Organic nutrients

: defining risk and managing transfers at catchment scale

Abstract

The context for this thesis is the development of tools to support water quality protection in agricultural river catchments. More specifically, the research investigates the use of faecal steroid biomarkers to detect slurry in incidental transfers from land to water, in combination with physico-chemical water quality parameters (total and total reactive phosphorus—TP, TRP, and suspended sediment—SS). As incidental transfers of organic slurry and associated nutrients are dynamic with runoff processes, the aim of the research was to develop a proxy approach for near-continuous monitoring of slurry nutrient transfers from land to water. Experiments were conducted from laboratory scale to catchment scale using cattle slurry.

At laboratory scale, the degradation of steroids under different conditions was investigated using a microcosm incubation study. It was confirmed that the steroid fingerprint was affected most by higher temperatures and the passing of time (p≤0.05 for all steroids across all orders of fitting), with four steroids (cholesterol, α-stigmastanol, campestanol and epi-coprostanol) being identified as more conservative (Following this, a lysimeter plot study was conducted where cattle slurry was applied to the plots before and after a slurry spreading closed period. In this experiment, the treatment of cattle slurry itself had no significant effect (p≥0.05), but sampling time did (p≤0.05), and there was also a weak correlation with TP.

Finally, a catchment scale experiment was performed which monitored steroid and high resolution P and SS concentrations during storm events. There was a positive correlation between key slurry related steroids with TRP (0.26-0.81) and TP/SS (0.08-0.29) indicating that a proxy approach could be developed using steroids.

More work is needed to improve these correlations, but the research here provides a robust framework for applying the proxy approach in repeated future experiments at different scales and with varying faecal matter sources.

Date of Award	Apr 2022
Original language	English
Sponsors	TEAGASC - Walsh Fellowships
Supervisor	Phil Jordan (Supervisor)