Martín Merino-Ibarra

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 More than half (56%) of the maximal water storage of the reservoir was withdrawn annually.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.

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.

Seasonal changes in the zooplankton abundances of the reservoir Valle de Bravo (State of Mexico, Mexico)

Abstract Valle de Bravo is one of largest drinking water reservoirs in Mexico, serving nearly 12% of Mexico Citys population of 26 million. We studied the monthly variations in the zooplankton density and diversity for one year (November 2004 to October 2005) at five different depths (2, 4, 8, 12, and 20 m) at each of the five sites of the reservoir. The water body was generally alkaline; pH decreased with increasing depth. Dissolved oxygen also decreased drastically with depth, from an average of 8 mg/L to less than 1 mg/L. Chlorophyll a concentration varied considerably (2.6 ± 0.06 to 12.5 ± 2.8 μg/L) both seasonally and with depth. Secchi depth averaged 1.65 m and varied between 0.63 and 3.21 m along the seasons but exhibited minimal differences among sites. Differences in zooplankton abundance and composition were small among sites, supporting the theory that anthropogenic disturbances affect the reservoir as a whole. The mean total zooplankton density was about 400 ± 293 ind./L, mostly composed of rotifer species, particularly Keratella cochlearis, Polyarthra vulgaris, and Trichocerca similis. Densities of K. cochlearis at 2-m depth exceeded 1800 ind./L during the rainy season (May-July). Average density of P. vulgaris was 200 ± 133 ind./L, while that of T. similis was half that amount. The dominant cladoceran taxa were Bosmina longirostris, Chydorus sphaericus, and Daphnia laevis. An inverse relationship between depth and zooplankton abundance and depth and diversity was observed. In contrast, we observed a direct relation between the mean rotifer and cladoceran density. Shannon-Wieners species diversity index ranged between 1.00 and 4.09. Fourteen of the rotifer species found are new records for Valle de Bravo and another 13 species observed earlier were not encountered in the present study. The overall trends in both the densities and dominance of rotifer species of the reservoir did not essentially change during the last five years. Our data point toward the need for an integrated management of Valle de Bravo.

Differential distribution of diatoms and dinoflagellates in a cyclonic eddy confined in the Bay of La Paz, Gulf of California

The differential distribution of diatoms and dinoflagellates in the Bay of La Paz, Gulf of California, Mexico, was analyzed in summer of 2009, when a cyclonic eddy confined in the bay dominated the circulation. An uplift of the nutricline in the eddy drove high concentrations of nutrients to the euphotic layer. A differential phytoplankton distribution was observed to be associated with the eddy: there was an abundance of dinoflagellates close to the center of the cyclonic eddy, whereas diatoms were more abundant at the periphery. A significant inverse correlation (R = −0.62, p < 0.002) was found between the temperature at 25 m depth and the dinoflagellates abundance. Based on the temporal evolution of chlorophyll measured by MODIS satellite images, and a conceptual model proposed for the lifecycle of eddies, the cyclonic eddy may have been an old decaying structure. The effect of the cyclonic eddy on the phytoplankton distribution in this small semienclosed region was apparently similar to that found in larger eddies in the open ocean, but this is the first time such a differential distribution has been found associated to a confined eddy.

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.

Sedimentary records of recent sea level rise and acceleration in the Yucatan Peninsula

Abstract Recent eustatic sea level rise (SLR) is one of the most striking manifestations of recent climate change as it directly impacts coastal activities and ecosystems. Although global SLR is well-known, local values differ due to vertical land motion, and changes in atmospheric pressure, ocean currents and temperatures. Although a reliable estimation of local SLR trends is needed to assess coastal zone vulnerabilities and plan adaptation strategies, instrumental records are usually short or sparse, especially in developing countries. Here we show that 210Pb-dated sedimentary records from mangrove saltmarshes can provide useful decadal records of local SLR trends. We quantified sediment accretion rates in sediment cores from remote mangrove saltmarshes of the Yucatan Peninsula. Best SLR records were observed for cores collected near mean sea level (MSL). During most of the XX century the SLR rate ranged from 1-2 mm yr-1, increased to a maximum of 4.5 ± 0.6 mm yr-1 and the acceleration was 0.13 mm yr-2. Assuming either a constant SLR rate or acceleration, by the end of this century MSL level will be 39 cm or 91 cm above the present value. Both coastal infrastructures and ecosystems will be negatively affected by SLR and society will need to adapt relatively fast to the new conditions.

Exploring biogeochemistry and microbial diversity of extant microbialites in Mexico and Cuba

Microbialites are modern analogs of ancient microbial consortia that date as far back as the Archaean Eon. Microbialites have contributed to the geochemical history of our planet through their diverse metabolic capacities that mediate mineral precipitation. These mineral-forming microbial assemblages accumulate major ions, trace elements and biomass from their ambient aquatic environments; their role in the resulting chemical structure of these lithifications needs clarification. We studied the biogeochemistry and microbial structure of microbialites collected from diverse locations in Mexico and in a previously undescribed microbialite in Cuba. We examined their structure, chemistry and mineralogy at different scales using an array of nested methods including 16S rRNA gene high-throughput sequencing, elemental analysis, X-Ray fluorescence (XRF), X-Ray diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transformed Infrared (FTIR) spectroscopy and Synchrotron Radiation-based Fourier Transformed Infrared (SR-FTIR) spectromicroscopy. The resulting data revealed high biological and chemical diversity among microbialites and specific microbe to chemical correlations. Regardless of the sampling site, Proteobacteria had the most significant correlations with biogeochemical parameters such as organic carbon (Corg), nitrogen and Corg:Ca ratio. Biogeochemically relevant bacterial groups (dominant phototrophs and heterotrophs) showed significant correlations with major ion composition, mineral type and transition element content, such as cadmium, cobalt, chromium, copper and nickel. Microbial-chemical relationships were discussed in reference to microbialite formation, microbial metabolic capacities and the role of transition elements as enzyme cofactors. This paper provides an analytical baseline to drive our understanding of the links between microbial diversity with the chemistry of their lithified precipitations.

Metabolism in a deep hypertrophic aquatic ecosystem with high water-level fluctuations: A decade of records confirms sustained net heterotrophy

Long-term and seasonal changes in production and respiration were surveyed in the Valle de Bravo reservoir, Mexico, in a period during which high water-level fluctuations occurred (2006–2015). We assessed the community metabolism through oxygen dynamics in this monomictic water-body affected by strong diurnal winds. The multiple-year data series allowed relationships with some environmental drivers to be identified, revealing that water level-fluctuations strongly influenced gross primary production and respiratory rates. Production and respiration changed mainly vertically, clearly in relation to light availability. Gross primary production ranged from 0.15 to 1.26 gO2 m−2 h−1, respiration rate from −0.13 to −0.83 gO2 m−2 h−1 and net primary production from −0.36 to 0.66 gO2 m−2 h −1 within the production layer, which had a mean depth of 5.9 m during the stratification periods and of 6.8 m during the circulations. The greater depth of the mixing layer allowed the consumption of oxygen below the production layer even during the stratifications, when it averaged 10.1 m. Respiration below the production layer ranged from −0.23 to −1.38 gO2 m−2 h−1. Vertically integrated metabolic rates (per unit area) showed their greatest variations at the intra-annual scale (stratification-circulation). Gross primary production and Secchi depth decreased as the mean water level decreased between stratification periods. VB is a highly productive ecosystem; its gross primary production averaged 3.60 gC m−2 d−1 during the 10 years sampled, a rate similar to that of hypertrophic systems. About 45% of this production, an annual average net carbon production of 599 g C m−2 year−1, was exported to the hypolimnion, but on the average 58% of this net production was recycled through respiration below the production layer. Overall, only 19% of the carbon fixed in VB is buried in the sediments. Total ecosystem respiration rates averaged −6.89 gC m−2 d−1 during 2006–2015, doubling the gross production rates. The reservoir as a whole exhibited a net heterotrophic balance continuously during the decade sampled, which means it has likely been a net carbon source, potentially releasing an average of 3.29 gC m−2 d−1 to the atmosphere. These results are in accordance with recent findings that tropical eutrophic aquatic ecosystems can be stronger carbon sources than would be extrapolated from temperate systems, and can help guide future reassessments on the contribution of tropical lakes and reservoirs to carbon cycles at the global scale. Respiration was positively correlated with temperature both for the stratification periods and among the circulations, suggesting that the contribution of C to the atmosphere may increase as the reservoirs and lakes warm up owing to climate change and as their water level is reduced through intensification of their use as water sources.

Microbial distribution and turnover in Antarctic microbial mats highlight the relevance of heterotrophic bacteria in low-nutrient environments

Maritime Antarctica has shown the highest increase in temperature in the Southern Hemisphere. Under this scenario, biogeochemical cycles may be altered, resulting in rapid environmental change for Antarctic biota. Microbes, that drive biogeochemical cycles often form biofilms or microbial mats in continental meltwater environments. Limnetic microbial mats from the Fildes Peninsula were studied using high-throughput 16S rRNA gene sequencing. Mat samples were collected from fifteen meltwater stream sites, comprising a natural gradient from ultraoligotrophic glacier flows to meltwater streams exposed to anthropogenic activities. Our analyses show microbial structure differences between mats are explained by environmental NH4+, NO3-, DIN, soluble reactive silicon and conductivity. Microbial mats living under ultraoligotrophic meltwater conditions did not exhibit a dominance of cyanobacterial photoautotrophs, as it has been documented for other Antarctic limnetic microbial mats. Instead, ultraoligotrophic mat communities were characterized by the presence of microbes recognized as heterotrophs and photoheterotrophs. This suggests that microbial capabilities for recycling may be a key factor to dwell in ultra-low nutrient conditions. Our analyses show that phylotype level assemblages exhibit coupled distribution patterns in environmental oligotrophic inland waters. The evaluation of these microbes suggests the relevance of reproductive and structural strategies to pioneer these psychrophilic ultraoligotrophic environments.

Anthropogenic impacts on tropical karst lakes: “Lagunas de Montebello,” Chiapas: Anthropogenic impacts on tropical karst lakes

Grupo de Investigación en Limnología Tropical, FES Iztacala, Universidad Nacional Autónoma de México, Tlalnepantla, Mexico Unidad Académica de Ecología y Biodiversidad Acuática, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Ciudad de México, Mexico Departamento de Dinámica Terrestre Superficial, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad de México, México Correspondence Javier Alcocer, Grupo de Investigación en Limnología Tropical, FES Iztacala, Universidad Nacional Autónoma de México, Av. de los Barrios No. 1, Los Reyes Iztacala, Tlalnepantla 54090, Estado de México, Mexico. Email: jalcocer@unam.mx Funding information DGAPA‐PAPIIT, Grant/Award Number: IN219215; Fondo Sectorial de Investigación y Desarrollo Sobre el Agua CONAGUA/ CONACYT, Grant/Award Number: 167603