Table 2.

Provisional recommended practices for SDC-MPN on natural phytoplankton assemblages in land-based testing for BWMS type approval, suitable for being evaluated through systematic comparisons

	Standard	Optimized
Growth medium
Source water	Filtered water from the original sample
Nutrient enrichment (options)	Reduced concentrations from typical growth media (include soil extract, multiple nitrogen sources)
Sterilization	Filter sterilization, pasteurization
Temperature (°C)	T in situ or ${\overline{T}}_{\mathrm{in}\mathrm{situ}}$	${\overline{T}}_{\mathrm{in}\mathrm{situ}}$ + 5 °C for ${\overline{T}}_{\mathrm{in}\mathrm{situ}}$ ≤20 °C decreasing linearly to 0 offset at 28 °C
Irradiance (μmol photons m−2 s−1)	Light/dark cycle ~10 % Ē 0 cf (~60–200)	Longer light period (e.g., 16 h) 18 % Ē 0 or $82+\left(4.7\cdot {\overline{T}}_{\mathrm{in}\mathrm{situ}}\right)+0.068\cdot \left({\left({\overline{T}}_{\mathrm{in}\mathrm{situ}}\right)}^2\right)$

Standard conditions are based on recommendations in the literature, intended to maximize the number of species that will grow. The optimized conditions proposed here are intended to support enhanced growth rates without significant reductions in the number of species that will grow, thereby shortening the time required to detect viable cells in an SDC-MPN assay and minimizing false negatives due to slowly growing isolates. Ambient water temperature is T _in situ (°C); the climatological average is ${\overline{T}}_{\mathrm{in}\mathrm{situ}}$; climatological cloud-free midday irradiance is Ē _0 cf (μmol photons m⁻² s⁻¹ PAR); and climatological midday irradiance is Ē ₀