Impacts of climatic change on agricultural nutrient losses in Finland

Changes in nitrate and particulate phosphorus losses from agricultural areas in Finland were estimated in a new equilibrium climate assuming an increase of 4.7 °C in temperature and 12% in precipitation as compared to the present climate. The assessment was mainly based on the use of mathematical simulation models. Process-oriented soil profile and field-scale models (SOIL/SOILN and modified CREAMS) were used to estimate potential nutrient losses for typical combinations of slopes, soils, crops and climatic regions in Finland. These model results were then combined with the geographical data sets to produce regional estimates of the impact of climate change. In addition, a simple drainage basin scale model based on the HBV runoff model was used to estimate the changes in nutrient losses from a typical agricultural drainage basin. The modeling results were compared with the observations of nutrient fluxes from normal years and years with exceptionally mild winters in an agriculturally loaded river. On the basis of the model estimations and the observations, the predicted increases in precipitation and temperature will most probably increase the nitrogen loss from agricultural areas to surface waters. The increase was predicted to be highest in south-western Finland. The main reasons for the increase are the acceleration of organic matter mineralization in agricultural soils and the increased water flow through the soil column. Particulate phosphorus losses showed a mean decrease for all agricultural land in Finland. The main causes for the decrease are the shorter period of frozen soil and the reduced snowfall, both of which reduce surface runoff. The regional differences in phosporus losses can be explained by differences in soil and crop composition and in the proportion of steeply sloping fields in different regions. The estimates of changes in nitrogen losses by the SOIL/SOILN model were generally in good agreement with estimates obtained by the drainage basin model. In the case of changes in phosphorus losses the CREAMS model gave a considerable reduction, whereas the drainage basin model predicted an increase. Observations from the years with exceptionally mild winters indicated an increase in nitrogen losses and no change in phosphorus losses. The assessment was based on the assumption that no changes in cropping patterns and cultivars would take place. Furthermore, a possible increase in yields was only partly taken into account.