Particulate organic matter (POM) composition in stream runoff following large storms: role of POM sources, particle size, and event characteristics

350 210 Stroud Water Research Center

Johnson, E.R., S. Inamdar, J. Kan, and R. Vargas. 2018. Journal of Geophysical Research 123(2):660–675.

doi: 10.1002/2017JG004249


Large storm events possess significant erosive energy capable of mobilizing large amounts of sediment and particulate organic matter (POM) into fluvial systems. This study investigated how stream POM composition varied as a function of the watershed POM source, particle size, storm event magnitude, and seasonal timing. POM composition was characterized for multiple watershed sources and for stream POM following storms in a second order forested stream. Carbon (C) and nitrogen (N) amount, C:N ratio and isotopic content (13C and 15N) were determined for solid phase POM, whereas dissolved organic C (DOC), total N concentrations and fluorescence characteristics were determined for solution/extracted POM. Key findings from this study were: (1) Composition of POM varied greatly with watershed sources with forest floor litter being C and N rich and labile while stream banks and bed were C and N poor and recalcitrant. (2) Summer storms mobilized more carbon and nitrogen rich labile sources, while winter events mobilized more carbon and nitrogen poor refractory material from near stream sources. (3) POM composition varied by size class, with the coarse POM (CPOM) showing more C and N rich and labile properties while the fine POM (FPOM) displayed more degraded and refractory properties. If climate variability increases the magnitude and intensity of large storm events, our observations suggest that this will not only increase the inputs of POM to aquatic systems but also result in the delivery of coarser, C and N rich, and more bioavailable POM to the stream drainage network.