Stressors and Soil Contamination - Sustainable Practices in Geoenvironmental Engineering - page 43

capability of a soil to sustain plant and animal life and their productivity within
their particular natural or man-managed ecosystem. The Soil Science Society of
America (SSSA) deines soil quality as
The capacity of a speciic kind of soil to function, within natural or managed ecosystem
boundaries, to sustain plant and animal productivity, maintain or enhance water and
air quality, and support human health and habitation. (Karlen et al., 1997)
• Any diminution of soil quality will impact on the capability of the soil to provide
the various functions such as plant and animal life support, forestry, and wood-
land productivity and will also result in the loss of biodiversity and nutrients.
Other prime examples of this can be found in the various activities associated
with mineral extraction and energy resource development. To appreciate the
impacts resulting from these activities, we can focus on the status of the biologi-
cal, chemical, physicochemical activities, and physical interactions that deine
the functioning of the ecosystem of interest. In addition, we can also study the
changes in land capabilities or land-use options.
2.3.4 Man-Made and Natural Combinations
It is not always easy or simple to distinguish between natural and anthropogenic stressor
sources that impact directly or indirectly on the geoenvironment. This is because many
geoenvironmental impacts are the result of a sequence combination of anthropogenic and
natural sources. A very good example of this is the previously mentioned AMD problem—
a problem that is triggered by the results of mining exposure of pyrite. The presence of
pyrite (FeS 2 ) in rock formations where coal and metalliferous mining occurs will create
problems for the environment if the pyrite is exposed to both oxygen and water. Given
favorable geological and hydrological conditions, we have the situation where oxidation
of the pyrite exposed during mining operations will produce ferrous iron (Fe 2+ ) and sul-
fate ( SO 2− ). For this irst chemical reaction step, we can conclude that the trigger for the
irst sets of reactions is a man-made event or source, i.e., mining of the rock formation.
Subsequent rate determining reactions, which may or may not be catalyzed by certain
bacteria (e.g., Thiobacillus ferrooxidans ), involve oxidation of the ferrous iron (Fe 2+ ) to ferric
iron (Fe 3+ ), to be followed later by hydrolysis of the ferric iron and its ensuing precipitation
to ferric hydroxide [Fe(OH) 3 ] if and when the surrounding pH goes above 3.5. Throughout
these processes, hydrogen ions are released into the water, thereby reducing the pH of
the surrounding medium. The sum total of the reaction products and the reducing pH
condition is commonly known as the AMD problem. This problem is a signiicantly large
problem because of the many sets of mining activities conducted all over the world, and
particularly because of the presence of pyrite in many of these mines. Acid contamination
of groundwater and other receiving waters creates conditions that are adverse to human
health and other biotic species. Chapter 4 will discuss the problem and impact of AMD in
detail—together with procedures for amelioration of AMD.
Another example of contamination of groundwater is the case of the arsenic-contaminated
aquifers in West Bengal and Bangladesh. These aquifers serve a signiicant portion of the
population of these two countries, and ingestion of water from these contaminated aqui-
fers has led to the development of arsenicosis in thousands of unfortunate individuals.
Tube wells sunk into the aquifers constitute a major drinking water supply source for the
two countries. Investigations on tube-well water supply showed concentrations of arsenic