Revealing organic carbon-nitrate linear relationship from UV spectra of freshwaters in agricultural environment

Olivier Thomas (1, 2, 3) , A. V. Jung (1, 2) , Jean Causse (1, 2) , M. V. Louyer (1, 2) , S. Piel , Estelle Baurès (1, 2) , Marie-Florence Thomas

1 Irset - Institut de recherche en santé, environnement et travail
2 EHESP - École des Hautes Études en Santé Publique [EHESP]
3 LERES - Laboratoire d'étude et de recherche en environnement et santé

A strong non linear relationship between nitrate and organic matter (assessed by dissolved organic carbon, DOC) has been recently demonstrated by Taylor and Townsend (2010), namely for freshwaters. In this context, our study explores this relation from the behavior of sets of normalized UV spectra (same area under each spectrum) of different water samples showing a hidden isosbestic point (HIP) around 225 nm. This HIP is linked to the existence of a simple relation between nitrate and DOC, the proportions of which vary according to the sampling location and environmental factors. In a second step, a simple linear model is proposed for nitrate-DOC relationship (α⋅NO3+β⋅DOC=1) and a validation is proposed for more than 150 samples of different Brittany rivers and lakes. For samples of the largest watershed, a complementary exploitation from data acquired during the different campaigns confirmed the seasonal evolution between spring (high nitrate/low DOC) and autumn (high DOC/low nitrate). Further investigation on other freshwater samples is needed in order to improve the limits of this linear model.

Mots clés: Water quality; Agricultural environment; UV spectrophotometry; Normalization; Model

Domaines: Sciences du Vivant [q-bio]

Olivier Thomas, A. V. Jung, Jean Causse, M. V. Louyer, S. Piel, et al.. Revealing organic carbon-nitrate linear relationship from UV spectra of freshwaters in agricultural environment. Chemosphere, 2014, 107, pp.115--120. ⟨10.1016/j.chemosphere.2014.03.034⟩. ⟨hal-01063932⟩