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The NH4-Digiscan is an in situ analyzer designed for measuring ammonium in estuarine, coastal, and shelf waters at depths of less than 3 m. This wet chemical analyzer uses micro-solenoid pumps to propel sample and reagents, a gas diffusion cell to isolate the analyte from the matrix, and a conductivity detector for analyte detection. Instrument measurements are stable for deployments of at least 30 d. In estuarine and coastal waters, the analyzer is capable of sampling hourly and has a detection limit of 0.2 µM. In shelf waters, the NH4-Digiscan can be configured to have a detection limit of 0.014 µM. The simple chemistry, in situ capability, and high resolution sampling minimizes the use of toxic reagents, minimizes many of the problems plaguing ammonium analyses, and adequately captures the high temporal variability of coastal waters, which is often undersampled. The analyzer has been successfully deployed on coastal moorings, benthic flux chambers, and on a drifter 500 km west of Monterey Bay, California. The system can also be easily configured for laboratory bench top analysis of discrete samples.

An ocean observatory that consists of an array of moored sensor platforms, telemetry, and data collection and dissemination software was designed for monitoring the biogeochemistry and physical dynamics of coastal and estuarine ecosystems. The Land-Ocean Biogeochemical Observatory (LOBO) consists of robust moorings that can withstand tidal currents and weather. The moorings are highly configurable, can be deployed in waters as shallow as 0.5 m, are relatively easy to maintain, and accommodate a complete array of standard and novel sensors. The sensors communicate with an on-board controller which relays data to shore in near-real time. Up to five LOBO moorings have been simultaneously deployed and maintained in Elkhorn Slough, California, since November 2003. Continuous hourly data of biological, chemical, and physical properties are relayed to shore, processed, and disseminated to users through a web interface in near-real time. This article describes the design, implementation, and functionality of the LOBO monitoring system.