Characterization and quantification of dissolved organic carbon releases from suspended and sedimented leaf fragments and of residual particulate organic matter.

Bank filtration is a powerful and established barrier for pathogens and organic pollutants. The aerobic degradation of the pollutants competes with the microbial respiration of dissolved and particulate organic matter (DOC and POC). The fate of terrestrial POC (tPOC) in bank filtration is currently not fully understood. In the present study, fallen leaves of different local trees were milled, characterized and investigated as tPOC in both batch and column experiments. The respective contents of carbon and nitrogen differed slightly, but the different leaves released significantly different DOC fractions as determined by size-exclusion chromatography. While high molecular weight biopolymers were degraded by indigenous microorganisms, humic substances were not degraded within 96days in batch experiments. DOC release and POC wash-out in column experiments led to a slight decrease of tPOC depositions, but more than 80% of the initial tPOC remained after 54days thus representing a long-term organics reservoir for microbial respiration. The release of humic substances from autumnal leaf litter inputs is a plausible explanation for comparably high DOC concentrations (approximately 4.5mg/L) in Berlin drinking water that mainly originates from lake bank filtration.