Carbon and nutrient accumulation in tropical mangrove creeks, Amazon region

Abstract

The Marapanim River estuary (MRE) is part of the Amazon estuarine system located in northern Brazil, which is characterized as having extensive mangrove forests. Given that previous studies reported CO2 and CH4 fluxes from mangrove creeks in this region, here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems. Sediment accumulation rates derived from 210Pb dating indicated that sampled cores represent the previous 24 (± 4) yr. The approximately 24-year total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) burial rates were estimated to be 192.5 (± 43.5), 15.3 (± 4.1) and 3.2 (± 0.8) g m−2 yr−1, respectively. A binary source mixing model based on carbon stable isotopes (δ13C) revealed that the sedimentary organic matter (OM) is mainly influenced by marine phytoplankton input (49% to 95%). Furthermore, the TOC accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests, suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove-colonized coastal zones. The highest contents, stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins. Our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration, directly related to grain size and OM sources.