Performance Demonstration Statement WET Labs Cycle-P Nutrient Analyzer.

Abstract

During this Performance Demonstration t he WET Labs Cycle-P was successfully tested in a fixed, surface mooring deployment at three test sites including freshwater, brackish water, and saltwater coastal environments. With the exception of an initial instrument exchange on day 2 of the first field test, the test instrument functioned continuously for all 4 weeks of each test. Data recovery was 84, 79, and 99% of the total potential for MD, MI, and AK test sites respectively. Several logistical problems prevented complete execution of all of the quality control testing, but based on the completed blank and standard test exposures the instrument appeared capable of accurately measuring a wide range of phosphate concentrations and functioning consistently over a four week interval. There was no apparent degradation of the on-board reagents or stan dards over the deployment period. Extremely low phosphate concentrations at the MD test site did not allow for meaningful data analysis and there appeared to be a significant impact from biofouling at this site after several weeks. At the AK test site dir ect comparisons of instrument to reference sample data were quite variable, ranging from 0.2 to 4.1 but with an overall mean of 1.5. The offset and variability seemed to improve over time with much better accuracy during the last two weeks of the deployment. Part of the variability may have been due to a mismatch in sample timing intervals and resulting averaging of timepoints. At the Michigan test site, the in situ measured concentrations were much more consistent and accurate. The instrument to reference sample ratio ranged from 0.3 – 1.9 with an overall mean of 1.04. Because of the complexity of the tests conducted and the number of variables examined, a concise summary is not possible. We encourage readers to review the entire document for a comprehensive understanding of instrument performance and to discuss results with the instrument manufacturer. The application of any post -deployment corrections, and manufacturer’s interpretation of the test results are presented in Appendix 1. In general, however, it appears that the fundamental technology has the capability to successfully measure phosphate in situ under a variety of field conditions.