Organic nitrogen in precipitation at the mid-Atlantic US coast - Methods evaluation and preliminary measurements

Recent studies have documented the importance of inorganic nitrogen deposited from the atmosphere to coastal waters. However, due to the limited number of field measurements and concerns about the reliability of measurement techniques, the aeolian flux of organic N is very uncertain. In this study we evaluate commonly employed collection and analytical techniques for dissolved organic nitrogen (DON) in precipitation, and provide preliminary estimates of organic-N wet fluxes at the mid-Atlantic U.S. Coast (Lewes, DE). Precipitation was sampled on a daily basis using an automated wet-only collector. Compared with UV photo-oxidation, persulfate wet chemical oxidation was more efficient at converting organic-N compounds to NO(3)(-). Side-by-side comparisons of white polyethylene buckets (typically employed in "acid rain" studies) with stainless steel buckets suggest that DON is lost in varying amounts to the plastic surfaces. Stability tests reveal that organic-N in precipitation can be quite labile under field conditions, with significant losses observed within a few hours in some samples. Based on analysis of 37 events collected from October 1993 through December 1994, the volume-weighted average concentration of DON in precipitation at the mid-Atlantic coast is greater than or equal to 9.1 mu mol l(-1). On an annual basis, organic-N comprises at least 20% of the total dissolved nitrogen in precipitation; on an event basis, it comprises as much as 64%. From the perspective of coastal ecosystem eutrophication, the atmospheric loading of DON would appear to represent an important exogenous source of N to local coastal waters such as the Delaware and Chesapeake Bays. (C) 1998 Elsevier Science Ltd. All rights reserved.