Assessing Blue Carbon Through the Decomposition Processes of Tea Bag Index (Tbi) in Tropical Monsoon (Amazon) and Semiarid Mangroves

Abstract

The high capacity of blue carbon storage in mangroves soils is related to a relatively low rate of organic matter (OM) decomposition in anoxic and saline soils. Therefore, studies concerning mangroves and the decomposition kinetics are relevant to evaluate factors that could either accelerate or reduce carbon storage; a pivot strategy to climate change adaptation. In order to assess this, we conducted an evaluation of OM decomposition using Tea Bag Index (TBI) - litter bags decomposition method - in Brazilian mangroves within two contrasting climate regions (monsoon and semiarid). Our results indicated a greater percentage of decomposition in a monsoonal Amazon region compared with a semiarid region for green tea (~25-days: Amazon = 75%; semiarid = 60%; ~90-days: Amazon = 85%; semiarid = 70%), and rooibos tea (~25-days: Amazon = 28%; semiarid = 20%; ~90-days: Amazon = 37%; semiarid = 30%). The decomposition rate (k) and stabilisation factor (S) pattern was consistent with what has been observed in wetland ecosystems, with higher values in ~25-days, at the beginning of burial, compared to after (~90-days) (kmean ~25-90days: Amazon = 0.03-0.01; semiarid = 0.02-0.01); (Smean ~25-90 days: Amazon = 0.10-0.13; semiarid = 0.28-0.16), indicating a trend towards the stabilisation of OM decomposition. In addition to climate differences, the OM concentration, k, and S values in the tropical monsoon and semiarid regions can be linked to regional environmental differences, such as tree canopy species and size, soil composition (mineralogy, iron oxide content, and others), river inputs, and tidal range. Therefore, these regional differences in the decomposition process along with distinct climate patterns are likely to be a consistent indicator that the carbon cycle can vary substantially along the tropical coastlines and is susceptible to global environmental changes.

Keywords: Climate change, Amazon, Semiarid, Decomposition, Mangrove