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With the aim to determine the contribution of development and reproduction to the variability in the elemental composition of zooplankton, we measured the carbon (C), hydrogen (H), nitrogen (N), and phosphorus (P) elemental composition of the planktonic crustacean assemblage in an alpine lake for a whole seasonal cycle. The species included three distinct living modes: a cladoceran, Daphnia pulicaria; a cyclopoid copepod, Cyclops abyssorum; and a calanoid copepod, Diaptomus cyaneus. For the three species, reproduction was the main cause of elemental variability. Adult females of the three species lost from 32% to 48% of their initial absolute C and H content during reproduction, which corresponded to a similar decrease in their lipid and carbohydrate content. The N content did not change in any of the three species, nor did the protein and chitin content. Daphnia and Diaptomus lost 35% and 56%, respectively, of their initial absolute P content during reproduction, whereas the P content of Cyclops did not change. The three species stored energy compounds under unfavorable conditions for later use in offspring production, but only Diaptomus and Daphnia mobilized stored P. Corresponding stoichiometric changes with reproduction included a decrease in C:N ratio for the three species; an increase in N:P ratio for Daphnia adult females and adults of Diaptomus; and a C:P ratio increase in Diaptomus females and decline in Cyclops females. Differences in C:P ratio changes corresponded with differences in allocation to their respective reproductive tissues. Diaptomus males and Daphnia females did not change their C:P ratio with reproduction. [ABSTRACT FROM AUTHOR]

This study shows that diatom sediment records can be used to investigate the long-term inorganic carbon dynamics in oligotrophic and poorly acid-buffered lakes. Using a training set of 115 high-mountain lakes in the Pyrenees, we found that both alkalinity and potential hydrogen (pH) independently explained some of the variability in diatom assemblages. Transfer functions for both variables were developed and applied to a Holocene record from Lake Redon and CO2 changes calculated. CO2 saturation broadly followed alkalinity, which in turn was related to summer and autumn air-temperature fluctuations. In general, warmer climate during the ice-free period led to higher supersaturation, due to increased alkalinity, which facilitated retention of CO2 from respiration, and decreased primary production (assessed by diatom fluxes). Only during the early Holocene, there were periods of extreme undersaturation, corresponding to cold periods of low alkalinity (<20 microequivalents per liter [µeq L-1]), and suggesting carbon limitation of primary production. The winter and spring climate, which determines the ice cover duration, appears to be relevant for CO2 saturation only during periods when the organic-matter content of the sediments was low (<22%). Longer periods of ice cover led to lower lake CO2 saturation, suggesting that the ice cover influence on internal nutrient loading may regulate lake productivity fluctuations under low allocthonous nutrient and organic-matter inputs. Alkalinity ∼20 µeq L-1 and sediment organic matter ∼22% appear as critical thresholds in the way lake CO2 levels respond to climate fluctuations. [ABSTRACT FROM AUTHOR]

Water chemistry and its ecological implications have been extensively investigated in temperate high‐mountain lakes because of their role as sentinels of global change. However, few studies have considered the drivers of water chemistry in tropical mountain lakes underlain by volcanic bedrock. A survey of 165 páramo lakes in the Cajas Massif of the Southern Ecuador Andes identified 4 independent chemical variation gradients, primarily characterized by divalent cations (hardness), organic carbon, silica, and iron levels. Hardness and silica factors showed contrasting relationships with parent rock type and age, vegetation, aquatic ecosystems in the watershed, and lake and watershed size. Geochemical considerations suggest that divalent cations (and related alkalinity, conductivity, and pH) mainly respond to the cumulative partial dissolution of primary aluminosilicates distributed throughout the subsurface of watersheds, and silica and monovalent cations are associated with the congruent dissolution of large amounts of secondary aluminosilicates localized in former hydrothermal or tectonic spots. Dissolved organic carbon was much higher than in temperate high‐mountain lakes, causing extra acidity in water. The smaller the lakes and their watersheds, the higher the likelihood of elevated organic carbon and metals and low hardness. The watershed wetland cover favored metal levels in the lakes but not organic carbon. Phosphorus, positively, and nitrate, negatively, weakly correlated with the metal gradient, indicating common influence by in‐lake processes. Overall, the study revealed that relatively small tropical lake districts on volcanic basins can show chemical variation equivalent to that in large mountain ranges with a combination of plutonic, metamorphic, and carbonate rock areas. [ABSTRACT FROM AUTHOR]