Thursday, March 21, 2013

What goes around, comes around.

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


Beldin, S. & Perakis, S., 2009. Unearthing Secrets of the Forest. [online] USGS Fact Sheet 2009-3078. Available at:

Conrandin, K. n.d.. The Nutrient Cycle. [online] Available at:

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.

Sustainable Scale Project, 2003 . Ecosystem Function and Services. [online] Available at:

Thinkquest, n.d.. Nutrient Cycles. [online] Available at: .

 USDA, NRCS & NSTA, 2010. Nutrient cycle. [illustration] Available at:

(This post is an excerpt  from one of my papers (Edinburgh Univ). If you need to cite it, email me for a complete citation).

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