Patterns of CO2 concentration and inorganic carbon limitation of phytoplankton biomass in agriculturally eutrophic lakes

Abstract

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 CO 2 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 CO 2 undersaturation occurs in a set of eutrophic lakes in the Pampa plains. Our results confirm that conditions of CO 2 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 CO 2 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. CO 2 depletion was more often observed at high irradiance levels, and shallow water. CO 2 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 CO 2 allowed us to develop criteria for detecting conditions of CO 2 limitation. For the first time, we provided whole-lake evidence of carbon limitation of phytoplankton biomass. CO 2 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.

Closed microbial communities self-organize to persistently cycle carbon

“…In addition, phototroph and bacterial biomass production also has substantial impacts on the uptake of other inorganic nutrients in these ecological contexts ( 29 ). High nutrient availability can result in competition for carbon in eutrophic environments, resulting in carbon limiting phototrophic growth ( 30 , 31 ).…”

Morphological, physiological, and transcriptional responses of the freshwater diatom Fragilaria crotonensis to elevated pH conditions

“…A recent study suggested elevated pH conditions have the potential to negatively affect algal communities beyond pHinduced carbon limitation (Zagarese et al, 2021). In a previous investigation, we demonstrated that the freshwater diatom Fragilaria crotonensis, which historically bloomed during the summer in Lake Erie (Hartig, 1987), exhibited lower growth rates and silica (Si) deposition rates at pH 9.2 in both monoculture and co-culture with M. aeruginosa (Zepernick et al, 2021).…”

“…Research has demonstrated Microcystis spp. blooms can increase lake pH to well above 9.0 via the photosynthetic depletion of CO 2 (Verspagen et al, 2014;Ji et al, 2020), a phenomenon recently termed "lake basification" (Zagarese et al, 2021;Zepernick et al, 2021). Basification events have been recorded in fresh waters including Lake Taihu, China and Lake Erie, U.S./Canada (Su et al, 2015;Wilhelm et al, 2020).…”

Increases in Picocyanobacteria Abundance in Agriculturally Eutrophic Pampean Lakes Inferred from Historical Records of Secchi Depth and Chlorophyll-a

“…Over the last two centuries, the Pampean landscape changed progressively from natural grasslands into cultivated grasslands and croplands due to animal production and intensive crops (wheat, corn, sunflower, and, since the mid-1990s, soybean) [7]. The process of agricultural intensification aggravated the eutrophication of shallow Pampean lakes through increased nutrients (N, P) and agrochemical inputs into the aquatic environment [8,9]. Since the last decade of the 20th century, Pampean lakes have experienced remarkable increases in nutrients (N and P) and chlorophyll-a concentration (Chla) and decreases in water transparency, estimated as Secchi disk depth (ZSD) [10].…”