Materials Needed for Exercise B

2-liter soda bottles or plastic pots

Bccsticks

Chinese cabbage

Soil mixture (equal parts peat moss and vermiculite for sand] -

Turnip

Wisconsin Fast Plants Rbr; seeds and kit supplies

FIGURE 8.1 GENETIC DIVERSITY OF BRASSICAS.

9.2. Leave it Wank if it is less than 50 per ml. If the genus is not listed in table 9.2, it has a value of 0. Add up all the index values to get the total score.

I 1. Totals above 20 indicate water with high levels of organic wastes, 15 to 19 indicate moderate levels, and below 15 indicate low levels, or organic pollution. However, the rainier score only evaluates organic pollution, and totals below 15 may also indicate the presence of other pollutants. You should also examine the diversity of algae in the water sample. Clean water tends to have high lev els of divcrsit) (many different genera present), while polluted waters have fewer taxa. Docs your water sample show evidence of pollution?

12. Compare your results with those of others in the class for the same water sample. Were the results die same? If there were differences, speculate on t he cause. Also compare the results of the other water samples used in class. Were all the samples polluted?

EXERCISE D: Effects of Nitrates and Phosphates on Algal Growth

In the natural environment, algal blooms occur period ically due to upwclling of nutrients or changing climatic conditions; however, in recent years, blooms have increased in frequency, distribution, and intensity around the world. Algal blooms can be found in most groups of algae, and thev have devastating impacts on both marine and freshwater ecosystems. When dense blooms occur, oxygen stress can develop. This chain of events often begins with nutrient-rich runoff that produces the algal bloom, similar to the polluted waters described in Exercise C. When the bloom organisms die. oxygen is used up by die bacteria that cause their decay. Depletion of oxygen can even lead to the death of the ecosystem. Blooms can also contribute to taste and odor problems when they occur in reservoirs supplying water to cities and towns.

.Algal blooms arc especially hazardous when the algae are capable of producing toxins. Although only a small percentage of algae are toxin forming, the result of blooms involving toxins can be dramatic. These blooms, called harmful algal blooms, can sometimes directly harm people; at other times, they can cause massive fish kills or accumulatc in shellfish. The shellfish are generally not affected, but they become poisonous to humans and other animals. Toxin-producing species arc found in various groups of algae, including the cyanobacteria, dinofiagellatcs, and diatoms. The dinofiagellatcs arc probably the best-known toxin producers, and blooms of these organisms have been called red tides.

The increased incidence of algal blooms is related to nutrient pollution, especially from agricultural runoff, human sewage, and animal wastes. The enhanced availability of nitrogen and phosphorus is believed to trigger bloom conditions. In this exercise, we will examine the effects of increasing levels of these nutrients on the growth of algae. We will be culturing a common freshwater alga (CJflorella) on a basal growth medium as well as on the same medium with four times and ten times the level of nitrate and phosphate. At the end of 2 weeks, we will evaluate the difference in the cultures.

Materials Needed for Exercise D

3 sterile test tubes, 15 ml

BokTs basal algae growth medium without nitrogen and phosphorus

Culture of Chlorelln

Growth chamber or bank of cool white fluorescent bulbs

Nitrate-phosphate (N-P) solution

Pipets and pipetor

Procedure for Exercise D

1 Obtain 3 sterile rest tubes; label them A, B, and C, and add your initials. Add 8.0 ml of BokTs basal growth medium to each tube. This medium has all the nutrients needed for algal growth except nitrogen and phosphorus. These will be added separately.

  1. Add 1 ml of the ChlorcUa culture to each tube.
  2. Add die remaining ingredients to each tube using the following cjiart. The control culture will have the lev

Algae—From Diversity to Dessert 121

els of nitrogen and phosphorus recommended in Hold's basic medium.

TUBE NUMBER

EXPERIMENTAL CONDITION

AMOUNT OF N-P SOLUTION TO ADD

AMOUNT OF DISTILLED WATER TO ADD

A

Control—basic level of N and P

0.1 ml

0.9 ml

B

4X basic level of N and P

0.4 ml

0.6 ml

C

lOx basic level of N and P

1.0 ml

None

4 Once you have added the N-P solution, place the lid on the tube and gently shake die solution to make sure everything is distributed.

  1. Place the tubes under a bank of cool white fluorescent lights or in a growth chamber.
  2. The cultures will need 10 to 14 days to grow. Check the cultures during the next 2 weeks. At the end of the time, evaluate the density of the cultures in the three tubes. Your instructor will indicate what method of evaluation to use.
  3. Which algae were most abundant in the polluted water you analyzed?
  4. How arc algal blooms related to oxygen stress in aquatic environments?
  5. Describe the industrial use of algal polysaccharides.

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