Characteristics of Environmental Media
Environmental media refer to abiotic components of the natural environment. The environmental media are comprised of Soil, Water and Air. They are the basic natural resources critical to all fish and wildlife habitats and all vegetative communities. Managing the different components of the environmental media will to a large extent help in managing the environment.
Most often when we talk of the environment, we refer to the soil, water and air and they carry and support the natural and human resources. So a good understanding of the environmental media will create an in-road into a better management of the natural and human resources.
The soil environment consists of a variety of physical, biological and chemical factors that affect the abundance and diversity of microbes found in the soil (Sylvia, 2005). The soil environment consists of a solid and porous fraction.
Within these fractions, a variety of chemical and physical factors are affected by microbes. These include, but are not limited to texture, temperature, pH, oxygen, cation exchange capacity and redox reactions.
The soil environment directly affects the types of microbes, as well as the rates of processes they perform. For example, microbial activity increases with temperature, which in turn affects rates of decomposition.
On the other hand, microbial processes directly affect their environments as well, contributing to the carbon and nitrogen cycles, which are important for microbial and plant health (Brady and Ray, 2010).
2. Solid Fraction
The solid fraction of the soil consists of mineral and organic matter, which is typically about 50% of the soil by volume and it has a dominant influence on heat, water, and chemical transport and retention process (Sylvia, 2005).
Most of the solid particles are derived from mineral sources such as decomposed rocks or sediments (Moravec et al., 2015). Soil organic matter consists of all of the organic components of a soil, including living biomass, decomposing tissue, and fully decomposed tissue called humus (Brady and Ray, 2010).
3. Soil Pores
The air filled pores of the soil typically have a similar distribution of gases as the atmosphere above the soil, with slightly lower oxygen and slightly more CO2 due to the respiration of microorganisms.
The soil atmosphere consists of about 18-20% oxygen near the surface, which decreases with depth. CO2 is around 1%, and N2 is about 78% of the soil air filled pore space (Brady and Ray, 2010).
4. Soil Aggregates
Soil aggregates are groups of soil particles that bind to each other more strongly than to adjacent particles.
The space between the aggregates provides pore space for retention and exchange of air and water. Aggregation affects erosion, movement of water, and plant root growth (Todar, 2016).
5. Soil Texture
Soil texture is defined as the distribution of sand (0.05-2.0 mm), silt (0.002-0.05mm), and clay (< 0.002mm) in soil. Soil texture indirectly influences properties such as: water holding capacity, porosity, aeration and nutrient availability.
Clay particles have a very high surface to volume ratio, which makes them very chemically active and have high nutrient availability. Due to the adhesion of water, soils high in clay will also have a high water holding capacity.
Soils with high clay content will often have a very active microbial community, especially in areas of the rhizosphere (Brady and Ray, 2010).
Soil salinity refers to the salt content in the soil. The concentrations and types of ions in solution in the soil can cause modifications in the dispersion of the clay fraction, degrading the original soil fraction.
The sodium ion, being monovalent, increases the width of the diffuse double layer on the surface of the clays, reducing the attractive forces between them with a consequent increase in particle dispersion (Maganhotto and Francisconi, 2012).
The consequence of this dispersion of the clay is also shown by a reduction in stability of the soil aggregates, which are thus easily transported by rain or irrigation.
Soil salinization is a big problem for soils in arid or semi-arid regions and agricultural soils throughout the world (Brady and Ray, 2010).
Bioavailability assesses what proportion of a contaminant present at a contaminated site is available for uptake by organisms. Bioavailability processes are the biological, chemical and physical processes that result in an organism being exposed to a contaminant present in the soil.
These processes are: release of the contaminant from the solid phase, transport of the contaminant to and across a biological membrane and, incorporation into a living organism.
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Bioavailable molecules must cross a biological membrane, which means the molecules have to interact with the aqueous phase.
Therefore, soil properties which control partitioning between the solid phase in soil and the pore water, such as pH, organic matter content, cation exchange capacity (CEC), and the concentration of clay minerals, have a significant impact on bioavailability (Hodson etal., 2011).
8. Soil pH
Microbes in the soil consume and release H+ through redox reactions and fermentation. Abiotic processes such as rainfall can also affect the pH of the soil.
In areas of high rainfall, acidic soils can be created through leaching of bases from the soil, while more basic soils are typically located in arid environments. pH affects microbial diversity because many microbial species cannot tolerate extreme levels of pH (high or low).
Alterations in pH can render essential microbe enzymes inactive and/or denature proteins within the cells and prevent microbial activity from occurring (Sylvia, 2005).
Soil temperature changes with depth: the surface soil (~0-20cm) is highly affected by the solar radiation. Moving deeper (~below 27cm) temperatures are very stable over time.
This is because heat moves in soil mainly by conduction, which does not allow much heat to reach deep in the soil profile. Soil temperature is also affected by the soil color, soil cover, and the water content of the soil.
A darker soil can absorb more heat compared to lighter color soil. A dry soil is more easily heated than a wet one due to the higher heat capacity of water (Brady and Ray, 2010).
Oxygen (O2) is a very important component of the productivity of both microbes and plant roots in the soil.
Oxygen has a very high electrical potential (Eh), meaning that it has a lot of potential to produce energy when used as an electron acceptor in an oxidation-reduction reaction (Brady and Ray, 2010).
Air is one the media people are easily exposed to. Invariably when it is contaminated it can affect human beings and animals in the environment. Air can be contaminated as a result of stationary sources, natural sources, area sources and mobile sources.
Sources of air pollution include combustion, building materials and consumer products. The exposure to air contaminants can be through inhalation and transfer through other media e.g. fomites.
Properties of Air
Air is said to be a mixture of gases. Air contains about 80% nitrogen and 20% oxygen. The properties of air are: Air occupies space, Air has weight, and Air can be compressed
The water resources system consisting of water (in rivers, aquifers, and lakes) and water- and land-based ecosystems (watersheds, wetlands, and floodplains) is essential for the sustenance and health of all species.
As a source of natural capital, the water resources system provides fundamental input for a whole array of human needs and economic development activities.
As a sink, it is used as a receptor for wastewater discharges from point and nonpoint sources of pollution.
Fresh water sustains the integrity of the ecosystems that serve important ecological and hydrological functions and that people, especially the poor, often depend on directly.
Hence, it is essential to maintain the stability, health, and productivity of the water resources system (Rafik and Hans, 2001).
Properties of Water
Water exists in all three phases – solid, liquid and gas at atmospheric temperatures and pressures.
Water has high melting and boiling points.
High heat capacity
High heat of fusion and vaporization.
Water is less dense as a solid than as a liquid
Water has high surface tension
Dissolves other compounds easily
Facilitates most chemical reactions in living systems.
In summary, managing the different components of the environmental media will to a large extent help in managing the environment. The environmental media constitutes the natural resources.
An imbalance in the equilibrium of any of the medium could cause hazards to the lives of humans, animals and plants.
Environmental media is made up of soil, air and water, their interplay that could affect the ecosystem and cause changes in the quality of lives of humans, animals and plants.
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