Biomedical subjects

H Guasch

Publications and source records attributed to H Guasch.

5 recordsLinked to original sources

PubMed2006

Influence of phosphate on the response of periphyton to atrazine exposure.

After indications from the literature that nutrient concentrations may modify the toxicity of herbicides to natural periphyton communities, this study aims to provide experimental proof for atrazine. In this microcosm experiment, phosphate (P) addition did not ameliorate atrazine toxicity to periphyton. Three weeks of P addition did not increase atrazine tolerance (measured as EC50 in acute toxicity tests), whereas exposure to atrazine under conditions that were either P-limited or non-P-limited clearly reduced the development of algal biomass. Long-term exposure to atrazine induced tolerance of the community to the herbicide, and this was not influenced by P addition. Tolerance induction in this microcosm experiment has been compared with previously published field data from the same area of study and indicates that tolerance induction by atrazine may take place under atrazine exposure in streams as well as in microcosms.

Atrazine↗

PubMed2004

Nuisance odours produced by benthic cyanobacteria in a Mediterranean river.

Geosmin dynamics in the Llobregat waters were related to the waxing and waning of benthic cyanobacterial mats developing in the river. Geosmin concentration in the water during 2002 reached a maximum of 204 ng L(-1), and coincided with an abundance of cyanobacteria in the river. Cyanobacterial mats were favoured by the high nutrient content of the waters. The cyanobacterial mats experienced a process of growth in thickness (attached forms), until they became unattached and drifted downstream (free-floating forms), accumulating in shallow areas of the river. Geosmin in the biofilm ranged from 0.55 +/- 0.97 ng geosmin per mg DW(-1) in the attached biofilms and 5.25 +/- 4.96 ng geosmin per mg DW(-1) in the free-floating biofilms. While the attached mats could be responsible for the local occurrence of geosmin at a given site, the free-floating mats became a relevant agent for the dispersion of the metabolite downstream. This impression was reinforced by the extremely high correlation between the geosmin content in the free-floating biofilm and in the water (r = 0.917, p = 0.00001). In order to reduce the geosmin concentration and accumulation of the cyanobacterial mats in shallow river waters, the nutrient content should be controlled and the natural flow conditions restored, to prevent the growth and accumulation of the geosmin-producing cyanobacterial mats.

Cyanobacteria↗

PubMed2003

Biofilm structure and function and possible implications for riverine DOC dynamics.

Biofilms are major sites of carbon cycling in streams and rivers. Here we elucidate the relationship between biofilm structure and function and river DOC dynamics. Metabolism (extracellular enzymatic activity) and structure (algae, bacteria, C/N content) of light-grown (in an open channel) and dark-grown (in a dark pipe) biofilms were studied over a year, and variations in dissolved organic carbon (DOC) and biodegradable DOC (BDOC) were also recorded. A laboratory experiment on 14C-glucose uptake and DOC dynamics was also performed by incubating natural biofilms in microcosms. On the basis of our field (annual DOC budget) and laboratory results, we conclude that light-grown biofilm is, on annual average, a net DOC consumer. This biofilm showed a high monthly variability in DOC uptake/release rates, but, on average, the annual uptake rate was greater than that of the dark-grown biofilm. The higher algal biomass and greater structure of the light-grown biofilm may enhance the development of the bacterial community (bacterial biomass and activity) and microbial heterotrophic activity. In addition, the light-grown biofilm may promote abiotic adsorption because of the development of a polysaccharide matrix. In contrast, the dark-grown biofilm is highly dependent on the amount and quality of organic matter that enters the system and is more efficient in the uptake of labile molecules (higher 14C-glucose uptake rate per mgC). The positive relationships between the extracellular enzymatic activity of biofilm and DOC and BDOC content in flowing water indicate that biofilm metabolism contributes to DOC dynamics in fluvial systems. Our results show that short-term fluvial DOC dynamics is mainly due to the use and recycling of the more labile molecules. At the river ecosystem level, the potential surface area for biofilm formation and the quantity and quality of available organic carbon might determine the effects of biofilm function on DOC dynamics.

Analysis of Variance↗

PubMed2003

Variability in zinc tolerance, measured as incorporation of radio-labeled carbon dioxide and thymidine, in periphyton communities sampled from 15 European river stretches.

Fifteen European rivers and streams belonging to watersheds in Sweden, the Netherlands, and Spain respectively, were sampled by allowing periphyton to colonize submerged glass substrata. Their zinc tolerances were quantified in short-term laboratory tests, where inhibition of photosynthesis in microalgae and thymidine incorporation in bacterial DNA was measured, and expressed as EC50 values. The variability in zinc tolerances was high reaching 1.5-2.5 orders of magnitude, ranging from 25-8145 microM for photosynthesis and 15-467 microM for thymidine assays. Based on the observed variability, uncertainty factors were estimated for the extrapolation of zinc toxicity data from river to river, both regionally and interregionally. Under the assumption to protect 95% of the observed communities the regional uncertainty factors were 1.7-4.3 and the interregional 2.4-8.6. The sampling sites were characterized in terms of biotope physiography, water chemistry, periphyton biomass, trace element content, and species composition. Multivariate analysis of the data using PLS (Projection to Latent Structure), was used to generate hypotheses about the relation between periphyton zinc tolerance and the 123 so-called predictor variables. Zinc contamination, phosphate, nitrogen nutrients, pH, calcium, bicarbonate, dissolved organic carbon, and various diatom species are important predictors for zinc tolerance in the entire data set representing all 15 river stretches. Regional models suggested that very different factors determined the zinc tolerance in the Swedish and Dutch periphyton. The results are interpreted in terms of Pollution-Induced Community Tolerance (PICT) and the bioavailability of zinc.

Adaptation, Physiological↗

PubMed2001

Effects of atrazine on periphyton under grazing pressure.

An experiment was carried out using indoor experimental channels to assess the long-term effect (18 days) of herbivores (Physella acuta, Gastropoda) on periphyton communities exposed to low levels of atrazine (14 microg l(-1)). We hypothesized that herbivorism modifies the response of periphyton to atrazine. Carbon incorporation, chlorophyll-a content, biovolume and algal taxonomic composition in the channels that contained atrazine were not significantly different from the control channels (not receiving atrazine). In channels with grazers and atrazine, there was a significant reduction of carbon incorporation and algal density. In this treatment, physiognomic forms and algal composition were significantly different from the others. The biomass of grazers (measured as change in dry mass) was not significantly affected by the addition of atrazine. Grazers maintained low levels of periphyton biomass, enhancing algal cell exposition to toxicant and inhibiting any adaptation of the algae to the toxic exposure. The increase in atrazine toxicity with grazing not only affected the metabolism, but also the structure of the algal community, which suggests that effects were not transient but permanent.

Animals↗