CF:CS model to estimate sedimentation rate from 210Pb activity

This function fits a "Constant Flux Constant Sedimentation Rate" (CF:CS) model to 210Pb activity data from different soil depths to estimate the sedimentation rate of the profile.

calc_SedimentationRate(x, reverse = TRUE, fix_a0 = FALSE,
  verbose = TRUE, ...)

Arguments

x	data.frame (required): Measured 210Pb activity at different soil depths with the following structure: | depth (cm )| activity (Bq/kg) | | [ ,1] | [ ,2] | |------------|------------------| [1, ]| ~~~~ | ~~~~ | [2, ]| ~~~~ | ~~~~ | ... | ... | ... | [x, ]| ~~~~ | ~~~~ |
reverse	logical (optional): Plot the y-axis in ascending order so that the soil surface is on top. Defaults to TRUE.
fix_a0	logical (optional): In the fitted model parameter a0 is the 210Pb activity at depth z=0. If the argument fix_a0 is TRUE, this function will take the first activity value (i.e., the value closest to the surface) as a fixed value in the equation. For fix_a0=FALSE parameter a0 is estimated by the model. Defaults to FALSE.
verbose	logical (optional):
...	Futher arguments passed to plot.

Value

A list with the following structure:

	Element	Data type
Description		$summary
		data.frame
	summary table of important model results
$data
data.frame		original input data
	$model
	nls
model output generated by	minpack.lm::nlsLM

Details

Model

$$ y = a0 * exp((l/s) * x) $$

• y = 210Pb activity at depth x (cm)

• a0 = 210Pb activity at depth x=0

• l = 210Pb decay constant (= 0.03114 a-1)

• s = sedimentation rate (cm/a)

• x = depth below surface (cm)

References

Szmytkiewicz, A., Zalewska, T., 2014. Sediment deposition and accumulation rates determined by sediment trap and 210Pb isotope methods in the Outer Puck Bay (Baltic Sea). Oceanologia 56(1), 85-106.

Examples

# Load example data (synthetic)
data(Pb)

# Apply the model
results <- calc_SedimentationRate(x = Pb,
                                  reverse = TRUE,
                                  fix_a0 = FALSE,
                                  verbose = TRUE)
#> 
#> Equation: activity ~ 100.288 * exp((0.03114/0.512) * depth)
#> Sedimentation rate: 0.512 ± 0.013 cm/a
#>