Runoff- and erosion-driven transport of cattle slurry: linking molecular tracers to hydrological processes

Abstract

Abstract. The addition of cattle slurry to agricultural land is a widespread practise, but if not correctly managed it can pose a contamination risk to aquatic ecosystems. The transport of inorganic and organic components of cattle slurry to watercourses is a major concern, yet little is known about the physical transport mechanisms and associated fluxes and timings of contamination threats. Therefore, the aim of the study was to ascertain the importance of flow pathway partitioning in the transport (fluxes and timing) of dissolved and particulate slurry-derived compounds with implications for off-site contamination. A series of rainfall-runoff and erosion experiments were carried out using the TRACE (Test Rig for Advancing Connectivity Experiments) experimental hillslope facility. The experiments allowed the quantification of the impact of changing slope gradient and rainfall intensity on nutrient transport from cattle slurry applied to the hillslope, via surface, subsurface, and vertical percolated flow pathways, as well as particulate transport from erosion. The dissolved components were traced using a combination of ammonium (NH + 4 ) and fluorescence analysis, while the particulate fraction was traced using organic biomarkers, 5β-stanols. Results showed that rainfall events which produced flashy hydrological responses, resulting in large quantities of surface runoff, were likely to move sediment and also flush dissolved components of slurry-derived material from the slope, increasing the contamination risk. Rainfall events which produced slower hydrological responses were dominated by vertical percolated flows removing less sediment-associated material, but produced leachate which could contaminate deeper soil layers, and potentially groundwater, over a more prolonged period. Overall, this research provides new insights into the partitioning of slurry-derived material when applied to an unvegetated slope and the transport mechanisms by which contamination risks are created.

The Importance of Sustained Grassland and Environmental Research: A Case Study From North Wyke Research Station, UK, 1982–2017

“…Faecal biomarker lipids called 5β-Stanols (that are only formed in the gut of rumens) were good tracers of soil-bound manure organic matter which remained at the top of a soil column even after intense leaching, whilst NH4 + and proteinaceous material were good tracers of dissolved manurial products. Experimental slopes (Lloyd et al, 2016) were used to show that rainfall producing 'flashy' hydrological responses resulted in large volumes of surface runoff, and were likely to move sediment and flush dissolved components of slurry-derived organic matter from the slope, increasing the contamination risk. Rainfall which produced slower hydrological responses were dominated by vertical percolated flows removing less sediment-associated organic matter, but produced leachate which could contaminate deeper soil layers, and potentially groundwater, over a longer period.…”