Alchichica is a warm-monomictic, oligotrophic lake whose phytoplanktonic biomass is dominated by large size (average ca. 55 lm) diatoms. The fast sinking phytoplankton leads to silica, and other nutrient exportation out of the productive zone of the lake. The aim of the present study was to identify and measure the sedimentation fluxes of the diatom species and their temporal dynamics to better understand the magnitude of silica and carbon fluxes.Sediment-traps were exposed at three different depths and collected monthly. A total of 13 diatom species were observed in the traps. The maximum diatom flux was in February (304 9 10 6 cells m -2 day -1 ) related to the winter diatom bloom. The diatom silica (DSi) fluxes varied from 2.2 to 2,997 mg m -2 day -1 and the diatom carbon (DC) fluxes from 1.2 to 2,918 mg m -2 d -1 . Cyclotella alchichicana was the main contributor ([98%) to the total DSi and DC fluxes. The annual diatom (15 9 10 9 cells m -2 year -1 ), DSi (147 g m -2 year -1 ) and DC (92 g m -2 year -1 ) fluxes are higher than in other aquatic ecosystems of similar or even higher trophic conditions. Our findings in Alchichica are indicative of the relevance of the phytoplankton type and size in understanding the role tropical and oligotrophic lakes play regarding silica and carbon fluxes. In addition, our results support previous findings suggesting that inland aquatic ecosystems are more important than formerly thought in processing carbon, and can, therefore, affect regional carbon balances.
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mg C m -2 ). C. patzcuaro is dominant and is present throughout the year, whereas Ch. austini is recorded only when the bottom water of the lake is oxygenated. A comparison with the analogous but temperate Lake Mergozzo in Italy illustrates the role that anoxia plays in tropical lakes by diminishing not only taxonomic richness (13 vs
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