[STM]

please i need simple definitions of the above terms and their implications in a water sample. I have checked the internet and obtained some information but I cant find a clear-cut definition on what they are and how they can be obtained experimentally.

What are they? How can they be obtained? What information does the result give?

Thank you

[mjc123]

Did you find this paper? http://onlinelibrary.wiley.com/doi/10.4319/lo.2012.57.5.1453/pdf. It uses both terms:
"Absorbance corrected for offset was then converted to Napierian absorption coefficient, a_g(λ) (m^-1). The dependence of a_g(λ) on λ is typically described using Eq. 1:
a_g(λ) = a_g(λ₀)e^-S(λ-λ₀)                      (1)
where λ₀ < λ and S is the spectral slope coefficient in the λ₀–λ-nm spectral range. Spectral slope coefficients were estimated using a linear fit of the log-linearized a_g(λ) spectrum over their respective spectral range and are reported here with units of nm^-1. Measurements of DOC and a_g(350) were used to calculate DOC-normalized absorption coefficients (a_g(350) : DOC), expressed here in units of L mol^-1 cm^-1."

From this I take it that Napierian absorption coefficient is the absorbance per unit length of the sample. (Napierian means using natural logs rather than log₁₀.) Thus A = ln(I₀/I_t) and a = A/l, where l is the path length.
Spectral slope coefficient is a measure of how the absorption coefficient changes with wavelength. In appropriate circumstances, over a relatively narrow wavelength range, it can be described by Eq. 1, i.e. it varies exponentially with wavelength.

[STM]

Thank you for response. It was highly helpful.