Response of streamflow and nutrient loads in a small temperate catchment subject to land use change

• Published in: Environmental monitoring and assessment Vol. 195; no. 12; p. 1418
• Main Authors: Ayele, Gebiaw T., Yu, Bofu, Bruere, Andy, Hamilton, David P.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2023; Springer Nature B.V
• Subjects: Adequacy; Afforestation; Afforestation effects; Ammonium nitrogen; Atmospheric Protection/Air Quality Control/Air Pollution; Earth and Environmental Science; Ecology; Ecotoxicology; Environment; Environmental Management; Environmental Monitoring; Eutrophication; Forests; Freshwater; Freshwater lakes; Hydrologic models; Inland water environment; Lakes; Land use; land use change; Loads (forces); Mathematical models; Monitoring/Environmental Analysis; New Zealand; Nitrogen; Numerical models; Nutrient loading; Nutrients; Pasture; pastures; Phosphorus; pollution load; Receiving waters; Reduction; Soil; Soil and Water Assessment Tool model; Soil water; statistical analysis; Statistical tests; Stream discharge; Stream flow; subwatersheds; total nitrogen; total phosphorus; Water quality; Watersheds; New Zealand; SWAT; New Zealand; Statistical test; Land use change; Non-stationarity; Water quality; Hydrological modelling; Lake Ōkareka
• ISSN: 0167-6369; 1573-2959; 1573-2959
• DOI: 10.1007/s10661-023-11828-z

The aim of this study was to quantify the effect of land use change (LUC) implemented to meet nutrient load targets for a freshwater lake in New Zealand. We used the Soil and Water Assessment Tool (SWAT) model in combination with a non-parametric statistical test to determine whether afforestation of 15% of a subcatchment area was adequate to meet assigned nutrient load targets. A regional management authority set nutrient load targets of reduction in total nitrogen (TN) by 0.9 t yr −1 and reduction in total phosphorus (TP) by 0.05 t yr −1 to avoid eutrophication in the receiving waters of a freshwater lake. The load reduction was designed to be achieved through 200 ha of LUC from pasture to trees. Analysis of nutrient loads before, during, and following LUC shows that a 15% increase in forest cover decreased the annual flow (7.2%), TP load (33.3%), and TN load (13.1%). As flow and water quality observations were discrete and at irregular intervals, we used a parametric test and the SWAT model as different lines of evidence to demonstrate the effect of afforestation on flow and water quality. Policymakers concerned with decisions about LUC to improve the quality of receiving waters can benefit from applying our findings and using a statistical and numerical modelling framework to evaluate the adequacy of land use change to support improvements in water quality.