Volante et al 2024 210pb 241 Am dating
Environmental Consequences of Rapid Urbanization in Central Florida
Introduction
Florida has been among the fastest growing states in the U.S. throughout the 20th century.
Urbanization has led to significant environmental stress and changes in the local ecology.
Accurately dated lake sediments help document environmental changes beyond monitoring records.
Key Elements Analyzed
Radionuclides Studied: Americium-241 (241Am), Cesium-137 (137Cs), Lead (Pb), Zinc (Zn), and Uranium-series radionuclides from Lake Bonny, Lakeland, Florida.
Sediment Dating Techniques: Utilized gamma-ray emitting radionuclides for contextualizing environmental change.
241Am and 137Cs played a crucial role in dating sediments due to their atmospheric deposition around 1952–1963.
Findings from Lake Bonny
Sediment Profile Characteristics
241Am peaks sharply in the sediment profile, indicating precise historical data.
137Cs peaks are broader and spread across two sediment layers, with an inventory of ~413 Bq/m2, lower than expected from atmospheric deposition.
Notable losses in the measurements indicate environmental factors affecting radionuclide retention.
Chemical Change and Sedimentation Rates
Highest sedimentation rates correlate with mid-20th century population growth.
Increased uranium and radium-226 inputs observed in the 1960s, likely due to phosphate mining activities.
Lead concentrations in sediments reflect the historical usage of leaded gasoline. Zinc remains at elevated levels, suggesting ongoing pollution.
Methodology
Study Site and Sample Collection
Lake Bonny is shallow and eutrophic, situated in an urban setting surrounded by Lakeland, Florida.
Lake Bonny is linked hydrologically to other nearby lakes, affecting its sediment composition.
Core extraction was performed to analyze sediment layers over various intervals.
Gamma Spectrometry
Employed a gamma spectrometer to measure radionuclide activities within the collected sediment samples.
Calibration methods ensured accurate measurements of radionuclides, with peak fallout years used to reference dating models.
Analytical Models and Results
210Pb Piecewise CRS Dating Model
Constant Rate of Supply (CRS) model application allows for variable sedimentation rates while assuming constant radionuclide deposition.
Utilized an open-source R package to construct an accurate piecewise model based on verified radionuclide activities.
Results on Metal Concentrations
Pb concentrations peaked in sediments between specific depths before falling to lower levels in more recent layers.
Significant revelations about Zn show it remains consistently high, indicating enduring pollution from urban runoff and degradation.
Discussion of Findings
Comparison of 210Pb, 241Am, and 137Cs
241Am shows more reliable peaks, indicating less geochemical mobility than 137Cs, which diffuses significantly in sediments.
The study highlights the importance of radionuclides for understanding ecosystem changes due to anthropogenic impacts.
Other Pollutants
Trends indicate that traditional pollutants (lead from gasoline, pesticides) worsened with urban development, while Zn pollution from tires and urban runoff continues.
Correlation between mass accumulation rates and population growth reflects construction impacts on sedimentation in lakes.
Conclusion
241Am proves preferable for validating 210Pb dating in environments with low clay content.
This research provides insights into human impacts on aquatic ecosystems through historical sediment analysis, crucial for future environmental management strategies.
Findings underscore the continuing challenge of urbanization and its long-term effects on lake ecosystems.