Build the Cl-anchored leachate end-member for LMF calibration

Constructs the leachate end-member L by computing the mean ratio of each ion to Cl across valid leachate samples, then anchoring to the median Cl concentration. This makes the end-member robust to EC variability between leachate samples while preserving the stable compositional fingerprint.

Usage

build_leachate_endmember(
  calibration_start,
  calibration_end,
  min_leachate_total_n_mgl,
  min_leachate_samples
)

Arguments

calibration_start

Calibration window start date.

calibration_end

Calibration window end date. Shifted backwards if leachate data do not extend this far.

min_leachate_total_n_mgl

Minimum total N (mg/L) for a leachate sample to be considered valid. Applied in original mg/L units before meq conversion. Filters out anomalous samples not representing genuine leachate.

min_leachate_samples

Minimum number of valid leachate samples required. Stops with an error if not met.

Value

A named list with elements:

L_values

Tibble with columns ion, mean_ratio, L (the end-member concentration in meq/L for each ion).

cl_anchor

Median Cl concentration (meq/L) used to anchor the end-member.

n_samples

Number of valid leachate samples used.

f_included

Logical; TRUE if F was included in the end-member.

window_start

Actual calibration window start used.

window_end

Actual calibration window end used.