Pre-Reading
Pre-Reading Activity
Discuss the following questions with a partner.
- What are ways that humans use freshwater?
- Brainstorm examples of different types of freshwater biomes.
- How do wetlands, like Everglades National Park (Figure 19), differ from lakes?
- Have you visited wetlands before? If so, where?
Read the definition of a key term in the reading and discuss the following questions.
percolation (n) the movement of water through the pores in the soil or rocks
- What is the verb form of percolation?
- Why is percolation important in freshwater biomes?
Reading 5: Freshwater Biomes [1]
Freshwater Biomes
Freshwater biomes include lakes and ponds (standing water) as well as rivers and streams (flowing water). They also include wetlands, which will be discussed later. Humans rely on freshwater biomes to provide aquatic resources for drinking water, crop irrigation, sanitation, and industry. These various roles and human benefits are referred to as ecosystem services. Lakes and ponds are found in terrestrial landscapes and are, therefore, connected with abiotic and biotic factors influencing these terrestrial biomes.
Lakes and Ponds
Lakes and ponds can range in area from a few square meters to thousands of square kilometers. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with deeper, cooler water. Light can penetrate within the photic zone of the lake or pond. Phytoplankton (algae and cyanobacteria) are found here and carry out photosynthesis, providing the base of the food web of lakes and ponds. Zooplankton, such as rotifers and small crustaceans, consume these phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Nitrogen and phosphorus are important limiting nutrients in lakes and ponds. Because of this, they are determining factors in the amount of phytoplankton growth in lakes and ponds. When there is a large input of nitrogen and phosphorus (from sewage and runoff from fertilized lawns and farms, for example), the growth of algae skyrockets, resulting in a large accumulation of algae called an algal bloom. Algal blooms can become so extensive that they reduce light penetration in water. As a result, the lake or pond becomes aphotic and photosynthetic plants cannot survive. When the algae die and decompose, severe oxygen depletion of the water occurs. Fish and other organisms that require oxygen are then more likely to die, and resulting dead zones are found across the globe. Lake Erie represents a freshwater and marine habitat where phosphorus control and storm water runoff pose significant environmental challenges.
Rivers and Streams
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The