Mathematical models help to quantify agricultural sediment and
phosphorus transfers and to simulate mitigation of pollution. This paper develops empirical models of the dominant sediment and
phosphorus event dynamics observed at
high resolution in a drained and undrained, intensive grassland field-scale lysimeter (1 ha) experiment. The uncertainties in model development and simulation are addressed using Generalized
Likelihood Uncertainty Estimation. A comparison of suspended
solids (SS) and total
phosphorus (TP) samples with a limited number of manual repeats indicates larger data variability at low
flows. Quantitative
uncertainty estimates for discharge (Q) are available from another study. Suspended solids-discharge (SS-Q) hysteresis is analyzed for four events and two drained and two undrained fields. Hysteresis loops differ spatially and temporally, and
exhaustion is apparent between sequential hydrograph peaks. A coherent empirical model framework for hysteresis, where SS is a function of Q and rate of change of Q, is proposed. This is evaluated taking the Q
uncertainty into account, which can contribute substantially to the overall
uncertainty of model simulations. The model simulates small hysteresis loops well but fails to simulate
exhaustion of SS sources and flushing at the onset of events. Analysis of the TP-SS relationship reveals that most of the variability occurs at low
flows, and a
power-law relationship can explain the dominant behavior at higher
flows, which is consistent across events, fields, and pathways. The need for further
field experiments to test hypotheses of sediment mobilization and to quantify data uncertainties is identified.
