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The impact of a changing hydrological cycle on Earth’s surface processes
The hydrological cycle is the cycle of processes by which water circulates between the earth’s oceans, atmosphere, and land, involving precipitation as rain and snow, drainage in streams and rivers, and return to the atmosphere by evaporation and transpiration.(Website 1) Throughout this essay I will emphasise the importance of this cycle together with the factors that affect the water quality correlated with the climate change and the direct impact upon three Earth geological surfaces.
The importance of the Hydrological Cycle
Figure 1 : the hydrological cycle (evaporation, condensation, precipitation, surface runoff, infiltration and transpiration and the transitions of water between the solid, liquid and gas phases) (website 2)
This process is extremely important for the biosphere, as it sustains all the life on Earth. Although water is continuously recycled, recent studies confirm that direct or indirect human activities (fossil fuels burning, factory pollution, etc.) have a huge impact upon the environment and continuous pollution may cause serious changes on the hydrological cycle, affecting both water quality and the processes that take place on Earth’s surface.
Factors that influence the water quality
Rapid growth of population and heavy industrialisation coupled with a weak effort to find a more suitable way of waste disposal are the main factors that induce water pollution.( Hennigan, 1969)
Figure 2: various sources of water pollution (website 3)
The chemical industry is one of the most important threats to water contamination. For example the most dangerous wastes that come from the fertilizer manufacturing plants are nitrogen and phosphorous and their varying chemical forms.
Nitrates can increase eutrophication, leading to the promotion of algae and macrophytes growth affecting thus the water quality. As for humans, the health hazards related to nitrates present in water are considered to be infant methemoglobinemia and cancer appearance.
Phosphates can affect the growth rate of aquatic plants that may fix atmospheric nitrogen. Under these circumstances, phosphate becomes the growth-limiting agent, and programmes to control eutrophication have generally sought to reduce available phosphate limits, to prevent excessive algal and macrophyte growth, with subsequent increase in nutrient retention. ( Bahadori et al,2013)
Bacterial pollution of water is the most serious threat, as diseases can be transmitted very easily through the underground water system. It only can be removed by filtration through a thick layer of porous and permeable sediments, but this happens only in certain areas. If the biological hazard will occur in one spot, it will be transmitted several kilometres from the initial place through water circulation, affecting a large area. That’s why it is very important to have a sewerage system carrying the human wastes away from the source, or to have a piped water supply. Journal (American Water Works Association, 1957)
Changes of the hydrological cycle affecting Earth’s surfaces
The chemical or biological pollution of water can lead to changes in climate and temperature that can affect the Earth’s surface processes.
Weathering is the chemical or physical process that changes the rock structures located on Earth surface. In order to occur, the rocks must be directly exposed to water and air. The weathering disintegration takes place at the sub-microscopic level, and therefore exposed rocks that contain complex pore systems, fracture surfaces and grain boundaries provide the perfect surface where the chemical weathering occurs. However, as the concentration of chemicals in the atmosphere increases, the process is accelerated. ( Siegesmund et al, 2002)
Chemical weathering rate depends on three main factors: temperature, amount of surface area and availability of water or natural acid. So, the rocks in the tropical environments experience the most severe weathering.( Siegesmund et al, 2002)
Figure 3: Cube dimensions versus surface area (website 4)
Because water is a dipolar molecule, it is categorized as a good solvent being able to dissolve many chemical compounds.(Mahhafy) In addition to this effect, water aids decomposition through acid action, hydrolysis and oxidation. A good example is the weathering of silicate minerals by carbonic acid that forms by the interaction of water with carbon dioxide from the atmosphere. The reaction is given below:
2KAlSi3O8+ H2O + 2H2CO3= Al2Si2O5(OH)4+ 2K+++4SiO2(aq)+ 2HCO3–
Other minerals that dissolve easily in water are halite and calcite. In particular, structures made out of limestone and marble contain calcite and are prone to chemical weathering by dissolution.(for example marble tombstones )
Erosion refers to the transportation of rock particles and minerals from the initial location to another. It is different from weathering as it is a dynamic element. The main force that induces erosion is gravity and the main agents are: wind, rain, running water, and glaciers. As the temperature increases, the amount of rain is also increased so the transportation of sediments is faster. The result is the rapid erosion of the river banks, producing a wider channel.
A good example of this process can found in the testimonies of Kansas residents. They stated that Cimarron River, which was a small meandering stream in 1914, began to increase after the flood from the same year. The channel at Point of Rocks was 66feet in 1874, but in 1916, a bridge of 644 feet was necessary to be built in order to cross the channel at that point. By 1939, the width was measured as being 1400 feet, so many houses were engulfed by the channel in 1944. (McLaughlin, 1947)
Figure 4: Aerial view of Cimarron River in the vicinity of Point of Rocks(lower left corner at N) and Elkhart bridge (upper right center) (McLaughlin, 1947)
The final step in the weathering-erosional system is deposition. The rock particles that are picked up and transported by an eroding agent will be deposited in a final location and the erosion agents will become deposition agents. The deposited sediments will then be arranged from largest to smallest, process known as horizontal sorting. The main factor that influence the sorting of the rocks is water. However if the flow is high, small particles like clay, sand and silt will be found in the depositional basin together with a large quantity of bigger sediment, including boulders, cobbles and pebbles.( The International Journal of Soil and Water Conservation, 1997)
|256 mm and up||Boulders|
|0.002mm and smaller||Clay|
Table 1 : The diameter of various sediments that can be found in depositional basins(Grotzinger et al, 2010)
The chemical and biological pollution of water is in a direct relation with the changes that occur in the processes on Earth’s surface. The release of toxic gases in the atmosphere contributes to the increase in temperature that directly affects the hydrological cycle. As the temperature is increased, the amount of water that is precipitated is also increased and surface processes such as weathering, erosion and deposition are accelerated causing rock decomposition, alteration of river banks or the high abundance of large sediments in the depositional basins.
Books and Journals
- Water Pollution Robert D. Hennigan BioScience Vol. 19, No. 11 (Nov., 1969) (pp. 976-978)
- Alireza Bahadori Malcolm Clark and Bill Boyd,2013. SpringerBriefs in Applied Sciences and Technology Essentials of Water Systems Design in the Oil, Gas, and Chemical Processing Industries,
- Siegesmund, S., Weiss, T. & Vollbrecht, A. (eds) 2002. Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies. Geological Society, London, Special Publications, 205
- The American Water Works Association, (April 1957) – Pollution of Ground Water World Health Organization Report Journal Vol. 49, No. 4 (pp. 392-396)
- The International Journal of Soil and Water Conservation, 1997.Rain erosion hazard evaluation by soil surface micro-topographic features – A case of the soil loss plots at ChiangDao experiment station, northern Thailand. (pp. 45-58.)
- Thad G. McLaughlin, (Mar., 1947). The Accelerated Channel Erosion in the Cimarron Valley in Southwestern Kansas. Journal of Geology Vol. 55, No. 2 (pp. 76-93)
- Grotzinger, J, Jordan, T H, Press, F and Siever, R (2010). Understanding Earth (6th Edition) pp