Chapter 11 - Environmental Impacts Of Agriculture

• farmlands often drained to produce more aerobic soils • wetland plant species and the anima,s they support ,au mot he angle to survive the changes

• natural ecosystems have small scale local variations in abiotic factors producing differences in hen composition of the communities of species found there • agroecosytems often replace diverse communities of indigenous species with a community of species that has fewer species, many of which may not be indigenous • many indigenous species will not be able to survive the new conditions or may be removed because they are predators or competitors

• soil is the growing medium in almost all agricultural systems • soil erosion is a natural process but poor soil management can lead to the rate of erosion exceeding the rate of formation, so the amount of soil present declines

• pesticides are deliberately used because they are toxic and are intended to kill pests • because pesticides are not species-specific, sensitive non target species may also be killed. • species may also be affected if inter relationships are affected such as the death of food species, pollinators, or pollution that favours competitor species

• the nutrients that were intended to stimulate crop growth, or are digestive wastes from livestock, can stimulate the growth of undesirable organisms • leached inorganic nutrients cause eutrophication • organic nutrients such as manure can cause deoxygenation of rivers and lakes because of the aerobic respiration of bacteria

• irrigation water can deplete the sources of the water, such as aquifers or rivers • agriculture changes evapotranspiration rates but the actual change depends on the ecosystem that was present before farming started. Rates can be reduced in areas where forests were removed