Sources of Organic and Inorganic Carbon in a Headwater Stream: Evidence from Carbon Isotope Studies

A combination of stable isotope studies and 14C dating were used to identify the main sources and processes controlling streamwater DOC and TIC in a temperate non-forested watershed. δ 13C values for terrestrial (-24.9 to -29.1‰) and aquatic (-30.5 to -33.5‰) plants were similar to values reported in the literature for similar ecosystems. δ 13C values for DOC in soil solution and streamwater were consistent with soil and terrestrial vegetation, indicating that the terrestrial ecosystem is the dominant source of aquatic DOC in this watershed. δ 13C values of soil atmosphere CO2 (-17.2 to -25.2‰) were slightly less negative than would be expected for production via aerobic soil microbial decomposition and root respiration. There was a close correspondence between δ 13C values (-15.5 to -21.5‰) for streamwater TIC and soil atmospheric CO2 in the central part of the catchment where the stream drains CO2-rich peats. 14C dating showed that although peat has been accumulating in the watershed for at least 2700 years, DOC in soil pore water and streamwater contains carbon of predominantly recent origin (post-AD 1955).