2. The significance of water
Contents
2.1 Experiences of water environments
Finland is full of water environments – they can be found both in cities and in the countryside. We all have our own personal relationship with water and the natural environments that surround it.
For some people, a water environment can mean a pond one passes every day on the way to school. The ways in which we perceive water are quite subjective. What kinds of experiences, thoughts, or dreams do you have about water environments?
A typical Finnish lake landscape.
What kinds of water-related activities did you do on your summer holiday? Did you go swimming or fishing, for example?
What did you see when you were near the water? Did you see birds or dragonflies, for example? Did you catch any fish?
What kinds of water environments are there near your school or your house? Is there a lake or a river near your school? Do you live near the Baltic Sea? Does a small brook or ditch flow past your school?
Most Finns live quite close to the Baltic Sea. Have you ever witnessed the water environment of the Baltic Sea yourself?
2.2 Video about water environments
2.3 The qualities of water
Liquid water is essential for the existence of living organisms. All cells contain water. The chemical reactions that sustain life occur inside water solutions.
Life on Earth first emerged in saline ocean water. However, as life moved to land, the importance of water for living organisms did not decrease at all.
All cells require water to sustain their vital functions. Only a few plants or animals can survive for long periods of time without water. The seed of a plant is an example of a resting form that is capable of surviving without water for a long period of time. In water environments, the changes in temperature are slower than they are on land. The specific heat capacity of water is high. This means that a lot of thermal energy can be bound into water molecules.
The thermal conductivity of water is also quite good. This means that water conducts heat very efficiently. Humans can dwell outside without protective equipment when the air temperature is at 10 degrees Celsius, but would quickly catch a cold when dwelling in water of the same temperature. Because of the thermal qualities of water, shore areas have different climate conditions compared to inland environments. For example, winter arrives later to sea shores than it does to inland areas.
For a plant growing in a water environment, the amount of water is not a restricting factor. On the other hand, water environments provide less oxygen and nutrients than land environments. Freezing and salinity also provide challenges for organisms that live in water environments. A frozen ice layer prevents light from entering the water and reduces its oxygen concentration.
- To warm up a kilogram of iron from room temperature to 100 degrees Celsius requires approximately ten times less energy than warming up a equivalent amount of water to its boiling point.
- When water cools down, it releases energy to its environment.
- The freezing/melting point of pure water is 0 °C. The boiling point of water is 100 °C.
Water is the basis of life.
2.4 The water cycle
In the water cycle, water evaporates from the water system (oceans, lakes, rivers, etc.) to the atmosphere, condenses into clouds, moves inland, precipitates onto land and finally flows back into the sea.
Evaporating water is pure and fresh. When the water rains back down to the ground, different salts begin to dissolve into it. These salts are then carried into the seas with the water.
When water evaporates from the ocean to the atmosphere, the salts remain in the ocean instead of evaporating with the water molecules. Over the course of millions of years, different salts have accumulated in the planet's seas and oceans. As a result of this, these areas of water have turned saline. The most common type of salt found in seawater is sodium chloride, but other types of salts can also be found in it.
Only three percent of Earth's water is non-saline fresh water. Most of it is stored in glacial ice (70 % of the planet's fresh water, meaning under 2 % of its total water). Fresh water is also found under the ground in the form of groundwater.
Only under one percent of fresh water appears as surface water in lakes, rivers, and ponds. Life is mostly found in unfrozen, liquid water, but even glaciers are inhabited by some simple organisms, such as unicellular algae.
Salts change the properties of the water into which they dissolve. The salt concentration of the oceans is approximately 3,5 %. Brackish water, which has a salt concentration of under one percent, is found in the Baltic Sea and other similar areas.
Terminology
- A lake is a continuous, unbroken area of water. The water of a lake does not flow in a certain direction.
- A pond is an area of water that is smaller than a lake. If the diameter of the area of water is less than 200 metres, it is often considered a pond instead of a lake.
- A sea is a large, saline area of water. Seas connect with one another and form oceans.
- A river is a channel through which water flows towards another river, lake, or sea. Brooks and ditches are smaller than rivers.
- Brackish water is water with a low salt concetration. The water of the Baltic Sea is considered to be brackish water.
2.5 The effects of salinity on organisms
Saline water has more salts than fresh water. The amount of salt influences many things, but most of all it influences the salt and water balance of living organisms.
Oceanic fish have adapted to living in the high salt concentrations of the oceans. If an oceanic fish moves into fresh water, its cells begin accumulating too much water. However, some oceanic species have adapted to both highly saline and less saline environments. Herring and cod are examples of such species.
Fresh inland water contains less salts than saline water. Because of this, freshwater fish must actively receive salts from the water and remove excess water from their systems.
Most freshwater species have adapted to environments with low salt concentrations, but require fresh water in order to reproduce. For example, salmon must move into rivers to spawn. However, some freshwater species such as pike have adapted to reproduce in brackish water.
The pike is an example of a freshwater fish that has adapted to reproduce in brackish water.