Protocols for Demonstrating the Performance of In Situ Nutrient Analyzers.

Abstract

There are a number of challenges in assessing nutrient concentrations in aquatic systems that point to the value of sustained in situ observations. High spatial horizontal variability is typical of many coastal, estuarine and fresh water systems, as are strong depth gradients. High temporal variability in natural background concentrations are typical of many locations, often in response to short-term forcing (e.g., vertical mixing) or input events (e.g., runoff, river discharge). A lack of consistent relationships to other variables often makes inferences regarding nutrient-related impacts from other, more easily measured proxies (such as chlorophyll-a fluorescence) problematic. Finally, in many aquatic ecosystems, assessing responses to nutrient inputs from various sources requires monitoring of multiple nutrient species. ACT Nutrient Analyzer Demonstration Protocols ACT PD01-014. In situ nutrient sensors can play an important role in addressing these challenges and offer promise for range of applications including: regulatory, applied, observing system and basic research. For any of these types of applications, users will be concerned about the traditional performance attributes including: reliability, comparability, affordability, and calibration before and through field deployments. However, specific system requirements and performance metrics will vary among the different types of applications. The in situ nutrient sensor technologies that appear likely to remain the dominant commercial options for the next decade are reagent-based in situ auto-analyzers (or fluidics systems) and an optical-based sensors, such as the spectrophotometric measurement of nitrate. The number of available commercial systems has expanded since 2003, and community support for expanded application and further development of these technologies appears warranted. Application in coastal observing systems, including freshwater as well as estuarine and marine environments, was a focus of a recent ACT workshop on in situ nutrient analyzers. Workshop discussion included possible refinements for sustained deployments as part of integrated instrument packages, and means to better promote broader use of nutrient sensors in observing system and management applications. Lastly, the workshop also made a number of specific recommendations concerning the testing protocols that will be used for this Nutrient Sensors Demonstration.