Optical properties of dissolved carbon in a high elevation tropical peatland ecosystem

Tropical peatlands are distributed mainly in coastal lowlands; however high elevation regions include a large prevalence of small and fragmented peatlands that are mostly understudied. Anthropogenic pressure to expand cattle farming, agriculture, and urbanization frontiers via artificial drainage of peatlands is increasing carbon losses to the atmosphere and streams. Here we present, the first characterization of dissolved carbon optical properties in ombrotrophic peat bogs of the Talamanca range of Costa Rica, across an altitudinal gradient (2,400-3,100 m asl) during the rainy season. Dissolved organic matter (DOM) sources and decomposition processes were evaluated in the light of dissolved organic and inorganic carbon (DOC and DIC), optical properties, excitation-emission matrices (EEMs), and major water chemistry. DOC concentrations ranged from 0.2 mg/L up to 47.0 mg/L, with a mean value of 12.5 ± 10.2 mg/L. DIC concentrations were below 2 mg/L and δ13CDIC values indicated a mixture between soil organic matter, CO2 in soil water, and in less degree DIC derived from bacterial CO2. Fluorescence intensity of humic-like peaks was 6-7 times greater than fresh-like peaks across all sites. Fluorescence peak ratios coupled with the biological and humification indexes point to a greater relative contribution of recalcitrant soil-derived DOM. EEMs denoted a high prevalence of humic and fulvic acids in the peat bogs, with particular high intensities in soluble microbial by-products-like and aromatic protein regions at three sites. Rainfall variability plays a remarkable role in controlling (acid and anoxic conditions) carbon storage and humification processes. Our data provides a baseline to underpin tropical carbon dynamics across high elevation peatlands.