Cronin, Thomas N., Holmes, Charles W., Dwyer, Gary (Duke University)
The next step is to complete the calibration of the Chione biochemistry to water chemistry. Field and laboratory growth experiments are being conducted on Chione for two purposes: 1) to have animals grown under documented conditions for calibrating water chemistry to shell chemistry; and 2) to determine whether the animal only adds shell material at certain times of the year or under certain environmental conditions. The information on animal growth patterns will allow placement of the water chemistry data obtained from individual growth layers into the proper temporal context.
Once calibration is complete, Chione will be extracted from radiometrically dated cores collected at strategic sites in Florida Bay. Molluscan shell chemistry and ostracode shell chemistry data from the cores will be compared to the monthly rainfall records in the early 20th century (available from NOAA) to determine the salinity ranges expected following given monthly rainfalls for specific sites prior to significant alteration of natural flow patterns. Stable isotope ratios and the variability in salinity from site to site will be used to differentiate sources of freshwater input.
Ostracodes molt as they proceed through various growth stages throughout the year. The adult test represents an essentially instantaneous secretion recording the salinity and temperature at that point in time. The Ca/Mg will be determined for ostracode tests by direct current plasma atomic emission spectrophotometry (DCP). The ostracode Loxoconcha matagordensis grows adult carapaces largely in the late spring and early summer (primarily June). These specimens therefore record the salinity at the typical onset of the rainy season. The timing of the onset of the rainy season and the extent of the initial drop in salinity are excellent indicators of the climatic patterns for the entire year (particularly in determining an El Nino or La Nina event).
In FY03 completion of the calibration of Mg/Ca in Chione shells to the salinity of the water will be done by conducting additional analyses on multiple specimens grown under the same water conditions, including paired valves from a single individual. These data will be used to calculate confidence levels on interpretations of salinity based on shell chemistry. The analyses will include specimens collected in the field in August of FY02; some of these specimens have been in the habitats since winter of 2001. The location of the habitats in close proximity to a water monitoring station will allow reconstruction of the water chemistry for that site. The data from the water monitoring station will be compared to project analyses of the shell layers added since winter of 2001. The results of this comparison will allow calibration of shell chemistry to water chemistry and provide a picture of what seasonal variations will look like in the shell record, a critical piece of down-core analyses). Multiple shells from the controlled salinity and temperature tanks in the lab also will be analyzed. These data will provide the ability to distinguish the role of salinity versus temperature in controlling the Mg/Ca ratio, and will allow calculation of confidence levels associated with salinity and temperature values based on shell chemistry.
Analyses of stable isotopes of oxygen and carbon will begin in FY03. Once calibration tests on Chione are successfully completed, experimention will begin with other molluscan species. Chione have not been found alive in modern Florida Bay in the northern transition zone (although they are present in cores), so we want to identify a good indicator species for the critical northern transitional zone. Also, Mercenaria and Periglypta, both in the family Veneridae like Chione, may be examined for their utility in monitoring the more open marine and reef environments.
In order to determine natural growth rates and species responses to environmental stressors and seasonal variations, Chione have been placed in habitats in Florida Bay near working water-monitoring stations beginning in January 2001. The in-situ variables of salinity, temperature, rainfall, etc. can be documented using the data from the water monitoring stations and our instrumentation. The habitats are periodically pulled and the animals digitally photographed to document growth. Dead specimens are removed and replaced with live individuals. Both living and dead specimens that show growth are periodically removed and are used in the calibration tests. These experiments will continue in FY03, and throughout the length of the project to gather data on the life span, reproductive patterns, and environmental factors that affect these animals. In FY03, additional species of molluscs may be added to begin the process of identifying other indicator species. By continuing these experiments over a period of years, data can be captured on seasonal changes and how the organism records these data biochemically within its shell. These data will allow umore accurate interpretion of the patterns seen in the shells and ultimately the downcore data.
In order to monitor change on a weekly basis, and to establish controlled water conditions in which to test the organism’s response to specific environmental variables, a series of tanks have been set up in the laboratory in Reston. The main growth tanks are kept at normal marine salinities and duplicate the in-situ habitats of Florida Bay as close as possible. These tanks act as a control and provide data for comparison against seasonal variation in growth seen in the habitats in Florida Bay. The water chemistry within all the tanks is monitored for multiple factors including; salinity, temperature, nitrate level, dissolved oxygen, ORP, etc. Additional experimental tanks have been set up to isolate the effects of a single variable on shell accretion and the resulting biochemical signature. An experiment begun in FY02 is monitoring growth under different salinities (15, 25, 35 and 45 ppt) and different temperatures (15, 25, 35 degrees C). These experiments will continue in FY03 with additional variables and species being tested. These tanks will also be "pulsed" with micronutrients such as strontium and magnesium to create a dated marker in the shell layers.
In FY03 we will attempt to design laboratory and/or field experiments to test the relationship between the stable isotopic signature in the shell (especially Carbon) and the isotopic composition of the water.
Influx of freshwater from the terrestrial Everglades into eastern Florida Bay plays a significant role in controlling salinity, along with direct rainfall (McIvor, 1994). Salinity surveys indicate a discrete freshwater plume moves southward from Taylor Slough into the basin south of Little Madeira Bay during periods of high flow. Cores from Dragover Bank and Russell Bank should provide data to document historical seasonal changes in salinity and freshwater supply to eastern Florida Bay. Areas of central Florida Bay have experienced hypersaline conditions since at least the 1980’s. These basins fall within the 'flow shadow', receiving little terrestrial influx of freshwater and little marine influx as well. Precipitation and evaporation are the dominant factors affecting salinity in this portion of the Bay. A critical question for restoration is whether these episodes of hypersalinity are a result of water management practices, or whether they are a natural phenomenon. Cores from Whipray Basin and Rankin Basin have been collected and standard faunal abundance analyses have been conducted. The preliminary indications are that Rankin Basin received significantly more freshwater influx in the past. This task will utilize biochemical analyses of molluscs and ostracodes to determine the seasonality of salinity changes and the sources of freshwater influx from the period prior to alteration of natural flow through the present, in order to provide managers and modelers with the necessary data for restoration targets and performance measures.
Cores from Dragover Bank, Russell Bank, Whipray Basin and Rankin Bight have been collected, processed, and sorted for standard faunal analyses. Specimens of Chione cancellata have been selected for sectioning and analysis. Work in FY03 will focus on analyzing these specimens for metal-calcium ratios (salinity) and stable isotopes (water sources). If additional molluscan species have been identified, these also will be analyzed. These data will be compiled with data on ostracode shell chemical analyses for verification and calibration of the salinity curves obtained from the molluscs.
Ostracodes molt as they proceed through various growth stages throughout the year. The adult test represents an essentially instantaneous secretion recording the salinity and temperature at that point in time. The Ca/Mg will be determined for ostracode tests by direct current plasma atomic emission spectrophotometry (DCP). The ostracode Loxoconcha matagordensis grows adult carapaces largely in the late spring and early summer (primarily June). These specimens therefore record the salinity at the typical onset of the rainy season. The timing onset of the rainy season and the extent of the initial drop in salinity are excellent indicators of the climatic patterns for the entire year (particularly in determining an El Niño or La Niña event). Ostracode analyses on the cores will be completed in FY02 and the data compiled with the molluscan data.
Molluscan and ostracode biochemical data will be plotted and compared to general downcore assemblage analyses already completed on three of the cores to look for patterns of change in seasonal, annual and decadal scale trends in salinity and sources of freshwater input over the last 100-200 years at these sites within Florida Bay. A comparison of the results from eastern and central Florida Bay will highlight any geographic variations in salinity and freshwater influx that existed prior to drainage alteration and allow comparison to the present day situation. By comparing these data to early 20th century rainfall records (available from NOAA), a determination can be made of what salinity ranges were following a given period of monthly rainfall, prior to significant alteration of natural flow.
1. Calibration of molluscan shell chemistry to water chemistry Calibration of Mg/Ca in Chione shells to the salinity of the water will continue in FY04 by conducting additional analyses on multiple specimens grown under the same water conditions, including paired valves from a single individual. These data will be used to calculate confidence levels on our interpretations of salinity based on shell chemistry. The analyses will include specimens collected in the field in August of FY02; some of these specimens have been in the habitats since winter of 2001. The location of the habitats in close proximity to a water monitoring station will allow us to reconstruct the water chemistry for that site. The data from the water monitoring station will be compared to our analyses of the shell layers added since winter of 2001. The results of this comparison will allow us to calibrate shell chemistry to water chemistry and provide us with a picture of what seasonal variations will look like in the shell record, a critical piece of our down-core analyses. Multiple shells from our controlled salinity and temperature tanks in the lab also are being analyzed. Analyses of the water samples will begin in FY04 using ICPMS. These data will provide us with the ability to distinguish the role of salinity versus temperature in controlling the Mg/Ca ratio, and will allow us to calculate confidence levels associated with salinity and temperature values based on shell chemistry.
Analyses of stable isotopes of oxygen and carbon will begin in FY04 and will be closely linked to work conducted on the Historical Changes in Salinity, Water Quality and Vegetation in Biscayne Bay Project. Once calibration tests on Chione are successfully completed, we will begin to experiment with other molluscan species. Chione have not been found alive in modern Florida Bay in the northern transition zone (although they are present in cores), so we want to identify a good indicator species for the critical northern transitional zone. Also, Mercenaria and Periglypta, both in the family Veneridae like Chione, may be examined for their utility in monitoring the more open marine and reef environments.
2. Establishing rates and requirements for molluscan shell accretion In order to determine natural growth rates and species responses to environmental stressors and seasonal variations, Chione have been placed in habitats in Florida Bay near working water-monitoring stations beginning in January 2001. The in-situ variables of salinity, temperature, rainfall, etc. can be documented using the data from the water monitoring stations and our instrumentation. The habitats are periodically pulled and the animals digitally photographed to document growth. Dead specimens are removed and replaced with live individuals. Both living and dead specimens that show growth are periodically removed and are used in the calibration tests. These experiments will continue in FY04, and FY05 to gather data on the life span, reproductive patterns, and environmental factors that affect these animals. In FY04, we will continue experiments on other species of mollusks begun in FY03 in order to identify other indicator species that can be used in cores. By continuing these experiments over a period of years, we capture data on seasonal changes and how the organism records these data biochemically within its shell. These data allow us to more accurately interpret the patterns we see in the shells and ultimately the downcore data.
3. Application of sclerochronology to interpretation of seasonal salinity patterns in Florida Bay Ostracode analyses on the cores, begun in FY 02, will continue in FY04 and be completed in FY05.
Molluscan and ostracode biochemical data will be plotted and compared to general downcore assemblage analyses already completed on three of the cores to look for patterns of change in seasonal, annual and decadal scale trends in salinity and sources of freshwater input over the last 100-200 years at these sites within Florida Bay. In addition, a statistical method of reducing the molluscan assemblage data to a single salinity value will be done for the cores. This method is based on results from field analyses and experiments done previously. A comparison of the results from eastern and central Florida Bay will highlight any geographic variations in salinity and freshwater influx that existed prior to drainage alteration and allow comparison to the present day situation. By comparing these data to early 20th century rainfall records (available from NOAA), we can determine what salinity ranges were following a given period of monthly rainfall, prior to significant alteration of natural flow. The next step is to forecast what the salinity should be under restored 'natural' flow following given amounts of rainfall. These data provide specific targets for restoration and for water management practices.
U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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