Fresh Water Systems
We have already discussed that less than one percent of Earth’s total water supply is readily available for consumption. This one percent is broken up into surface water, water that is above ground, and groundwater, water that is underground.
Lakes, Ponds, and Wetlands
Large bodies of water above land are basically large holes in the ground where water can be stored. We often refer to these large bodies of fresh water as lakes, ponds, and wetlands. One major difference between a lake and a pond is the depth of water, in a lake sunlight cannot reach the bottom, likewise in a pond sunlight reaches all the way to the bottom; this can create an odd circumstance where ponds can take up more area than a lake. Wetlands have many different characteristics, but one common trait is that water saturates them all or most of the time. Wetlands normally have low clarity, which means there is a large amount of matter suspended in the water.
Streams and Rivers
Streams and rivers are both fast-flowing waterways. These waterways vary greatly, flowing at different speeds, having different temperatures and clarity levels. Generally, the faster a waterway flows the more oxygen is able to dissolve in the water, benefiting fish and plants. One interesting fact is that colder rivers can contain more oxygen, further benefiting the waterway ecosystem.
Up until now we have focused on visible freshwater, however water underground is another important source of water. Most precipitation that falls to the lands sinks down into the Earth’s surface, trickling downwards between cracks and pores. Eventually, it will reach a layer of bedrock, a tightly condensed layer of hard minerals. This bedrock forms a barrier, stopping water from flowing deeper, causing the water to backup and fill the pores and cracks.
A watershed, or drainage basin, is an area of land that drains into a body of water, such as rivers, ponds, wetlands, lakes, or even oceans. The area can be small or large and often flow into each other. All land is considered part of a watershed, farms, prairies, forests, and even cities. In North America, a continuous ridge of mountain ranges divides the continent into two main drainage areas. On one side, water flows northeast to Hudson Bay or southeast to the Gulf of Mexico. On the other side, water flows west to the Pacific Ocean. This long ridge of mountains dividing North America is called the Continental Divide.
The landforms determine the size of a watershed, their speed and direction of flow. Higher ground often directs water to flow to lower land masses, these upstream areas of a watershed are called headwaters. Likewise, the end point of the flowing water at the end of a watershed is referred to as the outflow. The outflow is usually a river mouth.
The geography of Alberta determines the direction water will flow. Generally, water located in northern and central Alberta moves towards the Arctic Ocean. East central and southern Alberta rivers flow into Hudson Bay. A very small amount of water in the southernmost area of Alberta ends up in the Gulf of Mexico. See the picture below to view Alberta’s watersheds, think about where the water is going and how water originating in Alberta can affect other areas.
As you may have noticed humans can have a large impact on watersheds by changing the land, for example, deforestation or urbanization. It is important for landowners to think about watersheds when they decide to build or change land masses to make sure they do not change downstream ecosystems.
A groundwater system is similar to a river system. However, it does not have channels that connect different parts of the drainage basin. Instead, a groundwater system has connecting pores. Soil and rock are permeable if the pore spaces are connected and water can pass through them. Sandstone is an example of a permeable rock.
Soil or rock that has many connected pores is highly permeable. Water can pass through it easily. Soil or rock is less permeable if the connected pore spaces are fewer in number or if the pores are fewer or smaller. Some material, such as clay, has small pore spaces or no pores at all. This material is impermeable. Water cannot pass through it.
Some types of rock, such as sandstone, are full of pores and can hold a lot of water. As every space in the rock becomes filled, the groundwater forms a sort of underground river system, connected by pores instead of stream channels. This system of water flowing through porous rock is called an aquifer. Like rivers on the surface, the water in aquifers moves, although its flow is very slow. It might take 80 years or more to travel through 1 km of sand. The layer of porous rock in which all pores are full of water forms a water table, as shown in the picture below. The level of a water table may change, rising closer to the surface in wet seasons and sinking lower in dry seasons.
Run-off and Erosion
Precipitated water that is not absorbed into the ground is referred to as run-off. Flat lands or areas with gentle slopes hold more water, allowing for more to evaporate or sink into the ground, likewise, steeper slopes cause water to run off into bodies of water before much evaporation or absorption can occur. The amount of vegetation, such as grass, can also affect how much run-off will occur. Plants use water and absorb it like sponges, later they give off water in a process called transpiration. Run-off water often causes erosion, the slow deformation of land masses. Vegetation is a key process to stop this erosion.
Most rivers begin their journey on steep slopes like a mountain range, headwaters are usually narrow, straight, and fast-moving. These fast moving waters can carry loose rocks and even boulders downstream. Finally when the slope flattens and the river slows down it deposits these rocks and boulders in a process called deposition. Rivers can carve steep valleys, especially in higher parts of the watershed (drainage basin), in lower parts deposits may cause fan-shaped deltas at the river’s mouth.
Monitoring River Flow
As you may imagine, making sure watersheds are healthy is very important for the ecosystem. Streamflow is the term used to determine the amount of water discharged by a watershed. It measures the amount of water (volume) that flows past a certain point over a period of time (velocity). People measure streamflow overtime to determine the average streamflow, this helps determine changes that could result in floods or droughts.
In Alberta we often struggle with too much water in the spring months coming from the glaciers and melted snow. However, agricultural, industrial, and municipal demands for water are very high, which results in some river channels drying up in the hotter summer months. Most of the water in Alberta is used for agriculture, mostly irrigation, it becomes important to monitor and manage our water consumption to ensure that we have enough water.
On the other hand, if the spring thaw happens very rapidly, coupled with rains, large volumes of water will flow down the river channels over a short period of time. Rivers can overflow and spill into low valley floors. This part of the river is called the flood plain. To help manage disastrous floods dams are often built to regulate the flow of water.
Another important part of river flow monitoring involves sediments. The greater the flow, the higher its ability to transport sediment. Like we discussed above, once it slows down the sediment is deposited. Scientists can examine sediment, whether it is suspended in water, rolling, bouncing along the bottom, or stationary.
Sediment plays a major role in transporting pollutants. By studying the quantity, quality and characteristics of sediment scientists and engineers can determine the source of pollutants. Once the sources and impact are known, steps can be taken to reduce the pollutants.
- Sediment particles released in fish habitats can carry toxic agricultural and industrial chemicals from run-off. These chemicals can cause abnormalities or death in fish.
- Some farming practices increase soil erosion and add sediment-borne toxic chemicals to the environment. Sediment data can help evaluate farming practices and their environmental effects.
- Deposition of sediment in rivers or lakes can decrease water depth. This can make navigation difficult or impossible.
- Sediment can affect the delivery of water. Water is often taken from streams and lakes for domestic, industrial, and agricultural uses. The presence of sediment in the water can wear out the pumps and turbines at the water supply station.
Groundwater carries with it any soluble contaminants, these undesirable substances caused by human activities are considered contamination. Groundwater can spread the effects of spills and dumps far beyond the site of the original contamination.
Groundwater contaminants come from two categories of sources. These are point sources and non-point sources. Point sources are those where the source of a pollutant is from a small, defined area. Leaking gasoline storage tanks, leaking septic tanks, and accidental spills are examples of point sources. So are municipal landfills and industrial waste disposal sites (think of a waste management site). Non-point sources are those where a pollutant comes from a wide area. Run-off from farmland treated with pesticides and fertilizers is an example of a non-point source.
The information on this page and it associated figures are adapted from the Science Focus 8.Science Focus 8, pp. 390-409