Recent rapid ecological change in Florida Bay is widely believed to result from long-term changes in water quality, particularly salinity and nutrients, that have been influenced by onshore flood control and drainage projects completed during the last century. Overlooked, however, is the natural rise of sea level (30 cm since 1850) and the increased depth of Florida Bay. Because sediment production rates are insufficient to compensate for the added volume of the bay, more marine water covers the bay than did a century ago. Therefore, even if the same amount of freshwater had been delivered to Florida Bay, salinity would have increased simply because there is more marine water to dilute.

Florida Bay is a shallow lagoon subdivided by mudbanks into several dozen subbasins, that vary from nearly normal marine to estuarine. Poorly documented transport processes erode fine-grained sediment from subbasins and leave many sediment starved (floored by exposed Pleistocene limestone). Mudbanks are eroding on their northern and eastern slopes, probably in response to winter storms. Newly produced, as well as older, eroded sediment preferentially accumulates in the lee and on top of mudbanks at rates as great as 1-4 cm/yr, as indicated by 210Pb and 222Ra analyses. These observations suggest the elevations of banktops are maintained during sea-level rise by a balance of erosion and deposition resulting in overall buildup and migration. Mudbank segmentation and restriction of the bay have outpaced sea-level rise and have allowed subbasins to remain highly variable in water quality. Thus, two natural processes, sea-level rise and sedimentation, require evaluation in order to understand ecosystem-scale change in Florida Bay and to plan related onshore restoration activities.

(This abstract was taken from the Florida Bay Science Conference Proceedings, 1995)

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