Groundwater & Wetlands
Groundwater: Subsuface water below the water table, which is the depth
where soil becomes water saturated (i.e. all pore spaces are water filled).
Wetland:
Areas of the surface soil layer that receive groundwater (i.e. the water
table is near or at the surface; or land covered with shallow water) with great
enough frequency to establish characteristic soils and plant communities.
Water gain within a
watershed is the balance
of precipitation and
evapotranspiration.
New Groundwater Formation
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Intensity/duration of precipitation.
Vegetation cover and evapotranspiration.
Topography and recharge zones. (Infiltration rate is called recharge.)
Extent of vadose (unsaturated) Zone
Sheet flow (runoff) versus infiltration
- Soil texture & permeability (courser the more infiltration)
- Soil water content & holding capacity (high values may impede infiltration)
/ percolation
Soil Overview
Profile of Soil Horizons:
Composition results from the type of geological
substrata (bedrock), weathering climate, age of
development, vegetation type. Layers
(horizons) are observed with depth, from more
organics at the surface to less weathered
bedrock fragments at depth.
Soil Texture Triangle:
Organics?
0.004-0.062 mm
0.004 mm
0.2 – 2 mm
Subsurface Habitats:
= vadose zone / unsaturated
= groundwater
= Geologic
substrata
Aquifer = groundwater that is contiguous (connected) over an area. They may be
unconfined from the surface, or confined from the surface by an impermeable or
semi-permeable geologic strata (layer) called an aquitard.
High Recharge:
(Storms; Flat terrain;
High permeability)
Porosity = amount of water held in a volume of sediment; fraction of
sediment volume as pores and fractures; often relates to permeability
but not always (e.g., biofilms; clays; disconnected channels).
Groundwater Flow
• Permeability will greatly influence flow:
- Finer & consolidated slower
- Courser & unconsolidated faster
- Channels faster
• Darcey’s Law: flow rate in porous
material increases with pressure and
shorter flow path.
-Tortuosity (length of flow path)
- Pressure (hydraulic head)
Which diagram illustrates a habitat
with faster flow rate and why?
Assume equal hydraulic head.
Hydraulic Head (Δh) & Gradient (HG)
All three wells are in the groundwater.
Explain the difference in “Artesian” flow.
Aquifer Flow and Oasis Formation:
Limestone Aquifers & Karst Topography
Time
Notice that rock more resistant to
weathering dissolution remains
as elevated features (hills &
cliffs). Caves, waterfalls, cinotes,
and vanishing streams are some
(Fig 4.5; Dodds, 2002)
* Pumped wells can deplete groundwater. * There may be connections with seawater.
Groundwater Meets Surface Water
Stream and lake hydrodynamics is influenced by ground water.
How it is influenced depends on the water table level; hence, precipitation.
Wet seasons when there’s a high water, groundwater may feed the stream
in addition to runoff events.
Dry seasons when the water table is low, sheet flow runoff may be the
only source of stream flow, in which case the stream feeds (recharges)
the groundwater.
Wet season
Dry Season
Zone of surface water (lakes or
streams) and groundwater interaction
Groundwater & Hyporheic Life
• Microbes Rule! (bacteria, fungi, protists)
• Biofilms are fed by DOC.
• Important microbial transformations of
elements depending on oxygen supply.
• Hyporheose:
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Hyporheic Zone is an ecotone.
Biofilms my have characteristic of both.
Stream fauna may be throughout.
Unique fauna exists (dark adapted, Family Bogidiellidae).
Lots still to be discovered!
Wetlands
• Characteristic hydric soil and hydrophytic vegetation as
signs of frequent surface saturation or inundation.
• Many types of wetlands: (Dodds, 2002; Table 4.3)
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Salt-marshes and (temperate, seawater influence)
Mangrove forests (tropical, seawater influence)
Tidal & non-tidal freshwater marshes
Deepwater (cypress) swamps
Northern (bogs & tundra) wetlands
Riparian forests/wetlands
Man-made (rice paddies & bioremediation)
• Function as nutrient and sediment traps; slow runoff and
facilitate recharge; most are highly productive.
Global Distribution
Depressional
Peatland bog
Coastal
Mangrove
(Matthews, 1993)
• Wetland ecosystem types are based on hydrologic regime,
climate, geomorphology, nutrient input and vegetation.
(Dodds, 2002; Table 4.5)
• Geomorphic: Peatlands; Coastal; Riverine; Depressional.
• Hydrologic Regime:
– Permanence, predictability (e.g. tidal), seasonality
– Primary water source:
• Precipitation; low throughput (ombrotrophic)
• Riverine; potentially high throughput (minerotrophic)
• Groundwater
• Climate determines the balance of precipitation and
evapotranspiration. (E.g., much less precipitation is
required for tundra wetlands than that for a tropical
savanna wetland.)
Human Impacts on Groundwaters;
Streams and Wetlands
• Groundwater or surface pumping:
– agriculture
– industry
– drinking waters.
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Clearing riparian forests & wetlands
Draining and filling for “development”.
Damming and flooding
Diversion channels for water supply.
Levee
Vanishing Florida Wetlands