Nutrient cycling and wetlands.
One main ecosystem service that benefits all forms of
life is nutrient cycling. Nutrient cycling is a biogeochemical process (i.e.
those that involve biological, geological and chemical pathways) and is the
basis for all life on earth; as well as being the basic requirement of the
producers [i.e. organisms and plants that convert energy from the sun into
food] (Beldin & Perakis, 2009). The biosphere is essentially a closed
system which recycles these nutrients between the environment and living organisms
(Thinkquest, 2012).
There is a constant natural cycle of these chemical
elements. “The nutrients used in the largest amounts (95-98%) are carbon (C),
hydrogen (H), and oxygen (O)”[Conrandin, 2012]; taken in as carbon dioxide
(CO2) and water (H2O). Macronutrients
essential for maintaining life include nitrogen (N), phosphorus (P), potassium
(K), calcium (C), and magnesium (Mg). There are also several micronutrients
essential for human consumption; some being boron (Bh), copper (Cu) and iron
(Fe) [Conrandin, 2012]. All of these nutrients go through specific cycles that
have an effect on ecosystems.
The basic
nutrient cycle shown below, illustrates how these nutrients move
from the physical world into the living world and return to the physical world.
Nutrient cycles have “self regulating mechanisms” (Borman & Likens, 1967)
to keep ecosystems in balance.
All nutrient cycles involve delicate and complex interactions.
Looking closely at one in particular, the nitrogen (N) cycle, will reveal the
many processes involved in these cycles. Nitrogen (N) cycling has three
principle stages; ammonification, nitrification and assimilation (Thinkquest,
2012).
Ammonification is the process
that occurs when bacteria decompose dead organic matter, using the nitrogen (N)
to create amino acids and proteins. The excess nitrogen (N) is released as
ammonium (NH4) for plant uptake. Nitrification occurs when
bacteria oxidize the ammonia (NH3), producing energy that is used to convert
carbon dioxide (CO2) into nitrites (NO2), hydrogen (H), and water (H2O). The
nitrites (NO2) are then converted into non toxic nitrates (N04) which result in
plant absorption. The assimilation of inorganic nitrogen (N)
[ammonium (NH4) and nitrate (NO2)] into organic compounds (i.e. protein, amino
acid and nucleic acids) “is one of the most important processes on earth”
(Thinkquest, 2012).
Particular ecosystems function at different equilibrium
states and different scales; maintaining different levels of nutrient cycling
and exchanges (The Sustainable Scale Project, 2012). Therefore, examining the nitrogen (N) cycle
within a specific ecosystem (freshwater wetlands); will give a concise account
of this biogeochemical process. Wetlands can be found in most climates all over
the world and have a “unique role in regulating global biogeochemical cycles”
(Reddy & DeLuane, 2008, p. 1). Wetlands sustain biota in many forms and
provide services as living filters for pollutants from terrestrial runoff and
the atmosphere. The biodegradation of organic compounds; nutrient cycling;
atmospheric exchange; processing capacities and plant response are all
controlled by the biogeochemical processes that occur in wetland ecosystems.
These wetland processes have a global effect on warming trends, carbon
sequestration and water quality (Reddy & DeLuane, 2008).
The nitrogen (N) cycle in freshwater wetlands plays a very
important role in regulating the overall health of the entire ecosystem. “In
general, larger amounts of nitrogen (N) cycle within freshwater wetlands than
flow in or out” (Bowden, 2008 p.313). Nitrogen (N) is present in both biotic
and abiotic transformations. It occurs naturally, as well as being introduced
by anthropogenic activity. Several factors control nitrogen cycling in
wetlands; water flow (hydrology), climate, landmass and vegetation. Hydrology
and climate are the main variables in nitrogen (N) cycling (Bowden, 2008). The figure below illustrates nitrogen (N) cycling in a wetland ecosystem.
The highest concentration of nitrogen (N) in wetlands occurs
in sediment. Plant production and plant decomposition determine the amounts of
nitrogen (N) present in the system (Bowden, 2008). The organic nitrogen (N) is uploaded by plants. Inorganic
nitrogen (N) is prevalent in the form of ammonium (NH4). Because the sediment
is in an aquatic environment, denitrification occurs (i.e. nitrogen (N) is metabolized and turned into
gas for energy generation). Consumers also distribute the nitrogen (N) by
ingesting the plants; thereby becoming nitrogen (N) transporters (Bowden,
2008). Nitrogen (N) is also added back into the system through a process called
nitrogen fixation (i.e. nitrogen (N) gas is reduced to ammonium [NH4]), making
it available to form organic nitrogen (N) and is assimilated by plant cells
[Thinkquest, 2010]).
When human induced factors begin to alter these natural
cycles, an imbalance of nutrients occurs; ecosystems lose their ability to self
regulate. This can have devastating consequences on the entire ecosystem and to
human health
References:
Bowden, William B., 1987. The Biogeochemistry of Nitrogen in Freshwater Wetlands. Biogeochemistry,
Vol. 4, No. 3, pp. 313-338.
Reddy, K.R. & DeLuane, R.D., 2008. Biogeochemistry of Wetlands: Science and Applications. Boca Raton,
Florida: CRC Press.
(This post is an excerpt from one of my papers (Edinburgh Univ). If you need to cite it, email me for a complete citation).
