Carbon and nitrogen loss rates during aging of lake sediment:: Changes over 27 years studied in varved lake sediment

We used a collection of ten freeze cores of annually laminated ( varved) lake sediment from Nylandssjon in northern Sweden collected from 1979 to 2007 to follow the long-term loss of carbon ( C) and nitrogen (N) due to processes that occur in the lake bottom as sediment ages. We compared specific years in the different cores. For example, the loss of C from the surface varve of the 1979 core ( sediment deposited during 1978) was followed in the cores from 1980, 1985, 1989, and so on until 2006. The C concentration of the sediment decreased by 20% and N decreased by 30% within the first five years after deposition, and after 27 yr in the sediment, there was a 23% loss of C and 35% loss of N. Because the relative loss of C with time was smaller than loss of N, the C: N ratio increased with increasing age of the sediment; the surface varves start with a ratio of similar to 10, which then increases to similar to 12.