Deposition, burial and sequestration of carbon in an oligotrophic, tropical lake

The amount of biogenic carbon that may be deposited, buried and eventually preserved (sequestered) in the sediments of a tropical, oligotrophic lake, was evaluated based on i) the temporal variation of the particulate organic carbon (POC) concentration in the superficial sediments in the deep zone of lake Alchichica, Puebla, Mexico; and ii) the POC accumulation and preservation in a 210Pb-dated sediment core from the lake. In lake Alchichica the POC concentration in the surficial sediments ranged between 12 and 60 mg POC g-1 (25 ± 12 mg POC g-1 dry weight). The magnitude of the sedimented POC in Alchichica was high and mostly of autochthonous origin. The POC concentrations recorded in the sediment core (16.6 to 31.6 mg g-1 dry weight) were comparable to the concentration range observed in the surface sediment samples collected during the study period, which signaled a high POC preservation capacity in the sedimentary column of lake Alchichica. The POC fluxes, estimated from the 210Pb-dated sediment core, varied between 14.9 and 35.3 g m-2 year-1 within the past century; and the maximum POC losses through diagenesis during this period were estimated to be lower than 25%. This study concludes that deep tropical lakes, exemplified by lake Alchichica, accumulate and preserve most of the POC deposited, playing an important role in regional carbon balances.