1.1: What is biogeochemistry?

Biogeochemistry is the scientific discipline that explores the interactions between living organisms and the physical and chemical aspects of the environment. It is a field that combines principles from biology, geology, chemistry, and environmental science to study the processes that govern the cycling of elements and compounds in ecosystems. Biogeochemists study how living organisms, including plants, animals, and microorganisms, interact with the solid Earth (geosphere).

In biogeochemical cycles, elements and compounds move through the atmosphere, hydrosphere (water bodies), lithosphere (Earth's crust), and biosphere (living organisms) in a series of complex processes. These processes include photosynthesis, respiration, decomposition, weathering, erosion, and sedimentation. Human activities, such as industrial processes and agriculture, can also significantly impact biogeochemical cycles.

Rather than flowing through an ecosystem, the matter that makes up living organisms is conserved and recycled. The six most common elements associated with organic molecules—carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur—take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath Earth’s surface or may rapidly move between reservoirs. Geologic processes, such as weathering, erosion, water drainage, and the subduction of the continental plates, all play a role in the cycling of elements on Earth. Because geology and chemistry have major roles in the study of this process, the recycling of inorganic matter between living organisms and their nonliving environment is called a biogeochemical cycle.

Human impact is an important part of biogeochemistry. Our activities can change the proportion of nutrients that are in reservoirs and in circulation. Deforestation disrupts nutrient cycling by removing trees that contribute organic matter to the soil. Pollution introduces chemicals that can alter soil and water chemistry, affecting plant and animal life.Coal is a reservoir of carbon, but the human use of fossil fuels has released carbon into the atmosphere, increasing the amount of carbon in circulation. Likewise, phosphorous and nitrogen are extracted from geological reservoirs and used and excesses of these elements have caused the overgrowth of plant matter and the disruption of many ecosystems. Excess fertilizer use can lead to nutrient runoff, causing algal blooms and oxygen-deprived "dead zones" in water bodies.

Water, which contains hydrogen and oxygen, is essential to all living processes. The hydrosphere is the area of Earth where water movement and storage occurs: as liquid water on the surface (rivers, lakes, oceans) and beneath the surface (groundwater) or ice, (polar ice caps and glaciers), and as water vapor in the atmosphere. Carbon is found in all organic macromolecules and is an important constituent of fossil fuels. Nitrogen is a major component of our nucleic acids and proteins and is critical to human agriculture. Phosphorus, a major component of nucleic acids, is one of the main ingredients (along with nitrogen) in artificial fertilizers used in agriculture, which has environmental impacts on our surface water. Sulfur, critical to the three-dimensional folding of proteins (as in disulfide binding), is released into the atmosphere by the burning of fossil fuels.

The cycling of these elements is interconnected and occurs on all scales, from microscopic to global and over minutes and millenia. The movement of water is critical for the leaching of nitrogen and phosphate into rivers, lakes, and oceans. The ocean is also a major reservoir for carbon. Thus, mineral nutrients are cycled, either rapidly or slowly, through the entire biosphere between the biotic and abiotic world and from one living organism to another.

Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during energy transformation between trophic levels. Rather than flowing through an ecosystem, the matter that makes up organisms is conserved and recycled. The law of conservation of mass states that matter is neither created nor destroyed. For example, after a chemical reaction, the mass of the products (ending molecules) will be the same as the mass of the reactants (starting molecules). The same is true in an ecosystem. Matter moves through different media, and atoms may react to form new molecules, but the amount of matter remains constant. Although the Earth receives energy from the Sun, the chemical composition of the planet is more or less fixed. Matter is occasionally added by meteorites, but supplies of essential elements generally do not change.

Understanding biogeochemistry is crucial for addressing environmental challenges, managing natural resources, and mitigating the impacts of human activities on ecosystems and the planet's overall health. Scientists in this field study how nutrients and pollutants move through ecosystems, impacting both natural habitats and human societies. Biogeochemistry is critical for understanding climate change feedback loops. Thawing permafrost releases stored carbon, amplifying global warming. Changes in ocean chemistry due to increased carbon dioxide levels (ocean acidification) affect marine ecosystems, disrupting biogeochemical processes. In summary, biogeochemistry is a multidisciplinary field that integrates biology, geology, chemistry, and environmental science to unravel the complex web of interactions between living organisms and their environment, with a focus on the cycling of elements and compounds crucial for life.

References

1. Books:
   • Schlesinger, W. H. (2013). Biogeochemistry: An Analysis of Global Change. Academic Press.
   • Falkowski, P., Scholes, R. J., Boyle, E., Canadell, J., Canfield, D., Elser, J., & Stemple, J. (2000). The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System. Science, 290(5490), 291-296.
2. Scientific Journals:
   • Biogeochemistry: A scientific journal dedicated to studies of chemical, physical, geological, and biological processes influencing the composition and behavior of the Earth's systems. (Published by Springer)
   • Global Biogeochemical Cycles: A journal focusing on biogeochemical processes in the Earth's systems and their responses to global change. (Published by Wiley)
   • Journal of Geophysical Research - Biogeosciences: A journal covering research articles on the biogeosciences, including the interface between biological, chemical, and physical processes in terrestrial and aquatic environments. (Published by Wiley)
3. Research Articles:
   • Falkowski, P. G., Fenchel, T., & Delong, E. F. (2008). The microbial engines that drive Earth's biogeochemical cycles. Science, 320(5879), 1034-1039.
   • Canfield, D. E., Glazer, A. N., & Falkowski, P. G. (2010). The evolution and future of Earth's nitrogen cycle. Science, 330(6001), 192-196.
   • Schimel, J. (2001). Biogeochemical models: implicit vs. explicit microbiology. Trends in Ecology & Evolution, 16(8), 365-369.
4. Review Articles:
   • Ward, B. B., Eveillard, D., Kirshtein, J. D., & Nelson, J. D. (2007). Importance of Extant and Extinct Forms of Dissimilatory Nitrite Reductase in Biogeochemical Cycles. Limnology and Oceanography, 52(6), 2276-2283.
   • Amundson, R., Austin, A. T., Schuur, E. A. G., Yoo, K., Matzek, V., Kendall, C., ... & Biogeochemical Research Community. (2003). Global patterns of the isotopic composition of soil and plant nitrogen. Global Biogeochemical Cycles, 17(1), 1031.