When significant area of trees are cut in a forest ecosystem, one common respons

Question

When significant area of trees are cut in a forest ecosystem, one common response is very high levels of NO3 loss from the ecosystem vis stream water until the stream water until the vegetation regrows. In the case of the well-known biogeochemical research site at Hubbard Brook, very high NO3 losses from the ecosystem were accompanied by high concentrations of cations such as Ca, Mg ad K in the stream water, but low concentration of SO4 when a forested catchment was experimentally cut and forest regrowth was suppressed for two years by applying a herbicide. Explain

(a) the general changes that are thought to have occurred in the ecosystem hydrology, nitrogen cycling, and soil characteristics in response to this forest cutting experiment. Explain the key specific changes (from among those identified in part a) caused:

(b) the high flow of NO3 out of the ecosystem from the soils,

(c) the high concentration of cations in the stream water, and

(d) the decline in streamwater SO4 concentration.

[20%]

Explanation / Answer

a) The series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms. The nitrogen cycle consists of four natural processes: nitrogen fixation, nitrification, denitrification, and decay. We alter the cycle by adding large amounts of nitric oxide into the atmosphere from cars, trucks, and airplanes. Add nitrous oxide from inorganic fertilizers, through destruction of forests we add nitrogen. Through runoff we add excess nitrates in bodies of water and remove nitrogen from topsoil when harvest nitrogen-rich crops. Nitrogen and hydrogen reacted under high pressure conditions to produce ammonia. Replaced saltpeter deposits as major source for nitrate based fertilizer. This N fertilizer ends up not staying in a tight plant soil cycle, it ends up in atmosphere and in water.

b) No3: More vulnerable to leaching . water moving through soil can strip out nitrate a lot easier than ammonium.

c)High concentration of cations can be indicative of environmental management problems such as those linked to acid deposition and land use.

d)Decline SO4 concentration can cause acid rains.

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