Debra A Willard, Ph.D.

We present paleoclimatic evidence for a series of Holocene millennial-scale cool intervals in eastern North America that occurred every ???1400 years and lasted ???300-500 years, based on pollen data from Chesapeake Bay in the mid-Atlantic region of the United States. The cool events are indicated by significant decreases in pine pollen, which we interpret as representing decreases in...

The Comprehensive Everglades Restoration Plan (CERP) lists restoration of the timing, quantity, and quality of the natural flow of freshwater as one its primary goals. Before restoration can occur, however, the baseline conditions of the environment prior to significant human alteration must be established and the range of variation within the natural system must be determined. In...

Tree islands are important centers of biodiversity in the Florida Everglades; they have two to three times the plant and animal diversity of the surrounding wetlands. This high diversity is due primarily to their higher elevation relative to the adjacent wetlands (fig. 1). In the natural Everglades system, water levels fluctuated seasonally with rainfall, and tree islands were the only...

An illustrated, descriptive atlas of pollen and spores from wetland plants of the Florida Everglades was compiled to facilitate identification of dispersed palynomorphs in sediments. The atlas includes 121 wetland species characteristic of eleven plant associations of the Florida Everglades including sloughs, sawgrass marshes, tree islands, wet prairies, cypress domes, mangrove forests...

During the twentieth century, the natural landscape of the Florida peninsula was transformed extensively by agriculture, urbanization, and the diversion of surface water features. The purpose of this paper is to present a numerical modeling study in which the possible impacts of this transformation on the warm season climate of the region were investigated. For three separate July–August...

We present pollen evidence documenting the response of sawgrass ridge and slough systems of the Florida Everglades to hydrologic changes during the last 3,500 years. Sediment cores and surface samples were collected in three transects across sawgrass ridges and sloughs in Water Conservation Area 3A to determine the age of the features, long-term variability in plant community composition

Until recently, the timing and cause of tree island formation have been poorly understood, with estimates of initial tree-island development as early as thousands of years ago to as recently as the last few decades. To increase our knowledge about the origins of these features, sediment cores were collected on and around tree islands. These cores were dated using radioisotopic techniques

During the last century, the environs of Biscayne Bay have been greatly affected by anthropogenic alteration through urbanization of the Miami/Dade County area. The sources, timing, delivery, and quality of freshwater flow into the Bay have been changed by construction of a complex canal system that controls movement of water throughout south Florida. Changes in shoreline and sub-aquatic

Palaeoclimate records from late-Holocene sediments in Chesapeake Bay, the largest estuary in the USA, provide evidence that both decadal to centennial climate variability and European colonization had severe impacts on the watershed and estuary. Using pollen and dinoflagellate cysts as proxies for mid-Atlantic regional precipitation, estuarine salinity and dissolved oxygen (DO) during...

We present paleoclimate evidence for rapid ( 100 years) shifts of ~2-4oC in Chesapeake Bay (CB) temperature ~2100, 1600, 950, 650, 400 and 150 years before present (years BP) reconstructed from magnesium/calcium (Mg/Ca) paleothermometry. These include large temperature excursions during the Little Ice Age (~1400-1900 AD) and the Medieval Warm Period (~800-1300 AD) possibly related to...

Palynological and geochemical analyses of sediment cores collected on two tree islands in the Florida Everglades indicate long-term hydrologic and chemical differences between tree islands and surrounding marshes and sloughs. Gumbo Limbo and Nuthouse tree islands are elongate, teardrop-shaped islands in Water Conservation Area 3B. Prior to tree island formation at both sites, pollen...

The Chesapeake Bay is the Nation's largest estuary and historically supported one of the most productive fisheries in the world. In addition to supporting aquatic communities and wildlife, the bay's watershed serves the economic and recreational needs of 15 million people. The fertile soils of the watershed support significant agricultural production. Unfortunately, the commercial...