PNtrap Project: Using trees and woody shrubs to intercept excess nutrient in farm and forestry runoff

Water protection has long been a cornerstone of EU environmental policy. It is the sector with the most comprehensive coverage in EU environmental regulations (Kallis & Butler 2001). In some European countries such as the Netherlands, France, Sweden and Italy, national and local governments have implemented substantial programmes aimed at combating excessive nutrient loss to watercourses from agricultural, silvicultural and waste treatment activities. It is generally accepted that agricultural operations contribute, in a significant manner, to increased nitrogen and phosphorous loss to water catchments and result in environmenatlly unacceptable occurrences such as eutrophication and algal blooms. The increase in N and P loading may be dealt with in a number of ways, including a reduction of input or better fertiliser management. However there remains two problems. One is the perseverance of high fertility in the catchment long after regulation or cessation of input and the other is the potential for lower yields as a result of policy change. Water catchment nutrient management is poorly developed in Ireland and runoff nutrient entering watercourses is increasing (Tunney et al 2001). This has a serious and detrimental effect on water quality as well as ecological processes. It has been demonstrated that many trees have the ability to intercept and absorb large volumes of nutrients (Hefting & de Klein 1998). Buffer plantations of, often, willow (Salix spp.) and other species may be established in order to effectively and efficiently intercept surface runoff of nitrate (N) and phosphate (P). In addition, such buffer plantations could themselves produce an annual crop requiring little management and low-priced technology to harvest. Yet, the science behind the application has not been established in Ireland. The PNtrap project is currently under development in the Forest Ecosystem Research Group in the Department of Environmental Resource Management, UCD. The aim of this innovative project is to investigate the nutrient interception and absorption properties (N and P) of broadleaved trees, especially native species and varieties, and the beneficial effect that this may have for watercourse management in relation to farm and forestry runoff. The objective is to develop trial plots and test scenarios in order to identify the optimum tree and woody shrub species. The PNtrap project will commence in late 2003 and will run for a minimum of three years. Though the primary aim of the project is to establish a scientific basis for the utilisation of trees and woody shrubs to intercept nutrient entering watercourses, it is hoped that this will reveal if woody buffer zones are capable of protecting water catchments from N and P enrichment in Ireland.