Tracing the flow-driven vertical transport of livestock-derived organic matter through soil using biomarkers

Little is known about the mechanisms that drive the movement of livestock-derived organic matter (LD-OM) in soil–water systems. This work investigates the partitioning of LD-OM in soil and identifies specific inorganic compounds and organic biomarkers that can be used to trace the movement of dissolved and soil-associated LD-OM fractions. Dairy cow slurry was applied to soil in lysimeters prior to a simulated rainfall event; leachate from the base of the lysimeters was collected at regular intervals during and after the rainfall until leaching ceased. Soil cores were taken after the rainfall for the analysis of soil-associated LD-OM derived compounds at different depths. Bulk elemental analysis (C and N) of leachate and soil samples showed that, in isolation, it lacked the sensitivity to trace the movement of LD-OM. Analysis of N species (, and ) and organic compounds using fluorescence spectroscopy was used to investigate the dissolved fraction of the LD-OM and showed that and low molecular weight proteinaceous fractions could be used to trace the dissolved component of slurry through soils. Pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) of bulk soil and high temperature (HT) GC–MS of total lipid extracts (TLEs) of the lysimeter soils and leachates were used to investigate the soil bound fraction. Stanols with 5β configuration were observed in the top 10 cm of soil and not in the leachates and therefore were determined as indicators of soil-bound LD-OM. The results provide new information about compounds that can be used to define the pathways of LD-OM transport in soil. Their application includes the investigation of sources of faecal contamination of water courses via (i) the dissolved fractions of LD-OM fractions and (ii) the redistribution of soil-associated LD-OM by erosion of surface soil layers.