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Sci Total Environ. 2019 Feb 15;651(Pt 1):851-858. doi: 10.1016/j.scitotenv.2018.09.205. Epub 2018 Sep 18.

Human-induced and natural carbon storage in floodplains of the Central Valley of California.

Author information

1
College of Agricultural and Environmental Sciences, Department of Viticulture and Enology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA. Electronic address: ksteger@ucdavis.edu.
2
Institute of Geography, Augsburg University, Alter Postweg 118, 86159 Augsburg, Germany.
3
US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA.
4
Environmental Systems, School of Engineering, University of California, Merced, 5200 North Lake Road, CA 95340, USA.
5
College of Agricultural and Environmental Sciences, Department of Viticulture and Enology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.

Abstract

Active floodplains can putatively store large amounts of organic carbon (SOC) in subsoils originating from catchment erosion processes with subsequent floodplain deposition. Our study focussed on the assessment of SOC pools associated with alluvial floodplain soils that are affected by human-induced changes in floodplain deposition and in situ SOC mineralisation due to land use change and drainage. We evaluated depth-dependent SOC contents based on 23 soil cores down to 3 m and 10 drillings down to 7 m in a floodplain area of the lower Cosumnes River. An estimate of 266 Mg C ha-1 or about 59% of the entire SOC stored within the 7 m profiles was found in the upper 2 m. Most profiles (n = 25) contained discrete buried A horizons at depths of approximately 0.8 m. These profiles had up to 130% higher SOC stocks. The mean δ13C of all deep soil profiles clearly indicated that arable land use has already altered the stable isotopic signature in the first meter of the profile. Radiocarbon dating showed that the 14C age in the buried horizon was younger than in overlaying soils indicating a substantial sedimentation phase for the overlaying soils. An additional analysis of total mercury contents in the soil profiles indicated that this sedimentation was associated with upstream hydraulic gold mining after the 1850s. In summary, deep alluvial soils in floodplains store large amounts of SOC not yet accounted for in global carbon models. Historic data give evidence that large amounts of sediment were transported into the floodplains of most rivers of the Central Valley and deposited over organically rich topsoil, which promoted the stabilization of SOC, and needs to be considered to improve our understanding of the human-induced interference with C cycling.

KEYWORDS:

Anthropogenic influences; Buried horizon; Deep soil carbon dynamics; Gold rush; Mercury; Radiocarbon dating

PMID:
30253367
DOI:
10.1016/j.scitotenv.2018.09.205
[Indexed for MEDLINE]

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