Seasonal variation in light utilisation,biomass production and nutrient removal by wastewater microalgae in a full-scale high-rate algal pond

There has been renewed interest in the combined use of high-rate algal ponds (HRAP) for wastewater treatment and biofuel production. Successful wastewater treatment requires year-round efficient nutrient removal while high microalgal biomass yields are required to make biofuel production cost-effective. This paper investigates the year-round performance of microalgae in a 5-ha demonstration HRAP system treating primary settled wastewater in Christchurch, New Zealand. Microalgal performance was measured in terms of biomass production, nutrient removal efficiency, light absorption and photosynthetic potential on seasonal timescales. Retention time-corrected microalgal biomass (chlorophyll a) varied seasonally, being lowest in autumn and winter (287 and 364 mg m^?3day^?1, respectively) and highest in summer (703 mg m^?3day^?1), while the conversion efficiency of light to biomass was greatest in winter (0.39 mg Chl- a per μmol) and lowest in early summer (0.08 mg Chl- a per μmol). The percentage of ammonium (NH₄–N) removed was highest in spring (79 %) and summer (77 %) and lowest in autumn (47 %) and winter (53 %), while the efficiency of NH₄–N removal per unit biomass was highest in autumn and summer and lowest in winter and spring. Chlorophyll-specific light absorption per unit biomass decreased as total chlorophyll increased, partially due to the package effect, particularly in summer. The proportional increase in the maximum electron transport rate from winter to summer was significantly lower than the proportional increase in the mean light intensity of the water column. We concluded that microalgal growth and nutrient assimilation was constrained in spring and summer and carbon limitation may be the likely cause.     

Rhizosphere effects on ion concentrations near different root zones of Norway spruce (Picea abies (L.) Karst.) and root types of Douglas-fir (Pseudotsuga menziesii L.) seedlings

In many temperate ecosystems, rates of atmospheric nitrogen deposition remain high over winter despite decreased agricultural activity over this season. The extent to which this nitrogen is accessible for plant growth over the following growing season may depend strongly on uptake by plants and soil microorganisms from late fall through early spring, when the majority of aboveground plant tissue has senesced. We added Ca(¹⁵NO₃)₂ (5 atom %¹⁵N) at a rate of 2 g m^?2 of N (corresponding to 100 mg ¹⁵N m^?2) to the surface of plots in a temperate old field during either late fall, winter, spring melt or early spring. We quantified the recovery of excess ¹⁵N in the soil microbial biomass and soil extracts following spring melt and in aboveground plant tissue at the peak of the plant growing season. Nitrate additions had no significant effect on total aboveground plant biomass, relative species abundance or percent tissue nitrogen. However, mean excess ¹⁵N in aboveground plant tissue varied significantly among treatments, with values of 8.1, 2.6, 0.3 and 7.3 mg m^?2 for late fall, winter, spring melt and early spring addition plots, respectively. Corresponding values of excess ¹⁵N were 3.1, 1.4 and 0.2 mg m^?2 in microbial biomass, and 0.17, 0.07 and 0.03 mg m^?2 in soil extracts, for late fall, winter and spring melt addition plots, respectively. Overall, these results indicate that nitrogen retention from late fall through early spring may depend highly on plant uptake in this system, and that only a small fraction of the nitrogen that accumulates in the winter snow pack may be available to plants.     

An analysis of long-term winter data on phytoplankton and zooplankton in Neusiedler See,a shallow temperate lake,Austria

In the last 40 years, the shallow steppe lake, Neusiedler See, was ice covered between 0 and 97 days. The North Atlantic Oscillation (NAO) as well as the Mediterranean Oscillation affected the lake and its conditions during winter. Both climate indices correlated negatively with the duration of ice cover and the timing of ice-out. Average winter phytoplankton biomass increased from less than 0.2 (0.05–0.84) mg FM l^?1 in the late 1960s/beginning of 1970s to 3.1 (1.72–5.61) mg FM l^?1 in the years 2001–2004. The increase in annual winter biomass of phytoplankton was associated with a significant shift in the composition of the algal assemblage. In the winter 1997/1998, diatoms contributed between 40 and 80% to the phytoplankton biomass while in 2006/2007 cyanoprokaryotes contributed 46%. Mean chlorophyll-a concentrations during winter were significantly correlated with those of total phosphorus (P_tot). Together with cold-water species (rotifer Rhinoglena fertöensis), perennial, eurythermal ones (copepod Arctodiaptomus spinosus) contributed to the zooplankton community. High zooplankton numbers were encountered when rotifers, particularly when densities of Rhinoglena fertöensis were high (r ² = 0.928). Zooplankton abundance and biomass varied from year to year but correlated positively with Chl-a (biomass ? r ² = 0.69; numbers ? r ² = 0.536). Winter zooplankton populations were primarily influenced by winter conditions, but in early winter also by survival of autumn populations, i.e., the more adults of Arctodiaptomus spinosus survived into winter, the higher was the zooplankton biomass in early winter. Phyto- and zooplankton dynamics in shallow lakes of the temperate region seem to critically depend on the biomass in autumn and on winter conditions, specifically on ice conditions and thus are related to climate signals such as the NAO.     

Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan

Winter phytoplankton communities in the shallow alkaline pans of Hungary are frequently dominated by picoeukaryotes, sometimes in particularly high abundance. In winter 2012, the ice-covered alkaline Zab-szék pan was found to be extraordinarily rich in picoeukaryotic green algae (42–82 × 10⁶ cells ml^?1) despite the simultaneous presence of multiple stressors (low temperature and light intensity with high pH and salinity). The maximum photosynthetic rate of the picoeukaryote community was 1.4 μg C μg chlorophyll a ^?1 h^?1 at 125 μmol m^?2 s^?1. The assimilation rates compared with the available light intensity measured on the field show that the community was considerably light-limited. Estimated areal primary production was 180 mg C m^?2 d^?1. On the basis of the 18S rRNA gene analysis (cloning and DGGE), the community was phylogenetically heterogeneous with several previously undescribed chlorophyte lineages, which indicates the ability of picoeukaryotic communities to maintain high genetic diversity under extreme conditions.     

Phytoplankton blooms under dim and cold conditions in freshwater lakes of East Antarctica

The seasonal variations of limnological (water temperature, light availability, turbidity, and chlorophyll a concentration) parameters were recorded continuously from January 2004 to February 2005 at two freshwater lakes: Oyako-ike and Hotoke-ike, Sôya Coast, East Antarctica. Water was in a liquid phase throughout the year, with temperatures ranging from 0 to 10°C. The maximum photosynthetically active radiation in Lake Oyako-ike was 23.16 mol m^?2 day^?1 (at 3.8 m) and Hotoke-ike was 53.01 mol m^?2 day^?1 (at 2.2 m) in summer, and chlorophyll a concentration ranged from ca. 0.5 to 2.5 μg L^?1 (Oyako-ike) and from ca. 0.1 to 0.8 μg L^?1 (Hotoke-ike) during the study period. Increase in chlorophyll a fluorescence occurred under dim-light conditions when the lakes were covered with ice in spring and autumn, but the signals were minimum in ice-free summer in both the lakes. During spring and summer, as a result of decreasing snow cover, the chlorophyll a concentration similarly decreased when PAR was relatively high, following periods of heavy winds. The autumnal and spring increase occurred under different PAR levels (ca. 20-fold and 90-fold stronger, respectively, in autumn in both the lakes). Differences in the autumn and spring increases suggest that the spring algal community is more shade-adapted than the autumn algal community. Antarctic phytoplankton appears especially adapted to low-light levels and inhibited by strong light regimes.     

Population dynamics and production of the small copepod Oithona spp. in a subarctic fjord of West Greenland

The small cyclopoid copepod Oithona is widely occurring in polar areas; however, knowledge of its biology and ecology is very limited. Here, we investigate the population dynamics, vertical distribution, and reproductive characteristics of Oithona spp. from late winter to summer, in a subarctic fjord of West Greenland. During winter–early spring, the abundance of Oithona spp. was low (1.8 × 10³ ind. m^?2) and the population was mainly composed of late copepodites and adults, whereas in summer, abundance peaked and younger stages dominated (1.1 × 10⁶ ind. m^?2). In general, all stages of Oithona spp. remained in the upper 100 m, with nauplii exhibiting a shallower distribution. Although no general seasonal migration was found, a deeper distribution of the adult females in winter was observed. The mean clutch size of Oithona spp. varied from 16 to 30 eggs per female, peaking in summer. Egg production rates (EPR) were low in winter–early spring (0.13 ± 0.03 eggs female^?1 day^?1) and reached maximum values in summer (1.6 ± 0.45 eggs female^?1 day^?1). EPR of Oithona spp. showed a significantly positive relationship with both temperature and protozooplankton biomass, and the development of the population seemed to be appreciably affected by temperature. Oithona spp. remained active throughout the study, stressing the key importance of these small copepods in high-latitude ecosystems, especially in periods when larger copepods are not present in the surface layer.     

Sea ice microbial dynamics over an annual ice cycle in Prydz Bay, Antarctica

Microbial community dynamics within the fast sea ice of Prydz Bay (68°S?78°E) were investigated over an annual cycle at two sites (1 and 3?km offshore) between April and November 2008. There are few long-term sea ice studies, and few that cover the phase of winter darkness when autotrophic processes are curtailed. Mean chlorophyll a concentrations in the ice column ranged between 0.76 and 44.8?μg?L^?1 at the 1-km site (Site 1) and 3.11–144.6?μg?L^?1 at the 3-km site (Site 2). Highest chlorophyll a usually occurred at the base of the ice. Bacterial concentrations ranged between 0.30 and 2.08?×?10⁸?cells?L^?1, heterotrophic nanoflagellates (HNAN) between 0.21?×?10⁵ and 2.98?×?10⁵?cells?L^?1 and phototrophic nanoflagellates (PNAN) 0–1.06?×?10⁵?cells?L^?1. While HNAN occurred throughout the year, PNAN were largely absent in winter. Dinoflagellates were a conspicuous and occasionally an abundant element of the community (maximum 17,460?cells?L^?1), while ciliates were sparse. The bacterial community showed considerable morphological diversity with a dominance of filamentous forms. Bacterial production continued throughout the year ranging between 0 and 22.92?μg?C?L^?1?day^?1 throughout the ice column. Lowest rates occurred between late June and early August. The sea ice sustained an active and diverse microbial community through its annual extent. The data suggest that during winter darkness the microbial community is dominated by heterotrophic processes, sustained by a pool of dissolved organic carbon.     

Changes in Ecosystem Function Across Sedimentary Gradients in Estuaries

The input of terrestrial silt and clay (hereafter mud) into coastal environments can alter sediment grain size distribution affecting the structure and functioning of benthic communities. The relationship between sediment mud content and macrofaunal community structure has been well documented, but not the effects on ecosystem function. In 143 plots from the mid-intertidal sites in 9 estuaries, we measured sediment properties, macrofaunal community composition and fluxes of O₂ and NH₄ ⁺ across the sediment–water interface to derive process-based measures of ecosystem function across the sand–mud gradient. We observed reductions in measures of macrofaunal diversity and decreases in the maximum density of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH₄ ⁺ efflux (NH₄ ⁺) and biomass standardized gross primary production (GPP_Chl-a ) also decreased with increasing mud content. Environmental predictors explained 34–39% (P = 0.005–0.01) of the total variation in ecosystem function in distance-based linear models. After partitioning out the effect of mud, A. stutchburyi abundance was positively correlated and explained 25 and 23% (P = 0.0001) of the variation of SOC and NH₄ ⁺, respectively. Also, mud content (negatively correlated) and temperature (positively correlated) explained 26% of variability in GPP_Chl-a (P = 0.0001). Our results highlight the importance of increased mud content and the associated reduction in the abundance of strongly interacting key species on the loss of ecosystem function in intertidal sand flats.     

Winter condition of marine plankton populations in Saanich inlet,B.C., canada. I. Phytoplankton and its surrounding environment

Weekly sampling was carried out in Saanich Inlet, British Columbia throughout the winter of 1975–1976. The surface water column was characterized by exposure to low solar radiation energy (<150 g cal·cm^?2 · day^?1), slight stratification with occasional vertical mixing, and abundant algal nutrients. Phytoplankton were mostly distributed above 5 m in the water column, with a fairly low biomass averaging <1 μgchla·1^?1. Dominant phytoplankton organisms were nanoflagellates occasionally accompanied by dinoflagellates as the second dominant. Centric diatoms, which were dominant in the blooms, were always present but less than a few percentage of the total phytoplankton biomass. Daily photosynthetic productivity was exclusively limited by available radiant energy. Low solar radiation and occasional mixing of the surface zone prohibited the centric diatoms from becoming dominant.     

Phytoplankton community composition and photosynthetic physiology in the Australian sector of the Southern Ocean during the austral summer of 2010/2011

Phytoplankton population dynamics play an important role in biogeochemical cycles in the Southern Ocean during austral summer. However, the relationship between phytoplankton community composition and primary productivity remains elusive in this region. We investigated the community composition and photosynthetic physiology of surface phytoplankton assemblages in the Australian sector of the Southern Ocean from December 2010 to January 2011. There were significant latitudinal variations in hydrographic and biological parameters along 110°E and 140°E. Surface (5 m) chlorophyll a (chl a) concentrations measured with high-performance liquid chromatography varied between 0.18 and 0.99 mg m^?3. The diatom contribution to the surface chl a biomass increased in the south, as estimated with algal chemotaxonomic pigment markers, while the contributions of haptophytes and chlorophytes decreased. In our photosynthesis–irradiance (P–E) curve experiment, the maximum photosynthetic rate normalized to chl a ( \(P_{ \hbox{max} }^{*}\) ), initial slope (α ^*), the maximum quantum yield of carbon fixation (Φ _{c max}), and the photoinhibition index (β ^*) were higher in the region where diatoms contributed >50 % to the chl a biomass. In addition, there were statistically significant correlations between the diatom contribution to the chl a biomass and the P–E parameters. These results suggested that the changes in the phytoplankton community composition, primarily in diatoms, could strongly affect photosynthetic physiology in the Australian sector of the Southern Ocean.     

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.     

Influence of suspended particulate matter on nutrient biogeochemistry of a tropical shallow lagoon,Chilika, India

The behaviour of suspended particulate matter (SPM), salinity profile, dissolved nutrients, total (T.Chl-a) and size fractionated chlorophyll-a (F.Chl-a) were studied seasonally at Chilika Lagoon, east coast of India, during 2008–2009. The study showed large spatio-temporal variations among these parameters. The concentration of dissolved inorganic nitrogen and inorganic phosphate were found to be maximum during the monsoon, followed by post- and pre-monsoon, although the mean N:P ratios, which indicate the relative availability of N with respect to P, were 9.13 ± 3.09, 16.57 ± 11.53 and 5.47 ± 3.13, respectively. It was evident from the results that during pre-monsoon and postmonsoon, the lagoon exhibits nitrogen limitation. Mean T.Chl-a biomass in the lagoon showed distinct seasonality with maximum values during the pre-monsoon (23.12 ± 9.75 mg m^?3) followed by monsoon and post-monsoon. Irrespective of seasons, maximum T.Chl-a was found in the northern part of the lagoon. SPM concentrations during the monsoon were relatively higher in the freshwater dominated zones compared to seawater dominated areas, indicating its riverine sources. The correlation between SPM and various dissolved nutrients (p < 0.05) suggests its influence on the physico-chemical conditions at varying levels. It is summarized that seasonal variation of SPM and nutrients contributed by rivers, wind induced re-suspension events and in situ  regeneration processes play a crucial role in the lagoon biogeochemical cycle.     

Structural variations of phytoplankton in the coastal seas of Yucatan,Mexico

A study was done of the relationship between hydrographic variables and the composition, abundance, community structure and biomass spectrums of coastal phytoplankton at scales greater than 100 km on the Yucatan Peninsula (SE Gulf of Mexico). This was done during the season of greatest environmental instability in the region, the northwind season (late fall to winter). Samples were collected at stations in the west (Campeche), north (Yucatan), and east (Quintana Roo) zones of the Peninsula. Measurements were taken of temperature, salinity, dissolved oxygen, dissolved inorganic nutrients (ammonia, nitrite, nitrate and phosphate) and chlorophyll a, and samples were taken for phytoplankton analysis. The hydrographic results showed the Campeche zone as having the lowest salinity (<35 psu) values, as well as the highest inorganic nutrient and chlorophyll a values, all of which are related to continental water contributions. The Yucatan zone had the lowest temperatures and the lowest inorganic nutrient values, indicating influence from the Yucatan Current and the Gulf of Mexico. A total of 159 phytoplankton species were identified, dominated by diatoms (>80%) and dinoflagellates. Phytoplankton exhibited greater concentration, richness, equitability and diversity in Campeche, while the lowest community structure values were had in the Quintana Roo zone. The ordination analysis demonstrated that the dominant genera were the diatoms Chaetoceros, Pseudonitzschia and Thalassionema. The biomass spectrums exhibited the lowest slope in environments of higher heterogeneity, with Campeche being the most disturbed and heterogeneous zone and Quintana Roo that with the least heterogeneity.     

Soil microbial community structure in European forests in relation to forest type and atmospheric nitrogen deposition

The objective of the present study was to evaluate the combined effect of vegetation and N deposition on microbial community composition in forest soils. For this, microbial biomass and community structure were assessed by ester linked fatty acid methyl ester (EL-FAME) analyses for 12 European forest sites representing different forest types (coniferous/deciduous) and differing in annual N loads (2?C40 kg?N?ha^?1). Microbial community composition was affected by vegetation as indicated by a higher proportion of the marker for arbuscular mycorrhiza (AM) fungi??16:1 11???in deciduous forest soils (1.2%?C5.7% of total EL-FAMEs) compared to acidic coniferous forest soils (0.5%?C1.6%). The two pine forest sites investigated showed the highest proportion of fungi (up to 28% of total EL-FAMEs) and the lowest proportions of Gram-negative and Gram-positive bacteria of all study sites. Nitrogen deposition rates were highly correlated with the ratios of cyclopropyl fatty acids to their precursors (r?=?0.82; P?<?0.01) and of bacteria to fungi (r?=?0.71; P?<?0.05). The two sites with the highest N deposition (??32.3 kg?N?ha^?1a^?1) were depleted in the marker fatty acids for AM fungi and other fungi. Our findings suggest that vegetation has a pronounced effect on microbial community structure, but this effect is masked by high N inputs (>30 kg?N?ha^?1a^?1).     

Harvest Date Effects on Biomass Yield,Moisture Content,Mineral Concentration,and Mineral Export in Switchgrass and Native Polycultures Managed for Bioenergy

Various local factors influence the decision of when to harvest grassland biomass for renewable energy including climate, plant composition, and phenological stage. However, research on biomass yield and quality related to a wide range of harvest timing from multiple environments and years is lacking. Our objective was to determine the effect of harvest timing on yield, moisture, and mineral concentration of switchgrass (Panicum virgatum L.) and native polyculture biomass. Biomass was harvested on 56 unique days ranging from late summer (2 September) to late spring (20 May) spanning 3 years (2009 to 2011) and seven sites in Minnesota, USA. Biomass yield varied considerably by location and year (range?=?0.7–11.7 Mg ha^?1) and was lowest during the winter. On average, there was no difference in biomass yield harvested in early fall compared to late spring. Biomass moisture content was lowest in late spring, averaging 156 g kg^?1 across all locations and years when harvested after 1 April. Biomass N concentration did not change across harvest dates; however, P and K concentrations declined dramatically from late summer to late spring. Considering the economic costs of replacing exported minerals and changes in revenues from biomass yield through time, biomass harvest should be conducted in late summer–early fall or late spring and avoided in winter. However, biomass managed for gasification should be harvested in spring to reduce concentrations of minerals that lead to slagging and fouling. Changes in biomass yield and quality through time were similar for switchgrass and native polyculture biomass. These biomass harvest recommendations are made from data spanning multiple years and locations and should be applicable to various growing conditions across the Upper Midwest.     

Spatiotemporal Variation of Bacterial Assemblages in a Shallow Subtropical Coastal Lagoon in Southern Brazil

A study on the bacterioplankton of Conceição Lagoon (27°34′ S–48°27′ W), Southern Brazil, was carried out in July 2005 (austral winter) and January 2006 (austral summer) to characterize the bacterial spatiotemporal distribution and to determine the heterotrophic and photoautotrophic bacterial dominance in hypoxic/oxic stratified waters. Bacterial abundance increased significantly (p?5 (winter) to 3.21?×?10⁶ cells mL^?1 (summer), heterotrophic coccus/rod-shaped (HCR) cells from 7.00?×?10⁴ to 3.60?×?10⁶ cells mL^?1, and heterotrophic filamentous (HF) bacteria from 2.90?×?10³ to 2.74?×?10⁵ cells mL^?1. Bacterial biovolumes also increased in summer with mean biovolumes of CCY ranging from 0.38 to 1.37 μm³, HCR cells from 0.31 to 1.12 μm³, and HF from 3.32 to 11.34 μm³. Principal component analysis showed that salinity, temperature, and light were the abiotic factors that better explained the temporal variability of bacterial assemblages. Bacterial heterotrophy dominated in the lagoon, excepted by the southern and part of central sector in January 2006, when autotrophic-dominated microbial community occurred. Spatially, bacterial assemblages were influenced by nutrient gradient, oxygen, and salinity with a positive relationship between biovolumes and nutrients and a negative relationship between abundance of coccus cyanobacteria and nutrients. area revealed a singular temporal pattern with hypoxic bottom waters in winter and oxygen-rich waters appearing in summer related with the availability of light and predominant microbes. Thus, oxygen consumption/production is likely to be regulated by the amount of light reaching the bottom, stimulating the production of oxygen by oxygenic phototrophs.     

Estimated copepod production rate and structure of mesozooplankton communities in the coastal Barents Sea during summer–autumn 2007

The southern Barents Sea is considered to be the most productive area in the Arctic Ocean; however, there are no assessments of daily production rates in the coastal waters. During the summer and autumn of 2007, we investigated the variation of mesozooplankton community structure relative to environmental conditions at 12 coastal stations. Copepods dominated the total zooplankton biomass and abundance during both periods. Diversity indices and the total biomass of zooplankton communities differed significantly between the two seasons. Cluster analyses revealed two distinct groups of stations which were associated with Ura Bay and the adjacent open sea, respectively. Daily production rates of the copepod species examined were calculated using three methods based on: (1) a temperature-dependent equation and (2) two multiple regressions that consider temperature, body weight, and chlorophyll a concentration. Significant seasonal differences for daily production rates were found using all three model equations (p?<?0.05): 358?±?188–1,775?±?791 versus 198?±?85–1,584?±?559?μg?dry?mass?m^?3?day^?1. Results of principal components analyses demonstrated that the abundance and biomass of herbivorous species were related to variation in chlorophyll a concentration while the abundance and biomass of other species (omnivorous copepods and Ctenophora) were related mainly with water temperature and salinity. Mesozooplankton biomass was higher during this study relative to previous studies. Computed copepod production rates were higher compared with other Arctic seas confirming a high productive potential of the coastal southern Barents Sea.     

Seasonal Dynamics of Mesozooplankton in Brazilian Coastal Waters

The composition, numerical abundance and seasonal distribution of mesozooplankton, in addition to copepod biomass, were studied in the São Sebastião Channel (SSC) during different seasonal periods and hydrographic regimes. Two stations were sampled every 3 months from January 1996 to July 1997 and also in July 1998 and January 1999. Temporal differences in oceanographic conditions in the SSC were observed; there was clear seasonal variation in the thermohaline structure. Phytoplankton composition, standing-stock and biomass also showed consistent seasonal variation, peaking during summer due to advection of cold and nutrient-rich South Atlantic Central Water (SACW). Sixty-nine mesozooplankton taxa were identified and counted. Mesozooplankton density also increased during summer, ranging from 93 to 12,774 ind  m^?3. In contrast, a unimodal peak of copepod biomass was recorded during winter and under the influence of the oligotrophic Coastal Water (CW), suggesting that copepod biomass at SSC is driven by resource control. There was no significant evidence of seasonal pattern in overall community composition or evidence of changes due to water mass advection. The mesozooplankton community was continuously dominated by coastal and warm-water species, particularly the copepods Acartia lilljeborgi, Paracalanus aculeatus, P. quasimodo, Parvocalanus crassirostris, Corycaeus giesbrechti and Oithona oswaldocruzi, the cladocerans Penilia avirostris and Evadne tergestina, in addition to the appendicularians Oikopleura longicauda and O. dioica, all of which are perennial species in the SSC. This taxonomic composition may represent an efficient biotic structure for rapid recycling of primary production during periods of SACW influence.     

Factors affecting biohydrogen production by unicellular halotolerant cyanobacterium Aphanothece halophytica

The effects of several physiological parameters on H₂ production rate in the unicellular halotolerant cyanobacterium Aphanothece halophytica were investigated. Under nitrogen deprivation, the growth of cells was inhibited, but H₂ production rate was enhanced approximately fourfold. Interestingly, cells grown under sulfur deprivation exhibited a decrease in cell growth, H₂ production rate, and bidirectional hydrogenase activity. Glucose was the preferred sugar source for H₂ production by A. halophytica, but H₂ production decreased at high glucose concentrations. H₂ production rate was optimum when cells were grown in the presence of 0.75 M?NaCl, or 0.4 μM?Fe³⁺, or 1 μM?Ni²⁺. The optimum light intensity and temperature for H₂ production were 30 μmol photons m^?2?s^?1 and 35 °C, respectively. A two-stage culture of A. halophytica was performed in order to overcome the reduction of cell growth in N-free medium. In the first stage, cells were grown in normal medium to accumulate biomass, and in the second stage, H₂ production by the obtained biomass was induced by growing cells in N-free medium supplemented with various chemicals for 24 h. A. halophytica grown in N-free medium containing various MgSO₄ concentrations had a high H₂ production rate between 11.432 and 12.767 μmol H₂ mg?chlorophyll a (chl a)^?1?h^?1, a 30-fold increase compared to cells grown in normal medium. The highest rate of 13.804 μmol H₂ mg?chl a ^?1?h^?1 was obtained when the N-free growth medium contained 0.4 μM Fe³⁺. These results suggested the possibility of using A. halophytica and some other halotolerant cyanobacteria thriving under extreme environmental conditions in the sea as potential sources for H₂ production in the future.     

The autumn mesozooplankton community at South Georgia: biomass, population structure and vertical distribution

Mesozooplankton were sampled at shelf and oceanic stations close to South Georgia, South Atlantic during austral autumn 2004 with a Longhurst Hardy Plankton Recorder. Onshelf biomass ranged from 2.18 to 5.75 g DM m^?2 (0–200 m) and was dominated by the small euphausiid Thysanöessa spp. At the oceanic stations (10.57–14.71 g DM m^?2, 0–1,000 m) large calanoids, principally Rhincalanus gigas comprised ～47–52% of biomass. Here Calanus simillimus was still active and reproducing in surface waters (0–11.2 eggs fem day^?1) but R. gigas and Calanoides acutus were largely resident in the warm deep water and undergoing their seasonal descent. A comparison with spring and summer data indicated increased abundance and biomass from spring through to summer followed by a decline towards autumn particularly over the shelf. Autumn values in oceanic waters differed little from summer. Mesozooplankton biomass in the surface 200 m of the oceanic stations as a proportion of that found in the top 1,000 m ranged from 63 to 78% of the total in spring and 62–73% in summer, but was only 23–29% of the total in this study, following redistribution down the water column.