Planktonic ciliates in a hypertrophic pond: functional role and importance

Taxonomical composition and abundance of the planktonic ciliate assemblage in a Lake Tezozomoc, a hypertrophic pond located into an urban park in Mexico City, was investigated along the rainy season (May to October). The aims of the study were to know the main trophic roles and ecological significance of ciliates in a highly productive environment. A low number of taxa (27) and a wide abundance fluctuation (104-387 cil ml(-1)) were found. The most abundant species (up to 162 cil ml(-1)) was Halteria grandinella, an oligotrich ciliate that graze on bacteria and picoplankton, but also several big body sized species that feed on pico and nanoplankton were abundant. Sudden temporal changes in species dominance occurred. Ciliate biomass was very high and fluctuated widely (1.6-88 10(6) microm(3) ml(-1)) being dominated by the >50 microm size fraction that mainly included the pico and nanoplankton feeders. Ciliates are a very important component in the plankton of hypertrophic lakes and their main control factor seems to be the grazing by big-body size Daphnia species.     

Polyhydroxybutyrate-Based Nanocomposites with Cellulose Nanocrystals and Bacterial Cellulose

Polyhydroxybutyrate (PHB) films nanoreinforced with hydrolyzed cellulose nanocrystals (CNC) and bacterial cellulose (BC) were prepared by solvent casting. The influence of different cellulose nanoparticles content (2, 4 and 6 wt% of CNC and 2 wt% of BC) on the PHB properties was studied. CNC nanocomposites presented good dispersion of the nanocrystals, improving transparency, mechanical and barrier properties of the PHB films. On the other hand, reduced thermal stability and mechanical properties were yielded by BC addition due to the intrinsic lower degradation temperature and higher length of the BC nanofibrils compared to CNC. Nanocomposites performance variation is mainly caused by the marked difference in nanoparticles structure. It was demonstrated that PHB–CNC films exhibited higher performance enhancement without detrimental effect of the pristine PHB properties.     

Black Carbon and Polycyclic Aromatic Hydrocarbon Emissions from Vehicles in the United States–Mexico Border Region: Pilot Study

The investigators developed a system to measure black carbon (BC) and particle-bound polycyclic aromatic hydrocarbon (PAH) emission factors during roadside sampling in four cities along the United States–Mexico border, Calexico/Mexicali and El Paso/Juárez. The measurement system included a photoacoustic analyzer for BC, a photoelectric aerosol sensor for particle-bound PAHs, and a carbon dioxide (CO₂) analyzer. When a vehicle with measurable emissions passed the system probe, corresponding BC, PAH, and CO₂ peaks were evident, and a fuel-based emission factor was estimated. A picture of each vehicle was also recorded with a digital camera. The advantage of this system, compared with other roadside methods, is the direct measurement of particulate matter components and limited interference from roadside dust. The study revealed some interesting trends: Mexican buses and all medium-duty trucks were more frequently identified as high emitters of BC and PAH than heavy-duty trucks or passenger vehicles. In addition, because of the high daily mileage of buses, they are good candidates for additional study. Mexican trucks and buses had higher average emission factors compared with U.S. trucks and buses, but the differences were not statistically significant. Few passenger vehicles had measurable BC and PAH emissions, although the highest emission factor came from an older model passenger vehicle licensed in Baja California.     

Interactions of uranium with polyphosphate

Inorganic polyphosphates (PolyP) are simple linear phosphate (PO(4)(3-)) polymers which are produced by a variety of microorganisms. One of their functions is to complex metals resulting in their precipitation. We investigated the interaction of phosphate and low-molecular-weight PolyP (1400-1900Da) with uranyl ion at various pHs. Potentiometric titration of uranyl ion in the presence of phosphate showed two sharp inflection points at pHs 4 and 8 due to uranium hydrolysis reaction and interaction with phosphate. Titration of uranyl ion and PolyP revealed a broad inflection point starting at pH 4 indicating that complexation of U-PolyP occurs over a wide range of pHs with no uranium hydrolysis. EXAFS analysis of the U-HPO(4) complex revealed that an insoluble uranyl phosphate species was formed below pH 6; at higher pH (> or = 8) uranium formed a precipitate consisting of hydroxophosphato species. In contrast, adding uranyl ion to PolyP resulted in formation of U-PolyP complex over the entire pH range studied. At low pH (< or = 6) an insoluble U-PolyP complex having a monodentate coordination of phosphate with uranium was observed. Above pH 6 however, a soluble bidentate complex with phosphate and uranium was predominant. These results show that the complexation and solubility of uranium with PO(4) and PolyP are dependent upon pH.     

Bacterial Cellulose from Simple and Low Cost Production Media by Gluconacetobacter xylinus

Bacterial cellulose pellicles were produced by Gluconacetobacter xylinus using non conventional low-cost carbon sources, such as glycerol remaining from biodiesel production and grape bagasse, a residue of wine production. The carbon sources assayed showed their suitability for microbial cellulose production, with relatively high production values such as 10.0 g/l for the culture medium with glycerol from biodiesel as carbon source and corn steep liquor as nitrogen source; and 8.0 g/l for the culture medium containing grape bagasse and corn steep liquor. Glucose, commercial glycerol and cane molasses were also assayed as carbon sources for comparison. The bacterial celluloses produced were characterized by means of scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Morphological analysis showed that bacterial cellulose microfibrils produced from the non-conventional media used were several micrometers long and had rectangular cross-sections with widths and thicknesses in the range of 35–70 and 13–24 nm, respectively. X-ray patterns showed crystallinity levels in the range of 74–79 % (area method), whereas both X-ray patterns and infrared spectroscopy evidenced the presence of peaks characteristic of Cellulose I polymorph. Besides thermal properties were similar to those found for the pellicle obtained from glucose. The study performed showed the suitability of using wine residues or glycerol remaining from increasing biodiesel production as cheap carbon sources for production of bacterial cellulose microfibrils, with similar characteristics as those obtained by use of more expensive carbon sources such as glucose or commercial glycerol. On the other hand, the low cost nitrogen sources used (corn steep liquor or diammonium phosphate) also contributed to the economy of the bioprocess.     

Climate change impact on countrywide water balance in Bolivia

There is increasing concern about the ongoing reduction in water supplies in the tropical Andes due to climate change effects such as glacier/snow melting resulting from rising air temperatures. In addition, extreme events and population growth are already directly affecting life and water renewability in the country. A countrywide integrated national plan for improving basin-scale water management in Bolivia is needed to assure water availability for agriculture, industry, mining, and human consumption. This study aims to provide a modeling tool to assess Bolivia’s past, current, and future water availability and identify basins at risk of water deficits. The Soil Water Assessment Tool was used to simulate the monthly water balance from 1997 to 2008, as well as the water balance projected to 2050 for the entire country. It considers possible changes in air temperatures and precipitation proposed by 17 Global Circulation Models as well as carbon dioxide projections derived from the Special Report Emission Scenario. Overall, model results were close to satisfactory compared to observations, with some exceptions due to lack of information for expanding the timeline and improving calibration. Based on the calculation of three hydrologic indicators, the study identifies basins that would be the most susceptible to water deficits for a baseline from 1997 to 2008, and in the event of the projected climate change, to 2050.