Flux of Inorganic Carbon as Dissolved, Suspended, and Bed Loads through a Karstic Basin (original) (raw)
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Aquatic Geochemistry, 2013
The hydrogeochemical and carbon isotope characteristics of the Krka River, Slovenia, were investigated to estimate the carbon transfer from the land ecosystem in the watershed. During the 3-year sampling period (2008)(2009)(2010), temperature, pH, electrical conductivity, major ion content, dissolved inorganic carbon (DIC) and dissolved organic carbon content, and the isotopic composition of DIC (d 13 C DIC ) were monitored in the main stream of the Krka River and its tributaries. The major solute composition of analysed waters is dominated by an input of HCO 3 -, Ca 2? and Mg 2? originating from carbonate dissolution. The Mg 2? /Ca 2? and Mg 2? /HCO 3 molar ratio values ranging from 0.24 to 0.71 and 0.05 to 0.30, respectively, indicate a high degree of dolomite dissolution relative to calcite. Dissolved CO 2 concentrations in the river were up to tenfold supersaturated relative to the atmosphere, resulting in supersaturation with respect to calcite and degassing of CO 2 downstream. The d 13 C values in river water range from -15.6 to -9.4 % and are controlled by the input of tributaries, exchange with atmospheric CO 2 , degradation of organic matter, and dissolution of carbonates. The mass balance calculations for riverine DIC suggest that the contribution from carbonate dissolution and degradation of organic matter have major influence, whereas the exchange with atmospheric CO 2 has minor influence on the inorganic carbon pool in the Krka River.
Chemical Geology, 2018
Exports of dissolved inorganic carbon (DIC) from karst aquifers are a significant contribution to the global carbon cycle. Contributions of particulate inorganic carbon (PIC) and dissolved organic carbon (DOC) in karst groundwater are often unaccounted for in carbon budgets. This investigation considers field chemistry, discrete samples, and continuous monitoring data collected between October 2016 and December 2016 to quantitatively evaluate the net export of dissolved solutes, total suspended sediments (TSS), and DOC within the Vadu Crişului karst basin in the Pădurea Craiului Mountains of northwest Romania. Measurements of carbon isotopes (δ 13 C) in DIC and in bedrock, specific ultraviolet absorption (SUVA), and carbon to nitrogen (C:N) ratios were used to evaluate the relative contribution of different sources of carbon to the aqueous system. δ 13 C DIC at the aquifer input trend toward an atmospheric signal in winter with lower DOC concentrations and SUVA values and C:N ratios corresponding to degraded carbon sources, illustrating the reduction in microbial respiration in soil with cold temperatures. At the spring, δ 13 C DIC values trend more toward a soil-based signal after storm events that bring increased DOC concentrations with SUVA values corresponding to significantly degraded carbon. Dissolution in this karst basin is principally driven by the carbonate equilibrium reactions, and direct meteoric recharge only accounts for 4 to 13% of observed discharge. Most recharge enters the karst basin through infiltration into dolines and epikarst on the Zece Hotare karst plateau, and this results in a broadly stable chemical signature of spring water. Storm events do have a significant impact on mechanical erosion and chemical processes operating in the karst basin; the addition of PIC and TSS flux increase landscape erosion rates by 1.1 to 1.2% and 7.9 to 8.3%, respectively, above the denudation rate computed by dissolved solutes (36.5-56.9 mm/ka). The modeled annual flux of DIC from this karst basin, 1.37 × 10 5 to 1.64 × 10 5 kg/yr, scales to a global CO 2 flux of 7.08 × 10 11 to 1.06 × 10 12 kg/yr. Adding a modeled flux of DOC increases the estimates of CO 2 flux by 12% to 22%, a significant addition to the global carbon cycle.
Geochimica et Cosmochimica Acta, 2019
The long-term change in surface water chemistry over time in remote areas is usually related to global change, including several processes such as global warming and acid atmospheric pollution. These cumulative factors limit the quantitative interpretation of the global warming effect on surface water acidification in relation to the atmospheric CO2 sink. To quantitatively estimate the impact of global warming on the atmospheric/soil CO2 uptake by carbonate weathering, the approach proposed here involves discriminating the proportion of [Ca+Mg] in waters resulting from soil carbonic acid dissolution (equal to the amount of CO2 uptake from soil / atmosphere) from the proportion resulting from strong acid pollution. This approach was applied to 5 karst hydrosystems located in France, far from local pollution sources and with several decades of hydrochemical monitoring. [Ca+Mg] from acid deposition represented between 16 and 25% of the total [Ca+Mg] concentration and the flux was positively correlated with the atmospheric deposition flux. This [Ca+Mg] increase is associated with increasing [Mg] and was found to be driven by the acid pollution inputs. 2 Equilibrating water with calcite in presence of carbonic acid will release [Ca+Mg] into solution. The input of strong acids from atmospheric pollution contributes more to magnesian calcite dissolution because its solubility is lower than that of calcite. Since the 1980s, the decrease in [Ca+Mg] production due to the decrease in acid atmospheric deposition has minimized the increase in [Ca+Mg] linked to CO2 partial pressure (pCO2) increasing with global warming. It was found that [Ca+Mg] from H2CO3 dissolution did not decrease with an increase in air temperature, as suggested by carbonate solubility. The annual fluxes of Ca+Mg from H2CO3 dissolution, calculated for an average flow, showed a positive gradient with air temperature, of about 0.061 mol.m 2 .yr-1°C-1 (±0.006). In low rainfall areas, the pCO2 increase with air temperature was stronger than in rainy areas. For an average specific discharge of 300 L.m-2 yr-1 , global warming is estimated to increase the CO2 uptake flux by about 204 micromol.L-1 .°C-1 (5.7% of the observed flux).
Chemical Geology, 1999
. The transfers and origins of dissolved inorganic carbon DIC were studied for a year in a soil-spring-stream system in the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side Ž . of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80% . Brown acid and podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO generated by oxidation 2 Ž 13 . of soil organic matter. The d C in catchment waters is highly variable, from about y22‰ in the springs and DIC piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of d 13 C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d 13 C of about y24‰ in winter and DIC 2 y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular Ž diffusion of soil CO in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on 2 .
Chemical Geology, 1999
The transfers and origins of dissolved inorganic carbon DIC were studied for a year in a soil-spring-stream system in the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side Ž. of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80%. Brown acid and podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO generated by oxidation 2 Ž 13. of soil organic matter. The d C in catchment waters is highly variable, from about y22‰ in the springs and DIC piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of d 13 C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d 13 C of about y24‰ in winter and DIC 2 y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular Ž diffusion of soil CO in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on 2. average is a result of isotopic equilibration of the aqueous CO with atmospheric CO .
Radiocarbon, 2015
Radiocarbon natural abundances (Δ14C) are being increasingly used to trace carbon cycling in stream ecosystems. To understand the ultimate sources of carbon, we determined the stable carbon isotope ratios (δ13C) and Δ14C values of dissolved inorganic and organic carbon (DIC and DOC, respectively) and of particulate organic carbon (POC) in two small streams in central Japan, one of which flows over limestone bedrock (Seri) and the other does not (Fudoji). Investigations over four seasons revealed that the Δ14C values of the DIC (from −238‰ to −174‰ for Seri and −23‰ to +10‰ for Fudoji) were less variable than those of the other carbon fractions (DOC: from −400‰ to −138‰ for Seri and −2‰ to +103‰ for Fudoji; POC: from −164‰ to −60‰ for Seri and −55‰ to +37‰ for Fudoji). Based on mass balance calculations using the δ13C and Δ14C values, the proportions of carbon in the DIC originated from (1) atmospheric CO2 were 47% to 57% for Seri and 74% to 90% for Fudoji, (2) organic matter degrada...
2022
The weathering rate of carbonate minerals is several orders of magnitude higher than for silicate minerals. Therefore, small amounts of carbonate minerals have the potential to control the dissolved weathering loads in silicate-dominated catchments. Both weathering processes produce alkalinity under the consumption of CO2. Given that only alkalinity generation from silicate weathering is thought to be a long-term sink for CO2, a misattributed weathering source could lead to incorrect conclusions about long-and short-term CO2 fixation. In this study, we aimed to identify the weathering sources responsible for alkalinity generation and CO2 fixation across watershed scales in a degrading permafrost landscape in northern Norway, 68.7-70.5 °N, and on a temporal scale, in a subarctic headwater catchment on the mountainside of Iskorasfjellet, characterized by sporadic permafrost and underlain mainly by silicates as the alkalinity-bearing lithology. By analysing total alkalinity (AT) and dissolved inorganic carbon (DIC) concentrations, as well as the stable isotope signature of the latter (δ 13 C-DIC) in conjunction with dissolved cation and anion loads, we found that AT was almost entirely derived from weathering of the sparse carbonate minerals. We propose that in the headwater catchment, the riparian zone is a hotspot area of AT generation and release due to its enhanced hydrological connectivity, and that the weathering load contribution from the uphill catchment is limited by insufficient contact time of weathering agent and weatherable material. By using stable water isotopes, it was possible to explain temporal variations in AT concentrations following a precipitation event due to surface runoff. In addition to carbonic acid, sulphuric acid, probably originating from pyrite oxidation, is shown to be a potential corrosive reactant. An increased proportion of sulphuric acid as a potential weathering agent may have resulted in a decrease in AT. Therefore, carbonate weathering in the studied area should be considered not only as a short-term CO2 sink, but also as a potential CO2 source. Finally, we found that AT increased with decreasing permafrost probability, and attributed this relation to an increased
Hydrology and Earth System Sciences, 2011
This work presents a study of the dissolved inorganic carbon (DIC) exchange associated with groundwater discharge and stream flow from two upstream catchments with distinct basement lithologies (silicate vs. carbonate). The effects of catchment lithology were evident in the spring waters showing lower δ 13 C DIC and alkalinity (−16.2 ± 2.7 ‰ and 0.09 ± 0.03 meq l −1 , respectively) in the silicate and higher values (−9.7 ± 1.5 ‰ and 2.0 ± 0.2 meq l −1) in the carbonate catchment. The streams exhibited relatively high δ 13 C DIC , −6.9 ± 1.6 ‰ and −7.8 ± 1.5 ‰, in silicate and carbonate catchments, respectively, indicating CO 2 degassing during groundwater discharge and stream flow. The catchment lithology affected the pattern of DIC export. The CO 2 degassing from stream and groundwater could be responsible for 8-55 % of the total DIC export in the silicate catchment, whereas the proportion is comparatively low (0.4-5.6 %) in the carbonate catchment. Therefore, the dynamic carbon exchange occurring at headwater regions and its possible variability with catchment lithology need to be examined for a more reliable carbon budget in river systems.
Journal of Hydrology, 2003
The total dissolved inorganic carbon (TDIC) and 13 C TDIC have been used as chemical and isotopic tracers to evaluate the contribution of different water components discharging at the Fontaine de Vaucluse karst spring near Avignon. At the same time they have been used to separate its flood hydrograph. Waters flowing from unsaturated zone (UZ) and saturated zone (SZ) show similar concentration in TDIC. In UZ and SZ water rock interactions do not obey to the same kinetic. The mixing rate between water coming from the UZ characterised by a short residence time and water from the SZ with a longer residence time has been evaluated in the spring discharge. In a hydrodynamic system, which is rather complex as it is open to the soil CO 2 in UZ and closed to the same CO 2 in the SZ, 13 C TDIC has excellent characteristics as an environmental tracer.