Eutrophication Laboratory Exercise

Purpose & Objectives

PURPOSE: To introduce students to the concept of eutrophication. To investigate the process of eutrophication.

LEARNING OBJECTIVES: Observe the effects of excess nitrogen and phosphates on an aquatic

ecosystem. Compare the growth of a algal species in different levels of nutrients. Predict if the observed eutrophication in their local environment is

due to excess nitrogen, phosphorous, or both.

Eutrophication

Eutrophication is the process in which a water body such as a lake becomes enriched with nutrients resulting in excess growth of primary producers. Natural eutrophication occurs over a long period of times – thousands of years- and ends with a deep water body becoming shallow or nonexistent. However, humans through various activities have sped up the process such that it occurs in decades. Eutrophication due to the action of humans is commonly referred to as “cultural eutrophication”.

In this laboratory exercise we will study the process of eutrophication growing the green algae Scenedesmus in various concentrations of phosphorous and nitrogen.

ALGAE photosynthetic organisms

contain chloroplasts with chlorophyll & other pigments; cell wall may or may not have flagella

microscopic forms are unicellular, colonial, filamentous macroscopic forms are colonial and multicellular most are free-living in fresh and marine water Primarily aquatic

Moist rocks, wood, trees, and soil Some are endosymbionts in protozoa, worms, corals Some associate with fungi to form lichens

ROLE OF ALGAE

provide basis of food web in most aquatic habitats produce large proportion of atmospheric O2

used for cosmetics, food & medical products Currently being research as a source of biofuel.

Scenedesmus

common green alga cells commonly occurr in colonies as multiples of two, with four or eight

cells being most common. The morphology of the colony can be varied based on nutrient

present. In a medium with low phosphorus or low salt concentration, the

Scenedesmus will grow unicellular, forming round or long elliptical cells.

Nitrogen and Phosphorous Sources

Granular Miracle Gro Fertilizer (24-8-16) 24% nitrogen 8% phosphate 16% potassium

Quick Start Liquid Miracle Gro Fertilizer (4-12-4) 4% nitrogen 12% phosphate 4% potassium

10% sodium nitrate (16-0-0)

10% sodium phosphate (20-0-0)

1:1 mixture of 10% sodium phosphate and sodium nitrate.

Setting up the experiment You will work in groups of 4. Working with your group label containers Control, 2 % fertilizer, 8 % fertilizer, and 16% fertilizer. Add 100 ml of Alga Gro medium to the 16oz container. Add 2ml of algal culture to each container. To the control no fertilizer is added. To container 2 add 2 ml of fertilizer and mix well. To container 3 add 8 ml of fertilizer and mix well. To container 4 add 16 ml of fertilizer and mix well. Cover each jar loosely with plastic wrap Place all containers under a light source or in a sunny location. Do not place in direct sunlight

because this may cause the culture to overheat. Prepare a wet mount of the algal culture. Record the number of organisms you observe in a

single field of view. If alga density is high, record the number as TNTC (too numerous to count). Allow alga culture to grow for 7 – 14 days. Observe and record changes in turbidity, color,

growth. You may also determine dissolved oxygen content, nitrate, and/or phosphate levels. Your teacher

will decide if these assays will be done. Prepare a wet mount of the algal culture. Record the number of organisms you observe in a

single field of

Making a Wet Mount

Place one drop of algal culture on the slide. Cover with a cover slip.. Observe at 40X. Count and record the number of organisms present per field of view.

microscope

Disposal

Please dispose of algal cultures responsibly. Do not pour cultures down the drain without treating them first. Algal cultures may be treated by adding bleach to the culture to make a 1% solution. Allow the bleach algal mixture to sit overnight. Pour down the drain with the water running. Alternately, cultures may be brought to a boil in a microwave safe container in the microwave. An odor may occur. However, the microwave is not contaminated.

Cyanobacteria

Anabena Oscillatoria