Plants and Soils of the Walnut Wetlands
Visitors: Use the links above to learn more about specific aspects of the Walnut Wetlands.
(Want to learn about "hydric" soils in the Walnut Wetlands area? Click here.)
Soil Descriptions
Soils are crucial for sustaining life
and are especially important in wetland environments. Soils can be formed
through various processes called soil-forming factors. These include the
relief or topography of the land, the organisms present in the environment,
the climate under which the soil was formed, the parent material or the
original minerals that gave rise to the soil, and the time that all of
these processes have been occurring.
Wetland soils help to serve many important environmental functions. Water
can be stored throughout the profiles of wetland soils, and they can also
act as giant filters to remove excess nutrients and contaminates. Each
soil will look a bit different, depending on where it is found in relation
to the water source.
The depth to the water table can be determined from where gray colors
are found in the soil profile. The higher these colors are found, the
higher the water table has risen. Soil texture and structure is influenced
by the water table, and other physical factors. Wetland soils are broken
into various layers or horizons based on similar characteristics. Common
horizon titles used by soil scientists include A, E, B and C.
Soil Profiles
Soil profiles are collected with a soil auger, a digging tool that allows scientists to extract a core, or narrow cylinder, of soil to a depth of a few feet or more. By observing the texture,color, and other characteristics of a profile, soil scientists get a picture of the processes that led to the soil's formation as well as the processes that continue to infleunce the soil. The following two soil profiles are from the Northern Floodplain of the Walnut Wetlands.
Map image showing the location of the soil profiles (left photo); site for Soil Profile 1 (right).
Soil Profile 1 was collected just adjacent to Walnut Creek.
Soil Profile 1 (Creekside Profile) Description:
A Horizon- This layer is the top15cm of the soil profile and has the highest percentage of organic matter. The layer was likely formed from decomposing plant and mineral materials. It has a large amount of sand, likely deposited from the floods of Walnut Creek.
B1 Horizon- The second layer or B1 horizon is similar to the A horizon and is found from 15-30cm. It also contains a large percentage of sand particles and has likely been deposited in recent times.
B2 Horizon- This third horizon has gray mottles, or patches of gray colors throughout the soil matrix. It is sandy, with a slight increase in clay composition throughout its thickness of 30-60cm. The water table comes into this layer throughout the year.
B3 Horizon- The fourth horizon is found from 60cm and beyond. The strong gray colors indicate that it is exposed to water frequently throughout the year. It has an even stronger increase in clay content, but is still predominately sandy.
Soil Profile 2 was collected further inland than the first profile, at a site approximately 150 feet north of Walnut Creek.
<Site
for Soil Profile 2.
Soil Profile 2 (Floodplain Profile) Description:
A Horizon- This layer is found in the top 36cm of the soil profile. It is composed of mineral materials, and has a silt-loam texture.
Bt1 Horizon- The second layer has a lower case t to indicate a clay increase. It is found from 36-48cm and has a silty clay texture.
Bt2 Horizon- This horizon is found from 48-66cm and also has a strong increase in clay percentage. It has a clayey texture and a high concentration of gray mottles indicating the presence of a water table at 48cm.
Bt3 Horizon- The final layer is found at 66cm and continues well below this point. The gray colors indicate that this soil is saturated throughout most of the year. It also has a heavy clay structure.
Soil Vocabulary:
Clay- The smallest fraction of the three soil particles, sand, silt and clay; clay has a sticky feeling when samples are rubbed.
Color- Physical trait of soil based on the amount of light reflected off the soil particles. Soil colors based on the Munsell Coloring System.
Gray Colors- Gray colors are found where water has come in contact with the soil. Gray colors arise from chemical reactions where oxygen is removed from the soil (see page on "Hydric" soils in this website).
Loam- a soil intermediate in texture between clay and sand, consisting of a mixture of clay, sand, gravel, silt.
Profile- A vertical section of soil extending from the topsoil into the parent material
Sand- The largest fraction of the three soil particles, sand, silt and clay; sand has a gritty texture when moist samples are rubbed.
Saturated- Fully filled or covered with water
Silt- The second smallest fraction of the three soil particles, sand, silt and clay; silt has a smooth feeling when moist samples are rubbed.
Silt-loam- A soil texture description; a texture containing components of silt and loam
Soil matrix- The soil matrix will have the same color and texture within a give horizon; the dominant characteristics in a horizon is the matrix area
Water table- The groundwater, specifically the top of the underground water column that comes into contact with soils
Click here to learn more about wetland soils...