Fatty acids and stable isotopes distribution in the mangrove dominated Parnaiba River Delta

Characterizing the origin and quality of the organic matter (OM) present in estuaries, as well as its export toward the ocean, is a key issue to better understanding the carbon cycle and its impact on global change. In this study, fatty acid markers and delta 13C and delta 15N values were used to characterize the particulate and sedimentary organic matter composition in the large mangrove-dominated Parnaiba Delta, known as a large reservoir of blue carbon. The presence of some long-chain fatty acids and other mangrove OM markers, such as the 18:20)6 and 18:30)3, indicated that the material produced in mangroves contributed largely to the particulate organic matter of water and sediments of the delta. Their presence in further oceanic stations also reveals the mangrove material is exported to the adjacent coastal ocean. In the main river channel, the higher contribution of 18:20)6 in the sediments than in the mangrove regions, indicated an additional source related to anthropogenic activities, probably agriculture. The branched fatty acids found in the samples point to the presence of bacteria and indicated the intense modifications of the organic matter in the region, reflecting the heterotrophic nature of the delta. In addition, the predominance of saturated fatty acids in the delta suggests that the organic matter exported to the coastal ocean is dominated by detrital material.