AUTOMATED PROCEDURE FOR DETERMINATION OF DISSOLVED ORGANIC NITROGEN AND PHOSPHORUS IN AQUATIC ENVIRONMENTS

A method is described for estimating dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) in aquatic environments. The method is based on ultraviolet oxidation under successive acid and alkaline conditions, and uses continuous-flow techniques. A number of pure organic nitrogen compounds were tested in the concentration range 2 to 40 mug-at N l-1. At the 10 mug-at N l-1 level, recovery ranged from 60 to 100% in deionized water, and from 40 to 80% in seawater (30 parts per thousand S). In general, recovery decreased with increasing nitrogen concentration. For pure organic phosphorus compounds, recovery ranged from 73 to 100% at the 5 mug-at P l-1 level. An application of the method to the surface water of a clay pond along the Atlantic coast of France for a period of 72 h under natural irradiance revealed very strong diel variations of dissolved organic nitrogen, but no significant trends for dissolved organic phosphorus.