Vulnerability to contamination by phosphorus in a zero-order basin with a high density of pigs and a history of slurry addition: extrapolation of an index

The application of phosphorus (P)-index methodology to assess the risk of water pollution from agriculture in river basins usually takes time and expends a great amount of resources. This study adapted the P-index methodology using digital mapping of key basin risk criteria for P loss in reference areas to evaluate the wider vulnerability to P loss in a zero-order basin with an intense concentration of pigs and with a history of pig slurry additions to the soil. The P content of eleven reference areas, where ten areas have received various applications of pig slurry and one area has no history of addition, was extrapolated to a zero-order basin using principal component analysis and analysis of hierarchical groupings. Estimated loss of soil and the distance between the P source and the watercourse were mapped using satellite images and in situ evaluations. The methodology of extrapolating was well correlated with a survey of P concentrations in land runoff and provides the potential to improve land management of those areas that are most vulnerable. Principal component analysis and hierarchical clustering analysis proved to be useful tools for the separation of areas with different slurry application times. Our results suggest that the P loss risk could be reduced through the adoption of soil conservation techniques such as reduced-tillage incorporating slurry and crop residue management to provide adequate soil protection, reduce the impact of raindrops and reduce erosion risk and transport of chemical pollutants to water bodies.