Silica production
| Biogenic silica production (32Si) |
|---|
| Approach: radiotracer (32Si) incubation; gross biogenic silica production |
| Context: incubation, in situ and lab |
| Spatial scale: point sample |
| Temporal scale: hours to days |
| Units: µmol Si cell-1 d-1; µmol Si L-1 d-1 |
| Community captured: bulk |
| Co-measurements: ambient [Si(OH)4], PAR, temperature, BSi |
Method Overview
Biogenic silica (opal) production rates are measured by the same 32Si tracer incubation approach as silicon uptake, but are reported as gross production rates in µmol Si L-1 d-1 or per-cell equivalents, reflecting the total rate of silica deposition into diatom frustules and other silicified structures. The rate encompasses both net frustule growth and the replacement of lost silica from dissolution during the incubation. 32Si(OH)4 is added at tracer concentration, cells are incubated under in situ or simulated conditions, filtered onto polycarbonate membranes, and the incorporated radioactivity is measured by low-energy beta counting[1].
Scale of measurement
Point samples requiring hours to days incubation. Depth profiles require incubations at each depth.
Data generated
Gross BSi production rates (µmol Si L-1 d-1); can be depth-integrated to give areal rates (mmol Si m-2 d-1). Together with BSi dissolution rate estimates, net BSi accumulation can be inferred.
Units & currency
Units are µmol Si L-1 d-1 or µmol Si cell-1 d-1. The currency is biogenic Si.
Sample size
Typical samples are 100–300 mL in volume.
Repositories & databases
Limitations
As for Silicon uptake: non-steady state conditions, bottle effects, and BSi normalization uncertainty. Silica dissolution during the incubation releases 32Si back into solution and can cause underestimation of gross production if the dissolution rate is high.
Example Applications & Protocols
Classic examples
- Brzezinski & Phillips (1997) Evaluation of 32Si as a tracer for measuring silica production rates in marine waters [1]
Recent applications
- Krause et al. (2011) Application of low-level beta counting of 32Si for the measurement of silica production rates in aquatic environments [2]
Common calculations/conversions
- ρSi (µmol Si L-1 d-1) = (32SiBSi / 32Sitotal added) × [Si(OH)4] / incubation time.
References
- ↑ 1.0 1.1 Brzezinski, M. A., & Phillips, D. R. (1997). Evaluation of 32Si as a tracer for measuring silica production rates in marine waters. Limnology and Oceanography, 42(5), 856–865. https://doi.org/10.4319/lo.1997.42.5.0856
- ↑ Krause, J. W., Brzezinski, M. A., Landry, M. R., Baines, S. B., Nelson, D. M., Selph, K. E., Taylor, A. G., & Twining, B. S. (2011). Application of low-level beta counting of 32Si for the measurement of silica production rates in aquatic environments. Marine Chemistry, 127, 40–47. https://doi.org/10.1016/j.marchem.2011.07.001