Field Testing of an Optical in Situ Nitrate Sensor in Three Irish Estuaries

Abstract

Abstract:ABSTRACTIn situ measurements of nitrate (NO3) were made using a submersible ultraviolet nitrate sensor (SUNA) in three Irish estuaries (Bandon, Blackwater and Lee) in January and February 2012. Measurements were compared against discrete water samples analysed in the laboratory. There was excellent agreement between the SUNA and laboratory measurements, with the variation in in-situ nitrate measurements explaining nearly 100% of the variation in laboratory measurements (r2 = 0.99, with a negative bias of ∼10%). In each estuary there was a conservative mixing relationship between salinity and nitrate, indicating that the main source of nitrate to these estuaries in winter is from the main inflowing river. The highest nitrate concentration of 235.2µM at salinity 0.7 was found in the Lee Estuary and the lowest concentration of 7.5µM at salinity 34.6 was found in Cork Harbour. The successful demonstration of this technology in Irish estuaries provides a powerful example of how future developments in this field will allow the real-time assessment of environmental conditions in these environments.