27.6: What are Biogeochemical Cycles?

The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited amounts. Therefore, these nutrients must be recycled through both biotic and abiotic components of the ecosystem, in processes generally called biogeochemical cycles.

Biogeochemical Cycles and Decomposition

The matter that makes up living organisms, like water, carbon, nitrogen, sulfur and phosphorous, exist in limited quantities within the ecosystem and must be conserved and recycled. This matter can take a variety of chemical forms and spend extended periods of time in the atmosphere, on or underneath the land, and in aquatic environments. A key component in the breakdown and recycling of nutrients in the ecosystem is decomposition, which is influenced by temperature, moisture, and nutrient availability. For example, organic material is decomposed much faster in rainforests compared to temperate environments, which have lower temperatures and more seasonal climates.

Human Activity

Human activities can also play a major role in altering the balance of biogeochemical cycles. For example, in 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history. This was a result of the agricultural addition of phosphorus over many years, coupled with changes in local weather patterns. The excessive nutrient levels––called eutrophication––promoted the growth of two toxic cyanobacteria species, Microcystis and Anabaena.

The matter that makes up living organisms is conserved and recycled amongst biotic, living, and abiotic, non-living factors within the environment, a process called biogeochemical cycling.

Four compounds or molecules, water, carbon, nitrogen, and sulfur have gaseous forms that are cycled through both the terrestrial and aquatic ecosystems as well as the atmosphere, making them part of global biogeochemical processes.

However, elements that are too heavy to occur as gasses like phosphorous only circulate through the terrestrial and aquatic ecosystems, a local biogeochemical process.

Both local and global biogeochemical recycling are connected through geological processes, such as the uplift of tectonic plates, weathering and erosion of rock deposits, and water drainage.