In the eighties, scientists focused on the ozone (O3) concentration reduction in the stratosphere. The Ozone Layer can filtrate some of the ultraviolet radiation B (UV-B; 280-315 nm) that comes from the sun, reducing its incidence on the Earths surface. Thus, the reduction of the ozone layer would cause deep negative effects to human health, such as enhanced skin cancer frequency, due to higher UV-B incidence. Then, several actions were taken world wide in order to reduce the ozone layer loss.
At the same time, as the UV-B radiation can also degrade dissolved organic carbon, specially the terrestrially-originated, the photo-degradation process in aquatic ecosystems received great attention from scientists as well. Several studies focused from the role of photo-degradation to ecosystem functioning (e.g. to microbial metabolism) to its possible effects on the carbon dioxide (CO2) emissions to the atmosphere. For instance, besides directly mineralizing the organic carbon into CO2, photo-degradation process also transforms organic molecules in such a way that it affects how much and how fast the bacteria also mineralizes it (Farjalla et al. 2009).
Last week, (August, 22nd, 2014), Dr. Rose Cory (Michigan University) and colleagues published a paper (Cory et al. 2014) in Science Magazine, of a three year study about the photo-degradation and the bacterial degradation in several aquatic ecosystems at Alaska (Artic). According to their study, the photo-degradation process can be responsible from 70% to 95% of the total CO2 production in those aquatic ecosystems. Furthermore, photo-degradation would be up to ten times higher than the bacterial CO2 production. As it contradicts the current paradigms, they brought back the photo-degradation topic to discussion. As the increased temperature predicted to the Polar regions, the thawing will probably expose huge amounts of organic matter. Thus, the photo-degradation will be responsible for even more CO2 emission to the atmosphere in a positive feedback to the greenhouse effect.
References:
Amado, A. M., Farjalla, V. F., Esteves, F. D., Bozelli, R. L., Roland, F., & Enrich-Prast, A. (2006). Complementary pathways of dissolved organic carbon removal pathways in clear-water Amazonian ecosystems: photochemical degradation and bacterial uptake. FEMS Microbiology Ecology, 56(1), 8-17.
Cole, J. J., Prairie, Y. T., Caraco, N. F., McDowell, W. H., Tranvik, L. J., Striegl, R. G., . . . Melack, J. (2007). Plumbing the global carbon cycle: Integrating inland waters into the terrestrial carbon budget. Ecosystems, 10(1), 171-184.
Cory, R. M., Ward, C. P., Crump, B. C., & Kling, G. W. (2014). Sunlight controls water column processing of carbon in arctic fresh waters. Science, 345(6199), 925-928. doi: 10.1126/science.1253119
Jonsson, A., Meili, M., Bergstrom, A. K., & Jansson, M. (2001). Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Ortrasket, N. Sweden). Limnology and Oceanography, 46(7), 1691-1700.
Raymond, P. A., Hartmann, J., Lauerwald, R., Sobek, S., McDonald, C., Hoover, M., . . . Guth, P. (2013). Global carbon dioxide emissions from inland waters. Nature, 503, 355-359. doi: 10.1038/nature12760
Tranvik, L., Downing, J. A., Cotner, J. B., Loiselle, S. A., Striegl, R. G., Ballatore, T. J., . . . Weyhenmeyer, G. A. (2009). Lakes and reservoirs as regulators of carbon cycling and climate. Limnology and Oceanography, 54(6, part 2), 2298-2314.
Author: André M. Amado (Depto. Oceanografia e Limnologia; PPG Ecologia – UFRN)
Language Review: Bruna Q. Vargas (Cultura Inglesa, Natal-RN)