Groundwater & WetlandsGroundwater: 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.

WatershedsAn area of land above a point in a stream that catches the water that flows down to that point.

Its boundary is typically higher ground, like the ridge of a hill or mountain.

New Groundwater Formation

/ percolation

• 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)

Soil Overview

0.004-0.062 mm

0.004 mm

0.2 – 2 mm

Soil Texture Triangle:

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.

Profile of Soil Horizons:

Organics?

= Geologic substrata

= vadose zone / unsaturated

Subsurface Habitats:

= groundwater

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.

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).

High Recharge:(Storms; Flat terrain; High permeability)

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 features of the karst landscape.

(Fig 4.5; Dodds, 2002)

* Pumped wells can deplete groundwater. * There may be connections with seawater.

Groundwater Meets Surface WaterStream 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 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:

– Hyporheic Zone is an ecotone.– Biofilms may have characteristic of both.– Stream fauna may be throughout.– Unique fauna exists (dark adapted, Family Bogidiellidae).– Lots still to be discovered!