31. Water in the Lithosphere

Photo 53:Waterfall in the Kananaskis area, Alberta. 2010-07-28

Streams and Rivers

Water is part of the Hydrologic Cycle, as discussed in the post on Unit 11. Once water enters the lithosphere, water is stored and transported in various ways. The driving force of transportation is gravity. “All streams run into the ocean, yet the ocean is never full,” so goes the ancient saying from the Tao Te Ching. This saying refers to the abundance in humbleness; to be like the ocean is to be below all other things, yet receive everything.

Photo 53 shows a beautiful waterfall, one of many in the Rocky Mountains. Streams and rivers are a major transporter of water. The amount of water that passes through a river, the discharge, depends on the gradient and on the source feeding the river. Discharge is measured in a hydrograph. In Alberta there is much seasonal variation, many streams dry up in the after the spring stormflow runoff. Other streams and rivers maintain a constant baseflow.

Surface Retention

Before water enters streams and rivers, it is held on and in the Earth's surface. Canopy interception occurs when vegetation holds water that evaporates before penetrating the soil. Water is absorbed by the soil during infiltration, as well as held in cracks and puddles, which is called surface retention. When these storage places are saturated (when the field capacity is reached), runoff occurs above and in the soil. Groundwater is stored in the zone of aeration, or vadose zone, just below the surface of the land, as well as in the zone of saturation, or phreatic zone, deeper in the Earth’s crust. The process of water passing through soil and rock is called percolation (like a coffee precolator). Porous layers of rock that can hold water are called aquifers.

Photo 54: Eutrophic disconnected oxbow arm, Whitemud Creek, Edmonton. 2011-05-04

Lakes

Where the water table below ground intersects the land surface, a lake, spring, or wetland appears. Lakes also form in low areas where infiltration, stream runoff, or evaporation is not able to transport all the water. Canada has 60% of all the world’s lakes. Lakes are classified in 4 categories based on nutrient content:

·         Oligotrophic lakes are clear but nutrient poor with very few types of organisms

·         Mesotrophic lakes are clear and have an average level of nutrients, mots lakes are Mesotrophic

·         Eutrophic lakes are nutrient rich with many plants and some algae

·         Hypertrophic lakes are excessive in nutrient content, lack oxygen, dirty water, and a many algae. This is often the cause of agricultural runoff or municipal sewerage.

Photo 54 is a former oxbow, which is now a horse-shoe shaped pond with no active river flow. This stale water falls in the Eutrophic category.