The water qualities of lakes, rivers and streams have been impeded by contaminan
ID: 33078 • Letter: T
Question
The water qualities of lakes, rivers and streams have been impeded by contaminants, excess nutrients and natural organic matter (NOM). When these compounds enter the water bodies, they change the mineral contents, pH and dissolved oxygen concentrations and thus imbalance the safe acceptable levels for aquatic life. Dissolved oxygen can be a limiting factor for survival of living species in an aquatic environment. If you were to lead an initiative that lead to the restorative measures of water bodies that have high levels of contaminants, what logical steps (list as many as you can please!!) would you take so that the implementation programme will be successful?
Explanation / Answer
Dissolved oxygen refers to the level of free, non-compound oxygen present in water or other liquids. It is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. In limnology (the study of lakes), dissolved oxygen is an essential factor second only to water itself. A dissolved oxygen level that is too high or too low can harm aquatic life and affect water quality.Behaviorally, fish may avoid low dissolved oxygen conditions by physically moving out of an area. Finally, low oxygen levels can also increase toxicity of contaminants to anadromous fish, including ammonia, zinc, lead, and copper
Chinook, coho, and steelhead have exhibited avoidance behavior of low dissolved oxygen water (Warren et al 1973). Juvenile chinook salmon strongly avoided low DO water (1.5 mg/l to 4.5 mg/l) areas during summer periods when temperatures were high, but did not exhibit similar behavior in fall when water temperatures were cooler (Whitmore 1960). Matthews and Berg (1996) explored the relationship between temperature and dissolved oxygen for rainbow trout: when faced between high temperature and low dissolved oxygen, trout typically were distributed closest to the water with the lowest temperature despite low oxygen content. Davis (1975) categorized response of freshwater salmonids into function without impairment, exhibition of initial oxygen distress, and significant portion of population affected. These criteria were developed to ensure adequate oxygen tension gradient to transfer oxygen to the blood as well as sufficient oxygen to fulfill metabolic requirements. At low temperatures where solubility of oxygen is high, the criteria were set to ensure oxygen tension gradient criteria were met. At high temperatures, higher saturation values were required to provide sufficient metabolic processes. Thus, the percent saturation values more effectively represent anadromous fish requirements than the mass per volume (mg/l) criteria.
Aquatic respiration and decomposition lower DO concentrations, while rapid aeration and photosynthesis can contribute to supersaturation. During the process of photosynthesis, oxygen is produced as a waste product. This adds to the dissolved oxygen concentration in the water, potentially bringing it above 100% saturation . In addition, the equalization of water is a slow process (except in highly agitated or aerated situations). This means that dissolved oxygen levels can easily be more than 100% air saturation during the day in photosynthetically active bodies of water .
Supersaturation caused by rapid aeration is often seen beside hydro-power dams and large waterfalls
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