The Importance of Wind Borne Dust to the Everglades

Holocene dynamics of the Florida Everglades with respect to climate, dustfall, and tropical storms

Authors:

Paul H. Glaser, Barbara C. S. Hansen, Joe J. Donovan, Thomas J. Givnish, Craig A. Stricker and John C. Volin

Abstract:

Aeolian dust is rarely considered an important source for nutrients in large peatlands, which generally develop in moist regions far from the major centers of dust production. As a result, past studies assumed that the Everglades provides a classic example of an originally oligotrophic, P-limited wetland that was subsequently degraded by anthropogenic activities. However, a multiproxy sedimentary record indicates that changes in atmospheric circulation patterns produced an abrupt shift in the hydrology and dust deposition in the Everglades over the past 4,600 y. A wet climatic period with high loadings of aeolian dust prevailed before 2800 cal BP (calibrated years before present) when vegetation typical of a deep slough dominated the principal drainage outlet of the Everglades. This dust was apparently transported from distant source areas, such as the Sahara Desert, by tropical storms according to its elemental chemistry and mineralogy. A drier climatic regime with a steep decline in dustfall persisted after 2800 cal BP maintaining sawgrass vegetation at the coring site as tree islands developed nearby (and pine forests covered adjacent uplands). The marked decline in dustfall was related to corresponding declines in sedimentary phosphorus, organic nitrogen, and organic carbon, suggesting that a close relationship existed between dustfall, primary production, and possibly, vegetation patterning before the 20th century. The climatic change after 2800 cal BP was probably produced by a shift in the Bermuda High to the southeast, shunting tropical storms to the south of Florida into the Gulf of Mexico.

Everglades Changing as Sea Level Rises

Just inland from the familiar salt-loving mangroves that line the Southern tip of the Florida Peninsula lie plant communities that depend on freshwater flowing south from Lake Okeechobee. These communities provide critical habitats to many wildlife species, and as salt water intrudes, it could spell problems for freshwater plants and animals alike.

Satellite imagery over the southeastern Everglades confirms long-term trends of mangrove expansion and sawgrass habitat loss near the shore. The trend is related to salt water intrusion caused by sea-level rise and water management practices, according to a new study published in the scientific journal Wetlands.

"I was very surprised at how well the results matched our understanding of long-term trends and field data.

Normally, we don't see such clear patterns," says Douglas Fuller, principal investigator of the study.

The findings show large patches of vegetation loss closer to the coast, approximately four kilometers from the shoreline, in and around a vegetative band of low productivity that has been shifting inland over the past 70 years. Growth trends were seen primarily in the interior, at about eight kilometers from the shore.

"Less salt-tolerant plants like the sawgrass, spike rush, and tropical hardwood hammocks are retreating. At the same time, salt-loving mangroves continue to extend inland," says Fuller, professor of Geography and Regional studies in the College of Arts and Sciences at the University of Miami.

Changes in water management, such as the implementation of the Comprehensive Everglades Restoration Plan, may help offset the possible effects caused by future salt water intrusion. "However, restoration may not suffice if sea-level rise accelerates in the coming decades," Fuller says.

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