The ecological situation of St. John’s Harbour has been a contentious issue in the city and province for many years. Physical oceanographers from Memorial have waded in and developed some pertinent insights.

St. John’s Harbour is a place where human activity and the marine ecosystem meet. A major factor in assessing the human impact on the harbour is how quickly water circulates into and out of the Narrows, the entrance to St. John’s Harbour.

A research team, consisting of Dr. Don Deibel and Dr. Ray Thompson from the Ocean Sciences Centre, and Dr. Len Zedel and Dr. Brad de Young from the Department of Physical Oceanography, investigated how this circulation actually works. Financial support came from Environment Canada via the Atlantic Coastal Action Plan.

“Basically, we were looking at the exchange of water in the harbour, trying to understand how water moved through the Narrows, and what the ecological implications were for this.” commented Dr. de Young. “(Local municipalities) dump biological materials that use up oxygen in the water. If that water is not replenished, then bottom water in the harbour could become anoxic.”

Such anoxic water is depleted of oxygen, and thus damages the ecosystem. However, according to Dr. de Young, “This does not seem to be happening.”

What they found, surprisingly, was that a powerful cycle of circulation effectively replaces the harbour’s water. “The good news here is that the exchange rate is reasonably substantial,” said Dr. de Young. “The timescale for the exchange of water is roughly five to 10 days, which is not long.”

The work of Dr. de Young and his colleagues is an excellent example of science in action. It involved postulating hypotheses, disproving them, then attempting new theoretical solutions and creating new approaches to test them. The researchers combined techniques from physics, oceanography, and biology to establish a multidisciplinary perspective on a practical problem in human-environment interaction.

Their first experiments showed their initial hypothesis on the circulatory regime in the harbour to be too simplistic. “In 1999, we put a single current meter in the Narrows. The harbour is kidney-shaped with a narrow channel entrance that is about 800 metres long and 200 metres across. We got some information, but discovered that the channel was more complex than we had thought originally,” Dr. de Young said. They had to devise a new method to unravel the complexities of the harbour’s circulatory system. “The following year, we put five current meters across the Narrows, a couple of hundred feet apart. With these data in hand we were able to look at the exchange in and out of the harbour.”

Two patterns can be discerned in the team’s data. “The exchange in the harbour is not solely regulated by the tides and the winds in the harbour. You expect the tides to be important — they slosh back and forth, moving a volume of water equivalent to the surface area of the harbour times the range of the tide, roughly twice a day. This you would expect to see.