Question

1. What are some lethal ranges for pH and what effect do they have on aquatic organisms?

2. Describe how the Hudson River salinity compares to other major rivers in the U.S. (use the ppt unit of measurement and the chart in your lab to help answer this question)

3. What are some factors that can contribute to the turbidity of water?

4. After a heavy rainfall, would you expect phosphate levels in the Hudson River to increase or decrease relative to after a period of dry weather? Why?

5. Explain the process of eutrophication, and how elevated phosphate levels can lead to low dissolved oxygen.

6. Why is it important to test two different sites for a river or a body of water?

7. Besides the dissolved oxygen, temperature, salinity, pH, and turbidity, what else could you investigate to see how healthy a river is.

Answer 1

pH stands for “power of Hydrogen”. In most simple terms it is a quantitative measure of the acidity or basicity of a substance. It can be considered similar to °C or °F which measures the amount of hotness or coldness of a body. However, there is a difference in pH and temperature scale. The temperature scale is linear but the pH scale is logarithmic meaning every successive number defers by a power of ten on pH scale.

The pH value ranges from 0 to 14 where 0 represents most acidic and 14 represents most basic. Water is considered to be neutral (midway between acid and base with a pH of 7). The value of pH is extremely critical for an organism to survive. While some organism(microbes) are accustomed to surviving in a slightly basic/acidic environment, they can do so only within a healthy range.

Most of the organism survive within a golden threshold pH range. This range lies in between pH 5 to pH 9. Extremities on either side prove dangerous to the survival of the organism.

• Most of the aquatic organism prefers a pH of 6.4 to 9 for their sustenance. pH value of 10 and above can prove dangerous to these organisms and they even die when pH crosses sustainable limits (deaths due to poisoning). Similarly, acid rain causes a decrease in the pH of the water. If the pH decrease is too much primary productivity of the phytoplankton are reduced.
• More the chances of pH being outside the golden threshold, higher the mortality rates. The decrease in pH also leads to increase the solubility of some toxins which leads to more mobility of the toxin compound and hence the increased risk of absorption. Moreover, toxins are engaged in the phenomenon of bioaccumulation.
• Similarly increase in pH can lead to increased solubility of nutrients such as phosphorous and this can lead to the case of eutrophication. In this process, excessive phytoplankton growth and consequential decay can cause decreased availability of dissolved oxygen for the aquatic organism in deeper depths and they can suffocate to death.