The composition and flux of particulate and dissolved carbohydrates from the Rhone River into the Mediterranean Sea

Abstract

Abstract.Carbohydrates are important components of the carbon cycle and may be used as indicators of the origin and the diagenetic status of marine and terrestrial organic matter. Nevertheless, comprehensive studies of both particulate (PCHO) and dissolved (DCHO) carbohydrates in rivers are scarce, and the seasonal and interannual variability of these compounds in relationship to the bulk particulate (POM) and dissolved organic matter (DOM) is largely unknown. For the period 2007-2009, we sampled once per month POM and DOM and measured the total suspended matter (TSM), POM, DOM, PCHO, and DCHO for the Rhône River, which flows into the Mediterranean Sea. Using these measurements, we estimated for the above parameters annual fluxes for the period 2007-2009. The estimated carbohydrate fluxes averaged 0.064 ± 0.026 × 10 10 moles C yr −1 for PCHO and 0.042 ± 0.008 × 10 10 moles C yr −1 DCHO, representing 6 % and 7 % of the annual flux of POC and DOC, respectively. During flood and low-water periods, POM variations were reflected into the PCHO pool, whereas this was not observed for DOC and DCHO, indicating a decoupling between particulate and dissolved organic matter. Our results also showed that flood and low-water periods may be differentiated using the ratios PCHO/DCHO and POC/DOC, which had a significant relationship.Based on the carbohydrate abundances in both the PCHO and DCHO pools, we conclude that this material mainly derives from allochthonous sources (vascular plants, bacteria and soils). Moreover, during flood events, an enrichment in mannose in POM was observed, probably reflecting an angiosperm source (leaves or grasses). By expanding our results to the northwestern Mediterranean Sea (Gulf of Lions), we found that the total organic carbon (TOC) fluxes of the Rhône River accounted for ∼1 % of the standing stock of seawater TOC. Considering that glucose is the most abundant carbohydrate in both particulate and dissolved organic matter pools (∼33 %), its annual flux in the northwestern Mediterranean Sea was estimated to 3.8 × 10 8 moles glucose.

DOC in the Mediterranean Sea

“…The major rivers (with a mean discharge higher than 10 km 3 year −1 ) are the Rhone, Po, and Ebro, with DOC concentrations of 134-218 μM. DOC concentrations in the Rhone and Po rivers are from multiyear observations (Table 13.1) (Panagiotopoulos et al, 2012;Pettine et al, 1998;Sempéré et al, 2000), leading greater confidence in the estimates. In contrast, DOC data are taken sporadically in some minor rivers (Table 13.4).…”

When riverine dissolved organic matter (DOM) meets labile DOM in coastal waters: changes in bacterial community activity and composition

“…Samples (~ 40-50 L) were collected on 2 nd May 2013 using automatic samplers installed at the station (Panagiotopoulos et al 2012) and 10-20 L Nalgene carboys that were previously cleaned with detergent and soaked in 2% of HCl for one week. The sampling date corresponded to a high flood event in the Rhône River (4,150 m 3 s -1 ).…”

“…This experimental study was conducted in the Gulf of Lion, one the most productive areas of the Mediterranean Sea, which is influenced by large inputs from the Rhône River (Durrieu de Madron et al 2011). The annual total organic carbon (TOC, particulate and dissolved organic matter) input from the Rhône River is 1.7×10 10 moles C and represents ~1% of the standing stock of TOC in the Gulf of Lion (Panagiotopoulos et al 2012), which is much higher than the average reported for the World Ocean (Smith and Hollibaugh 1993), and highlights the main role played by the Rhône River in the Mediterranean carbon cycle (Sempéré et al 2000). …”

Dicarboxylic and Oxocarboxylic Acids in the Arctic Coastal Ocean (Beaufort Sea‐Mackenzie Margin)

“…The Mackenzie River carries DOM of autochthonous and allochthonous origins, including the degrading remains of vascular plant materials in aged soils (Hedges et al, 1997;Raymond & Saiers, 2010) and the organics derived from recent vascular plant production (Spencer et al, 2012). The DOC content in the Mackenzie River is 2.5 times more elevated than in the Rhône River, and the particulate organic carbon carried by the Mackenzie River (40 × 10 10 gC/year; Doxaran et al, 2012) is twice higher than the particulate organic carbon carried by the Rhône River (19 × 10 10 gC/year, Panagiotopoulos et al, 2012). The DOC content in the Mackenzie River is 2.5 times more elevated than in the Rhône River, and the particulate organic carbon carried by the Mackenzie River (40 × 10 10 gC/year; Doxaran et al, 2012) is twice higher than the particulate organic carbon carried by the Rhône River (19 × 10 10 gC/year, Panagiotopoulos et al, 2012).…”