Ian C. Grieve

Soil variation with altitude on Volcan Barva, Costa Rica.

Summary Soils were examined from each of six primary forest plots at altitudes of 100 m, 500 m, 1000 m, 1500 m, 2000 m and 2600 m on Volcan Barva, Costa Rica. All were on volcanic parent materials. There was evidence of decreasing intensity of weathering and organic matter decomposition with increasing altitude. Subsoil clay content decreased from 80% at 100 m altitude to less than 10% at 2000 m. Ratios of free to total iron decreased from 0.3 to less than 0.1. Organic matter in the surface horizons increased from 18% to 49% over the same altitude range. The uppermost site at 2600 m was formed on younger and less weathered material and had greater concentrations of exchangeable bases than all the other sites. There was no evidence that the nutrients measured were less well supplied at high altitudes, and forest changes with altitude were not caused by any soil changes examined in this study.

Variations in chemical composition of the soil solution over a four-year period at an upland site in southwest Scotland

Abstract Soil solution chemical composition was monitored over a period of almost four years in a peaty soil in the Loch Dee catchment, southwest Scotland. Solutions were acidic with mean pH of 4.2 in the surface 20 cm and of 4.7 at 60 cm. The increase in pH was associated with increased Ca concentrations but no increase in Al. Annual cycles in solution concentrations were identified, with winter peaks in Cl, Na and Mg, and a late summer peak in dissolved organic carbon (DOC) and Fe. Variations in DOC were related to temperature and rewetting of dry soil. Maximum DOC and Fe followed the drought summer of 1984 with concentrations of 60 and 13 mg 1−1 respectively at one sampler. Variations in Al concentrations were partly related to DOC and partly to pH. Inorganic monomeric forms of Al were predominant. DOC also contributed significantly to the overall ionic balance.

Human impacts on soil properties and their implications for the sensitivity of soil systems in Scotland

Abstract Human activities have had pronounced impacts on soil properties. Conifer afforestation in the uplands has caused significant decreases in soil pH and in the quality and turnover of organic matter. Acid deposition has increased soil acidity by a similar amount to conifer afforestation but has been shown to affect soils at greater depths. Acid deposition has also increased the mobility of trace metals in the soil and therefore increased metal concentrations in drainage waters. Applications of sewage sludge to the soil have been shown to increase metal concentrations, although most of the Scottish soils affected have high trace metal binding capacities. Intensification of arable cultivation in the lowlands has reduced organic matter concentrations, structural stability and soil workability, and has had effects on soil erodibility. Human trampling, while highly localised, affects sensitive mountain soils in popular areas, leading to loss of surface organic horizons, and therefore, carbon storage. The future impacts of human activities on the soil may be exacerbated by changing climate, and the need to monitor and predict these will not diminish.

Effects of forest cover and topographic factors on TOC and associated metals at various scales in western Scotland.

Studies at the stream catchment scale have yielded inconclusive evidence of the effects of forest land use on the concentrations of organic carbon in drainage waters. The aim of this paper is to examine the effects of forests on carbon in drainage waters at the plot scale by comparing concentrations of total organic carbon (TOC) and associated metals in soil solutions from sites under forest and moorland vegetation. At an upland site in south-west Scotland soil solution TOC, aluminium and iron concentrations varied with land cover. Mean concentrations of all three determinands were at least 1.5 times greater under forest than under moorland, despite considerable spatial and temporal (seasonal) variability. TOC in soil solutions was also found to vary significantly with both relief and altitude. The altitude effect was particularly marked, with an increase of 26 mg x l(-1) x 100 m(-1) increase in altitude found at an upland site in west-central Scotland. There were no differences in chloride, sulphate or base cation concentrations between forest and moorland sites. Differences in aluminium concentrations could not be linked to atmospheric scavenging at the forest sites, but were closely linked to differences in TOC.

A comparison of soil aggregate stability tests using soils with contrasting cultivation histories

Abstract A turbidimetric test and two wet sieving tests were used to measure aggregate stabilities of soils from five neighbouring fields with different cropping histories. Turbidimetry more clearly reflected differences in cropping history than either wet sieving procedure, and was also more rapid and reproducible. Wet sieving with slow wetting was a more sensitive indicator of small differences in stability of unstable soils than sieving after rapid wetting. The tests involving rapid wetting revealed differences among fields related to cropping history and organic carbon content. The small differences in clay and plastic limit moisture contents of the fields were not clearly reflected by the results of all the tests. Clay content correlated significantly only with the slow wetting test, moisture content at the plastic limit only with turbidimetry, although this latter relationship is probably not causal, but may reflect control of both variables by organic carbon.

Effects of human disturbance and cryoturbation on soil iron and organic matter distributions and on carbon storage at high elevations in the Cairngorm Mountains, Scotland

Soil profiles were sampled at 43 sites on granitic parent material at altitudes ranging from 970 to 1300 m in the Cairngorm Mountains, Scotland. Many soils under undisturbed vegetation showed evidence of iron and organic matter translocation with distinctive Bh or Bs horizons. Approximately 50% of the sites sampled had no or partial vegetation cover, due either to human . activity trampling or active geomorphic processes such as cryoturbation on patterned ground. Exposed cols and summit ridges were most heavily affected by trampling with extensive areas of path development and some erosion. Trampling was principally associated with loss of the upper soil horizons and cryoturbation processes with disturbance of horizon development. Median total organic matter at the vegetated sites ranged from 4.8 to 22.0 kg m y2 with a median of 9.5 kg m y2 . There was significantly less total organic matter at the unvegetated sites with median of 4.6 kg m y2 and range from 1.5 to 11.9 kg m y2 . There was little difference in total organic matter between sites where vegetation disturbance was due to human trampling or to cryoturbation. q 2000 Elsevier Science B.V. All rights reserved.

Effects of catchment liming and afforestation on the concentration and fractional composition of aluminium in the Loch Fleet catchment, SW Scotland.

Abstract Concentrations of total, total monomeric and organic monomeric forms of aluminium and of iron, anions and dissolved organic carbon (DOC) in streams draining one forested and two moorland catchments in southwest Scotland were measured over a 3-year period. Catchments were limed during the study and comparisons of stream chemistry were made before and after liming under the two land-use types. Within individual events, DOC and anion concentrations increased with increasing discharge, and aluminium concentrations showed little change with discharge. In the pre-liming phase as a whole, organic monomeric Al was strongly correlated with DOC and inorganic monomeric Al was strongly correlated with anions, particularly Cl. The forested catchment had higher mean DOC and SO4, but lower mean Al. After liming, Al concentrations were reduced, by up to 80% for monomeric forms, and these low levels prevented observation of correlations with DOC and anions. Liming treatments were effective in both forested and moorland catchments, lasted for at least 2.5 years after treatment, and low rates of application to bog areas were as effective as entire catchment treatments.

Effects of parent material on the chemical composition of soil drainage waters

Abstract Exchangeable base cations, soil solution chemistry and response to acid leaching in laboratory leaching columns were compared for three soils developed in till parent materials derived from rocks ranging from basalts to acid schists. There were only small differences in base saturation and pH and no differences in soil solution chemistry for the three soils. In a column experiment, columns of B horizon material were leached with artificial rainwater. Adsorption of sulphate in two of the three soils investigated made a significantly greater contribution to neutralisation of the added H + than cation release from weathering or ion exchange. The results suggest that differences in drainage water chemistry from different rock types cannot be explained simply by differences in weathering potential or ion exchange processes.

Effects of the centrifuge drainage method on total organic carbon concentrations in soil solutions from peaty soils

This paper investigates the effects of centrifuge speed, time and different filter media at the base of the soil column on the concentrations of total organic carbon (TOO in soil solutions extracted by the centrifuge drainage method. With increasing time at 1000 rev min−1 centrifuge speed, the volume of solution extracted increased as a logistic growth curve, but TOC concentrations decreased from initial values of 28 mg 1−1 to 15 mg 1−1 after 60 min. Increased centrifuge speed, and therefore applied suction, resulted in increased volumes of solution but TOC concentrations decreased from 33 mg 1−1 at 500 rev min−1 (equivalent to 15 kPa suction) to 12 mg 1−1 1 at 4000 rev min−1 (948 kPa). These findings suggest that leaching of organics from roots or microbial matter with increasing pressure was not significant in the peaty soil examined. Rather, fine particulate carbon probably contributed to the larger measured TOC concentrations at low suctions. In a comparison of filters, mean TOC concentrations were approximately 1.5 times greater when the centrifuge tube contained a glass wool filter or no filter, as these transmitted more fine particulate carbon. Sodium concentrations were more than 3 times greater and pH 1.7 units greater in solutions extracted through glass wool due probably to ion exchange on the filter. No effects on calcium or magnesium concentrations were found. It was concluded that centrifuge extraction through glass fibre filters and applying suction of 60 kPa for 1 h is suitable for studies of TOC in peaty soils.

Quantifying the threat to archaeological sites from the erosion of cultivated soil

Ploughing is probably the greatest agent of attrition to archaeological sites world-wide. In every country, every year, a bit more is shaved off buried strata and a bit more of the past becomes unreadable. On the other hand, people must eat and crops must be planted. How can the fields be best managed to get the best of both worlds? Perhaps the most pressing need for resource managers is to know how quickly a particular field is eroding: negotiation and protection is then possible. Up to now that has been difficult to measure. The new procedure presented here, which draws on the unexpected benefits of nuclear weapons testing, shows how variation in the concentration of the radioisotope 137Cs can be used to monitor soil movements over the last 40 years. The measurements allow a sites ‘life expectancy’ to be calculated, and there are some promising dividends for tracking site formation processes.