Comparison of impacts of human activities and climate change on water quantity and quality in Finnish agricultural catchments

摘要

We studied the influence of human activities and climate change on water quantity and quality. Human activities included methods of agricultural policy, i.e. land use and management practices. Finland started to follow EU's agricultural policy in 1995. In this study our main objective was to find out whether the original targets of the Finnish Agri-Environmental Programme (FAEP) were achieved. We analyzed trends in discharge, water quality and climate parameters in 37 years long time-series in two catchments. We focused on the suspended sediment and phosphorus concentrations and loads, the main interests to FAEP. We found an increasing trend in mean annual temperature, especially in spring and late summer-early autumn. There was no statistical significant change in annual runoff. Increasing winter runoff in the other catchment could be explained by the increased number of days when temperature was above zero degrees making snowmelt possible. In this area high potential sediment delivery occurred in early winter. FAEP succeeded in decreasing the suspended sediment load by reduced tillage and wintertime vegetation cover. In controlling the phosphorus loads FAEP succeeded only in the catchment with erosion sensitive soils. In the catchment where soils were less sensitive for erosion increase in the dissolved reactive phosphorus load exceeded the benefits of the reduced particulate phosphorus load. Climate change may increase the suspended sediment load by increasing winter runoff. Even then, instead of decreasing the suspended sediment loads FAEP should rather focus on dissolved nutrients as they cause eutrophication in receiving waters.