Single Turnover Active Fluorometry (STAF) is an established method for the quantitative assessment of phytoplankton photosynthesis. Importantly, it allows for evaluation of primary productivity by phytoplankton (PhytoPP), providing valuable data to further our understanding of the global carbon cycle.
LabSTAF is the first of a new generation of research-grade active fluorometers developed within the NERC-funded OCEANIDS programme. Additional, ongoing funding for STAF development is provided through the EU-funded Technologies for Ocean Sensing (TechOceanS) programme.
The included Windows-based RunSTAF software provides for a wide range of experimental setups, manual control or highly automated operation, real time data analysis and easy access to primary data in csv format.
..to system control
The standard LabSTAF has a high dynamic range, allowing for measurements from extreme oligotrophic to mesotrophic and even some eutrophic conditions. The High Biomass (HB) version of LabSTAF extends the high end of the dynamic range by a factor of ten. This opens the application of STAF to, for example, the continuous assessment of biomass accumulation within algal growth ponds.
- The use of high performance, hard-coated optical filters removes the need for filtrate blank correction in most cases
- The provision of two fluorescence detection wavebands allows for quantification of and correction for the package effect through the Dual Waveband Measurement (DWM)
- The inclusion of seven fluorescence excitation LED wavebands allows for rapid and highly automated spectral correction by generating the Photochemical Excitation Profile (PEP)
- An integrated actinic light source providing 10 to > 1600 µmol photons m-2 s-1. The light source is driven by DC to avoid the potential for measurement artefacts associated with Pulse Width Modulation (PWM)
- The sample chamber block includes a circulating water jacket that avoids intersection with all optical paths to allow for the use of underway water for sample temperature control
- FLC automation includes dynamic optimisation of the FLC protocol using a new method for continuous assessment of the Ek parameter
- Real time data analysis provides 39 fluorescence parameters, in addition to the standard FLC parameters, and including options for the correction of baseline fluorescence
- A wide range of export functions to provide access to primary data. They can be used to extract data from a single file or across multiple files
Comparison with FastOcean and Act2 systems
LabSTAF represents a significant update to Chelsea’s well-established combination of FastOcean Fast Repetition Rate fluorometer (FRRf) and Act2 laboratory system for running FLCs. One important change has been a switch from the 1 µs FRRf ‘flashlets’ on a 2 µs pitch incorporated within FastOcean to the solid excitation pulse used within LabSTAF. This contributes to a more than ten-fold improvement in sensitivity and a halving of the standard Single Turnover (ST) pulse, from 200 µs to 100 µs. Decreasing the length of the ST pulse decreases the rate of double hits from around 27% to around 12%, which makes it possible to apply ST pulses at a higher frequency.
- Direct measurement of phytoplankton photosynthetic rates, per unit volume per unit time, allowing for the assessment of PhytoPP
- Autonomous acquisition of STAF data at high resolution, with the potential to contribute to the verification of satellite-based models of PhytoPP
- Rapid photophysiological screening of phytoplankton samples using scintillation vials
- Tracking the development of algal blooms and changes in community structure
- Analysis of diurnal cycles in phytoplankton photosynthesis and cell metabolism
- Autonomous continuous underway measurements on research vessels and ships of convenience
- Real time assessment of the impact of environmental change on phytoplankton photosynthesis, including ambient light, temperature, nutrient enrichment and pollution events
LabSTAF In Depth
The two most common fluorescence-based methods used to probe photosynthesis are Single Turnover Active Fluorometry (STAF) and the Multiple Turnover Pulse Amplitude Modulation (PAM) approach. The STAF method is by far the best option for making measurements from optically thin suspensions of phytoplankton (as found in the world’s oceans and most lakes and rivers) while the PAM method is suited to samples with high optical density (such as macroalgae and seagrasses).
The Fluorescence Light Curve (FLC)
For many users, the most important application of LabSTAF is the fully automated acquisition of consistent Fluorescence Light Curve (FLC) data from cultures or natural samples. The combination of LabSTAF hardware and RunSTAF software allows for the highly automated acquisition of FLCs, with options for real time light step adjustment, automated sample exchange and system cleaning. As an example, these features have been used to run LabSTAF systems continuously for several weeks while plumbed into the underway water supply on board research vessels.
Rapid screening of multiple samples
Although a great deal of effort has been applied to the development of FLC automation, the system allows for much shorter automated protocols to be run. A manual control option is also available to the user. The large sample chamber provides a range of options when using these features. One option is to pour a sample of between 10 and 20 mL directly into the sample chamber. Alternatively, rapid measurements can be made from smaller samples within scintillation vials.
LabSTAF, primary productivity and the dual incubation method
Primary productivity by phytoplankton (PhytoPP) accounts for approximately half of the carbon fixed by photosynthesis on a planetary scale. While satellite remote sensing of ocean colour operates on the widest possible spatial scales and is arguably the only means to assess PhytoPP in the context of global biochemical cycles and climate, the algorithms used to estimate PhytoPP from satellite data rely on large datasets of in situ measurements. The established reference for quantifying PhytoPP directly is the 14C tracer-based approach which falls short of providing data at the required temporal and spatial resolution. The scarcity of in situ PhytoPP measurements has been limiting the development and validation of remote sensing algorithms of PhytoPP and is preventing adequate parameterization in regional and global ecosystem and climate models. STAF, as an optical method, can assess PhytoPP autonomously at vastly higher spatial and temporal resolution and at a fraction of the cost of 14C tracer-based methods.
While 14C tracer-based methods measure carbon fixation directly, STAF measures the rate at which the reducing power required for carbon fixation is provided by Photosystem II (PSII) photochemistry. RunSTAF has been optimized for improved estimates of this rate and incorporates highly automated protocols to allow for Package Effect Correction (PEC) and spectral correction through application of a Photochemical Excitation Profile (PEP). Additional data processing tools to correct for baseline fluorescence (from sources other than photochemically active PSII complexes) are also included within RunSTAF.
STAF-derived values of PSII photochemistry can be converted to rates of carbon fixation through the electron to carbon ratio (Φe,C). Determination of this ratio requires parallel STAF-based measurement of PSII photochemistry and 14C tracer-based measurement of carbon fixation. The large sample chamber incorporated within LabSTAF allows for the use of 24 mL scintillation vials, enabling 14C-spiked samples to be used to assess carbon assimilation in parallel with STAF measurements. Development of this ‘dual incubation’ approach has removed many of the methodological inconsistencies that have inhibited practical assessment of the number of electrons (assessed through STAF) required to fix each carbon (assessed through 14C-fixation). While such dual incubations cannot be performed at high resolution, representative measurements made within a specific environment will provide values that improve the accuracy of the conversion between PSII photochemistry and carbon assimilation.
Basic specifications of the LabSTAF unit
|Power supply||140 – 400 mA at 24 V (3.4 – 9.7 W)|
|Dimensions (mm)||236 (H) x 328 (W) x 429 (D)|
|Mass (approx.)||8.1 kg|
|Sample Chamber||10-20 mL sample volume, down to 4 mL with scintillation vial|
|Excitation wavebands (wavelength)||Central wavelengths at: 416, 452 x2, 473, 495, 534, 594, 622 nm|
|Actinic light source||Blue-enhanced, collimated DC output from 10 to > 1600 μmol photons m–² s–¹|
|Detection limit||Can resolve F∨ with an amplitude equivalent to the fluorescence signal generated under 452 nm excitation by 0.001 mg m-3 of chlorophyll a|
|IP rating||IP64 (protected from water spray from any direction)|
Basic specifications of the LabSTAF power pack
|Power requirements||Mains (110 to 220 V AC)|
|Dimensions (mm)||259 (W) x 201 (D) x 114 (H)|
|Mass (approx.)||2 kg|
|IP rating when closed||IP64 (protected from water spray from any direction)|
|IP rating when in use||IP40 (protected against entry by tools but not protected against moisture)|
Basic specifications of the LabSTAF spares kit
|Dimensions (mm)||424 (W) x 340 (D) x 173 (H)|
|Mass (approx.)||5.2 kg|
|IP rating when closed||IP64 (protected from water spray from any direction)|
Contents of the LabSTAF spares kit
- Peristaltic pump, including pump unit, pump head with 6 mm bore tubing installed, power cables, interface cable
- Solenoid unit, including cable
- Flow through unit and flow through stirrer unit
- Calibration plug
- Sample chamber lid
- Surface Go 3, including keyboard and power cables
- Additional spares, including tubing, O-rings, silicon grease