Phytoplankton ecology in the Southern Benguela current. I. Biochemical composition

Investigations on phytoplankton communities in a nearshore region off the Cape Peninsula revealed three types of upwelled water. During active upwelling temperatures were < 10 °C and concentrations of inorganic nutrients were high (Type 1). Maturing upwelled water was characterized by temperatures > 10°C and nitrate concentrations varying between 2 and 15 μg-at. NO₃-N · 1^?1 (Type 2), while aged upwelled water (Type 3) contained low concentrations of nitrate (<2 μg-at. NO₃-N · 1^?1) at temperatures > 10°C. During the summer of 1978–1979 diatoms dominated the communities from October to January but microflagellates were dominant in February and March. In both types of community, low concentrations of ATP, chlorophyll a, protein and carbohydrate were measured in Type 1 water with protein/carbohydrate ratios being > 1. In Type 2 water concentrations of chlorophyll a, ATP and protein were high and the protein/carbohydrate ratio was > 1. Concentrations of chlorophyll a and ATP remained high in Type 3 water but the protein/carbohydrate ratio decreased to < 1 due to an increase in the concentration of acid-soluble glucan. It was concluded that the communities were in an active phase of growth in Type 1 and Type 2 water when adequate nutrients were available, but were in a slow-growing phase in Type 3 water when nitrate concentrations were low. Correlation coefficients, simple linear regressions and stepwise multiple regressions between biochemical and environmental variables confirmed that nitrate was the nutrient most closely related to the biochemical composition of phytoplankton. Using linear regression equations of biochemical variables on glucan it was estimated that chlorophyll a existed in a ratio of ≈ 1: 1 between living phytoplankton and bacteria/detritus, while the percentage of ATP was high in the phytoplankton component of Type 1 water but low in that of Type 2 water. The percentage of protein in detritus was greater than in living phytoplankton, and the carbohydrate content of living phytoplankton increased as the upwelled water matured from Type 1 and Type 2 to Type 3.     

Physiological responses of phytoplankton communities in the Irish Sea to simulated upwelling

Understanding the dynamics of upwelling systems, especially the interactions between nutrients and light, has benefited from the application of models of varying complexity. Validation of such models using unialgal cultures or field observations has often proven difficult, but short-term incubations of contained natural assemblages and use of instantaneous physiological indicators offer an alternative approach. In May and June 1996, phytoplankton communities deep in the euphotic zone were sampled from nearly identical physical environments. Replicate samples (20 l volume) were incubated on deck at 50% surface irradiance with either no nutrient additions (Controls) or additions of 20 μM nitrate (Enrichments). Over 24 h, variable fluorescence (F _v:F _m), nitrate reductase activity (NR), nutrients, chlorophyll a and particulate C and N were monitored. Initial chlorophyll a (～3 μg l^?1), phosphate (～0.2 μM), nitrate (～1.5 μM) and silicate (～3 μM) were similar in both months. Changes in NR and F _v:F _m indicated clear physiological responses to changes in irradiance and added nitrate that differed between months. In May, Controls and Enrichments responded in the same way. F _v:F _m stayed constant (0.5), chlorophyll a increased slightly, and NR activity increased markedly in all samples. In contrast, in June, treatments responded quite differently. F _v:F _m was near the theoretical maximum (0.7–0.8) initially and remained constant in Enrichments, but fell sharply in Controls. Declines in controls were also seen for chlorophyll a, and NR activity. Thus, the addition of 20 μM nitrate had a significant effect even though ambient levels of nitrate (>1 μM) should not have been limiting. Small (<20 μm) flagellates predominated in the May samples, but in June large and chain-forming centric diatoms constituted a significant proportion of the phytoplankton community. We conclude that the response of a phytoplankton community to environmental changes can depend on factors that are poorly represented by bulk measurements of chlorophyll, nutrients and particulate elements.     

Effects of glaciers on nutrient concentrations and phytoplankton in lakes within the Northern Cascades Mountains (USA)

We compared nitrate concentrations, phytoplankton biomass, and phytoplankton community structure in lakes fed by glacier melt and snowmelt (GSF lakes) and by snowmelt only (SF lakes) within North Cascades National Park (NOCA) in Washington State, USA. In the U.S. Rocky Mountains, glacier melting has greatly increased nitrate concentrations in GSF lakes (52–236 µg NO₃–N L^?1) relative to SF lakes (1–14 µg NO₃–N L^?1) and thereby stimulated phytoplankton changes in GSF lakes. Considering NOCA contains approximately one-third of the glaciers in the continental U.S., and many mountain lakes that receive glacier meltwater inputs, we hypothesized that NOCA GSF lakes would have greater nitrate concentrations, greater phytoplankton biomass, and greater abundance of nitrogen-sensitive diatom species than NOCA SF lakes. However, at NOCA nitrate concentrations were much lower and differences between lake types were small compared to the Rockies. At NOCA, nitrate concentrations averaged 13 and 5 µg NO₃–N L^?1 in GSF and SF lakes, respectively, and a nitrate difference was not detectable in several individual years. There also was no difference in phytoplankton biomass or abundance of nitrogen-sensitive diatoms between lake types at NOCA. In contrast to the Rockies, there also was not a significant positive relationship between watershed percent glacier area and lake nitrate at NOCA. Results demonstrate that biogeochemical responses to global change in Western U.S. mountain lake watersheds may vary regionally. Regional differences may be affected by differing nitrogen deposition, climate, geology, or microbial processes within glacier environments, and merit further investigation.     

The past and future of phytoplankton in the UK's largest lake,Lough Neagh

Lough Neagh is the largest lake in the UK and has been extensively monitored since 1974. It has suffered from considerable eutrophication and toxic algal blooms. The lake continues to endure many of the symptoms of nutrient enrichment despite improvements in nutrient management throughout the catchment, in particular a permanently dominant crop of the cyanobacterium Planktothrix agardhii. This study examines the historical changes in the Lough, and uses the PROTECH lake model to predict how the phytoplankton community may adapt in response to potential future changes in air temperature and nutrient load. PROTECH was calibrated against 2008 observations, with a restriction on the maximum simulated mixed depth to reflect the shallow nature of the lake and the addition of sediment released phosphorus throughout the mixed water column between 1 May and 1 October (with an equivalent in-lake concentration of 2.0 mg m⁻³). The historical analysis showed that phytoplankton biomass (total chlorophyll a) experienced a steady decline since the mid-1990s. During the same period the key nutrients for phytoplankton growth in the lake have shown contrasting trends, with increases in phosphorus concentrations and declines in nitrate concentrations. The modelled future scenarios which simulated a temperature increase of up to 3 °C showed a continuation of those trends, i.e. total chlorophyll a and nitrate concentrations declined in the surface water, while phosphorus concentrations increased and P. agardhii dominated. However, scenarios which simulated a 4 °C increase in air temperature showed a switch in dominance to the cyanobacteria, Dolichospermum spp. (formerly Anabaena spp.). This change was caused by a temperature related increase in growth driving nutrient consumption to a point where nitrate was limiting, allowing the nitrogen-fixing Dolichospermum spp. to gain sufficient advantage. These results suggest that in the long term, one nuisance cyanobacteria bloom may only be replaced by another unless the in-lake phosphorus concentration can be greatly reduced.     

Impact of DOC trends resulting from changing climatic extremes and atmospheric deposition chemistry on periphyton community of a freshwater tropical lake of India

Recent measurements have demonstrated unprecedented increase in atmospheric deposition of nutrients in many parts of India. To determine whether atmospheric nutrient inputs would increase phytoplankton growth and catchment dissolved organic carbon (DOC) flushing to constrain benthic algae, we analyzed NO₃ ^? and PO ₄ ^?3 in atmospheric deposits; nutrients and DOC in runoff and lake water and standing crop biomass of phytoplankton and periphyton at Jaisamand Lake of Rajasthan, India. Atmospheric deposition of NO₃ ^? (7.18–29.95 kg ha^?1 year^?1) and PO ₄ ^?3 (0.56–2.15 kg ha^?1 year^?1) showed a consistently rising trend across the year. Microbial biomass and activity in catchment increased in response to atmospheric deposition. Lake DOC and nutrients showed strong coherence with their terrestrial and atmospheric fluxes. Phytoplankton development showed significant linearity with atmospheric input of nutrients. Air-driven input appeared to have compensated the nutrient constraints to phytoplankton during drought. The N:P stoichiometry of deposition and that of lake water indicated that, although there was a seasonal switchover to N- or P-limitation, phytoplankton were mainly co-limited by N and P due probably to the synergistic effects of combined N + P enrichment in the pelagic zone of the lake. Periphyton standing crop showed inverse relationship with phytoplankton and lake DOC. The study indicated that enhanced phytoplankton development and terrestrial DOC flushing in response to atmospheric nutrient input attenuated light penetration to constrain algal periphyton. We suggests that data on these issues may be considered in developing aquatic ecosystem models to establish future links between changing air–water–land interactions and associated shifts in lake ecosystem functioning for more accurately predicting climate change drivers and designing integrated lake basin management strategies.     

Phytoplankton ecology of Loch Achray (Scotland)

Loch Achray is a warm monomictic lake in the Scottish highlands with water temperature ranging from 4 °C to 18.7 °C. The oxygen distribution is mainly clinograde with saturation values ranging from 76 to 112%. The general pattern of nutrient variation is irregular particularly for phosphate. Dissolved silica (measured as silicate) showed a range of 24 μg at. Si l⁻¹; phosphate varied from 0.24 to 0.03 μg at. P l⁻¹ while nitrate ranged from 3.5 to 15.2 μg at. N l⁻¹. The pH remained below 7 for the entire year and the alkalinity was very low, ranging from 2.5 to 6 mg CaCO₃ 1⁻¹. The examination of net samples showed Loch Achray to possess a poor phytoplankton population, consisting mainly of desmids and a few diatoms. The quantitative investigation showed a different picture of variation. There was no clear phytoplankton increase till May when a simultaneous increase occurred involving Melosira, Asterionella, Tabellaria fenestrata and Cyclotella. In July the population was dominated by Anabaena, while Cyclotella and Staurastrum became dominant in August.     

Dust mediated transfer of phosphorus to alpine lake ecosystems of the Wind River Range,Wyoming, USA

Alpine lakes receive a large fraction of their nutrients from atmospheric sources and are consequently sensitive to variations in both the amount and chemistry of atmospheric deposition. In this study we explored the spatial changes in lake water chemistry and biology along a gradient of dust deposition in the Wind River Range, Wyoming. Regional differences were explored using the variation in bulk deposition, lake water, sediment, and bedrock geochemistry and catchment characteristics. Dust deposition rates in the Southwestern region averaged 3.34 g m^?2 year^?1, approximately three times higher than deposition rates in the Northwestern region (average 1.06 g m^?2 year^?1). Dust-P deposition rates ranged from 87 µg P m² day^?1 in the Northwestern region to 276 µg P m² day^?1 in the Southwestern region. Subalpine and alpine lakes in the Southwestern region had greater total phosphorus (TP) concentrations (5–13 µg L^?1) and greater sediment phosphorus (SP) concentrations (2–5 mg g^?1) than similar lakes elsewhere in the region (1–8 µg L^?1 TP, 0.5–2 mg g^?1 SP). Lake phosphorus concentrations were related to dissolved organic carbon (DOC) across vegetation gradients, but related to the percent of bare rock, catchment area to lake area, and catchment steepness across dust deposition gradients. Modern phytoplankton and zooplankton biomasses were two orders of magnitude greater in the Southwest than in the Northwest, and alpine lakes in the Southwest had a unique diatom species assemblage with relatively higher concentrations of Asterionella formosa, Pseudostaurosira pseudoconstruens, and Pseudostaurosira brevistriata. These results suggests that catchment controls on P export to lakes (i.e. DOC) are overridden in dominantly bare rock basins where poor soils cannot effectively retain dust deposited P.     

The phytoplankton of Lake Atnsjøen, Norway – a long-term investigation

Quantitative samples were collected from Lake Atnsjøen five times per year in the growth seasons 1990–2000. The samples were analysed for variation in the phytoplankton composition, and the total volume and volume of the main groups of algae were calculated. Lake Atnsjøen is a large, deep and unregulated lake with a surface area of 4.8 km² and a maximum depth of 80.2 m. It is a nutrient-poor, oligotrophic lake with a maximum phytoplankton volume varying between 125–393 mm³/m³ in the years 1990–2000. The phytoplankton community is dominated by species of the groups Chrysophyceae and Cryptophyceae. The chrysophytes dominate the phytoplankton in the early part of the growth season (May–June) while the cryptophytes increase throughout the season and dominate in the autumn. Among the chrysophytes different species of chrysomonads were most frequent together with common species of the genus Dinobryon like D. borgei, D. cylindricum var. alpinum and D. crenulatum. A total of 22 species or taxa of chrysophytes were recorded in the samples. Common among the cryptomonads were several species of the genus Cryptomonas. Most important quantitatively, however, were Rhodomonas lacustris and Katablepharis ovalis. The succesion of the phytoplankton throughout the growth season was similar from year to year in quantitative as well as qualitative terms, but some changes were recorded after the great flood in 1995. Canonical Correspondence Analysis (CCA) shows a slight, but significant, phytoplankton community change over the succeeding years.     

Statistical analysis of phytoplankton biomass in coastal waters: Case study of the Wadden Sea near Lauwersoog (The Netherlands) from 2000 to 2009

As the most important indicator of the coastal ecosystem, various studies on phytoplankton have frequently been proposed in coastal waters. In this study, the statistical analysis of phytoplankton biomass (in terms of chlorophyll a) is performed in the Wadden Sea near Lauwersoog (53.4167° N, 6.2000° E), The Netherlands, determined by the 10-year's historical dataset from 2000 through 2009. Boxplot analysis is introduced to give insight in the seasonal variations of phytoplankton biomass and physical–chemical conditions. Annually, a big difference is found in chlorophyll a, showing that the maximum values occur in the months of April and July, and the minimum values occur in winter (December, January, and February). The phytoplankton biomass is positively correlated with the physical conditions (salinity, light intensity, and water temperature), and is negatively correlated with the nutrients (nitrate, ammonium, and silicate). Factor analysis distinguishes the driving variables that represent most of the total variance using three extraction methods (principal component analysis, unweighted least squares, and maximum likelihood). Nitrate dominates the main activity in the first rotated component/factor, and ammonium contributes the most in the second rotated component/factor. The findings of this study are significant for understanding the roles of the environmental conditions upon the phytoplankton variability, and for reducing the overlapping information to characterize the driving variables.     

At high temperature lipid production in Ettlia oleoabundans occurs before nitrate depletion

Temperature and light intensity effects on biomass and lipid production were investigated in Ettlia oleoabundans to better understand some fundamental properties of this potentially useful but poorly studied microalgal species. E. oleoabundans entered dormant state at 5 °C, showed growth at 10 °C, and when exposed to light at 70 μmol photons per square meter per second at 10 °C, cells reached a biomass concentration of >2.0 g?L^?1 with fatty acid methyl esters of 11.5 mg?L^?1. Highest biomass productivity was at 15 °C and 25 °C regardless of light intensity, and accumulation of intracellular lipids was stimulated by nitrate depletion under these conditions. Although growth was inhibited at 35 °C, at 130 μmol photons per square meter per second lipid content reached 10.37 mg?L^?1 with fatty acid content more favorable to biodiesel dominating; this occurred without nitrate depletion. In a two-phase temperature shift experiment at two nitrate levels, cells were shifted after 21 days at 15 °C to 35 °C for 8 days. Although after the shift growth continued, lipid productivity per cell was less than that in the 35 °C cultures, again without nitrate depletion. This study showed that E. oleoabundans grows well at low temperature and light intensity, and high temperature can be a useful trigger for lipid accumulation independent of nitrate depletion. This will prove useful for improving our knowledge about lipid production in this and other oleaginous algae for modifying yield and quality of algal lipids being considered for biodiesel production.     

Long-term nutrient trends and harmful cyanobacterial bloom potential in hypertrophic Lake Taihu,China

Rapid economic development in China’s Lake Taihu basin during the past four decades has accelerated nitrogen (N) and phosphorus (P) loadings to the lake. This has caused a shift from mesotrophic to hypertrophic conditions, symptomized by harmful cyanobacterial blooms (CyanoHABs). The relationships between phytoplankton biomass as chlorophyll a (Chla) and nutrients as total nitrogen (TN) and total phosphorus (TP) were analyzed using historical data from 1992 to 2012 to link the response of CyanoHAB potential to long-term nutrient changes. Over the twenty year study period, annual mean Chla showed significantly positive correlations with both annual mean TN and TP (P < 0.001), reflecting a strong phytoplankton biomass response to changes in nutrient inputs to the lake. However, phytoplankton biomass responded slowly to annual changes in TN after 2002. There was not a well-defined or significant relationship between spring TN and summertime Chla. The loss of a significant fraction of spring N loading due to denitrification likely weakened this relationship. Bioavailability of both N and P during the summer plays a key role in sustaining cyanobacterial blooms. The frequency of occurrence of bloom level Chla (>20 μg L^?1) was compared to TN and TP to determine nutrient-bloom thresholds. A decline in bloom risk is expected if TN remains below 1.0 mg L^?1 and TP below 0.08 mg L^?1.     

Grazing effects of a freshwater bivalve (Corbicula leana Prime) and large zooplankton on phytoplankton communities in two Korean lakes

This study examined the effects of a freshwater filter feeding bivalve (Corbicula leana Prime) and large zooplankton (>200 μm, mostly cladocerans and copepods) on the phytoplankton communities in two lakes with contrasting trophic conditions. A controlled experiment was conducted with four treatments (control, zooplankton addition, mussel addition, and both zooplankton and mussel addition), and each established in duplicate 10-l chambers. In both lakes there were significant effects of mussel grazing on phytoplankton density and biomass. The effects were greater in mesotrophic Lake Soyang than in hypertrophic Lake Ilgam. Effects of zooplankton grazing did not differ between these lakes, and zooplankton effects on phytoplankton were much less than the effects of mussels. Although mussels exerted a varying effect on phytoplankton according to their size, mussels reduced densities of almost all phytoplankton taxa. Total mean filtering rate (FR) of mussels in Lake Soyang was significantly greater than that in Lake Ilgam (p=0.002, n=5). Carbon fluxes from phytoplankton to mussels (977–2,379 μgC l^?1d^?1) and to zooplankton (76–264 μgC l^?1 d^?1) were always greater in Lake Ilgam due to the greater phytoplankton biomass (p<0.01, n=6). Based on the C-flux to biomass ratios, the mussels consumed 170–754% (avg. 412%) of phytoplankton standing stock in Lake Soyang, and 38–164% (avg. 106%) in Lake Ilgam per day. The C-flux to biomass ratio for mussels within each lake was much greater than for large zooplankton. Mussels reduced total phosphorus concentration by 5–34%, while increasing phosphate by 30–55% relative to the control. Total nitrogen also was reduced (by 9–25%), but there was no noticeable change in nitrate among treatments. The high consumption rate of phytoplankton by Corbicula leana even in a very eutrophic lake suggests that this mussel could affect planktonic and benthic food web structure and function by preferential feeding on small seston and by nutrient recycling. Control of mussel biomass therefore might be an effective tool for management of water quality in shallow eutrophic lakes and reservoirs in Korea.     

Seasonality of phytoplankton in subarctic Lake Saanajärvi in NW Finnish Lapland

We studied the phytoplankton seasonality in the subarctic Lake Saanajärvi, Finnish Lapland, in two successive years with slightly different weather conditions. The total number of taxa studied during the period was 148. Characteristic phytoplankton species were chrysophytes Uroglena sp., Chrysococcus spp., Dinobryon spp and diatoms Cyclotella spp. The results were analysed in relation to weather patterns and physico-chemical variables measured from the lake during the 2 years. The seasonal dynamics of phytoplankton were characterized by (1) maxima in total densities during autumn and minima in winter; (2) different species reaching maximum and minimum densities during different seasons; (3) close to equilibrium state during strong thermal stratification in 1997 with dominance of only a few taxa; and (4) two annual maxima in species diversity at the beginning of the thermal stratification and during the autumn overturn. According to canonical ordinations, calcium buffer capacity, nutrients and temperature all play a role in regulating algal biomass and species compositions. With regard to physical factors, the length of the mixing cycle, thermal stability of the water column and water temperature seem to have a major control over the plankton dynamics. The length of the ice-free season seems to be more decisive for biomass production than the thermal stability during this period, which, in turn, appears to affect the algal biodiversity.     

九龙江河口浮游植物的时空变动及主要影响因素

于2009年春（5月）、夏（8月）、秋（11月）在九龙江河口水域进行了水文、化学和生物的生态完全示范区综合外业调查,研究了九龙江河口浮游植物的种类组成、密度分布、季节变化、空间差异及主要影响因素,并结合前期资料分析了年际变动。结果表明,九龙江河口的浮游植物共记录7个门类75属134种。主体是硅藻,绿藻次之,甲藻和蓝藻较少,黄藻检出率高,裸藻和金藻零星检出。种类组成的空间差异大,绿藻在河口内区淡水水域比硅藻更占优势, 中肋骨条藻（Skeletonema costatum）、短角弯角藻（Eucampia zodiacus）、圆筛藻（Coscinodiscus spp.）、颗粒直链藻（Melosira granulata）、微小小环藻（Cyclotella. caspia）是河口区咸淡水水域及近海区的主要种类。浮球藻（Planktosphneria gelotinosa）、栅藻（Scenedesmus spp.）、盘星藻（Pediastrim spp.）、小席藻（Phormidium tenus）是河口内区淡水水域的主要种类。根据浮游植物的生态类型及其生境特征大致可分为三大类群。浮游植物密度夏季最高,平均为358.68103cells/L,密集中心的季节变化明显,密度分布由优势类群的密度分布决定。中肋骨条藻和短角弯角藻的数量庞大,导致优势种突出,多样性降低,种间分布不均匀,群落结构简单化。与史料比对,种类组成因淡水藻类的列入而更丰富,密度年际降低,中肋骨条藻仍是第一优势种,但优势度有较大降幅,优势类群有重大年际变化,细胞个体较小的种类占优。盐度和营养盐对浮游植物的分布及密度变化造成极大的时空差异,存在线性、复合线性、多项回归等复杂的相关关系。     

Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): the effect of nutrients,climate and the investigator on phytoplankton-based water quality indices

We analysed long-term changes in phytoplankton composition in relation to hydrological, meteorological and nutrient loading data in the large (270 km²) shallow (mean depth 2.8 m) Lake Võrtsjärv. Nutrient loads to the lake were heavy in the 1970s and 1980s and decreased considerably thereafter. The average nutrient concentrations for 1985–2004 (1.6 mg l^?1 of total nitrogen and 53 μg l^?1 of total phosphorus) characterize the lake as a eutrophic water body. All four calculated taxonomic indices showed a unidirectional deterioration of the lake’s ecological status, despite reduced concentrations of nutrients. We focused our analysis on the PTSI index, which revealed a stepwise change between the years 1977 and 1979 that coincided with a large increase in water level, but also with a change of investigator. After correcting input data for possible investigator-induced differences, the step change remained because it was caused by major changes in the whole phytoplankton community. The previous dominant Planktolyngbya limnetica was replaced by two species of seasonally altering Limnothrix. Among phytoplankton functional groups, there was a decrease in all groups comprising small-sized phytoplankton species, such as X1, E, F, J, N and an increase in S1 and H1, both represented by filamentous cyanobacteria. Our results suggest a non-linear response of phytoplankton to changing nutrient loadings, and that the change observed between 1977 and 1979 was a regime shift triggered by water level change. High shade tolerance of the new dominants, and their ability to create shade, obviously stabilized the new status making it resistant to restoration efforts.     

Photoprotective acclimation of micro- and nano-size phytoplankton assemblages in the Indian sector of the Southern Ocean

Phytoplankton in the mixed layer is exposed to increasing levels of light when transported to the surface layer of the ocean. The photoprotective response of natural assemblages of phytoplankton can differ among community structures. We investigated photoprotective acclimation and xanthophyll cycle pigments in size-fractionated natural phytoplankton assemblages during the austral summer in the Indian sector of the Southern Ocean. We estimated concentrations of phytoplankton pigments in the micro-size fractions (>20 μm) and nano-size fractions (2–20 μm) by subtracting concentrations in the <20 μm fractions from concentrations in the bulk samples, and by subtracting concentrations in the <2 μm fractions from concentrations in the <20 μm fractions, respectively. Changes in the ratios of the xanthophyll cycle pigments diadinoxanthin (DD) and diatoxanthin (DT) were determined at three optical depths in the mixed layer and during 48 h deck incubations under solar photosynthetically available radiation and ultraviolet radiation. Large variations in (DD + DT)/Chl a in the mixed layer (percent coefficient of variation >67 %) and in deck incubation bottles under variable light conditions (>75 % of the temporal variation) for the micro-size fractions suggest a higher potential for photoprotective acclimation than for the nano-size fractions. Decreases in DT/(DD + DT) with increases in the optical depth of the mixed layer (ζ _MLD) suggest that larger variations in light availability in the mixed layer might predict lower values of DT/(DD + DT) at the surface, regardless of cell size.     

Physiological and metabolic analysis of nitrate reduction on poly-gamma-glutamic acid synthesis in Bacillus licheniformis WX-02

Nitrate is an important nitrogen source for organism, but whether and how nitrate improves poly-γ-glutamic acid (γ-PGA) production of bacterial is not clear. The effect of nitrate on γ-PGA production of Bacillus licheniformis WX-02 was investigated. By addition of 50 mmol/L nitrate, the γ-PGA yield reached 12.3 ± 0.21 g/L, which increased 2.3-fold compared to the control. The mechanism of enhanced γ-PGA production was further investigated by analysis of nitrate reduction, physiology, pyruvate overflow metabolism and energy synthesis. Nitrate reduction was only carried out in the middle stage of γ-PGA fermentation. The result of consumption of nutrients showed that glucose uptake was not effected and the l-glutamic acid utilization efficiency increased from 48.3 to 77.0 %. The date of overflow metabolism obtained from high-performance liquid chromatography showed that the metabolism of pyruvate, formate, lactate and acetoin was both heightened by nitrate reduction, while the 2,3-butanediol biosynthesis was decreased. Meanwhile, the change of energy indicated that more ATP was synthesized during nitrate reduction. In summary, nitrate was a positive effector of γ-PGA biosynthesis in B. licheniformis WX-02 and nitrate reduction affected multi-metabolism pathways, including glycolysis, overflow metabolism and energy metabolism.     

Phytoplankton as a monitoring tool in a tropical urban shallow reservoir (Garças Pond): the assemblage index application

This study aimed at evaluating phytoplankton as a monitoring tool for water quality assessment in an urban shallow eutrophic reservoir considering temporal and vertical scales. Garças Reservoir is located in the Parque Estadual das Fontes do Ipiranga Biological Reserve (23°38′08″S and 23°40′18″S; 46°36′48″W and 46°38′00″W) that lies in the southeastern part of the Municipality of São Paulo, southeast Brazil. Samplings were carried out monthly during 8 consecutive years (1997–2004) following the water column vertical profile (5 depths: subsurface, 1, 2, 3 m and ~20 cm from the bottom). Abiotic variables analyzed were: water temperature, electric conductivity, DO, pH, total alkalinity, free CO₂, dissolved inorganic carbon, N series, P series and SiO₄H₄. Biological variables studied were: total density, total biomass and chlorophyll a, which were integrated arithmetically. At the beginning of the 8 year series, Garças Reservoir was an eutrophic ecosystem with 20% of its surface covered by Eichhornia crassipes (phase I: January 1997–March 1998). Water hyacinth reached 70% of pond surface coverage (phase II: April 1998–August 1999), and then it was mechanically removed (phase III: September 1999–December 2004). After this intervention, drastic alteration in the limnological features was detected, leading to the conclusion that removal of the aquatic macrophyte modified nutrient dynamics drastically reduced water transparency and led to photosynthetic productivity and phytoplankton biomass increase, the latter becoming a physical barrier to light penetration. Twenty one functional groups ‘sensu’ Reynolds were identified. Cyanobacteria contribution played the main role during the drastic alterations that occurred after water hyacinth removal. Results of ecological status of reservoir using Q index showed statistical difference among the 3 limnological phases (one way ANOVA; F = 119.4; P = 0.000). Regarding Q index classification, Garças Reservoir limnological phases were characterized as follows: (1) phase I: 0 ≥ Q ≤ 2.9, medium to bad; (2) phase II: 1.4 ≥ Q ≤ 3, tolerable to medium; and (3) phase III: 0 ≥ Q ≤ 1.5, bad to tolerable ecological states.