Question

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Nitrogen Species in Environmental Waters 1. Discuss the process of denitrification of an environmental water body. Use chemical equations to support your response. 2. Describe the process of decay associated with organic matter in an aquatic ecosystem.

Answer 1

1) The process of denitrification can be carried by three different methods.

(a) Ion exchange:

The nitrates dissolved in water are exchanged by similarly charged ions. As the water containing nitrate is passed to a bed of resin beds, reaction takes place and the denitrification is carried out.

NO3- + H2O +2 e- = NO2- +2OH-

(b) Biological denitrification process:

It is carried by using microbes such as alcaligenes, pseudomonas and paracoccus which breaks down NO3 to metabolize oxygen and nitrogen gas is released.

6NO3- +5CH3OH= 3N2 +5CO2

(c) Chemical reduction:

Acids are used as reducing agent to produce ammonia. But this process requires catalyst or high heat and pressure.

4Fe+10H+ + NO3- =4Fe2+ +NH4+ + 3H2O

2)

Organic matter breakdown is a complex chemical transformation process. Break down of organic matter is concerned with chemical alteration of organic matter, physical fragmentation and finally release of mineral nutrients. Organic matter break down is a biological process since it is the soil organisms (microorganisms, earthworms, microarthropods, ants beetles etc) which are performing the chemical and physical changes.

Break down starts when organism dies. The organic material is colonised by micro-organisms which uses enzymes to oxidise the organic matter to obtain energy. For leaves and roots their surfaces are colonised by microorganisms even before they die. Soil animals such as earthworms take part in the decompostion of organic matter by incorporating it into the soil.

During decomposition of the organic molecules, organic matter are broken down into simpler organic molecules that require further decomposition into mineralised nutrients. The compounds in organic matter differ in the ease with which microorganisms can break them down. The first organic compounds to be broken down are those that are easy to break down, incluing amino acids and sugars.