Upload
sian
View
51
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Near-surface Geologic Environments. Bruce Herbert Geology & Geophysics. Hierarchy model of Landscapes. Descriptions start at small scales Describe flow between these systems Describe spatial and temporal variation at higher scale. Hierarchy model of contaminated near-surface environments. - PowerPoint PPT Presentation
Citation preview
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Near-surface Geologic Environments
Bruce HerbertGeology & Geophysics
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Hierarchy model of Landscapes
■ Descriptions start at small scales
■ Describe flow between these systems
■ Describe spatial and temporal variation at higher scale
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Hierarchy model of contaminated near-surface environments
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Components of Near-surface Environments
■ Hydrology■ Sediment & rock
mineralogy■ Organic matter■ Gaseous composition■ Aqueous chemistry■ Morphology & Structure
There is a strong correlation between hydrology and composition & structure.
WHY?
Important Components
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Hydrologic Flow Regimes
■ The hydrology of the subsurface environment in part determines the fate of pollutants. ■ The rate of water flow affects the attainment of chemical equilibrium by the subsurface
geochemical processes. ■ Hydrologic flow paths also determine the type of solid surfaces that can interact with
dissolved compounds. ■ The most fundamental distinction between hydrologic regimes is the differences
between the unsaturated and saturated zones
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Components of Landscape Prisms
Landscape Prism
For a landscape prism, we are typically interested in:
■ Mineralogy■ Soil & ground water
chemistry■ Organic matter
composition■ Composition of soil
gases■ Microbial ecology
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Soils and Regoliths
■ Water is under negative hydraulic pressure.
■ Recharge water has high concentrations of O2 and CO2
■ Solid phase is dominated by unconsolidated sediment and organic matter
■ Soil are biologically active because of the large inputs of plant debris to these systems.
■ Flow of contaminants to groundwater usually passes through unsaturated zone first.
Upward movement of water by capillarity in glass tubes of different
diameter and capillarity in soils.
Unsaturated zone: pore spaces are filled with gases and water
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Saturated Zones
■ Saturated zone: pore spaces are filled with water. ■ Boundary between the saturated and unsaturated zone is the capillary
fringe.■ Groundwater, lake and estuary, wetlands.■ Porosity can vary between 0 to 60%■ Organic carbon is usually less than 2% except for shales, lignites or
other C rich zones.■ Much lower biological activity in this zone compared to the
unsaturated zone.■ Solid phase can be consolidated rock or unconsolidated sediment
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Saturated Zones: Flow Systems
■ A hydrologic flow system is a subsurface region where hydrologic flow lines remain adjacent throughout the region■ Local flow systems■ Intermediate flow systems■ Regional flow systems
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Saturated Zones: Local Flow Systems
■ The recharge area at a topographic high and the discharge area at a topographic low are adjacent.■ Hydrologically active: residence times of water are on the order of
days to years.■ These systems are relatively open in respect to nutrients and O2.
This makes them biologically active.■ Roughly 80 to 90% of all ground water contamination events are
in local flow systems.
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Saturated Zones: Intermediate Flow Systems
■ Recharge and discharge areas are separated by one or more topographic highs.■ These aquifers produce a high percentage of GW used for human
consumption.■ Much lower biological activity due to lower amounts of O2 and
nutrients.
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Saturated Zones: Regional Flow Systems
■ Recharge area occupies the water divide and the discharge area occurs at the bottom of the basin.■ Ground water has a long residence time. Typically the water has a
high salt content.■ Some anaerobic microbial activity
ENVIRONMENTAL GEOCHEMISTRY AT TEXAS A&M UNIVERSITY
http://environmentalgeochemistry.pbworks.com//
Watersheds as Geologic Systems
Texas WatershedsFor a drainage basin, we are typically interested in:
■ Soil type & bedrock geology
■ Surface & ground water chemistry
■ Basin hydrology■ Sediment composition■ Fluvial landforms■ Channel morphology