The organic carbon budget of an oligotrophic temperate peatland lake

Lakes play a key role in the global carbon cycle, transporting, processing and storing organic carbon (OC) along the land-ocean aquatic continuum. There are, however, surprisingly few complete lake OC budgets, particularly for certain lake types and geographical areas. An OC budget for Lough Feeagh (Ireland), an oligotrophic, peatland lake in a temperate oceanic location, was estimated for one year using both direct measurements and elements calculated from literature. It was constructed as a simple mass balance model that constrained the key OC processing rates. The total OC input to the lake during 2017 was estimated to be 2544 t C, of which it was estimated that 51% was imported as dissolved OC (DOC) in surface water, 4% in ground water, 1% in rainwater, and 3% was fixed in the lake as net ecosystem production. The remaining 41% was carried into the lake as particulate OC (POC) in surface water. The total C exported was estimated to be 2892 t C, of which 46% and 11% were exported as DOC and POC in the surface water outflow, respectively, 26% was deposited as sediment and 17% was mineralized and emitted as CO2 to the atmosphere. The results highlight the substantial volume of OC turned over in the lake during the study period. Moreover, it emphasizes how lakes in temperate, humic systems, common on the western edge of Europe, are important to the processing and fate of OC mobilized from their catchments.