Role of photochemical reactions in the biogeochemical cycling of detrital carbon in aquatic environments

Cover figure: Atomic force microscopic image of <0.1 µm filtered water of Lake Valkea-Kotinen sampled on 6 August 1996 displaying detrital and/or viral particles. Fifty µl of the filtered water was allowed to evaporate to dryness on a crystal of mica (diameter of 1 cm). The image was taken with a multi mode atomic force microscope by the courtesy of dr. S. J. 3 To my teachers 4 CONTENTS 1. List of original papers and the author's contribution 1 2. Abbreviations and definitions 2 3. Abstract 3 4. 9. Spectrum of the quantum yield for photochemical mineralization of dissolved organic carbon in a humic lake. Limnology and Oceanography (in the press). mineralization of synthetic lignin in lake water indicates rapid turnover of aromatic organic matter under solar radiation. Biodegradation (in the press). I. Anssi Vähätalo planned the experiments, conducted the measurements, analysed and interpreted the results under supervision of Kalevi Salonen. II. Anssi Vähätalo wrote the paper, developed the theoretical models, planned the experiments, conducted all measurements, analysed and interpreted the results. Kalevi Salonen and Mirja Salkinoja-Salonen supervised the work. Petteri Taalas provided the ozone data. III. Anssi Vähätalo wrote the paper, planned the experiments, conducted all measurements, analysed and interpreted the results. Kalevi Salonen and Mirja Salkinoja-Salonen supervised the work. Annele Hatakka provided synthetic 14 C-lignin and contributed to the supervision of the use of 14 C-labelled lignin. IV. Anssi Vähätalo wrote the paper, planned the experiments, conducted all measurements, analysed and interpreted the results. Kalevi Salonen supervised the work. V. Anssi Vähätalo wrote the paper, planned the experiments, conducted all measurements excluding pigment analyses, analysed and interpreted the results. Morten Søndergaard supervised the work. Louise Schlüter analysed the pigments and Stiig Markager provided expertise in the use of LI-1800 spectroradiometer. Abbreviations 2 2. Abbreviations and definitions CDOM Dissolved organic matter absorbing solar radiation at 290-700 nm. Biodegradation Degradation mediated by organisms. Degradation Reduction in the complexity of detritus. Detritus Dead organic carbon, distinguishable from living organic and from inorganic carbon, lost by non-predatory means from any trophic level (egestion, excretion, secretion, etc.) or from sources external to the ecosystem that enter and cycle in the system (allochthonous organic carbon; Wetzel 1984). Detrivore An organism utilizing detritus. DIC Dissolved inorganic carbon (CO 2 , HCO 3-, CO 3 2-). DOC Dissolved organic carbon. DOM Dissolved organic matter. Extracellular Enzymes located outside the cell membrane. enzyme High molecular Detritus that …