Contribution of small mountainous rivers to particulate organic carbon input in the Bay of Biscay

Abstract

The Nivelle River, a typical Pyrenean mountainous watershed reaching the Bay of Biscay (Atlantic Ocean), was sampled with high resolution during 1996. The particulate organic carbon (POC) contents during successive floods shows that there is a graduated impoverishment of the organic fraction of suspended particulate matter (SPM) from the first flood to the next ones, reaching a threshold value (3%) attributed to allochtonous fraction (soil). On the basis of the high frequency data of water discharge and POC concentration, an annual POC flux was established: 845 tons, corresponding to a specific POC flux of 5.3 tC km À2 yr À1 . This value was obtained during a dry period and must be considered as a minimum value for longer time scale. The POC originated mostly from soil (55%) and riparian/litter ($40%) with a very minor (<5%) contribution of autochthonous POC. Thirty-two percent of the annual POC flux was carried in 1% of time and 66% in 10% of time. The specific POC yield, 5.3 tC km À2 yr À1 , if extended to the whole mountainous area of the southern coast of the Bay of Biscay (19,000 km 2 ), leads to an estimated POC flux around 100,000 t yr À1 . Although small Cantabrian mountainous rivers contributed to only 28% of the freshwater discharge in the Bay of Biscay, their POC load was estimated to account for 70% of the total POC inputs in the Bay.

Chemical characteristics of particulate organic matter from a small, mountainous river system in the Oregon Coast Range, USA

“…In contrast, other biomarker classes (benzoic acids, amino acid-derived and fatty acid-derived products) with important nonvegetation sources (e.g., algae, bacteria) were primarily (*60%) transported by fine particles. These data highlight contrasts in the transport of particulate constituents by SMRS (e.g., Coynel et al 2005) and suggest different biogenic components may have distinct routing mechanisms and residence times within the watershed.…”

“…2c). The relatively few samples collected over one year, precludes us from investigating seasonal changes in particle compositions and evaluating the effects of sequential flood events on particle loads and characteristics (e.g., Coynel et al 2005). Nevertheless, because our samples cover a range of Q and hydrologic conditions (e.g., rising and falling limbs, early and late season), we believe that they are representative of typical winter flows when the majority of sediment and POM is discharged from the Alsea watershed.…”

“…2c). Further insight into this issue necessitates more frequent sampling of a flood event in order to understand if and how processes such as hysteresis may affect suspended particle compositions (e.g., Coynel et al 2005).…”

“…Small, mountainous river systems (SMRS) deliver over half of the global sediment supply to the world's oceans (Milliman and Syvitski 1992) and may account for a similar fraction of the global particulate organic matter (POM) flux (Lyons et al 2002;Gomez et al 2003;Coynel et al 2005). The importance of SMRS has motivated an increasing number of studies focused on determining the characteristics of these systems, which contrast markedly from the fifty or so largest rivers of the world.…”

“…Overall, this comparison demonstrates that the Santa Clara River, far from being 'a prototypical small mountainous river' (Masiello and Druffel 2001), is part of a continuum of SMRS with contrasting hydroclimate, geology, vegetation and land use. Where appropriate, we extend our comparison to other SMRS such as the temperate Nivelle River draining the schist-dominated Western Pyrenean Mountains (Coynel et al 2005), the typhoon dominated, wet-tropical rivers of Taiwan (e.g., Kao and Liu 1996;Hilton et al 2008a, b) and the heavily impacted systems of the North Island of New Zealand (e.g., Gomez et al 2003).…”