Environmental Engineering Reference
In-Depth Information
4.3.1.2 Climate
Climate is a major factor in determining the kind of plant and animal life on and in
the soil. It determines the amount of water available for weathering minerals.
Warm, moist climates encourage rapid plant growth and thus high biomass
production (primary productivity). The opposite is true for cold, dry climates.
High primary productivity does not necessarily result in high soil organic matter
levels as much of the fixed carbon (C) is sequestered in standing biomass. In
addition, organic matter decomposition (and the demand for soil O
2
) is accelerated
in warm, moist climates. In saturated soils, partially decomposed organically
enriched material may accumulate, such as in bogs, fens, and swamps.
4.3.1.3 Landscape Position or Topography
Topography in terms of landscape position causes localized changes in moisture
and temperature. Even though the landscape has the same soil-forming factors of
climate, organisms, parent material, and time, drier soils at higher elevations may
be quite different from the wetter soils where water accumulates. Wetter areas may
have reducing conditions that will inhibit proper root growth for plants that require
a balance of soil O
2
, water, and nutrients. Landscape position is an important soil
forming factor for hydric soil development. A hydric soil is only going to occur in
landscapes that allow for an excessive accumulation of water to cause soil satura-
tion and reduction in the upper part.
Figure
4.1
illustrates a few common landscapes. Older terraces, or soils on
second bottom positions, usually have developed B horizons (soil layers
characterized by illuviated clay or organic matter). Recent soils deposited in
floodplains or first bottom positions usually do not have a developed B horizon.
Instead, they may have stratified layers varying in thickness, texture, and composi-
tion. Differences in climate, parent material, landscape position, and living
organisms from one location to another as well as the amount of time the material
has been in place all influence the soil forming process.
4.3.1.4 Organisms
Plants affect soil development by supplying upper layers with organic matter,
recycling nutrients from lower to upper layers, and helping to prevent erosion.
Microbial activity is the driving force behind the development of soil morphological
features that are used as Field Indicators. Soil microbes have adapted to a wide range
of soil conditions and are rarely a limiting factor in the development of hydric soil
indicators.
