Source and Presence of Urea in Maryland’s Estuarine Waters.

Since the presence of the neurotoxin domoic acid in the coastal waters of California resulted in significant mortalities among marine life concern has risen regarding urea which is used by the filamentous diatom Pseudo-nitzschia sp. as an energy source but results in the production of domoic acid. The diatoms containing domoic acid are filtered by shellfish which in turn become contaminated with the toxin. With increased use of urea and poultry litter as fertilizers in watersheds of the Chesapeake Bay researchers have seen increasing levels of urea in the estuarine zones of the Bay, in many cases above the 600 ppb threshold considered to be the level at which Pseudo-nitzschia sp. can begin produce domoic acid. While there is no immediate threat, there is the need to investigate the source and potential for urea to be an issue in the future. This talk will present findings from studies on the Manokin River, farm ditches and mesocosms aimed at examining what conditions favor the presence of urea in surface waters, and if those conditions would allow urea to enter estuarine zones at levels considered to be significant. From the Manokin River we found in late summer significant levels of urea which at times exceeded the 600 ppb threshold, all occurred following rain events. In ditches we again found urea at levels above 600 ppb, again following rain events but after the water had become stagnant. The ditches were recreated in mesocosms which also produced urea, but in this case not at levels seen in the ditches or open water. We feel that there is the potential for urea to become a more significant problem in the future.