Performance of a Parsimonious Phosphorus Model (SimplyP) in Two Contrasting Agricultural Catchments in Ireland

Abstract

The Agricultural Catchment Program (ACP) has collected over a decade’s worth of high frequency data for a number of hydrologic and chemical indicators at agricultural catchments around the Republic of Ireland. This dataset provides an excellent foundation for conducting robust modelling studies assessing long term hydrochemical dynamics in agricultural sites, within the context of EU regulations around the protection of water quality.To examine the risks of phosphorus (P) export from agricultural catchment in this context, the parsimonious phosphorus model SimplyP was applied to two ACP study sites. These sites are in close proximity and are of similar size to each other but have contrasting physical characteristics and hydrochemical dynamics. Site “A” is dominated by grasslands with heavy soils and is P export risky, while site “B” is primarily arable land-use on lighter soils and has a lower risk of P export.In these catchments, SimplyP was used to simulate streamflow, sediment, and phosphorus (PP, TRP, TP) over the period of 2010 – 2019. The model is calibrated and validated independently three times to different objective functions (NSE, KGE, NSE log) to provide models focused on peak flows, balanced, and low flows, respectively. Model performance is evaluated over the entire calibration and validation period, as well as year-by-year assessments, which highlights the influence of meteorological and antecedent moisture conditions on model behaviour.