Development of improved flow analysis prototype method for measuring and understanding agricultural non-point source (NPS) nitrogen (N) and phosphorus (P) pollution

Abstract

The loss of nitrogen (N) and phosphorous (P) through continuous surface runoff by rainfall after fertilizing and leaching into groundwater has become a critical issue that causes eutrophication of rivers, lakes, and even drinking water, resulting in agricultural non-point source (NPS) pollution of up to 50 % of pollution load. Traditionally, N and P were measured using the laboratory's flow injection analysis (FIA) method before evaluating the pollution load, which could meet urgent requirements in the fast response, prevention, and control of agricultural NPS pollution. Herein, we propose an improved flow analysis (perturbation dispersion) method by integrating chemical reaction chambers to measure nitrogen and phosphorus in water automatically and continuously. The as-fabricated system was validated with real samples from Qianjiang, Hubei Province. The experimental results drew a correlation coefficient of 0.91449 for ammonium nitrogen between the existing lab-based flow analysis method and the innovative (improved) flow analysis method. The correlation coefficients of 0.99828, 0.85129, and 0.99206 for nitrate nitrogen, ammonium nitrogen, and phosphorus were calculated from the measurement results. The detection limits of 0.55, 0.20, and 0.025 mg/L with relative standard deviations (RSD) of 0.8 %, 5.7 %, and 0.9 % were observed for NH4+–N, NO3––N, and PO43− measurements, respectively. This work facilitates the online and continuous control of the NPS pollution load and timely expands the flow injection analysis (FIA) techniques for understanding the pollutants in water and farmland environments.