Cross-Scale Interactions Among Climate, Land-Use, and River-Water Quality – New Zealand

Relationships between land use and water quality are complex with feedbacks, legacy effects, and cross-scale interactions (CSI). 

CSI occur when processes at one spatial or temporal scale interact with processes at finer or broader scales. In systems where CSI are connected, a change in an environmental driver such as climate or land use can result in positive feedbacks and cascading events that lead to dramatic and widespread changes in system dynamics. This project used sophisticated geospatial tools to analyze multi-resolution environmental datasets over multiple spatio-temporal scales to assess how CSI between changing climate and land use affect river water quality in New Zealand (NZ) from hours to decades, and from small catchments to regional drainage basins. Using MODIS BRDF-adjusted reflectance data (C6), we created a land disturbance dataset for NZ from the year 2000 to 2017 with 8-day temporal resolution and 463-m spatial resolution. This national-scale land disturbance dataset, the first of its kind, revealed that intense land uses such as livestock grazing and forest clear-cuts leave the land bare for considerable periods. When compared with one of the most comprehensive river water quality datasets in the world, we found that these intense land uses have led to excess sediment runoff and nutrient enrichment in almost half of NZ’s rivers. Over time, the CSI among climate, land use, and river water quality have led to nonlinear patterns where landscapes have switched from supply-limited to transport-limited in terms of sediment runoff. Nutrient runoff has been transport-limited (i.e., a function of rainfall frequency-magnitude-duration) for most impacted rivers. Due to best management practices (and possibly from the conversion of sheep farming to cattle farming), sediment concentrations have been declining in 34 of the 77 rivers we measured, while nitrogen concentrations have increased in 33 of 77 rivers. While clearer rivers are seen as an improvement in water quality; when combined with increasing nutrients, warmer water, and lower flows, the perfect recipe for toxic algae blooms is created, which has only recently been brought to the public’s attention. Our results indicate that this problem could worsen given the increasing trends we found in water temperatures, inorganic nutrients, and water clarity.    

Published Papers directly linked with the project:

JP Julian, KM de Beurs, RJ Owsley, B.C., Davies-Colley, AE Ausseil. 2017. River water quality changes in New Zealand over 26 years: response to land use intensity. Hydrology and Earth System Sciences 21, 1149-1171

I Kamarinas, JP Julian, AO Hughes, BC Oswley, KM de Beurs. 2016. Nonlinear Changes in Land Cover and Sediment Runoff in a New Zealand Catchment Dominated by Plantation Forestry and Livestock Grazing. Water 8 (436)

KM de Beurs, BC Owsley, JP Julian. 2016. Disturbance analyses of forests and grasslands with MODIS and Landsat in New Zealand. International Journal of Applied Earth Observation and Geoinformation 45, 42-54

TV Tran, KM de Beurs, JP Julian. 2016. Monitoring forest disturbances in Southeast Oklahoma using Landsat and MODIS images. International Journal of Applied Earth Observation and Geoinformation 44, 42-52

JP Julian, NA Wilgruber, KM de Beurs, PM Mayer, RN Jawarneh. 2015. Long-term impacts of land cover changes on stream channel loss. Science of the Total Environment 537, 399-410

Other Papers derived from methodology developed for this project:

KM de Beurs, NS McThompson, BC Owsley, GM Henebry. 2019. Hurricane damage detection on four major Caribbean islands. Remote Sensing of Environment

D Kingfield, K de Beurs. 2017. Landsat Identification of Tornado Damage by Land Cover and an Evaluation of Damage Recovery in Forests. Journal of Applied Meteorology and Climatology