ISUS/SUNA nitrate measurements in networked ocean observing systems

Sustaining measurements of water quality parameters in sensitive watershed habitats is challenging, particularly during critical periods such as spring blooms, and major run off events. Direct, in situ measurements of nitrate have been difficult to obtain until the development of the ISUS (In Situ Ultraviolet Spectrometer, Johnson & Coletti 2002) and more recently the next generation SUNA (Submersible Ultraviolet Nitrate Analyzer). These chemical-free optical sensors have now been operating in a wide range of challenging environments over the past five years. Performance evaluations of these instruments, lessons learned, and environmental insights obtained will be discussed, as well as results from these sensors under the recent ACT (Alliance for Coastal Technologies) Nutrient Sensor Technology Demonstration Program.