Seasonal and diel relationships between the isotopic compositions of dissolved and particulate organic matter in freshwater ecosystems

摘要: A study of the isotopic composition organic matter was conducted in a freshwater marsh over seasonal and diel time scales to determine sources dissolved (DOM) processes leading its formation. Bulk C N compositions bacterial fraction (0.2–0.7 μm) particulate (POM; 0.7–10 were compared on basis with change δ13C DOM. The bulk data support idea that DOM was, part, derived from breakdown larger fractions. POM compositionally similar throughout year, based comparison individual amino acids each fraction. Annual variation greater relative fractions indicating microbial reworking an important factor determining proteinaceous component 13C enrichment serine leucine suggested during most productive times year. Changes more significant daily, seasonal, where values ranged by 6‰ followed changes chlorophyll concentrations. Although for only −29 −28‰ same period, alanine −30 −22‰. Alanine is directly synthesized pyruvate therefore good metabolic indicator. revealed importance autotrophic versus heterotrophic activity influencing composition. Diel phenylalanine, common pathways phytoplankton bacteria, both POM. isoleucine valine, through different distinctly This disparity indicated decoupling pools, which suggests source bacterial-derived at night. results this demonstrate use contributions scales.