4. The samples may have very different values for pH and alkalinity, yet they we

Question

4. The samples may have very different values for pH and alkalinity, yet they were all collected from sites in and around Wilkes-Barre. Why (1 point)? List at least three ideas that could explain the differences (3 point). 5. Explain how land use (forest, residential, agricultural field, urban, etc.) might influence the pH and alkalinity of water samples (2 points)? How does geology affect the carbonate alkalinity of natural water samples (2 points)? To answer this question, review the "pH and Alkalinity" factsheet by Addy et al. (2004) posted on the class D2L site. Also consider the type of minerals or rocks that contain ions that contribute to carbonate alkalinity. 6. 7. Note any differences between the two precipitation samples in terms of pH and alkalinity Recall that sample 1 was collected in a bucket from direct precipitation while sample 2 was collected from a roof downspout. What might explain these differences (2 points)?

Explanation / Answer

4.DIFFERENCE VALUES FOR pH AND ALKALINITY OF THE SAMPLES:

pH:

pH is a measure of how acidic or basic (alkaline) a solution is. It measures the hydrogen ion (H+) acitivity in a solution, and is expressed as a negative logarithm. The pH measurements are given on a scale of 0.0 to 14.0. Pure water has a pH of 7.0 and is neutral; water measuring under 7.0 is acidic; and that above 7.0 is alkaline or basic. Most estuarine organisns prefer conditions with pH values ranging from about 6.5 to 8.5. values of pH are based on the logarithm scale, meaning that for each 1.0 change of pH, acidity or alkalinity changes by a factor of ten; that is a pHof 5.0 is ten times more acidic than 6.0 and 100 times more acidic than 7.0. When the hydrogen and hydroxyl ions are present in equal number (the neutral point), the pH of the samples is 7.

The role of pH in the Esturine Ecosystem:

Water's pH is affected by the minerals dissolved in the water, aerosols and dust from the air, and human-made wastes as well as by plant and animals through photosynthesis and repiration. Human activities that cause significant, short- term fluctuations in pH or long-term acidification of a waterbody are wxceedingly harmful. For instance, algal blooms that are often intiated by an overload of nutrients can cause pH to fluctuate dramitically over a few hour period, gratly stressing local organisms.

Alkalinity:

Alkalinity (also known as "buffer capacity") is a measure of the capacity of wate to neutralize acids. Alkaline compounds such as biocarbonates,carbonates and hydroxides, by combining with the hydrogen ions and lower the acidity of the water ( there by increasing pH). They usually do this soils, salts, sertain plant activities, and certain industrial waste water discharges. Some water can test on the acid side of the pH scale and still rank high in alkalinity. This means that, while the water might be acidic, it still has a capacity to buffer, or neutralize acids. Total alkalinity is measured by measuring the amount of acid (e.g.,sulfuric acid) needed to bring the sample to a pH of 4.2. At this pH, all the alkaline compounds in the sample are "used up". The result is reported as milligrams per litre of calicium carbonate (mg/l CaCo3).

The role of Alkalinity in the Esturine Ecosystem:

Measuring alkalinity is important in the determining the estuary's ablity to neutralize acidic from rainfall or waste water. Without this acid-neutralizing capacity, any acid added to a body of water would cause an immediate change in pH. This buffering capacity of water, or its ability to resist pH change, is critical to aquatic life. The estuary's capacity to neutralize acids will bary between the fresh water reaches of the estuary and the portions with higher salinity.

5. pH and Alkalinity influences of land use (forest, agricultural, residential and urban field):

Agriculture field:

Recently, some growers have expressedconcern about the " high pH" of their irrigation water and its potential adverse effects on plants. Alkalinity and pH are two important factors in determining the suitability of water for irrigation plants. The desirable range for irrigation water is 0 to 100 ppm calcium carbonate levels between 30 and 60 ppm are considered optimum for most plants. Irrigation water tests should always include both pH and alkalinity tests. In most cases irrigation with water having a "high pH" (7) causes no problems as long as the alkalinity is low. This water will probably have little effect on growing medium pH because it has little ability to neutralize acidity. This increase may be so large that normal lime rates must be reduced by as much as 50%. In effects the water acts as a dilute solution of limestone. The problem is most serious when plants are grown in small containersbecause small volume of soil are poorly buffered to pH change.

Forest:

The number of areas remaining under the influences of acdity has increased. At all levels ofthe ecosystems, biodiversity decreses with acidification, due to the elimination of species that are most sensitive to low pH. Forest ponds belongs to specific group that varied in location, a huge amount of leaf litter, and isolation from other aquatic enviroments the ranged in a base mean pH from 3.0 to 9.0 has been found to be an important factor influencing gastropod fauna.

urban and residential area:

Unfortunately due to global warming, carbon dioxide emissions in our atmosphere have increased throughout the years. Dissolved carbon dioxide and pH level of water share an inverse relationship as seen in the graph below. As CO2 concentration increases, the pH level decreases. In turn, as CO2 concentration decreases, the pH level increases. Carbon dioxide can enter water bodies from a variety of sources including the atmosphere, runoff from land, release from bacteria in the water and respiration by aquatic organisms. In addition, the amount of hydrogen particles affect the level of pH. As organic substances decay, carbon dioxide forms and combines with water to produce a weak acid called carbonic acid. Large amounts of carbonic acid lower the pH of water, making the water acidic. Furthermore, natural, unpolluted rainwater can be as acidic as 5.6 pH because it absorbs CO2 as it falls.

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