Patterns of CO2 concentration and inorganic carbon limitation of phytoplankton biomass in agriculturally eutrophic lakes.
Zagarese, H. E., Sagrario, Mlag, Wolf-Gladrow, D., Noges, P., Noges, T., Kangur, K., Matsuzaki, S. S., Kohzu, A., Vanni, M. J., Ozkundakci, D., Echaniz, S. A., Vignatti, A., Grosman, F., Sanzano, P., Van Dam, B. and Knoll, L. B.
Laboratorio de Ecologia Acuatica, Instituto Tecnologico de Chascomus (INTECH), CC 164 (B7130IWA) Chascomus, Provincia de Buenos Aires, Argentina. Electronic address: horacio.zagarese@iib.unsam.edu.ar.
Instituto de Investigaciones Marinas y Costeras (IIMYC), Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, CONICET, J. B. Justo 2550, Mar del Plata 7600, Argentina.
Alfred-Wegener-Institut Helmholtz Zentrum fur Polar- und Meeresforschung (AWI), Postfach 12 01 61, Bremerhaven D-27515, Germany.
Estonian University of Life sciences, Institute Agriculture & Environmental Sciences, Centre for Limnology, Tartumaa EE-61117, Estonia.
National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506Japan.
Department of Biology, Miami University, Oxford, OH 45056, United States.
Waikato Regional Council, 401 Grey Street, Hamilton 3216, Environmental Research Institute, The University of Waikato, Gate 1, Knighton Road, Hamilton 3240, New Zealand.
Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa Avenida Uruguay 151, Santa Rosa, La Pampa L6300CLB, Argentina.
Facultad de Ciencias Veterinarias, Universidad Nacional del Centro de la Provincia de Buenos Aires (UNC), Tandil, Argentina.
Institute of Coastal Research, Helmholtz-Zentrum Geesthacht (HZG), Geesthacht 21502, Germany.
Itasca Biological Station and Laboratories, University of Minnesota Twin Cities, Lake Itasca, MI 56740, United States.
Lake eutrophication is a pervasive problem globally, particularly serious in agricultural and densely populated areas. Whenever nutrients nitrogen and phosphorus do not limit phytoplankton growth directly, high growth rates will rapidly lead to biomass increases causing self-shading and light-limitation, and eventually CO2 depletion. The paradigm of phytoplankton limitation by nutrients and light is so pervasively established, that the lack of nutrient limitation is ordinarily interpreted as sufficient evidence for the condition of light limitation, without considering the possibility of limitation by inorganic carbon. Here, we firstly evaluated how frequently CO2 undersaturation occurs in a set of eutrophic lakes in the Pampa plains. Our results confirm that conditions of CO2 undersaturation develop much more frequently (yearly 34%, summer 44%) in these agriculturally impacted lakes than in deep, temperate lakes in forested watersheds. Secondly, we used Generalized Additive Models to fit trends in CO2 concentration considering three drivers: total incident irradiance, chlorophyll a concentration, and lake depth; in eight multi-year datasets from eutrophic lakes from Europe, North and South America, Asia and New Zealand. CO2 depletion was more often observed at high irradiance levels, and shallow water. CO2 depletion also occurred at high chlorophyll concentration. Finally, we identified occurrences of light- and carbon-limitation at the whole-lake scale. The different responses of chlorophyll a and CO2 allowed us to develop criteria for detecting conditions of CO2 limitation. For the first time, we provided whole-lake evidence of carbon limitation of phytoplankton biomass. CO2 increases and eutrophication represent two major and converging environmental problems that have additive and contrasting effects, promoting phytoplankton, and also leading to carbon depletion. Their interactions deserve further exploration and imaginative approaches to deal with their effects.
Water Research 190: 116715 (2021)