Agriculture
; Catchments
; Complex networks
; Environmental impact
; Fertilizers
; Forestry
; Land use
; Multivariant analysis
; Nutrients
; Rivers
; Runoff
; Vegetation
; Water quality
; Agricultural intensification
; Environmental problems
; Large river system
; Multivariate statistical analysis
; Nutrient concentrations
; Predictor variables
; River water quality
; Spatial and temporal changes
; Water resources
; agricultural intensification
; catchment
; environmental impact
; human activity
; land use
; livestock farming
; nutrient enrichment
; river system
; river water
; water quality
; New Zealand
; Bos
; Ovis aries
英文摘要:
Relationships between land use and water quality are complex with interdependencies, feedbacks, and legacy effects. Most river water quality studies have assessed catchment land use as areal coverage, but here, we hypothesize and test whether land use intensity - the inputs (fertilizer, livestock) and activities (vegetation removal) of land use - is a better predictor of environmental impact. We use New Zealand (NZ) as a case study because it has had one of the highest rates of agricultural land intensification globally over recent decades. We interpreted water quality state and trends for the 26 years from 1989 to 2014 in the National Rivers Water Quality Network (NRWQN) - consisting of 77 sites on 35 mostly large river systems. To characterize land use intensity, we analyzed spatial and temporal changes in livestock density and land disturbance (i.e., bare soil resulting from vegetation loss by either grazing or forest harvesting) at the catchment scale, as well as fertilizer inputs at the national scale. Using simple multivariate statistical analyses across the 77 catchments, we found that median visual water clarity was best predicted inversely by areal coverage of intensively managed pastures. The primary predictor for all four nutrient variables (TN, NO/, TP, DRP), however, was cattle density, with plantation forest coverage as the secondary predictor variable. While land disturbance was not itself a strong predictor of water quality, it did help explain outliers of land use-water quality relationships. From 1990 to 2014, visual clarity significantly improved in 35 out of 77 (34g77) catchments, which we attribute mainly to increased dairy cattle exclusion from rivers (despite dairy expansion) and the considerable decrease in sheep numbers across the NZ landscape, from 58 million sheep in 1990 to 31 million in 2012. Nutrient concentrations increased in many of NZ's rivers with dissolved oxidized nitrogen significantly increasing in 27g77 catchments, which we largely attribute to increased cattle density and legacy nutrients that have built up on intensively managed grasslands and plantation forests since the 1950s and are slowly leaking to the rivers. Despite recent improvements in water quality for some NZ rivers, these legacy nutrients and continued agricultural intensification are expected to pose broad-scale environmental problems for decades to come.
Department of Geography, Texas State University, San Marcos, TX, United States; Department of Geography and Environmental Sustainability, University of Oklahoma, Norman, OK, United States; National Institute of Water and Atmospheric Research (NIWA), Hamilton, New Zealand; Landcare Research, Palmerston North, New Zealand; Landscape and Land Use Change Institute (LLUCI), University of Oklahoma and Texas State University, Oklahoma, TX, United States
Recommended Citation:
Julian J,P,, De Beurs K,et al. River water quality changes in New Zealand over 26 years: Response to land use intensity[J]. Hydrology and Earth System Sciences,2017-01-01,21(2)