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Coastal Lagoons
| Article
# : |
18057 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
5 / 1990 |
2,057 Words |
| Author
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Bjorn Kjerfve
Bjorn Kjerfve is professor of marine and geological sciences
at the University of South Carolina in Columbia, and visiting
professor in geochemistry at Universidad Federal Fluminnese in
Niteroi, RJ, Brazil. He is an oceanographer interested in
transport processes in lagoon and estuaries. |
A black gondola glides quietly along a canal whose shimmering waters reflect medieval palaces. This idyllic image of Venice is being threatened, however, by the inexorable processes of nature.
The high winds and tides from the Adriatic Sea spill sea water regularly into the Venice lagoon, flooding city streets three dozen times per year. Within another generation, this historic city, which exists within the confines of a coastal lagoon with an average water depth of only two feet, could become entirely inundated.
Three sets of 800-foot-long floodgates are being constructed to regulate water exchange between the lagoon and the Adriatic. Although the floodgates will help to limit inundation, they are also likely worsen water quality and increase siltation of shipping channels in this most famous of coastal lagoons.
The reasons for Venice's flooding are well known. It is due to a combination of processes, including global sea level rise, wind and tide-induced high waters, and land subsidence resulting from the pumping of groundwater for industrial uses.
Poorly Understood Neighbors
This situation is, however, not unique to Venice. All coastal areas are subject in varying degrees to the same environmental processes. Unfortunately, biological, chemical, geological, and physical processes for lagoon environments are neither well known nor comprehensively understood, which becomes a problem when managing and developing lagoon resources. Management plans for lagoons are often formulated based on how estuaries function, because estuarine processes are reasonably well understood. Coastal lagoons, on the other hand, react very differently to hydrological, meteorological, and tidal driving forces that do estuaries. Also, they often do not respond the same way ecologically to natural and anthropogenic inputs of sediment, nutrients, and pollutants.
Coastal lagoons are inland marine water bodies that formed as sea level rose in response to climatic warming between 5,000 and 16,000 years ago. The huge rise in sea level caused complete reshaping of shorelines globally. Many low-lying coastal areas became inundated by a thin cover of seawater and eventually separated from the ocean as ridges of sand deposits formed by the action of wages and winds. As these barrier ridges were breached in one or more places, often during hurricanes, coastal lagoons
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