High temporal resolution monitoring of inorganic nitrogen load in drainage waters

Abstract

Nitrate (NO₃⁻), ammonium (NH₄⁺) and pH were monitored with a novel flow cell equipped with ion-selective electrodes (ISEs) in a drainage pipe during one year. The high temporal resolution of the measurements (six measurements per hour) allowed the detection of diurnal oscillations in pH, NO₃⁻ and NH₄⁺ concentrations, the relation of variations in concentrations to discharge rates changing during rain events, understanding of the processes resulting in such variations and tracing of unpredictable manure spills. Annual loads estimated from random samples collected every second day tended to underestimate the “true” loads calculated from quasi-continuous electrode measurements by 550% for NH₄⁺ and 22% for NO₃⁻.