Their depletion is thought to be from water erosion of the soil and over cropping of land, they aren't able to replenish themselves as fast. Weathering of rocks also makes sulfates available to terrestrial ecosystems.
There are global nutrient cycles, which occur when ecosystems become linked on a global scale. For example, the water cycle shows how water moves through different states and ecosystems.
Earth acts as a closed system for the movement of matter, and a biogeochemical cycle includes the chemical, geological and biological pieces of this pathway.
In a study done by Parmesan etal, the distribution and population dynamics of several species of butterflies were monitored in response to the increased temperatures. Although the Earth constantly receives energy from the sun, its chemical composition is essentially fixed, as additional matter is only occasionally added by meteorites.
These cycles are called biogeochemical cycles, because they include a variety of biological, geological, and chemical processes.
The breakdown of clay is done by leeching the minerals out of the soil. Researchers are trying to understand all of the various pathways and flows of each of the biogeochemical cycles in order to understand how human activities affect these cycles.
For example, strontium can behave like calcium in the body. This process takes carbon dioxide and converts it into methane.
Phosphate is most often in the form of phosphate salts, which is released from weathered rock and dissolved in ground water where plants take it up. Thus, by virtue of photosynthesizing organisms photoautotrophsthe water cycle is an important part of both the oxygen and the hydrogen cycles.