Particulate Organic Matter Composition in Stream Runoff Following Large Storms: Role of POM Sources, Particle Size, and Event Characteristics

Abstract

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, total N concentrations, and fluorescence characteristics were determined for solution/extracted POM. Key findings from this study were the following: (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 showing more C and N rich and labile properties, while the fine POM 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.

Streambank Legacy Sediment Contributions to Suspended Sediment‐Bound Nutrient Yields from a Mid‐Atlantic, Piedmont Watershed

“…Storm suspended sediments for fingerprinting were collected from the upstream and downstream sampling sites (Figure 1) using passive samplers. These samplers were modified from Phillips et al (2000) and Johnson et al (2017) and were designed to collect a composite sample of sediment over the duration of an event. The samplers were constructed from 4 in.…”

Wrack and ruin: Legacy hydrologic effects of hurricane-deposited wrack on hardwood-hammock coastal islands

“…A nonlinear least squares optimization of the bucket model (per observations from the leachate trays) resulted in an S max of 19.9 mm (figure S3 in supplemental materials). Although litter leachate trays are commonly deployed in forest ecohydrological research (e.g., Campbell et al 2007, Johnson et al 2018, we note that flow pathways through natural litter deposits may be more efficient, explaining why the modelling exercise yielded higher storage estimates. These water storage capacity estimates exceed all forest litter storage values that have been estimated to date (ranging from 0.2-8.0 mm (Gerrits and Savenije 2011).…”

Particulate macronutrient exports from tropical African montane catchments point to the impoverishment of agricultural soils

“…Similarly, the study of Johnson et al (2017) in a forested catchment in the Piedmont region, Maryland (USA) showed that sediment sources from forest floor litter had the highest TC and TN concentrations compared to near-stream sources such as stream bed and stream banks. The fresher material from the forest floor was likely the least degraded resulting in higher C and nutrient concentrations (Johnson et al, 2018). Old growth forests maintain a tight nutrient cycle through high and diverse aboveground biomass.…”

“…Sediments and their associated organic C and nutrients, such as N and P (Horowitz, 2008;Johnson et al, 2018;Quinton et al, 2001) may impact streams by reducing benthic communities, primary productivity and water storage capacity of water reservoirs (Hunink and Droogers, 2011;Tamene et al, 2006) and by increasing turbidity (Stenfert Kroese et al, 2020b;Tamooh et al, 2014). In nutrient-limited freshwater systems, an excess of nutrients can cause eutrophication (Jarvie et al, 2019;Smith et al, 2017;Smith and Schindler, 2009), inducing algal blooms and promoting invasive weeds (e.g.…”