Response of macroinvertebrate and diatom communities to human‐induced physical alteration in mountain streams

It is generally argued that epilithic diatoms and macroinvertebrates are highly sensitive to changes in water quality, while only a few studies have been conducted on their response to physical disturbance. The main purpose of this research is to investigate whether these two communities respond to physical river disturbance like banks, substrate and flux alteration induced by human action. We sampled 12 high‐altitude streams in the Gran Paradiso National Park, a protected area where the main human activities are limited to hiking and high‐altitude pasture. The sampled stretches of the rivers were characterized with respect to their geomorphological features and possible human modifications. Water uptake for power supply, riverbed and bank modifications represented the main human activities which could determinate alterations in community structure and composition. Habitat structure was evaluated using the Southern European River Habitat (RHS–SE), while the biological status of the river has been estimated by means of the following biotic and diatomic indices: IBE, BMWP, ASPT, Ephemeroptera, Plecoptera and Trichoptera families (EPT) for macroinvertebrates, EPI‐D, IBD and IPS for diatoms. A general concordance between chemical parameters and structure of biological communities was observed. On the other hand, the RHS–SE highlighted the main geomorphological features and detected some slight physical alterations, as quantified by the indices Habitat Modification Score (HMS) and Habitat Quality Assessment (HQA). In short, our findings demonstrate that morphological alterations, even if slight, affect biological diversity and the presence of some specific taxa, while biological indices are independent of the level of physical modifications. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Diatomaceous Lessons in Nanotechnology and Advanced Materials

Silicon, in its various forms, finds widespread use in electronic, optical, and structural materials. Research on uses of silicon and silica has been intense for decades, raising the question of how much diversity is left for innovation with this element. Shape variation is particularly well examined. Here, we review the principles revealed by diatom frustules, the porous silica shells of diatoms, microscopic, unicellular algae. The frustules have nanometer‐scale detail, and the almost 100 000 species with unique frustule morphologies suggest nuanced structural and optical functions well beyond the current ranges used in advanced materials. The unique frustule morphologies have arisen through tens of millions of years of evolutionary selection, and so are likely to reflect optimized design and function. Performing the structural and optical equivalent of data mining, and understanding and adopting these designs, affords a new paradigm in materials science, an alternative to combinatorial materials synthesis approaches in spurring the development of new material and more nuanced materials.     

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.     

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.     

Are protected areas effective in preserving Alpine stream morphology and biodiversity? A field study in the oldest Italian National Park

Global changes and local pressures related to the exploitation of water resources are significantly reducing streams' biodiversity and threatening their ecological balance. This trend concerns both the lowland rivers flowing in densely populated areas and the mountain headwaters, where the effects of global change are dramatically evident and often accompanied by alterations in river hydro-morphology. From mountains to lowlands, regulation and morphological alterations such as bank reinforcement, water abstractions, dams, and weirs are among the most significant threats for river ecosystems. Protected areas and especially large national parks constitute an effective strategy to face the loss of biodiversity, but little is known about their effectiveness regarding lotic environments. To examine the recent trend in aquatic communities in Alpine protected areas, we carried out biological sampling of benthic communities and hydro-morphological status assessment in 12 high-altitude streams within the oldest Italian National Park, that is, the Gran Paradiso National Park, located in the heart of the Western Alps, and we compared results with a previous survey performed in 2005, by keeping the same experimental design. Our results detected minimal changes in the hydro-morphology of the studied watercourses. Biomonitoring indices associated with benthic communities likewise did not provide evidence of significant differences. Conversely, diatom communities were more uniform in 2020 compared to 2005, and a slight species turnover occurred over the 15-year interval. Despite this, our findings underline the effectiveness of protected areas for the conservation of running water environments because they limit hydro-morphological alterations, thus increasing the resilience of aquatic communities to climate change.     

Boronic Acid Moieties Stabilize Adhesion of Microalgal Biofilms on Glassy Substrates: A Chemical Tool for Environmental Applications

Photosynthetic organisms such as diatoms microalgae provide innovative routes to eco-friendly technologies for environmental pollution bioremediation. Living diatoms are capable to incorporate in vivo a wide variety of chemical species dispersed in seawater, thus being promising candidates for eco-friendly removal of toxic contaminants. However, their exploitation requires immobilization methods that allow to confine microalgae during water treatment. Here we demonstrate that a biofilm of Phaeodactylum tricornutum diatom cells grown on the surface of a glassy substrate bearing boronic acid protruding moieties is stably anchored to the substrate resisting mechanical stress and it is suitable for removal of up to 80 % metal ions (As, Cr, Cu, Zn, Sn, Pb, Sb) in a model polluted water sample. Control experiments also suggest that stabilization of the biofilm adhesion occurs by interaction of boronic acid surface groups of the substrate with the hydroxyl groups of diatoms extracellular polysaccharides.