The Water Cycle and Ecosystem Function

Healthy watersheds naturally clean, filter, and store water. They also provide key nutrients and habitat for native flora and fauna, making them vitally important to not only human health, but the health of our entire ecosystem. In What is a Watershed? we discussed how water enters the watershed from rainwater and collects in drainage areas. But this is only a small part of the story of the water cycle.

Did you know that the water cycle is a closed loop system?

There is no new water that arrives from elsewhere, our water that exists on Earth has always been here, it continuously cycles through the atmosphere and moves between the ocean, rain, and rivers. When water arrives into the watershed it can either flow over the surface in streams and rivers, seep into the ground to recharge groundwater aquifers, or return to the atmosphere through the process of evapotranspiration. Let’s take a look at each of these processes a little more closely.

Surface Water Flow

Surface water flow is probably the easiest and most recognisable step in the water cycle. As rain falls, or snow melts, water flows over the surface in rivers, creeks and streams, and is carried downward by gravity, eventually accumulating in lakes or dams or draining out into the ocean. Rivers and streams also rely on groundwater flowing back to the surface to replenish the surface flow. In mountainous regions like the Sunshine Coast, snow and ice accumulates in the winter and gradually melts in the spring and summer, providing crucial top-ups to surface water flows.

Groundwater Aquifers

Groundwater moves through and is held underground in the cracks and spaces in soil, sand, and rock. The permeability of the soil is crucial for groundwater to be able to be absorbed. Groundwater generally flows downward, choosing the path of least resistance, until it reaches a fully saturated zone at the level of the water table.

An aquifer is an underground layer of permeable rock, soil, and/or sand that allows water to move through. Groundwater may eventually begin to collect in these aquifers where it may be tapped with wells to provide drinking water for human use. In fact, two thirds of the world's freshwater drinking supply comes from groundwater aquifers! On the Sunshine Coast we are increasingly relying on two prolific aquifers in West Howe Sound, for our water supply. Groundwater aquifers are very sensitive to unsustainable extraction and can dry up if the water is extracted faster than it is replenished.

Evaporation and Transpiration

As the rain falls, it may be intercepted by vegetation, mountains, or human-made structures before it is absorbed into the ground or flows over the surface. In the case of vegetation, the water can either be absorbed by plants to aid in photosynthesis or released through the pores of the leaves in a process called transpiration. Because it is difficult to measure whether the water has absorbed or transpired (released), it is described as a combined  process and referred to as evapotranspiration. Either way, the excess water is released back into the atmosphere as part of the recycling process.

The process of evaporation also occurs on mountains or human-made surfaces where water is heated up by the sun, allowing the water to evaporate and become water vapor that is carried by the air. The sun even evaporates some water back from flowing streams and rivers. Additionally, solid ice and snow, through the process of sublimation, can turn directly into gas. As the water vapor rises, it condenses to form clouds and when the condensed water vapor becomes heavy enough it will fall to the earth again as rain, snow, or ice, thus recycling the water and closing the loop on the water cycle.

Why is vegetation so important to the water cycle?

Native healthy vegetation naturally stores, cleans and filters water, making it crucial in maintaining clean drinking water. But if some of the water is intercepted by vegetation before it reaches the ground, thereby making it unable to be collected for human use, how can this be a good thing?

“Within a watershed, everything is connected to everything else”, (Credit Valley Conservation, n.d.).

When we talked about groundwater aquifers, the permeability of the soil is crucial for allowing water to seep in and vegetation plays a huge role in determining whether water is able to seep into the ground. “In a forest watershed, most rain is quickly absorbed by the soil”, (Smith, 2005). This is because the water is intercepted by vegetation and detritus (organic matter such as fallen leaves and decaying organisms) which allows a smoother transition into groundwater as opposed to flowing quickly over hard, impermeable, surfaces. Additionally, tree roots and mycorrhizal networks hold soil in place and layers of detritus help to cushion the falling water and prevent soil from loosening and contaminating streams. In this way, forests mitigate erosion and flooding and allow the water to be absorbed into the ecosystem, and the ground. Consequently, native vegetation is a vitally important factor in maintaining clean drinking water.

How does the ecosystem function within a healthy watershed?

When watersheds are healthy they provide water, habitat, and food sources for native plants and animals, including humans! By moving sediment downstream and into soils, they cycle and convert these nutrients into forms that living organisms can use. Watersheds even influence air quality by absorbing pollutants, something that is even more relevant on the Sunshine Coast with the emergence of wildfire smoke becoming a consistent issue.

What happens after the water reaches our watershed?

Another step in the water cycle is the collection of water and treatment of water for  human use. “While water is provided by nature, many of us rely on a complex network of pipes, pumps, equipment, and people provided by our community’s municipal water systems to safely deliver clean water to our taps”, (How Do Our Water Systems Work? - Value of Water, 2020).

The Sunshine Coast Regional District’s main water source is Chapman Lake, in the Tetrahedron Provincial Park. (See our drone footage of Chapman Lake at the bottom of this page).

Water from Chapman Lake is collected from an intake in Chapman Creek and piped to a treatment facility down stream. The treatment process involves many steps with the main goals being to remove suspended particles, debris, and algae and disinfect from bacteria and viruses. Once treated, the water is pumped to homes and businesses via large pipes, referred to as water mains.

Other drinking water sources on the Sunshine Coast include Aquifer 547 and Aquifer 548 (Keats Island); Aquifer 560 (Elphinstone-Gibsons-Granthams); Aquifer 552 (Hopkins-Langdale); Ruby Lake (Egmont/Pender Harbour), Garden Bay Lake (North Pender); McNeil Lake (South Pender) Waugh Lake (Egmont).



Aquifer: An underground layer of permeable rock, soil, and/or sand that allows water to move through.

Drainage Area: The area which all the water drains into from upstream sources.

Drainage Basins / Catchments: Smaller drainage areas that feed into sub-watersheds, may be referred to as drainage basins or catchments.

Drainage Divides: Established watersheds are separated from one another by the height of the land.

Ecosystem: An ecosystem consists of the plants, animals, and other organisms, along with weather and landscapes, which work together to form a biological community of life in a particular a geographic area.

Evaporation: The process of a liquid changing to a gas. Whereby water evaporates to become water vapor.

Evapotranspiration: A term used to describe the combined process of evaporation and transpiration.

Gravity: Gravity is a fundamental interaction which causes mutual attraction between all things that have mass.

Groundwater: Water that is held underground in the cracks and spaces in soil, sand and rock. It is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers.

Permeability: The ability of a material to allow the passage of a liquid, such as water. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas impermeable materials, such as clay, don't allow water to flow freely.

Precipitation: In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull.

Photosynthesis: "Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar." (National Geographic, 2022).

Sublimation: "The process by which snow or ice becomes water vapor without first melting and passing through the liquid phase." (National Geographic, 2022).

Swales: A swale is a marshy depression between ridges that allows for water to pool and soak into the ground.

Transpiration: The process of excess water diffusing through the pores in the leaves of plants.

Water Table: As groundwater accumulates and creates a saturated zone it reaches its maximum level, this level is referred to as the water table.



BC Tomorrow Society (2017, April 25)
British Columbia Watersheds

Capital Regional District (2013, December 23)
Watershed Basics: The Water Cycle

Credit Valley Conservation (no date)
The Water Cycle

National Geographic (2022, July 15)

Smith, S. S., PhD (2005, May 10)
Watersheds (PennState Extension)

Water Science School (2022, October 2)
The Water Cycle (U.S. Geological Survey)

Drone Footage of Chapman Lake

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