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ABSTRACT: Macroalgae blooms, a frequent consequence of eutrophication in coastal areas, affect the photosynthetic activity of sediments dominated by microphytobenthos (MPB). Light spectra, steady-state (after 1 h) microprofiles of O2 , gross photosynthesis (Pg ), community respiration in light (RL ) and net community photosynthesis (Pn ) were measured in diatom- and cyanobacteria-dominated communities below increasing layers of Ulva. Photosynthetic photon flux (PPF) decreased exponentially with increasing layers of algae and the light spectrum was increasingly enriched in the green and deprived in blue and red regions. Sediment Pg , Pn and RL decreased as the number of Ulva layers increased; however, 1.6 times higher macroalgal density was necessary to fully inhibit cyanobacteria Pg compared with diatoms, indicating that cyanobacteria were better adapted to this light environment. Long-term (3 weeks) incubations of diatom-dominated sediments below increasing layers of Ulva resulted in a shift in the taxonomic composition of the MPB towards cyanobacteria. Hence, changes in the light climate below macroalgal accumulations can negatively affect the photosynthetic activity of sediments. However, spectral niche differentiation of MPB taxonomic groups and concurrent changes in the MPB community may provide sediments with increased resilience to the detrimental effects of eutrophication.
Environmental Microbiology Reports 06/2012; 4(3):316-25. · 3.23 Impact Factor
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ABSTRACT: Macroalgae blooms, a frequent consequence of eutrophication in coastal areas, affect the photosynthetic activity of sediments dominated by microphytobenthos (MPB). Light spectra, steady-state (after 1 h) microprofiles of O2, gross photosynthesis (Pg), community respiration in light (RL) and net community photosynthesis (Pn) were measured in diatom- and cyanobacteria-dominated communities below increasing layers of Ulva. Photosynthetic photon flux (PPF) decreased exponentially with increasing layers of algae and the light spectrum was increasingly enriched in the green and deprived in blue and red regions. Sediment Pg, Pn and RL decreased as the number of Ulva layers increased; however, 1.6 times higher macroalgal density was necessary to fully inhibit cyanobacteria Pg compared with diatoms, indicating that cyanobacteria were better adapted to this light environment. Long-term (3 weeks) incubations of diatom-dominated sediments below increasing layers of Ulva resulted in a shift in the taxonomic composition of the MPB towards cyanobacteria. Hence, changes in the light climate below macroalgal accumulations can negatively affect the photosynthetic activity of sediments. However, spectral niche differentiation of MPB taxonomic groups and concurrent changes in the MPB community may provide sediments with increased resilience to the detrimental effects of eutrophication.
Environmental Microbiology Reports 01/2012; 4(3):316-325. · 3.23 Impact Factor
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ABSTRACT: ABSTRACT: Freezing is a common treatment for the preservation of sediment samples. To test the role of microphytobenthos (MPB) abundance in the release of intracellular nutrients to the pore water due to cell breakage after freezing, referred to as freeze-lysable inorganic nutrients (FL-IN), parallel extractions were carried out from intertidal sediment cores collected in winter and summer from Cádiz Bay. After the determination of net production and dark respiration rates with O2 microsensors, sediment cores were subcored and sliced into several layers. The samples were divided into 2 fractions; the first was centrifuged to extract pore water (fresh) and the other was frozen at –80°C, thawed and centrifuged to extract pore water after freezing. NO2–, NO3–, NH4+ and PO43– were measured in the pore water extracted by both procedures. Chlorophylls a and c were extracted from the same sediment fractions. Freezing produced a significant increase in the pore water concentrations of all inorganic nutrients. Therefore, if the variable of interest is the inorganic nutrient concentration, pore water should be extracted from fresh samples. In addition, FL-IN correlated significantly with chlorophylls a and c (p < 0.01), r2 ranged from 0.54 for NO3– to 0.94 for NH4+, indicating that most FL-IN were released from MPB biomass. The relationships between chlorophyll a and FL-IN in winter and summer were significantly different, suggesting that nutrient accumulation by MPB changes seasonally and might affect nutrient cycling in intertidal sediments.
Marine Ecology Progress Series 01/2010; 403:155-163. · 2.71 Impact Factor
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ABSTRACT: The role of the nitrate-reducing, sulfide-oxidising bacteria (NR-SOB) in the nitrate-mediated inhibition of sulfide net production by anaerobic wastewater biofilms was analyzed in two experimental bioreactors, continuously fed with the primary effluent of a wastewater treatment plant, one used as control (BRC) and the other one supplemented with nitrate (BRN). This study integrated information from H(2)S and pH microelectrodes, RNA-based molecular techniques, and the time course of biofilm growth and bioreactors water phase. Biofilms were a net source of sulfide for the water phase (2.01 micromol S(2-)(tot)m(-2)s(-1)) in the absence of nitrate dosing. Nitrate addition effectively led to the cessation of sulfide release from biofilms despite which a low rate of net sulfate reduction activity (0.26 micromol S(2-)(tot)m(-2)s(-1)) persisted at a deep layer within the biofilm. Indigenous NR-SOB including Thiomicrospira denitrificans, Arcobacter sp., and Thiobacillus denitrificans were stimulated by nitrate addition resulting in the elimination of most sulfide from the biofilms. Active sulfate reducing bacteria (SRB) represented comparable fractions of total metabolically active bacteria in the libraries obtained from BRN and BRC. However, we detected changes in the taxonomic composition of the SRB community suggesting its adaptation to a higher level of NR-SOB activity in the presence of nitrate.
Water Research 08/2007; 41(14):3121-31. · 4.86 Impact Factor
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ABSTRACT: Biogenic production of sulfide in wastewater treatment plants involves odors, toxicity and corrosion problems. The production of sulfide is a consequence of bacterial activity, mainly sulfate-reducing bacteria (SRB). To prevent this production, the efficiency of nitrate addition to wastewater was tested at plant-scale by dosing concentrated calcium nitrate (Nutriox) in the works inlet. Nutriox dosing resulted in a sharp decrease of sulfide, both in the air and in the bulk water, reaching maximum decreases of 98.7% and 94.7%, respectively. Quantitative molecular microbiology techniques indicated that the involved mechanism is the development of the nitrate-reducing, sulfide-oxidizing bacterium Thiomicrospira denitrificans instead of the direct inhibition of the SRB community. Denitrification rate in primary sedimentation tanks was enhanced by nitrate, being this almost completely consumed. No significant increase of inorganic nitrogen was found in the discharged effluent, thus reducing potential environmental hazards to receiving waters. This study demonstrates the effectiveness of nitrate addition in controlling sulfide generation at plant-scale, provides the mechanism and supports the environmental adequacy of this strategy.
Biotechnology and Bioengineering 04/2006; 93(4):801-11. · 3.95 Impact Factor
