Distribuição geoquímica de carbono, nitrogênio e fósforo em perfis de sedimento estuarino do rio Parnaíba - PI, Nordeste do Brasil

Abstract

Human impacts on global biogeochemical cycles have been widely studied, effects such as climate change, ecosystem loss and degradation, and increased effluent emissions in aquatic systems are progressively becoming the focus of management efforts to prevent environmental damage. The Parnaíba River Delta is the largest open sea delta in the Americas, with unique ecological importance for wildlife conservation and fishing resources. However, little is known about the biogeochemistry of this ecosystem. This study aims to evaluate total organic carbon, total nitrogen and total phosphorus in sedimentary profiles and surface samples of the Parnaíba-NE estuary. For this purpose, 4 profiles were collected along the lower estuary of the Parnaíba River. The samples were collected with PVC tubes of 5 cm diameter and variable height, generating two profiles of 30 cmand two profiles of 45 cm, which have been sectioned in every 5 centimeters and finally analyzed. Total organic carbon (TOC), total nitrogen (NT), and total phosphorus (P-Total) presented concentrations ranging from 1968 to 2559 u.ug-1of NT, 0.36% to 3.77% of TOC and 548 to 889 u.ug-1of P-total in profile 1 (P1); 1073 to 2358 u.ug-1NT, 3.64% to 5.59% COT E 200 to 534 u.ug -1of P-total in profile 2 (P2); 1386to 1875 u.ug-1NT and 4.07% to 5.41% TOC and 470 to 665 u.ug-1of P-total profile 3 (P3) and 240 to 1210u.ug-1NT and 3.96% to 5.8% of COT and 48 to 142 u.ug -1of P-total in profile 4 (P4). Given the low urbanization and incipient industrial development in the Parnaíba River basin, the values found are closer to a tropical river still not very impacted when compared to other tropical rivers near large metropolises such as the Rio Jaguaribe and Capibaribe. From the C: N ratio, it was determined that mangroves are the main contributors to the contribution of organic matter (OM) to the Parnaíba Delta. These data are important to characterize the Parnaíba River in an initial state of anthropic influence, making it possible to evaluate and monitor future variations in these levels in the face of a scenario of regional and global changes in thenatural organic matterbiogeochemical cycles in tropical estuaries.