Dr. Macdonald directs interdisciplinary programs to study the environmental
pathways of contaminants including their delivery, transport, and elimination
from aquatic systems. A variety of settings are studied including Arctic shelves
and basins, British Columbia fjords, the Strait of Georgia, and lakes in the
Fraser River basin. He determines the behaviour of contaminants in the context
of natural systems bringing to bear such tools as water-mass analysis, transient
and steady state tracers, stable isotope analyses (oxygen, carbon and lead), the
determination of particle fluxes and sedimentation rates, multivariate
statistics and modeling. Most of the major contaminant groups have been studied
including PAH, metals, radionuclides, organochlorines, and other synthetic
organic compounds like the nonylphenol ethoxylates. Dr. Macdonald focuses on
site-specific contaminant sources including chlor-alkali plants, pulp mills,
mine-tailing disposal and municipal outfalls, as well as broader contaminant
issues such as long-range atmospheric transport of semi-volatile contaminants to
the Arctic Ocean and Georgia Basin, and the potential impacts of oil exploration
on Canada's western Arctic shelves. Contaminants are
studied according to how they enter and leave natural water bodies and how they
impinge on natural biogeochemical cycles. Multivariate statistical techniques as
well as dated sediment cores are used to distinguish between anthropogenic
contaminants and their natural counterparts. Often, more than one anthropogenic
source contributes to contaminant loadings, in which case the same techniques
are used to work out the relative strength of each source. Insight and data
developed through these studies is incorporated into national and international
environmental assessments.
As a strong component of the strategy to study aquatic pathways, Dr. Macdonald
has also directed studies on the ocean organic carbon cycle and on processes
affecting ice, runoff and stratification in the Arctic Ocean. These two cycles -
freshwater and organic carbon - have been central to recent change in ocean
systems. Accordingly, Dr. Macdonald been leading efforts to synthesize our
knowledge of Arctic systems, their vulnerability to change and the consequences
for humans and ecosystems. Much of this work is summarized in chapters of the
forthcoming Canadian Arctic Contaminants Assessment Report (CACAR II) and the
second Arctic Monitoring and Assessment Program (AMAM) Report.
In collaboration with colleagues from the Department of Fisheries and Oceans,
other government departments and universities, Dr. Macdonald has published his
work in over 100 papers contributed to the open literature.
Dr. Macdonald originally trained in physical chemistry, switching to
oceanography as a postdoctoral fellow, where he investigated the effects of
pressure on solubility of solid-phase carbonate. He was introduced to the Arctic
during the Beaufort Sea Program in the mid-1970s, where he investigated the
distribution of low-molecular-weight hydrocarbon gases in shelf waters. Being
interested in natural biogeochemical cycles, he found it relatively easy to
incorporate contaminants in his studies, viewing them partly as signs of human
impacts on the oceans and partly as tracers of biogeochemical processes. Because
we often start our study of a contaminant long after it has been impacting our
oceans, he has been particularly interested in developing hindcast contaminant
trends. For this, dated sediment cores have a proven ability to determine dates
of contaminant entry, sources, source strength, and residence times for particle
reactive contaminants. Accordingly, Dr. Macdonald has studied contaminant
records in sediments from ocean basins, coastal regions, and B.C. interior
lakes. Along the way, sediments proved to be more than passive recorders of
contaminants. Because small animals live in the sediments and forage them for
food, the sediments often rework the original contaminant signal while, at the
same time, providing a re-entry route for the contaminant into the biosphere.
Therefore, models have been developed and applied to cores to account for this
active role they play in contaminant cycling. A natural extension of this work
has been to use ice cores from landfast ice in the Arctic Ocean, together with
stable isotope measurements, to follow river plume spreading under the ice in
the Arctic nearshore. This work has led to insights into freshwater balances on
Arctic shelves and the consequences of recent climate change.
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