Keywords: Mecanique des sols ; Drainage ; Ecoulement souterrain Reference Record created on 2004-09-07, modified on 2016-08-08

Applications of soil physics.

Life cycle and management of carbon-14 from nuclear power generation

Transverse vertical dispersion in groundwater and the capillary fringe.

Organic and inorganic carbon (C) fluxes transported by water were evaluated for dominant hydrologic flowpaths on two adjacent headwater catchments in the Brazilian Amazon with distinct soils and hydrologic responses from September 2003 through April 2005 The Ultisol-dominated catchment produced 30% greater volume of storm-related quickflow (overland flow and shallow subsurface flow) compared to the Oxisol-dominated catchment Quickflow fluxes were equivalent to 32 ± 02% of event precipitation for the Ultisol catchment, compared to 25 ± 03% for the Oxisol-dominated watershed (mean response ±1 SE, n = 27 storms for each watershed) Hydrologic responses were also faster on the Ultisol watershed, with time to peak flow occurring 10 min earlier on average as compared to the runoff response on the Oxisol watershed These different hydrologic responses are attributed primarily to large differences in saturated hydraulic conductivity (Ks) Overland flow was found to be an important feature on both watersheds This was evidenced by the response rates of overland flow detectors (OFDs) during the rainy season, with overland flow intercepted by 54 ± 05% and 65 ± 05% of OFDs for the Oxisol and Ultisol watersheds respectively during biweekly periods Small volumes of quickflow correspond to large fluxes of dissolved organic C (DOC); DOC concentrations of the hydrologic flowpaths that comprise quickflow are an order of magnitude higher than groundwater flowpaths fueling base flow (196 ± 17 mg l−1 DOC for overland flow and 88 ± 07 mg l−1 DOC for shallow subsurface flow versus 050 ± 004,mg l−1 DOC in emergent groundwater) Concentrations of dissolved inorganic C (DIC, as dissolved CO2–C plus HCO3−–C) in groundwater were found to be an order of magnitude greater than quickflow DIC concentrations (215 mg l−1 DIC in emergent groundwater versus 11 mg l−1 DIC in overland flow) The importance of deeper flowpaths in the transport of inorganic C to streams is indicated by the 40:1 ratio of DIC:DOC for emergent groundwater Dissolved CO2–C represented 92% of DIC in emergent groundwater Results from this study illustrate a highly dynamic and tightly coupled linkage between the C cycle and the hydrologic cycle for both Ultisol and Oxisol landscapes: organic C fluxes strongly tied to flowpaths associated with quickflow, and inorganic C (particularly dissolved CO2) transported via deeper flowpaths

http://www.css.cornell.edu/faculty/lehmann/publ/Biogeochemistry%2081,%2045-57,%202006%20Johnson.pdf

DOC and DIC in Flowpaths of Amazonian Headwater Catchments with Hydrologically Contrasting Soils

Laboratory experiments involving both homogeneous and heterogeneous porous media are used to demonstrate that fluid flow and solute transport will occur regularly in the capillary fringe (CF), including both vertical (upward as well as downward) and horizontal flow velocities. Horizontal flow above the water table appears to be limited primarily to the region of high water saturation (i.e., the CF), an observation supported by numerical modeling and consistent with the literature. Beyond observations presented in prior literature, it was observed that exchange of water within the CF with water below the water table is active, with flux both from the CF downward across the water table and from the region below the water table, upward into the CF. This flux is enhanced by the presence of physical heterogeneity. These findings strongly contrast the common conceptualization of predominantly downward vertical fluid flow through the unsaturated zone, with transition to fully three-dimensional flow only below the water table. Based on these observations, it is suggested that the CF may affect, far more significantly than is usually assumed, the natural geochemical and microbial conditions present in the region of transition from unsaturated to saturated ground water flow.

G Manni

Papers

A large-scale laboratory experiment to determine the mass transfer of CO2 from a sandy soil to moving groundwater