THE ECOLOGICAL SIGNIFICANCE OF DISSOLVED ORGANIC-CARBON IN ACIDIFIED WATERS

Acidification, liming and other anthropogenic effects alter the amount s and character of the humic material and its manifold roles. Although the transfer of DOC from soils to surface waters is an incidental fea ture of terrestrial ecology, the reactive chemistry of DOC makes it of great importance in the ecology of the aquatic ecosystem. It is, ther efore, important to identify the complex nature of the humic material in order to understand its biological role in aquatic ecosystems. Humi c substances may buffer against acidification, but may also add acidit y to surface waters. This may be an important factor in the northern p art of Sweden, whereas further south pH is primarily attributed to ant hropogenic sources. There is large spatial and temporal variation in t he transport of DOC from the terrestrial environment, which varies the ecosystem effects mediated by the humic material on the ecosystem. Th e humic material can affect biological processes through several diffe rent mechanisms, either directly through interfering with metabolic pr ocesses or indirectly by altering the bioavailability of nutrients or toxicants.