ACT/MERC Workshop: Ballast Water Compliance Monitoring Using Fluorometry
3
Key Conclusions and Recommendations:
Below is a brief summary of consensus reached during workshop discussions. While based on
scientific facts and expert opinions, additional testing and confirmation of these statements will
follow and a more detailed document, with additional scientific support, will be drafted. The
goal of the follow-up document will be to expand on, and further justify, the following
conclusions and recommendations, if they are found to be valid.
1.
If fluorometry is to be used to detect exceedance of the standard for live organisms of size 10-
50 μm, it will require two keys measurements: (1) bulk chlorophyll (total amount of chlorophyll,
which includes both viable and non-viable/free chlorophyll)
and (2) active fluorescence as either
the
quantum efficiency of photosystem II (F
v
/F
m
, which reflects phytoplankton physiological
response) or
variable chlorophyll fluorescence (F
v
, which can be translated into viable biomass).
Given that variable fluorescence is calculated as the difference between the minimum and
maximum fluorescent signals, F
v
may also be able to exclude unpredictable baseline/background
fluorescence (e.g., variable levels of free chlorophyll and CDOM).
F
m
= a measure of total chlorophyll biomass
F
v
= variable chlorophyll fluorescence and a proxy photosynthetically active biomass
F
v
/F
m
= quantum efficiency of Photosystem II electron transport and a measure of
photosynthetic activity or function
Furthermore, multispectral/multi-wavelength (blue, green and red) instruments will be necessary
to address taxonomic differences in photosynthetic excitation and emission characteristics.
2.
A combination of measurements with chlorophyll levels ≥ 1 μg/l and F
v
/F
m
ratios ≥ 0.3 is
proposed as a clear threshold of exceedance of the discharge standard for the 10-50 μm size
fraction, i.e., taken together, these values represent many more than 10 live organisms per ml
(independent of size class). However, this hypothesis requires validation based on the following
information to be collected from the literature, empirical studies, or both:
a)
Literature review of relationships among chlorophyll, F
v
/F
m
, phytoplankton densities
(e.g., based on vital analyses or counts of cells with cytoplasmic contents), phytoplankton
taxonomic composition (e.g., size, shape, and pigments), and organism physiological
state, for diverse natural waters (multiple/representative geographic regions), with
consideration of methods used to collect the original data;
b)
Empirical studies that compare fluorometers, chlorophyll, and F
v
/F
m
values with direct
cell counts (vital stain, epifluorescent methods) described in the ETV Protocol for
certification testing of ballast water treatment systems. These studies could be conducted
during land-based or shipboard tests of treatment systems;
c)
Literature review and/or empirical study of systematic differences in estimates of F
v
/F
m
using different instruments/approaches;
d)
Literature review and/or empirical study of background or water quality interferences
(e.g., CDOM, light scattering) and interrogation conditions (e.g., light environment
before/during measurement) on fluorometric estimates of chlorophyll and F
v
/F
m
. How
important are these issues/errors and, if important, how can they be avoided? How
should fluorometers be properly blanked or their signal corrected for pathlength
amplification prior to use in ballast water compliance monitoring? Should there be a
standard light treatment (e.g., dark-acclimated vs. low-light-acclimated) prior to use in
ballast water compliance monitoring?
1,2,3 5,6,7