title: Revealing organic carbon-nitrate linear relationship from UV spectra of freshwaters in agricultural environment.
abstract: 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.
authors.affiliation: EHESP Rennes, Sorbonne Paris Cité - CS 74312, 35043 Rennes Cedex, France; Inserm, U 1085 (IRSET), LERES - CS 74312, 35043 Rennes Cedex, France; European University of Brittany (UEB), France. Electronic address: olivier.thomas@ehesp.fr.
authors.forename: O
authors.initials: O
authors.lastname: Thomas
authors.affiliation: EHESP Rennes, Sorbonne Paris Cité - CS 74312, 35043 Rennes Cedex, France; Inserm, U 1085 (IRSET), LERES - CS 74312, 35043 Rennes Cedex, France; School of Environmental Engineering (EME), Campus de Ker Lann, 35170 Bruz, France; European University of Brittany (UEB), France.
authors.forename: A V
authors.initials: AV
authors.lastname: Jung
authors.affiliation: EHESP Rennes, Sorbonne Paris Cité - CS 74312, 35043 Rennes Cedex, France; Inserm, U 1085 (IRSET), LERES - CS 74312, 35043 Rennes Cedex, France; European University of Brittany (UEB), France.
authors.forename: J
authors.initials: J
authors.lastname: Causse
authors.affiliation: EHESP Rennes, Sorbonne Paris Cité - CS 74312, 35043 Rennes Cedex, France; Inserm, U 1085 (IRSET), LERES - CS 74312, 35043 Rennes Cedex, France; European University of Brittany (UEB), France.
authors.forename: M V
authors.initials: MV
authors.lastname: Louyer
authors.affiliation: Saur R&D - Les Cyclades, 1 rue Antoine Lavoisier, 78280 Guyancourt, France.
authors.forename: S
authors.initials: S
authors.lastname: Piel
authors.affiliation: EHESP Rennes, Sorbonne Paris Cité - CS 74312, 35043 Rennes Cedex, France; Inserm, U 1085 (IRSET), LERES - CS 74312, 35043 Rennes Cedex, France; European University of Brittany (UEB), France.
authors.forename: E
authors.initials: E
authors.lastname: Baurès
authors.affiliation: School of Environmental Engineering (EME), Campus de Ker Lann, 35170 Bruz, France; European University of Brittany (UEB), France.
authors.forename: M F
authors.initials: MF
authors.lastname: Thomas
mesh_terms: D000383:Agriculture; D002244:Carbon / Q000737:chemistry*; D060106:Lakes / Q000737:chemistry*; D016014:Linear Models; D009566:Nitrates / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D009566:Nitrates; D002244:Carbon
keywords: Agricultural environment; Model; Normalization; UV spectrophotometry; Water quality