Soil Ecology

© 2007 Donald G. McGahan (aka soilman) All Rights Reserved

Ecosystem, Ecology, Biogeochemistry, and Ecosystem Ecology

The discussion of soil solids and pores includes information that is fundamental to understanding soils many roles. Soil might be described and considered passive when used as a noun, such as when it is considered an environment either as habitat or setting.

The physical and biological factors along with their chemical interactions that affect an organism or a group of organisms.
A biophysical environment can vary in scale from microscopic to global in extent.
The number of biophysical environments is countless, given that each living organism has its own environment.
a sub-discipline of biology—often confused with the environment—which studies the interactions among organisms and their environment.
A cohesive conglomeration of interrelated and interdependent parts that is either natural or man-made. Every system is delineated by its spatial and temporal boundaries, surrounded and influenced by its environment, described by its structure and purpose, or nature, and expressed in its functioning.
Systems Ecology
An interdisciplinary field of ecology, a subset of Earth system science, that takes a holistic approach to the study of ecological systems, especially ecosystems.
Dynamically interacting systems of organisms, the communities they make up, and the non-living components of their environment.

Soil may also be used as a noun as an ecosystem, which invokes soils truer nature, as a system who’s sum of interactions are greatly influenced by biological organisms

Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and niche construction, regulate the flux of energy and matter through an environment.

The scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, the hydrosphere, the pedosphere, the atmosphere, and the lithosphere).
In particular, biogeochemistry is the study of the cycles of chemical elements, such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space through time.
The field focuses on chemical cycles which are either driven by or influence biological activity.
Particular emphasis is placed on the study of carbon, nitrogen, sulfur, and phosphorus cycles.
Biogeochemistry is a systems science closely related to systems ecology.

Note that in the definition of Biogeochemistry is the concept of spheres.

The worldwide sum of all ecosystems.
It can also be termed the zone of life on Earth.
An all-encompassing term for those portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground (which includes permafrost).
There is a wide overlap with the hydrosphere.
The combined mass of water found on, under, and above the surface.
Commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity.
On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.
The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.
The outermost layer of the Earth that is composed of soil and subject to soil formation processes.
It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere.
The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere (air in and above the soil), biosphere (living organisms), lithosphere (unconsolidated regolith and consolidated bedrock) and the hydrosphere (water in, on and below the soil). The pedosphere is the foundation of terrestrial life on Earth.

Being a system, the soil–when considered as an ecosystem–is decidedly different than ecology, although it is not uncommon to mistake the distinction between ecology and ecosystem.

While ecology is decidedly a scientific analysis and study of interactions among organisms and their environment, ecosystems are a super set of systems science. They are defined by boundaries. Ecosystem studies are confounded when the boundaries of the system are not explicitly and clearly defined. The system scale can be large or small.

Much has been accomplished in studying fluxes across systems boundaries, but because the “black box” nature of systems studies it is often unsettling. It is likely that this frustration with the “black box” nature of system studies is the basis of attempts to quantify the ecology within the ecosystem. This has spawned ecosystem ecology. Thus, ecosystem ecology attempts to examine how ecosystems work inside the resultant “grey box”. The purpose is to relate interactions between biotics and abiotic pools of energy and nutrients. Therefor, ecosystem ecology distinguishes itself from biogeochemistry by slightly, but decidedly, leaning toward emphasizing populations of organisms instead of emphasizing pools of energy, elements, and elemental cycling. Biogeochemistry, despite “bio” being prominent in the name does not place extra emphasis on interactions between organisms within the system; that extra emphasis is decidedly so for ecology. Therefor, biogeochemistry is geochemistry at the earths surface where biological organisms greatly influence energy and chemical reactions, but does so without invoking exhaustive–and exclusionary to non-biological mediated components–efforts focused on interactions between biologic organismic pools within the system.

Thus, while biogeochemistry and ecosystem ecology are related, ecosystem ecology can be said to emphasize organisms more than biogeochemistry. Both biogeochemistry and ecosystem ecology look at fluxes across systems boundaries and attempt to examine processes within the system, but ecosystem ecology is decidedly more greatly prejudiced toward organismal contribution to fluxes both within, and across, system boundaries.

While the following treatment is decidedly not a discussion of biotics, the information is necessary to understand ecosystem ecology, biogeochemistry, environment, the physical (habitat) aspect of ecology studies, and the environment.

Soil and Environment

The Relevance of Soil Texture, Structure, and Depth

Soil texture (particle size distribution), structure (particle arrangement), and depth of pedon all influence the flow and quality of underground and surface water and the environmental behavior of hazardous chemicals. These three soil properties largely control the land’s ability to:

  • Take in, retain, and release water.
  • Maintain plant cover and resist erosion.
  • Retain, destroy, or leak hazardous materials from spills, waste disposals, pesticides, and fertilizers.

The extensive charged surfaces of clay minerals and humus give soils the ability to retain toxic compounds, as well as water and plant nutrients, which should otherwise readily leave the soil and pass into groundwater. So fine-textured soils, with high clay content, usually retain nutrients and toxins better than do course-textured soils. Likewise, retention tends to increase with increasing soil thickness. But few soils effectively retain loosely held ions such as nitrate and chloride, which accordingly move readily to the groundwater.

In all but the coarsest soils, structure (particle arrangement) determines the size and continuity of poor spaces between the particles and aggregates. These pores control the flow of water, petroleum, or any other fluid and solutes in said fluid into and through the soil.

Soil structure, unlike texture, is readily altered by management, especially at the ground surface, with high positive and negative effects on fluid flow rates. For instance, drought, cultivation, overgrazing, clearcutting, and traffic–by animals, people, or machines–can lead to compaction and crust formation, which impede the entry of water. Water that does not enter the soil profile, runs off the surface, carrying eroded soil and attached substances and microbes. Soil erosion is a major source of non-point pollution of lakes and waterways, especially with mineral sediments, humus, phosphate, and other pollutants that are so well retained that they seldom appear an underground waters. Non-point pollution, in contrast with point pollution, has a diffuse source.

Much of the physical and chemical conditions in soil set the stage for ecology.