In Situ Optical Sensors for Measuring Nitrate in Florida Waters.

Assessing the impact of nutrient concentrations on aquatic ecosystems requires an in depth understanding of dynamic biogeochemical cycles that are often a challenge to monitor at high spatial and temporal resolution. Traditional sampling approaches involving discrete samples and laboratory analyses can be constrained by analytical costs, field time, and logistical details that can fail to accurately capture both spatial and temporal changes. Optical in situ sensors may provide the opportunity to continuously monitor a variety of water quality parameters at a high spatial or temporal resolution. This work explores the suitability of a Submersible Ultraviolet Nitrate Analyzer (SUNA) produced by Satlantic, to accurately assess in situ nitrate concentrations in freshwater systems in north Florida. SUNAs with different path lengths were used to evaluate the effect of instrument path length on nitrate measurements when optical interferences are present. Instrument accuracy and precision was assessed over a range of nitrate concentrations, light absorbing interference (colored dissolved organic matter), and light scattering interference (turbidity). Mitigation