The impact of physical processes on algal growth

Mixing and transport processes in surface waters strongly influence the structure of aquatic ecosystems. The impact of mixing on algal growth is species-dependent, affecting the competition among species and acting as a selective factor for the composition of the biocoenose. Were it not for the ever-changing ”aquatic weather”, the composition of pelagic ecosystems would be relatively simple. Probably just a few optimally adapted algal species would survive in a given water-body. In contrast to terrestrial ecosystems, in which the spatial heterogeneity is primarily responsible for the abundance of niches, in aquatic systems (especially in the pelagic zone) the niches are provided by the temporal structure of physical processes. The latter are discussed in terms of the relative sizes of physical versus biological time-scales. The relevant time-scales of mixing and transport cover the range between seconds and years. Correspondingly, their influence on growth of algae is based on different mechanisms: rapid changes are relevant for the fast biological processes such as nutrient uptake and photosynthesis, and the slower changes are relevant for the less dynamic processes such as growth, respiration, mineralization, and settling of algal cells. Mixing time-scales are combined with a dynamic model of photosynthesis to demonstrate their influence on algal growth.

ALGAL GROWTH POTENTIAL AND NUTRIENT LIMITATION IN SPRING IN THREE-GORGES RESERVOIR, CHINA

In China, especially in Three-Gorges Reservoir, our knowledge of the algal growth potential and nutrient limitation was still limited. In the spring of 2006, the water column ratios of total nitrogen/total phosphorus were investigated and algal bioassays performed to determine algal growth potential of waters and nutrient limitation of mainstream and Xiangxi Bay of Three-Gorges Reservoir. The results showed sampling sites in mainstream were co-limited by N and P or P-limited alone, and sites in Xiangxi Bay were N-limited alone. Fe likely played an important role in determining the appearance and disappearance of algal blooms of Three-Gorges Reservoir. Native algae, Pseudokirchneriella subcapitata and Cyclotella meneghiniana, had high growth potential in Three-Gorges Reservoir.

Nutrients limiting the Algal Growth Potential (AGP) in the Gulf of Riga, eastern Baltic Sea, in spring and early summer 1996

In May, June and July 1996, samples wcre collected along one transect greatly influenced by river discharge (eastern side of the gulf), along one transect slightly influence by river discharge (western side), at one station Iocated in the mouth of the main river (River Daugava), at one station located in the center of the Gulf and at several nearshore locations of the western side. Ratios of rnolecular concentrations of in situ dissolved ioorganic nitrogen, phosphorus and silicon, as weIl as enrichment bioassays were llsed to dctcrrnine which nutrient (s) lirnited the potential biomass of phytoplankton. Both comparison of (NO.d-N02+NJ.L): P04 (DIN: DIP) values with Redfic1d's ratio and bioassay inspection led to the sarne conclusions. Phosphorus was clearly the nutrient most limiting for the potcntial biornass of test species in nitrogen- rich waters, which occurred in mid spring, in the upper layer of the southern-eastern part of the Gulf which is greatly influenced by river discharge. In late spring, with the decrease of the total DIN reserve, nitrogen and phosphorus showed an equallimiting role. In deeper layers of this area and out of the river plume (western side and central part of the gulf), nitrogen was the limiting nutrient. In summer, whcn river discharge was the lowest, a11 DIN concentrations but one ranged between 1.6 and 2.6 µM, and the whole area was nitrogen-limited for both the cyanobacterial and the algal test strains. In 74% of the samples for which nitrogen was the limiting nutrient, phosphorus was recorded to be the second potentially limiting nutrient. In contrast, silicon never appeared as limiting the growth potential of either Microcystis aeruginosa or Phaeodactylum tricornutum; phosphorus was the limiting nutrient when DIN: Si03 values were >1 (in May), but DIN: Si03 was <1 when nitrogen was limiting (June and July). The authors conclude that the recently reported decrease of silicon loading in coastal waters and its subsequent enhanced importance in pushing the outcome of species competition towards harmful species may not yet be the most important factor for the Gulf of Riga. Iron appeared for 12% of the tests in the list of nutrients limiting the potential biomass. Tentative results also indicated that a significant fraction of the nitrogen (~,4 µg-atom N 1(-1) taken up by Microcystis aeruginosa may have been in the form of dissolved organic nitrogen (DON). It is thus also suggested tentatively that more attention be paid to these nitrients during further research in the Gulf of Riga.

Algal Photosynthetic Dynamics in Urban Lakes under Stress Conditions

Urban lakes form vital ecosystems supporting livelihood with social, economic and aesthetic benefits that are essential for quality life. This depends on the biotic and abiotic components in an ecosystem. The structure of an ecosystem forms a decisive factor in sustaining its functional abilities which include nutrient cycling, oxygen production, etc. A community assemblage of primary producers (algae) plays a crucial role in maintaining the balance as they form the base of energy pyramid in the ecosystem. Algae assimilate carbon in the environment via photosynthetic activities and releases oxygen for the next level of biotic elements in an ecosystem. Besides these, algal cells rich in protein serve as food and feed, used as manure and for production of biofuels. Understanding algal photosynthetic dynamics helps in assessing the level of dissolved oxygen (DO), food (fish, etc.), waste assimilation, etc. Algal chlorophyll content, algal biomass, primary productivity and algal photosynthetic quotient are some of the parameters that help in assessing the status of urban lakes. Chlorophyll content gives a measure of the growth, spread and quantity of algae. Unplanned rapid urbanization in Bangalore in recent times has resulted in either disappearance of lake ecosystems or deteriorated the lake water quality impairing the ecological processes. This paper computes algal growth, community structure, primary productivity and composition for three major lakes (T G Halli, Bellandur and Varthur lakes) under contrast levels of anthropogenic influences.

Algal biofuel: bountiful lipid from Chlorococcum sp proliferating in municipal wastewater

Algae biofuel have emerged as viable renewable energy sources and are the potential alternatives to fossil-based fuels in recent times. Algae have the potential to generate significant quantities of commercially viable biofuel apart from treating wastewater. Three algal species, viz. Chlorococcum sp., Microcystis sp. and Phormidium sp. proliferating in wastewater ponds were isolated and cultured in the laboratory myxotrophically under similar wastewater conditions. Chlorococcum sp. attained a mean biomass productivity of 0.09 g. I(-1)d(-1) with the maximum `biomass density of 1.33 g I-1 and comparatively higher lipid content of 30.55% (w/w) on the ninth day of the culture experiment. Under similar conditions Microcystis sp. and Phormidium sp. attained mean biomass productivities of 0.058 and 0.063 g I-1 d(-1) with a total lipid content of 8.88% and 18.66% respectively. Biochemical composition (carbohydrates, proteins, lipids and phosphates) variations and lipid accumulation studies were performed by comparison of the ratios of carbohydrate to protein; lipid to protein (L/P) and lipid to phosphates using attenuated total reflectance-Fourier transform infrared spectroscopy which showed higher L/P ratio during the stationary phase of algal growth. Composition analysis of fatty acid methyl ester has been performed using gas chromatography and mass spectrometry. Chlorococcum sp. with higher productivity and faster growth rate has higher lipid content with about 67% of saturated fatty acid dominated by palmitate (36.3%) followed by an unsaturate as linoleate (14%) and has proved to be an economical and viable feedstock for biofuel production compared to the other wastewater-grown species.

Effects of temperature on the threshold of phosphorus for algal blooms

Algal blooms, worsening marine ecosystems and causing great economic loss, have been paid much attention to for a long time. Such environmental factors as light penetration, water temperature, and nutrient concentration are crucial in blooms processes. Among them, only nutrients can be controlled. Therefore, the threshold of nutrients for algal blooms is of great concern. To begin with, a dynamic eutrophication model has been constructed to simulate the algal growth and phosphorus cycling. The model encapsulates the essential biological processes of algal growth and decay, and phosphorus regeneration due to algal decay. The nutrient limitation is based upon commonly used Monod's kinetics. The effects of temperature and phosphorus limitation are particularly addressed. Then, we have endeavored to elucidate the threshold of phosphorus at different temperature for algal blooms. Based on the numerical simulation, the isoquant contours of change rate of alga as shown in the figure are obtained, which obviously demonstrate the threshold of nutrient at an arbitrary reasonable temperature. The larger the change rate is, the more rapidly the alga grows. If the phosphorus concentration at a given temperature remains larger than the threshold the algal biomass may increase monotonically, leading to the algal blooming. With the rising of temperature, the threshold is apparently reduced, which may explain why likely red tide disasters occur in a fine summer day. So, high temperature and sufficient phosphorus supply are the major factors which result in algal growth and blowout of red tide.

Experiments using an artificial stream to investigate the seasonal growth of chalk-stream algae

Research into the production ecology of chalk streams using a large artificial recirculating stream is described. Physical chemical processes including calcium and inorganic phosphate levels, and exchange of gaseous carbon dioxide in both a simple closed system and a circulating system with gravel substrate have been monitored in both light and dark conditions. Further experiments were concerned with the seasonal changes in algal growth over the gravel substrate with constant water velocities and replenishment. The algal population, composed mainly of the diatoms Achnanthes minutissima, Meridion circulare, Nitzschia fonticola and Synedra ulna reached a peak in mid May and declined rapidly during June. Concentrations of phosphate phosphorus fell as the diatoms grew but was not thought to limit growth. Silicate concentrations followed the diatom cycle closely but never fell below 0.8 mg/l Si. It is possible that one of the nutrients may have been limiting the rate of growth due to steep diffusion gradients through the algal mat. In the last summer and autumn a hard calcareous crust composed of the green alga Gongrosira incrustans and the blue green alga Homeothrix varians , developed. The channel stream is compared with the natural conditions found in chalk streams.

Modelling algal blooms

This is the final report on the research project to develop predictive models to quantify algal blooms in relation to environmental variables. The project's objectives were to develop models simulating the impact of vertical structure and mass transfer upon the dynamics of planktonic algae, including cyanobacteria, in lakes and reservoirs, to assess the potential of sedimentary phosphorus to sustain algal growth following reduction in external loading and to expand and enhance formulations to predict behaviour of blue-green algal populations and to incorporate these into a model software package. As part of the project a strategy for the production of a user-friendly packaging for the modelling software PROTEC-2 adaptable to particular sites was developed.

Increased toxicity of Karenia brevis during phosphate limited growth: ecological and evolutionary implications

Karenia brevis is the dominant toxic red tide algal species in the Gulf of Mexico. It produces potent neurotoxins (brevetoxins [PbTxs]), which negatively impact human and animal health, local economies, and ecosystem function. Field measurements have shown that cellular brevetoxin contents vary from 1–68 pg/cell but the source of this variability is uncertain. Increases in cellular toxicity caused by nutrient-limitation and inter-strain differences have been observed in many algal species. This study examined the effect of P-limitation of growth rate on cellular toxin concentrations in five Karenia brevis strains from different geographic locations. Phosphorous was selected because of evidence for regional P-limitation of algal growth in the Gulf of Mexico. Depending on the isolate, P-limited cells had 2.3- to 7.3-fold higher PbTx per cell than P-replete cells. The percent of cellular carbon associated with brevetoxins (%C-PbTx) was ~ 0.7 to 2.1% in P-replete cells, but increased to 1.6–5% under P-limitation. Because PbTxs are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth. The %C-PbTx was inversely related to the specific growth rate in both the nutrient-replete and P-limited cultures of all strains. This inverse relationship is consistent with an evolutionary tradeoff between carbon investment in PbTxs and other grazing defenses, and C investment in growth and reproduction. In aquatic environments where nutrient supply and grazing pressure often vary on different temporal and spatial scales, this tradeoff would be selectively advantageous as it would result in increased net population growth rates. The variation in PbTx/cell values observed in this study can account for the range of values observed in the field, including the highest values, which are not observed under N-limitation. These results suggest P-limitation is an important factor regulating cellular toxicity and adverse impacts during at least some K. brevis blooms.

Effects of arsenate on the growth and microcystin production of Microcystis aeruginosa isolated from Taiwan as influenced by extracellular phosphate

Arsenic pollution and eutrophication are both prominent issues in the aquaculture ponds of Taiwan. It is important to study the effects of arsenic on algal growth and toxin production in order to assess the ecological risk of arsenic pollution, or at least to understand naturally occurring ponds. The sensitivity of algae to arsenate has often been linked to the structural similarities between arsenate and phosphate. Thus, in this study we examined the effects of arsenate (10(-8) to 10(-4) M) on Microcystis aeruginosa TY-1 isolated from Taiwan, under two phosphate regimes. The present study showed that M. aeruginosa TY-1 was arsenate tolerant up to 10(-4) M, and that this tolerance was not affected by extracellular phosphate. However, it seems that extracellular phosphate contributed to microcystin production and leakage by M. aeruginosa in response to arsenate. Under normal phosphate conditions, total toxin yields after arsenate treatment followed a typical inverted U-shape hormesis, with a peak value of 2.25 +/- 0.06 mg L-1 in the presence of 10(-7) M arsenate, whereas 10(-8) to 10(-6) M arsenate increased leakage of similar to 75% microcystin. Under phosphate starvation, total toxin yields were not affected by arsenate, while 10(-6) and 10(-5) M arsenate stimulated microcystin leakage. It is suggested that arsenate may play a role in the process of microcystin biosynthesis and excretion. Given the arsenic concentrations in aquaculture ponds in Taiwan, arsenate favors survival of toxic M. aeruginosa in such ponds, and arsenate-stimulated microcystin production and leakage may have an impact on the food chain.

Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions.

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions.

Effects of nonylphenol on the growth and microcystin production of Microcystis strains

Both organic pollution and eutrophication are prominent environmental issues concerning water pollution in the world. It is important to reveal the effects of organic pollutants on algal growth and toxin production for assessing ecological risk of organic pollution. Since nonylphenol (NP) is a kind of persistent organic pollutant with endocrine disruptive effect which exists ubiquitously in environments, NP was selected as test compound in our study to study the relationship between NP stress and Microcystis growth and microcystin production. Our study showed that responses of toxic and nontoxic Microcystis aeruginosa to NP stress were obviously different. The growth inhibition test with NP on M. aeruginosa yielded effect concentrations EbC50 values within this range of 0.67-2.96 mg/L. The nontoxic M. aeruginosa strains were more resistant to NP than toxic strains at concentration above 1 mg/L. Cell growth was enhanced by 0.02-0.2 mg/L NP for both toxic and nontoxic strains, suggesting a hormesis effect of NP on M. aeruginosa. Both toxic and nontoxic strains tended to be smaller with increasing NP. But with the increased duration of the experiment, both the cell size and the growth rate began to resume, suggesting a quick adaptation of M. aeruginosa to adverse stress. NP of 0.05-0.5 mg/L significantly promoted microcystin production of toxic strain PCC7820, suggesting that NP might affect microcystin production of some toxic M. aeruginosa in the field. Our study showed that microcystin excretion was species specific that up to 75% of microcystins in PCC7820 were released into solution, whereas > 99% of microcystins in 562 remained in algal cells after 12 days' incubation. NP also significantly influenced microcystin release into cultural media. The fact that NP enhanced growth and toxin production of M. aeruginosa at low concentrations of 0.02-0.5 mg/L that might be possibly found in natural freshwaters implies that low concentration of NP may favor survival of M. aeruginosa in the field and may play a subtle role in affecting cyanobacterial blooms and microcystin production in natural waters. (c) 2006 Elsevier Inc. All rights reserved.

Kinetic modelling of growth and storage molecule production in microalgae under mixotrophic and autotrophic conditions

In order to improve algal biofuel production on a commercial-scale, an understanding of algal growth and fuel molecule accumulation is essential. A mathematical model is presented that describes biomass growth and storage molecule (TAG lipid and starch) accumulation in the freshwater microalga Chlorella vulgaris, under mixotrophic and autotrophic conditions. Biomass growth was formulated based on the Droop model, while the storage molecule production was calculated based on the carbon balance within the algal cells incorporating carbon fixation via photosynthesis, organic carbon uptake and functional biomass growth. The model was validated with experimental growth data of C. vulgaris and was found to fit the data well. Sensitivity analysis showed that the model performance was highly sensitive to variations in parameters associated with nutrient factors, photosynthesis and light intensity. The maximum productivity and biomass concentration were achieved under mixotrophic nitrogen sufficient conditions, while the maximum storage content was obtained under mixotrophic nitrogen deficient conditions. © 2014 Elsevier Ltd.

Toxicity of cypermethrin on growth, pigments, and superoxide dismutase of Scenedesmus obliquus

Cypermethrin is a synthetic pyrethroid that is particularly toxic to crustaceans. It is therefore applied as a chemotherapeutant in farms for the treatment of pests. The effective concentrations of cypermethrin on the inhibition of Scenedesmus ohliquus growth at 96h (96h EC50) were determined to be 50, 100, 150, 200, and 250mg/L. Algal growth, pigment fractions, and the activity of superoxide dismutase (SOD) in the algal cells were measured in the exponential phase after exposure to cypermethrin. The results show that higher concentration of cypermethrin is inhibitory for growth and other metabolic activities and the 96h EC50 of cypermethrin to S. ohliquus is 112 +/- 9 mg/L; the potential application of SOD activity in S. ohliquus as a sensitive biomarker for cypermethrin exposure is also discussed. (C) 2004 Elsevier Inc. All rights reserved.