Concentrations of dissolved organic matter (DOM) in lakes are often an order of magnitude greater than concentrations of particulate organic matter; nevertheless, the biogeochemical analysis of DOM is described in only a few textbooks on limnology (most thoroughly by Wetzel). The orgins of dissolved organic substances are largely photosynthetic; DOM is either autochthonously synthesized by littoral and pelagic flora through secretions and autolysis of cellular contents, or allochthonously generated in terrestrial systems of the drainage basin, composing largely of humic substances refractory to rapid microbial degradation. The role of DOM in lacustrine ecosystems, as energy source and system regulator, however, is still poorly known. The aim of this book is: (1) to present state-of-the-art reviews of the role of dissolved autochthonous and allochthonous organic matter in pelagial and littoral zones; and (2) to focus attention on poorly understood but critical topics and hence to provide direction for future research activity.

Dissolved organic matter (DOM) is an essential parameter of quality and aquatic ecosystem functioning. The production of DOM in soils and its fate as it moves through the catchment were studied during experiments conducted at different scales, from the soil microcosm to the catchment, using natural abundance tracing of stable carbon isotopes (13C). At the catchment scale, we highlighted the role of wetlands in the formation of dissolved organic carbon (DOC). During discharge events we nevertheless observed the mobilisation of several sources of DOC to feed rivers. During laboratory experiments, we demonstrated that forest type influences the fate of water extractable organic carbon content in soil. The substitution of native forests by Douglas plantations reduces carbon inputs into the soil and mineralisation rates of soil organic carbon, which also depend on temperature. However, the water extractable organic carbon content of forest soils, which is influenced by the forest type, depends neither on carbon mineralisation rate nor temperature. We have therefore concluded that in the surface horizons of forest soils, the DOC mainly originates, not from the decomposition of soil organic matter but rather, from the vegetation via litter leachate.

Limnology is increasingly concerned with water supply and the relation of man to aquatic environments. Without the continued availability of pure water, all progress in technology and other fields of human life will be to no avail. The global problems concerning clear water are already extremely pressing. More limnology knowledge is needed to solve these problems. The responsibility of man to save water and to take more intensive care of the environment is raised in many of the papers, in this book. This emphasizes the necessary and unquestionable relevance of limnology to human society. Too often the abuse of water usage reflects the neglect of scientific results. Limnologists have a responsibility to ensure that administrators understand what is going on. The coverage of the book is wide, including papers on microbiology to engineering sciences. The biology of waters is handled at both species and ecosystem levels. The geographical distribution of topics ranges from the tropics to northern temperate areas. In fact, limnology is increasingly becoming a science which is, rightly, relevant to everyday life, not just an academic subject.