Biomarker responses to short-term experimental warming: assessing organic matter sensitivity in Amazonian Lakes

Amazon is the largest tropical rainforest in the world, with an important role in the global carbon cycle. However, the increase of the average temperature may alter the  biological activity in the sediments of Amazonian lakes, which will afect this natural equilibrium. This work aimed to evaluate the influence of a short-term experimental warming of sediments of two Amazonian lakes, to understand the sensitivity of organic matter to global warming effects. The experimental warming was conducted at two different temperatures (25 and 29 ºC) for 10 days. The sediments were then submitted to organic matter extraction, fractionation into aliphatic and aromatic hydrocarbons, and polar compounds. All fractions were analyzed by gas chromatography coupled to mass spectrometry (GC-MS) to obtain chemical fingerprint of the extracts. Different classes of compounds were evaluated: n-alkanes, bacterial terpenoids, sterols, and carboxylic acids. Results showed that Lake P presented an increase in microbial activity for both temperatures due to the increase of bacterial biomarkers concentration, while no significant difference was observed for Lake A. Also, n-alkane and sterol distribution indicated that the organic matter in the Lake A was more recalcitrant to warming than Lake P, because most results showed no difference between the original sediment and the sample submitted to 25 ºC, but a substantial alteration after 29 ºC warming. On the other hand, Lake P showed a decrease of n-alkane concentration after warming at 25 ºC, but similar trends between the two experiments (25 and 29 ºC) were observed, probably due to n-alkane degradation during microbial digestion. These results indicate that Lake P is more prone to environmental changes in comparison to Lake A. Also, this work shows the impact of global warming to the organic matter transformation and preservation in Amazonian lakes.