Environment
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Estuaries
What many people refer to as a river on PEI is really an estuary. In an esturay, fresh water from a stream mixes with salt water from the ocean. Estuaries generally become more salty (or saline) as they approach the ocean.
All Island estuaries are different, even those that are located in the same general area. Some of the main differences include the following:
Size: Some estuaries are deep and wide, while others are shallow and narrow
Tidal range: Some Island estuaries have a much larger tidal range (the difference in height between high and low tides) than others. Estuaries located on the south (Northumberland Strait) shore of PEI have tidal ranges of almost 3 metres (10 feet). On the north (Gulf of St. Lawrence) shore, the tidal range is much smaller (about 1 metre or just over 3 feet). Some north side estuaries, located inside a large bay, have even smaller tidal ranges because of their distance from the open ocean.
Salinity: Some Island estuaries are very salty or saline. Others are predominantly fresh water. In the larger, deeper estuaries, there can be a layering (or stratification) of salinities. Heavy, relatively unmixed, salt water occurs near the bottom and lighter, more mixed water, occurs near the surface. Highly stratified estruaries can sometimes have water quality issues.
Flushing Time: Although we often think of an estuary as being an open system -- what flows in is taken right out by the tide -- this is generally not the case. The time that the fresh water stays in an estuary before it is flushed out can vary greatly. Some estuaries, or portions of estuaries, can have flushing times of only a few days. For others, it can be weeks or even months. The differences are due to the amount of fresh water entering the system, the size of the estuary, the size of the tidal range, and the location in the estuary.
Water quality problems in estuaries can be complex. Identifying the cause of poor water quality and potential solutions is best done by an oceanographer or someone who can look at tides and currents and at the physical structure of an estuary.
