Performance Demonstration Statement YSI 9600 Nitrate Monitor.

Abstract

A key to the successful adoption, and transition to operational use, of new technologies is broad community awareness and confidence. The Alliance for Coastal Technologies (ACT) has therefore completed a Performance Demonstration of in situ nutrient analyzers/sensors with the goal of aiding in technology refinement and building user acceptance of these novel instruments. The fundamental objectives of this Performance Demonstration were to: (1) highlight the potential capabilities of in situ nutrient analyzers by demonstrating their utility in a broad range of coastal environments with varying nutrient concentrations, (2) promote the awareness of this emerging technology to the scientific and management community responsible for monitoring coastal environments, and (3) work with manufacturers that are presently developing new or improved sensor systems by providing a forum for rigorously evaluating their products using an objective, third-party, nationally distributed testing program. We wish to highlight several fundamental differences in the protocols between an ACT Performance Demonstration and a Performance Verification. First, participating manufacturers were asked to perform all of the required set-up and calibration procedures prior to deployment and to extract the data from the test and submit it in a final concentration specific format. In addition, manufacturers facilitated the testing of laboratory reference standards (made in deionized water with certified SPEX nutrient standards) at the beginning and end of the test. Secondly, there was no laboratory component for directly testing the stated instrument performance capabilities under controlled conditions. Thirdly, field tests were conducted at a subset of four of the eight partner test sites. Lastly, we provided manufacturers with results of initial and final laboratory reference standards, on-board instrument standards and field reference samples to facilitate post-test correction of the in situ determined nutrient concentrations. This procedure is highly recommended for any application of these technologies and provides a better measure of the potential for in situ analyzers to capture accurate time series once appropriate calibrations and controls are applied. In this Demonstration Statement, we present the performance results of the YSI 9600 Nutrient Monitor under diverse environmental conditions in moored deployment tests. A total of three different field sites were used for testing, including: estuary, coastal ocean, and riverine environments. Complete time series data were successfully retrieved in two or the three tests. A software/communication problem resulted in an unsuccessful test at Resurrection Bay, AK and no data will be presented for that test. At the estuarine site in Chesapeake Bay, the YSI 9600 reported 100% of expected data and generally tracked observed variations in nitrate concentrations that ranged between 0.03 – 0.19 mgN/L. Regressed instrument versus reference sample data produced an R2 of 0.93, however, there was a significant calibration offset with YSI 9600 predicted concentrations equal to ca. 60% of lab determined concentrations, on average. A slight decay in the accuracy was observed over the course of the 4 week deployment during the test. At the riverine test site in Michigan, the YSI 9600 also reported 100% of expected data and generally tracked observed variations in nitrate concentrations that ranged between 0.5 – 2.7 mgN/L. Regressed instrument versus reference sample data produced an R2 of 0.89, and the observed calibration offset was much less, with YSI 9600 predicted concentrations equal to ca. 83% of lab determined concentrations, on average. We encourage readers to review the entire document for a comprehensive understanding of instrument performance and to discuss results with the instrument manufacturer. In general, however, it appears that the fundamental technology has the capability to successfully measure in situ nitrate concentrations under a variety of field conditions.