Aquatic Ecosystems of

Streams and Rivers

I. Life in the StreamsA. Plants and animals living in the fast moving water of

streams and rivers have developed special adaptations for life in those habitats.

1. Plant adaptations a. Plants have long, thin, flexible stems allowing them to withstand changes in current flow. b. They have strong root systems to hold them firmly in place.

2. Examples of animal adaptations a. Burrowing in the bottom sediments helps mussels to avoid ever changing currents. b. A broad, flat foot to allows snails stick to rocks. c. River otters’ oily coat to keeps them dry and warm. d. Most fish have streamlined bodies allowing them to remain stable in currents.

e. Bottom dwelling fish have flattened heads and large pectoral fins angled to help them stay on the bottom in swift currents, like catfish and many darter species. f. Fish without swim bladders remain on the bottom of streams, staying low and feeding even when the waters become swift. Many darter species fall in this category.

DarterCatfish

B. Understanding Stream Order 1. For most people a stream is a stream, but understanding the evolution of streams will help you understand the life within a stream. 2. Stream order begins when rain or precipitation collects at the top of a watershed giving rise to the headwaters of each stream. Water flows downhill in tiny trickles or runoff. Combined trickles carve out a small stream channel by erosion. This first small stream channel is called a first-order stream and does not have any tributaries. And the process continues.

3. Here are two extremes examples of stream order. The largest watershed in the US belongs to the Mississippi River. This river is a 10th-order stream by the time it empties into the Gulf of Mexico. The world’s largest river is the Amazon River in Brazil. It carries more water into the ocean than any other and is a 12th-order stream when it reaches the Atlantic Ocean. 4. Knowing stream order and whether it has a perennial or intermittent flow can help predict what aquatic life it can support.

II. Stream Orders A. First-and second-order streams. 1. The water is shallow with an often rocky bottom. 2. There are few aquatic plants. 3. A lack of food limits the number of animals that can live there. 4. The benthic community of organisms, make up early order streams. This includes benthic macroinvertebrates, such as mussels, aquatic insects, and microinvertebrates. The benthos is a key part of the food web.

5. Organisms depend on any food source that makes it’s way into the stream.6. Moving downstream, food becomes more abundant and diverse, and so does the aquatic community.

7. Animals are grouped by the way they eat. a. Shredders chew and tear leaves and stems into tiny bits. b. Filtering and gathering collectors eat the small pieces not eaten by shredders. c. As the channel widens downstream and sunlight hits the bottom of the stream, algae grows on rocks and plant stems. The Grazers (snails) feed on the alga. d. Small fish in the headwaters are mostly predators consuming all organisms except the grazers.

B. Third- through fifth-order streams 1. These streams have both rooted and floating aquatic plants and algae. 2. With more food available, more types of animals have niches in which to live. 3. Grazers such as snails and water pennies eat the growing number of plants. 4 Collectors increase as the diverse plant population increases, while shredders begin to decrease. 5. As fish species diversify, they live in the deeper and more varied mid-level streams.

C. High-order streams 1. The product of two streams coming together, combining the individual characteristics of the streams and nutrients from each watershed combine. 2. Contain few rooted plants because the water is too deep and turbid (cloudy). 3. There are more collectors than shredders in big rivers where mussels are a major group living in the river’s benthic zone. 4. Fish play a major role in the food web. Some species are scavengers, omnivores or predators. 5. Predators range in size from tiny zooplankton to 300 pound alligator gar.

A. Biologists look for pollution sensitive macroinvertebrates living on the stream bottom to tell if the water is good or polluted. B. There are species of stoneflies, caddisflies and mayflies that are sensitive to pollution, as are certain fish and mussels. C. Sensitive species are often called indicator species. The presence of pollution sensitive species generally indicates good quality water.

III. Water Quality

D. Examples

1. Streams and rivers has always played a major role in human existence. 2. Rivers carries freshwater to the ocean, forming ecologically important wetlands and estuaries.

E. Saving Rivers and Streams for the future

3. Runoff carries whatever has been placed in the land to streams or rivers often polluting them with harmful contaminants.

4. Laws are in place restricting contamination of Texas’ waters, but pollution of the past still affects some water bodies. 5. Water pollution can happen with accidental chemical spills or through illegal dumping of contaminants.

6. Dumping harmful materials down your toilet can possibly reach our water sources.

F. Human Impact 1. Local and distant land use practices, channel modifications, groundwater depletion, and changes to stream flows from dams and reservoir operations affect streams and rivers.

2. Nearly 200 reservoirs along Texas rivers provide flood control, generate hydroelectric power, and supply water to municipalities, industries, and agriculture. 3. Keeping the streams and rivers healthy is important to everyone. The healthiest streams and rivers are those that flow freely and have natural characteristics. 4. Few rivers and streams remain completely free flowing or free from non-point or point- source pollution.