Browsing by Subject "LAND-USE"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Iron Age landscape changes in the Benoué River Valley, Cameroon
    (Quaternary Research (United States), 2019-09-01) Wright, DK; MacEachern, S; Ambrose, SH; Choi, J; Choi, JH; Lang, C; Wang, H
    Copyright © 2019 University of Washington. Published by Cambridge University Press. The introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon (13C/12C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen (15N/14N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ15N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ13C and δ15N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.
  • Thumbnail Image
    ItemOpen Access
    Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration
    (Elementa, 2018-01-01) Billings, SA; Hirmas, D; Sullivan, PL; Lehmeier, CA; Bagchi, S; Min, K; Brecheisen, Z; Hauser, E; Stair, R; Flournoy, R; De Richter, DB
    © 2018 The Author(s). Roots and associated microbes generate acid-forming CO2 and organic acids and accelerate mineral weathering deep within Earth's critical zone (CZ). At the Calhoun CZ Observatory in the USA's Southern Piedmont, we tested the hypothesis that deforestation-induced deep root losses reduce root- and microbially-mediated weathering agents well below maximum root density (to 5 m), and impart land-use legacies even after ∼70 y of forest regeneration. In forested plots, root density declined with depth to 200 cm; in cultivated plots, roots approached zero at depths >70 cm. Below 70 cm, root densities in old-growth forests averaged 2.1 times those in regenerating forests. Modeled root distributions suggest declines in density with depth were steepest in agricultural plots, and least severe in old-growth forests. Root densities influenced biogeochemical environments in multiple ways. Microbial community composition varied with land use from surface horizons to 500 cm; relative abundance of root-associated bacteria was greater in old-growth soils than in regenerating forests, particularly at 100-150 cm. At 500 cm in old-growth forests, salt-extractable organic C (EOC), an organic acid proxy, was 8.8 and 12.5 times that in regenerating forest and agricultural soils, respectively. The proportion of soil organic carbon comprised of EOC was greater in old-growth forests (20.0 ± 2.6%) compared to regenerating forests (2.1 ± 1.1) and agricultural soils (1.9 ± 0.9%). Between 20 and 500 cm, [EOC] increased more with root density in old-growth relative to regenerating forests. At 300 cm, in situ growing season [CO2] was significantly greater in old-growth forests relative to regenerating forests and cultivated plots; at 300 and 500 cm, cultivated soil [CO2] was significantly lower than in forests. Microbially-respired δ13C-CO2 suggests that microbes may rely partially on crop residue even after ∼70 y of forest regeneration. We assert that forest conversion to frequently disturbed ecosystems limits deep roots and reduces biotic generation of downward-propagating weathering agents.
  • Thumbnail Image
    ItemOpen Access
    The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin
    (Journal of Geophysical Research: Biogeosciences, 2014-04) Mann, PJ; Spencer, RGM; Dinga, BJ; Poulsen, JR; Hernes, PJ; Fiske, G; Salter, ME; Wang, ZA; Hoering, KA; Six, J; Holmes, RM
    Dissolved organic carbon (DOC) and inorganic carbon (DIC, pCO2), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (8) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO2in savannah and tropical forest catchments ranged between 2,600 and 11,922 μatm, with swamp regions exhibiting extremely high pCO2(10,598-15,802 μatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios. Key Points Vegetation cover predominately controls fluvial C concentration and composition Small streams (20 m wide) and wetlands are significant sources of aquatic CO2Changing vegetation cover, or hydrologic conditions impact regional carbon budgets ©2014. American Geophysical Union. All Rights Reserved.
  • Thumbnail Image
    ItemOpen Access
    The changing model of soil revisited
    (Soil Science Society of America Journal, 2012-06-14) De Richter, DB; Yaalon, DH
    In 1961, the late Marlin G. Cline wrote a remarkable essay entitled, "The Changing Model of Soil" for the 25th Anniversary Issue of the Soil Science Society of America Proceedings. Cline was most impressed with how geomorphology was enriching pedology, and with the increasingly sophisticated views of soil time and of the processes of soil formation. We revisit Cline's general objectives by re-evaluating the changing model of soil from the perspective of the early 21st century, and by taking stock of the application of soil models to contemporary needs and challenges. Today, three ongoing changes in the genetic model of soil have far-reaching consequences for the future of soil science: (i) that soil is being transformed globally from natural to human-natural body, (ii) that the lower boundary of soil is much deeper than the solum historically confi ned to O to B horizons, and (iii) that most soils are a kind of pedogenic paleosol, archival products of soil-forming processes that have ranged widely over the life of most soils. Together and each in their own way, these three changes in the model of soil impact directly human-soil relations and give structure and guidance to the science of anthropedology. In other words, human forcings represent a global wave of soil polygenesis altering fluxes of matter and energy and transforming the thermodynamics of soils as potentially very deep systems. Anthropedogenesis needs much better quantifi cation to evaluate the future of soil and the wider environment. © Soil Science Society of America.