Get absorbance peaks and indices
abs_parm.RdTakes a dataframe of absorbance data and calculates optical properties for each sample. If data was collected at greater than 1 nm intervals, data will be interpolated to 1 nm intervals.
Arguments
- abs_data
a dataframe containing the absorbance data, where each column is a sample
- waves
optional, a vector of wavelengths in nm to extract from the absorbance data
- meta
the metadata table for the sample run, should include DOC data in mg/L
- r_thresh
the minimum \(\text{R}^{2}\) value for the spectral slopes for the slope to be included in the table
- keep_all
a logical, TRUE will return all samples even those without DOC data, FALSE will only return samples with DOC data
Details
Absorbance indices based on Hansen et al. 2016. Measurements are defined as follows:
SUVA254, SUVA280, SUVA350, SUVA370: SUVA at 254, 280, 350, and 370 nm. Units of \(\text{L mgC}^{-1} \text{m}^{-1}\). Typically higher values are associated with greater aromatic content.
SVA412, SVA440, SVA480, SVA510, SVA532, SVA555: SVA at 412, 440, 480, 510, 532, 555 nm. Units of \(\text{L mgC}^{-1} \text{m}^{-1}\). Typically higher values are associated with greater aromatic content.
S275_295: Spectral slope between 275 to 295 nm.
S290_350: Spectral slope between 290 to 350 nm.
S350_400: Spectral slope between 350 to 400 nm.
Spectral slopes are found with a nonlinear fit of an exponential function to the absorption spectrum, typically higher values are associated with lower molecular weight materials and/or lower aromaticity.
SR: Spectral slope S275_295 divided by spectral slope S350_400, negatively correlated to DOM molecular weight and generally increases on irradiation.
References
Hansen, A. M., Kraus, T. E. C., Pellerin, B. A., Fleck, J. A., Downing, B. D., & Bergamaschi, B. A. (2016). Optical properties of dissolved organic matter (DOM): Effects of biological and photolytic degradation. Limnology and Oceanography, 61(3), 1015–1032. https://doi.org/10.1002/lno.10270