The Prince Edward Island Department of Environment, Energy, and Forestry is reporting that anoxic events have been reported in several Island estuaries over the last week. Reports of milky-white or cloudy-greenish discolorations and strong “rotten-egg” odors have been received from areas such as Wheatley River, Hunter River (River Clyde), Anderson’s Creek (New London Bay), French River, Granville River, Found’s Creek, Covehead Bay, Brackley Bay, Montague River, Cardigan River, Mill River and Montrose River. These events were discovered and reported either by members of the community or by staff of the Department of Fisheries, Aquaculture and Rural Development and the Department of Environment, Energy and Forestry.
Anoxia occurs as a result of the decay process of large amounts of plant material (phytoplankton or algae) in the water. Excessive plant growth is the result of enrichment (typically with nitrogen and phosphorus) of the water of the estuary. The events are also associated with the depletion of oxygen (hypoxia, low oxygen or anoxia, no oxygen) from the water column as a result of the decay process. The lack of oxygen can also lead to the death of fish and shellfish at the area in question.
“The presence of increased nitrates in our ground water and our surface water is something our government has committed itself to addressing. With improved nutrient management and with guidance from studies like the report of the Commission on Nitrates in Groundwater, we can gradually improve water quality so that these anoxic events become less common,” said George Webster, Minister of Environment, Energy and Forestry.
Increased nutrients in the estuary come from human activities in the watershed. North shore estuaries are more susceptible to these conditions than south shore estuaries as a result of the naturally low tidal ranges on the north shore.
“Sea lettuce in particular loves nitrogen and grows rapidly in these estuaries,” said Cindy Crane, surface water biologist with the Department of Environment, Energy and Forestry. “What happens is that it gets to a point that the mats of sea lettuce are so thick that plants further down are deprived of light and they start to die. When these plants decay, that just strips the oxygen out of the water and the whole system can collapse very quickly.”
Fish, including eels, mummichogs, sticklebacks and flat fish have been reported dead in both the Wheatley and Cardigan Rivers at this time. Anoxic events are known to last from several days or a week or more depending on weather conditions and prevailing tides.
The public can report the observation of anoxic conditions to the Department of Environment, Energy and Forestry at 368-5000.