NOVA: an automated nutrients online variable analyzer for terrestrial input observation

Abstract The simultaneous measurement of ammoniacal nitrogen (NH 4 + −N) and total phosphate (TP) in terrestrial inputs is imperative for the effective monitoring of estuaries. Conventional laboratory analyses are laborious and time-consuming, and are also susceptible to degradation during transportation. In order to overcome these limitations, the nutrient online variable analyzer (NOVA) was developed. NOVA employs a single microfluidic syringe pump for the purpose of ensuring accurate control of inlet volume, and automates both sample dilution and tubing lubrication according to concentration range. This process serves to suppress errors that typically arise from multi-channel inconsistencies. Laboratory calibration and field deployments confirmed the robustness of NOVA, with correlation coefficients ( R 2 ) reaching 0.9993 for NH 4 + −N and 0.9995 for TP. The system demonstrated high adaptability and reproducibility under varying environmental conditions. Subsequent memory-effect tests demonstrated negligible carry-over, with T -values of −0.0133 for high-concentration samples and −0.0050 for low-concentration samples. The outcomes of this study demonstrate the capacity of NOVA to accurately and reliably quantify both NH 4 + −N and TP.