Impact of Deforestation (1966-1968)
a. Transpiration – water lost through the leaves of plants (actually from any surface of the plant); this water had carried mineral nutrients up from the roots – thus the nutrient cycles and hydrologic cycle are interconnected.
b. Evaporation – water lost from any surface other than a plant; e.g. lake, soil
surface, animal skin tends to moderate temperature in the area, allows
hydrologic cycle to continue, and may lead to concentration of salts in the soil water.
c. Evapotranspiration – evaporation + transpiration.
d. Aquifer – an underground bed or stratum of earth, gravel, or porous stone that contains water.
e. Groundwater – the supply of freshwater under the earth’s surface in an aquifer or soil that forms the natural reservoir for man’s use—usually too deep to be tapped by plants or evaporated.
In some arid regions of the world this is the only source of water—it accounts for 66 times more water than found in fresh water lakes and streams.
Movement of ground water occurs as the result of gravity; an area where ground water reaches the surface and runs off is a SPRING—a well drilled into an aquifer is an ARTESIAN WELL.
routes are available to water that falls on land in the
Evapotranspiration - approximately 70%
Surface runoff - approximately 27%
Ground water - approximately 3%
Transpiration is related to the mechanism of nutrient uptake. Runoff is responsible for gross movement of soluble and solid particles.
Cycling – refers to a two-way exchange between living and non-living components within the ecosystem.
Chemicals are continuously withdrawn from an abiotic reservoir (air, water, land), utilized by and circulated through the biotic portion, and returned in one form or another to an abiotic reservoir.
Because chemicals cycle between the living and non-living components, the terms “BIOCHEMICAL CYCLING” or NUTRIENT CYCLING are used to describe the process.
It should be apparent that the movement of water and air is vital to the transport of chemicals such as N, P, C, H, O, and S, between and within ecosystems.
Precipitation (rain and snow) were very acidic as the result of increased hydrogen and sulfate ions translocated from the northern sections of the country (pH approximately 4).
More nitrogen and phosphorus were brought into the ecosystem by rain or snow than are lost in the drainage waters.
During the initial period of study, the surface runoff increased:
Year 1 – 40 percent
Year 2 – 28 percent
Year 3 – 26 percent
If this water were spread evenly over the surface of the area, it would represent approximately 14 inches over the entire surface.
Nitrate concentrations in the drainage areas increased from 2 ppm to 90 mg/liter – an increase of 450%.
The average loss of nitrogen-nitrate (3 years) was more than twice the amount of nitrogen taken up by the undisturbed system yearly.
If all of the nitrogen were to come in only from precipitation and there were no losses whatsoever, it would take about 43 years for the system to make up the amount of nitrogen lost into the stream waters in three years – if there were normal losses each year as in the undisturbed system, it would take about 100 years to replenish the nitrogen—the reason for these statistics is related to the nitrogen cycle.
In an undisturbed forest, decay produces ammonium compounds. This ammonium either may be taken up by vegetation or converted by microorganisms to nitrate and then taken up by vegetation and held within the system. Loss of vegetation causes ammonium compounds to be converted to nitrate and leached from the system (runoff). This represents a change in the nitrogen cycle.
Because of the nitrate leaching into drainage streams, stream pH decreased from 5.1 to 4.3 – the result of nitric acid formation in the streams. This increase in nitrogen caused pollution of the streams for drinking.
Additionally, there was a net loss of calcium, magnesium and sodium and increased deposition in the downstream ecosystem, leading to increased fertility and increased productivity. Increased surface temperature, higher nutrient concentrations, higher stream temperature, reduced oxygen capacity—all resulted in eutrophication in the downstream ecosystems.
1. Clear cutting of forests – same pattern of nutrient loss and eutrophication of drainage waters – nitrogen loss leads to change in productivity.
2. Road building and power lines – represent a double threat; lands are opened to erosion and the space consumed by roads is taken out of production and subsequent production may be low on abandoned roadbeds.
Over much of the country, stream temperature has increased and pH has decreased.