Use of fatty acids as tracer of organic matter input associated with level of land urbanization.

Suspended sediments (SSs) were examined regarding the content of fatty acids (FAs) to associate them with sources of soil entry into the river. The source of organic matter was traced through fatty acid distribution, as well as erosion. Also, TOC, TN, and TOC/NT were used to support the results of FAs. For this, a tropical river was chosen to understand the main source of input considering the level of land occupation along the river. The Barigui river, in southern Brazil, was segmented in four distinct areas regarding the soil occupation (P1, P2, P3, and P4). Nine sampling campaigns were conducted from Nov/2014 to Nov/2015 using a time-integrated sampler. Site P1 has the lowest level of urbanization and showed the lowest concentration of FAs (16.35 μg-1). In contrast, site P4, the most urbanized, showed the highest content of fatty acids, including those associated with erosion, 378.53 μg g-1, specifically those with long chains. The mean concentrations of the saturated fatty acids (FAs) was 283.40 μg g-1, monounsaturated fatty acids (MUFAs) was 79.46 μg g-1, and polyunsaturated fatty acids (PUFAs) was 15.66 μg g-1. Twenty-seven fatty acids were examined, nevertheless C15:0, C16:0, C18:0, and C18:1ω9 prevailed in all samples. Generally, those acids indicate sewage inputs. Statics analyses were used to find the relation between the source of organic matter (autochthonous, allochthones, and anthropogenic) and FAs. Finally, the input of organic matter is associated with land occupation, which can be distinguished by FA distribution.