Cycles in the Ecosystem PA 4.6

I. Matter Cycles Unlike the continuous flow of energy from the sun, the matter that is found on the Earth is in a closed system. That means that the amount we have now is the same amount we had a million years ago. Matter continuously cycles through out the parts of an ecosystem, going from the environment to living organisms and back to the environment.

There are several major cycles that are at work in an ecosystem but we are going to focus on three: The water cycle The carbon cycle The nitrogen cycle Let’s start with the water cycle…

Do you know how much of the human body is water? Earth is considered the water planet with over 70% of surface covered with water. More importantly, most living things are dependent on water and cannot exist without it. Do you know how much of the human body is water? a. 65% How long can we survive without water? a. 3-5 days depending on conditions.

So the water you are drinking today, is the same water the dinosaurs bathed in 65 million years ago. Sounds gross…but isn’t because of the water cycle.

D. The Water Cycle The water cycle (like all the other cycles) is driven by the energy of the sun. The purpose of the water cycle is to collect, purify and distribute the water found on the Earth. There are six major steps to the water cycle.

Evaporation – the energy of the sun causes water to evaporate (from mainly the oceans), changing from liquid water to water vapor. Condensation – as the water vapor cools, it condenses into cloud droplets.

Precipitation – as the cloud droplets grow, they form rain (or snow or both) which falls back to the earth. Runoff – if the precipitation falls on land, it washes downhill by gravity into lakes, rivers, or ponds and eventually the ocean.

Percolation/infiltration – some of the water seeps into the ground and becomes groundwater. Transpiration – groundwater is absorbed by plants and given off by the leaves of plants due to the energy of the sun and respiration.

The water cycle can be extremely fast or slow depending on the location and climate. Humans are affecting the water cycle through pollution. Pollution limits the amount of water that is available for use by humans and other living organisms.

LET’S REVIEW…. Condensation Runoff

Carbon We are considered carbon-based life forms. Carbon is the building block of life. It is essential for DNA, proteins, fats, and carbohydrates. Carbon dioxide, CO2, is an essential greenhouse gas that helps maintain heat in Earth’s atmosphere. Carbon can be found in the atmosphere, oceans, and in rocks. Let’s review the carbon cycle…

The carbon cycle has three natural steps. I. Photosynthesis – Producers (Plants) on the land and in the ocean take in CO2 and build organic molecules with the carbon. Decomposition

II. Respiration – the carbon stored in organic molecules (like sugars) are used by the producers and consumers for energy. (These carbon molecules travel through the food web). Cellular respiration releases CO2 back into the atmosphere or water.

III. Decomposition – when the waste products or remains of dead organisms are broken down by decomposers, CO2 is released back into the atmosphere and oceans or settle/combine with sediments in the soil. Decomposition

The carbon cycle has parts that exchange carbon very quickly (photosynthesis and respiration) and has parts that can take millions of years. (formation of fossil fuels – coal and oil) Humans affect through deforestation and the burning of fossil fuels. Fewer trees result in less CO2 absorbed from the atmosphere. Burning fossil fuels releases carbon that was stored deep in the ground for millions of years.

Let’s review the Carbon cycle…

Nitrogen Nitrogen is the most abundant gas found in the Earth’s atmosphere. Nitrogen is also an important component in organic compounds such as proteins, DNA, and chlorophyll. However, the form of nitrogen that is most abundant, N2, is not usable by producers or consumers. So how do we get the nitrogen that we need…enter the nitrogen cycle.

The nitrogen cycle is driven by bacteria and has five basic steps. Nitrogen-fixation – bacteria found in the roots of plants (mainly legumes) convert N2 gas into ammonia (NH3) Ammonification – decomposers break down organism remains and releases ammonia.

III. Nitrification – another type of bacteria convert the ammonia (NH3) into nitrates (NO3). Nitrates are a form of nitrogen that are usable by producers. (Lightening can also change N2 into NO3) IV. Assimilation – is the uptake of nitrates by producers. Consumers get nitrogen by consuming producers or other consumers.

V. Denitrification – another type of bacteria breaks down the nitrates back into nitrogen gas. (N2) Nitrogen content is a limiting factor for plant growth.

Humans are affecting the nitrogen cycle by adding nitrogen-containing fertilizers to the environment and through the burning of fossil fuels. (Nitrogen oxides are emitted which can cause acid rain)

Let’s review the Nitrogen cycle…

Any Questions????

Ecological Succession

Let’s focus on primary succession. Ecological Succession is a process in which the communities of an ecosystem change over time. There are two types of succession: primary and secondary. Both types of succession follow a similar pattern. Let’s focus on primary succession. A. Primary succession occurs in places where an ecosystem has never existed before. This could be a newly formed volcanic island or land exposed from a receding glacier.

B. As the exposed rock is weathered, the first species appear B. As the exposed rock is weathered, the first species appear. These species are called pioneer species. They are small, grow quickly, and need minimal resources to survive. Often are mosses and lichens.

C. The pioneer species breakdown the rock to form soil C. The pioneer species breakdown the rock to form soil. This allows other species to grow among the mosses and lichens. Eventually the other species out compete with the pioneer species and change the community.

D. At each stage, competition among the species causes a change in the dominant community. In the later stages, larger, slower growing species displace the smaller, faster growing species.

As the ecosystem ages, the community becomes more diverse As the ecosystem ages, the community becomes more diverse. The process of succession will continue until the ecosystem reaches a climax community. A climax community is the last stage of succession. If left undisturbed, the ecosystem will stay at the climax community. The Oak-Hickory forests of PA is a climax community.

Disturbances in the ecosystem, such as fire, flood or human activity, can slow the process of succession down. If the disturbance is catastrophic, like a tornado or volcanic eruptions, the process may have to start over from the beginning. Which leads us to….

Secondary succession is the process that begins in an ecosystem that has been disturbed or destroyed. Typically occurs on abandoned farmlands, burned or cut forests, etc…

I. Secondary succession has similar stages compared with primary succession. Remember that secondary is regenerating an existing ecosystem. Primary is forming a new ecosystem where none existed before.