Long-term patterns of peat accumulation and organic matter decomposition in Costa Rican peatlands

Abstract

Abstract. Tropical peatlands, compared to their boreal counterparts, are vastly understudied despite acting as a significant terrestrial carbon sink, sequestering 100—300 Gt of carbon. In particular, the low number of field-based studies from Latin America and the Caribbean limits our knowledge of these important wetland ecosystems. Across the tropical Panamerican region, peatland location, soil characteristics, inception ages, and carbon accumulation histories remain largely unknown. These datasets are needed to inform a mechanistic understanding of why peat develops in certain areas but not in others, both in terms of peat initiation conditions as well as the factors that enable peat to subsist over centuries and millennia. Here we present extensive, high-resolution laboratory datasets from 11 peat cores from 4 peatland types from Costa Rica (high-elevation, riverine, coastal palm swamp, and mangrove). A multi-proxy palaeoecological approach was employed to shed light on the successional pathways and past conditions that have allowed these peatlands to form, as well as to provide a first estimate of their carbon stock. The core characterization includes radiocarbon dating, loss-on-ignition, carbon and nitrogen content, and plant macrofossils. Fourier transform infrared spectroscopy (FTIR) was also used to assess changes in organic matter quality across sites and over time. The averaged peatland carbon stock in Costa Rica is estimated at 1080 MgC ha−1, making these ecosystems exceptionally rich carbon stores that are comparable to values found in lowland Amazonian peatlands. Overall, this research provides a basis for understanding long-term carbon accumulation within Caribbean tropical peatlands.