En el centro de México el fenómeno de “El Niño” provoca una reducción en la precipitación. Estas variaciones interanuales en el clima pueden modificar el comportamiento de mezcla-estratificación de los lagos, reflejándose a veces en los sedimentos que se acumulan año con año en sus fondos, sobrepuesto a las tendencias de cambio climático de mayor duración. Presentamos datos preliminares de una evaluación del potencial de los sedimentos del lago de Alchichia para registrar cambios climáticos de períodos medio y corto, analizando diatomeas, calcinación y pigmentos totales en un núcleo de 168 cm de longitud (Alchi-III) recuperado de la orilla NE del lago. Dos fechas de 14-C en sedimento total proporcionan un marco cronológico aproximado. La concentración de pigmentos totales resultó ser un indicador paleoambiental pobre, dado que se pierde el contenido de pigmentos en los sedimentos por debajo de 56 cm, indicando que la concentración depende de procesos de degradación. La preservación de diatomeas fue pobre, limitada a los 44 cm superiores. La alta alcalinidad y pH de este lago parece favorecer la disolución del sílice de las diatomeas, limitando el potencial de este lago para estudios paleolimnológicos. El conjunto de diatomeas de los 44 cm superiores indica que el lago ha sido un sistema alcalino-subsalino durante el pasado reciente (últimos ca. 300 años), con una disminución muy reciente del nivel lacustre. No se detectaron evidencias de fluctuaciones climáticas de período corto de tipo El Niño, pero la estratigrafía y los datos de calcinación sugieren que en un pasado reciente (> ca. 300 años ?) el lago tuvo un episodio de aguas más alcalinas y con un nivel lacustre menor que el actual.doi:

The present long-term (1993–2013) study was aimed at identifying the effects of global change on the environmental characteristics and the plankton community of the tropical, high-altitude Lake Alchichica, Puebla, Mexico. We found no statistically significant increasing trend in air temperature, but an increase from 2002 to 2013, and interannual variability in the meteorological variables. Accordingly, the water temperature rose from 1993 to 2003 and remained similar until 2013. Nonetheless, on a longer-term (1966-2018), longer than the period considered in the present study, air and water temperatures showed an increasing trend in the range considered indicative of climate change. The lake displayed a characteristic warm monomictic thermal pattern but exhibited interannual variability. The planktonic community composition and structure remained similar. The small chlorophytes (e.g., Monoraphidium minutum) dominated the phytoplankton abundance, while the large diatom Cyclotella alchichicana dominated the biomass. The calanoid copepod Leptodiaptomus garciai dominated both the zooplankton abundance and biomass. However, as the temperature increased the large-size phytoplankton (i.e., C. alchichicana) abundance and biomass increased, but the small-size phytoplankton abundance and biomass, as well as the adult copepod abundance and biomass, decreased. The increase in temperature could have favoured the large-size over the small-size phytoplankton. In addition, the temperature increase could have negatively affected the calanoid copepods in two different ways—direct association with the negative effects of higher temperatures on the physiology of the copepods, or indirect association with the negative effects of higher temperatures on the small-size phytoplankton, which diminish the copepods’ food resource.

Detecting determinism and nonlinear properties from empirical time series is highly nontrivial. Traditionally, nonlinear time series analysis is based on an error-prone phase space reconstruction that is only applicable for stationary, largely noise-free data from a low-dimensional system and requires the nontrivial adjustment of various parameters. We present a data-driven index based on Fourier phases that detects determinism at a well-defined significance level, without using Fourier transform surrogate data. It extracts nonlinear features, is robust to noise, provides time-frequency resolution by a double running window approach, and potentially distinguishes regular and chaotic dynamics. We test this method on data derived from dynamical models as well as on real-world data, namely, intracranial recordings of an epileptic patient and a series of density related variations of sediments of a paleolake in Tlaxcala, Mexico.

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but the variability of their biogeochemical dynamics is still poorly documented, particularly in tropical systems. To contribute to the extending of information on tropical reservoirs and to increase the insight on the factors affecting N and P cycling in aquatic ecosystems, we here report on a long-term N and P mass balance (2003–2018) in Valle de Bravo, Mexico, which showed that this tropical eutrophic reservoir lake acts as a net sink of N (−41.7 g N m⁻² y⁻¹) and P (−2.7 g P m⁻² y⁻¹), mainly occurring through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m⁻² y⁻¹ and 4.2 g P m⁻² y⁻¹). The N mass balance also showed that the Valle de Bravo reservoir has a high net N atmospheric influx (31.6 g N m⁻² y⁻¹), which was 1.3 times the external load and likely dominated by N₂ fixation. P flux was driven mainly by external load, while in the case of N, net fixation also contributed. During a period of high water level fluctuations, the net N atmospheric flux decreased by 50% compared to high level years. Our results outlining water regulation can be used as a useful management tool of water bodies, by decreasing anoxic conditions and net atmospheric fluxes, either through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load. These findings also sustain the usefulness of long-term mass balances to assess biogeochemical dynamics and its variability.

High-mountain lakes (HMLs) are remote, extreme, and sensitive ecosystems recognized as sentinels of global change. Lakes El Sol and La Luna are very close to each other inside the crater of the Nevado de Toluca volcano, but they differ morphometrically and limnologically. This study aimed to identify the seasonal fluctuation of the phytoplankton communities of these two tropical HMLs. El Sol phytoplankton comprised 50 taxa (chlorophytes, diatoms, charophytes) and La Luna 28 taxa (diatoms, euglenoids). The abundance of phytoplankton in El Sol was three times higher than in La Luna, and the biomass in El Sol was five times higher than in La Luna. Tropical seasonality was reflected differently in each lake. In El Sol, the highest phytoplankton abundance occurred in the rainy season, while the highest biomass was recorded in the dry/warm season. Conversely, in La Luna, abundance and biomass were more prominent in the dry/cold season. The study found that no meteorological or limnological factors could explain the seasonal dynamics of the taxonomic richness, abundance, or biomass of the phytoplankton communities in both lakes. The differences between the lakes are likely due to the more extreme conditions of La Luna, such as lower pH, ultra-oligotrophy, and increased exposure to ultraviolet radiation (UVR). Additionally, the introduction of rainbow trout into El Sol in the 1950s may have also contributed to the differences.