The nutrient cycle describes how nutrients move from the physical environment into living organisms, and subsequently are recycled back to the physical environment. This movement of nutrients, essential for life, from the environment into plants and animals and back again, is a vital function of the ecology of any region. In any particular environment, the nutrient cycle must be balanced and stable if the organisms that live in that environment are to flourish and be maintained in a constant population.
The 4 main nutrients we talked about were
Nitrogen
Water
Carbon
Phosphorus
Let's start with the cycle that everyone is most familiar.
Water cycle
-This cycle is the process by which water circulates between the Earths' oceans, atmosphere, and land. It involved precipitation as rain or snow, drainage in streams and rivers, and returns to the atmosphere by evaporation and transpiration.
Precipitation is any form of water coming back down to Earth, ex: rain, sleet, hail, snow...
Evaporation is when water is being turned from liquid for into gas form, moving from the Earth into the atmosphere.
Transpiration is very similar to evaporation, because it is being changed from liquid form into gas form into the atmosphere. The difference is where they start. Evaporation can start from puddle, lake, or ocean, while transpiration is being released from a plant.
Condensation is when the gas is being turned back into liquid
Nitrogen Cycle
This is the cycle by which nitrogen is converted into various chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Nitrogen is the most abundant nutrient in the air at 79%. Most organisms cannot use the nutrient in this form, the nitrogen must be "fixed", before they can use it. Animals get nitrogen from plants, or from animals that have eaten plants.
Nitrogen fixation takes a lot of energy and can occur from the atmospheric or biological processes. In the atmosphere the enormous energy of lighting breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to the Earth.
The other form is biological fixation, which only some bacteria and archaea are able to do. These organisms work together with plants, legumes, and some animals.
Once bacteria or lightning have turned the nitrogen into a usable form, the plants are able to absorb the nutrient. Plants are then eaten by animals, which transfers the nutrient into the animal. If that animal is eaten by another animal, the nutrient is moved once again into the other animal. Once that animal dies, the nutrient is recycled back into the ground. It is then either taken back up by plants, or bacteria is able to convert it back into the atmospheric nitrogen.
Carbon Cycle
All living things are made of carbon. Carbon is also a part of the ocean, air, and even rocks. Because the Earth is a dynamic place, carbon does not stay still. It is on the move!
In the atmosphere, carbon is attached to some oxygen ins a gas called carbon dioxide. Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon like coal and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters the atmosphere as carbon dioxide.
Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world. But humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than there was about 150 years ago, and Earth is becoming a warmer place. In fact, ice cores show us that there is now more carbon dioxide in the atmosphere than there has been in the last 420,000 year.
Phosphorus Cycle
Phosphorus cycles through the lithosphere (ground), hydrosphere (water), and biosphere (living organisms), but does not go into the atmosphere.
Over time, rain and weathering cause rocks to release phosphate ions and other minerals. This inorganic phosphate is then distributed in soil and water. Plants take up inorganic phosphate from the soil. The plants may then be consumed by animals. Once in the plant or animal, the phosphate is incorporated into organic molecules such as DNA. When the plant or animal dies, it decays, and the organic phosphate is returned to the soil. Within the soil, organic forms of phosphate can be made available to plants by bacteria that break down organic matter to inorganic forms of phosphorus. Phosphorus in soil can end up in waterways and eventually oceans. Once there, it can be incorporated into sediments over time.
When fields are over fertilized (through commercial fertilizers or manure), phosphate not utilized by plants can be lost from the soil through leaching and water run-off. This phosphate ends up in waterways, lakes and estuaries. Excess phosphate causes excessive growth of plants in waterways, lakes and estuaries leading to eutrophication. Eutrophication is a process where waterways, lakes, and shallow sea areas receive excess nutrients that stimulate excessive plant or algae growth. This excessive growth depletes the available oxygen in the water and causes other organisms to die off. Steps are being taken in agriculture to reduce phosphate losses in order to maximize the efficiency of fertilizer and effluent applications.
Practice Problems
1. The atmosphere contains ____ which is needed for photosynthesis
2. Which nutrient does not cycle through the atmosphere?
3. Which nutrient uses lightening as part of its cycle?
4. Plants need bacteria to incorporate this nutrient into a usable form.
5. Evaporation of water from plants is called ____.
6. The most abundant nutrient in the atmosphere is _____.
7. This nutrient cycles through ecosystems by photosynthesis, cellular respiration, and decomposition. As well, ocean mixing and volcanic eruptions can cycle this nutrient. Human activities that change the natural cycling of this nutrient include the burning of fossil fuels. Which nutrient does he above paragraph refer to?
8. This nutrient is the most prevalent gas in Earth’s atmosphere. It cycles through ecosystems via plants. Unusable in its normal form, once it is converted by lightning in the atmosphere or special bacteria in the soil or water it is absorbed by plants and enters food webs. Human activities, such as the burning of fossil fuels, and the use of fertilizer in agriculture, have more than doubled the amount of the nutrient in the biosphere in the past 50 years. Which nutrient does the above paragraph refer to?
9. This nutrient is cycled through ecosystems by the chemical and physical weathering of rocks. Stores of this nutrient are often buried deeply in the ground as sedimentary rock for thousands of years. Like other nutrients, it is absorbed through plant roots and becomes available to animals when they consumer these plants. Human activities that change the natural cycling of this nutrient include the use of fertilizers and detergents, which greatly increase the amounts of this nutrient in ecosystems. Which nutrient does the above paragraph refer to?