Gloria Vilaclara

A survey of pathogenic and free-living amoebae inhabiting swimming pool water in Mexico City

A survey of pathogenic and free-living amoebae in swimming pool waters of Mexico City was performed. Among the organisms isolated those which have public health importance were Naegleria fowleri Carter and Acanthamoeba castellanii Douglas. Amoebae of the genera Acanthamoeba, Naegleria, and Vahlkampfia were recovered in their cystic stage while those specimens of the genera Amoeba, Entamoeba, Thecamoeba, and Vanella were recovered only in their trophic stage during this study. Amoebae were concentrated through filtration procedures and subsequently cultured in different culture media. Nonpathogenic amoebae also isolated by culture included: Amoeba proteus (Pallas) Leidy, Amoeba striata Penard, Paratetramitus jugosus Page, Acanthamoeba astronyxis Ray and Hayes, Vahlkampfia avara Page, Vahlkampfia inornata Page, Thecamoeba verrucosa Ehrenberg, and Vanella mira Schaeffer. Trophozoites of Entamoeba gingivalis Gros, were also recovered, both directly and by culture. Most commonly found were amoebae of the species Naegleria gruberi Schardinger (59.02%), N. fowleri (16.77%), and A. castellanii (7.64%). Least-frequently found amoebae belonged to the species Thecamoeba verrucosa (0.12%). All isolated strains of N. fowleri and A. castellanii were thermophilic at 45 and 40 degrees C, respectively, and also pathogenic when inoculated into white mice. More populated by amoebae were those swimming pools of the indoor type with an inner side garden. It was also shown that the free residual chloride values of 0.50 to 1.5 mg/liter, ordinarily used in pool waters, are not adequate for elimination of amoebae.

52 000 years of environmental history in Zacapu basin, Michoacan, Mexico: the magnetic record

Abstract Mineral magnetic and total organic carbon (TOC) measurements were performed on a 10.9 m long core from Zacapu basin, central Mexico. The sequence, dated by AMS 14 C, spans the last ca. 52 kyr. Curie temperature measurements, low-temperature susceptibility and low-temperature remanence indicate that the magnetic fraction is characterized by oxidized titanomagnetites with variable Ti content. Low S 300 ratios reflect the existence of high-coercivity iron oxide phases. These characteristics are considered to reflect the presence of goethite rather than hematite, formed in relatively wet, organic conditions, where soil-forming processes were intense. Comparison between magnetic and TOC results suggests that the sediments record relatively humid conditions before 35 kyr BP, and a later trend towards drier conditions. A probable hiatus is recorded before 25 kyr, and relatively dry conditions after this time that persisted throughout the Late Glacial Maximum and Mid Holocene, at 4.8 kyr. These results contrast with previous observations of deep lake phases in the neighboring Lake Patzcuaro, considered to be result of increased precipitation between 34 and 21 kyr BP.

Changing water, phosphorus and nitrogen budgets for Valle de Bravo reservoir, water supply for Mexico City Metropolitan Area

Abstract Ramírez-Zierold JA, Merino-Ibarra M, Monroy-Ríos E, Olson M, Castillo FS, Gallegos ME, Vilaclara G. 2010. 2010. Changing water, phosphorus and nitrogen budgets for Valle de Bravo reservoir, water supply for Mexico City Metropolitan Area. Lake Reserv. Manage. 26:23-34. Valle de Bravo reservoir (VB) provides water supply to the Mexico City Metropolitan Area and other surrounding cities. Nutrient loading to this reservoir increased 276% for phosphorus (P) and 203% for nitrogen (N) in a single decade. During 2002–2005, P and N mean loadings to VB were 120.8 × 103 kg P/y and 591.8 × 103 kg N/y. These loadings were quite variable because of source variations from uncontrolled domestic and agricultural inputs. More than half (56%) of the maximal water storage of the reservoir was withdrawn annually. Water withdrawal removed 22% of the P input. Comparative examination of P and N mass balances showed that most (85%) of the P input to VB accumulates in the sediments. Despite the hypolimnetic anoxia that VB exhibits from March to October, net P accumulation in the sediments is normally observed. Our results confirm that although VB behaves as a warm monomictic water body, its mean hypolimnetic temperature increases throughout the stratification period. Nitrogen limitation was indicated by the dissolved inorganic nitrogen (DIN) to total dissolved P (DIN:TDP = 8.3, molar) ratio during stratification periods. We estimated that N2 fixation exceeded denitrification. This net fixation could double the N loading from rivers and sewage. Management recommendations include (a) gauging of river and sewage inputs to VB, (b) reduction of P input through treatment of sewage from VB town and (c) monitoring and regulating fertilizers and other nonpoint source inputs in the Amanalco watershed. Valle de Bravo reservoir is similar to other eutrophic tropical lakes and reservoirs that could also improve their water quality through these management practices.

Sedimentary multiproxy response to hydroclimatic variability in Lagunillo del Tejo (Spain)

Lagunillo del Tejo is a small groundwater-fed sinkhole lake in the karst region of the Iberian Range (central-eastern Spain), which undergoes significant lake level fluctuation in response to rainfall variability. The aim of this study is to understand the record of water level fluctuations in Lagunillo del Tejo over the last two-and-a-half centuries. This information could be used in future studies to interpret longer sedimentary sequences. We analysed photosynthetic pigments, diatoms and cladoceran remains in sediment sequences recovered from the deepest part of the lake. The paleoecological proxies traced two different communities which have switched their prevalence during the past: (1) a planktonic community of algae, including diatoms, chlorophytes, cryptophytes and cyanobacteria, and phototrophic bacteria associated with higher lake level and water column seasonal stratification; (2) a littoral community with the higher levels of macrophyte pigments and associated epiphytic diatoms and chydorids, all of which indicate lower lake level. The levels of coherence between different proxies, each having an independent mechanistic link to lake-level variability, enhance the reliability of palaeolimnological inferences. The high-resolution stratigraphical data from the upper part of the core was compared with lake-level inferences from instrumental rainfall series (1859–2005) to establish the correspondence between Lagunillo del Tejo sediment sequences and climate record.

Phytoplankton composition changes during water level fluctuations in a high-altitude, tropical reservoir

Abstract To understand the responses of phytoplankton to water level fluctuations (WLFs) in tropical conditions at high altitude, limnological monitoring was performed monthly in Valle de Bravo (VB) reservoir, a waterbody affected by relatively strong WLFs due to water scarcity in central Mexico during 2008–2009. The thermal behaviour of the reservoir was warm, monomictic (Nov–Feb), and water levels fell to 12 m below capacity. Observed hypolimnetic temperature increases in VB are considered indirect evidence of boundary mixing events, previously attributed to internal waves driven by strong diurnal winds along a 7 km fetch. Unusually low biomasses were observed during circulation, probably due to low light availability (Zeu/Zmix < 1), grazing, and relatively low temperatures (<20 °C). In contrast, enhanced phytoplankton biomass was observed throughout stratification, which could be explained by nutrient inputs to the epilimnion through boundary mixing, as previously proposed for VB, and by higher (>20 °C) temperatures. Dominant species were Cyclotella ocellata, Fragilaria crotonensis, Woronichinia naegeliana, and Microcystis wesenbergii. Nitrogen-fixing cyanobacteria (Nostocales), a recurrent problem in this reservoir, were markedly less abundant than during high-water periods (2002–2005), probably due to dissolved inorganic nitrogen (DIN) inputs from the hypolimnion. A profuse formation of heterocysts was observed at the same time that DIN and the DIN to soluble reactive phosphorus ratio (DIN:SRP) were low (<2 μmol L−1 and ~1 respectively), suggesting heterocyst development could be a complementary proxy to assess DIN limitation. Intense water level decreases in this reservoir resulted in increasing biomasses of planktonic diatoms and a significant decrease in noxious algae such as Nostocales, thus ameliorating the water quality of the reservoir.

A comparison between the spatial distribution pattern of flagellates and some physicochemical parameters in a waste stabilization pond

Protozoological and physicochemical analyses were performed in a waste stabilization pond at Sto. Tomas Atzingo, a small town near Mexico City, in order to discern the internal dynamics of the pond water through the study of the spatial distribution pattern of flagellates and the parallel water volume distribution pattern of some selected physicochemical determined parameters. The statistical method applied to the data obtained was by cluster analysis. The results showed a slight trend to heterogeneity in the system, when it was evaluated through the physicochemically determined parameters. On the other hand, the spatial distribution pattern of the flagellates pointed out a remarkable heterogeneity in the pond. In systems like the one studied where the main feature is an organic matter overload, such a difference in findings indicates a low correlation between the biological parameters, in this case the flagellates, and the physicochemical variables, that should be considered when evaluating the water quality of such systems, either through the physicochemical, the biological or both scopes.

Seston dynamics in a saline Mexican lake

Organic and inorganic matter in aquatic ecosystems may occur in both dissolved and particulate form. Seston is the particulate matter present in the water column that is composed of 2 fractions: organic and inorganic matter (MARGALEF 1983, WETZEL 1983). Inorganic matter could be lithogenic (clay and silt), biogenic (silica), andlor originated by chemical precipitation (carbonates) (EFFLER et al. 2002, PENG & EFFLER 2005). The study of seston mass and composition is important to understanding the dynamics of the organic and mineral matter (PUNNING et al. 2003). Previous studies from a wide diversity of geographic regions covering temperate and tropical zones report organic matter as the most abundant fraction of seston, predominantly particulate organic carbon that exhibits seasonal dynamics similar to those of chlorophyll a (CALLIERI 1997, JÃRVINEN et al. 1999, BRZÁKOVÁ et al. 2003, PUNNING et al. 2003); however, the seston of some lakes, such as Lake Maggiore, could be dominated by the inorganic fraction during certain periods (CALLIERI 1997). Although previous studies on warm, monomictic Lake Alchichica relate to dynamic aspects such its hydrodynamics (ALcOCER et al. 2000), nutrient concentration (SÁNCHEZ SILVA 2006), and phytoplankton biomass (SÁNCHEZ REYES 2001), the dynamics ofthe seston concentration, distribution, and composition was unknown. The purpose of this investigation was to analyze the seasonal and vertical variation of seston in Lake Alchichica to better understand the organic and inorganic matter dynamics in tropical, saline lakes.