SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

concluded that essentially all of the organic
matter in upper St. Lawrence Estuary
sediments was from terrestrial sources.
Another study, which measured the concentrations
of organic matter and the ratios
of carbon to nitrogen in the organic matter,
challenged this conclusion on the basis of
the sedimentary carbon/nitrogen ratios.
These researchers calculated that terrestrial
material accounted only for 3-50% of the
organic material.
The resolution of this controversy
became one of the goals of a project
designed to monitor the organic carbon in
the St. Lawrence River discharge. Twice
monthly samples were collected from the
River for more than four years. The results
of this combined study, which measured
both carbon isotope and carbon/nitrogen
ratios, showed that there are pronounced
seasonal variations in both sources and
quantity of the organic matter in the River.
Through most of the year, terrestrial matter
dominates the river input, but there are
important contributions from organic
matter produced in the river at some times
of year. The organic matter in upper
Estuary sediments is mostly terrestrial
material. These results made an important
contribution to an understanding of the
fluxes of organic carbon into the Gulf. The
design of this program reflected an increasing
awareness that careful measurements of
the chemical inputs to estuaries is essential
to the understanding of geochemical cycles
in nearshore waters.
Trace Metal Geochemistry
The study of trace metals in estuaries has
undergone radical changes in the last 20
years. These changes include advances in
analytical methods for measuring trace
metals in both dissolved and particulate
phases and the development of sample
collection, storage and preservation techniques
necessary to avoid the contamination
of samples. Because the concentrations
of many trace metals are very low in
seawater, it is difficult to collect a sample
whose metal concentrations have not been
significantly changed by airborne metal
particles from the research ship, by exposure
to metal components of the sampling
equipment or even by exposure to plastics
whose manufacture requires the use of
metal compounds.
Trace metal geochemists at BIO were
among the first to recognize the importance
of estuarine processes in controlling fluxes
of trace metals across the continental
shelves to the deep ocean. As in the organic
carbon studies, this recognition led to a
concentration of effort on the St. Lawrence
Estuary and the Saguenay Fjord and to the
detailed description of river inputs and
their seasonal cycles. Furthermore, these
workers realized that the Gulf system, with
its restricted connections with the Atlantic
and the large distances between its principal
inlets and outlets, could serve as an
excellent setting in which to measure the
transports of materials through the coastal
zone into the open ocean. At about the
same time, calculations of water fluxes
through Cabot Strait became available.
Chemical oceanographers combined this
physical oceanographic information with
their chemical expertise to construct a
global model predicting the residence times
of trace metals in the world’s oceans.
Similar approaches have also been used in
the construction of budgets for organic
matter, nutrients, and suspended matter for
the Gulf of St. Lawrence. Geochemical
budgets compare the inputs of a chemical
to an area like the Gulf of St. Lawrence
with its outputs. If the inputs to an area
exceed the outputs, there must be processes
active within the region that cause the loss;
conversely, if outputs exceed inputs,
processes with the region must be producing
the chemical.
Mercury Pollution in the Saguenay
Fjord
The history of studies on mercury pollution
in the Saguenay Fjord provides both an
example of how basic research is important
in the resolution of environmental problems
and an illustration of how advances in
a number of fields may be required to
reach correct answers. As part of a study
on the trace metals in the sediments of the
Gulf system, abnormally high levels of
mercury in the sediments of the Saguenay
Fjord were discovered. An examination of
the distribution of mercury in the region
suggested that a chlor-alkali plant on the
Saguenay River was the source of most of
this pollution.
An increasing awareness that a number
of Canadian water bodies were contaminated
with mercury led to government
regulations on discharges from chlor-alkali
plants in 1971. Post-regulation concerns
included questions of whether industry was
complying with the discharge regulations
and how quickly and to what extent
affected water systems might recover. A
budget was developed for mercury inputs
which predicted that the water in the
Saguenay system would recover from the
mercury pollution in as short a period as
two years, whereas Saguenay sediments
would require much longer periods to be
free of contamination. The balancing of
this budget required a surprisingly large
flux of mercury through the Saguenay in
1973, two years after the regulations were
imposed. This result suggested either that
industry had not complied with the discharge
limits or that mercury was being rereleased
from sediments contaminated
prior to 1971.
Concurrent with this work, another
group at BIO was actively investigating the
history of sediment deposition in the
Saguenay Fjord. Once again analytical
method development was an important
part of this program. Lead-210 is a
naturally occurring radioactive isotope of
lead that is produced in the atmosphere,
from which it is scavenged and transported
into freshwater and coastal sediments. It
was first realized in the early 1970’s that
lead-210 could be used to date sediment
cores from some coastal environments. It
was further realized that the sediments at
the head of the Saguenay Fjord were ideal
for this technique. Simultaneous determination
of the age of sediments and the
mercury concentration in sediment cores
showed that the mercury contamination
began at the same time as the start-up of
the chlor-alkali plant, and that mercury
inputs to the sediments decreased dramatically
at the depth in the cores deposited in
1971. These results were consistent with
industry complying with government
regulations. This and later work showed
that the high mercury fluxes in the budget
for 1973 were due to remobilization of
mercury from sediments in the Saguenay
River that had been accumulated prior to
1971.
Petroleum Hydrocarbon Geochemistry
A number of major oil spills which
occurred in the late 1960’s and early
1970’s, including the grounding of the
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