Generally, eutrophication occurs when the rate of nutrient accumulation is greater than the rate of nutrient removal (Heggie, 2006). Because of unnecessary high nutrient content of the soil, plants experience stunted growth, (as indicated in some of its salient features) fishes die in rapid succession, and a general deterioration of water quality. Nitrogen and phosphorus are generally the nutrients which cause these problems, but in estuaries located in temperate regions nitrogen is effective in maintaining plant growth.
An estuary has an opening to a body of water, a sea or lake, and as such all nutrients accumulated in the estuary will be transferred to the lake or sea.
This process is called eutrophication. Simply, it is defined as the process by which bodies of water age and becomes productive (http://www. umanitoba. ca/institutes/fisheries/eutro. html). Because nutrients from estuaries are accumulated to these bodies of water, they become nutrient sufficient, resulting in pollution. Algal and bacterial growth in the bodies of water becomes prominent.
This causes a general depletion of oxygen in the shallower parts of these bodies of water.
The next step is decomposition. When nutrients settle to the bottom of a body of water, bacteria growth is expected. Because oxygen is needed in the decomposition process, it will deplete the oxygen content of the deeper section of a body of water. Fish kills would be prominent. Pollution would result if the rate of nutrient accumulation becomes unstoppable. Because nutrients are passing from the drainage area (catchment), this will help oxidize some of the other complement nutrients in the area (Chen et. al. , 2007). When this happens, the body of water becomes an avenue of toxic wastes from chemical reactions.
The rate of productivity of the lake or part of the sea becomes a part of its deterioration process. This is further aggravated by the increased activities of humans in areas close to estuaries. The wastes and chemicals dumped by humans in lakes or bodies of water cause a general decline of nutrient fulgurations. The estuary however unlike the eutrophication process that occurs in the lakes and seas attached to it experiences, in the short-run, a net downward rate of nutrient accumulation (the rate of nutrient accumulation is less than the rate of nutrient removal).
This depletes the soil of the necessary nutrients to maintain plant growth. However because of the added pollution from the farms (which passes from the catchment), the estuary also suffers from toxic wastes sip into the soil. The relative acidity and toxicity of the soil (around the estuary) stunts plant growth, and possibly a long-term drying of the surrounding land. In the long-run, because the toxicity level of the estuary is balanced with the toxicity level of the lake, the rate of nutrient accumulation becomes almost similar from that of the rate of removal.
This constancy in the eutrophication equation becomes irreversible, since it would involve structuring the whole body of water attached to the estuary The effects of eutrophication on the estuary are as follows: 1) diversity of species generally decreases, 2) biomass increases, 3) there is an increase of turbidity, 4) the rate of sedimentation increases, 5) development of anoxic conditions (General effects of eutrophication, http://www. lenntech. com/eutrophication-water-bodies/eutrophication-effects. htm).
Because of certain types of species cannot withstand the increased toxicity of the water, they move to other environments. Species that depend on them for food also leave the place. Plant and animal biomass also becomes apparent. When plant and animal biomass dies, decomposition results in the general depletion of the estuary’s supply of oxygen (http://www. jamstec. go. jp/jamstec-e/tech/tech_3g/eutroE. html) Turbidity (measure of the loss of water’s transparency) also becomes a permanent feature of the estuary.