Environmental Engineering Reference
In-Depth Information
material releasing nitrate (nitrogen) from the surface, can act as a fertiliser for the
growth of algae and plants.
There is a serious concern about autochthonous eutrophication (increase in the rate
of production of carbon or the accumulation of carbon in an aquatic ecosystem)
in the costal marine environment [32]. The most common cause for this type of
eutrophication is the anthropogenic enrichment with fertilising nutrients including
nitrogen and phosphorus. Until the 1970s this was not considered as a potentially
important pollutant of the coastal marine ecosystem by marine ecologists. The impact
of nutrient enrichment and the central role of phosphorus in eutrophocation are newly
identiied as a concern by limnologists.
3.4.3 Dissolved Oxygen
DO in the marine environment plays a vital role in the biodegradation process. One
cubic meter of air contains around 270 g of oxygen. The same volume of marine water
in equilibrium with the air holds only 5-10 g of oxygen, depending on its temperature
and salinity. Solar energy warms the surface water in the marine environment, which
makes them less dense than the cooler water present in the bottom surface of the
ocean. The more the density difference between the warmer fresher surface water
and the cooler bottom, saltier water, the more wind and tidal energy is required to
mix them. When the water is strongly stratiied because of the density difference,
the water present at the bottom will not come into contact with air for many days
or months. As microbial respiration happens in the deeper water, the higher rate of
respiration is seen in the summer, which leads to more and more oxygen depletion.
Once the oxygen is consumed completely by the microbes, the water and sediments
become anoxic, which leads to the production of toxic hydrogen sulide. This kills
some organisms, which may not tolerate those conditions. Oxygen concentrations
vary in greater amounts in many costal systems from hour to hour, and from day to
day, with high and low tides. In many places oxygen levels vary with depth and wind
movements and tidal mixing. Microorganisms degrade polymers in two ways, the
irst is through an aerobic process and the second is through an anaerobic process:
C POLYMER + O 2 → CO 2 + H 2 O + C RESIDUE + C BIOMASS
(3.1)
 
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