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).

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.