Phosphorus cycle and climate change
The phosphorus cycle is a crucial biogeochemical process that describes the movement of phosphorus through various ecosystems, including rocks, soil, and living organisms. Phosphorus is essential for life, playing a key role in cellular functions, energy transfer, and genetic information storage. Unlike many other nutrients, phosphorus does not significantly cycle through the atmosphere and is primarily found in terrestrial environments. The cycle can be disrupted by human activities, particularly through the excessive use of phosphorus-rich fertilizers, which can lead to nutrient runoff and eutrophication in aquatic systems. This results in harmful algal blooms that deplete oxygen levels in water, adversely affecting fish and other aquatic life.
Climate change exacerbates these issues, as deforestation, particularly of tropical rainforests, disrupts the natural phosphorus recycling processes. The loss of trees not only leads to nutrient runoff but also contributes to increased carbon dioxide levels in the atmosphere, further amplifying global warming. Additionally, rising CO2 levels lead to ocean acidification, potentially hindering the ability of marine organisms, such as plankton, to utilize dissolved phosphates. This chain reaction threatens the entire marine food web, highlighting the interconnectedness of the phosphorus cycle and climate change. Understanding these dynamics is essential for addressing ecological and environmental challenges.
Subject Terms
Phosphorus cycle and climate change
Definition
The chemical element phosphorus is essential for terrestrial life. Plants, animals, fungi, and microorganisms use phosphorus for intercellular signaling. They also use it to make membrane lipids that compose the cell membrane; molecules such as adenosine triphosphate (ATP) that store usable chemical energy and transfer it from one reaction to another; and deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), which store genetic information. Some animals also use phosphorus to make bones and teeth.
The phosphorus cycle is a biogeochemical cycle that describes the movement of phosphorus through rocks, living organisms, and water. Because phosphorus and phosphorus-based compounds are typically solids at terrestrial ranges of temperature and pressure, the atmosphere does not play a significant role in the movements of phosphorus. Phosphorus, therefore, is usually found on land, in rock and soil minerals, and in salts that form oceanic sediments. Since phosphorus-containing compounds are poorly soluble, phosphorus is a limiting factor for plant growth in marine environments.
In rocks, phosphorus is found primarily in marine sedimentary rocks (in the mineral apatite), guano deposits (bird and bat droppings) in tropical caves, and in some calcium-rich volcanic rocks. Erosion of phosphorus-containing rocks redistributes it throughout the soil and water. Plants take up this phosphorus, herbivores eat the plants, carnivores eat the herbivores, and phosphates absorbed by animals eventually return to the soil by excretion of urine and feces and by decomposition after death. Phosphorus enters aquatic ecosystems by means of rainwater runoff, sewage seepage, natural mineral deposits, and industrial wastes. The poor solubility of phosphorus-containing compounds causes them to settle on lake bottoms and the ocean floor. Tectonic uplifting of such sediments and their subsequent erosion returns them to the phosphorus cycle.
Significance for Climate Change
In the environment, phosphorus is found in combination with oxygen, and it forms ions such as phosphate (PO4-3), hydrogen phosphate (HPO4-2), dihydrogen phosphate (H2PO4-1), and phosphoric acid (H3PO4). In rocks, phosphorus can also exist as metaphosphate (PO3-1), which is also known as phosphite.
Phosphorus is mined, largely, for the production of fertilizers. The use of phosphate minerals and their products as fertilizers has increased tremendously global food production. However, fertilizers have also increased phosphates in runoff waters.
Phosphorus moves quickly through plants and animals, but slowly through soils or oceans. Thus, the phosphorus cycle is one of the slowest of all biogeochemical cycles. Consequently, phosphorus is usually the limiting nutrient that controls biological productivity in many terrestrial and marine environments. Excess dissolved phosphorus leads to uncontrollable aquatic biological growth and water-quality problems. This process, called eutrophication, causes explosive algal growth or “algal blooms.” Algal blooms rapidly utilize all the available nutrients, and after the algae die, thick pads of dead organisms fall to the bottom and oxidize. This reduces dissolved oxygen and creates an inhospitable environment for fish. Animals that depend upon fish as a food source or the water for reproduction are adversely affected by such events. Consequently, sharp increases in phosphorus influx tend to reduce animal populations.
Serious disruption of the phosphorus cycle occurs during cutting of tropical rain forests. Rain-forest ecosystems are supported by highly efficient mineral recycling. Heavy rainfall leaches nutrients like phosphorus from the soil, but warm, moist conditions favor high decomposition rates. Fungi called mycorrhizae form special relationships with the roots of rainforest trees, and this symbiotic association between the tree and the fungus allows the trees to absorb phosphorus before it enters the soil. This prevents phosphorus loss by leaching. Cutting down rainforest trees leaves phosphorus in the soils and copious rain waters drive it into the lakes or oceans. Excess phosphorus kills sea creatures and also affects the predators that depend on these creatures for their survival. With the death of the large trees, there is not enough plant life to hold the soil in place and accelerated erosion ensues. Thus tree loss initiates a vicious cycle of erosion, nutrient loss, plant death, further erosion, more nutrient loss, and so on.
Rain forests play a major role in the regulation of global weather patterns and the balance of carbon dioxide (CO2) in the atmosphere. Tropical rainforest destruction puts large amounts of CO2 into the air and concomitantly removes the trees that are responsible for removing CO2, thus exacerbating atmospheric warming on a global scale.
Increased atmospheric CO2 levels also increase ocean acidity. Acidification of the ocean decreases the ability of plankton to use dissolved phosphates. This would effectively starve plankton for phosphorus, and subsequently starve any organism that eats plankton and all organisms that depend on plankton eaters, thus causing a cascade of extinctions.
Bibliography
Filippelli, Gabriel M. “The Global Phosphorus Cycle: Past, Present, and Future.” Elements 4 (2008): 89-95.
Föllmi, K. B. “The Phosphorus Cycle, Phosphogenesis, and Marine Phosphate-Rich Deposits.” Earth-Science Reviews 40 (1996): 55-124.
Oelkers, E. H., and E. Valsami-Jones. “Phosphate Mineral Reactivity and Global Sustainability.” Elements 4 (2008): 83-87.
Oelkers, E. H., E. Valsami-Jones, and T. Roncal-Herrero. “Phosphate Mineral Reactivity: From Global Cycles to Sustainable Development.” Mineralogical Magazine 72 (2008): 337-340.
"The Phosphorus Cycle." LibreTexts, 8 Oct. 2024, bio.libretexts.org/Courses/Gettysburg‗College/01%3A‗Ecology‗for‗All/20%3A‗Biogeochemical‗Cycles/20.05%3A‗The‗Phosphorus‗Cycle. Accessed 17 Dec. 2024.