An Ecosystem's Disturbance by a Pollutant

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Freedman defines a pollutant as "the occurrence of toxic substances or energy in

a larger quality then the ecological communities or particular species can

tolerate without suffering measurable detriment" (Freeman, 562). Although the

effects of a pollutant on an organism vary depending on the dose and duration

(how long administered). The impact can be one of sublethality to lethality, all

dependent upon the factors involved. These factors need to be looked at when

determining an ecosystem's disturbance by a pollutant.

Some of the most frequent pollutants in our ecosystem include: gases such as

sulphur dioxide, elements such as mercury and arsenic, and even pollution by

nutrients which is referred to as eutrophication. Each of these pollutants pose

a different effect on the ecosystem at different doses. This varied effect is

what is referred to as dose and duration. The amount of the pollutant

administered over what period of time greatly affects the impact that the

pollutant will have on an ecosystem and population.

Pollutants can affect both a population and an ecosystem. A pollutant on a

population level can be either non-target or target. Target effects are those

that can kill off the entire population. Non-target effects are those that

effects a significant number of individuals and spreads over to other

individuals, such is the case when crop dusters spread herbicides, insecticides.

Next we look at population damage by a pollutant, which in turn has a

detrimental effect on the ecosystem in several ways. First, by the killing of an

entire population by a pollutant, it offsets the food chain and potentially

kills off other species that depended on that organism for food. Such is the

case when a keystone species is killed. If predators were the dominant species

high on the food chain, the organisms that the predator keep to a minimum could

massively over produce creating a disturbance in the delicate balance of

carrying capacity in the ecosystem. Along with this imbalance another potential

problem in an ecosystem is the possibility of the pollutant accumulating in the

(lipophilic) fat cells. As the pollutant makes it way through the food chain it

increases with the increasing body mass of the organism. These potential

problems are referred to as bioconcentration and biomagnificaiton, respectively.

Both of these problems being a great concern of humans because of their location

on the food chain. These are only a few of the impacts that a pollutant can have

on a population and ecosystem.

Another factor to consider is the carrying capacity when evaluating the effects

of a pollutant on an ecosystem. A carrying capacity curve describes the number

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