Diffuse pollution often comes from various sources. These sources comprise variety of pollutants which often comes as by product of some activities and ultimately enter into the environment affecting the entire ecosystem. Because of the persistent nature of some of such chemical, they may pose substantial threat to the life, especially to the wild lives, which are unaware of their effects. Here, the given case study comprises of urban conurbation of 500 thousand inhabitants, medium to small sized chemical plant on the outskirts, city bypass with heavy traffic at peak times, small farmland with pig farm north of the conurbation and a river going through the town. All of these contributors mostly discharge pollutants of different nature; here the types of pollutants from individual sources, their possible impact and the most efficient remediation measures are discussed on one to one basis.
Pollutants from small farmyard and Pig farms
Farm yard
Sediments, nitrogen and phosphorus from fertilizer and pesticides residue can be expected from the farmyard. Sediments enter into the surface water either from eroding stream banks or from surface runoff due to improper plant cover and wrong tillage practices. These sediments create turbidity in water bodies, which reduces the amount of light reaching lower depth of water body, and can inhibit the growth of submerged aquatic plants which ultimately affect the other species like fish and shellfish, which are dependent on those plants for survival (Vanoni, V,A, 2006).
Sediments affect different life forms in different way in aquatic system. Thin films of fine sediment can inhibit or eliminate population of invertebrates like mayflies and stoneflies where as other better adopted species like midge larvae may increase in number; this is how it can disturb the existing equilibrium of ecosystem (Merrington, et al, 2002). Silt can smother spawning beds by infilling the matrix of coarse gravel stream bed. This reduces oxygen availability and kills fish eggs. According to Merrington, et al (2002), Progressive reduction in number and diversity with increase suspended sediments is noted.
Nitrogen and phosphorus from fertilizer may enter into the water bodies. Excess amount of nitrogen becomes limiting nutrient in salt water system whereas excess amount of phosphorus becomes limiting nutrient in fresh water system (Howerth, R, et al, 2000 ). Excess amount of these nutrients leads to eutrophication and ultimately when these plants decomposes consumes oxygen and creates hypoxic condition in water bodies, such condition again kill the other living organism in water bodies due to lack of oxygen (Selman, et al, 2008).
Pesticides used to kill the pests in farm can enter into the water bodies by various means such as runoff, wind transport and atmospheric deposition. Those pesticides can kill the fish and wildlife, poison food sources and can destroy the habitat that animal use as protective cover. (Dowd, B, M et al, 2008)
Mitigation Measures
Legume establishment in farmland allows nitrogen to be fixed in the soil and reduce the need of synthetic fertilizer thereby reducing the chance nitrogen loss. Vegetative filter stripes placed between cropland and water bodies reduce the amount of sediments, nutrients and pesticides transported to water bodies. (www.uaex.edu/others_Areass/Publications/PDF/FSA-9527.pdf)
To reduce the eutrophication, it is essential to modify the land management so as to minimise the nutrient and sediment loss. Simple management system can also help a lot in this regard. Soil testing to know the nutrient condition of soil, fertilizer management, use of perennial crops and water and erosion control measure can be helpful in reducing sediment loss (Weaver, D, M and Prout A,L, 1993).
Improvement of soil infiltration capacity also helps to reduce surface flow of water thereby reducing soil and nutrient loss. Adoption of minimum tillage practice especially during risk period like autumn helps to reduce soil and nutrient loss. Establishment of farm track sediment trap also prevent the sediment from entering into the water bodies.
(http://www.helcom.fi/BSAP/ActionPlan/otherDocs/en_GB/agri_measures/)
Pollutants from Pig farm
Pathogens are the other threat; the waste from pig farm, especially of faecal origin contains pathogens of various natures. Bacteria, Virus and parasitic worms are common in such cases. Agricultural feeding and excreta are the major sources of nutrient discharge on coastal water worldwide which can alter threaten the life there, as about 60% of coastal rivers and bays in USA have been moderately to severely degraded by nutrient pollution (Howarth, et al, 2002). So the improperly managed animal waste and waste water can pollute the water bodies with pathogens and nutrients.
Mitigation Measures
The waste from swine farm can be deposited on properly lined lagoon to prevent it from leaching. The size of the lagoon according to farm size also needed in order to prevent it from overflowing and can be produced organic manure (EPA, 2003). Thus produced manure can be applied in farm as organic manure which in turn helps to increase the income of farmer as organic product has better market value.
Pollutants from Heavy Transportation
Heavy traffic also can cause adverse effect on aquatic environment. Road runoff can be polluted by heavy metals and oils, due to the abrasion of tyres, breaks and road surfaces and leakage of lubricants, metals from corrosion (Ristenpart, 2003). This occurs from city roads and highways with no strict correlation to traffic intensity. Fuel oil and chemical through accidents or spillages, on loading and unloading are the other sources of pollution. Parking lots represent a large runoff producing in urban environments, which is often contaminated with petrol, oil and other toxic metals. Oil is found as the cause of more than 20% of the Scottish water pollution incidents (SEPA ,2009)
Polycyclic aromatic hydrocarbon and unburned fuel from exhaust emission, Salt during winter months, Detergents and grease from vehicle cleaning also flow to the water bodies. The emission from the vehicle deposit on the atmosphere and come down with rain water and reach ultimately in the water system (Kennish, 1996).
Mitigation Measures
Permeable surfaces can be used to reduce runoff from paved areas, which results in the reduction of pollutants load from entering the water body and allows some pollutants to be broken down at sites (SEPA,2009).
The road surfaces are generally made up of porous asphalt which helps to reduce the solid load of road runoff as these particles infiltrate into those pores. These solids can be transported to the unused hard shoulders by a type of pumping effect of the tyres and again may flow towards the water body. To avoid plugging, the shoulders have to be cleaned periodically (Berbee et al., 2002)
Settling basin are widely used to treat the pollutants but the efficiency of removal of heavy metal is found very low at about 20%-40% and the costs are more than ten times higher than the waste water treatment (Berbee et al., 2002). According to Ristenpart, 2003, investigations at German highways by Lange et al. (2003) confirm the low efficiencies of concrete settling basins but determined much better ones for earth basins planted with reed (67-84 % for SS, COD and metals, 96 % for PAH). So for the better result earthen basin with reed plant can be used for the removal of heavy metals.
Diffuse pollution from urban settlement
Water bodies near the large cities are often gets polluted with the sewage. According to Kennish, (1996), Sewage waste cause eutrophication and deplete dissolved oxygen on coastal waters in many regions of the world, especially those in proximity to large metropolitan centres. This has becomes a major source of nutrients and pathogens in the aquatic environment (Kennish, 1996). Sewage effluent and sewage sludges contain heavy metals. It is a major problem in developing part of the world where sewer system is not proper. Though the developed countries have sophisticated system of sewage management, there is always chance of leakage from some faulty connection and beside this; there is need of sewage treatment before disposing into the water bodies in order to prevent it from pollution. Organochlorine compounds used in the various domestic woks also pollute the aquatic environment (Kennish, 1996).
As the city harbours 500 thousand people, there must be large number of buildings for residential and commercial purposes. As the roof of most of the buildings contains zinc and copper, the runoff from building roof can be a major source of zinc and copper emission due to corrosion and abrasion of roof surfaces and gutters (Ristenpart, 2003)
Mitigation Measures
Reduction in the use of persistent pollutants at the source can be a better solution. But the modification of human behaviour is must, reduction of litter, proper dumping of waste oil and solvent and the reduction or application of alternatives to pesticides can be helpful to reduce the toxic load in aquatic system.
A study done by Ristenpart, 2003 found that the covering of gutters and other construction elements with an impermeable EPDM rubber foil reduces emissions by 90 %.
Storm water can be collected and re -used for toilet flushing, washing-machines and garden irrigation. Surplus storm water can be infiltrated into the ground by swales, trenches etc. This method reduces the volume of water that flow towards the river or sea as overland flow and as the volume reduces the amount of pollutants that can carry also reduces.
Though storm water collects the urban pollutants and carries to the water body, the pollutants they carry differs in volume from place to place. Identification of sources of more toxic pollutants and place where the pollutants load becomes higher is necessary in order to make the treatment more effective and economical. By doing so higher concentration of pollutants can be separated from the urban runoff and can be stopped from reaching into the water bodies (Ristenpart,2003).
Low impact development technique, installation of green roofs, improved chemical handling can reduce the volume of pollutants in urban runoff. Urban runoff mitigation system also includes infiltration basin, bio retention system, constructed wetlands and retention basin (Blake, E,E, 2007).
Construction of structure that reduce the velocity and the flow of runoff also help to reduce the pollutants discharge and allow sediments to settle down.
Pollutants from Industries
Industries mainly pollute the water bodies in two ways, through chemical discharge and thermal discharge.
Chemical plants produces waste of various nature and are often toxic. Corrosive and heavy metals and other toxic substances could make severe damage if they enter into the water bodies. So it is most essential to detoxify it before releasing into the sewerage system. Treatment of sewage at the origin is the most appropriate method for this.
Thermal pollution results from the continuous discharge of cooling water being used in cooling system. The heated water when discharge back into the water bodies cause temperature increase, that can have effect on both fresh water and marine life. Increase in temperature decrease the dissolved oxygen in water (Badr, et al, 1995). Reduction in dissolved oxygen affects the aquatic organism and also increases the metabolic rate and result in food source shortage causing a rapid declination in population. The increased temperature may become suitable for the organisms and they may shift to another location.
Thermal pollution can be controlled through various means. Cooling ponds, cooling towers and cogeneration are widely in practice (Badr, et al, 1995). Cooling pond are the bodies of water which cool the water through evaporation, convection or radiation. Cooling towers transfer heat to the atmosphere through evaporation but in cogeneration the waste heat is used to heat the houses or used in the industrial heating purposes. In my view for thermal pollution, cogeneration is the most appropriate one, as it uses the waste heat and thereby saves lots of money and fuel for energy. It also helps to reduce the possible emission from fuel, which is supposed to use for the heating purpose.
River (landscape for walking, Dog exercise and fishing) and Pollution
As the banks of the river is extensively used for walking, dog exercising and fishing, the river can get polluted with dog's excreta, throwaway of people and the waste from fishing activity. So it is essential to make people aware of that and for this purpose display board can be placed at some places. Strict regulation and fine can be imposed to the offender and waste bins should be placed in adequate number.
Beside all the above mention measures, State can provide funding to build pollutants reducing structure in household or community level, as it is in practice in Germany successfully (Ristenpart,2003). This effort can encourage people to make such structures. Another most important aspect is legal, strict regulation should be made in order to control production of pollutants at sources.
Justification for the above mentioned Pollution control measures
According to Pretty et al (2000), the total environmental cost of agriculture of U.K., in the year 1996 was £ 2.3 billion, according to the report; the cost for pesticide, for phosphate and soil, for nitrate, for micro organism was £ 120 million, £55 million, £16 million and £ 23 million respectively. Every pollutant that release from different sources harms the environment and lives in various ways. Some adverse impact can be restored while some are irreversible. Losses of species due to pollution just cannot be compared with the money, so it is essential to treat such pollutants before releasing it into the water bodies. Most of the treatment and prevention method mentioned above are simple methods and does not cost much money. Only the heavily toxic pollutants should be treated with advanced technologies to make that free of chemicals or to lessen the concentration of pollutants in water. As the government is spending huge amount of money for the treatment procedure it is better to adopt above mentioned practices to lower the concentration of pollutants in water bodies. And in my belief, those are much more economical and environmentally friendly technologies than other complex treatment mechanism.
Most of the above mentioned methods demand simple physical structure, which is relatively cheaper in comparison with complex treatment process and most of them are preventive methods rather than treatment. So these methods are environmentally sustainable and technologically feasible too, as it does not demand sophisticated technologies.
People always want to live in safe and clean environment and by applying these methods, they can achieve that in lower cost and without side effect of that methods. As many complex pollutants treatment processes pollute the environment in other way, in my opinion, people can easily accept these methods.
As these methods helps to reduce the pollutants and helps to purify the water without side effect, it should be legally permissible too. Low cost and simple technologies make it easily achievable for the local administration. This sort of technologies helps country to meet the standards set by European Union in low cost, so it can be advantageous for the government too.
Conclusion:
Diffuse pollution has emerged as a major type of pollution in the world. Pollutants from agricultural practices, industries, transportation and urban runoff are the major contributors of this type of pollution and pollute the fresh water system like river and lakes and coastal areas significantly. In this particular city conurbation also, these are the major sources of pollutants. But the sources of this sort of pollution are difficult to figure out, as there is not a particular point of origin, so the treatment measures also becomes difficult and expensive. But by applying simple measure, such as construction of physical barriers, changing agricultural practices and changing of human behaviours can reduce the pollutant load from diffuse source significantly and makes it economical too. Ban on the use of potentially toxic chemicals and use of alternative for those chemicals also helps to reduce the pollutants on diffuse sources. Beside these, implementation of strict regulation, and financial assistance from the government to make such physical structure and treatment facility to lower the pollutants, is necessary. By applying these methods, diffuse pollution can be reduced significantly.
