The use of periphyton communities for nutrient removal from polluted streams

The results of experiments on the efficiency of periphyton communities for nutrient removal from polluted streams in a continuous flow-through are given. The artifical stream (5 m × 0.7 m × 0.5 m) was made of wood, with silon (a kind of nylon) screens, as a substratum for periphyton growth. The elimination of nutrients was monitored by ammonium, nitrite, nitrate and orthophosphate analyses. In addition, the elimination of organics and the decrease in trophic state were determined. During two field experiments a marked elimination of nitrogen and phosphorus was demonstrated. The maximum efficiency of ammonium and orthophosphate removal was 80% and 70%, respectively. Organic removal reached 35% (C.O.D._Mn-Kubel) and 54% (B.O.D.₅). Inorganic and organic nutrient elimination caused significant changes in periphyton community structure in the outflow portion of the through, evaluated by the saprobic index and the similarity coefficient. The experiments confirmed that periphyton communities are a useful means of nutrient removal from polluted streams.     

Copepods associated with reef corals: a comparison between the Atlantic and the Pacific

Endoparasitic copepods are very numerous in Indo-West Pacific corals. In West Indian corals they were thought to be absent, but recent studies have shown that a varied endoparasitic copepod fauna exists as well. Striking is the taxonomic composition of the coral-inhabiting copepods:In the Indo-West Pacific Lichomolgidae and Xarifiidae are the dominant families, both are absent in the West Indies. On the other hand, Corallovexiidae and Asterocheridae dominate in the West Indies; the former family is absent and the latter is apparently rare and not very diversified in the Indo-West Pacific.     

Combined Oxygen and Nitrous Oxide Microsensor for Denitrification Studies

The construction of a microsensor which can be used to measure O₂ and N₂O simultaneously is described. The microsensor exhibited a linear response to both O₂ and N₂O, and the response to N₂O was independent of the O₂ concentration and vice versa. The N₂O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter⁻¹. The signals for O₂ and N₂O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O₂ and N₂O were measured in a biofilm which was exposed to acetylene to block the N₂O reductase activity of denitrifying bacteria. O₂ penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N₂O concentration at 1.4 mm depth increased from 32 to 411 μmol liter⁻¹ after the addition of the inhibitor. The shape of the N₂O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm.     

Linear dichroism and orientational studies of carotenoid Langmuir-Blodgett films

The linear dichroism of single monolayers of lutein, zeaxanthin and a mixture of lutein and synthetic phosphatidylcholine has been measured. The angle of orientation of the carotenoid molecules was found to lie between 45° and 51° relative to the plane of the solid support. Although the adsorbed monolayers were mostly in a monomeric state, microscopic observations, as well as the II-A isotherms, indicated the existence of crystalline islets. The results have been interpreted in connection with Haidinger's polarization brushes.     

Heterochromatin in mitotic chromosomes of theVirilis species group ofDrosophila

The amount of heterochromatin in the genome of ten members of thevirilis species group was determined as the length of C-band chromosome material relative to the total karyotype length. Thevirilis phylad (Drosophila virilis, D. novamexicana, D. americana americana, andD. americana texana) has significantly greater amounts of heterochromatin in the genome than do members of the montana phylad (D. montana, D. lacicola, D. flavomontana, D. borealis, D. ezoana, D. littoralis). Thus, the significant karyotypic change accompanying diversification of these species has involved reduction in their total constitutive heterochromatin. These changes have apparently involved reductions in the amount of centromeric heterochromatin in the autosomes.     

A burst of CO2 from photosynthesizing leaves after a temperature decrease under constant light conditions

A transient CO₂ burst from seedlings of some plant species was observed after a rapid temperature decrease. The magnitude of the CO₂ release depended on initial temperature, oxygen concentration and light intensity. To obtain a maximal value of CO₂ release, the temperature had to decrease by more than 8°C. The phenomenon was detected only in the light, and was confined to C₃ species. It was inhibited by low oxygen concentration, indicating its possible connection with photorespiration.     

A Comparison of Internal Standards for Plant Cytophotometry

Plant cell nuclei were compared with chicken erythrocyte nuclei for use as internal standards for microspectrophotometry. The amount of DNA per nucleus and the coefficient of variation for measurement of individual nuclei were determined for cells from dormant embryos of Pinus taeda and Pinus coulteri, from onion root tips and from chicken erythrocytes. The chicken erythrocytes had the least variability and thus were best suited for use as a standard. Onion root tips were least suitable, with a coefficient of variation 2 1/2 times that of erythrocytes. Although onion root tips have been used as an internal standard in other studies, their mitotic activity, in contrast with the nonreplication of DNA of mature erythrocytes, is reflected in a broad distribution of nuclei with values in the 2C-4C range. Coulter pine mature embryos were at the 3C level, whether dry or hydrated, while loblolly pine embryos were in the 2C state. This confirms previous reports. The coefficient of variability for the pine embryo cells was 1 1/2 times that of erythrocytes for nonhydrated seeds and twice the erythrocyte value for hydrated seeds. The larger 2C values for pine (26 pg for P. taeda and 17 pg for P. coulteri) are closer to values expected for many plant species than the 3 pg level of the chicken erythrocytes. Dormant P. taeda embryo cells (2C) are suggested as an alternative where the experimental material has large DNA values and/or chicken erythrocytes are difficult to procure. Large sample size is recommended for the plant materials if they are to be used as internal standards in Feulgen cytophotometry.     

Methanogenesis in an Upflow Anaerobic Sludge Blanket Reactor at pH 6 on an Acetate-Propionate Mixture

High-rate anaerobic digestion can be applied in upflow anaerobic sludge blanket reactors for the treatment of various wastewaters. In upflow anaerobic sludge blanket reactors, sludge retention time is increased by a natural immobilization mechanism (viz. the formation of a granular type of sludge). When this sludge is cultivated on acid-containing wastewater, the granules mainly consist of an acetoclastic methanogen resembling Methanothrix soehngenii. This organism grows either in rods or in long filaments. Attempts to cultivate a stable sludge consisting predominantly of Methanosarcina sp. on an acetate-propionate mixture as substrate by lowering the pH from 7.5 during the start-up to approximately 6 failed. After 140 days of continuous operation of the reactor a filamentous organism resembling Methanothrix soehngenii prevailed in the sludge. The specific methanogenic activity of this sludge on acetate-propionate was optimal at pH 6.6 to 6.8 and 7.0 to 7.2, respectively.