Performance Demonstration Statement American Ecotech NUT 1000.

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 American Ecotech NUT 1000 during a surface mapping tests in Monterey Bay, CA. This field exercise was designed to demonstrate the capacity of test instruments for high frequency and resolution sampling of ambient phosphate concentrations provided in a flow through sampling stream drawn from 1m during an underway survey. Water sampling was conducted both in the highly turbid and eutrophic waters of the Moss Landing Harbor as well as more oceanic conditions of outer Monterey Bay during a 7 hour cruise. The reported measurements from the NUT 1000 were highly linear over an order or magnitude range between 10 – 120 µgP/L when regressed against laboratory analyzed reference samples. However, the initial calls from the instrument consistently over-estimated phosphate concentrations by around 50 µgP/L due to an internal calibration issue most likely associated with the higher refractive index of seawater relative to the calibration standard solutions. Simple post-correction of the instrument data provided excellent agreement with the laboratory reference data throughout the range of observed concentrations. In addition to the surface mapping application, two moored application tests were attempted, but distinct instrument malfunctions resulted in aborted tests at both locations. It should be noted that this instrument as configured was not designed for mooring applications. In general, however, it appears that the fundamental technology of the NUT 1000 has the capability to successfully measure in situ phosphate concentrations over a wide range of water quality conditions and can be particularly effective for rapid, survey-based applications due to its high sampling rate capability and extreme portability. We encourage readers to review the entire document for a comprehensive understanding of instrument performance and to discuss results with the instrument manufacturer.