River water quality changes in New Zealand over 26 years: response to land use intensity

摘要: Abstract. Relationships between land use and water quality are complex with interdependencies, feedbacks, legacy effects. Most river studies have assessed catchment as areal coverage, but here, we hypothesize test whether intensity – the inputs (fertilizer, livestock) activities (vegetation removal) of is a better predictor environmental impact. We New Zealand (NZ) case study because it has had one highest rates agricultural intensification globally over recent decades. interpreted state trends for 26 years from 1989 to 2014 in National Rivers Water Quality Network (NRWQN) consisting 77 sites on 35 mostly large systems. To characterize intensity, analyzed spatial temporal changes livestock density disturbance (i.e., bare soil resulting vegetation loss by either grazing or forest harvesting) at scale, well fertilizer national scale. Using simple multivariate statistical analyses across 77 catchments, found that median visual clarity was best predicted inversely coverage intensively managed pastures. The primary all four nutrient variables (TN, NOx, TP, DRP), however, cattle density, plantation secondary variable. While not itself strong quality, did help explain outliers use–water relationships. From 1990 2014, significantly improved out 77 (34∕77) catchments, which attribute mainly increased dairy exclusion rivers (despite expansion) considerable decrease sheep numbers NZ landscape, 58 million 31 million 2012. Nutrient concentrations many NZ's dissolved oxidized nitrogen increasing 27∕77 catchments, largely nutrients built up grasslands forests since 1950s slowly leaking rivers. Despite improvements some rivers, these continued expected pose broad-scale problems decades come.