Particulate organic matter (POM) export from catchments: role of particle size, sources, headwater drainage area and storm event magnitude
Date
2016
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Publisher
University of Delaware
Abstract
High-runoff events can trigger rapid and highly variable fluxes of sediment and ecologically-important solutes from small catchments and these can be difficult to characterize due to their transient nature. We investigated the quantity and sources of particulate organic matter (POM) during storm events in a forested network of first and second order streams in the mid-Atlantic, Piedmont region of the USA. We compared stable isotope ratios (13C and 15N) of three size classes of particulate organic carbon (POC) and nitrogen (PN) to those of potential sediment end members to infer proportional source contributions. Additionally, we explored hydrologic controls on POM source and elemental and isotopic composition using samples from discrete time points along storm event hydrographs. Our findings indicate that plant litter contributes the greatest proportion to the coarse fraction and that valley bottom wetlands consistently contribute to POM. While resuspension of coarser mineral bed sediments dilutes the carbon and nitrogen content of sediments at larger drainage areas, fine POM was increasingly mobilized from the bed. The C:N ratios and isotopic quality of fine particles suggest this pool of POM has undergone aquatic microbial processing. Higher maximum discharges mobilized material from the forest floor O horizon (litter and humus) to the channel, while more intense precipitation flushed stream bed POM. Precipitation events are projected to increase in frequency and magnitude in the northeastern United States under changing climate scenarios. Understanding the potential for hydrologically-driven changes to POM efflux from headwater sources may help to explain altered biogeochemical cycles within their higher-order watersheds.