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Carbon flux and landscape evolution in epigenic karst aquifers modeled from geochemical mass balance
Author(s) -
Florea Lee J.
Publication year - 2015
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.3709
Subject(s) - karst , aquifer , carbonate , bedrock , geology , carbon cycle , dissolution , hydrology (agriculture) , flux (metallurgy) , saturation (graph theory) , carbon dioxide , dolomite , total inorganic carbon , dissolved organic carbon , groundwater , environmental science , geochemistry , geomorphology , ecosystem , oceanography , chemistry , paleontology , ecology , geotechnical engineering , mathematics , organic chemistry , combinatorics , biology
This paper considers the contributions of epigenic karst processes as a major element of the carbon cycle and a significant agent of landscape evolution. Geochemical models developed from monitoring data and water samples are used to estimate the variation and magnitude of dissolved inorganic carbon (DIC) flux in karst landscapes at several scales, from local to global. At the local scale, the Cumberland River watershed of southeast Kentucky, these geochemical models are also used to evaluate the potential role of sulfur in the production of DIC and to compute an estimated rate of landscape erosion. Geochemical modeling using ionic species and modeled discharge reveal a variable rate of DIC flux driven by large fluctuations in calcite saturation and discharge. Ratios of reaction products and principal component analyses (PCA) suggest that some bedrock dissolution may be driven by the oxidation of reduced sulfur derived from brines entrained into the karst aquifers. Over the 3730 km 2 of carbonate exposure in the Cumberland River, 25.8–62.4 Gg/yr of carbon dioxide (CO 2 ) is conveyed from the atmosphere through the dissolution of carbonate. At the global scale, this translates to 123–296 Tg/yr of CO 2 delivered by karst processes into the aqueous system. The bedrock portion of DIC equates to a flux of 32.6 ± 2.6 m 3 – 35.2 ± 2.8 m 3 of bedrock during the period of study of which 29% was dolomite. This translates to a landscape erosion rate of 13.1–17.9 mm/ka in the 3.45–4.32 km 2 of carbonate exposure in the studied watershed. Based upon 16+ km of cave survey data spanning a vertical range of 72 to 75 m above base level, this suggests that cave development in the watershed spans the Plio‐Pleistocene. Using the modeled erosion rates, the ages of cave levels, 4.03–5.71, 3.08–4.56, 1.57–2.43, 1.01–1.67, 0.45–0.91, and < 0.45 Ma, are in good agreement with regional studies of Plio‐Pleistocene landscape evolution in the Appalachian Lowland Plateaus. Copyright © 2015 John Wiley & Sons, Ltd.