Humans are changing the nitrogen cycle primarily by increasing the amount of biologically available nitrogen in the environment through various activities. The main ways humans alter the nitrogen cycle include:

• Industrial fixation of atmospheric nitrogen to produce nitrogen-based fertilizers using processes such as the Haber-Bosch method. This artificial nitrogen fixation produces about 80 Tg of nitrogen per year, which is a major contribution compared to natural sources.
• Extensive use of nitrogen fertilizers in agriculture that leads to nitrogen runoff into water bodies, causing nutrient imbalances, eutrophication, and dead zones in aquatic ecosystems.
• Burning fossil fuels releases nitrogen oxides into the atmosphere, contributing to air pollution and acid rain, and altering nitrogen deposition patterns.
• Conversion of natural ecosystems like forests and grasslands into agricultural land increases nitrogen fixation and mobilization.
• Overall, these human activities have doubled the amount of global nitrogen fixation since the 1940s, increased nitrogen mobility, and caused long-term ecological consequences such as altered nutrient cycles, soil acidification, loss of biodiversity, and impaired ecosystem functions.

Thus, humans are significantly accelerating and disrupting the natural nitrogen cycle, leading to environmental pollution and ecosystem degradation.