Input rates, decay losses and accumulation rates of carbon in bogs during the last millennium: internal processes and environmental changes
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In peatlands the balance between litter input and decay loss in the oxic acrotelm determines the rate of carbon input to the anoxic catotelm with carbon lost at very slow rate. In the acrotelm the C/N-quotient decreases with depth and indicates the loss of carbon from the acrotelm. On one boreo-nemoral and three subalpine ombrotrophic bogs in Sweden the carbon losses in the acrotelm plus the apparent carbon-accummlation rates in the catotelm for the last millennium revealed a constant carbon-sequestering rate up to the end of the nineteenth century equalling that in recent Sphagnum-dominated communities. On the boreo-nemoral bog the carbon-accumulation rate in the catotelm decreased by 50% over the same period while it remained constant on the subalpine bogs. A catotelm with permafrost may have provided more constant conditions for the carbon accumulation than a rising water level creating anoxic conditions. Due to vegetation changes, the recent carbon sequestering in the peat-forming communities is lower than previously and only just enough to compensate for the integrated losses. It is argued that because of internal processes the bogs up to the end of the nineteenth century had obtained or were approaching a steady-state with regard to the carbon input to the catotelm and the supply of mineral nutrients. In contrast, an increased climatic humidity around 1000 cal. BP resulted in high carbon-accumulation rates in the boreo-nemoral bog. Climate could have triggered the recent vegetation changes, but an increased nitrogen deposition is also a probable reason.