1. Modal Impacts
Transportation contributes significantly to the pollution of the hydrosphere
in various ways ranging from air pollution fallouts to the construction and
maintenance of infrastructure such as roads, railways and ports. The first type
of impacts are related to the transport modes.
Air Pollution Fallouts
- Fallouts occur when a pollutant goes from an airborne state (gas, solid
or liquid) towards a solute or colloidal state. Water is a very good solvent
for several pollutants, notably acid depositions. Fallouts are accelerated
and concentrated in an area by rainy conditions.
- As an important source of air pollution, transportation accounts on a
similar scale for fallouts. In some areas transportation may account for up
to 25% of nitrogen fallouts in water. It is estimated that acid rains
may account for more than 75% of the growth of acidity of lakes.
- Since fallouts are a continuous accumulation and occur over a longer period
than most water pollution sources, they have a higher impact on still-water
(lentic) environments than running-water (lotic). The most notable and destructive
fallouts are sulfuric and nitric acids that may alter the pH of water if they
are present in sufficient concentrations. Several northeastern United States
and eastern Canadian lakes have seen their entire fish population destroyed
as a result of increased acidity levels. It also includes damage to forests
like reduced photosynthesis (sparse foliage) and acidified soils (limited
nutrients). Nitrous oxides may affect the ecological balance of marine life
by favoring algae blooms.
- Other fallouts such as HC/VOC and lead are poisonous and may disrupt marine
life if they accumulate in the aquatic food chain. Particulate fallouts, when
in sufficient quantities, may increase the turbidity of water and thus reduce
the photosynthesis capacity of aquatic plants. A long term accumulation of
air pollution fallouts of various nature will contaminate and disrupt whole
aquatic ecosystems.
Marine Vessels Discharges and Spills
- After unloading their bulk loads like oil, coal, nitrates and mineral
products, marine vessels require cleaning. Since this practice is restricted
in several port and coastal areas, operators wait until they are in international
waters to proceed. Oil products residuals carried by tankers are the major
source for discharges.
- It is estimated that for every million tons of oil carried, one ton
is spilled through washouts. Once a spill has occurred, it is extremely
difficult to contain it. From 1989 to 1992, 105 accidental oil spills by tankers
were accounted worldwide, totaling 991,000 tons of oil being spilled. Annually,
an average of 1.1 million tons of oil comes from discharges and 400,000 tons
are spilled. They depend on the nature of the residue discharged.
- Petroleum products are the most harmful and include environmental
effects like the destruction/disruption of aquatic plant/animal life and of
shore ecosystems. Since most marine life is in neritic (continental shelf)
and epipelagic (less then 100 meters) zones, it is particularly vulnerable
to marine vessels discharges. The
Exxon Valdez oil spill is a well known example of such an occurrence.
2. Infrastructure Impacts
The second type of impact involves transport infrastructures.
De-Icing of Infrastructure and Runoffs
- Salt (NaCl) has the characteristic of lowering the melting point of water
and thus presents an useful compound for keeping safe road conditions in sub-zero
climates. Other elements like sand and gravel are also added to provide adherence.
- Runoffs occur when substances accumulated by a surface (notably a road)
are dissolved / carried by water and evacuated elsewhere. It is often the
convergence of a surface to a point. De-icing of transportation infrastructure
(roads, parking lots, airfields etc.) is almost the only artificial source
of salt release in the environment. Salt mostly comes from mining (halite)
or in fewer proportions from sea water evaporation. Other compounds like calcium
and magnesium can be used, but they work more slowly and cost ten times as
much.
- Lubricants (from car leakages - engine, brakes, and transmission), heavy
metals (Zn, Cd, Cu, Ni, Cr and Fe from abrasion of tires and brake linings)
and dry fallouts (HC/VOC, particulates) account for harmful sources of runoffs.
- Since road infrastructure (parking lots, roads, drainage systems) occupy
a significant land surface in developed countries, it is the major source
of runoffs. For instance, while highways occupy 5-8% of the urban catchment
area, it contributes for as much as 50% of the total suspended solids, 16%
of the total HC and 75% of the total metal inputs to a receiving stream.
- High concentrations of salt, notably chlorine ions, in fresh water environments
disrupt life cycles and may be fatal to some organisms like larvae. Runoffs
from infrastructure will alter the turbidity and the oxygen level of water
(warm water holds less oxygen), and contaminate the food chain. It may increase
the eutrophication process of several lakes, particularly in recreational
areas where dirt roads are dense. De-icing salt has the tendency to accumulate
in snow and soils beside roadways. During early springtime, nearly all the
salt accumulated will be released in the hydrographic system where it will
contaminate ground water and interfere with the growth of plants and the reproduction
cycle of aquatic life, particularly vulnerable at this time of year.
- Infrastructure runoffs collected by the sewage system of urban areas often
converge at evacuation points and contaminate whole hydrographic systems at
high concentrations. It is worth noting that most cities have 30 to 70% of
their surface occupied by roads and parking space. They thus represent important
sources of runoffs.
Construction and Maintenance of Infrastructure
- Several transportation infrastructures have important territorial handholds.
When a transportation infrastructure is built over a hydrological environment
like a river, wetland or a coastal area, disruption occurs.
- The maintenance of transportation infrastructure, particularly harbor
and waterways (dredging), have also a significant impact. Each mode needs
a specific set of infrastructure that interfere with hydric systems.
- Road infrastructure accounts for most of the territorial handhold of
transportation with structures like bridges and parking facilities. Railways
have also an important handhold over continental hydric systems. Maritime
transportation, by its intrinsic link with hydric systems have several disruptive
infrastructure like piers, canals, harbors and terminals. Airports have similar
effects when constructed over wetland. Dredging accounts alone for 80% of
the waste released in aquatic environments.
- The most widespread effect of transportation infrastructure on hydric
systems is the removal of natural habitats along shorelines. The aquatic /
land interface to which several animal and vegetal species depend is considerably
reduced. Further, a modification of the aquatic environment occurs, particularly
during dredging in port harbors and along waterways. This notably influences
the turbidity of water and destroys habitats. Roads and rails, when running
through wetland, reduce the water regeneration / purification capacity by
splitting available areas and disrupting water flows. Large ports occupy extensive
areas along the shorelines of waterways and coasts. The construction and maintenance
of those infrastructure have thus extensive impacts over aquatic environments.
The construction of canals changes whole hydrographic systems by altering
water flows (quantity and speed) at regional and often at continental levels.
Copyright © 1998-2008, Dr. Jean-Paul Rodrigue, Dept. of Economics & Geography,
Hofstra University. For personal or classroom use ONLY. This material (including
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