Response of epiphytic diatom communities from the tailwaters of glen Canyon Dam,Arizona, to elevated water temperature

The composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from reservoirs.     

Phytoplankton Distribution in Saginaw Bay

Phytoplankton cell counts were made on samples taken in Saginaw Bay during each of 11 cruises from April 1980 through November 1980. A spring assemblage numerically dominated by diatoms was followed by a brief period of dominance by green algae. Blue-green algae were numerically dominant from July through October when diatoms again became the dominant taxonomic group. Two regions of the bay were recognized based on the results of cluster analysis and principal component analysis of the average phytoplankton assemblage. The inner bay was typified by algal species with a Saginaw River origin and/or species typical of eutrophic waters in the Great Lakes. The outer region was typified in part by species of open Lake Huron. Wild Fowl Bay and the area to the southwest of Oak Point each have unique phytoplankton assemblages and are apparently not well integrated with the rest of the bay. On occasion, stations at or near the eastern side of the Saginaw Bay-Lake Huron interface have phytoplankton assemblages similar to inner bay and/or Wild Fowl Bay or Oak Point waters. Taken together, these findings indicate a possible strong nearshore effect on transport of Saginaw Bay populations to Lake Huron. The nearshore effect modifies the effect of Saginaw River on the phytoplankton of the Saginaw Bay-Lake Huron system.     

PREDICTING RIVER DIATOM REMOVAL AFTER SHEAR STRESS INDUCED BY ICE MELTING

The augmentation of fine particles and water velocity may have important effects on river biota, which have not been fully clarified. The aim of this study is to relate the removal of diatoms to changes in environmental variables during high‐stage flow in alpine streams. To achieve this goal, we adopted a path analysis approach. We hypothesized a causal model relating diatom presence to environmental predictors, and we tested it against data collected in two alpine rivers in NW Italy (Aosta Valley): Dora di Veny, directly fed by glaciers of the M. Bianco massif, and Savara, fed by springs. Total suspended solids (TSS) and velocity values were much higher in Dora di Veny, with a maximum velocity of 2.9 m s^?1 and a maximum TSS of 2180 mg L^?1. Absence of epilithic diatoms was recorded only three times in Savara, whereas it occurred in roughly half the samples in Dora di Veny. Diatom recolonization after natural removal generally occurred in early autumn, with a dominance of tightly attached forms. According to our path model, the explanatory variables causally related to the presence/absence of diatoms were water velocity, TSS and river feeding. The model estimated both direct and indirect effect weights of water velocity, thus discriminating the respective roles of shear stress (velocity) and abrasion of the substrates/increased turbidity (TSS, partly mediated by velocity). Our model allowed estimation of TSS and velocity threshold values and therefore inferences on the impact of physical alterations induced by natural or human causes. From a practical point of view, this may represent an applied outcome in the environmental impact assessment of engineering works and other human activities that could increase the TSS in rivers. Copyright © 2011 John Wiley & Sons, Ltd.     

三种硅藻产多不饱和脂肪酸分析

采用f/2培养基,对3种硅藻:牟氏角毛藻(Chaetoceros mualleri)、三角褐指藻(Phaeoda-ctytuum tricornutum)、硅藻舟形藻(Navicala incerta)进行培养及脂肪酸组成研究。牟氏角毛藻和三角褐指藻的生长周期短,生物量较高。3种硅藻的脂肪酸组成相近,主要的脂肪酸是C14:0,C16:0,C16:1(n-7)和C20:5(n-3),多不饱和脂肪酸中C20:5(n-3)(EPA)含量最高,其中三角褐指藻中的EPA含量达到11.7%。3种硅藻的DHAC22:6(n-3)含量都较低。通过调整三角褐指藻和牟氏角毛藻的培养条件,可以提高EPA含量,作为优良的水产饵料。     

Analysis of organo-silica interactions during valve formation in synchronously growing cells of the diatom Navicula pelliculosa

Biologically formed silica is produced at ambient conditions under the control of molecular and physicochemical processes that are apparently integrated in biosilica morphogenesis, but the mechanisms are not yet fully understood. With the recent identification of small polypeptides and proteins that are encapsulated inside the biosilica and functional in silica polymerization in vitro, it is of importance to determine whether interactions between inorganic silica species and these organic compounds occur in vivo. A time-resolved analysis of valve formation in synchronously growing cells of the diatom species Navicula pelliculosa enabled us to characterize the relevant chemical bonds by attenuated total reflectance Fourier-transformed infrared (ATR-FTIR) spectroscopy. Typically, inorganic bonds of Si-O-Si (bands at 1058, 843 cm(-1)), Si-OH (3689 cm(-1)), and P=O (1239 cm(-1)) and organic bonds of proteinaceous matter (with the amide I and II bands at 1642 and 1543 cm(-1), respectively) were positively identified during one cycle of valve formation. The observed variations in FTIR band intensity and location represented specific interactions between organic and inorganic molecules during the major silicification event, during which stretching of the Si-O bonds was predominantly noticed. The experimentally obtained frequencies (nu) of the major bonds corresponded to those that were obtained by MM+ and PM3 FTIR simulations for organo-silica interactions based on biomolecules that are proposed to be involved in biosilica formation. The results indicated that hydrogen bonds originated from interactions, albeit weak, between organic phosphate or amine groups to the inorganic hydroxyl groups or oxygen atoms from the silicic acid and/or silica. The existence of covalent P-O-Si bonds and electrostatic interactions could not be excluded. These interactions clearly suggest that biomolecules actively contribute to the silica polymerization process during valve formation in N. pelliculosa, and also might act comparably in other diatoms species in which similar biomolecules have been identified.