The document herewith deals with the geography, geology, and climate of the Mexican territory as the basis to further explain the development of Limnology as a science in this country. An early knowledge started with the Aztecs, with evidence of practical solutions for a life within a lake. After the conquest of the American territories by the Spaniards, the exploration of the new territories provided the main source of information relative to natural resources. In 1938, the Mexican government established the Estación Limnológica de Pátzcuaro and the pioneer studies appeared under the name of Spanish scientists not only here but also at the Universidad Nacional Autónoma de México and the Instituto Politécnico Nacional. During the 1970s, the participation of Mexican limnologists began and the attempt to build-up a conceptual framework in its own for lakes, reservoirs, and rivers. This article outlines the main limnological characteristics of Mexican water bodies, highlights the peculiarities of a transitional zone between the tropics and subtropics, and describes the government structure for management and administration. A fast development in this area of knowledge got underway with the creation of the Asociación Mexicana de Limnología in 1997 and the collaboration with international counterparts.

Lago de Patzcuaro is a historically important freshwater fishery in Mexico. The lake is presently characterized by a persistent bloom of cyanobacteria, specifically dominated by recognized producers of toxic microcystins (MCYSTs). We evaluated MCYSTs in sestonic and dissolved fractions of the water column, as well as representative fish species (silversides, Chirostoma spp.; Goodea sp.; and carp, Cyprinus carpio) obtained from local markets and small commercial catches during the bloom. Samples were evaluated primarily by enzyme-linked immunosorbent assay (ELISA), and secondarily by protein phosphatase (PPase) inhibition assay and liquid chromatography-mass spectrometry (LC-MS). Sestonic MCYST concentration (0.02-0.36 µg/L) generally correlated inversely with distance from the bloom, supporting the bloom as the source of the toxin. Several MCYST variants, including MC-LR, -LA and -LY, as well as didemethyl variants, were identified by LC-MS/MS analysis. All three species of fish bioaccumulated MCYSTs in relevant tissues, and toxin content correlated with trophic level, with highest and lowest levels measured in phytoplanktivorous and zooplanktivorous representatives, respectively. Detection of MCYST in silversides and Goodea sp. is particularly relevant because both are consumed in their entirety, including viscera (e.g., liver) known to primarily accumulate MCYST. These results indicate that Lago de Patzcuaro is indeed characterized by a toxigenic bloom, and that commercially important fish species from the lake accumulate toxic MCYST in tissues relevant to human consumption. As such, this system may represent an ideal model of the trophic transfer of MCYSTs and its relevance to human and environmental health.

No abstract

No abstract

The present research focused on the functional role of the phytoplankton of an economically important endorheic tropical lake from the perspective of algal growth bioassays. The algal growth potential of the lake water was compared for littoral and pelagic sites during the wet and dry seasons. Algal growth potentials at open waters reached minimum and maximum values following the seasonal alternation of dilution (by rain) and concentration (by evaporation) respectively. Conversely, at southern littoral stations high algal growth responses related to the availability of nutrients from point contamination sites. There was no such effect at nearby offshore sites or elsewhere in the lake which suggests filtration and competitive interactions for these nutrients between phytoplankton and littoral macrophytes. Nitrogen and phosphorus both acted consistently as limiting nutrients at open waters by colimitation. Nitrogen to phosphorus ratios seemed to approach equilibrium where limitation easily shifted to one element or the other temporally and spatially.