J. M. Hollis

Pesticides in rainfall in Europe.

Papers and published reports investigating the presence of pesticides in rainfall in Europe were reviewed. Approximately half of the compounds that were analysed for were detected. For those detected, most concentrations were below about 100 ng/l, but larger concentrations, up to a few thousand nanograms per litre, were detected occasionally at most monitoring sites. The most frequently detected compounds were lindane (gamma-HCH) and its isomer (alpha-HCH), which were detected on 90-100% of sampling occasions at most of the sites where they were monitored. For compounds developed more recently, detection was usually limited to the spraying season. A classification of pesticides according to their deposition pattern is proposed.

MACRO—DB: a decision-support tool for assessing pesticide fate and mobility in soils

Abstract A decision-support tool (MACRO—DB) for predicting pesticide fate and mobility in soils is described. MACRO—DB consists of soil, pesticide, climate and crop databases linked to parameter estimation routines and a simulation model (MACRO). The system currently allows access to three soils databases: SEISMIC ( c. 400 UK benchmark soils), MARKDATA (26 Swedish soils), and a database that the user can develop independently. Automatic estimation procedures (pedo-transfer functions) translate the soil information into model parameter values. Two pesticide databases are available. The PETE database contains information for over 600 common compounds. The user can also develop a parallel database for new compounds. Sorption and degradation constants are calculated automatically, combining soil and compound properties. A weather database contains long-term daily meteorological data and a weather generator enables synthetic daily weather data to be derived from long-term average climatic data. A separate database contains information on typical planting and harvest dates, root depths, etc. for some common agricultural crops. To account for parameter uncertainty, the user can simulate ‘worst-case’ or ‘average-case’ soil scenarios, utilizing available information on the mean and typical ranges of soil organic carbon content and pH. The user can view and analyse simulation results with flexible, in-built, graphical procedures.

Leaching of pesticides and a bromide tracer through lysimeters from five contrasting soils

In each of two seasons, undisturbed lysimeters 0.8 m in diameter and 1.05 m in length taken from five soil types were cropped with winter wheat. They received autumn applications of the pesticides isoproturon and linuron as well as a bromide tracer and spring applications of dimethoate and MCPA. Leachate was collected at regular intervals and concentrations of the various solutes determined. Rainfall from December to March was 290 and 191 mm in the first and second seasons, respectively. Both springs were exceptionally dry with less than 50% of the mean April-to-June rainfall of 138 mm. Total flow from the lysimeters ranged from 335 to 477 mm (and from 0.78 to 3.95 pore volumes) over the two seasons. Leaching to drainage of bromide highlighted soils where preferential flow was influential with total losses ranging from 24% of applied for a strongly structured, alluvial clay loam to 79% for an unstructured sand. Leaching to drainage of isoproturon (Koc ≈ 100 ml g−1) was observed from all but a peat soil with losses greater (0.31–1.01% of applied) from the clay loam and a deep medium loam, where patterns of leaching clearly indicated preferential flow mechanisms, than from the sand and a light loam over gravel (0.04–0.18% of applied) where a broad breakthrough curve indicated that matrix flow was more important. Linuron (Koc ≈ 500 ml g−1) was detected in occasional samples of leachate from the clay loam, the light loam over gravel and the medium loam during the first season only (maximum loss 0.12% of applied). The sandy soil, often considered most vulnerable to leaching, gave the smallest total losses of pesticide of the four mineral soils, whilst significant preferential flow in the deep, medium loam was believed to result from a compacted topsoil. Neither of the spring-applied pesticides was detected in the leachate, as flow following application was very small and relatively slow. © 2000 Society of Chemical Industry

Identification of key climatic factors regulating the transport of pesticides in leaching and to tile drains

BACKGROUND Key climatic factors influencing the transport of pesticides to drains and to depth were identified. Climatic characteristics such as the timing of rainfall in relation to pesticide application may be more critical than average annual temperature and rainfall. The fate of three pesticides was simulated in nine contrasting soil types for two seasons, five application dates and six synthetic weather data series using the MACRO model, and predicted cumulative pesticide loads were analysed using statistical methods. RESULTS Classification trees and Pearson correlations indicated that simulated losses in excess of 75th percentile values (0.046 mg m(-2) for leaching, 0.042 mg m(-2) for drainage) generally occurred with large rainfall events following autumn application on clay soils, for both leaching and drainage scenarios. The amount and timing of winter rainfall were important factors, whatever the application period, and these interacted strongly with soil texture and pesticide mobility and persistence. Winter rainfall primarily influenced losses of less mobile and more persistent compounds, while short-term rainfall and temperature controlled leaching of the more mobile pesticides. CONCLUSIONS Numerous climatic characteristics influenced pesticide loss, including the amount of precipitation as well as the timing of rainfall and extreme events in relation to application date. Information regarding the relative influence of the climatic characteristics evaluated here can support the development of a climatic zonation for European-scale risk assessment for pesticide fate.

Development of agro-environmental scenarios to support pesticide risk assessment in Europe

This paper describes work carried out within the EU-funded FOOTPRINT project to characterize the diversity of European agricultural and environmental conditions with respect to parameters which most influence the environmental fate of pesticides. Pan-European datasets for soils, climate, land cover and cropping were intersected, using GIS, to identify the full range of unique combinations of climate, soil and crop types which characterize European agriculture. The resulting FOOTPRINT European agro-environmental dataset constitutes a large number of polygons (approximately 1,700,000) with attribute data files for i) area fractions of annual crops related to each arable-type polygon (as an indicator of its probability of occurrence); and, ii) area fractions of each soil type in each polygon (as an indicator of its probability of occurrence). A total of 25,044 unique combinations of climate zones, agricultural land cover classes, administrative units and soil map units were identified. The same soil/crop combinations occur in many polygons which have the same climate while the fractions of the soils and arable crops are different. The number of unique combinations of climate, soil and agricultural land cover class is therefore only 7961. 26-year daily meteorological data, soil profile characteristics and crop management features were associated with each unique combination. The agro-environmental scenarios developed can be used to underpin the parameterization of environmental fate models for pesticides and should also have relevance for other agricultural pollutants. The implications for the improvement and further development of risk assessment procedures for pesticides are discussed.

SWAT—A Semi‐empirical Model to Predict Concentrations of Pesticides Entering Surface Waters from Agricultural Land

A semi-empirical model called SWAT has been developed to predict concentrations of agriculturally applied pesticides moving to surface waters, an aspect which is not well described by current models for pesticide fate. The model is based upon a direct hydrological link established between soil type and the amount of water moving rapidly to streams in response to rainfall. Attenuation factors describe the decrease in concentrations of pesticide between field application and loss in water moving from the site into surface waters. Evaluation of model predictions against available field data from three sites and four soil types in England shows that SWAT is capable of predicting the transient peak concentrations of a wide range of pesticides during rapid water movement to streams in response to rainfall. Predicted concentrations were too great when rainfall initiated water movement to streams very soon after pesticide application, particularly for the more mobile pesticides, and some predictions for pesticides sorbed very strongly to soil were relatively poor. Almost all of the predicted concentrations were within one order of magnitude of measured values.

The development of a hydrological classification of UK soils and the inherent scale changes.

Although soil is of major importance in influencing river hydrology, there is often a lack of soil hydrological data available to quantify the ameliorating effects of soil on steam flow. The HOST classification (Hydrology of Soil Types) was developed using pedotransfer rules and functions to derive a set of semi-quantified soil attributes from existing soil morphological information as surrogates for the missing hydraulic data. The rules were applied to the soil horizon information and were scaled to the catchment level through the known relationships between soil horizons and soil taxonomic units and between soil taxonomic units and 1:250 000 scale soil map units. The resulting classification, however, is not scale-specific and is capable of predicting river flow indices at the catchment scale (r2 = 0.79) and of predicting the dominant pathways of water movement through individual soil profiles.

SWBCM: a soil water balance capacity model for environmental applications in the UK

Abstract The paper presents a daily-time step, multi-horizon capacity model of soil-water balance (SWBCM—Soil Water Balance Capacity Model) suitable for ecological and environmental applications investigating the spatial and temporal variability of soil water content determined by changes in soil hydraulic conductivity, soil water storage capacity and the pathways of water movement through the soil and across soil types. SWBCM simulates soil water content at horizon level and encompasses limits on the amount of drainage from one horizon to the next to allow the formation of temporary perched water tables, lateral drainage, matric potential and surface runoff. The model incorporates a dynamic sub-model of grass growth (SWARD—Dowle, K., Armstrong, A.C., 1990. A model for investment appraisal of grassland drainage schemes on farms in the UK. Agric. Water Manage. 18, 101–120; Armstrong, A.C., Castel, D.A., Tyson, K.C., 1995. SWARD: a model of grass growth and the economic utilisation of grassland. In: Pereira L.S., van den Broek B.J., Kabat P., Allen R.G. (Eds.), Crop-Water Simulation Models in Practice. Wageningen Press, Wageningen, The Netherlands, pp. 189–197). SWBCM’s predictive ability is tested across a range of soil types under permanent grass in the UK and outputs are compared with predictions made by MACRO (Jarvis, N.J., 1994. The MACRO Model Version 3.1. Technical Description and Sample Simulations. Swedish University of Agricultural Sciences, Department of Soil Sciences, Reports and Dissertations 19, Uppsala, Sweden, 51 pp.), a mechanistic solute transport model which incorporates a physically-based preferential flow model in which total soil porosity is divided into two flow domains (macro-pores and micro-pores), each characterised by a flow rate; soil water flow in the micro-pore domain is modelled using Richards’ equation. In the modelling experiment, SWBCM simulations have been shown to provide good approximations of point-scale experimental data under a range of soil, climate and drainage management conditions in the UK. SWBCM simulations are close to those developed by the mechanistic MACRO model, suggesting that the capacity model can be applied to describe the water balance of multi-horizon UK soil profiles. The modelling approach used is considered to be applicable to the wide range of soil lower boundary conditions, ranging from free-draining to impermeable, occurring in the field and to simulate transient perched water tables that commonly occur in most temperate, high latitude countries such as the UK.

SEISMIC: a desktop information system for assessing the fate and behaviour of pesticides in the environment

Presented is a description of the SEISMIC desktop information system, a management tool to aid the assessment of the fate and behaviour of potential environmental contaminants. Its databases draw upon a detailed knowledge of the natural environment where the complex interaction of different land use practices together with various soil, hydrological, climatic and hydro-geological factors go towards determining the relative vulnerability of land and water resources in different geographical areas. When combined with a detailed understanding of the physico-chemical behaviour of potential contaminants, such as pesticides, the likely environmental impacts of differing land management practices can be evaluated. One means to achieve such an understanding is through the combined use of mathematical models and environmental databases capable of supporting geographical assessments of likely and hypothetical scenarios. This paper describes the Soil Survey and Land Research Centres (SSLRC) unique national Spatial Environmental Information System-SEISMIC, which allows the researcher to access a comprehensive store of environmental information for England and Wales. The principles used to establish SEISMIC could be applied for any other area in the world where there is an appropriate information base.

Evaluating Changes in Soil Organic Matter with Climate Using CENTURY in England and Wales

Soil organic C (SOC) dynamics are complex, and models have been developed for predicting future changes, validated using only individual site data. In this study, we used the CENTURY model to predict changes in SOC between 1978 and 2000 using input weather data for 1978 to 2000 from the UK Meteorological Office and soil property input data derived from the National Soil Inventory (NSI). The predicted changes in SOC from the model simulation were validated using the resampled NSI data for the period 1994 to 2000. The modeling results indicate that CENTURY gave unacceptable predictions of change for three specific soil types. When these were omitted from the accuracy assessment, model predictions were statistically acceptable for all ecosystem types with model efficiency (ME) decreasing in the order: seminatural grassland (ME = 0.63) > woodland (ME = 0.27) > arable (ME = 0.08) > managed grassland (ME = 0.02). When comparing the overall measured rates of change, CENTURY correctly predicted the direction but underpredicted the magnitude of change. Once this utility was established, CENTURY was used to predict nation-level climate change-induced changes in SOC with the UKCIP02 (UK Climate Impacts Program of 2002) scenarios for the 2020s, 2050s, and 2080s, each of which comprise four emissions scenarios. The modeling predictions suggest that the predicted changes between scenarios were small. However, within that, the greatest decrease (of 1.54% SOC) will be in seminatural grassland under the high emissions scenario. The future predicted pattern of change in SOC is greater in managed grassland (reduction of 0.27-0.39% SOC) than arable land (reduction of 0.03-0.05% SOC).