates may be significantly underestimated.     

Development and use of a database of hydraulic properties of European soils

Many environmental studies on the protection of European soil and water resources make use of soil water simulation models. A major obstacle to the wider application of these models is the lack of easily accessible and representative soil hydraulic properties. In order to overcome this apparent lack of data, a project was initiated to bring together the available hydraulic data which resided within different institutions in Europe into one central database. This information was then used to derive a set of pedotransfer functions applicable to studies at a European scale. These pedotransfer functions predict the hydraulic properties from parameters collected during soil surveys and can be a good alternative for costly and time-consuming direct measurement of these properties. A total of 20 institutions from 12 European countries collaborated in establishing the database of draulic operties of uropean oils (HYPRES). This database has a flexible relational structure capable of holding a wide diversity of both soil pedological and hydraulic data. As these data were contributed by 20 different institutions it was necessary to standardise both the particle-size and the hydraulic data. A novel similarity interpolation procedure was successfully used to achieve standardization of particle-sizes according to the FAO clay, silt and sand particle-size ranges. Standardization of hydraulic data was achieved by fitting the Mualem-van Genuchten model parameters to the individual θ(h) and K(h) hydraulic properties stored in HYPRES. The HYPRES database contains information on a total of 5521 soil horizons (including replicates). Of these, 4030 horizons had sufficient data to be used in the derivation of pedotransfer functions. Information on both water retention and hydraulic conductivity was available for 1136 horizons whereas 2894 horizons had only information on water retention. Each soil horizon was allocated to one of 11 possible soil textural/pedological classes derived from the six FAO texture classes (five mineral and one organic) and the two pedological classes (topsoil and subsoil) recognised within the 1:1 000 000 scale Soil Geographical Data Base of Europe. Next, both class and continuous pedotransfer functions were developed. By using the class pedotransfer functions in combination with the 1:1 000 000 scale Soil Map of Europe, the spatial distribution of soil water availability within Europe was derived.     

The biological and physical stability and resilience of a selection of Scottish soils to stresses

The ability of soil to resist and recover from anthropogenic and environmental stresses defines stability and resilience, respectively; an understanding of this ability is critical to sustainable land-use. In this study of 26 soils from across Scotland, we examine the influence of soil properties and antecedent conditions on physical and biological resilience to stress. The sites studied covered a wide range of soil types and land management, including serpentine soil from the Shetland Islands, a catena on the Highland Boundary Fault, and young aeolian sandy soils on the east coast. Biological resilience was measured as CO₂ evolution from soil with added plant residues after either a transient (heat) or a persistent (copper) stress. Measures of physical resilience were: (i) compression and expansion indices following rapid uniaxial compression (to 50 kPa) and relaxation; and (ii) void ratio changes due to an overburden stress and subsequent cycles of wetting and drying. Evolution of CO₂ from soil with added plant residues after heat or copper stress ranged from 23% to >100% that of the unperturbed soil, while the air-filled void ratio after the overburden stress ranged from 70% to >100% that of the unperturbed soil. Soils were grouped into quartiles based on their resistance to and recovery after each of the four prescribed stresses. Soil organic carbon (SOC) content correlated strongly with resilience after biological and physical stresses, particularly resistance to Cu stress ( r = 0.72) and recovery from compression ( r = 0.67), whereas there were no strong correlations between resilience following heat and any of the measured soil characteristics, although both land use and soil class were helpful in separating the responses. Resistance to compression was negatively correlated with SOC ( r =−0.63).     

Comparison of soil carbon stocks in Scottish soils between 1978 and 2009

The change in soil carbon (C) stock over a 19–31‐year period (mean 25 years) has been measured at 179 sites on a 20‐km grid across Scotland. Sampling was by horizon from a profile pit. Although soil bulk density determinations were absent at the first sampling time, we used bulk density values from the second sampling time calibrated against NIR spectra to predict the missing values. There was no detectable change in overall total soil C stock (mean ± standard error, to a depth of 100 cm), which was 266 ± 15 and 270 ± 15 t C ha^?1 for the first and second sampling times, respectively, or generally in C stock within specific vegetation or soil types. The exception was for soils under woodland, excluding those on deep peat, which exhibited a significant (P = 0.05) gain of 1.0 t C ha^?1 year^?1. Soils under woodland (mainly coniferous plantation) also showed a significant (P = 0.04) increase in C content (g kg^?1), a significant decrease in bulk density (P = 0.006) and an increase in the thickness of the Litter‐Fermentation‐Humus (LFH) layer (P = 0.06). Recalculating the C stock to a depth of 15 cm showed a significant increase in overall C stock (when deep peat sites were excluded) as well as specifically in moorland and woodland soils, suggesting that had we sampled only to 15 cm, we would have reached a different conclusion. Both improved grassland soils and those initially under arable cultivation showed a significant decrease in C content. However, the mean thickness of Ap horizons increased from 29 to 32 cm, with a concomitant decrease in C content and a slight increase in bulk density; this we ascribe to deeper ploughing between the sample periods. In the context of possible soil C losses, we can be 95% confident that the mean loss does not exceed 0.2% year^?1 and 99% confident that it does not exceed 0.4% year^?1.     

The translocation of caesium and silver by fungi in some Scottish soils

Abstract

The caesium and silver content of the fruitbodies of fungi growing on some Scottish grassland sites have been measured. The distribution of caesium and silver in the soils has been measured and correlated with ergosterol as a measure of fungal biomass. Soil beneath individual fruitbodies and fairy rings was sampled from a clay loam, grassland site (Hogarth Park) in southwest Scotland, a sandy loam (Troon, southwest Scotland) and a peaty soil (Glensaugh, northeast Scotland). There is little or no information about the translocation of metals in soil by fairy ring fungi. Considerable variation in the ability of the fungi to translocate and accumulate the metals was observed. Cortinarius and Mycena Sp. and Suillus grevillei accumulated caesium and silver, whereas additionally Coprinus comatus, Entoloma Sp., Hygrocybe psittacina and Psathyrella Sp. accumulated silver. Clitocybe and Inocybe Sp., Lycoperdaceae and Marasmius oreades formed the fairy rings. Along diametric transects of each ring in most cases there were maxima in the ergosterol contents of the soil corresponding with the enhanced vegetative growth. There were also maxima in the caesium contents of the soil most of which corresponded to those of ergosterol. Site selection was an important factor in determination of the relationship between ergosterol and caesium. At a single site level of analysis a quantitative relationship between ergosterol and caesium was apparent only for one site, but overall the enhancement was significantly linearly correlated implying translocation by the fungi had occurred. No correlations between ergosterol and silver contents was observed.     

The determination of field-saturated hydraulic conductivity in some Scottish soils using the Guelph permeameter

Abstract. Soil hydraulic conductivities are frequently required for process-based modelling of the soil water regime. Field-saturated hydraulic conductivity was measured with the Guelph permeameter in 10 soil series with a range of structures and textures. The permeameter offers a range of options for calculating conductivities depending on soil conditions, particularly homogeneity of pore distribution within each horizon. However, even horizons described as massive or apedal were not sufficiently homogeneous to satisfy the boundary conditions entirely.
Hydraulic conductivities were calculated by the one head, fixed α* procedure; α* is an index of capillarity. No direct correlations were found between hydraulic conductivity and land use. However, the average hydraulic conductivity of coarse textured topsoils which were mainly under arable agriculture was less than that of the finer textured topsoils largely under grassland. Even limited structural development increased the hydraulic conductivities of fine textured, compact subsurface horizons. It is important to match the adopted procedure to the soil conditions both during the determination of flow rates in the field and in the subsequent analyses.     

Differences in silica release from soils of two Scottish associations as assessed by trimethylsilylation

The amounts of monomeric silica released on trimethylsilylation of a range of Soil Groups of the Darleith Soil Association, developed on glacial till derived from Carboniferous age lavas of basic and intermediate composition, is significantly higher than the amounts released from corresponding Soil Groups of the Lauder Soil Association, developed on glacial till derived from Devonian age conglomerates and sandstone. Monoremic silica release values for the leached soils within an association are, in general, higher than those of the gley soils. For all soil profiles the eluvial horizon released the smallest amount of monomeric silica with the maximum amount being released, in most instances, from the illuvial horizon. Ferromagnesian minerals and crystalline clay minerals, in particular vermiculite and chlorite in the Darleith Association soils, release monomeric silica under acid conditions. For both the Darleith and Lauder Association soils the principal source of monosilicic acid is thought to be aluminosilica gel of low Si:A1 ratio.     

Sewage sludge application to land – a preliminary assessment of the sensitivity of Scottish soils to heavy metal inputs

Abstract. The projected increase in sewage sludge used on land within many countries in the European Community will provide a major source of entry for several heavy metals into the soil. Although the application rate of sewage sludge to agricultural land is constrained by maximum annual additions of heavy metals, there is a need to know the sensitivity of those soils to heavy metal inputs which are physically suited for application. A rulebased classification using weighted parameters designed to assess the metal binding capacity of soil and the risk of groundwater pollution has been applied to soils data held within the Macaulay Land Use Research Institute's National Soils Inventory The classification uses soil pH, organic matter content, texture and soil colour as a surrogate for iron oxide concentration. The results indicate that some metals, for example cadmium and zinc are potentially more mobile in soils than others such as lead, but that the majority of soils display a strong or very strong binding capacity for all the metals. However this pattern can only be sustained if the soil pH values are maintained at their present values; a fall of one pH unit marks a dramatic shift towards the weak and moderate binding classes. The approach is largely unvalidated but does provide a useful framework for incorporating our mechanistic understanding of processes into wide area soil quality assessments and in identifying future research opportunities.     

The forms of cobalt in some Scottish soils as determined by extraction and isotopic exchange

The results of fractionation and correlation studies provided evidence that cobalt in soils is associated predominantly with the soil oxide fraction, particularly the manganese oxides. Only a small proportion of the total cobalt present in soils was extracted by acetic acid, EDTA, pyrophosphate or hydroxylamine. Cobalt extracted with these reagents was considered to be derived principally from easily reducible manganese oxides, although the origin of the cobalt extracted by acetic acid in particular was not well defined. The bulk of the cobalt present in soils appeared to be occluded by more highly crystalline oxide materials or was present in the structures of primary and secondary minerals. Labile cobalt in soil was assessed by extraction with acetic acid and EDTA and by determination of isotopically exchangeable cobalt. The amounts of cobalt extracted by both EDTA and acetic acid were highly dependent on the length of extraction period and on the temperature of extraction. Neither of these reagents appeared likely to give good estimates of the quantity or intensity factors of soil cobalt supply to plants as defined by the isotopic exchange determinations.     

Changes in the carbon concentrations and other soil properties of some Scottish agricultural soils: Evidence from a resampling campaign

The change in soil carbon (C) concentration, soil pH and major nutrients for approximately 1,000 topsoil sampled from on-farm experimental sites over a thirty-year period from 1950 to 1980 in north-east Scotland are summarized. This period coincided with increased agricultural intensification, which included regular liming and fertilizer additions. During 2017, 37 of these sites were resampled and reanlaysed. While pH and extractable phosphorus (P) and potassium (K) increased over this period, there was no detectable change in the percentage loss on ignition. Composite soil samples were taken by auger from a depth of 0–15 cm and compared with the corresponding archived samples collected at the initiation of each experiment. Analysis of these resampled soils indicated no significant change in soil carbon (C), although soil pH, extractable magnesium (Mg) and K and Nitrogen (N) concentrations were significantly greater (p < .001) but extractable soil P concentration was significantly less (p = .015) compared with the original samples. Even though measuring C concentration alone is a poor indicator of overall changes in soil C stocks, it does provide a relative quick “early warning” of C losses that would justify a more comprehensive measure of stocks.     

Effect of liming on extractable Zn, Cu, Fe and Mn in selected Scottish soils

Ten naturally acidic Scottish soils have been limed with CaCO₃ at 0,0.25, 0.50, 0.75, 1.00 and 1.25 times the recommended lime requirement, and then subjected to three cycles of alternate wetting to field capacity at 20°C for 1 month and drying for 1 month. The Zn, Cu, Fe and Mn extracted by DTPA solution, both at pH 7.3 and also after adjustment to match the final soil pH, were measured by flame AAS. The same elements were determined in ammonium acetate extracts, for extractants buffered at pH 4.8, pH 7.0 or at the final soil pH. The effect of extractant pH upon the amounts of trace elements removed is discussed for the two extractants, with particular reference to Zn. The influence of soil pH upon the amounts of trace elements extracted is also considered. There appears to be a distinct relationship between rate of decrease of DTPA-extractable Fe with increasing soil pH and the effect of pH upon DTPA-extractable Zn, high rates of decrease of extractable Fe being associated with a more continuous decline in extractable Zn with increasing soil pH. Possible reasons for this relationship are discussed, in the light of an experiment conducted to examine the effect of Fe and A1 on loss of Zn from solution at high pH. DTPA-extractable Cu varied little with increasing soil pH.     

The calculation of base cation release from the chemical weathering of Scottish soils using the profile model

To investigate the weathering rates of different soil parent materials which occur in Scotland, a study has been undertaken in which detailed soil mineralogy has been used to calculate base cation release. To calculate base cation release, this data, and supplementary soil chemistry and physical attribute data, have provided the input to the PROFILE model. The model is a multi-layer, steady state, deterministic model in which the soil is represented by a series of mixed tank reactors, each of which has the mineralogical, physical and chemical attributes measured for individual soil horizons. The major parent materials from which Scottish soils have developed are glacial till, derived from acid to basic igneous rocks, schist and other metamorphic types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments and Permo-Trias sediments. For each of the parent materials, three soil profiles were analysed and used with the PROFILE model. The base cation release rates, calculated for these parent materials in the top 50cm of the soil profile, varies between 0.2 and 3.2 keq/ha/yr, although, for a given parent material, the range was usually quite small. In general, these results compare very favourably with those suggested for the calculation of critical loads using an empirical approach proposed at Skokloster. In comparison with current rates of deposition, this suggests many of these soils are being acidified and that for many soil-plant combinations, the critical load may be exceeded.