What are biogeochemical cycles?

Biogeochemical cycles are systems through which essential elements and compounds cycle between living organisms and the nonliving components of the environment. This process involves the continuous movement of substances such as water, carbon, nitrogen, and phosphorus through biological (living) and geological (nonliving) realms. In biogeochemical cycles, nutrients are recycled, connecting organisms and their physical surroundings.

These cycles are termed "closed" because they do not typically involve the loss of these substances from the system on a global scale; rather, they are transformed and reused within ecosystems. For example, carbon is absorbed from the atmosphere by plants during photosynthesis, which then integrates into the biological community through food webs, ultimately being returned to the atmosphere or soil as organisms die and decompose.

In contrast, other options refer to different ecological processes. The notion of energy transfer relates to food chains or food webs without specifically capturing the recycling of elements. Species migration patterns focus on organism movement rather than element cycling. The mention of external inputs might pertain to disturbances or changes in ecosystems rather than the intrinsic processes of nutrient cycling that biogeochemical cycles embody.