UGC-NET (NTA) Environmental Sciences, June-2019

Ecological systems are hierarchical in nature - at each level, components interact with the physical environment (matter and energy)

Fig.: Most commonly recognized ecological hierarchy. The organism is the simplest level within this hierarchy while the ecosphere is the most complex

and produce functioning systems. The most recognized ecological hierarchy, from the simplest to the most complex, is illustrated in Figure. This hierarchy organizes the living systems on the planet into seven levels.

Each level is composed of the levels below (i.e., populations are composed of organisms, communities are composed of populations, ecosystems are composed of communities, etc.). Energy and material can flow among levels. It is important to note that ecological systems need not be confined to the traditional ecosystem level of the hierarchy.

An ecological system can be any system with biotic and abiotic components. Further, most ecological system are hierarchical and Figure may not explain all ecological phenomena well - for example, nutrient cycling does not fit well within this hierarchy; however, this is a fundamental ecological process that transcends the levels of organization diagrammed in Figure.

The complexity of ecological systems is a result, in part, from the interactions across these levels. At any given level in the hierarchy, interactions among components of lower levels produce emergent, irreducible properties that cannot be predicted from studying individual components of these lower levels.

The wind is a source of free energy which has been used since ancient times in windmills for pumping water or grinding flour. The power P available in the wind impinging on a wind driven generator is given by:where C is an efficiency factor known as the Power Coefficient which depends on the machine design, A is the area of the wind front intercepted by the rotor blades (the swept area), pis the density of the air (averaging 1.225 Kg/m³ at sea level) and v is the wind velocity.

Note that the power is proportional to area swept by the blades, the density of the air and to the cube of the wind speed. Thus doubling the blade length will produce four times the power and doubling the wind speed will produce eight times the power. Atmospheric turbulence is the set of seemingly random and continuously changing air motions that are superimposed on the wind's average motion.

Atmospheric turbulence impacts wind energy in several ways, specifically through power performance effects, impacts on turbine loads, fatigue and wake effects, and noise propagation.

Salinity gradient solar ponds are large bodies of water that act as solar collectors and heat storages. A solar pond is a simple and lowcost solar energy system that collects solar radiation and stores it as thermal energy for a relative longer period.

Because of movement and mixing of the fluid both at the top and the bottom, the solar pond is characterized by three zones: a surface convective zone, a non-convective concentration gradient zone, and a lower convective zone (Fig.). The surface convective zone (SCZ) usually has a small thickness, around 10 to 20 cm.

It has a low, uniform concentration, which is close to zero, as well as a fairly uniform temperature, which is close to the ambient air temperature. The nonconvective zone (NCZ) is much thicker and occupies more than half the depth of the pond. Both concentration and temperature increase with depth in this zone. It serves principally as an insulating layer and reduces heat losses in the upward direction.

Some of the heat collection also takes place in this zone and it serves also as part of the thermal storage. The lower convective zone (LCZ) is comparable in thickness to the non-convective zone.

Both the concentration and the temperature are nearly constant in this zone. It serves as the main heat-collection as well as thermal-storage medium. The lower convective zone is often referred to as the storage zone or as the bottom layer.

I- Surface convective zone SCZ
II- Concentration gradient zone NCZ
III - Lower convective zone LCZ
Fig.: Schematic diagram of a solar pond

Gasification is a process that converts organic- or fossil fuel-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700°C), without combustion, with a controlled amount of oxygen and/or steam.

Biomass gasification is a renewable alternative that has the potential to decrease CO2 emissions. However, efficient energy and resource utilization is essential. Previous works had shown that biomass is most costeffectively used for heating purposes or electricity generation. But to increase the overall efficiency, biomass gasification could be integrated in industrial processes.

The gasification is an old thermo-chemical conversion technology with a change of the chemical structure of the biomass at 800 - 1000°C in the presence of a gasifying agent (for instance air, oxygen, steam, CO2, or mixtures of these components) enables the promotion of steam reforming reactions and thus it consists another method of producing a H2 rich gas from biomass.

Gasification is a thermochemical process for destruction of feedstocks (i.e. biomass, lignocellulosic residues, agriculture waste, refuse derived fuel and organic wastes) to produce energy carrier.

Mountains have a significant effect on the amount of sunlight reaching an area, as well as on local temperature and rainfall. South - facing slopes in the Northern Hemisphere receive more sunlight than nearby northfacing slopes and are therefore warmer and drier.

These abiotic differences influence species distribution; for example, in many mountains of western North America, spruce and other conifers occupy the north-facing slopes, whereas shrubby, drought-resistant plants inhabit the south-facing slopes. In the himalaya north facing slopes have luxuriant growth of forest whereas shrubs drought resistant vegetation inhibits the south facing slopes.

Decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. Carbon in the atmosphere is taken up by plants and phytoplankton and converted into proteins, carbohydrates and fats.

Decomposers are able to break down this material and release carbon back into the atmosphere and the cycle can begin again. Without decomposers, the carbon would remain locked in dead organisms and could only be released through combustion.

If all decomposers were to die off, these nutrient cycles would be severely disrupted and the essential elements, perhaps with the exception of carbon, would not be available for life to continue. Nitrogen and phosphorus would be locked in dead material.

In all probability, life as we know it would not continue and there would be a huge build up of dead material with many compounds locked inside these bodies.

Suppose we conduct the following statistical experiment. We select a random sample of size n from a normal population, having a standard deviation equal to σ. We find that the standard deviation in our sample is equal to s. Given these data, we can define a statistic, called chi-square, using the following equation:
x² = [(n - 1) x s²]/σ²
The distribution of the chi-square statistic is called the chi-square distribution.

Clay minerals likely are the most utilized minerals... not just as the soils that grow plants for foods and garment, but a great range of applications, including oil absorbants, iron casting, animal feeds, pottery, china, pharmaceuticals, drilling fluids, waste water treatment, food preparation and paint.

There are four type of clays:

Kaolinite- also includes dickite and nacrite; formed by the decomposition of orthoclase feldspar (e.g. in granite); kaolin is the principal constituent in china clay.

Illite- also includes glauconite (a green clay sand) and are the commonest clay minerals; formed by the decomposition of some micas and feldspars; predominant in marine clays and shales.

Smectites or montmorillonites - also includes bentonite and vermiculite; formed by the alteration of mafic igneous rocks rich in Ca and Mg; weak linkage by cations (e.g. Na⁺) Ca⁺⁺) results in high swelling/shrinking potential

Vermiculite is a hydrous phyllosilicate mineral. It undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently, and the effect is routinely produced in commercial furnaces.

Vermiculite is formed by weathering or hydrothermal alteration of biotite or phlogopite. Large commercial vermiculite mines currently exist in Russia, South Africa, China, and Brazil.