Scaling issues in sustainable management of nutrient losses

To establish strategies for sustainable nutrient management, the priority of each identified element for different user groups and the issue of data transferability from one scale to the next need to be addressed. This is important to avoid developing policies and strategies using inaccurate data. This paper provides a thorough background on such issues and provides data from specific case studies to reflect the impact of scale on the usability and transferability of data. These data show that using information obtained in a laboratory setting for larger scales can generate major errors. Data are also provided regarding the spatial variability in total N and total P measured at different sub-watersheds within a large watershed. Results from this case study indicate that there is a definite spatial variability in N and P loadings, which makes it difficult to transfer and extrapolate from data measured at one sub-watershed to the entire watershed. Therefore, it can be concluded that using either measured or simulated data obtained at a small scale to respond to questions for larger scales may be erroneous. Such difficulty may be due to the inherent spatial variability in soils, nutrients, biology and other features of the landscape.