Optical techniques for the determination of nitrate in environmental waters: Guidelines for instrument selection, operation, deployment, maintenance, quality assurance, and data reporting

Abstract

The recent commercial availability of in situ optical sensors, together with new techniques for data collection and analysis, provides the opportunity to monitor a wide range of water-quality constituents on time scales in which environmental conditions actually change. Of particular interest is the application of ultraviolet (UV) photometers for in situ determination of nitrate concentrations in rivers and streams. The variety of UV nitrate sensors currently available differ in several important ways related to instrument design that affect the accuracy of their nitrate concentration measurements in different types of natural waters. This report provides information about selection and use of UV nitrate sensors by the U.S. Geological Survey to facilitate the collection of highquality data across studies, sites, and instrument types. For those in need of technical background and information about sensor selection, this report addresses the operating principles, key features and sensor design, sensor characterization techniques and typical interferences, and approaches for sensor deployment. For those needing information about maintaining sensor performance in the field, key sections in this report address maintenance and calibration protocols, quality-assurance techniques, and data formats and reporting. Although the focus of this report is UV nitrate sensors, many of the principles can be applied to other in situ optical sensors for water-quality studies.

Wood chip denitrification bioreactors can reduce nitrate in tile drainage

“…This sensor, designed and constructed by scientists at the Monterey Bay Aquarium Research Institute, allowed real-time NO 3 -N monitoring of the tile drainage. ISUS sensors and the related SUNA (submersible UV nitrate analyzer) sensor have been shown to provide accurate NO 3 -N determination in a variety of ground and surface waters (Pellerin et al 2013;Sackmann 2011).…”

Quantifying watershed‐scale groundwater loading and in‐stream fate of nitrate using high‐frequency water quality data

“…A regression of depth and width-integrated discrete nitrate plus nitrite concentrations with sensor nitrate concentrations on 11-22 dates shows that the two were strongly correlated (r 2 5 0.97-0.99) across a range of flow conditions at all three sites (Figure 2). Sensor bias relative to laboratory measurements were corrected as described in Pellerin et al [2013]. This is the primary step in our postprocessing, as burst data and metadata (such as the fitting parameter) are used in real-time to assure high data quality.…”

“…All instruments were equipped with an external nylon brush wiper (Zebra-Tech, New Zealand) that cleaned the optical windows prior to every sampling interval. Nitrate sensor performance was checked prior to and during field deployments as explained in Pellerin et al [2013]. Briefly, this includes blank and standard checks, as well as comparison to discrete samples collected at or near the site.…”

In situ response of bay productivity to nutrient loading from a small tributary: The Delaware Bay-Murderkill Estuary tidally-coupled biogeochemical reactor

“…Exceptions were nitrate and chlorophyll; the turbid water column, high DOC (Pellerin et al, 2013), or initial instrument calibration, probably affected the quality of our SUNA NO 3 measurements. Fortunately, the observed interference appeared to be consistent and therefore the LOBO measurements were corrected using direct comparisons with discrete samples.…”