Alterations made to biogeochemical cycles by humanity. Biogeochemical cycles are the set of natural processes that allow the circulation of elements essential for life on Earth, such as carbon, nitrogen, sulfur, and phosphorus. These cycles play a crucial role in maintaining ecosystems and in the functioning of different organisms. However, human activities have drastically altered these cycles, causing negative effects on the environment and the quality of life on the planet. In this video, we explore how intensive agriculture, industrialization, and the use of fossil fuels have impacted biogeochemical cycles and what implications this has. Carbon cycle: Since the beginning of global industrialization at the end of the 19th century, human activity has affected the carbon cycle and carbon stores with deforestation and the burning of fossil fuels, altering the amount of carbon fixed and increasing its presence in the atmosphere. Like these processes, soil erosion and sediment runoff have also caused a direct loss in the form of carbon dioxide (CO2), harming the capacity of soils to support plant growth. Acting as carbon sinks, atmospheric carbon dioxide has increased by 2% in the last 100 years. This is one of the gases that trap the sun's heat in the atmosphere, resulting in a greenhouse effect that contributes to climate change. Methane, another greenhouse gas, is also generated by various human activities such as livestock production and rice cultivation. Furthermore, it is 22 times more effective than carbon dioxide at trapping heat. It is an explosive gas that generates safety and health problems in places where it occurs. Global warming brings various consequences such as an increase in heat waves, droughts, the intensity of rainfall, rising sea levels, and various impacts on biodiversity and food security. Some of the anthropogenic carbon has been absorbed by the ocean in response to the increase in atmospheric carbon dioxide, helping to balance the planet's climate. However, this capacity is not unlimited. CO2 causes a decrease in the pH of the water, which has occurred mainly in the last 50 years and is known as ocean acidification, which decreases the concentrations of ions. Carbonate affects the skeletons of marine organisms such as corals, mollusks, echinoderms, and fish larvae. It is estimated that the levels of acidification reached in the oceans by the end of the 21st century will cause the mass death of coral reefs. The nitrogen cycle: various human activities have significantly impacted the nitrogen cycle. The burning of fossil fuels, changes in land use, and the use of chemical fertilizers can increase the nitrogen available in an ecosystem by considerable amounts, causing alterations in both terrestrial and aquatic ecosystems. The use of chemical fertilizers has increased considerably in recent decades due to the process known as ABBOs, which fixes nitrogen from the atmosphere for use in agriculture and also demands a lot of energy derived from the use of fossil fuels. The intensive use of these fertilizers has induced environmental problems due to nitrate leaching and the emission of nitrous oxide, since the nitrogen not used by plants can leave the soil and be incorporated into other processes such as denitrification. This unused nitrogen, generally in the form of nitrate, filters through the soil. Soil seeps into groundwater, rivers, and streams, and can eventually reach coastal systems. In these aquatic ecosystems, the excessive arrival of nutrients like nitrogen can lead to an increase in the biomass of plants and algae, whose decomposition depletes oxygen, causing the death of fish and shellfish, as well as changes in the taste and smell of the water, the loss of coral reefs, and alterations in food webs, biodiversity, and habitat degradation. This process is known as eutrophication. In these systems, the bloom of toxic algae, which increases the mortality of various species, is beneficial. Eutrophication has also been associated with an increase in infectious diseases by influencing the abundance, composition, virulence, and survival of waterborne pathogens, in addition to affecting the hosts and vectors of these pathogens in various ways. Nitrogen oxides produced during the combustion of coal, natural gas, or oil react with water in the atmosphere, forming nitric acid and contributing to the generation of acid rain. Nitrous oxide, originating as an intermediate in the nitrogen cycle, can causing ozone layer depletion and acting as a greenhouse gas contributing to global warming. Phosphorus cycle: the surge in the use of chemical fertilizers after World War II has affected the nitrogen and phosphorus cycles. These have contributed to the amount of dissolved phosphorus, as have deforestation, erosion, and water pollution with wastewater. The extraction of phosphate rock from mineral deposits for use in the production of fertilizers and other chemicals is also another important cause of cycle disruption. Deforestation followed by burning converts the phosphorus stores in trees into ash, making the element susceptible to leaching and transport by runoff. Subsequently, erosion occurs, leading to the loss of the O and A horizons, where the highest amount of organic phosphorus is found. Human food waste and, to some extent, detergents have also contributed to the dissolved phosphorus load in rivers, which is considered double that provided under natural conditions. All this phosphorus reaches the oceans, causing Along with nitrogen, eutrophication processes in coastal areas affect the carbon cycle in the soil. Erosion carries away both organic and inorganic phosphorus, producing a loss in soil fertility and food production. The loss of nutrients is, in turn, worsened by the deficient productivity of plants, which cannot fully perform their soil-protecting function, generating a serious picture of degradation. All this process affects the carbon, nitrogen, and phosphorus cycles. Phosphate rocks, from which phosphorus is extracted, are considered a finite resource that requires millions of years to recover. Although world reserves are still sustainable in the long term, they are concentrated in a few countries, which generates a dependence on international trade for food production by nations with a scarcity of the resource. Regarding the sulfur cycle, some fairly common human activities have released sulfur compounds into the atmosphere. One of these is open-pit mining, which exposes large quantities of metallic sulfide, giving rise to acid mine drainage. The second activity that contributes between a third and half of the sulfur dioxide that reaches the atmosphere is the burning of fossil fuels. Originating from industrial and automotive emissions, the increased emission of these elements into the atmosphere produces the formation of sulfuric acid compounds, which dissolve in rainwater, reducing its pH and causing acid rain along with nitric acid. This process generates various alterations in ecosystems, such as the acidification of soils and water sources, the leaching of minerals and nutrients, the release of toxic compounds, the inhibition of microorganism activity, the alteration of photosynthesis and plant metabolism, and a greater susceptibility to pests and diseases. Regarding human constructions, it can affect structures made of stone, concrete, and metal.