Physical and Chemical Properties of Water

Physical Properties

Lack of Desiccation. All organisms need water to survive; this applies especially to creatures living in water that would die if removed. In water these organisms are kept constantly wet and only survive because of it.

Support. Water has the ability to physically support the weight of life forms, lifting smaller more fragile life forms higher where they can receive light, heat and nutrients. These organisms are often at the base of the food chain and are extremely important for sustaining life in and around the water.

The support provided by water also makes swimming and paddling much easier due to its density. Creatures can push water away to move where as in air they could not. This support also allows plants to float on the surface, this can be in the form of free floating plants or plants rooted to the bottom with the upper most part extending out of the water. These plants provide food and shelter for animals.

Surface Tension. Water has a high surface tension; this means that there is a strong cohesion between water molecules. This allows some life forms to stand and move over the surface of the water because the force of cohesion is stronger than the force put upon it by the life form. This level of tension works in a similar way when trapping small creatures that fall in, because they put such a small force on the water they do not sink, in these cases they will provide food for surface dwelling animals. This tension also helps creatures to hang from the surface to breath, as the molecules force together and hold the creature in place.

Temperature. Water has a reasonably constant water temperature, the change in water temp is a gradual rather than rapid process, and this is because it can absorb large amounts of heat energy before it actually starts to get hot. This provides a consistent environment for life, rather than the swinging temperatures of air. Oxygen dissolves naturally when it comes into contact with air; lower temps of water dissolve greater amounts of oxygen, which is used to sustain life. The lower temps also dissolve more CO2 causing them to have lower pH levels: which tend to provide a greater biodiversity compared to more alkaline waters.

Temperature is also the instigator for thermocline formations (if deep enough), creating separated areas with very different temperatures and this variation in temp causes the habitat to almost become two separate habitats.

Ice. The surface layers of water are affected most dramatically by temperatures dropping, at these times this layer will freeze and become ice, because water is less dense at freezing point it will float and stay at the surface leaving warmer waters deeper down. The water will have no contact with air and wind for fresh circulation of oxygen, which will cause death in organisms that breathe oxygen. Ice will also cause damage to plants putting extra pressure on roots and decreasing its nutrient supply. The total coverage of ice is dependant on how still the water is, (some lakes are large enough to have wave action and this movement can prevent the ice from forming).

Waves. Water can be moved by wind, with strong enough directional force a wave can occur. In areas with regular wind made waves there will be erosion of banks and plants from the continual stress of the heavy water. Waves can also circulate the water spreading oxygen and nutrients.

Transparency. Water is naturally clear, (it is discoloured by chemicals, organisms and sediments). This transparency is what allows photosynthesis and growth to occur in plants beneath the water. Light penetration can be impaired by organisms (algae, water lilies etc), sediments (soils, pollution) and shadow (from boats, trees, walls). Some natural staining can occur from peat, which turns water brown and also iron, turning water red. All this turbidity can have a negative affect on the aquatic plants ability to produce oxygen. There gets to a certain depth and turbidity where plants can only just survive as their oxygen out equals their intake per day. Any lower than this and the plant cannot survive.

Chemical Properties

Dissolved minerals. The level of minerals in a body of water will essentially determine what will live there, as they are essential plant nutrients. These minerals can come from several sources:when manure is put on soil to fertilise bacteria and fungi break it down, this process produces Nitrates. These minerals get in to the soil and when it rains, leach through the soils into the body of water. The plants then use the Nitrate for growth. Phosphates will work in a similar way.

They can also be produced by dead organic matter (DOM) breakdown in the water and from detergents and wastewater being washed in. Sulphates and chlorides are naturally present in water but can also be washed in too. Minerals such as calcium carbonate and magnesium carbonate are also essential to aquatic life and determine water hardness; the more present the harder the water. Water hardness is closely linked with pH levels and so is important for sustaining life. Calcium and magnesium in water will affect alkalinity, certain species will not be able to tolerate alkaline waters and others will thrive, so levels are relevant to biodiversity and the types of species found in the habitat.

These minerals are all dissolved when they come in contact with water, this chemical process make minerals far easier to absorb and for use by plants, this will then benefit the growth and health of the vegetation in and around the water.

With a lot of minerals coming from surface water run off and leached groundwater you tend to find ponds and lakes on lowlands to be very high in these nutrients (eutrophic) and the abundance of algae is usually an indication of this. Ponds or lakes situated on higher ground will often have lower levels of nutrients in varying levels.

Dissolved gases. Oxygen is the most important gas to sustain life in waters, when air and water come in contact oxygen is dissolved into the water. This allows the species living in the water to breath. Oxygen is also produced by plant life in the water from photosynthesis. The temperature of the water greatly affects how much oxygen can be absorbed, the cooler the water the greater the amount of oxygen that can be dissolved. Oxygen is lost at night when plants respire, absorbing oxygen and producing CO2, it can also be lost through an abundance of algae sitting on the surface of the water blocking the light, which then restricts photosynthesis.

There are also varying amounts of CO2 present in water, produced by respiration from plants and animals, too much CO2 in water can be very detrimental to pond life.

Acidity. The pH of water is dependant on various factors; the geology of the area will provide certain types and levels of minerals, which can influence the pH level along with their presence in the surrounding soils. The pH level is directly linked to species found in a pond or lake, high levels of acidity can kill fish or cause so much stress that weight, size, ability to hunt or flee may become impaired and ultimately the species may no longer survive on the site. reducing biodiversity and upsetting the balance of the ecosystem.

Small fluctuations can occur to the pH level at night when plants are producing CO2 but the fluctuations are minimal and the levels are generally quite stable.

Organic matter. The bulk of organic matter found in the water sits at the bottom, it comes from the death of macrophytes (algae) and leaves that have fallen from trees and been blown into the water. All this DOM sinks and eventually gets broken down by bacteria and fungi.

During this process CO2 is given off and oxygen used up and so links directly to the oxygen supply and nutrient values.

Shallower bodies of water will have a rich substrate because of the presence of vegetation at the bottom, compared to this deeper bodies like lakes will have less of this richness because plants cant survive at that depth because of the lack of light. You have to be careful with the shallower pond because this level of organic matter can build up substantially and reduce the water depth over a few years. Organic matter also comes from the breakdown of reedy plants, their structure allows for slower decomposition and produces detritus: which is an essential food for many smaller species living in the water.