51 Ecosystem and Eutrophication Lab
Lab Objectives
- Define eutrophication and explain how human behaviors lead to eutrophication
- Explain how algae blooms are detrimental to aquatic ecosystems
- Explain how zooplankton might impact algae blooms caused by cultural eutrophication
- Predict the effects of changes in an aquatic ecosystem using a computer model
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An ecosystem is defined as an association of life and the physical environment. Ecosystems take into account both living organisms and nonliving components like water, soil, light, etc. Ecosystems can be either terrestrial (desert, forest, grassland) or aquatic (coral reef, pond, estuary).
Within ecosystems, scientists study energy transformations. Energy typically enters the ecosystem from the sun and is transferred to photosynthetic organisms (primary producers) and then to organisms that need to eat others for energy, the consumers or heterotrophs. An ecosystem will typically have several levels of consumers. The transfer of energy from organism to organism can be illustrated through trophic levels. A trophic level includes all organisms with the same number of transfer steps away from the energy input into an ecosystem. A simple trophic level diagram for a forest ecosystem is illustrated below. Notice that photosynthetic organisms like plants are on the first trophic level, one step away from the energy source. The squirrel is a primary consumer (eating plants directly) but on the second tropic level two steps away from the primary energy source. At each step along the pathway some energy is lost as heat. Therefore at higher tropic levels there are fewer organisms (as noted by the pyramid shape), and most ecosystems support no more than four or five total trophic levels.
Ecosystems are changing due to human behaviors. Humans negatively impact natural ecosystems through activities such as deforestation, hunting, and pollution. Today’s lab focuses on the impact of eutrophication on aquatic ecosystems. Through eutrophication bodies of water acquire extremely high concentrations of nutrients. The source of these nutrients can be natural or artificial. Humans cause cultural eutrophication through behaviors like runoff from agricultural fields, wastewater from sewage treatment plants, and excess detergents running into bodies of water. The excess nutrients fuel photosynthesis causing an increased growth in algae, a photosynthetic primary producer protist, and an algae bloom. During the bloom, the algae cover the surface of the water. When the algae die, decomposers in the ecosystem break down the protists using up the oxygen available in the aquatic environment through respiration. As oxygen levels decrease (hypoxia), fish die, and the balance of the ecosystem is destroyed.
In an effort to understand ecosystems and human impact on ecosystems, scientists often use models. Modeling of ecosystems serves two main functions. First, the model represents scientists’