Programmable Flow Injection Ocean Nutrient Analyzer (pFIONA)
What is pFIONA?
pFIONA is an autonomous, in situ nutrient analyzer developed in the Chemical Oceanography Laboratory at Moss Landing Marine Laboratories.
The instrument is designed to measure dissolved phosphate and silicate concentrations in seawater at high temporal resolution, typically on an hourly sampling interval.
pFIONA operates using programmable flow injection analysis (pFI) coupled with spectrophotometric detection.
Seawater samples are continuously introduced into the system and mixed with colorimetric reagents, producing analyte-specific absorbance signals that are quantified to determine nutrient concentrations.
How does pFIONA work?
The system uses microfluidic flow injection analysis, in which precise volumes of seawater and reagents are delivered and mixed through a controlled flow system. Mixing is achieved using two pumps that regulate the introduction of sample and reagents into the flow path.
These reactions produce colored complexes proportional to phosphate or silicate concentrations, which are measured using spectrophotometry. Absorbance is then converted to concentration using calibration relationships.
The instrument is programmed for automated, repeated sampling, enabling continuous hourly measurements without manual intervention.
Why is pFIONA innovative?
pFIONA enables high-frequency (hourly) nutrient measurements, capturing sub-daily variability that is not resolved by traditional discrete sampling methods.
The system integrates automated sampling, reagent handling, and spectrophotometric analysis, reducing the need for manual processing and minimizing analytical error.
It also reduces reagent consumption, sample handling, and overall labor compared to conventional laboratory-based analyses.
Additionally, pFIONA provides real-time data through a user interface (UI), allowing for immediate visualization and interpretation of nutrient dynamics in coastal systems.
pFIONA components view.
pFIONA deployed at the MLML Shore Lab Seawater Intake Monitoring Station.
What are nutrients?
- Nutrients are dissolved chemical compounds in seawater that are required for biological growth and metabolic processes. These include key elements such as nitrogen, phosphorus, and silicon, which fuel primary production by marine phytoplankton.
- Phosphorus, typically in the form of phosphate (PO₄³⁻), is essential for phytoplankton because it is a fundamental component of ATP (energy transfer), nucleic acids (DNA and RNA), and cell membranes.
- Silicon, in the form of dissolved silicic acid (Si(OH)₄), is used by diatoms to construct their silica cell walls (frustules), making it critical for the growth of this important phytoplankton group.
Why do we measure nutrients?
- Measuring nutrient concentrations provides insight into ocean health, biogeochemical cycling, and ecosystem dynamics.
- Nutrient data can be used to identify pollution sources, detect eutrophication, and track changes in primary productivity and phytoplankton community structure.
Monterey Bay bottom-up controlled trophic food web.
Where do nutrients come from?
Upwelling
Northwesterly winds drive offshore Ekman transport, bringing cold, nutrient-rich deep water to the surface. Strongest April–August, with pulsed upwelling and relaxation. Upwelling begins near Point Año Nuevo and is transported into Monterey Bay via an upwelling jet.
Internal Tides
Internal waves propagate through the submarine canyon to Moss Landing, moving along isopycnals and elevating deep, nutrient-rich water, creating localized nutrient pulses.
Rivers and Estuaries
Freshwater input from Elkhorn Slough and the Pajaro River delivers terrestrial nutrients from sediments and agricultural runoff. Tidal exchange forms nutrient-rich plumes that enhance productivity.
Retention Zone
Circulation in northern Monterey Bay (Soquel Cove) increases residence time, allowing warm, nutrient-rich waters to accumulate, enhancing productivity and sometimes harmful algal blooms.
Monterey Bay nutrient sources and circulation: upwelling, internal tides, and river inputs supply nutrients, while circulation retains and redistributes them within the bay.
Nutrient Monitoring Stations in Monterey Bay:
Explore the following websites to access nutrient data across Monterey Bay. These include monitoring sites at the Monterey and Santa Cruz Wharves through the Central and Northern California Ocean Observing System (CeNCOOS); the Moss Landing seawater intake station, which hosts the pFIONA instrument providing phosphate and silicate measurements; and the Elkhorn Slough National Estuarine Research Reserve, which offers data from sites spanning the entire length of the slough.