Over the past 150 years, there has been a significant increase in human activities, including construction, agriculture, mining, and the consumption of fossil fuels. As awareness of the impact of these activities on human and environmental systems grows, establishing accurate timelines of ecological change has become increasingly important. Chronologies derived from sediment core profiles typically utilize the activities of radionuclides deposited and stratified within the physical environment. One of the most widely used radionuclides for establishing chronologies over approximately the past 150 years is ²¹⁰Pb.The ²¹⁰Pb radiometric dating technique is among the most widely employed methods for dating sediments deposited within the last 100 to 150 years across lacustrine, estuarine, marsh, and marine environments. The technique was first applied to lake sediments by [30], following its initial development for dating ice cores by [23]. Since then, ²¹⁰Pb dating has become an essential tool for determining sediment chronologies, bottom core ages, and sedimentation rates.

In addition to establishing sediment accumulation histories, ²¹⁰Pb dating has played a crucial role in studies of erosion rates, accelerated eutrophication, atmospheric circulation patterns, the residence time of tropospheric aerosols, and air-sea exchange processes ([23]; [30]; [35]; [40]; [7]; [45]; [22]).

²¹⁰Pb is a naturally occurring radionuclide from the ²³⁸U decay series, commonly found in the Earth’s crust. It decays through various intermediates to reach stable ²⁰⁶Pb. One significant intermediate is ²²⁶Ra (t_1/2 = 1600 years), which transforms into noble gas ²²²Rn (half-life = 3.825 days). Because ²²²Rn is gaseous, it can escape from the soil into the atmosphere, disturbing the initial secular equilibrium with ²³⁸U. Once in the air, ²²²Rn decays and eventually forms ²¹⁰Pb through short-lived progeny. Atmospheric ²¹⁰Pb has a half-life of 22.26 years and quickly adheres to aerosol particles. These ²¹⁰Pb bearing aerosols typically reside in the troposphere for less than a week ([23]; [13]; [35]; [31]). Through dry and, especially, wet deposition, which accounts for approximately 90% of atmospheric input ([15]), ²¹⁰Pb is deposited onto the Earth’s surface. In aquatic systems like lakes, ²¹⁰Pb becomes part of the bottom sediments ([13]). Research indicates that dissolved ²¹⁰Pb in river water is efficiently removed by adsorption onto suspended particles ([13]; [12]; [29]; [21]). The ²¹⁰Pb originating from atmospheric ²²²Rn decay is known as unsupported ²¹⁰Pb (²¹⁰Pb_unsup), because its activity is not sustained by in-situ ²³⁸U decay. Conversely, ²¹⁰Pb produced within sediment from the decay of sediment-bound ²²⁶Ra is called supported ²¹⁰Pb (²¹⁰Pb_sup). ²¹⁰Pb_unsup reaches lake sediments mainly through direct atmospheric deposition and, to a lesser extent, via particle transport from inflowing rivers and catchment runoff. However, studies consistently show that catchment contributions are minor compared to direct atmospheric input, with most of the ²¹⁰Pb_unsup retained in soils and not reaching lake sediments ([30]; [13]; [12]; [31]).

The total ²¹⁰Pb activity (²¹⁰Pb_tot) measured in sediment samples includes both supported and unsupported fractions. The ²¹⁰Pb_sup activity, typically expressed in disintegrations per minute per gram (DPM g^–1) of dry sediment, is assumed to stay relatively constant over time due to secular equilibrium with its parent ²²⁶Ra. The ²¹⁰Pb_unsup activity is determined by subtracting the supported component from the total activity. If ²¹⁰Pb_unsup does not significantly migrate after deposition, its activity decreases with depth in sediment cores due to radioactive decay. This decay profile serves as the foundation of ²¹⁰Pb-based dating methods. Determining the age of sediment layers is crucial for understanding the timescales of geochemical processes and the impacts of human activities. Moreover, sedimentation rates derived from ²¹⁰Pb dating are essential for environmental remediation efforts, land-use planning, and comprehending the physical and chemical dynamics within aquatic systems. Lakes, serving as repositories for eroded particles from their catchments, preserve sediment records that enable the reconstruction of historical erosion and deposition events. The Adirondack region, marked by cold, snowy winters and cool, wet summers, offers a unique environment for studying such processes. Precipitation is distributed evenly throughout the year, while temperature, frost-free season length, and other meteorological variables like wind speed and cloud deposition fluctuate with elevation. These climatic factors affect the deposition of ²¹⁰Pb into lake systems.

Climate change has significantly impacted the Adirondack region. A study on lake ice in the area reported rapid changes between 1975 and 2007, with ice cover durations decreasing by up to 21 days, primarily due to delayed freeze-up and, to a lesser extent, earlier breakup ([11]). The Adirondack Mountains have been extensively affected by acidic atmospheric deposition and associated watershed biogeochemical changes over the past century. Previous regional investigations have documented long-term declines in sulfate and nitrate deposition, changes in surface-water chemistry, and evidence of partial ecological recovery in Adirondack lakes following reductions in atmospheric emissions ([34]; [20]). Because sediment records preserve signals of these environmental changes, the development of accurate sediment chronologies using radionuclides such as ²¹⁰Pb and ¹³⁷Cs is essential for reconstructing temporal variations in sediment accumulation and environmental processes within Adirondack Lake ecosystems. These changes are expected to alter growing seasons, vegetation patterns, and runoff dynamics, which can affect ²¹⁰Pb deposition and cycling. Furthermore, the region’s watersheds are biogeochemically sensitive, particularly to atmospheric inputs of sulfate, nitrate, and radionuclides like ²¹⁰Pb. Acid deposition from sulfur and nitrogen oxides has historically impacted the region, although emissions have declined significantly since the passage of the U.S. Clean Air Act Amendments of 1990. However, the behavior and fate of ²¹⁰Pb under these evolving conditions remain poorly studied. This investigation is part of a broader research initiative aimed at monitoring historical atmospheric deposition of elemental carbon and trace elements across lake sediments from the Midwest to the Adirondack Park region ([26]; [41]). As part of this study, four sediment cores from West Pine Pond (WP), a high-altitude, remote lake in the Adirondack Park, were dated, and sedimentation rates were calculated. The sediment chronologies were constructed using three commonly applied ²¹⁰Pb dating models: the Constant Initial Concentration (CIC), Constant Flux-Constant Sedimentation (CF-CS), and Constant Rate of Supply (CRS) models ([1]; [39]; [25]). To validate the ²¹⁰Pb derived age models, profiles of ¹³⁷Cs, an independent tracer of atmospheric fallout, were also analyzed ([24]).

Recent advances in ²¹⁰Pb sediment dating have emphasized the importance of selecting appropriate models to account for non-ideal depositional conditions and spatial heterogeneity. A comprehensive review by [2] highlights the development of numerous models and the growing recognition of model-dependent uncertainties in sediment chronologies. Furthermore, recent studies have demonstrated that traditional models such as CIC and CRS may not adequately capture sediment dynamics in systems with variable porosity or episodic deposition, prompting the development of alternative approaches and model validation strategies ([3]). These developments underscore the need for multi-model comparison and independent validation using tracers such as ¹³⁷Cs, as applied in the present study.

While ²¹⁰Pb dating has been widely applied to lake sediments, relatively few studies have combined multi-core analysis, multi-model comparison, and independent validation using ¹³⁷Cs within a single lacustrine system to evaluate both chronological accuracy and spatial variability in sedimentation processes. This study addresses this gap by integrating multi-model comparison with independent chronological validation and environmental interpretation, providing a more comprehensive framework for assessing sediment chronologies in complex depositional environments.

Sediment cores were collected from West Pine Pond (WP), a remote lake in the Adirondack Park region of upstate New York. The Adirondack Park covers approximately 6 million hectares and is predominantly forested, with mountainous terrain and more than 3,000 lakes and ponds. It encompasses the largest wilderness area east of the Mississippi River ([32]; Adirondack Lakes Survey Corporation). Many lakes in this region are located at relatively high elevations and are remote from major roads and highways. West Pine Pond (approximately 44˚20' N, 74˚25' W) has a surface area of 25.5 ha and a catchment area of 235 ha, with a mean water depth of approximately 5.5 m.

Four sediment cores (WP-1, WP-2, WP-3, and WP-5) were collected in September 2005 from the deep depositional region of the lake at a water depth of approximately 13 m. The geographic coordinates of the individual coring stations, recorded using a Global Positioning System (GPS), were 44˚20.2830' N, 74˚25.5830' W (WP-1); 44˚20.2730' N, 74˚25.5830' W (WP-2); 44˚20.2790' N, 74˚25.5790' W (WP-3); and 44˚20.2810' N, 74˚25.5790' W (WP-5). The four stations were closely spaced within the deep depositional basin, with approximate inter-core distances ranging from 3.7 to 18.5 m.

Coring was conducted from a rowboat using a gravity-driven coring device fitted with removable plastic tubes having an internal diameter of 5.12 cm. The recovered sediment cores were approximately 55 cm long, and the sediment-water interface was retained intact during core recovery, preserving the uppermost sediment layer. Immediately after recovery, the cores were sectioned in the field to minimize physical disturbance and post-collection redistribution of sediment. The cores were sliced horizontally into sections with thicknesses that were multiples of 0.125 inch (3.18 mm). Each sediment section was transferred to a clean, pre-weighed plastic cup (5 cm internal diameter) with a lid and maintained at 4˚C during transport to the laboratory. Upon arrival at the laboratory, the samples were refrigerated at 4˚C and subsequently freeze-dried using a LABCONCO freeze dryer (Model 7753020) prior to radionuclide analysis.

Freeze-dried sediment samples were homogenized to create a fine powder. Approximately 0.4 - 3 g of sediment from each slice was accurately weighed, and the activity of 46.5 keV γ-ray from ²¹⁰Pb was measured using a non-destructive well-type high-purity germanium detector (HPGe) manufactured by Canberra Inc. (Meriden, CT). The well dimensions were 20 mm in diameter and 40 mm in length. The detector provided high efficiency and low background for low-energy γ radiation (20 - 400 keV). It has a resolution of 1.21 keV and 2.18 keV (FWHM) at γ-ray energies of 59.5 keV and 1332.5 keV from ²⁴¹Am and ⁶⁰Co, respectively. The detector is shielded from background radiation by a 6-inch (15.24 cm) thick Pb container and is positioned inside a room constructed of 6-inch-thick steel plates from pre-World War II iron. Teflon tubes (outer diameter: 19 mm; length: 110 mm) with screw caps were employed to count the γ-rays of ²¹⁰Pb, filled with sediments up to the 5 ml marking. A latex protective cover was wrapped around the tubes to shield the detector from contamination. Details of this detector have been provided elsewhere ([37]).

An independent verification of the ages derived from ²¹⁰Pb was provided by measurements of ¹³⁷Cs radioisotope (t_1/2 = 30.17 yr) activity ([5]; [45]). Unlike naturally occurring ²¹⁰Pb, ¹³⁷Cs is an artificial radioisotope that was introduced into the atmosphere from nuclear weapons testing and, in some regions such as Russia, Norway, Sweden, and parts of Central Europe, from the 1986 Chernobyl reactor accident ([44]; [22]). Because the source of ¹³⁷Cs differs from that of ²¹⁰Pb, ¹³⁷Cs can serve as an independent chronological marker for verifying dates obtained from ²¹⁰Pb dating. Global fallout of ¹³⁷Cs increased after 1954, reaching a maximum in the Northern Hemisphere in 1963 (Figure 1), and subsequently declined following the 1963 Partial Test Ban Treaty ([5]; [17]). However, studies have shown that due to the post-depositional mobility of ¹³⁷Cs, the record of this radionuclide in the sediment column can become degraded ([10]). The activity of 661.7 keV γ-rays of ¹³⁷Cs was measured using a high-efficiency, p-type, closed-end HPGe detector in a 2-inch plastic jar. The spectrometers were calibrated with NIST-traceable ²¹⁰Pb and ¹³⁷Cs standards in the same matrix as the analyzed sample. The counting time varied from 1000 to 4000 minutes.

Figure 1. ¹³⁷Cs deposition in lake sediments due to global nuclear testing.

Total ²¹⁰Pb activity was determined from the 46.5-keV gamma-ray photopeak and expressed on a dry-sediment mass basis (dpm g^–1). Supported ²¹⁰Pb (²¹⁰Pb_sup) was determined separately for each core from the deepest sediment intervals in which the measured total ²¹⁰Pb activity approached a relatively constant asymptotic value, indicating that the unsupported component had become negligible. The activities of these deep intervals were averaged to obtain a core-specific supported ²¹⁰Pb activity, and the associated uncertainty was determined from the uncertainties and variability of the measurements included in the average. The resulting ²¹⁰Pb_sup activities were 0.90, 1.36, 0.93, and 1.11 dpm g⁻¹ for WP-1, WP-2, WP-3, and WP-5, respectively.

Unsupported ²¹⁰Pb activity (²¹⁰Pb_unsup) for each sediment interval was calculated by subtracting the corresponding core-specific supported activity from the measured total ²¹⁰Pb activity:

Sediment intervals were included in the ²¹⁰Pb chronology while measurable ²¹⁰Pb_unsup remained distinguishable from the supported component within the measurement uncertainty. At greater depths, where total ²¹⁰Pb activity approached the supported value, the sediment was below the practical ²¹⁰Pb dating horizon.

For gamma-spectrometric quality control, freeze-dried and homogenized sediment samples were measured in Teflon tubes using the well-type HPGe detector described above. Sample geometry was maintained consistently with the calibration geometry, and detector efficiency calibration was performed using NIST-traceable standards ([42]). Because attenuation of the low-energy 46.5-keV gamma ray is sensitive to sample composition, density, and counting geometry, density-dependent attenuation/self-absorption corrections were determined using the GESPECOR Monte Carlo software ([43]). The sample-specific density and measurement geometry were incorporated into the GESPECOR calculations to correct the 46.5-keV counting efficiency for differences between calibration standards and sediment samples.

Detector background was characterized using a 4000 min background measurement under the same counting configuration. Background counts in the 46.5-keV region were incorporated into the net-peak activity and detection-limit calculations. Minimum detectable activities (MDA) were determined using the detection-limit procedure described elsewhere ([19]), incorporating the measured background, counting time, detector efficiency, ²¹⁰Pb gamma-ray emission probability, and dry sample mass. Samples were counted for 1000 - 4000 min, with longer counting times used where necessary to improve counting statistics for low-activity sediment intervals. The combined use of controlled counting geometry, NIST-traceable efficiency calibration, GESPECOR density/self-absorption correction, long-duration background measurements, and MDA evaluation provided quality control for the low-energy ²¹⁰Pb measurements.

The ²¹⁰Pb_unsup profile was evaluated only over sediment intervals for which the activity was above the minimum detectable activity (MDA). The practical dating horizon was defined as the depth at which ²¹⁰Pb_unsup activity decreased below the MDA. Sediment intervals below this horizon were not used for age determination, and no extrapolation of ²¹⁰Pb_unsup activity or additional residual unsupported ²¹⁰Pb inventory was assigned below the measured horizon.

Three commonly used ²¹⁰Pb dating models for sediment cores are the Constant Initial Concentration (CIC), Constant Flux-Constant Sedimentation (CF-CS), and Constant Rate of Supply (CRS) models. In this paper, we provide a summary of each. The details of these models can be found in [6]. Although all three models are based on key assumptions, the optimal model will differ depending on the environment and the expected constancy of ²¹⁰Pb influx to sediments, as well as the mass accumulation rate:

1) ²¹⁰Pb is removed from the atmosphere and the water column and is quickly sequestered into sediments.

2) Once deposited, the ²¹⁰Pb in the sediment is immobile.

3) The sedimentation process will be uninterrupted.

Measurement uncertainties in ²¹⁰Pb and ¹³⁷Cs activities were derived primarily from counting statistics, with additional contributions associated with background subtraction, detector-efficiency calibration, sample geometry, and density-dependent corrections. These measurement uncertainties provide the analytical basis for assessing the precision of the radionuclide activity profiles used in the sediment chronology calculations.

Uncertainty in model-derived ages and sediment accumulation rates depends not only on the analytical uncertainty of the measured ²¹⁰Pb activities but also on the assumptions and mathematical formulation of the individual dating models. In the CIC and CF-CS approaches, uncertainty is associated with the regression parameters used to determine the mean sedimentation or mass accumulation rate. CRS-derived quantities are additionally sensitive to uncertainties in the cumulative unsupported ²¹⁰Pb inventory because the chronology is calculated from the fraction of total inventory remaining beneath a given sediment horizon.

A mathematical framework for propagation of measurement uncertainties through the CIC, CF-CS, and CRS calculations is provided in AppendixA. The framework identifies the principal sources of uncertainty and their propagation into model-derived quantities.

The sediment chronologies developed for West Pine Pond preserve a valuable historical record of environmental change within the Adirondack region over approximately the past century. The deeper sediment intervals coincide with periods of intensive logging, watershed disturbance, and enhanced erosion that characterized portions of the Adirondacks during the late 19th and early 20th centuries, whereas the more recent sediments indicate comparatively stable depositional conditions. Elevated near-surface unsupported ²¹⁰Pb activities and relatively consistent modern sedimentation rates suggest reduced sediment delivery in recent decades, likely associated with forest regrowth, watershed stabilization, and improved land-use management throughout the region.

The reconstructed sediment records also coincide with major changes in atmospheric deposition across the northeastern United States. Previous studies have documented substantial declines in sulfate and nitrate deposition in the Adirondacks since the implementation of air-quality regulations, particularly following the Clean Air Act and subsequent emission-control programs. These reductions have been linked to improvements in lake-water chemistry and partial ecological recovery in Adirondack aquatic systems. The preservation of a distinct ¹³⁷Cs fallout horizon corresponding to the 1963 atmospheric nuclear testing maximum further confirms the integrity of the sediment record and indicates limited post-depositional mixing or disturbance within most cores.

Although long-term sedimentation patterns in West Pine Pond appear relatively stable, CRS-derived depth profiles revealed localized and depth-dependent variations in sediment accumulation among the four cores, consistent with sediment focusing, hydrological variability, episodic sediment inputs, or changes in watershed conditions.

Overall, the combined application of CIC, CF-CS, and CRS ²¹⁰Pb dating models together with independent ¹³⁷Cs validation provides a robust framework for reconstructing sedimentation dynamics and environmental change in lacustrine systems. The results provide a chronological framework for interpreting documented environmental recovery and landscape changes in the Adirondack region, while also highlighting the continuing influence of climatic and watershed-scale processes on sediment transport and deposition.

This study provides a comprehensive ²¹⁰Pb and ¹³⁷Cs based chronostratigraphic reconstruction of four sediment cores from West Pine Pond, offering one of the most detailed assessments of recent sedimentation processes in a remote Adirondack Lake. All three ²¹⁰Pb dating models CIC, CF-CS, and CRS were evaluated, but the CIC model consistently yielded chronologies most consistent with the independently observed ¹³⁷Cs fallout peak from 1963 in three of the four cores. Long-term sedimentation rates were remarkably uniform across the lake, ranging from 0.18 to 0.20 cm yr^–1, while mass accumulation rates (0.0106 - 0.0177 g cm^–2 yr^–1) demonstrated only moderate spatial variability. CRS-derived depth profiles revealed localized and depth-dependent variations in sediment accumulation among the four cores, consistent with sediment focusing, hydrological variability, episodic sediment inputs, or changes in watershed conditions. The agreement between measured ²¹⁰Pb inventories and derived ²¹⁰Pb_unsup fluxes and values previously reported for regional lakes supports the reliability of the radiometric measurements and the reconstructed chronologies.

The clarity of the ¹³⁷Cs peak in most cores and the absence of major sediment mixing further strengthen confidence in the depositional integrity of the cores and the preservation of environmental signals. Together, these chronologies capture approximately 150 years of environmental history, providing essential insights into sediment accumulation, atmospheric deposition, and watershed processes in the Adirondack Park.

Beyond methodological validation, the sediment records reflect broader environmental trends, including reductions in erosion and pollutant deposition associated with forest recovery, improved land-use practices, and national air-quality regulations. As such, this study not only contributes to regional geochronology but also establishes a valuable baseline for tracking future environmental change, climate-driven hydrological responses, and ecosystem recovery in sensitive high-elevation lake systems. Continued monitoring and application of multi-model radiometric dating will remain critical for understanding the long-term dynamics of Adirondack lakes and other comparable environments worldwide. This study demonstrates that multi-model ²¹⁰Pb analysis, when combined with independent ¹³⁷Cs validation, provides a robust and transferable framework for reconstructing sediment chronologies in heterogeneous lacustrine environments.

The authors are grateful to Karen Roy, Jed Dukett, Susan Capone, Paul Casson and James S. Webber for advice on lake selection and sediment coring. This work was partly funded by an NSF grant ATM 0503850.

AK: Writing—review & editing, Writing—original draft, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization, Project design, measurements. TA: Writing—review & editing, Data curation, Visualization, Validation, Methodology.

(UncertaintyPropagationFramework)

A.1Generalpropagationequation

Uncertainty propagation for ²¹⁰Pb-based chronologies follows standard error propagation principles, where the combined variance of a derived quantity is expressed as a function of the variances of the contributing variables.

For a function:

the combined variance is:

where σ x i 2 is the variance of variable x i , and ∂ U / ∂ x i represents the sensitivity coefficient. Correlations between variables are assumed negligible.

A.2Unsupported²¹⁰Pb

Unsupported activity is defined as:

with propagated uncertainty:

A.3CICModel

The CIC model is given by:

Taking natural logarithms:

The regression slope:

CIC age:

With uncertainty:

A.4CF-CSModel:

where m is cumulative mass depth.

regression slope be:

The accumulation rate is:

Mass depth:

The variance of cumulative mass depth is:

A.5CRSModeluncertainty

where,

Inventory uncertainty:

The uncertainty in age is:

A.6CRSMassaccumulationrate

The CRS mass accumulation rate is:

With uncertainty:

A.7²¹⁰PbFlux:

A.8Sedimentfocusingfactor

The sediment focusing factor (FF) is: