SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Research
Arrow in Chedabucto Bay, N.S., showed
the necessity of having information available
on the background concentrations of
oil in the environment to properly assess
the impact of such accidents. Unlike almost
every other measurement carried out by
the Chemical Oceanography Division at
BIO, the methods for determining the
concentration of the dissolved/dispersed
fraction of petroleum in seawater have
remained the same since the first Gulf
survey was carried out in 1970. Therefore,
the oil measurements made in the Gulf
over the period 1970-1979 represent the
only direct measurements on the history of
pollution inputs to the Gulf.
Analysis of this data (Levy 1985) has
shown that the most important source of
petroleum for the Gulf of St. Lawrence is
the open Atlantic (large amounts of water
flow through Cabot Strait into the Gulf
from the Atlantic Ocean). Background
concentrations in the Gulf declined through
the 1970’s, presumably due to regulations
restricting discharges of oil from ships on
the high seas. These conclusions, however,
are reached at the limit of the precision of
the data. Further advances in understanding
might have to wait for new developments
in analytical methods.
Where to from Here?
Does this analysis of the relationships
between sampling and analytical methods,
geochemical expertise, and physical oceanography
say anything about the way future
efforts should be directed in chemical
oceanography in the Gulf of St. Lawrence?
A consideration of recent developments in
these fields might indicate where advances
in chemical oceanography in the Gulf of St.
Lawrence might come next, although the
problems most ripe for solution may not be
the ones of highest priority.
A number of analytical methods have
either been significantly improved or made
available for the first time since the BIO
field work in the Gulf was conducted.
Advances in gas chromatography, for
example, have led to much greater reliability
and lower detection limits in the
determination of chlorinated environmental
pollutants such as DDT and the PCB's.
New studies on these compounds would
have a better chance at understanding their
fate in the marine environment than earlier
studies which could only detect these
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materials at a few contaminated sites.
Other chlorinated organic compounds (e.g.
camphenes and dioxins) have become of
environmental concern in recent years.
Analytical methods for their determination
may be sufficiently well developed to allow
examination of selected samples in potentially
contaminated locales.
Just as the growth of agricultural crops is
limited by the availability of nutrients such
as nitrogen and phosphorus in soil, plankton
growth in the sea is limited by the
availability of nutrients. In the Gulf, the
availability of nitrogen (most often found
in the form of the nitrogen compound,
nitrate) is thought to be the limiting factor.
It is now apparent that a full understanding
of the marine cycling of nitrogen must
include consideration of ammonia as well
as simple nitrogen-containing organic
compounds such as urea. Methods for
ammonia, albeit painstaking ones, have
been available for some time, but have yet
to be applied to the Gulf in a large scale
program. Reliable analytical methods for
organic nitrogen compounds require
further work.
Recent evidence suggests that colloids
may be important in the geochemistry of
both trace organic and trace inorganic
constituents. Colloids are very small
particles that cannot be trapped by normal
filters and which do not settle to the
bottom. Some studies of metal-organic
interactions in colloids are available, but
both better methods and more field-based
research is required to understand the
importance of this phase in areas like the
St. Lawrence Estuary. Sampling colloids is
technically very difficult, but the recent
application of high volume filtration
techniques developed in medical research
to the separation of the colloidal phase in
seawater shows promise.
It is also now recognized that further
advances in understanding the geochemistry
of both natural and man-made organic
materials requires the study of individual
classes or individual organic compounds.
Selecting the important compound types
from the bewildering suite of organic
chemicals that make up marine organic
matter will not be simple, but may be the
only way to gain additional insights into
important geochemical processes.
Understanding the nature of the variability
of chemical concentrations in coastal
environments would be an important
advance in the chemical oceanography of
regions like the Gulf of St. Lawrence.
Current chemical models of the Gulf
consider seasonal variability in a very
simple way - data may not even be
available for all seasons. Almost no
information is available on other scales of
variability in the Gulf. Are there important
multi-year cycles or long term trends? Are
there very rapid changes associated with
daily or tidal cycles that could significantly
alter our view of the important processes
controlling chemical distributions? The
answers to such questions would have
important practical applications. For
example, it would be necessary to know
the natural variability of a trace metal
distribution in order to determine whether
concentrations were being altered by an
industrial discharge - i.e. is an increase in
concentration due to natural variability or
indicative of increasing pollution?
Another direction that new work should
take results from recent physical oceanographic
studies of the Gulf. They suggest
that the dynamics of the Gulf are potentially
quite different from the descriptions
that have been used as bases for chemical
models in the past. Water flows into the
Gulf through the Strait of Belle Isle may be
much larger than previously believed. Such
flows could transport chemicals into the
Gulf. They also may make it necessary to
re-determine the water flows through
Cabot Strait, which were calculated
assuming that no water exchange occurs
through the Strait of Belle Isle. Previous
chemical oceanographic models on the
Gulf should be reexamined in view of these
recent developments in physical oceanography.
Existing data may not be adequate
to evaluate the importance of the area near
the Strait of Belle Isle to the chemical
oceanography of the entire Gulf system.
Due to previous ideas on its importance, its
relative isolation and its long period of ice
cover, it has received comparatively little
attention on chemical oceanographic
cruises. Additional sampling in the Strait of
Belle Isle, and along the north shore of the
Gulf where inflow would be most intense,
may be required. Cooperative work with
physical oceanographers may be required
to develop improved chemical models for
the Gulf of St. Lawrence.