Particulate organic matter export by two contrasting small mountainous rivers from the Pacific Northwest, U.S.A.

Abstract

[1] We investigated the export of particulate organic matter (POM) to the ocean by two contrasting small, mountainous rivers, the Umpqua and Eel Rivers, by collecting suspended sediment samples over a range of discharges and analyzing them for a variety of constituents, including organic carbon, nitrogen, biomarkers with distinct biochemical sources, and isotopic compositions (d 13 C and Δ 14 C). Concentrations of all measured constituents in both rivers increased as a function of discharge, resulting in their export being dominated by short-lived, wintertime high-discharge events. In the Umpqua River, marked compositional contrasts between low-and high-discharge conditions were consistent with a shift in the provenance of POM from biogenic sources dominated by non-vascular plant sources at low flows to contributions from vascular plant sources of moderate 14 C ages (~300 years before present) dominating at high flows. In contrast, POM from the Eel River, which was highly diluted by mineral sediment at all discharges, had significant contributions from petrogenic sources and displayed lower concentrations of recognizable biomarkers. Both rivers had comparable yields of biogenic POM, which appeared to be moderately degraded and originated primarily from surface soils in erosion prone areas of the watersheds. While tectonic/ geologic differences help explain the contrasts in sediment and petrogenic POM yields between the two watersheds, ecological factors such as vegetation coverage, productivity, and soil carbon are more important in influencing the composition of biogenic POM mobilized from these systems.

Perspectives on the Terrestrial Organic Matter Transport and Burial along the Land-Deep Sea Continuum: Caveats in Our Understanding of Biogeochemical Processes and Future Needs

“…Therefore, systematic δ 13 C and δ 15 N investigations in hadal environments may shed some lights about whether the dark ocean is an environment of substantial terrestrial C pool or not. In addition, radiocarbon ( 14 C) measurements of particles and sediments in hadal trenches, similar to studies made from other river and marine realms (Bauer et al, 1992;Raymond and Bauer, 2001;Goñi et al, 2013), may provide additional constraints on age, fate and reactivity of OM and therefore provide clues about the transport mechanism and the nature of particles and sediments in the dark ocean.…”

Sediment flow paths and associated organic carbon dynamics across a Mediterranean catchment

“…Apart from the indications of OC mineralisation, the MOC concentration of suspended sediments was low and very variable (3.8-0.1 %), which can be attributed to the diverse characteristics of the events that mobilise material from different sources (Smith et al, 2013;Goñi et al, 2013;Sanchez-Vidal et al, 2013) or to sediments mobilised by different erosion processes (Nadeu et al, 2011(Nadeu et al, , 2012.…”

“…Differences in OC pools between sediment deposits can also be the result of transport conditions due to higher or lower rainfall intensity (Martínez-Mena et al, 2012;Zhang et al, 2013) or to the discharge. Smith et al (2013) related high discharge rates with transport of modern C, associated with erosion and the release of organic matter (Sanchez-Vidal et al, 2013), and C from vascular sources (Goñi et al, 2013). Low flows were associated with export of fossil OC (Smith et al, 2013) from biogenic sources dominated by non-vascular plants (Goñi et al, 2013) or from freshwater primary producers (Sanchez-Vidal et al, 2013).…”

“…Smith et al (2013) related high discharge rates with transport of modern C, associated with erosion and the release of organic matter (Sanchez-Vidal et al, 2013), and C from vascular sources (Goñi et al, 2013). Low flows were associated with export of fossil OC (Smith et al, 2013) from biogenic sources dominated by non-vascular plants (Goñi et al, 2013) or from freshwater primary producers (Sanchez-Vidal et al, 2013). A comparison of the particle sizes of the studied sediments and soils of the catchment points to a selection of transported material in a downstream direction.…”

Evaluating the Surface Response of Discharge Events in a New Zealand Gulf-ROFI

“…The balance between river inflows, tidal oscillations, and wind stirring processes at the respective boundaries regulates the distribution and fate of material, nutrients and biota. River plume responses for small discharges are not well understood, despite small mountainous rivers delivering disproportionate quantities of particulate organic carbon (POC) to the global budget (Wheatcroft et al, 2010;Goni et al, 2013). Here, the focus is on understanding responses during individual discharge events and evaluating the cumulative role of material transport for a coastal system.…”