Friday, December 17, 2010

Is the Suwannee Sound an Estuary?

An Estuary - NOAA image
I recall first learning that an estuary is “an arm of the sea.” Later the definition expanded to include “a drowned river mouth.” Still later, more technical definitions cited the characteristic prolonged mixing of fresh- and sea-waters and the input of nutrients carried by fresh waters flowing down from the land. The resulting abundance of nutrients has wide-ranging effects, and estuaries vie with grasslands and rainforests as the world’s most productive ecosystems.

The Suwannee River bight poses some problems for purists. Although the old river mouth clearly has been drowned by relatively recent (in geologic terms) rises in sea level, in no simple respect can the zone in which its mixing of fresh and salt water be described as “an arm of the sea.” It is closed on only one side by land and on the other side it is open to the Gulf of Mexico. This region where the waters of the Suwannee mix with the ocean waters of the Gulf of Mexico bears little superficial resemblance to the Chesapeake Bay, San Francisco Bay, or other familiar estuaries where the river mouth is closed in on two sides. Flowing over the relatively shallow waters of the Florida platform, however, the fresh water discharged by the Suwannee mixes only gradually with the sea water of the Gulf and occasionally overwhelms it. From the mouth of the present-day Suwannee to the Cedar Keys and beyond, the brackish waters of this mixing zone are rich in nutrients. They are highly productive both of sea life and the shore-based life dependent on it. Archaeologists believe that the Native Americans inhabiting the area in prehistoric times fed almost exclusively on foods from these waters, and they are estimated to have been at least three times as abundant as the region’s current human population.
USGS Map Showing the Suwannee Estuary

Should one call it “the Suwannee Estuary?” Why not, because how else to best describe it? The USGS describes it as an estuary and shows it in dark blue on the adjacent map (click to enlarge).

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