Use Of In Situ Optical Sensors To Understand The Spatial and Temporal Variability Of Nitrate.

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 the high spatial and temporal resolution necessary to understand these complex processes.  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.  In situ optical instruments 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 concentration in several freshwater systems in north Florida.  The SUNA was deployed to measure nitrate at five different water bodies selected to represent a range of watershed land uses and water chemistry in the region.  In situ nitrate measurements were compared to standard laboratory methods to evaluate the effectiveness of the SUNA’s operation.  Other optical sensors were used to measure the spectral properties of absorbance, fluorescence, and turbidity (scatter) in the same Florida water bodies.  Data from these additional sensors were collected to quantify possible interferences that may affect SUNA performance.  In addition, data from the SUNA and other sensors are being used to infer information about the quality and quantity of aqueous constituents besides nitrate.  A better understanding of the capabilities and possible limitations of these relatively new analytical instruments will allow researchers to more effectively investigate biogeochemical processes and nutrient transport and enhance decision-making to protect our water bodies.