Description:
In an extensive investigation of an acidified catchment area at Lake Gårdsjön, SW Sweden, variables in terrestrial and lake ecosystems were determined. The lake catchment approach enables an evaluation to be made of the relative importance of sediment processes in the functioning of acid lake ecosystems. In this synthesis attempts have been made to quantify sediment buffering, to assess sediment release and retention of heavy metals and phosphorus, and to present an organic carbon budget. The buffer effect of sediment in the acid Lake Gårdsjön is small, but may have been more important during the earlier course of acidification. Cation budgets (Ca, Mg, Na, K) and experimental studies indicate that sediment may act as a source of cations in acidified lakes. Cation exchange, together with denitrification and other alkalifying processes in the sediment, maintain interstitial water pH at pH 6.0-6.6, except for the uppermost 0-2 cm of sediment. The sediment in Lake Gårdsjön acts as a sink for all analyzed heavy metals, except Mn and Co. Dissolved allochthonous organic carbon is the largest source of carbon. The respiration rate in the sediment is not found to be significantly reduced in acid lakes compared to non-acidified lakes. However, low abundance of detritivorous invertebrates reduces the decomposition rate of leaf litter.