ORGANIC NITROGEN IN PRECIPITATION AT THE MID-ATLANTIC US COAST - METHODS EVALUATION AND PRELIMINARY MEASUREMENTS

Recent studies have documented the importance of inorganic nitrogen de posited from the atmosphere to coastal waters. However, due to the lim ited number of field measurements and concerns about the reliability o f measurement techniques, the aeolian flux of organic N is very uncert ain. In this study we evaluate commonly employed collection and analyt ical 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-ox idation, persulfate wet chemical oxidation was more efficient at conve rting organic-N compounds to NO3-. Side-by-side comparisons of white p olyethylene buckets (typically employed in ''acid rain'' studies) with stainless steel buckets suggest that DON is lost in varying amounts t o the plastic surfaces. Stability tests reveal that organic-N in preci pitation 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 vo lume-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 an nual basis, organic-N comprises at least 20% of the total dissolved ni trogen in precipitation; on an event basis, it comprises as much as 64 %. From the perspective of coastal ecosystem eutrophication, the atmos pheric loading of DON would appear to represent an important exogenous source of N to local coastal waters such as the Delaware and Chesapea ke Bays. (C) 1998 Elsevier Science Ltd. All rights reserved.