Stable isotope analysis of dissolved organic carbon in Canada's eastern coastal waters

Abstract

The application of carbon stable isotope analysis of dissolved organic carbon (δ13C‐DOC) from natural seawater has been limited owing to the inherent difficulty of such analysis, with order of magnitude differences in interfering ions and analyte concentrations. High temperature catalytic oxidation allows for the attenuation of these interferences by precipitation of inorganic ions on quartz chips upstream from the oxidation catalyst. Using a chemical trap, the OI 1030C combustion DOC analyzer unit can be coupled to an IRMS, allowing for the analysis of low DOC content saline waters with relatively high throughput. The analytical limitations and large water volumes traditionally required for these types of analyses have prevented any large‐scale δ13C‐DOC studies. Here, we present δ13C‐DOC signatures for surface and bottom waters obtained along Canada's East Coast. Included in the study are samples from the Esquiman channel (between Newfoundland and Labrador), Lake Melville, the Saglek and Nachvak Fjords, the Hudson Strait and finally covering the salinity gradient across the St. Lawrence Estuary and Gulf. Measured δ13C‐DOC signatures ranged from predominantly marine values of −19.9 ± 0.3‰ (vs. VPDB) off the coast of Newfoundland to predominantly terrestrial signatures of −26.9 ± 0.1‰ in Lake Melville. We observed a large spread in δ13C‐DOC signatures for samples with a salinity of ≈ 35 between −19.9‰ and −23.3‰ demonstrating the difficulty associated to selecting a marine end‐member to be used in stable isotope mixing models to determine the fate of organic matter along the freshwater‐marine continuum.

From canals to the coast: dissolved organic matter and trace metal composition in rivers draining degraded tropical peatlands in Indonesia

“…We observe in-stream processing of DOM, but the total DOM exported from tropical peatlands exceeds the processing capacity of the rivers which drain them and a large proportion of DOM is transported to the ocean. We find persistently high DOC concentrations in both drainage canals and blackwater rivers draining degraded peatlands, consistent with the range of previously reported values in Borneo (Moore et al, 2011;Cook et al, 2018) and in the upper range of blackwater rivers in Sumatra (Baum et al, 2007;Rixen et al, 2008). We also find indicators of in-stream processing of DOM.…”

“…The resulting fluvial export of dissolved organic matter (DOM) has been recognized as an important component of the carbon budget of tropical peatlands that could increase with deforestation and peatland exploitation (Moore et al, 2011;Gandois et al, 2013). Indonesia alone contributes over 10 % of the global riverine dissolved organic carbon (DOC) input into the ocean (Baum et al, 2007), as a result of both high peatland coverage and high precipitation rates. This proportion is likely to increase with rapid peatland conversion to agriculture, which destabilizes long-term peat C stocks (Moore et al, 2013).…”

Interactions between iron and organic carbon in a sandy beach subterranean estuary

“…Several methods have been used to determine the origin of OC in aquatic systems: optical indices of CDOM (Couturier et al, 2016;Kim et al, 2012), lignin oxidation products (Shen et al, 2015), OC fingerprints, and molecular composition by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) (Linkhorst et al, 2017;Seidel et al, 2014) as well as the relative contribution of specific amino acids (Shen et al, 2015). OC origin has also been explored by examination of the  13 C signature of DOC ( 13 C-DOC) in soils (Kaiser et al, 2001;Palmer et al, 2011), stream waters (Bouillon et al, 2012;Palmer et al, 2011;Raymond and Bauer, 2001;Sanderman et al, 2009), groundwater from mangrove tidal creeks (Maher et al, 2013), fjords (Yamashita et al, 2015), and estuaries (Barber et al, 2017b;Osburn and Stedmon, 2011). Here, we present the first attempt to discriminate the origin of OC in beach groundwater using the  13 C signature of DOC.…”

“…The detection limit is 0.05 mg/L and analytical uncertainties were <2% for concentrations higher than 1 mg/L. Samples for DOC concentrations in 2015 and  13 C-DOC in 2013 and 2015 were analyzed using a modified Aurora OI 1030 high-temperature catalytic oxidation unit coupled to a chemical trap (GD-100; Graden Instruments) and a GV Isotope Ratio Mass Spectrometer (Isoprime) as described in detail in Lalonde et al (2014a) and Barber et al (2017b). The standards used for isotopic signatures and DOC concentrations were in-house calibrated β-alanine (40.4% OC, -26.1 ± 0.1‰) and sucrose (42.1% OC, -11.8±0.1‰) dissolved in 18.2 mΩ/cm milli-Q water (Barber et al, 2017b).…”

Terrestrial exports of dissolved and particulate organic carbon affect nearshore ecosystems of the Pacific coastal temperate rainforest

“…On average, concentrations were highest during the winter (1.31 ± 0.05 mg L −1 ) and summer (1.23 ± 0.15 mg L −1 ), and lowest during the autumn (0.93 ± 0.05 mg L −1 ) (Supporting Information Table S6). δ 13 C‐DOC across all marine stations shifted seasonally, between −24.57 ± 0.26‰ (outlet adjacent) or −24.41 ± 0.30‰ (midchannel) in winter, indicating more terrestrial material, and −22.25 ± 0.06‰ (outlet adjacent) or −22.24 ± 0.14‰ (midchannel) through the summer, suggesting a greater contribution from marine autochthonous production (Barber et al 2017) (Figs. 2D, 3).…”