Article

WATER POLLUTION: FROM THE PERSPECTIVE OF CHANGES IN URBAN TRAFFIC AND CLIMATE CHANGE

by Sharika sha

WATER POLLUTION: FROM THE

PERSPECTIVE OF CHANGES IN URBAN

TRAFFIC AND CLIMATE CHANGE



The impacts of changing urban traffic and climate change on urban water quality

have drawn much attention of researchers in recent years. Emissions from an

increased number and different types of motor vehicles influence pollutant build-up

on roads. Likewise, changes in the rainfall characteristics due to climate change

influence pollutant wash-off. This chapter discusses the important concepts

underlining water pollution, pollutant build-up and wash-off in urban areas as well

as climate change, urban traffic changes and their impacts on urban stormwater

quality. Urban traffic and the climate change characteristics have been discussed

from both global and regional perspectives. Additionally, a detailed discussion on

primary water pollutants is included to provide context in relation to their role in

water pollution.


Urban Water Pollution


Water is fundamental for the long-term sustainability of urban areas. Pollution of

local water bodies in an urban area can pose risks in terms of human and ecosystem

health. The continuous rise in urban population will cause an increase in urban

traffic which in turn can have a significant impact on pollutant build-up on urban

roads. The pollutants that accumulate on urban roads are washed away during surface runoff and eventually transported to local water bodies. However, surface

runoff is not the only factor that impairs urban water quality. According to Shepherd

et al. (2006), groundwater flow as well as baseflow also impacts on urban water

quality. Water pollution may be caused by easily identifiable sources, referred to as

point sources of pollution, or indirectly from multiple sources, referred to as nonpoint sources of pollution. According to the United Nations Environmental Glossary

(UNEG 1997), the anthropogenic sources of emissions that are located at spatially

identifiable points such as, sewage treatment plants, power plants cause point source

water pollution. Non-point sources of water pollution are diffused and pollutants

enter the receiving water body from unspecified outlets. Anthropogenic sources such

as, agriculture, urban areas, mining, construction, dams and channels as well as

natural sources such as, forestry and saltwater intrusions are the common non-point

sources of water pollution.

The urban water cycle is comprised of water supply, wastewater disposal and

stormwater drainage (Markopoulos 2008). The management of surface runoff from

urban roads is part of the stormwater drainage component of the urban water cycle.

The increased area of paved surfaces due to expanding urbanisation reduces

infiltration, whilst causing surface runoff to exhibit higher peak flows, shorter times

to peak and accelerated transport of pollutants and sediments (Niemczynowicz

1999). The situation worsens with increased urban traffic volume as well as changed

rainfall patterns due to climate change (Mahbub et al. 2010a).


Primary Water Pollutants


   The water pollutants of concern in urban stormwater runoff include:

• Gross Pollutants

 • Solids

• Nutrients

• Oxygen-demanding materials

• Toxicants (Heavy metals and Hydrocarbons)

(Adams & Papa 2000)

The following discussion gives an overview on each of these pollutants.


Gross pollutants


   Litter or gross pollutants discarded on road surfaces is the most visible matter

identified as water pollutants. This is generally not a major source of water pollution

(Sartor & Boyd 1972). As litter tend to deposit on the road surface, their foremost

impact is related to visual aesthetics. Sartor and Boyd (1972) classified litter as

originating from three major sources: packaging materials, printed materials and

intentionally disposed waste materials. Packaging materials include paper, plastic,

metal and glass. These are discarded either intentionally or otherwise.


Solids


      Matter that remains as residue on evaporation and drying at 103° to 105° C is

defined as solids (Sawyer et al. 1994). Solids exist in various forms in nature, e.g.,

dissolved, suspended, volatile, and fixed. The term “sediments” is sometimes used

for suspended solids. The undissolved substance in a solid sample in water on

filtration is referred to as suspended solids (Sawyer et al. 1994). The determination

of the amount of dissolved and undissolved matter is accomplished by undertaking

tests on filtered and unfiltered portions of the samples. Volatile solids are referred to

as organic matter that volatilises at 550°C ignition from a solid sample and the

residual matter remaining as ash is referred to as fixed solids. With regards to urban

stormwater pollution, solids are eroded from pervious surfaces or washed off from impervious surfaces by stormwater. Sewer systems also contribute to the

accumulation of solids at the bed and on the walls of the sewers during dry periods

(Novotny & Olem 1994).

The physical effects of suspended solids on the ambient environment are increased

turbidity, abrasion of fish gills and other sensitive tissues, reduction in visibility, loss

of riparian vegetation leading to reduced shade and refuge, and destruction of

spawning areas (Adams & Papa 2000). However, the chemical effects of suspended

solids on the receiving water are much more adverse in nature. High suspended

solids load increases the portability of various other pollutants by acting as a mobile

substrate through processes such as adsorption and absorption (Sartor & Boyd 1972;

Hoffman et al. 1982; Shinya et al. 2000; Settle et al. 2007). The adsorption

phenomenon concerns the adherence of a chemical substance from a liquid or gas

phase to a solid interface (e.g., onto the surface of a particle). Absorption is the

phenomenon where a chemical substance passes an interface and penetrates into a

different phase (Hvitved-Jacobsen et al. 2010). Organic matter as well as humic

substances can also result in binding of metals through a process known as

complexation which refers to a reaction between metal ions or atoms and naturally

occurring substances/ligands present in the organic matter (Charlesworth & Lee

1999; Ellis & Revitt 1982; Hering & Morel 1988).


Nutrients


  Nutrients are defined as substances assimilated by living organisms that promote

growth (EPA 2010). In the context of urban water quality, major elements (e.g.,

nitrogen and phosphorus) and trace elements (e.g., sulphur, potassium, calcium, and

magnesium) are considered as nutrients. Amongst these, nitrogen and phosphorus are the key parameters for the assessment of eutrophication, which is the process of

acquiring high concentrations of nutrients by the receiving water. The processes

taking place in a water body would be virtually impossible to reverse where there is

a significant input of nutrients. A closed cycle originates where the nutrients are

converted to plant matter and released back into the water environment on their

decomposition. Common measures of nutrients are total nitrogen, nitrates, ammonia,

total Kjeldahl nitrogen (TKN), total phosphorus, total organic carbon, and indirectly,

algal mass and chlorophyll a (Wanielista & Yousef 1993).

Adams and Papa (2000) attributed the sources of nutrients to leaching from

vegetation, agricultural fertilisers in runoff, runoff flowing through pastures, parking

lots and lawns and wastewater discharges. Nutrients can stimulate aquatic algal

blooms and excessive macrophytic (aquatic plants) growth, causing depletion of

dissolved oxygen on their death and decay (Wanielista & Yousef 1993). Most

aquatic organisms struggle to survive with depleted levels of dissolved oxygen in

such water bodies suffering from a condition referred to as ‘hypoxia’ (EPA 2010).

Visual impacts of nutrients include colour, turbidity, floating matter and slimes.

Nitrogen in the form of ammonia and nitrates and phosphorus occurring as

orthophosphates are readily available for plant growth. However, Hvitved-Jacobsen

et al. (2010) have reported that excessive amount of the molecular form of ammonia

(NH3), when washed-off into the water body, exerts acute toxic effects by

obstructing the diffusion of ammonia through fish gills. De Jong et al. (2009) have

suggested that drought resulting from climate change can reduce the nitrogen uptake

by plants resulting in increased amount of nitrogen remaining in the soil. Most of this residual nitrogen remains as nitrates which is water soluble. This high nitrate

level can cause algal growth and eutrophication. High nitrate levels in drinking

water can cause methaemoglobinemia (blue baby syndrome) and stomach cancer

(Chambers et al. 2001).

The inorganic compounds of phosphorus, usually referred to as orthophosphates and

polyphosphates, are the principal sources of phosphorus pollution in urban water

(Sawyer et al. 1994). These are water soluble phosphorus compounds and are used

in public water supply as a means of controlling corrosion. Goudier et al. (2009)

have shown that the addition of orthophosphate at a treatment rate of 1 mg PO4

3-/L

can control the fixed bacterial multiplication (biofilm) on the pipe walls. However,

increase in heavy-duty household synthetic detergents can cause a large amount of

excess polyphosphates in the water supply in urban areas. Phosphorus pollution

manifests in the form of algal or cyanobacterial bloom in surface water and in

extreme cases in fish deaths, and fish and shellfish containing algae toxins fatal to

humans (Heinonen-Tanski & Wijk-Sijbesma 2005; Hwang & Lu 2000).

Oxygen Demanding Materials

Oxygen demanding materials in urban water bodies are derived from plants,

animals, and soil organic matter. Oxygen usage in water systems takes place through

microbiological processes which are particularly important in relation to the

following phenomena (Hvitved-Jacobsen et al. 2010):

• Biodegradation of organic matter

• Dissolved Oxygen (DO) mass balances

• DO depletion

 In order to characterise the biodegradation of organic matter several parameters,

such as, BOD (biological oxygen demand), COD (Chemical oxygen demand), TOC

(total organic carbon), and DOC (dissolved organic carbon) are used (SchaarupJensen & Hvitved-Jacobsen 1991). Whilst BOD and COD are measures of oxygen

consumption during decomposition of both organic and inorganic substances in

water bodies, total organic carbon (TOC) is a direct expression of the total organic

content present in the water body and is used as a measure of organic carbon content

irrespective of the different oxidation state of organic matter (Xun et al. 2010). The

dissolved organic carbon (DOC) is the filtered fraction of TOC and is regarded as

the most reliable measure of many simple and complex organic molecules making

up the dissolved organic load in a natural water body (Thurman 1985; Kay et al.

2009).

The decomposable organic compounds are discharged into watercourses from

various natural and anthropogenic sources. Thurman (1985) described the natural

sources of organic carbon as precipitation, canopy drip, groundwater, interstitial

water of soil and sediment, snowmelt, as well as phytoplankton, zooplankton, and

bacteria in lake and river water. Industrial activities can also alter the steady state of

the global carbon cycle. For example, incomplete combustion of fossil fuels and

biomass materials are regarded as the source of excessive amount of black carbon

transported through riverine systems or aerosols into the marine environment from

land (Dickens et al. 2004).

An appropriate concentration of dissolved oxygen (DO) is necessary to maintain

aquatic life. Excessive oxidisable matter in water can create a substantial oxygen demand on the water column, causing potential DO level depletion due to

biodegradation. Organic matter also acts as a substrate (i.e., surface or medium) for

invertebrates, bacteria, and fungi and can cause excessive growth of such

microorganisms in the water body (Hvitved-Jacobsen et al. 2010). Garcia-Ochoa et

al. (2010) described that both the oxygen consumption and oxygen transfer rate into

water bodies by microorganisms can affect the dissolved oxygen (DO) mass

balance. The alteration of DO mass balance and DO depletion can affect the

transport and accumulation of dissolved and colloid organic fractions as well as the

particulate organic fractions that might accumulate in sediments in the water bodies.

Substantial loads of oxygen demanding substances often lead to adverse conditions

such as fish kills, foul odours, unsightly discolouration, and slime growth (Sartor &

Boyd 1972).


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