Estuaries

ESTUARIES occur where rivers empty into the sea. They are transition zones between the fresh water of RIVERS and the salt water of the ocean. Like all transition ecosystems, they are places of tremendous BIODIVERSITY. Nutrients wash down the river to mix with and enrich the near-shore marine environment. Estuaries are among the richest, most productive, most diverse ecosystems on earth. But they are also among the most endangered: just as sediments and nutrients flow downstream, so do pollutants from industrial, agricultural and settlement activities. Estuaries not only bear the brunt of human waste and contamination, they often suffer physical alteration from diking and industrial and settlement developments.

Estuaries perform a number of ecological functions. A variety of habitat types are found in and around estuaries, including shallow open waters, freshwater and salt marshes, sandy beaches, mud and sand flats, rocky shores, OYSTER reefs, river deltas, tidal pools, SEAGRASS and KELP beds, and wooded swamps. The WETLANDS adjacent to many estuaries filter out sediments, nutrients and pollutants. Because of the richness of life in estuaries—from myriad microscopic organisms to many types of large specialized plants and animals—they provide permanent and seasonal habitat for numerous plants, animals and fish. They provide critical staging and nesting habitat for hundreds of thousands of migratory birds and waterfowl. Their often sheltered tidal waters are safe places for spawning fish and shellfish; in this way they are regarded as nursery grounds. The seaward boundaries of estuaries—whether reefs, barrier islands or fingers of land, mud or sand—help to diminish the full brunt of the ocean's force and act as buffers against storm surges.

Estuaries also provide important economic and cultural benefits. Most commercial species of fish and shellfish either have their beginnings in estuaries or are nurtured in one at some point (see FISHING, COMMERCIAL). Estuaries of large sediment-laden rivers like the FRASER R are major places of deposition where extensive areas of rich AGRICULTURAL lands build up. Harbours and ports are often built on estuaries, and they provide a wealth of TOURISM and recreation opportunities.

Estuaries are found along less than 3% of BC's 7,000-km-long indented, island-dotted coastline, yet they are used by about 80% of all coastal wildlife.
by Maggie Paquet