Wetland response to natural and anthropogenic forcing in the Everglades, United States, and Nile Delta, Egypt
This dissertation uses state-of-the-art palynological analysis, quantitative paleoenvironmental analysis (modern analog technique, detrended correspondence analysis, and cluster analysis) and geochronology ( 14C, 210Pb, and biostratigraphy) on wetland sediments from the ridge, slough and tree island landscape of the Florida Everglades, USA, and sedimentary sequences of the Nile Delta, Egypt. Extended periods of aridity during the Holocene affect the vegetational composition of both wetland plant communities. The changes in regional rainfall are driven by the mean position of the Intertropical Convergence Zone. Tree island initiation/expansion, sawgrass ridge initiation/expansion, and community variation in the delta is centered on global climate events at 5,000, 4,200, 2,800, and 1,000 (Medieval Warm Period), and 400 (Little Ice Age) years cal BP. The changes in vegetation are linked to the same climate events but the vegetation response within and between sites are not simultaneous. Tree islands responded to periods of aridity ∼2,800 years cal BP and sawgrass ridges did not respond until an aridity event ∼1,000 years cal BP. Delta vegetation responded to various aridity events around 6,000, 5,000, 4,200, 3,200 years cal BP.^ Both the Everglades and the Nile Delta experienced thousands of years of land use pressure, however the greatest changes in vegetation occurred during the 20th century. Pollen assemblages from ridge and tree island sites reflect the extended decrease in hydroperiod associated with water management. In the Nile Delta, after the closure of the Aswan High Dam there us a change in the dominant vegetation from brackish marsh to fresh water marsh.^ The response of vegetation in the Everglades and the Nile Delta to periods of global aridity also corresponds to well-documented cultural transitions. The expansion of tree islands coincides approximately with the change from the Archaic to the Glades Native American cultures (∼2,500 years cal BP). In the Nile Delta, the response of vegetation to the catastrophic failure in Nile flow, ∼4,200 years cal BP, occurs during a period of major shift in Middle Eastern cultures. ^
Christopher E Bernhardt,
"Wetland response to natural and anthropogenic forcing in the Everglades, United States, and Nile Delta, Egypt"
(January 1, 2009).
Dissertations available from ProQuest.