Alfonso Lugo

Phytoplankton dynamics in a deep, tropical, hyposaline lake

The annual variation of the phytoplankton assemblage of deep (64.6 m), hyposaline (≈8.5 g 1−1) Lake Alchichica, central Mexico (19 ° N, 97° W), was analyzed in relation to thermal regime, and nutrients concentrations. Lake Alchichica is warm monomictic with a 3-month circulation period during the dry, cold season. During the stratified period in the warm, wet season, the hypolimnion became anoxic. N—NH3 ranged between non detectable (n.d.) and 0.98 mg 1−1, N—NO2 between n.d. and 0.007 mg 1−1, N—NO3 from 0.1 to 1.0 mg 1−1 and P—PO4 from n.d. to 0.54 mg 1−1. Highest nutrient concentrations were found in the circulation period. Chlorophyll a varied from 1 to 19.8 μg 1−1 but most values were 1% PAR) usually comprised the top 15–20 m. Nineteen algae species were identified, most of them are typical inhabitants of salt lakes. Diatoms showed the highest species number (10) but the small chlorophyte Monoraphidium minutum, the single-cell cyanobacteria, Synechocystis aquatilis, and the colonial chlorophyte, Oocystis parva, were the numerical dominant species over the annual cycle. Chlorophytes, small cyanobacteria and diatoms dominated in the circulation period producing a bloom comparable to the spring bloom in temperate lakes. At the end of the circulation and at the beginning of stratification periods, the presence of a bloom of the nitrogen-fixing cyanobacteria, N. spumigena, indicated nitrogen-deficit conditions. The well-stratified season was characterized by low epilimnetic nutrients levels and the dominance of small single-cell cyanobacteria and colonial chlorophytes. Phytoplankton dynamics in tropical Lake Alchichica is similar to the pattern observed in some deep, hyposaline, North American temperate lakes.

Effect on the planktonic community of the chemical program used to control water hyacinth (Eichhornia crassipes) in Guadalupe Dam, Mexico

Abstract Guadalupe Dam is a reservoir located into the Metropolitan area of Mexico City, which had been infested with water hyacinth (Eichhornia crassipes) for more than 12 years. In 1993 a management program was conducted in the reservoir. The main activities included the use of aquatic herbicides and mechanical control. The goal of this study was to monitor the composition and fluctuation of the planktonic community during the chemical control program. Five sampling stations were selected. Six samplings were made during the period of herbicides applications (July to November 1993) and one sampling more, used as control, was performed four months after the last application (March 1994). Herbicides diquat and 2,4-D amine were used in the chemical control program. Variables measured included temperature, dissolved oxygen, pH, chlorophyll a and numbers of phytoplankton, ciliates, rotifers, cladocerans and copepods. The reservoir is eutrophic, with high concentrations of chlorophyll a and low values of Secch...

Phytoplankton of cenotes and anchialine caves along a distance gradient from the northeastern coast of Quintana Roo, Yucatan Peninsula

This work details the taxonomic composition of suspended algae (phytoplankton and tycoplankton) communities in five cenotes (sinkholes) and two anchialine caves in northeastern Quintana Roo, Mexico. The sample set of cenotes are Casa, Nohoch Nah Chich, Maya Blue, Cristal, and Carwash, as well as the two associated caves leading from the cenotes of Maya Blue and Cristal. The site distribution represents a distance gradient with respect to the coastline with which we observe the effects of tidal movement and the mixing of waters (e.g. saline water and freshwater) on the composition of the suspended algae communities. Two sample sets were taken, one at the end of the dry season (March–April 1995) and the second at the end of the rainy season (September–October 1995) with the goal of comparing the contrasting climatic conditions of the region. A total of 79 species were identified, of which, diatoms were the most important with respect to species richness with a total of 75% of species. The floristic composition is very similar between the freshwater cenotes. The distance of a cenote site with respect to the coastline was a determining factor in the species composition. Casa Cenote is the most distinct of the sample set for the presence of marine species due to its proximity to the coastline. The tides are a large determining factor of the floristic composition of Casa Cenote with 24% all species identified in this study found exclusively in this system. The anchialine system species are transported from the cenotes and the adjacent cave systems. The largest percentage or species (95%) are freshwater, and only 5% of the total number of identified species are of marine origin. It is recognized that the most distant cenotes from the coast, Carwash and Cristal, as well as Maya Blue and Nohoch Nah Chich, are the most similar, despite being part of different cave systems. In these inland systems the marine species decreased drastically (2.4% in Nohoch Nah Chich and no marine species in the remaining cenotes). Marine species are found at the halocline of the caves.

Littoral benthos of the saline crater lakes of the basin of Oriental, Mexico

Two saline crater lakes in the basin of Oriental, Puebla-Tlaxcala-Veracruz, were investigated for littoral benthic macroinvertebrates. Fifty taxa were identified with the oligochaetes, amphipods, chironomids and leeches the dominant organisms. These four taxa made up to 99 per cent in both number and biomass. Limnodrilus hoffmeisteri, Hyalella azteca, Tanypus (Apelopia) sp. and Stictochironomus sp. were the most abundant organisms. Unlike other saline lakes which have a littoral benthos dominated by chironomids, Alchichica and Atexcac were dominated by oligochaetes (70–73 per cent). The gastropod, Physa sp., was found up to a salinity of 8 g L-1; in other studies, it has been found in lower salinities. L. hoffmeisteri is also a typical inhabitant of freshwater lakes, particularly of deep waters. It was dominant in the shallow, saline waters of the two lakes studied. Salinity did not affect species richness. Alchichica, the most saline of the six crater lakes of Puebla (salinity, 7.4 g L-1), had 30 per cent more species than the freshwater lakes, and double the species number of Atexcac. It seems the main factor controlling species richness and the density and biomass of organisms in Alchichica and Atexcac is the presence of aquatic vegetation. It does this by increasing habitat heterogeneity and providing food and protection against predators.

The macrobenthic fauna of a former perennial and now episodically filled mexican saline lake

Totolcingo (El Carmen), a large and now episodically filled playa lake in the east-ernmost portion of the Mexican Plateau, filled with water in 1993. Water persisted for just one month (May). Alkaline (pH ≈ 10), saline (K25 up to 30,000μS/cm) waters, dominated by NaHCO3 and Na2CO3, characterized the lake. The fauna was depauperate. The components of the fauna wereEphydra (Hydropyrus)hians Say (ephydrid),Limnodrilus hoffmeisteri Claparede (tubificid), andBerosus sp. (Coleoptera). The species in the lake were widely dispersed and typical inhabitants of saline lakes. Possible reasons for the depauperate fauna include (a) overall physical and chemical conditions, (b) unpredictable hydrology, and (c) the short (one month) inundation period prevented colonization.

Nutrient limitation in a tropical saline lake: a microcosm experiment

There is increasing evidence that nitrogen limitation is of widespread occurrence in tropical lakes. Nonetheless, data on the deep tropical Lake Alchichica (Mexico) show that dissolved inorganic nitrogen (DIN) to soluble reactive phosphorus (SRP) ratio fluctuates widely. To elucidate further the role of nitrogen and phosphorus limitation on the phytoplankton growth in tropical saline lakes, we present the results of a series of nutrient enrichment experiments with natural assemblages of Lake Alchichica phytoplankton conducted monthly for a year. Our assays indicate that phosphorus and nitrogen alternate in limiting Lake Alchichica phytoplankton biomass. Phosphorous limited phytoplankton growth most (41.7%) of the time, followed by nitrogen (33.3% of the time), and both nutrients for the rest of the time (25.0%). This alternation in nitrogen and phosphorus responsible for phytoplankton growth limitation in Lake Alchichica is attributed to the combination of natural conditions (e.g., young volcanic terrain rich in phosphorus) that would favor nitrogen limitation and anthropogenic impacts (e.g., agricultural nitrogen fertilization) which would cause phosphorus limitation.

CYCLOTELLA ALCHICHICANA SP. NOV. FROM A SALINE MEXICAN LAKE

Cyclotella alchichicana sp. nov. is described from Lake Alchichica, Puebla, Mexico, a saline and alkaline crater-lake in Central Mexico. The new species is similar to C. quillensis from which it distinguished by the arrangement of the marginal fultoportulae and by the external opening of the rimoportula that is elongated slit-like and lacking the external projection on the mantle. Some habitat and ecological data where C. alchichicana has been observed are provided.

Oligochaetes from six tropical crater lakes in Central Mexico: species composition, density and biomass

The assemblage of littoral oligochaetes in six crater lakes in Central Mexico, was studied throughout a yearly cycle. To establish species composition, richness, density and biomass, 14 localities were sampled in the lakes. A total of eight species belonging to the families Naididae (five species), Tubificidae (two species), and Enchytraeidae (one species) were found. The dominant species, Limnodrilus hoffmeisteri, contributed with up to 99% in both abundance and biomass. Sediment organic matter is the most important environmental variable explaining the differences in density and biomass. Seasonal (dry and rainy seasons) changes were not significant for density and biomass. Higher density and lower biomass values characterized these lakes in contrast to other tropical and subtropical lakes worldwide. The small size of the dominant species L. hoffmeisteri was recorded in all lakes and explained the low biomass recorded in the area of study. The correlation between L. hoffmeisteri and four other species (Dero (Dero) nivea, D. (D.) digitata, Nais variabilis and Tubifex tubifex) was negative. The naidid species were positively correlated (>0.5) to each other.

Isabela Crater-Lake: a Mexican insular saline lake

The Isabela Crater-Lake is a bright-green, hypersaline lake (68–112.5 mS cm-1) on Isabela Island off the Pacific coast of Nayarit, Mexico. Some salient features were documented in November 1993. It appears meromictic, with three well-defined strata separated by sharp pycnoclines. Surface water was warm (32 °C) reaching a subsurface (0.5–1 m) maximum temperature (33 °C), declining gradually to 26.7 °C at maximum depth (17.5 m). Dissolved oxygen was near saturation at the surface, attained 145 percent saturation at 0.5 m, but was completely absent by 2.5 m. Eh was maximum at the surface (123 mV), declining to a minimum at 3 m (–261 mV), and was about –240 mV from 3.5 m to the bottom. The pH varied from 9.3 in surface waters to slightly acid (6.4) in deep anoxic layers. Atypically, NO3 was more abundant than NH4 in both aerobic and anaerobic strata. PO4 and SiO2 concentrations were extremely high. The planktonic microbial community was formed by four groups: bacteria (photosynthetic sulfur bacteria and heterotrophic bacteria), phytoflagellates (mainly cryptomonads), heterotrophic nanoflagellates ( Spumella spp., Bodo spp.) and ciliates (Hypotricha and Oligotricha). Bacteria occurred throughout the water column, but other biota were restricted to surface waters.

SEASONAL DISTRIBUTION OF AIR-BORNE PROTOZOA IN MEXICO CITY AND ITS SUBURBS

A survey was carried out over a 1-yr period to isolate protozoa suspended in the air of Mexico City and its suburbs. Sampling stations were placed at four cardinal points of the metropolitan area. Selective media were used to culture the protozoa isolated. Specialized taxonomic keys were used for identification and a statistical analysis was performed to determine the correlations between physicochemical and biological parameters. 63 strains were isolated. Species of Kinetoplastida and Chrysomonadida were most abundant, namely species of the genera Bodo, Cercobodo, Monas and Helkesimastix. Amoeboflagellates found included Mastigamoeba and Tetramitus. The only ciliate isolated was Colpoda steini. The greatest number of strains was yielded by Bodo repens and Cercobodo radiatus. Several times during the period of the study SO2, O3, CO, NO, and NO2 exceeded the permissible levels established by the Mexican government. From the results of this study it was concluded that the ability of protozoa to form cysts and cyst size were important factors for their presence, survival, abundance and diversity in the atmosphere. The main source of air-borne protozoa was the soil. Factors that favored the incidence and diversity of the isolates were wind speed and direction, high relative humidity, generation of frequent dust-storms, resuspension of protozoa by vehicular traffic, proximity to garbage dumps and large extensions of bare soil, and temperature (the latter only when it did not favor the production of high levels of O3). Factors that were hostile to the aerial protozoa were industry and their contaminants, and high concentrations of O3 and SO2, especially in winter time when thermal inversions occurred. Soil cover was also associated with a reduction in the incidence and diversity of the aerial protozoa. This study demonstrates that there are viable cysts of protozoa in the atmosphere of Mexico City, that may have potential importance in the case of certain kinds of human allergies and diseases. Further research is needed to find out the aerial presence of viable cysts of obligatory, amphizoic or opportunistic protozoan parasites, and to clarify the qualitative and quantitative effects of the local meteorological and physico-chemical environment on the free-living protozoa present in the atmosphere.