Dissolved inorganic carbon sourcing using δ¹³C_DIC from a karst influenced river system

Abstract

Rivers, representing the primary conduits of dissolved inorganic carbon (DIC) from the continents to the oceans, are important components to the global carbon cycle. To better understand the complex carbon cycling dynamics within two nested, mixed lithology watersheds, two sites were studied along the karst influenced upper Green River in south‐central Kentucky, USA. Weekly samples were collected from June 2013 through May 2014 and analyzed for δ13CDIC. The mixing model IsoSource was employed to better understand source partitioning differences over seasonal time spans and across the two nested basins. In both the lithologically mixed upstream basin (53% carbonate rocks, 47% siliciclastic) and carbonate rock dominated downstream basin (96% carbonate rocks in the drainage area between Greensburg and Munfordville, 78% in the total area upstream from Munfordville), DIC was primarily derived from soil respiration. The proportion of DIC from dissolved carbonate minerals derived from the downstream carbonate rock dominated basin was similar to the upstream basin, due to carbonate mineral dissolution having such a consistent effect on the overall DIC content of the river. Seasonally, soil respiration provided the most DIC from fall to winter. Early spring precipitation, combined with limited seasonal photosynthesis, shifted groundwater to be the primary source of DIC, bringing in a flush of carbonate mineral‐rich water during higher flows. This study provides insight into carbon dynamics across multiple lithologies and the important influence of seasonality using carbon isotope sourcing to determine carbonate mineral dissolution variability and aid in understanding its contribution to global carbon flux quantification. Copyright © 2015 John Wiley & Sons, Ltd.

Spatiotemporal variations of dissolved inorganic carbon and controlling factors in a small karstic catchment, Southwestern China

“…In most karstic aquifer networks, particularly the underground conduits, it is difficult for sufficient atmospheric CO 2 to enter the water because of the lower pH (<5.6) (Wu et al ., ) in rainfall and the higher p CO 2 in water (>10 −3.5 atm) (Li et al ., ; McClanahan et al ., ). In this study, the higher p CO 2 in underground water (>10 −3.5 atm) indicates that the atmospheric contribution to DIC can be ignored in UGW.…”

“…This observation might be explained by the limited increment of these ions during the big storm event in which the increased flow generated a dilution effect. In addition, slightly negative values of f (log p CO 2 ) in most phreatic aquifers might be ascribed to the consumption of soil CO 2 by carbonate dissolution or weak CO 2 degassing from conduit outlets resulting from turbulence during rainfall pulses, and there was not a large enough supplement of additional CO 2 along the flow pathway to offset this depletion (McClanahan et al ., ).…”

“…The kinetics of carbonate dissolution are more rapid than silicate weathering induced by carbonic acid, which results in a net carbon sequestration into calcites [Equation ] (McClanahan et al ., ). Carbonate weathering offers both a sink and a source of atmospheric carbon.…”

Seasonal δ13CDIC sourcing and geochemical flux in telogenetic epikarst of south‐central Kentucky

“…Further, soil moisture increased at both sites in response to winter storms, as did soil temperature. Diurnal fluctuations in surface temperature are also present at both sites throughout the study, indicative of solar radiation heating during the day and a reduction in solar radiation at night (Pu et al ., ; McClanahan et al ., ), thus dominating the response within the systems despite the seasonal influence.…”

“…The gap in data is a result of the logger pulled for maintenance. [Colour figure can be viewed at wileyonlinelibrary.com] L. JACKSON AND J. S. POLK etMcClanahan et al, 2016), thus dominating the response within the systems despite the seasonal influence.…”