Algal Regrowth Research Articles

Analysis of Growth Inhibition for Microcystis aeruginosa with Periodic Ultrasonic Irradiations

Objectives : To confirm both efficiency and sustainability of algal growth inhibition, various laboratory-scale experiments were conducted and the growth inhibitory effect of Microcystis aeruginosa (M. aeruginosa) was investigated through ultrasonic re-irradiation during the regrowth period after the first ultrasound irradiation.Methods : Experiments with different times of irradiation [i.e., control group A (0 hr), experimental group B (2 hr) applied with only the first ultrasound irradiation, and experimental group C (0.5 hr), D (1 hr), and E (1.5 hr) applied with both first and second irradiations] were performed.Results and Discussion : As a result of both Chlorophyll-a (Chl-a) concentration and cell number of M. aeruginosa, the experimental group (B) with only first ultrasound irradiation (2 hr) displayed rapid regrowth of algae after initial decrease whereas the experimental group (C, D, and E) with both first ultrasound irradiation (2 hr) and second ultrasound irradiation (0.5 hr, 1 hr, and 1.5 hr) confirmed the delay of algae regrowth. Based on the specific growth rate constant (µ) and first order decay rate constant (k), algal growth from the experimental groups (C, D, E) with the secondary ultrasound irradiation was more significantly inhibited due to repetitive inactivation of algae growth. According to the SEM and TEM results, damages to algae cells were clearly observed under the influence of ultrasound, and both decrease in gas vesicles and rupture of cell membrane in M. aeruginosa were also monitored.Conclusion : Through this study, the algae growth inhibitory effect by ultrasonic irradiations was confirmed, and the re-irradiation of ultrasound contributed to the repetitive inactivation of algae growth, indicating that the second ultrasonic irradiation time required to inhibit algal regrowth can be reduced compared to the first irradiation. Therefore, periodic ultrasonic irradiation is required for long-term inhibition of algae growth in stagnant waters, but the appropriate frequency of ultrasonic irradiation may vary depending on the influence of various complex factors such as the size of the stagnant waters, the frequency of algal blooms, water temperature, light irradiation, nutrients, flow rate, etc. Finally, many field studies under various conditions are warranted to establish an optimized ultrasound irradiation protocol.

Allelopathic Efficiency of Plant Extracts to Control Cyanobacteria in Hydroponic Culture

Cyanobacteria rapidly form harmful algal blooms (HABs) that cause serious nutritional imbalances in crop production via hydroponics. Allelopathic extracts from plants can be applied as a solution for ecologically sustainable control of algal blooms. In this study, the effects of 11 aqueous extracts of 10 allelopathic plants in controlling Microcystis aeruginosa were evaluated. Among the extracts, walnut husk and rose leaf extracts exhibited high inhibitory levels for efficient control of algae. High inhibitory levels were achieved owing to large amounts of water-soluble tannins, especially tannic acid. The effective extracts were applied to a hydroponic system cultivated on leafy perilla vegetables. Although the severe doses (IC90) did not guarantee complete algal control due to partial algal regrowth, walnut husk and rose leaf extracts only exerted strong persistent effects on algae control. Persistent algae inhibition contributed to the increase in perilla growth and leaf quality. Rose leaf was potentially a more useful resource for controlling algae in a hydroponic system because the application of rose leaf extract efficiently controlled the algae and was less toxic to perilla growth. In contrast, the treatment of walnut husk extract also controlled algae but inhibited perilla growth with pale green leaves.

Bioremediation of copper polluted wastewater-like nutrient media and simultaneous synthesis of stable copper nanoparticles by a viable green alga

Environmentally benign, algae-mediated biosynthesis of valuable copper-based materials in wastewater, combined with cupric ion (Cu2+) bioremediation, has the potential to reduce the cost of wastewater treatment and generate high quality biosolids. This study investigated the ability of a wild-type strain of Chlamydomonas reinhardtii to bioremediate free Cu2+ in wastewater-like nutrient media during the biosynthesis of copper nanoparticles (Cu NPs). The color of supernatants from treated Cu-polluted media provided a first indication of Cu-based NPs formation in the aqueous phase. Analysis by fluorescein diacetate hydrolysis, observations of cell morphology, and algal regrowth experiments after treatment showed that algal viability was crucial for efficient Cu2+ reduction to Cu NPs. UV–vis absorption spectroscopy demonstrated that sulfur-free medium, which enables sustained hydrogen photoproduction in alga, was not the most efficient in NPs formation. Dark-field scanning transmission electron microscopy (STEM) images overlapped with Cu signal map from energy dispersive X-ray spectrometry (EDS) and high-resolution transmission electron microscopy confirmed the presence of polydisperse, spherical, and well-dispersed sub-10 nm Cu NPs crystallites exclusively in algae-treated heavily Cu-polluted media (10 mg L−1). STEM and EDS also demonstrated the affinity of Cu NPs for carbon-rich (organic) objects. Overall, this study demonstrates the feasibility of Cu2+ bioremediation from the wastewater-like complex nutrient media and the simultaneous biosynthesis of Cu NPs by viable green microalga.

Assessment and mechanisms of microalgae growth inhibition by phosphonates: Effects of intrinsic toxicity and complexation

The effects of phosphonates, the heavily-used antiscalants in reverse osmosis systems, on microalgae are controversial, although they are harmless to most aquatic organisms. Herein, we assessed the inhibitory effects of etidronic acid (HEDP) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) on algal growth and revealed the mechanisms involved in both intrinsic toxicity and complexation. The phosphonates showed weak influences on Scenedesmus sp. LX1 in the first 4 d of cultivation. In contrast, a significant growth inhibition was observed subsequently with half maximal effective concentrations of 57.6 and 35.7 mg/L for HEDP and DTPMP, respectively, at 10 d. The phosphonates had little effect on cellular energy transfer and oxidative stress, quantified by adenosine triphosphate level and superoxide dismutase activity, respectively, demonstrating weak intrinsic toxicities to algal cells. Phosphonates blocked the algal assimilation of iron ions through complexation. Severe iron deficiency limited photosynthetic activity and caused chlorophyll decline, resulting in a functional loss of the photosystem followed by complete algal growth inhibition at the late cultivation stage. Our findings point to a potential ecological impact wherein harmful algal blooms are induced by the natural degradation of phosphonates due to the release of both iron and phosphate ions that stimulate algal regrowth after disinhibition.

Amphoteric starch-based bicomponent modified soil for mitigation of harmful algal blooms (HABs) with broad salinity tolerance: Flocculation, algal regrowth, and ecological safety

The treatment of harmful algal blooms (HABs) by in-situ flocculation is an emerging technology capable of efficiently removing HABs from natural waters. However, differences in salinity, pH and algal species in freshwaters and seawaters can influence the flocculation treatment. In this study, we developed a bicomponent modified soil using amphoteric starch (AS) and poly-aluminium chloride (PAC) in order to effectively flocculate microalgae under broad salinity conditions. Specifically, the impacts of water salinity (0–3.3%), pH (3–11), and algal species (Microcystis aeruginosa and marine Chlorella sp.) were investigated in order to evaluate efficiency, dosage and mechanisms of algae flocculation. The results showed that AS-PAC modified soils possessed excellent resistance to salinity change due to the anti-polyelectrolyte effect of AS, which contributed to 99.9% removal efficiency of M. aeruginosa in fresh and saline waters, and Chlorella sp. in marine water, respectively. The dosage of the flocculant modifier was only 10–20% of that of another proven modifier (i.e. Moringa oleifera), which substantially reduced the material cost. The high salinity tolerance of algal flocculation by the AS-PAC modified soil was attributed to the synergistic processes of charge neutralization and netting-bridging. Thus, this study has developed a universal flocculant and revealed fundamental mechanisms for the mitigation of HABs under broad salinity conditions.

Interaction between 1,2-benzisothiazol-3(2H)-one and microalgae: Growth inhibition and detoxification mechanism

Isothiazolinones, such as 1,2-benzisothiazol-3(2H)-one (BIT), are widely used as biocides for bacterial growth control in many domestic and industrial processes. Despite their advantages as biocides, they are highly toxic and pose a potential risk to the environment. This study investigated the inhibition process and detoxification mechanism involved in microalgal survival and growth recovery after BIT poisoning. BIT could seriously inhibit the growth of Scenedesmus sp. LX1, Chlorella sp. HQ, and Chlamydomonas reinhardtii with half maximal effective concentrations at 72 h (72h-EC50) of 1.70, 0.41, and 1.16 mg/L, respectively. The primary inhibition mechanism was the BIT-induced damage to microalgal photosynthetic systems. However, the inhibited strains could recover when their growth was not completely inhibited. The influence of this inhibiting effect on subsequent algal regrowth was negligible or weak. BIT consumption was the primary reason for their recovery. Notably, algae did not die even if their growth was completely inhibited. If the BIT concentration did not exceed a certain high level, then the inhibited algae could recover their growth relatively well. Microalgal generation of reduced glutathione (GSH) and the oxygen radical scavenging enzymes, superoxide dismutase (SOD) and catalase (CAT), played a key role in detoxification against BIT poisoning.

Influence of grazing on triclosan toxicity to stream periphyton

Summary Interactions between emerging contaminants and other drivers of community structure and function are poorly known. We used laboratory microcosms to investigate the single and combined effects of grazing and triclosan toxicity on the structure and function of stream periphyton. Grazing alone strongly reduced algal biomass, but also reduced oxidative stress and increased periphyton productivity and phosphorus (P) uptake capacity. This suggests that grazed algal communities can compensate for reduced biomass by enhanced growth after being released from grazing. Triclosan exposure (11.6 ± 1.1 μg L−1) reduced the detoxification capacity and P‐uptake capacity of periphyton and altered diatom taxonomic composition. This indicates that triclosan at environmentally relevant concentrations affects the capacity of periphyton to remove dissolved nutrients and to cope with toxicant mixtures commonly occurring in streams. Triclosan exposure and grazing pressure had negative synergistic effects on algal size‐class distribution and diatom mortality, since the effects of triclosan were higher than expected when periphyton was subject to grazing. Periphyton exposed to toxic substances such as triclosan had a lower capacity to cope with grazing than unexposed communities, because toxicity can limit algal regrowth after release from grazing and promote the loss of less abundant species. This synergism may have important implications because grazing pressure will magnify the negative effects of toxicants on community structure and ecosystem functions such as primary production and nutrient cycling.

The effects of an invasive habitat modifier on the biotic interactions between two native herbivorous species and benthic habitat in a subtidal rocky reef ecosystem

Range expanding species can have major impacts on marine ecosystems but experimental field based studies are often lacking. The urchin Centrostephanus rodgersii has recently undergone a southerly range expansion to the east coast of Tasmania, Australia. We manipulated densities of C. rodgersii and algal regrowth in urchin barrens habitat to test effects of the urchin on biotic interactions between two native herbivores, black-lip abalone (Haliotis rubra) and another urchin (Heliocidaris erythrogramma), and their benthic habitat. After 13 months, removals of only C. rodgersii resulted in overgrowth of barrens habitat by algae and sessile invertebrates. Densities of abalone increased (+92 %) only in patches from which C. rodgersii was removed and algal regrowth allowed. In contrast, densities of H. erythrogramma increased in all treatments (+45, +28, +25 %) in which C. rodgersii was removed, irrespective of the algal regrowth manipulations. These results suggest that C. rodgersii has a negative influence on the densities of abalone through competition for food and on densities of H. erythrogramma through competition for preferred habitat. Densities of abalone (+65 %) but not H. erythrogramma (+25 %), were lower in the patches from which C. rodgersii and canopy algae regrowth were removed relative to patches from which only C. rodgersii was removed (+92 and +28 %, respectively). These results suggest that C. rodgersii overgrazing of canopy-algae results in loss of structural complexity which could increase abalone susceptibility to predation, cause abalone to seek shelter in cryptic microhabitats and/or prevent their return to patches where canopy algae are absent. The ongoing spread of C. rodgersii and expansion of barrens habitat in eastern Tasmania will continue to negatively affect populations of these two native herbivores and their associated fisheries at a range of spatial scales. This example shows that habitat modifying species which become highly invasive can have disproportionate negative impacts on the structure and dynamics of the recipient community.

Succession and accrual of benthic algae on cobbles of an upland river following scouring

Flow releases from dams can be used to scour benthic algae, simulating the effects of natural spates and maintaining benthic algae in an early successional stage for increased grazer palatability. The timing of releases needs to consider the natural periodicity of flow events and the speed of regrowth and community succession changes. We studied benthic algal regrowth and succession using manipulative field experiments during summer and winter in the upland regulated Severn River, New South Wales, Australia. Benthic algal biomass accrual as chlorophyll a and community changes were determined after artificially scoured cobbles were returned to the river. In summer, algal biomass and diversity on scoured cobbles took 2 weeks to return to levels similar to reference cobbles and 5 weeks in winter. Chlorophyll a during summer was initially 0.24 ± 0.06 mg m−2 on scoured cobbles, but by day 16 had increased to 9.74 ± 1.97 mg m−2 and was no longer significantly different from reference cobbles. In winter, chlorophyll a was initially 0.47 ± 0.13 mg m−2 on scoured cobbles, but by day 37 had increased to 44.7 ± 10.9 mg m−2 and was no longer significantly different from reference cobbles. Peak chlorophyll a accrual during summer and winter was 1.64 and 2.63 mg m−2 d−1, respectively. Early succession in both experiments was dominated by diatoms such as Cocconeis, Synedra, and Fragilaria. A proliferation of the filamentous green alga Stigeoclonium was indicative of a late succession community. The implications for flow management based on resetting of benthic algae by scouring in riffle reaches of rivers are discussed.

Pathways for algal recolonization in seasonally‐flowing streams

Summary1. In semi‐arid climates, seasonally‐flowing streams provide most of the water required for human use, but knowledge of how water extraction affects ecological processes is limited. Predicted alterations in stream flows associated with the impacts of climate change further emphasize the need to understand these processes. Benthic algae are an important base for stream food webs, but we have little knowledge of how algae survive dry periods or respond to altered flow regimes.2. We sampled 19 streams within the Grampians National Park, south‐eastern Australia and included four components: a survey of different drought refuges (e.g. permanent pools, dry biofilm on stones and dry leaf packs) and associated algal taxa; a survey of algal regrowth on stones after flows recommenced to determine which refuges contributed to regrowth; reciprocal transplant experiments to determine the relative importance of algal drift and regrowth from dry biofilm in recolonization; direct measurement of algal drift to determine taxonomic composition in relation to benthic assemblage composition.3. Algae showed little specificity for drought refuges but did depend on them; no species were found that were not present in at least one of the perennial pool, dry biofilm or leaf pack refuges. Perennial pools were most closely correlated with the composition of algal assemblages once flows resumed, but the loss or gain of perennial pools that might arise from stream regulation is unlikely to affect the composition of algal regrowth. However, regulated streams were associated with strong increases in algal density in dry biofilm, including increased densities of Cyanobacteria.4. A model for algal recolonization in seasonally‐flowing streams identified three pathways for algal recolonization (drift‐dependent, dry biofilm‐dependent and contributions from both), depending on whether streams are diatom‐dominated or dominated by filamentous algae. The model predicted the effects of changes to stream flow regimes on benthic algal recolonization and provides a basis for hypotheses testable in streams elsewhere.

Herbivory, current velocity and algal regrowth: how does periphyton grow when the grazers have gone?

Summary1. An experiment conducted in streamside channels was used to document the regrowth of grazed periphyton. Our objective was to determine the relative importance of current velocity, grazing duration, and grazer type in shaping the trajectory of algal and periphytic regrowth.2. The grazing mayflies Baetis bicaudatus and Epeorus longimanus were used alone and in combination to create three grazing treatments at slow, medium and fast current (2–5, 15–20 and 30–40 cm s−1, respectively). Duration treatments consisted of 2, 4, 6, 8, 10 days of grazing. Chlorophyll a and ash‐free dry mass (AFDM) accumulation on grazed tiles was measured (as periphytic AFDM and chlorophyll a, respectively) at 2, 4, 6, 8 and 10 days following the removal of grazers.3. Chlorophyll a and AFDM was best predicted by interactions between current velocity, grazing duration and regrowth time.4. The two grazer species did not differ in their effect on Chlorophyll a and AFDM during the period of periphytic regrowth that followed grazing.5. Longer grazing duration reduced periphytic biomass, but also accelerated algal regrowth, and this growth enhancement was more pronounced at slower current velocities.6. Data from this study suggest that herbivory can have important historical effects on periphytic accrual.

Drought refuges affect algal recolonization in intermittent streams

AbstractDrought refuges enable the biota of intermittent streams to survive dry periods, but their roles in sustaining algal assemblage structure and productivity are not known. This study determined the importance of two types of drought refuge (dry biofilm, permanent pools) for benthic algal regrowth in four intermittent streams in the Grampians National Park, Victoria, Australia. Dry biofilm was removed by scrubbing randomly chosen stones from two dry riffles in each of two streams with permanent pools and two streams without permanent pools. Algae were sampled from scrubbed and control stones at one, six and sixteen weeks after flow resumed. Removal of dry algal biofilm resulted in lower algal densities on stones from both stream types, and scrubbed stones had similar densities of algae after one week, regardless of the presence or absence of permanent pools. Algal density on stones exposed to both refuge types was more than an order of magnitude higher than the density on stones exposed to either one or neither refuge. The effects of biofilm removal on algal density were still apparent after six weeks of flow and assemblage composition differed between streams with and without permanent pools. Dry biofilm was an important drought refuge for algae in both stream types, but epilithic algal density in streams with permanent pools developed more rapidly than streams that were completely dry over summer. Loss of permanent pools from intermittent streams due to water abstraction may substantially reduce algal productivity after flow resumes, which may limit the supply of autochthonous carbon. Copyright © 2004 John Wiley & Sons, Ltd.

Grazer Control of Stream Algae: Modeling Temperature and Flood Effects

A computer model for epilithic algae and grazer biomass in streams is modified to better predict the effects of temperature and is calibrated for diatoms and mayflies. Mayflies are predicted to maintain low diatom biomass provided that (1) temperatures remain within their preferred range (10-207C); and (2) mayfly populations are not adversely affected by floods. Algal blooms are predicted to occur in mayfly-dominated streams above 207C—temperatures common in pasture streams over summer. We hypothesize that mobile bed streams are susceptible to blooms during summer low flows following floods because (1) they usually lack temperature tolerant snail grazers; and (2) mayfly recovery lags behind algal regrowth, and there is a short period when algae escape from ''top-down'' grazer control. Proliferations of periphytic algae (algal blooms) have been documented in a number of New Zealand rivers with stoney beds draining agricultural catchments (Biggs and Price 1987) and adversely affect ecosystem structure and function, river aesthetics, and some water uses. Most conspicuous are blooms of filamentous green algae, although proliferation of diatoms and blue-green algae are also of management concern. Algal blooms only occur sporadically, when the rates of accrual (au- totrophic fixation plus colonization) exceed the rates of loss (sloughing, flow disturbance, and consumption by grazers). Benthic macroinvertebrate grazers (principally aquatic in- sects) have a significant negative effect on algal biomass; for example, Welch et al. (1992) showed that 3,000 grazers m 22

Algal growth on building sandstones: effects of chemical stone cleaning methods

Abstract Biological growths including algae, lichens, bacteria, fungi and mosses are common on building sandstones wherever suitable conditions occur. Some growths, such as lichens, may be considered desirable since they can give a mature appearance to a facade, but others are often considered undesirable as they can be disfiguring and may lead to, or exacerbate, stone decay. The disfiguring of buildings and monuments by biological growths, particularly on recently cleaned buildings, is therefore a cause of some concern. Following stone cleaning, re-soiling from inorganic sources may take many years, however, re-soiling in the form of green algal growths may occur within only a few months. This paper reviews the factors which influence algal growth on building sandstone and summarizes the results of research into the effects of chemical stone cleaning with respect to algal re-growth. Results indicate that residues of some phosphate-rich stone cleaning chemicals can act as nutrients accelerating algal growth on vulnerable building sandstones.

Algal and Lichen Growth Following Chemical Stone Cleaning

Chemical cleaning methods have commonly been used to remove soiling from sandstone building facades. There has been anecdotal evidence suggesting that algal regrowth on facades can be increased following cleaning. It is shown here that both algal and lichen growths on sandstones may be substantially increased following chemical cleaning if the cleaning agents leave residues of phosphate (a nutrient normally in limited supply) in the sandstone. The growth of algae and lichens on samples of chemically-cleaned sandstones has been followed over five years. The effects of chemical residues with respect to biological growths were found to vary substantially depending on the characteristics of the sandstone. Phosphate may be chemically bound to iron compounds in sandstones. Iron-rich sandstones can therefore retain more residual phosphate than iron-poor sandstones. The duration of increased algal growth was found to vary from two years (iron-poor sandstone) to over five years (iron-rich sandstone). Where the sandstone was of low porosity and algal growth was consequently slow to become established, increased algal growth could be delayed until three years following cleaning. Lichens appeared to be stimulated by lower amounts of phosphate, and increased lichen growth was found to be of longer duration than increased algal growth. Biological growths can be disfiguring, may encourage soiling and some are capable of causing damage to stone. These results indicate that phosphate-bearing chemical cleaning methods should be used with caution on porous stone types in situations where biological growths could cause problems.