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Hydrochemistry and Dissolved Inorganic Carbon (DIC) Cycling in a Tropical Agricultural River, Mun River Basin, Northeast Thailand.

ABSTRACT: Dissolved inorganic carbon isotope composition (δ¹³C_DIC), together with major ion concentrations were measured in the Mun River and its tributaries in March 2018 to constrain the origins and cycling of dissolved inorganic carbon. In the surface water samples, the DIC content ranged from 185 to 5897 μmol/L (average of 1376 μmol/L), and the δ¹³C_DIC of surface water ranged from -19.6‱ to -2.7‱. In spite of the high variability in DIC concentrations and partial pressure of carbon dioxide (pCO₂), the δ¹³C_DIC values of the groundwater were relatively consistent, with a mean value of -16.9 ± 1.4‱ (n = 9). Spatial changes occurred in the direction and magnitude of CO₂ flux through water-air interface (F_CO2). In the dry season, fluxes varied from -6 to 1826 mmol/(m²·d) with an average of 240 mmol/(m²·d). In addition to the dominant control on hydrochemistry and dissolved inorganic carbon isotope composition by the rock weathering, the impacts from anthropogenic activities were also observed in the Mun River, especially higher DIC concentration of waste water from urban activities. These human disturbances may affect the accurate estimate contributions of carbon dioxide from tropical rivers to the atmospheric carbon budgets.

SUBMITTER: Li X

PROVIDER: S-EPMC6765941 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Increasing dissolved inorganic carbon (DIC) concentrations associated with ocean acidification can affect marine calcifiers, but local factors, such as high dissolved organic carbon (DOC) concentrations through sewage and algal blooms, may interact with this global factor. For calcifying green algae of the genus Halimeda, a key tropical carbonate producer that often occurs in coral reefs, no studies on these interactions have been reported. These data are however urgently needed to understand future carbonate production. Thus, we investigated the independent and combined effects of DIC (pCO2 402 μatm/ pHtot 8.0 and 996 μatm/ pHtot 7.7) and DOC (added as glucose in 0 and 294 μmol L-1) on growth, calcification and photosynthesis of H. macroloba and H. opuntia from the Great Barrier Reef in an incubation experiment over 16 days. High DIC concentrations significantly reduced dark calcification of H. opuntia by 130 % and led to net dissolution, but did not affect H. macroloba. High DOC concentrations significantly reduced daily oxygen production of H. opuntia and H. macroloba by 78 % and 43 %, respectively, and significantly reduced dark calcification of H. opuntia by 70%. Combined high DIC and DOC did not show any interactive effects for both algae, but revealed additive effects for H. opuntia where the combination of both factors reduced dark calcification by 162 % compared to controls. Such species-specific differences in treatment responses indicate H. opuntia is more susceptible to a combination of high DIC and DOC than H. macroloba. From an ecological perspective, results further suggest a reduction of primary production for Halimeda-dominated benthic reef communities under high DOC concentrations and additional decreases of carbonate accretion under elevated DIC concentrations, where H. opuntia dominates the benthic community. This may reduce biogenic carbonate sedimentation rates and hence the buffering capacity against further ocean acidification.

Dataset Information

Hydrochemistry and Dissolved Inorganic Carbon (DIC) Cycling in a Tropical Agricultural River, Mun River Basin, Northeast Thailand.

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