The Effects of Pollution on Freshwater Resources
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This document is downloaded from DR‑NTU (https://dr.ntu.edu.sg) Nanyang Technological University, Singapore. The effects of pollution on freshwater resources Lim, R. P. 1987 Lim, R. P. (1987). The effects of pollution on freshwater resources. In AMIC‑CDG‑COMCON‑UKM Workshop on Mass Media and the Protection of the Environment : Kuala Lumpur, Sep 28‑Oct 10, 1987. Singapore: Asian Mass Communication Research and Information Centre. https://hdl.handle.net/10356/101055 Downloaded on 04 Oct 2021 14:42:26 SGT ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library The Effects Of Pollution On Freshwater Resources By RPLim Paper No.9 •i * *o^ THE EFFECTS OF POLLUTION ON FRESHWATER RESOURCES ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library R.P. Lin Zoology Department University of Malaya 59100 Kuala Lumpur Malaysia Introduction Water is the life blood of all living things on this planet. Civilisations were created in areas where water was plentiful and many present day settlements can still be found close to water sources. Although three quarters of the planet is covered with water, freshwater represents less than 3 percent of its total volume (Table 1). The distribution of this resource is temporally and spatially uneven and this makes its exploitation difficult ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library due to the heterogenous demograhic patterns of the human population. With the advent of industrialisation and large-scale agriculture to meet the needs of a burgeoning and materially sophisticated population the demands on the planet's finite water resources has increased tremendously. Not only do industrial and agricultural activities consume water but they also cause the deterioration of water resources through the input of pollutants such as organic matter and poisons. The degradation of water quality reduces the availability of water to sustain increasing economic and social activities. Such perturbations also cause changes in the ecosystem to the detriment of its inhabitants and terrestrial life forms that depend on water for survival. In order to understand more fully the implications of pollutants on our water resources an insight of the the hydrological cycle would be pertinent in understanding the process by which water is recycled in the biosphere. Further, 1 freshwater systems under undisturbed conditions would provide some perspective of the_ naturnl rnnriifinn of vnrrr rnnnrrn mid its regulation in supply. Next we can look at the effect pollutants have on water and its biota. This change in water quality will affect the utility of water resources. In addition, activities on land such as logging, mining and urbanisation have tremendous disruptive impacts on the regulatory capacity of riverATTENTsIO Nbecaus: The Singea pooref Cothpyerig hclost Act apep lieconnectivits to the use of this dyo cumbetweeent. Nanyna ngth Teec hnlanologidca l Uannivde rsity Library water phases in a watershed. The Linggi River Basin, as a case study, will serve to illustrate the impact of pollution on water resources in a basin. The hydrological cycle The finite water resources on this earth can continuously sustain life activitiesonly because of the hydrological cycle. This cycle consists of several processes involving the movement of water from the atmosphere onto the land and oceans where it is stored for various lengths of time before it is recycled back to the atmosphere (Fig. 1). During its cycle water goes through three phases: precipitation, evaporation, and surface and groundwater runoff. In each phase water is transported, temporarily stored, and undergoes a change in its state (i.e. gaseous, liquid and solid states). Water is evaporated into the atmosphere from land and its water bodies, and the oceans. Evaporation occurs directly from precipitation, precipitation intercepted by vegetation, oceans, lakes and reservoirs, rivers, and plant transpiration. The rate of evaporation in each site is influenced by a multitude' of dynamic environmental factors. Once the water reaches the earth's surface it may be transpired by plants, may run over the surface of the land into streams as surface runoff, or may inflitrate into the ground ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library (Fig. 1). A large proportion of the intercepted water and surface runoff water is returned to the atmosphere by evaporation. Much of the inflitrated water may be temporarily stored as soil moisture and evapotranspired while the remainder will percolate into the deeper zones and stored as groundwater for longer periods. Groundwater is continually being renewed through absorption by roots of plants, outflow as springs, and seepage into streams. The runoff phase" is also very complex and is influenced by the vegetation, geology and pedology, and climate. How clean, clear water is maintained i Although tropical humid regions of Southeast Asia receive a substantial amount of rainfall every year, much of this precipitates during the monsoon seasons which may extend over a few months. This often results in higher river discharge during the wet season and reduced discharge during the dry season even under undisturbed forest conditions". However, the amplitude of discharge over the seasons is relatively small compared with J 3 denuded land. The smoothening out of variations of flow is greatly influenced by vegetation. The great moderating ability of the tropical rain forest comes from the fact that the dense multistoried canopy intercepts raindrops and reduces the rate at which it reaches the ground surface through a complex process of leaf drips and stem flows. This allows sufficient time for the water to percolate into the soil to recharge the groundwater reservoir. Surface runoff is also reduced. During the dry period much of the water that flows in rivers and streams is derived from the groundwater reservoir. ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Clean, clear water in undisturbed rivers is maintained through the efficient nutrient cycling of the forest which reabsorbs much of the inorganic ions leached from litterfall. Its nutrient status would largely depend on the geological makeup of the watershed. The vegetation" also plays a vital role in preventing the direct impact of raindrops on the soil surface causing erosion through the loosening of soil particles. Clear waters and channel volume is thus maintained. It is clear that vegetation within a watershed is imperative to maintaining clean rivers and hence sustainable water resources. How we pollute our water resources Economic and social development not only demands greater J 4 amounts of water but also causes degradation of water resources. Rivers are commonly treated as convenient dumps for effluent produced from domestic, industrial, and agricultural activity. Effluent produced can range from organic material such as food, faeces, agricultural wastes, to poisons like heavy metals and pesticides, to erosional material like sand, mud, and silt. Fortunately, rivers are capable of processing some of this material through oxidation-reduction, absorption-adsorption, and precipitation processes. These involve physical, chemical and biological activities. However, this capability is limited and ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library any excessive loading of effluent will result in the breakdown of the system. Groundwater resources can also be contaminated by persistent poisons produced in industry as well as those used in agriculture. The main types of * pollutants produced in developing countries are domestic and agriculturally based effluent. This is due to the inadequacy of sewerage treatment facilities to cope with rapidly growing populations. Industrialisation and education has resulted in large rural urban migration to service the industries. Often this leads to the development squatter areas with little or no sanitary facilities. The river thus serves as a convenient sewage facility. Organic matter places high demands on dissolved oxygen during oxidative breakdown to inorganic components. Under normal circumstances, such as undisturbed watershed conditions, 5 dissolved oxygen is sufficient for aerobic oxidation with the release of harmless, odourless carbon dioxide. However, when excessive organic matter is inputed into rivers, anaerobic oxidation (putrefaction) occurs with the release of toxic and odorous gases such as methane or hydrogen sulfide which are lethal to the aquatic biota. Depletion of dissolved oxygen is detrimental to the biota as it is required for metabolic purposes. Organic matter is also rich in nitrogen and phosphorus. ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library When oxidised these nutrients become available to the algae. Under natural conditions these nutrients especially phosphorus are low enough to limit production of algae and thus maintain clean, clear water. When this nutrient limitation is removed as in most polluted waters algae grow excessively and form surface scum which inhibits the production of oxygen throughout the water column. The resulting anaerobic condition leads to the degradation