Refraktäre organische Substanzen "Humus" und Gewässerversauerung

A review of recent literature on the role and fate of organic matter in the acidification process as well as gaps in our knowledge is given. The conclusions may be highlighted in the following hypotheses. 1) During the postglacial development of soils and vegetation in the catchments, organic acids play a causative role. 2) In the recent acidification process by mineral acid deposition, organic acids act as object rather than subject. This role may be summarized as: Overall: Increased deposition of mineral acids results in decreased levels of dissolved organic matter in surface waters. Detail 1: Increased deposition of mineral acids results in decreased organic matter mobilization from soils and wetlands. Detail 2: Increases in the concentrations of mineral acids in soils, sediments, and surface waters will result in decreased microbial breakdown of organic matter. Detail 3: Increased concentration of mineral acids affect the dissociation of organic acids and alter the physical structu re of dissolved humic substances, leading to an immobilization. Detail 4: Increased concentrations of mineral acids increase the rate at which dissolved organic matter is lost from surface waters to the sediments mainly through co-precipitation with hydrolyzing metals (e.g., Al, Fe) that are themselves mobilized from the soils by mineral acids. These hypotheses are by no means mutually exclusive, they overlap functionally and may reinforce one another. There exists evidence that acidified humic substances exhibit an elevated toxicity towards aquatic invertebrates. These statement should substanciated by further studies, including mechanisms.