Question answered by Gregg Losinski, Environmental Science Educator
This is a great question based on an interesting observation. Like many great questions, the answer may not be a simple one. Without knowing what exactly was being observed it is hard to give a definitive answer, but the potential answers are all possible. The most important thing to first understand is that even though the South Fork of the Snake River is beautiful and seemingly wild, it is actually highly influenced by man’s activities in many ways.
Unlike a naturally flowing river whose flow peaks with the spring runoff and then dwindles down through the summer and fall, the South Fork is actually part of a huge water storage system primarily designed to harness the water for agricultural uses, although some flood control and hydroelectric power generation does also take place. What this means is that the natural flow of the river is disrupted and water is held back in the spring, not allowed to run to the Pacific Ocean immediately as it once did. Instead, the water is released in summer when it is needed to grow agricultural crops. Water managers must play a delicate balancing game when it comes to letting water go and when to store it. Once it flows downstream it is lost to local agriculture. If too much is held back than there could be all kinds of reservoir storage issues when the snows melt next spring.
Spring runoff is usually very muddy with the soil it carries. When runoff is trapped in Palisades Reservoir the suspended soil has a chance to settle out, resulting in clearer flows later. Clearer water during the warm summer months allows for more penetration and heating by the sun’s rays, resulting in increased plant and algae growth. When the need for irrigation is over, flows are often increased to make room for the next year. These increased flows can dislodge vegetation and algae.
Another factor that can result in increased plant growth is the introduction of things that act as fertilizers. In this case, many of the possible sources are related to human activities that can introduce nitrates into the aquatic system. Sources of nitrates can range from fertilizers, livestock, and even septic systems. Sunlight, nitrates, and warmer water temperatures can all combine to increase plant and algae growth. Because so many people want to live, work, and recreate along the South Fork it is possible that we are loving it to death.
What are Algae?
Micro algae are microscopic organisms that grow naturally in all waters. They are composed of one or many cells grouped together in a colony. Like plants, they contain chlorophyll, but they lack true stems, roots, and leaves.
Freshwater algae are found growing underwater on rocks and mud in streams and rivers. They are usually more abundant in slower streams than in fast flowing rivers.
Algae are the basis of most aquatic food webs. They are food for many small aquatic invertebrates, and in turn, these small creatures are food for larger animals such as fish.
Algae also provide important habitats for invertebrates and fish.
Grow Some Algae
Materials: Water from a pond or river that may contain algae, 4 glass bottles with lids, aluminum foil, dropper, fish food
- Label the four bottles:
- With sun and nutrients
- With sun and without nutrients
- Without sun and with nutrients
- Without sun and without nutrients
- Add an equal amount of water to each bottle. Fill about 2/3 full.
- Add 5 drops of fish food to the two bottles labelled “nutrients.”
- Pick the bottles marked “Without sun and with nutrients” and “Without sun and without nutrients.” Wrap these bottles in aluminum foil to block sunlight.
- Place all four bottles in a sunny window. Which bottle do you think with grow the most algae?
Algae make their own energy or food from the sun, but they also need water, correct temperature and nutrients to grow.
Wash hands after collecting water and handling the fish fertilizer. Throw out all collected water after experiment and wash thoroughly to prevent infection.