Trialling stream rehabilitation tools to attenuate nitrate export and improve stream health in agricultural waterways [article]

Brandon Clement Goeller, University Of Canterbury
Increased nutrient loading in agricultural drainage ditches and small streams caused by land use intensification is a driver of global change and poses significant challenges for managing freshwater ecosystems globally. These headwater waterways can disproportionately influence downstream nutrient loads and ecosystem processes that affect nutrient cycling. I undertook this research within the Canterbury Waterway Rehabilitation Experiment in agricultural headwater waterways to: 1) characterize
more » ... e hydrological and catchment-scale drivers of agricultural catchment nitrate loads, 2) implement nitrate removal tools targeting the key nutrient sources along the stream network, and 3) evaluate the in-stream and ecosystem-level impacts of stream rehabilitation. My findings highlight how nutrient loads in these lowland, spring-fed waterways can be highly dynamic, dominated more by groundwater than local run-off, and increase our general understanding of the scales and locations to implement nitrate loss rehabilitation tools. The substantial nitrate fluxes I measured from upstream springs, and from tile and open tributary drains, should be targeted for rehabilitation at the farm-scale to complement catchment-scale and land-based nitrate management. Therefore, I tested the suitability and performance of three small (< 30 m³) edge-of-field denitrifying woodchip bioreactors implemented as part of a multi-tool, multi-scale, riparian rehabilitation programme. Rehabilitation enhanced downstream nitrate flux attenuation under losing stream hydrological conditions (i.e., decreasing discharge along the reach) post-rehabilitation, whereas there were no significant changes in this relationship over time in the control waterway. Therefore, hydrological variability not only drove waterway nitrate export, but also influenced the performance of riparian nitrate attenuation tools. To enhance in-stream nutrient removal and retention, I experimentally added woodchips to the channels of four waterways with low dissolved organic carbon and [...]
doi:10.26021/8050 fatcat:bd2mk43afjet5e6iupblwxs2xi