Karen Terry, University of Minnesota Extension Service, Regional Extension Educator, 218-998-3927

Like other ecosystems such as forests, prairies, and oceans, Minnesota’s rivers and streams are complex ecosystems made up of interdependent components. The health and stability of riverine ecosystems depend on these components functioning in a balanced way. In recent times, scientists have categorized rivers into five major components: hydrology, biology, water quality, geomorphology, and connectivity. However, it is important to note that these categories are somewhat artificial because there is a lot of overlap between them. This article will look at the first three components. The other two components will be covered in the next issue.

Healthy rivers are a balance of elements that can be grouped into five components: hydrology, biology, water quality, geomorphology, and connectivity.

Hydrology relates to the flow of water through a watershed. Water is often discussed in terms of quantity, but the timing of the water moving through the watershed is important, too. An area may receive an average of 15 inches of precipitation in a year, but if that falls in a single week, versus at intervals throughout the year, it makes a significant difference within the ecosystem. Human actions can greatly alter the flow of water. In agricultural settings, for example, wetlands and small streams have been drained, ditched, straightened, and tiled in efforts to move the water off the surface of the land faster. In developed areas, such as along lakeshores and in cities, water moves off of impervious surfaces very quickly, and enters nearby waters. In these ways and others, humans have changed the timing of the water moving through watersheds, resulting in negative impacts on rivers.

The biology component encompasses all living things in rivers, both plants and animals. Diverse communities of plants and animals cannot exist without diverse habitat types within the ecosystem. Healthy rivers are typically made up of combinations of deep, slow pools and shallow, fast riffles, and such rivers are better able to support all the life stages of a species. A change in the population of a plant or animal is often the first indication that the balance of the five components has been disturbed. A decline in water quality, for instance, may be detected as a drop in numbers of gamefish in a river.

The water quality component relates to the chemical and physical properties of river water. These properties are not the same for all rivers, and they can vary within certain amounts on each river. Temperature, for example, varies considerably from cold-water streams to warm-water streams. Even within a warm-water stream the temperature can vary some without causing the system to become unstable. In addition to temperature, water quality is also determined by levels of sediment, oxygen, nutrients, alkalinity and pH, and contaminants. Water quality is closely linked to hydrology and biology.

Watch this space in the next issue of From Shore to Shore, for the second article in this series that will describe what relationship geomorphology and connectivity have with healthy rivers.

Posted in Lakes |