projects > historical changes in salinity, water quality, and vegetation in biscayne bay
Historical Changes in Salinity, Water Quality, and Vegetation in Biscayne Bay
During the last century, Biscayne Bay has been greatly affected by anthropogenic alteration of the environment through urbanization of the Miami/Dade County area, and alteration of natural flow. The sources, timing, delivery, and quality of freshwater flow into the Bay, and the shoreline and sub-aquatic vegetation have changed. Current restoration goals are attempting to restore natural flow of fresh water into Biscayne and Florida Bays and to restore the natural vegetation, but first we must address what was the environment like prior to significant human alteration in order to establish targets for restoration. This project is designed to examine the natural patterns of temporal change in salinity, water quality, vegetation, and benthic fauna in Biscayne Bay over the last 100-300 years and to examine the causes of change.
The objectives of this project are to examine in broad context the historical changes in the Biscayne Bay ecosystem at selected sites on a decadal-centennial scale, and to correlate these changes with natural events and anthropogenic alterations in the South Florida region. Specific emphasis will be placed on historical changes to 1) amount, timing, and sources of freshwater influx and the resulting effects on salinity and water quality; 2) shoreline and sub-aquatic vegetation; and 3) the relationship between sea-level change, onshore vegetation, and salinity. In addition, a detailed examination of historical seasonal salinity patterns will be derived from biochemical analyses of molluscs, ostracodes, foraminifera and corals. The corals will allow us to compare marine and estuarine trends, examine the linkage between the two systems, and will provide precise chronological control. Land management agencies (principally SFWMD, ACOE and Biscayne NP) can use the data derived from this project to establish performance criteria for restoring natural flow, and to understand the consequences of altered flow. These data can also be used to forecast potential problems as upstream changes in water delivery are made during restoration.
The first year four to eight sediment cores will be collected in Biscayne Bay from areas identified by discussions with the client agencies (SFWMD, Biscayne NP, and ACOE). Sampling and analyses of selected cores will follow methods established by the Florida Bay Ecosystem History Projects (Brewster-Wingard, USGS, GD; Orem, USGS, GD). Cores will be dated using Pb-210 geochronology and C-14 where appropriate (Holmes, USGS, GD).
Data gathered from monitoring sites (28 sites in Florida Bay have been collected 2X/year beginning with the first 15 sites in 1995) will serve as proxy data for interpreting the downcore faunal and floral remains. Additional modern data will be gathered from Biscayne Bay in cooperation with Barbara Lidz’s Chemical Pollutants and Toxic Effects on Benthic Forams, Biscayne Bay Project (USGS). A series of downcore geochemical analyses will evaluate past changes in nutrients (C,N,P,S), shell geochemistry (salinity and temperature), and stable isotopes (salinity and sources of water). The analyses of the indicator-species and the shell geochemistry work will be an extension of ongoing and completed ecosystem history work in Florida Bay that has focused on historical salinity patterns (Brewster-Wingard and others). The nutrient analysis portion of this project (scheduled to begin in year 2) will coordinate with ongoing water chemistry studies in south Florida (Orem and Krabbenhoft).
Stable isotopic data from water samples will be analyzed to determine the origin of variations in salinity in Biscayne Bay. Freshwater from precipitation, runoff and groundwater have unique O and H isotopic signatures, so the sources of freshwater influx can be traced. These data are essential in assessing the impact of water management practices on the Bay and the input of groundwater into the system. This method was developed in Florida Bay, utilizing samples collected since 1993, and will now be applied to Biscayne Bay.
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