Optical sensors measuring fluorescent dissolved organic matter (fDOM) are increasingly being used in water quality studies because they provide proxy measurements for dissolved organic matter concentrations (DOC). Similarly, chlorophyll-a (chl-a) fluorescence sensors have gained popularity as a means to measure phytoplankton concentration, biomass, and even primary productivity using various approaches. As additional sensors are grouped for in situ monitoring, field calibration checks are becoming quite time consuming for even the basic set of sensors (i.e. pH, specific conductivity, turbidity) that require ongoing verification over timescales ranging from weekly to semi-annual intervals. As such, there is a critical need to establish a means to verify calibrations using a simple, fast, and efficient method in the field to standardize USGS measurements among sensors and across the landscape. Here, we present the results of a mixed standard solution capable of simultaneously verifying calibrations for multiple sensors including fluorescence of dissolved organic matter (fDOM) and fluorescence of chlorophyll-a (fChl).

Optical sensors measuring fluorescence of non-biological sources (e.g., dissolved organic matter, wastewater, hydrocarbons, fluorescent dyes, etc.; hereafter referred to as fDOM) are increasingly used in water quality studies because they provide proxy measurements for a variety of contaminants and constituents of concern including metals, wastewater effluent, and DOM (measured in the lab as dissolved organic carbon, (DOC)) concentrations. Similarly, sensors measuring biological (algal) fluorescence (hereafter referred to as chlorophyll (fChl) and phycocyanin (fPC), have gained popularity to measure phytoplankton concentration, biomass, and even primary productivity. As additional sensors are coupled with ongoing field monitoring, field calibration checks are becoming quite time consuming for even the basic set of sensors (i.e., pH, specific conductivity, turbidity) that require ongoing verification over timescales ranging from weekly to semi-annual intervals. As such, there is a critical need to establish a means to verify calibrations using a simple, fast, and efficient method in the field, allowing for the standardization of United States Geological Survey (USGS) measurements across the entire agency. Here, we present the results of testing a multiparameter field standard (MPFS), an experimental mixed standard solution capable of simultaneously verifying calibrations for multiple fluorescence sensors (fDOM, fChl, and fPC).

The USGS CAWSC Organic Matter Research Laboratory (OMRL) provides laboratory services and support to regional and national projects in the analysis of organic matter using the latest methods in absorbance and fluorescence spectroscopy. Optical measurements such as absorbance and fluorescence are used to gain insight into dissolved organic matter (DOM) composition, and can also serve as proxies for more expensive and difficult to obtain measurements. These techniques are relatively rapid and inexpensive and allow for the comprehensive tracking of DOM dynamics in aquatic ecosystems ranging from rivers and lakes to estuaries to open marine systems. Absorbance spectra and fluorescence matrices were simultaneously collected on filtered water samples at room temperature (21 °C) in an acid-cleaned 1 cm quartz cuvette using a spectrofluorometer equipped with a charge-coupled device (CCD) (Aqualog®, Horiba Instruments, New Jersey, U.S.A.). Excitation and absorbance scans were performed using a double-grating monochrometer, a 150 W Xenon arc lamp, a 5 nm bandpass, and a 1 s integration time at wavelengths of 240-800 nm. Emission spectra were collected with a CCD at approximately 2.3 nm (4 pixel) intervals at wavelengths of 245–800 nm. Excitation and absorbance wavelengths were scanned from low to high energy (i.e., VIS to UV) to reduce UV exposure of the sample, thus limiting the effects of photobleaching during analysis. Laboratory fluorescence measurements collected on the Aqualog can provide validation or verification of field-based instrument fluorescence measurements where the sensor arrays are encompassed by the full Aqualog array (Booth and others, 2023). This approach may be superior to the other correction approaches where interferences are large, especially in cases where the field sensor measurements constitute less than 10% of the fully corrected value. For projects that already collect discrete samples during field sensor maintenance visits, the cost and effort is minimal for the data quality benefit. Data presented here were analyzed by the U.S Geological Survey California Water Science Center Organic Matter Research Lab, Sacramento CA. This release contains vectorized fluorescence data measured on the Aqualog ® fluorometer January-December 2021.

Here, we present the results supporting Table 2 in Field Techniques for Fluorescence Measurements Targeting Dissolved Organic Matter, Hydrocarbons, and Wastewater in Environmental Waters: Principles and Guidelines for Instrument Selection, Operation and Maintenance, Quality Assurance, and Data Reporting. Table 2 shows comparisons from an Aqualog 800 benchtop fluorometer standardized to quinine sulfate equivalents (QSE) with excitation (ex) and emissions (em) equivalent to fluorescence of dissolved organic matter (fDOM) sensors from multiple manufacturers. Data are reported from two standard reference materials (SRM) and the mean, minimum, and maximum from 76 environmental samples. No replicates were collected for environmental samples; therefore, the relative standard deviation is not available.

Optical sensors measuring fluorescence of dissolved organic matter (fDOM) are increasingly used in water quality studies because they provide proxy measurements for a variety of contaminants and constituents of concern including metals and wastewater effluent. Similarly, sensors measuring fluorescence of chlorophyll (fChl) and phycocyanin (fPC) have gained popularity to measure phytoplankton concentration, biomass, and even primary productivity. Optical sensors require calibration using a calibration standard solution which is diluted from a working stock solution. However, preparation of stock solutions is challenging because they are difficult to prepare accurately, need to be prepared in a laboratory setting, and the final diluted calibration standards need to be used immediately because they degrade quickly. Consequently, technicians are not always confident with their preparation technique or the accuracy of diluted calibration standards. As such, there is a critical need for working stock solutions to be prepared and verified in a laboratory by experienced personnel so field fluorescence sensors measuring fDOM, fChl, and fPC can be standardized across the entire agency. Before the USGS National Field Supply Service (NFSS) can provide working stock solutions to sensor users, a laboratory stability study was conducted to determine the shelf-life and ideal storage conditions for stocks prepared using quinine sulfate (used for fDOM sensor calibration) and rhodamine (used for fChl and fPC calibration). Working stock solutions were prepared at the start of the experiment and stored in a variety of materials (glass, high density polyethylene, and low density polyethylene) at two temperatures (4 and 25 degrees Celsius). Benchtop and sensor measurements were made approximately weekly on calibration standard solutions that were prepared from the working stock solutions to test stock stability over a 3-month period from September 2022 to February 2023.

The use of field-deployable fluorescence sensors to better understand dissolved organic matter concentrations and composition has grown immensely in recent years. Applications of these sensors to critical monitoring efforts have also grown to encompass post-fire monitoring, wastewater tracking, and use as a proxy for various contaminants. Despite the growth, it is well known that these sensors are subject to various interferences and require corrections for temperature, turbidity, and concentration effects. Although temperature corrections are widely applicable across sensors, the turbidity and concentration corrections can be site-specific and/or sensor-specific. The corrections can even be subject to changes in manufacturing within a sensor type, as has been raised as a concern for the USGS’s most widely used fDOM (fluorescence of dissolved organic matter) sensor manufactured by Xylem/YSI. Currently there is limited guidance on the proper corrections for sensors used within the USGS. As the use of these sensors continues to grow, the need for greater standardization of the measurements among sites and through time will also grow. This data release compiles the measurements collected from multiple lab experiments using Elliot Silt Loam. The data contained herein will be used to assess the variability of fDOM corrections for turbidity.

Here, we present data supporting temporal variability and sources of PFAS in the Rio Grande through an arid urban area using high-frequency sampling and novel samplers. Data are compiled into two tables: 1) full fluorescence spectra in vectorized format, and 2) summary file of concentrations of total dissolved nitrogen and commonly extracted field-based sensor arrays. Data are reported from two sites at Rio Grande, New Mexico during a 24-hour collection period. Two field blanks, one field replicate, and two laboratory replicates are reported for 26 environmental samples.

Here we report optical data collected as part of a collaborative study between USGS Pennsylvania Water Science Center, Pennsylvania Department of Environmental Protection and Water Mission Area Proxies Project. The optical measurements reported here were collected to aide in the characterization of water sources and mixtures and establish proxies (surrogates) for per- and poly-fluorinated alkyl substances within the Neshaminy Creek basin. Data are compiled into three tables: 1) full fluorescence spectra in vectorized format, 2) full absorbance spectra, and 3) summary file of commonly extracted optical indicators and field-based sensor arrays.

The USGS CAWSC Organic Matter Research Laboratory (OMRL) provides laboratory services and support to regional and national projects in the analysis of organic matter using the latest methods in absorbance and fluorescence spectroscopy. Optical measurements such as absorbance and fluorescence are used to gain insight into dissolved organic matter (DOM) composition, and can also serve as proxies for more expensive and difficult to obtain measurements. These techniques are relatively rapid and inexpensive and allow for the comprehensive tracking of DOM dynamics in aquatic ecosystems ranging from rivers and lakes to estuaries to open marine systems. Absorbance spectra and fluorescence matrices were simultaneously collected on filtered water samples at room temperature (21 °C) in an acid-cleaned 1 cm quartz cuvette using a spectrofluorometer equipped with a charge-coupled device (CCD) (Aqualog®, Horiba Instruments, New Jersey, U.S.A.). Excitation and absorbance scans were performed using a double-grating monochrometer, a 150 W Xenon arc lamp, a 5 nm bandpass, and a 1 s integration time at wavelengths of 240-800 nm. Emission spectra were collected with a CCD at approximately 2.3 nm (4 pixel) intervals at wavelengths of 245–800 nm. Excitation and absorbance wavelengths were scanned from low to high energy (i.e., VIS to UV) to reduce UV exposure of the sample, thus limiting the effects of photobleaching during analysis. Data presented here were analyzed by the U.S Geological Survey California Water Science Center Organic Matter Research Lab, Sacramento CA. This release contains full spectra absorbance data measured on the Aqualog ® fluorometer January-December 2021.

This U.S. Geological Survey (USGS) Data Release provides spatial water-quality data collected from Milford Lake, Kansas, on July 27 and August 31, 2015. All data are reported as raw measured values and are not rounded to USGS significant figures. Continuous water-quality monitors were used to measure water temperature, specific conductance, turbidity, pH, chlorophyll, phycocyanin, dissolved oxygen, fluorescent dissolved organic matter (fDOM), and nitrate (only collected at 1.0-meter depth) at thirty-second intervals at depths of 0.5-, 1.0-, and 1.5-meters throughout the lake.