Origins, fates, and ramifications of natural organic compounds of wetlandsThis article is part of a larger document. View the larger document here.
Much of the organic carbon for heterotrophic metabolism in aquatic ecosystems is soluble and derived from structural compounds of higher plants of terrestrial and wetland-littoral sources of both lake and river ecosystems. The chemical recalcitrance of this organic matter and its oxidative utilization are fundamentally different from many sources within the aquatic ecosystems. Within the lake or river, complex physical interactions occur that can greatly modify rates of utilization and biochemical reactions. Natural photolysis by photosynthetically active radiation, UV-A and UV-B, can result in the partial degradation of these macromolecules, reactivate complexed enzymes, and generate simple organic compounds and nutrients. A portion of the dissolved organic matter is photolytically degraded completely to CO2. The chemical recalcitrance of these organic compounds (a) represents a fundamental, often dominant, subsidy of organic matter that drives metabolism in fresh waters and (b) is an essential aspect of metabolic stability in aquatic ecosystems. Climatic changes affect this metabolic stability in both positive and negative ways but, generally, will increase instabilities.