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Topic #1: Estuarys
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Jean-Francoise Hamel and Annie Mercer."Cold-water Riches."Sea Frontiers October 1994: pp.26-31. The progressive mixing of sea water with a partially enclosed body of fresh water constitutes the definition of an estuary, which can also be characterized by its typical circulation and ecosystem. The down-stream portion of the St. Lawrence river offers one of the finest examples of an estuary. Making its way through the Quebec province for more than 300 miles and draining a territory of more than 258,000 square miles, the St Lawrence estuary's huge proportions have earned it the title of the largest estuary on the planet. Its shores often lose sight of each other, as they can be separated by as much as 30 miles of foggy blue. Its most intimate secrets lay 1,000 feet below the surface. Seasonal gyres and strong currents also constitute important features of this very complex hydrologic system. As the snow melts in early spring, the waters of numerous tributaries rush into the St. Lawrence with their load of terrigenous sediments. After the flood, the estuary becomes stratified with a warm, lighter layer near the surface and a denser, colder layer below. The surface layer, rich in nutrients supplied by the spring thaw and the winter mixing, becomes the site of intense primary production, as algae cells, mostly diatoms, intensify their photosynthetic activity and multiply. Before the end of summer, the nutrients at the base of this frantic activity become depleted in the isolated upper water layer, and the productivity slows down. In some areas, particular wind motions along the coast create upwelling zones, where colder and richer water is brought to the surface, supplying the primary elements to maintain the bloom. The variable conditions of salinity, temperatures, and nutrient availability found over an estuarine system demand particular adaptations from organisms that want to survive in this environment will dominate in a certain habitat or during a certain time of the year. The crowded shores of the St. Lawrence are a promising prelude to its mysterious underwater treasures. Expecting the turbid greenish water to conceal an equally dull marine life would be a mistake. The sea floor flourishes with sparkling colors, bright enough to make a coral reef turn pale with envy. Even if the water temperature oscillates around 32 degrees Fahrenheit at 30 feet, soft corals are abundant and their fragile pink silhouettes decorate the beds of brown algae. Once in a while the flexible arms of the brittlestar emerge from the edge of a boulder, and when we lift its refuge, the delicate animal immediately slides toward another. Almost every inch of the rocky substrate is covered with encrusting algae, growing larvae, and sessile organisms like sponges, and tunicates. Unfortunately, the fragile ecosystems revealed during our expedition face a growing danger from over-fishing and pollution. The St. Lawrence River and its estuary represent one of the most-traveled maritime routes in North America, exceeding the combined traffic of the Panama and Suez canals. More than 19,000 commercial vessels, carrying more than 111 million tons of merchandise, and close to 7,000 fishermen roam the territory each year. Many boats carry toxic products such as pesticides and petroleum, and more than 200 spills were recorded during the last decade. Healthy and flourishing, the St. Lawrence estuary has much to offer and must be protected.
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