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.