Aquatic Natural Organic Matter (NOM) fuels heterotrophic respiration. The fraction Dissolved Organic Matter (DOM) is operationally defined as material in water samples passing through 0.45 - 0.7 micron filters. Amino acid fluorescence of DOM serves as a proxy for DOM bioavailability. However, bacterial cells, only largely removed by filtration, also demonstrate amino acid fluorescence. The objective of this study was to determine contributions of bacterial cells to amino acid fluorescence in freshwaters. Unfiltered bacterial suspensions demonstrated amino acid fluorescence proportional to bacterial cell concentration; however, 0.22 micron filtration removed most fluorescence. For freshwaters, losses in amino acid fluorescence (up to 60%) with varying pore size filtration largely paralleled losses in particulate material. Using reported retention efficiencies for 0.7 micron filters, bacterial cells in natural waters may account for 5 - 50% of amino acid fluorescence in freshwaters, thereby potentially confounding the interpretation of amino acid fluorescence as a proxy for labile DOM.Master of Scienc
