John A. Catt

An absolute chronology for the raised beach and associated deposits at Sewerby, East Yorkshire, England

The raised beach sediments revealed in the cliffs at Sewerby, East Yorkshire are widely regarded as Ipswichian in age. Previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported. These provide the first absolute date for the Sewerby site of 120.84 +/- 11.82 ka, which places the blown sand at the boundary between oxygen isotope stages (OIS) 5e and 5d. As the underlying raised beach is little older than the blown sand, it probably formed during OIS Stage 5e as suggested by the faunal evidence.

Soils as indicators of quaternary climatic change in mid-latitude regions

Abstract Soils result from changes to uppermost layers of the earths crust occuring beneath stable land surfaces. Soil properties are determined by five factors or groups of factors: climate, organisms, relief, parent material and time. Quantitative climatic interpretation of soils depends upon mathematical relationships between individual soil properties and climatic factors (i.e., climofunctions). These are difficult to establish and often cannot be applied to diagenetically modified buried soils, so most climatic interpretations of soils are qualitative or semi-quantitative. Soil features formed by frost action are the most reliable climatic indicators. Most soils continue to develop over time. However, many soil dating techniques provide only a single date some time during the period of soil formation. The beginning and end of a soil development period are best determined by reference to dated deposits over as large an area as possible, but stratigraphical interpretation of soils is still impeded by imprecise definitions and procedures. The soil chronosequences developed in the major loess deposits of Europe and Asia provide the best evidence for climatic change throughout the Quaternary. However, only major (glacial-interglacial) cycles are well expressed. To obtain more detailed evidence of weaker (interstadial) cycles it is necessary to study chronosequences in mid-latitude regions which were generally moister for much of the Quaternary. However these soils are less well preserved and present additional difficulties of interpretation because of greater variation in parent material, relief and time as soil-forming factors.

The Validation of Pesticide Leaching Models

The validation of pesticide leaching models presents particular problems where the number of model predictions is far in excess of the observed data. Normally, however, there are more frequent field observations for other parameters (notably the site hydrology) than for pesticide concentrations in either water or soil. A five-stage validation procedure which takes advantage of the most frequently available observations and which tests each of the components of the model in a cumulative way, is thus advocated: Stage 1: Parameterisation of the model using only independently measured parameters. Stage 2: Hydrological validation: the validation of the predictions of water movement and water content of the soil. Stage 3: Solute movement validation: where field data are available for solutes other than pesticide, the model should first be validated for them, especially if they are more abundant than the pesticide observations. Conserved solutes such as chloride or bromide are preferred, although nitrate may be used for short periods. Stage 4: Pesticide fate in the soil: models should use parameters of pesticide fate derived from independent studies. Stage 5: Pesticide leaching: only in the last stage are the relatively small number of pesticide observations compared with the model predictions with respect to patterns and orders of magnitude of occurrence. With this scheme, the results of each stage are carried forward to the next, and confidence in the model is built with each stage. This is illustrated using the CRACK-P model and hydrological, nitrate and pesticide data from the Brimstone Farm Experiment Oxfordshire, UK.

Evaluating pesticide leaching models: the Brimstone Farm dataset

Abstract This paper describes the Brimstone Farm dataset used for the comparison of pesticide leaching model performance. The tasks set to the modellers are then described. The soil of the site is heavy clay, in which cracks have a major effect on the hydrology. Data are presented for the leaching of isoproturon and mecoprop from two contrasting plots. Contrasting soil moisture states, resulting from different cropping, result in higher drainage rates from the wetter plot, which were associated with higher and earlier losses of isoproturon to the drains. No mecoprop was detected in the drainflows from this site.

Development and testing of a model for predicting tillage effects on nitrate leaching from cracked clay soils

Both water movement and nitrate leaching in structured soils are strongly influenced by the nature of the macro-porosity. That macro-porosity can however also be manipulated by choice of tillage operations. In order to investigate the potential impacts of tillage on rates of nitrate leaching from structured soils, a model specific to these soils, CRACK-NP was developed. The model, its application and validation for an experimental site on a heavy clay soil (Verti-Eutric Gleysoil) at Brimstone Farm, Oxfordshire, UK, is described. The model considers the soil as a series of aggregates whose size is also the spacing of the macro-porosity. Water and solutes move in the macro-pores, but within the peds they move only by diffusion, internal infiltration and root uptake (evaporation). The model reflects the influence of diffusion limitation in the release of solutes to by-passing water. The model was then used to investigate the influence of variable ped spacings which were created by variations in tillage practices. The results both from the model and from the field data demonstrated that finer soil structures, which have larger surface contact areas and shorter diffusion path lengths, present greater opportunities for interaction between peds and the water moving around them, and so release more nitrates through the drainage waters.

Stratigraphy and origin of New Forest brickearths, England

The thin, loamy brickearth deposits overlying the flinty terrace gravels of the New Forest are divided into older and younger members. The Lower (older) Brickearth includes sediments thought to be mainly loess, with some aeolian sand and possible river floodloam (overbank sediment). These share the common feature of palaeo-argillic soil horizons in their upper layers. Two separate phases of pre-Holocene temperate pedogenesis often can be distinguished in the palaeo-argillic horizons. The Lower Brickearth is the most extensive pre-Devensian loess in Britain. The Upper (younger) Brickearth consists mainly of Late Devensian (Oxygen Isotope Stage 2) loess, but its lower layers also contain fine sand derived mainly from local Tertiary strata. Both brickearths occur on all the terrace surfaces of the New Forest and indicate that the terraces date from Oxygen Isotope Stage 6 or earlier.