Biogeochemical flows 

Summary

Biogeochemical flows have been greatly perturbed by human activity, and it is crucial that we, as citizens, play a significant role in raising this issue. The anthropogenic agitation of these global element cycles, focusing on nitrogen (N) and phosphorus (P) as essential elements, have been and continue to be significantly impacted by human activities such as agriculture and industry. The release of reactive forms of N and P into land and oceans has profound effects on ecosystem composition and long-term Earth system dynamics. The planetary boundaries for these elements, particularly phosphorus, are being exceeded globally due to the significant amounts being introduced into ecosystems, leading to issues like eutrophication and anoxia. The boundary for nitrogen is breached as well due to high application rates of industrially fixed N fertilisers. Both boundaries highlight the need for sustainable management of nutrient flows, and it is in our hands to maintain ecosystem health and balance. 

Further details

Biogeochemical flows reflect anthropogenic perturbation of global element cycles. The boundary has been transgressed.

Currently, the planetary boundaries framework considers nitrogen (N) and phosphorus (P) as these two elements constitute fundamental building blocks of life, and their global cycles have been markedly altered through agriculture and industry. Anthropogenic impacts on global carbon cycling are equally fundamental but are addressed in the climate and biosphere integrity boundaries. As our understanding of human perturbation of element cycles advances, other elements could come into focus under this boundary, opening up exciting and hopeful avenues for future research. 

For both N and P, the anthropogenic release of reactive forms to land and oceans is of interest, as altered nutrient flows and element ratios profoundly affect ecosystem composition and long-term Earth system effects. Some of today’s changes will only be seen on evolutionary time scales, while others already affect climate and biosphere integrity. For details of the measurement issues please refer to Steffan et al (Steffen et al., 2015)

What we can do

Learn what you can about this issue. Express concern about the boundary, and grow what you can, using a balanced and sustainable gardening approach, even if it is only sprouts and carrot tops in the kitchen! Support organic growers and ask them what they do about this overuse of nitrogen and phosphorous. Give us feedback so we can assess these activities further!

Applying fertilisers, if you use them at all, in the proper amount, at the right time of year and with the right method, can significantly reduce how much fertiliser reaches water bodies. Keeping animals and their waste out of streams keeps nitrogen and phosphorus out of the water and protects stream banks. Remember – fertilisers like this wash out of the soil, compost does not. So consider methods like no-dig systems where you add a layer of compost each year (for example, look at Charles Dowding at https://www.youtube.com/watch?v=0LH6-w57Slw).

Never fertilise your lawn! Dig it up and grow plants, flowers, and vegetables! If you are too busy, allow others (contact your local Permaculture Association) to ‘farm’ your land in exchange for a portion of the crop.

References

Steffen, W., Richardson, K., Rockström, J., Cornell, S. E., Fetzer, I., Bennett, E. M., . . . Sörlin, S. (2015). Planetary boundaries: Guiding human development on a changing planet. Science, 347(6223), 1259855. doi:doi:10.1126/science.1259855

Other references used include:

S. R. Carpenter, E. M. Bennett, Reconsideration of the planetary boundary for phosphorus. Environ. Res. Lett. 6, 014009 (2011). 

C. Liu, H. Tian, Global nitrogen and phosphorus fertilizer use for agriculture production in the past half century: Shifted hot spots and nutrient imbalance. Earth Syst. Sci. Data 9, 181–192 (2017). 

W. J. Brownlie, M. A. Sutton, K. V. Heal, D. S. Reay, B. M. Spears(eds.), Our Phosphorus Future (U.K. Centre for Ecology & Hydrology, 2022). 

T. Zou, X. Zhang, E. Davidson, Improving phosphorus use efficiency in cropland to address phosphorus challenges by 2050. Earth Space Sci. Open Archive, (2020). https://doi. org/10.1002/essoar.10504095.1 

D. Cordell, S. White, Life’s bottleneck: Sustaining the World’s phosphorus for a food secure future. Annu. Rev. Environ. Res. 39, 161–188 (2014). 

Food and Agriculture Organisation of the United Nations (FAO), “World fertilizer trends and outlook to 2022 – Summary Report, Rome” (2019); www.fao.org/3/ca6746en/ ca6746en.pdf) SCIENCE ADVANCES | RESEARCH ARTICLE Richardson et al., Sci. Adv. 9, eadh2458 (2023) 13 September 2023 13 of 16 Downloaded from https://www.science.org on September 15, 2023 

M. A. Adams, N. Buchmann, J. Sprent, T. N. Buckley, T. L. Turnbull, Crops, nitrogen, water: Are legumes friend, foe, or misunderstood ally? Trends Plant. Sci. 23, 539–550 (2018). 

P. M. Vitousek, D. N. L. Menge, S. C. Reed, C. C. Cleveland, Biological nitrogen fixation: Rates, patterns and ecological controlsin terrestrial ecosystems. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 368, 1621 (2013). 

83. M. V. B. Figueiredo, A. E. S. Mergulhão, J. K. Sobral, M. A. L. Junio, A. S. F. Araújo, Biological nitrogen fixation: Importance, associated diversity, and estimates, in Plant Microbe Symbiosis: Fundamentals and Advances (Springer, 2013), pp. 267–289