Thayara S Carrasco1, Silvina Botta2, Rodrigo Machado3, Elton P Colares1, Eduardo R Secchi1,2. 1. Programa de Pós-graduação em Biologia de Ambientes Aquáticos Continentais, Instituto de Ciências Biológicas, Universidade Federal do Rio Grande, 96203-900, Rio Grande, RS, Brazil. 2. Laboratório de Ecologia e Conservação da Megafauna Marinha - ECOMEGA, Instituto de Oceanografia, Universidade Federal do Rio Grande, 96203-900, Rio Grande, RS, Brazil. 3. Grupo de Estudos de Mamíferos Aquáticos do Rio Grande do Sul (GEMARS), 95560-000, Torres, RS, Brazil.
Abstract
RATIONALE: Stable carbon and nitrogen isotope ratios are widely used in ecological studies providing important information on the trophic ecology and habitat use of consumers. However, some factors may lead to isotopic variability, which makes difficult the interpretation of data, such as the presence of inorganic carbon in mineralized tissues. In order to remove the inorganic carbon, acidification is a commonly used treatment. METHODS: The effects of two methods of acidification were tested: (i) dentin acidification with 10% HCl using the 'drop-by-drop' technique, and (ii) dentin acidification in an 'HCl atmosphere', by exposing the dentin to vaporous 30% hydrochloric acid. Results were compared with untreated subsamples. The stable carbon and nitrogen ratios of untreated and acidified subsamples were measured using an elemental analyzer coupled to an isotope ratio mass spectrometer. RESULTS: The nitrogen isotopic ratios were statistically different between the two acidification treatments, but no significant changes in carbon isotopic ratios were found in acidified and untreated samples. CONCLUSIONS: The results indicated that acidification had no effect on carbon isotopic ratios of Neotropical otter tooth dentin, while introducing a source of error in nitrogen isotopic ratios. Therefore, we conclude that acidification is an unnecessary step for C and N stable isotope analysis.
RATIONALE: Stable carbon and nitrogen isotope ratios are widely used in ecological studies providing important information on the trophic ecology and habitat use of consumers. However, some factors may lead to isotopic variability, which makes difficult the interpretation of data, such as the presence of inorganic carbon in mineralized tissues. In order to remove the inorganic carbon, acidification is a commonly used treatment. METHODS: The effects of two methods of acidification were tested: (i) dentin acidification with 10% HCl using the 'drop-by-drop' technique, and (ii) dentin acidification in an 'HCl atmosphere', by exposing the dentin to vaporous 30% hydrochloric acid. Results were compared with untreated subsamples. The stable carbon and nitrogen ratios of untreated and acidified subsamples were measured using an elemental analyzer coupled to an isotope ratio mass spectrometer. RESULTS: The nitrogen isotopic ratios were statistically different between the two acidification treatments, but no significant changes in carbon isotopic ratios were found in acidified and untreated samples. CONCLUSIONS: The results indicated that acidification had no effect on carbon isotopic ratios of Neotropical otter tooth dentin, while introducing a source of error in nitrogen isotopic ratios. Therefore, we conclude that acidification is an unnecessary step for C and N stable isotope analysis.