datetime_col: column with datetime of each concentration measurement Note that if there are duplicated datetime in the same f_fluxid only the first row will be kept
f_start: column with datetime when the measurement started
f_end: column with datetime when the measurement ended
f_fluxid: column with ID of each flux
start_cut: time to discard at the start of the measurements (in seconds)
end_cut: time to discard at the end of the measurements (in seconds)
Returns
a df with the modeled gas concentration, slope, intercept, std error, r square and p value of the linear model