Occurrence of organic colloids in the stratified estuary of the Krka River (Croatia).

International audienceAlong a vertical profile of a stratified estuary, we determined organic carbon in the following fractions: low molecular weight (LMW-OC 0·7 μm). The results showed abundant concentrations of organic colloids accounting for: 40% of total organic carbon (TOC) in the overlying brackish water (salinity 2), 22% in the underlying marine water (salinity 38) and 19% (±5%) for intermediate salinity samples (salinity 3–31). Upon contact with seawater (in the salinity range 2–5) both DOC and COC concentrations decreased drastically (44 and 47 μM respectively), whereas POC slightly increased (11 μM), being consistent with previous laboratory and field studies, and indicating that at low salinities, the colloidal fraction is actively involved in the DOC physicochemical aggregation. In the halocline, we observed that organic colloids and relatively degraded particles accumulated together in the lowest part of the interface (salinity 31). Because previous studies in the same area have shown accumulation of degraded cells and fragments in the bottom of the halocline, we suggest that large colloids (COC in this study) at the interface probably originated from fragmentation of non-living organisms or aggregates. Furthermore, it is likely that these processes which are enhanced in a highly stratified estuary, are partly responsible for the DOC non-conservative dilution observed along this profile

Dissolved and colloidal organic carbon in the Rhone Estuary: comparison of the UV-persulfate and HTCO method.

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Ultrafiltration of seawater with a zirconium and aluminum oxide tubular membrane: application to the study of colloidal organic carbon distribution in an estuarine bottom nepheloid layer.

International audienceFor separation of organic colloids in fresh and saline waters, a cross-flow ultrafiltration system was built with a new type of membrane made of zirconium and aluminum oxides. This membrane had a tubular design (16 cm long, 4 cm wide) and a porosity of 10 nm. The suitability of the system for organic carbon studies was first tested by laboratory experiments. In the conditions determined, we obtained acceptable values of dissolved organic carbon (DOC) blank (less than 4 μmol Cl−1) and minimal material adsorption on the membrane. Our special unit was applied to seawater samples collected from the bottom nepheloid layers (BNL) off the Rhône Delta (France). Material defined as colloidal matter in the size range of 0.01–0.7 μm was isolated by filtration on GF/F filters, followed by ultrafiltration. Organic carbon was measured in the so-called dissolved (DOC 0.7 μm) fractions. COC displayed a wide range of concentrations, from 7 μmol Cl−1 (COC/DOC = 7%) offshore, up to 88 μmol Cl−1 (COC/DOC = 49%) near the mouth, whereas truly dissolved carbon remains constant (tDOC = 89 ± 10 μmol Cl−1). In fact, a strong negative correlation was found between COC concentrations near the sediment and the distance from the mouth, indicating that in the area investigated, the major part of the colloidal material does not reach the open ocean. Furthermore, COC concentrations were positively correlated with POC concentrations, suggesting a particulate origin of colloids in the Rhône BNL

Dissolved organic carbon in seawater: confirmation of previous underestimation

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Carbon inputs of the Rhône River to the Mediterranean Sea: Biogeochemical implications

International audienceSince the damming of the Nile, the Rhône River is the main freshwater and sediment supplier to the Mediterranean Sea. We estimated for the period 1987–1996, the dissolved and particulate organic carbon (DOC and POC), dissolved inorganic carbon (DIC), and total suspended matter (TSM) fluxes of the Rhône River to the Mediterranean Sea to be 1.1 ± 0.2, 1.6 ± 0.5, 16.2 ± 0.3 × 1010 moles C yr−1, and 9.9 ± 6.4 × 106 t yr−1, respectively. PIC flux was estimated to be 8.2 ± 5.4 × 109 moles C yr−1. On the basis of literature data, we estimated that nearshore bacterial respiration of Rhône derived labile‐POC and ‐DOC (LPOC and LDOC) might produce in a few days ∼0.21 and 0.12 × 1010 moles CO2 yr−1, respectively. Extended to the whole Mediterranean, this study suggests that bacterial respiration of labile organic carbon derived from Mediterranean rivers might rapidly (days) produce 2.6‐11 × 1010 moles CO2 yr−1. On the continental shelf, up to 4.7 × 1010 moles of organic carbon introduced by primary production and Rhône export would escape each year to sedimentation and bacterial mineralization and would be exported off the shelf. Moreover, as total carbon fixed by phytoplankton exceeds (+ 5.2 × 1010 moles C yr−1) the CO2 produced by bacterial respiration (on average), the biological system on the shelf, could be considered as an autotrophic system and then a sink for atmospheric CO2. However, these numbers need further examination because of the the large uncertainties associated currently to the bacterial growth efficiency values (± 100%

Application of the wet oxidation method for dissolved organic carbon analysis in the Southern Ocean

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Origines et comportement du carbone organique dans l'estuaire de la Loire

info:eu-repo/semantics/publishe

Nutrients (organic C, P, N, Si) in the eutrophic River Loire (France) and its estuary

The Loire estuary has been surveyed from 1982 to 1985 by 13 isochronous longitudinal profiles realized at low tide. Nutrient (SiO2, NO3-, NH4+, PO3-4, particulate organic carbon or POC) patterns are very variable depending on the season, the estuarine section [river, upper-inner estuary, upstream of the fresh-water-saline-water interphase FSI, the lower-inner estuary characterized by the high turbidity zone (HTZ), the outer estuary] and the river discharge. Biological processes are dominant. In the eutrophied River Loire (summer pigment > 100 μg l-1), the high algal productivity (algal POC > 3 mg l-1) results in severe depletion of SiO2, PO43-, NO3-. The enormous biomass (55 000 ton algal POC/year) is degraded in the HTZ where bacterial activity is intense. As a result, there is generally a regeneration of dissolved SiO2 and PO43-, a marked NH4+ maximum, while NO3- is conservative or depleted when the HTZ is nearly anoxic. Other processes can be considered including pollution from fertilizer plans (PO43-, NH4+) and from a hydrothermal power plant (NH4+). In the less turbid outer estuary, nutrients are generally conservative. Major variations of concentrations are observed in the lowest chlorinity section (Cl- < 1 g kg-) and also upstream the FSI, defined here as a 100% increase in Cl-. Nutrient inputs to the ocean are not significantly modified for SiO2 and NO2-, but are increased by 70% and 180% for PO43- and NH4+ and depleted by 60% for POC. Odd hydrological events, especially some floods, may perturbate or even mask the usual seasonal pattern observed in profiles. © 1988.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Transport and fate of Danube Delta terrestrial organic matter in the northwestern Black Sea mixing zone

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