Predicting groundwater source contributions to stream flow using end-member mixing analysis

Abstract

Aims The aim of our MBIE-funded Transfer Pathways programme is to determine the sub-surface pathways which nutrients take to get from their land-based source to the receiving stream environment. One of the methods tested in this programme is end-member mixing analysis (EMMA), which uses principal components analysis (PCA) to estimate the proportional contribution of end members to stream samples. Determining source contributions to flow is valuable because it enables groundwater flow pathways to be better constrained within spatially distributed models, and increases our ability to relate land-use to stream impacts. The PCA approach has been applied to two contrasting baseflow-dominated catchments, the Pokaiwhenua Stream (43,175 ha) in the upper Waikato, and Spring Creek (~1,350 ha), on the Wairau Plain.