Recent natural and anthropogenic ecosystem change to the marine environments of Biscayne Bay, Florida

Author

Christopher Paul Williams, Southern Illinois University CarbondaleFollow

Date of Award

12-2009

Degree Name

Doctor of Philosophy

Department

Geology

First Advisor

Ishman, Scott

Abstract

A series of modern sediment samples from seven sites and five sediment cores collected in central and southern Biscayne Bay were analyzed for benthic foraminifers. The goal of the research was to determine important foraminiferal assemblages in the modern environment, and use these data to assess the distributions of marine ecosystems over the past 100-400 years. Two of the cores are from localities in the mid-bay, whereas three represent near-shore sites. The latter cores were collected under the supposition that near-shore sites may be more sensitive to recent ecosystem change that may not be so readily apparent at the mid-bay sites. Seven assemblages were identified from these data that appear robust enough to be recognized at the regional level in Biscayne Bay. The assemblages identify a range of haline environments in Biscayne Bay both presently and in the recent past. None of the assemblages is typical of a continental shelf assemblage after Rose and Lidz (1977), but the conditions within Biscayne Bay include assemblages indicative of polyhaline-euhaline restricted circulation environments and mesohaline brackish environments. The near-shore cores reveal a pattern of assemblages indicative of increasing salinity. There is clearly a natural component of the ongoing Holocene marine transgression. However, there are key data which show sudden increases in salinity via rapid changes to the benthic foraminiferal assemblages. At Middle Key, salinity increases at the time of construction of the Key West Extension of the Florida East Coast Railway. Increased marine species at the top of the core corroborate the findings of Ishman et al. (1998) from a core in Manatee Bay. The foraminiferal assemblages near the top of the cores at Black Point North and at Chicken Key show a shift toward higher salinity conditions. Ostracode and mollusk data in Wingard et al. (2004) reveal an increase of genera that are tolerant of wide ranges of salinity. This manner of salinity fluctuations is not correlative to any patterns observed historically in any of the cores from Biscayne Bay. Recent changes to the marine ecosystems in Biscayne Bay reflect both natural and anthropogenic changes. It is necessary to determine appropriate restoration of natural sheet and groundwater flows to Biscayne Bay as part of the ongoing Everglades restoration to reduce the high stress of salinity fluctuations that are a recent alteration to the natural ecosystems in Biscayne Bay.