In this project modern surface samples were collected from 26 sites in Biscayne Bay. The primary biota analyzed were 1)benthic foraminifera, 2)ostracodes, 3)mollusks, 4)dinoflagellate cysts, 5)pollen and macro-plant material. The distribution of the biota was quantified to determine relationships with environmental conditions. These reslults were used to interpret historical faunal and floral changes recorded in shallow sediment cores. Water samples, ostracode and foraminiferal shells collected from the modern sediment samples are being analyzed for trace element geochemistry to derive a calibration equation to calculate absolute salinity in down-core samples.
Shallow cores (1-2 meters) were collected along a north-south transect within Biscayne Bay for analysis of the downcore faunal and floral assemblages over the last 150 years. Quantitative down-core assemblage diagrams will be drawn up and the various faunal and floral data will be compared to look for correlated changes among the groups analyzed. Determinations of salinity, bottom conditions, nutrient supply and various other physical and chemical parameters of the environment will be made for each sample based on the fauna and flora present. Data from all cores will be integrated to search for regional patterns of change in diversity and distribution of the fauna and flora; data from Biscayne Bay will supplement and be correlated to onshore data and to data from Florida Bay. The integrated data set will be analyzed to see if detected changes in biota correlate to alterations in physical parameters and/or historic records of human-induced modifications of the environment. Living assemblages will be collected twice a year to provide data on habitat distribution, preferred substrates and seasonality of the living biota for interpretation of the down-core assemblages.
This project is one segment in a group of coordinated USGS projects examining the biota, geochronology, geochemistry, sedimentology, and hydrology of southern Florida, Florida Bay and the surrounding areas. Data are being compiled from terrestrial, marine, and freshwater environments in onshore and offshore sites in order to reconstruct the ecosystem history for the entire region over the last 150 years.
Modern biotic data are assembled from bottom grab samples; parameters such as salinity, depth, substrate, water clarity etc. are recorded for each site. Geochemical analyses are conducted on ostracode and foraminiferal shells. Historic data is assembled by analyzing the fauna and flora present in shallow cores (<2 meters) sampled at 2 centimeter intervals. Data from the core are converted into percent abundances and plots of salinity and substrate preferences assembled. Data are analyzed from cores to determine any patterns that exist, for example, significant changes in assemblages of mollusks, benthic foraminifera, and ostracodes that occur at the same depth. Determine salinity, bottom conditions, nutrient supply and any other physical or chemical parameters that might be indicated by the fauna and flora present. Obtain age estimates using lead 210 and exotic pollen.
References on modern environmental tolerances of specific biotic elements are used in interpreting the data. Data on rainfall, canal flow, construction, etc. is used to interpret possible causes of change seen in the cores. Modern fauna and flora are assumed to be a good proxy for environmental conditions over the last 150 years.
Five biotic elements are examined independently for each core before the data are compiled, thus each group serves as a cross check (quality control) on the reliability of the results seen in the other groups. Quality control is also provided by the methods of initial core selection. Several cores are collected from each site, x-rayed and visually examined for signs of bioturbation or disturbance. Lead 210 profiles are constructed and the down-core abundance of exotic pollen is examined. All of these indicators must demonstrate that the core represents relatively undisturbed sediments before the core is analyzed for the biotic components.
The primary limitation is the small sampling size constrained by the core diameter. This may not provide a representative sample for the site, particularly for the mollusks.