The Sulfur Cycle

 The Sulfur Cycle

Photo from:https://www.vectorstock.com/royalty-free-vector/sulfur-cycle-biogeochemical-cycle-vector-35552339

Sulfur is an essential element for the macromolecules of living things and is involved in the formation of proteins.

Sources of Atmospheric Sulfur

• Atmospheric sulfur enters the atmosphere in three ways: decomposition of organic molecules, volcanic activity and geothermal vents, and burning of fossil fuels by humans.
• Sulfur dioxide (SO2) is the main form of atmospheric sulfur.

Deposition of Sulfur on Land

• Sulfur is deposited on land through precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents.
• Rainfall dissolves sulfur dioxide in the form of weak sulfuric acid (H2SO4), which can fall to the ground as acid rain.
• Sulfur can also fall directly from the atmosphere as fallout, and weathering of rocks releases sulfates into the soil.

Terrestrial Ecosystems and Sulfur

• Terrestrial ecosystems use soil sulfates (SO42-) taken up by plant roots.
• When plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide (H2S) gas.

Sulfur in the Oceans

• Sulfur enters the ocean through runoff from land, atmospheric fallout, and underwater geothermal vents.
• Some ecosystems rely on chemoautotrophs using sulfur as a biological energy source.
• Sulfur in the ocean supports marine ecosystems in the form of sulfates.

Human Activities and the Sulfur Cycle

• Human activities, such as burning fossil fuels, release large amounts of sulfur dioxide into the atmosphere, leading to acid rain.
• Acid rain lowers the pH of lakes, damaging aquatic ecosystems and affecting the man-made buildings 

The Phosphorus Cycle

 The Phosphorus Cycle

Photo from :https://www.sciencedirect.com/topics/earth-and-planetary-sciences/phosphorus-cycle (K.C. Ruttenberg, in Encyclopedia of Ocean Sciences, 2001)

I. Introduction to Phosphorus

• Phosphorus is a major component of nucleic acids, phospholipids, and also makes up the supportive components of bones.

II. Natural Occurrence of Phosphorus

• Phosphorus occurs in nature as the phosphate ion (PO4 3-).
• Phosphate runoff can occur from human activities and natural surface runoff when phosphate-containing rock is weathered and leached into rivers, lakes, and the ocean.
• Phosphate-containing ocean sediments form from ocean organisms and volcanic ash, aerosols, and mineral dust, and are moved to land over geologic time by uplifting of the Earth's surface.

III. Reciprocal Exchange of Phosphorus

• Phosphorus is exchanged between phosphate dissolved in the ocean and marine organisms.
• The movement of phosphate from the ocean to land and through the soil is slow, with an average residence time in the ocean between 20,000 and 100,000 years.

IV. Human Impact on the Phosphorus Cycle

• Excess phosphorus and nitrogen from fertilizer runoff and sewage cause excessive growth of algae.
• The death and decay of these organisms depletes dissolved oxygen, leading to dead zones in lakes and at the mouths of rivers, causing harm to aquatic organisms.

V. Examples of Dead Zones

• Dead zones are areas of water bodies where aquatic life cannot survive because of low oxygen levels. Dead zones are generally caused by significant nutrient pollution, and are primarily a problem for bays, lakes and coastal waters since they receive excess nutrients from upstream sources. The number of dead zones has increased, with over 400 present as of 2008.
• The Gulf of Mexico, particularly the Mississippi River basin, has one of the worst dead zones measuring over 8,463 square miles.

The Nitrogen Cycle

  The Nitrogen Cycle

Photo from: https://www.britannica.com/science/nitrogen-cycle(Written and fact-checked by 

The Editors of Encyclopaedia Britannica)

I. Introduction

The nitrogen cycle is a complex process involving the conversion of atmospheric nitrogen into organic nitrogen through nitrogen fixation by bacteria, which is then incorporated into living organisms. This process is crucial for the functioning of ecosystems as nitrogen is a key element for life. The cycle also involves the conversion of organic nitrogen back into gaseous nitrogen through ammonification, nitrification, and denitrification by bacteria. 

Human activities, such as fossil fuel combustion and the use of artificial fertilizers, can disrupt the nitrogen cycle and have negative impacts on the environment, including acid rain, greenhouse gas effects, and eutrophication of water bodies. Eutrophication of water bodies is a process where excessive nutrients, particularly nitrogen and phosphorus, enter water systems, leading to an overgrowth of algae and other aquatic plants. The excessive growth of algae can lead to the depletion of oxygen in the water as they decompose, which in turn can result in the death of aquatic fauna and disrupt the balance of the ecosystem. The marine nitrogen cycle is similar, with marine bacteria and archaea playing a vital role. 

II. Nitrogen Fixation

• Cyanobacteria, found in aquatic ecosystems, play a key role in nitrogen fixation by converting nitrogen gas (N2) into ammonia (NH3).
• Rhizobium bacteria live symbiotically in the root nodules of legumes and provide organic nitrogen to the plants.

III. Organic Nitrogen

• Organic nitrogen is essential for ecosystem dynamics, as it limits processes such as primary production and decomposition.
• Nitrogen fixation converts atmospheric nitrogen into organic nitrogen that is incorporated into living organisms.

IV. Nitrogen Conversion

• Nitrogen in living organisms is eventually converted back into gaseous nitrogen by bacteria in a process called denitrification.
• The nitrogen conversion process includes ammonification, nitrification, and denitrification.
• Ammonification involves the conversion of nitrogenous waste from animals into ammonium by certain bacteria and fungi.
• Nitrification converts ammonium into nitrites and then nitrates by nitrifying bacteria.
• Denitrification occurs when bacteria convert nitrates into nitrogen gas, allowing it to re-enter the atmosphere.

V. Human Impact on the Nitrogen Cycle

• Human activities, such as combustion of fossil fuels and use of artificial fertilizers in agriculture, release nitrogen into the environment.
• Nitrogen oxides from combustion can cause acid rain and greenhouse gas effects, contributing to climate change.
• Fertilizer runoff can cause eutrophication in water bodies, leading to overgrowth of algae and oxygen depletion, harming aquatic fauna.

VI. Marine Nitrogen Cycle

• Similar nitrogen conversion processes occur in marine ecosystems, performed by marine bacteria and archaea.
• Some nitrogen falls to the ocean floor as sediment and can be moved to land in geologic time, contributing to the terrestrial nitrogen cycle.

VII. Conclusion

• The nitrogen cycle is a complex process that involves nitrogen fixation, organic nitrogen incorporation, and nitrogen conversion by bacteria.
• Human activities can impact the nitrogen cycle, highlighting the need for sustainable nitrogen management to protect ecosystems and minimize environmental harm.

Which of the following statements about the nitrogen cycle is false? 

1. Ammonification converts organic nitrogenous matter from living organisms into ammonium (NH 4+). 2. Denitrification by bacteria converts nitrates (NO 3−) to nitrogen gas (N2). 3. Nitrification by bacteria converts nitrates (NO 3−) to nitrites (NO2−) 4. Nitrogen fixing bacteria convert nitrogen gas (N 2) into organic compounds.

The false statement about the nitrogen cycle is:

3. Nitrification by bacteria converts nitrates (NO3−) to nitrites (NO2−).

In reality, nitrification by bacteria is a two-step process that converts ammonium (NH4+) to nitrites (NO2−) and then to nitrates (NO3−), not directly from nitrates to nitrites.

The Carbon Cycle

 The Carbon Cycle

Photo from:https://www.geeksforgeeks.org/carbon-cycle/

I. Introduction

The carbon cycle is the process by which carbon, in the form of carbon dioxide gas, is exchanged between the atmosphere, living organisms, and the Earth's geologic processes. It involves rapid carbon exchange among living organisms through processes like photosynthesis and respiration, and long-term cycling of carbon through burial and fossilization of organic matter. Human activities, such as burning fossil fuels and deforestation, have disrupted the balance of the carbon cycle, leading to an increase in atmospheric carbon dioxide levels and contributing to climate change. Carbon is the fourth most abundant element in living organisms. Carbon is present in all organic molecules and plays a crucial role in the structure of macromolecules. Carbon compounds contain energy and fossilized carbon from plants and algae is used as fuel by humans.

II. Rapid Carbon Exchange among Living Organisms

• Carbon dioxide gas exists in the atmosphere and is dissolved in water.
• Photosynthesis, carried out by plants and algae, converts carbon dioxide gas into organic carbon.
• During photosynthesis, plants and algae absorb carbon dioxide from the atmosphere and use it to synthesize organic compounds, such as carbohydrates, proteins, and lipids.
• Organic carbon is then transferred through the food web as organisms consume other organisms, leading to a rapid exchange of carbon among living organisms.
• Respiration, carried out by all living organisms, including plants and animals, releases carbon dioxide back into the atmosphere as a byproduct of cellular metabolism. This rapid exchange of carbon among living organisms helps to maintain the balance of carbon in the atmosphere and is a critical component of the carbon cycle.

III. Long-term Cycling of Carbon through Geologic Processes

• Long-term storage of organic carbon occurs when dead plant and animal matter, also known as detritus, is buried deep underground and becomes fossilized over millions of years.
• Volcanic activity, such as volcanic eruptions and degassing of magma, also releases carbon dioxide stored in the Earth's crust back into the atmosphere.
• Human activities, such as deforestation, land use changes, and the burning of fossil fuels, have significantly increased the amount of carbon dioxide released into the atmosphere, contributing to the current climate change concerns.

The Water Cycle

 The Water Cycle

The Water Cycle © normaals Photos from :https://www.australianenvironmentaleducation.com.au/education-resources/the-natural-water-cycle/

I. Introduction

The water cycle is a fundamental process that involves the continuous movement of water through different stages, including evaporation, condensation, precipitation, subsurface water flow, surface runoff, and streamflow. It is driven by the Sun's energy, which heats the oceans and surface waters, leading to evaporation and sublimation of water into the atmosphere. Precipitation occurs when water vapor condenses into clouds and falls back to Earth as rain or snow. Surface runoff and groundwater flow replenish streams, lakes, and oceans with fresh water. 

The water cycle is essential for maintaining water availability for all living organisms, including humans, but human activities such as groundwater depletion and pollution can disrupt this delicate balance. Understanding the core concepts of the water cycle is crucial for addressing water-related issues and managing water resources sustainably. The availability of fresh water is limited, with less than one percent of it being present in lakes and rivers, and it is crucial for ecosystem dynamics and human survival.

II. Processes of the Water Cycle

• Evaporation and Sublimation: Driven by the Sun's energy, liquid surface water and frozen water (ice) are converted into water vapor in the atmosphere.
• Condensation and Precipitation: Water vapor condenses into clouds as liquid or frozen droplets, and eventually falls back to Earth's surface as precipitation (rain or snow).
• Subsurface Water Flow: Precipitated water may infiltrate the soil and percolate into the subsoil and bedrock, forming groundwater.
• Surface Runoff and Snowmelt: Precipitated water that does not infiltrate the soil may flow over the surface as runoff or snowmelt, and can make its way into streams, lakes, or the oceans.
• Streamflow: Streams and rivers are fed by surface runoff, snowmelt, and groundwater, and they play a significant role in the water cycle by transporting water from land to the oceans.

III. Interactions with Terrestrial Environments

• Vegetation and Evapotranspiration: Rainwater encounters vegetation before it reaches the soil surface, and a significant percentage of water evaporates from the surfaces of plants through a process called evapotranspiration.
• Groundwater: Water that infiltrates the soil and percolates into the subsoil and bedrock forms groundwater, which is an important reservoir of fresh water.
• Aquifers: Groundwater is stored in aquifers, which are layers of rock or sediment that contain water and serve as a source of drinking or irrigation water. However, many aquifers are being depleted faster than they are being replenished, leading to concerns about groundwater sustainability.

IV. Environmental Effects of Runoff

• Mineral Cycling: Rain and surface runoff play a role in cycling minerals, such as carbon, nitrogen, phosphorus, and sulfur, from land to water.
• Environmental Impacts: Runoff can carry pollutants from the land, such as fertilizers and pesticides, into water bodies, leading to water pollution and ecosystem degradation.

V. Conclusion

• The water cycle is a complex system involving various processes that are driven by the Sun's energy and play a crucial role in maintaining water availability on Earth.
• Human activities, such as groundwater extraction and pollution, can have significant impacts on the water cycle and freshwater resources.
• Sustainable management and conservation of water resources are essential for ensuring the availability of freshwater for ecosystems and human societies.