Biogeochemical Cycles PDF

Introduction ============ Biogeochemical cycles are a series of biological, geological and chemical processes that 'recycle' elements on Earth. Major cycles important for understanding human impact on climate systems and biogeochemical cycles: 1. 2. 3. Common issue with three cycles: Humans...

Introduction ============ Biogeochemical cycles are a series of biological, geological and chemical processes that 'recycle' elements on Earth. Major cycles important for understanding human impact on climate systems and biogeochemical cycles: 1. 2. 3. Common issue with three cycles: Humans have increased the production of one or more compounds/forms of the elements. The natural processes cannot keep up with human production rate and there is a 'build-up' or excess in one or more reservoirs. Carbon Cycle: ============= **[Important terms:]** 1. 2. 3. 4. **[Important process-]** 1. 2. 3. 4. **[Sinks-]** 1. 2. 3. 4. **[Sources-]** 1. 2. **[Human impact on carbon cycle-]** Humans have utilised carbon trapped in the land sinks in the form of coal, petroleum, natural gas and limestones for various industries. This has released large quantities of otherwise stably stored carbon into the atmosphere, where it is causing major changes in the Earth's climate system and contributing as a greenhouse gas. The practice of agriculture has also released carbon as deforestation has reduced the ability of the terrestrial habitat to absorb carbon from the atmosphere. The increased carbon concentration in the atmosphere has increased the absorption of CO2 by the oceans. This has caused a decrease in the ocean's capacity to serve as a sink, worsening the situation by causing the biggest sink of carbon in current times to be at risk of getting saturated (full). The increased greenhouse effect has caused melting of ice sheets and thawing of permafrost. This has subsequently released the trapped CO2 and methane back into the atmosphere, thus increasing the greenhouse gas effect (reinforcing feedback loop). Nitrogen Cycle: =============== The recycling of nitrogen mostly occurs through biological activities. **[Important terms-]** 1. 2. 3. Phosphorus Cycle: ================= The recycling of phosphorus is also biological in nature. There are no technical terms for any processes here as far as I know, just shoot me a message if there was something and I'm too blind to have noticed it. Human impacts on Phosphorus and Nitrogen cycles: ================================================ I am clubbing the two since most of the human intervention here and the effects are similar. Humans use nitrogen and phosphorus for fertilisers. Nitrogen is mostly obtained from N2 in the atmosphere while phosphorus is processed from phosphate minerals present on the Earth's crust. Both elements get accumulated in the soil due to extensive use of fertilisers and saturate the soil. They are helpful for plant growth in small quantities but can be toxic if they build up too much in the soil, killing the microorganisms and even plants surviving on the soil. This leads farmers to use more fertilisers thus creating a positive (reinforcing) feedback loop. For nitrogen specifically- it is required for creating proteins in plants. Many plants rich in proteins (like chickpeas) have a symbiotic relationship with nitrogen fixing bacteria. These bacteria help provide the ammonia (NH3) needed by plants to make proteins but die in environments where there is excess of ammonia. Extensive use of fertilisers has caused deterioration in this symbiotic relationship, causing plants to now rely on fertilisers alone for meeting ammonia needs. Both phosphorus and nitrogen fertilisers are inefficient as large quantities of fertilisers remain unused in the soil they were applied to. The man-made fertilisers are also not as efficiently absorbed by plants as the compounds made by microorganisms as a result of their biological activity. The excess fertilisers dissolve with rain water and can seep deeper into the ground and contaminate local groundwater supply. They also can flow out of the field as surface runoff into lakes and cause eutrophication. Extra stuff =========== This is doubtfully important from the perspective of exams so don\'t bother with these for now, these are just things I've mentioned in my sustainable development tutorial and think can be helpful knowledge to have later in life when arguing with a geologist because for some stupid reason they deny climate change. Thermohaline currents- These are just warm/cold water currents that flow through the world's oceans. They drive the ENTIRE climate system on Earth and are the reason why the pole's have any marine life surviving there. The warm waters of the tropics (equatorial region) are less dense as they have low salinity (high precipitation and high capacity for holding salt) and the cold waters of the polar regions are denser (low precipitation and less capacity for holding salt). As per the laws of physics (and nature) the dense waters move towards the equator to balance the density while the warmer waters move towards the polar regions to fill the void left by the colder waters. This circulates the temperatures and salinity of the oceans and ensures that the nutrient rich (because more minerals are formed in cold waters) waters are circulated worldwide. This is also why coral reefs are supported by tropical water habitats as the cold nutrient rich water moves towards these regions. The aquatic life in polar regions also thrives as the warmth of the warm water currents ensures the temperatures are optimum for survival. The current carbon cycle messes with the thermohaline currents as one major factor contributing to the thermohaline currents in the difference in temperature between poles and equator. The global warming crisis causes the poles to heat up and hence the flow of these currents slows down. This causes the overall weather system to lag, causes delays in atmospheric currents and degrades the marine habitats. Albedo- The net reflection of the sunlight by the Earth's surface is called albedo. The lighter a surface, the more light it reflects as a general rule of thumb. Ice sheets reduce temperatures of their surroundings by increasing albedo as they reflect almost the entire sunlight falling on them. This is why snow capped mountains are almost always covered in snow and why the Antarctic ice sheet is almost always entirely frozen. Forests have low albedo as the trees absorb the light while fields have higher albedo as less light is absorbed by crops as compared to trees. This is why deforestation for agriculture causes heating of the land. Many solids suspended in air (aerosols) reflect light well and hence cause an increase in albedo. Due to this many countries in the tropics use artificial sprinklers to spray water as aerosol to reduce heat in the cities during summers. This is a double edged sword however as aerosols also cause respiratory problems when present in high quantities.