Biogeochemical cycles are the pathways by which elements like carbon, phosphorus, nitrogen and sulfur, or compounds like water, flow between living organisms and the environment. Human activities can alter these cycles be producing or consuming in different quantities. For example, agricultural fertilizer and soil erosion have substantially increased levels of biologically available nitrogen and phosphorous in natural systems. Human production of biologically available nitrogen, primarily driven by the synthetic production of nitrogen fertilizer, is now greater than all forms of natural production combined. Flow of phosphorous into the oceans, primarily driven by the use of fertilizer from mines and livestock manure, is roughly three times the preindustrial level. Excess nitrogen decreases plant diversity in terrestrial ecosystems, and the combination of excess nitrogen and phosphorous in water bodies leads to algal blooms and eutrophication.