Phytoplankton from two Dams in Central Mexico
Synopsis
Reservoirs are environments where phytoplankton develop and sustain food webs. This study explores the structure of the phytoplankton community in two dams and its relationship with six limnological variables from El Llano and Taxhimay reservoirs during September and October 2022. Microalgae were collected in surface layer in three sampling sites with a 20 μm net mesh opening, which were preserved with formaldehyde. The specific richness, the Shannon-Wiener index, the canonical correspondence analysis (CCA), the association quotient, organic contamination, and diatom index were determined. The samples obtained during the two months were markedly different; both ecosystems recorded a warm temperature from 15 to 22°C, pH between 7-8, well oxygenation (5.8 to 9.6 mg/l), low mineralization, and conductivity. Fifty-five species were determined, and six are new records for Mexico. The abundance by taxonomic classes in all the sampling stations was markedly higher for Bacillariophyceae; in particular, observed in Taxhimay in T1 October, with 21,476 cell/ml. Asterionella formosa was dominant in both reservoirs, with 79.9 to 96.4 % of the abundance. The H’ was recorded from 0.21 to 1.54 bits/ind., it represents variation between the sampling stations and the study months. The CCA positively related conductivity and temperature with Aulacoseira granulata var. angustissima, A. granulata f. curvata, Monactinus simplex, and Microcystis panniformis. The three indexes indicate eutrophic environments. Furthermore, it is recommended to monitor phytoplankton, in particular, the abundance of Microcystis and other Cyanophyceae, as they are harmful algae.
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