Assessing Biomass and Production of Bacteria in Eutrophic Lake Mendota, Wisconsin

Estimates were made of the biomass and production of heterotrophic bacteria in the epilimnion of Lake Mendota, Wis. Cell counts were done with epifluorescence microscopy and varied from 3 × 10⁵ bacteria per ml in winter to 3 × 10⁶ bacteria per ml in summer. Cell volumes were measured in scanning electron micrographs. The average cell volume was 0.159 μm³. Annual variations and depth distribution were studied. Production was estimated from the frequency of dividing cells and from dark radioactive sulfate uptake. Annual productivity and daily average productivity were very close with both methods: 107 to 205 g of C per m² per year for sulfate and 89 to 117 g of C per m² per year for frequency of dividing cells. Zooplankton feeding removed 2 to 10% of the bacterial net production annually. When compared with biomass changes and losses due to zooplankton feeding, production values were very high. Therefore, it was suggested that other loss factors have to be more important than zooplankton feeding in controlling the bacterial population. Bacterial heterotrophic production was about 50% of gross primary production.     

Periphyton production in an Appalachian river

Periphyton primary production was measured by ¹⁴C uptake on natural substrates in two sections of the New River, Virginia, U.S.A. Production ranged from 6.71 ± 0.43 mg C g^–1 h^–1 in summer to 1.47 ± 0.22 mg C g^–1 h^–1 in late autumn in the hardwater reach and from l.90 ± 0.10 mg C g^–1 h^–1 to 0.12 ± 0.08 mg C g^–1 h^–1 in the softwater reach. Production in the hardwater reach was 3–5 times greater than in the softwater reach and significantly correlated with dissolved inorganic carbon (DIC) concentration (r² = 0.506). No significant correlation was found between periphyton production and photosynthetically active radiation (PhAR). Extrapolation of periphyton production to a 135 km reach of the New River yielded an estimated annual input of 2 252 T AFDW from this source. Estimates of allochthonous (excluding upstream contributions) and aquatic macrophyte inputs to this same reach were 64 T AFDW and 2 001 T AFDW, respectively. While periphyton is not a large source of organic matter, its high food quality and digestibility make it an important component of the New River energy dynamics.     

周丛藻类及其在水质净化中的应用

周丛藻类广泛存在于自然界水体中,具有生物量大、生态功能强、水质响应灵敏等特征.周丛藻类通过吸收代谢利用、吸附和络合等过程去除水体污染物质,用于水质净化,具有耐污能力强,N、P去除效果好,藻类细胞回收利用价值高等优点,推广应用前景广阔.近年开发的藻丛刷系统、周丛藻类 生物膜系统和周丛藻类水产养殖系统等已经成功用于畜禽水产养殖废水、生活污水处理.而周丛藻类的生存规律、对污染物浓度的生理响应机理和污染物质吸收利用的分子生物学机制仍有待进一步研究.     

Periphyton production in Fort River, Massachusetts

SUMMARY. The primary production and general ecology of a periphyton community of a New England, lowland stream were studied over a seventeen-month period. Temperature, light, periphyton chlorophyll-α, and community structure were monitored regularly. Seasonally distinct chlorophyll peaks coincided with the light maximum in early May, just prior to the appearance of leaves of riparian trees, and again in autumn after terrestrial leaf fall. During midwinter, despite low light and temperature levels and high stream discharge, mean chlorophyll concentrations remained similar to summer values.
A mathematical expression relating periphyton photosynthesis per unit chlorophyll-α to temperature, light and periphyton density was established with submersible light-dark chambers in situ . Survey data collected over the study period were employed in the empirical equation to estimate seasonal variations in periphyton primary production. Weekly mean daily estimates of periphyton gross production ranged from < 0.1 g O₂ m⁻², during midwinter, to 6.5 g O₂ m⁻² during early May. Estimated annual periphyton gross production and respiration were 0.58 and 1.27 kg O₂ m⁻², respectively. Factors influencing seasonal variations of Fort River periphyton standing crop are discussed.     

Periphyton diatoms in a ditch near Tienhoven

Summary In august 1975, together with other field situations, the diatom composition of a ditch near Tienhoven was studied. Special attention was given to the importance of the different macrophyte species for their epiphytic diatoms. On 5 different sampling stations several parts of every macrophyte species were sampled for diatoms. They were prepared on a special way for determining the species and relative abundance. 119 Species and varieties were found. Most taxa occurred at station 5. The lowest number of taxa was found at station 4. The diatom composition shows a slight relation with the kind of substrate. However, the environmental factors of the surrounding water seem to be more important. To get a good idea of the epiphytic diatom composition on a station at least parts of 50% of the macrophyte species have to be sampled. Some ecological characters of the sampling stations are discussed.     

Redox Transformations of Arsenic Oxyanions in Periphyton Communities

Periphyton (Cladophora sp.) samples from a suburban stream lacking detectable dissolved As were able to reduce added As(V) to As(III) when incubated under anoxic conditions and, conversely, oxidized added As(III) to As(V) with aerobic incubation. Both types of activity were abolished in autoclaved controls, thereby demonstrating its biological nature. The reduction of As(V) was inhibited by chloramphenicol, indicating that it required the synthesis of new protein. Nitrate also inhibited As(V) reduction, primarily because it served as a preferred electron acceptor to which the periphyton community was already adapted. However, part of the inhibition was also caused by microbial reoxidation of As(III) linked to nitrate. Addition of [¹⁴C]glucose to anoxic samples resulted in the production of ¹⁴CO₂, suggesting that the observed As(V) reduction was a respiratory process coupled to the oxidation of organic matter. The population density of As(V)-reducing bacteria within the periphyton increased with time and with the amount of As(V) added, reaching values as high as ~10⁶ cells ml⁻¹ at the end of the incubation. This indicated that dissimilatory As(V) reduction in these populations was linked to growth. However, As(V)-respiring bacteria were found to be present, albeit at lower numbers (~10² ml⁻¹), in freshly sampled periphyton. These results demonstrate the presence of a bacterial population within the periphyton communities that is capable of two key arsenic redox transformations that were previously studied in As-contaminated environments, which suggests that these processes are widely distributed in nature. This assumption was reinforced by experiments with estuarine samples of Cladophora sericea in which we detected a similar capacity for anaerobic As(V) reduction and aerobic As(III) oxidation.     

Seasonal Dynamics of Periphyton in a Large Tropical Lake

Tropical aquatic systems are generally assumed to have little seasonality in productivity patterns. However, this study indicated that there was substantial seasonal variation in epilithic productivity and biomass in tropical Lake Tanganyika, due primarily to seasonal patterns in lake hydrodynamics that influence nutrient availability. Although they support much of the lake’s biological diversity, epilithic algae made a minor contribution to the total energy budget in Lake Tanganyika. A comparison among large, oligotrophic lakes revealed no significant latitudinal trends in periphyton productivity or biomass. However, Lake Tanganyika has relatively low benthic algal biomass and is therefore more efficient at photosynthesis than the temperate lakes. The influence of wave action and consumer density and diversity may be important in moderating productivity of the epilithic community.     

The Effects of Ultraviolet Radiation and Nutrient Additions on Periphyton Biomass and Composition in a Sub‐Alpine Lake (Castle Lake,USA)

Rising levels of ultraviolet radiation (UVR) striking the Earth's surface have led to numerous studies assessing its inhibitory effects on phytoplankton and periphyton in aquatic systems. Mineral nutrients such as nitrogen (N) and phosphorus (P) have been shown to increase aspects of algal metabolism and compensate for UVR inhibition. An in situ substratum enrichment technique and UV shielding was used to assess the effects of nutrient additions on periphyton exposed to different levels of UVR in Castle Lake, California during July‐August, 1997. UV shielding had no effect on total periphyton biomass, but caused shifts in species composition. The dominant periphyton species, Anabaena circinalis RAB., demonstrated sensitivity to ambient levels of UV radiation possibly due to UV inhibition of N2 ‐fixation. Total diatom biovolume decreased when shielded from UVR. Phosphorus additions continually elicited an increase in periphyton biovolume at all levels of analysis. These results suggest an interaction between nutrient status/availability and UV sensitivity.     

Diatom Succession and Interaction in Littoral Periphyton and Plankton

Periphyton and plankton samples were collected at four littoral stations in a relatively shallow, eutrophic lake (Elk Lake, B.C., Canada) over a six month period from August 1967 to January 1968. The most abundant planktonic diatoms demonstrated a pattern of seasonal succession typical of temperate lakes, and all were present in the periphyton. This pattern was identical at all stations:Fragilaria crotonensis was dominant from August to October,Asterionella formosa in November and December, andMelosira italica (plusM. varians) in January.F. virescens, although never dominant, peaked in October. Periphyton communities were dominated byAchnanthes minutissima, Cocconeis placentula, F. crolonensis andF. virescens. Considerable station variation in successional patterns occurred over different exposure periods; station differences were least in those samples immersed for monthly intervals, and greatest in those immersed for a cumulative four-month period. Interaction between the phytoplankton and periphyton was illustrated by the occurrence of species common to both habitats. A decrease in cell numbers and percent abundance of these species in planktonic populations coincided with their increase in the periphyton, a relationship which appeared dependent on the breakdown of thermal stratification in November. For example, following turnover,F. crotonensis andA. formosa settled out of the plankton and correspondingly increased in percent abundance in the periphyton. This interdependence was less evident in the four-month samples, whereA. minutissima andC. placentula dominated throughout the entire period and appeared to out-compete the more typical planktonic components for diminishing substrate area. Species interaction or competition was accentuated as exposure duration and periphyton total cell standing crops increased and species diversity decreased, and appeared to account in part, for station differences in successional patterns.     

Assessing Predictors of Changes in Protein Stability upon Mutation Using Self-Consistency

The ability to predict the effect of mutations on protein stability is important for a wide range of tasks, from protein engineering to assessing the impact of SNPs to understanding basic protein biophysics. A number of methods have been developed that make these predictions, but assessing the accuracy of these tools is difficult given the limitations and inconsistencies of the experimental data. We evaluate four different methods based on the ability of these methods to generate consistent results for forward and back mutations, and examine how this ability varies with the nature and location of the mutation. We find that, while one method seems to outperform the others, the ability of these methods to make accurate predictions is limited.     

Assessing Teratogenic Changes in a Zebrafish Model of Fetal Alcohol Exposure

Fetal alcohol syndrome (FAS) is a severe manifestation of embryonic exposure to ethanol. It presents with characteristic defects to the face and organs, including mental retardation due to disordered and damaged brain development. Fetal alcohol spectrum disorder (FASD) is a term used to cover a continuum of birth defects that occur due to maternal alcohol consumption, and occurs in approximately 4% of children born in the United States. With 50% of child-bearing age women reporting consumption of alcohol, and half of all pregnancies being unplanned, unintentional exposure is a continuing issue². In order to best understand the damage produced by ethanol, plus produce a model with which to test potential interventions, we developed a model of developmental ethanol exposure using the zebrafish embryo. Zebrafish are ideal for this kind of teratogen study^3-8. Each pair lays hundreds of eggs, which can then be collected without harming the adult fish. The zebrafish embryo is transparent and can be readily imaged with any number of stains. Analysis of these embryos after exposure to ethanol at different doses and times of duration and application shows that the gross developmental defects produced by ethanol are consistent with the human birth defect. Described here are the basic techniques used to study and manipulate the zebrafish FAS model.     

同步化培养后莱茵衣藻生物量和总RNA含量的变化

为了探索莱茵衣藻经光/暗同步化培养后的细胞生长和总RNA的变化规律。本研究检测了16h光/8h暗同步化培养后莱茵衣藻的生物量和总RNA含量的变化规律。结果,在同步化培养结束后的前28h,莱茵衣藻的生物量呈现有节律的阶梯增长;在同步化培养结束后的28～48h,这种阶梯式增长方式逐步消失。在同步化培养结束后的前24h,总RNA含量呈现有节律的峰-谷-峰变化;在同步化培养结束后的24～48h,这种变化幅度逐步减小,节律周期也逐步缩短。对比同步化培养后莱茵衣藻生物量和总RNA含量的变化可以得出,同步化培养后莱茵衣藻的同步化节律仍然可以维持一定时间;但随着连续光培养时间的延长,这种节律逐步消失,通过测定生物量和总RNA含量的变化可以跟踪同步化培养后莱茵衣藻的同步化变化。     

Periphyton chemistry and nitrogenase activity in a northern Everglades ecosystem

Cyanobacterial peri­phyton communities are a dominant feature of oligotrophic Everglades marshes, however, little is known regarding the biogeochemical aspects of this ecosystem component. This study was undertaken to investigate the potential for N₂ fixation in the peri­phyton communities of a hydrologically-controlled portion of the northern Everglades marsh (Water Conservation Area 2A, WCA-2A). The objectives of this research were to characterize the temporal patterns of nutrient composition and N₂ fixation of the natural WCA-2A peri­phyton communities and to compare fixation rates of peri­phyton with those of other ecosystem components in both natural and nutrient-impacted WCA-2A areas. In general, N₂ fixation (measured by the acetylene reduction (AR) method) of natural WCA-2A peri­phyton was enhanced under light conditions showing a nitrogenase pattern characteristic of autotrophic cyanobacteria. Winter (November–March) rates of AR expressed per gram organic carbon (gOC) ranged from 147–240 nmol C₂H₂ g OC^–1 h^–1, while summer rates were elevated with an observed peak of 1148 nmol C₂H₂ g OC^–1 h^–1 in July 1998. This translates into an estimated yearly contribution of approximately 10 g N m^–2 to an unimpacted WCA-2A slough ecosystem. Nitrogenase activity did not correlate seasonally with nutrients (Ca, Mg, Fe, N, P, Mn), but closely followed measured N stable isotopic ratios (¹⁵N) in floating peri­phyton. In oligotrophic marsh areas, AR (on a weight basis) decreased in the order floating peri­phyton > benthic peri­phyton floc > soil > water > detrital plant biomass, while highest AR rates were observed for detrital biomass in areas impacted by agricultural discharges.     

Short-Term Temporal Changes in Tree Live Biomass in a Central Amazonian Forest, Brazil

We monitored seventy-two 1 ha permanent plots spread over 64 km² of terra firme forest at Reserva Ducke (Manaus, Amazonas, Brazil) over 2-yr intervals to assess the effects of a soil and topographic gradient on the rate of change in the aboveground tree live biomass (AGLB). AGLB increased significantly over the 2-yr intervals, exhibiting a mean rate of change of 1.65 Mg/ha/yr (bootstrapped 95% CI: 1.15, 2.79). The rate of change varied according to tree size class; understory and sub-canopy trees exhibited higher rates of change. Over the whole period, the rate of change was not related to soil or topographic features of the plots, but there was evidence that the relationships varied depending on the year of measurement. In the plots monitored between 2001 and 2003 we found a significant relationship between AGLB change and the soil textural gradient, but this relationship was not evident in plots monitored between 2002 and 2004. This suggests that both the temporal variation in the soil–biomass change relationship and the size structure of the forest need to be included in models of biomass change in Amazonia. We also noted that the rate of biomass change is sensitive to the equation used to estimate AGLB. Allometric models that incorporate wood-density data provide higher per plot AGLB estimates, but lower rates of change, suggesting that variations in floristic composition have important implications for carbon cycling in diverse tropical forests.
Abstract in Portuguese is available at http://www.blackwell-synergy.com/loi/btp .     

Species Diversity of Periphyton Communities in the Littoral of a Temperate Lake

Species diversity of littoral periphyton sampled from Elk Lake (B. C., Canada) was dependent on station location and period of substrate exposure. Site differences were not statistically related to physico-chemical variables. However, diversity was negatively correlated with age of the communities and standing crop, and appeared to be associated with biological interaction or competition for available substrate surface. Further investigation revealed that the Shannon-Weaver index, as commonly applied, was inappropriate for data summarization since it reflected only the changes in evenness of the most abundant species. Components of the diversity index, as illustrated by the periphyton, were discussed.     

Biological significance of the Gornoslinkinskaya Riverbed Depression in the Irtysh

Distribution of fish in the Gornoslinkinskaya Riverbed Depression in the Irtysh is considered in relation to the time of day and to the season. Fish aggregations are characterized quantitatively and by their size and species composition. The major part of the fish population of the depression consists of fish juveniles. The biological significance of the riverbed depression is polyfunctional. The universal traits of the ecosystems of large river basins and mechanisms of their occupation by fish are discussed.     

Community-Level Analysis of psbA Gene Sequences and Irgarol Tolerance in Marine Periphyton

This study analyzes psbA gene sequences, predicted D1 protein sequences, species relative abundance, and pollution-induced community tolerance in marine periphyton communities exposed to the antifouling compound Irgarol 1051. The mechanism of action of Irgarol is the inhibition of photosynthetic electron transport at photosystem II by binding to the D1 protein. The metagenome of the communities was used to produce clone libraries containing fragments of the psbA gene encoding the D1 protein. Community tolerance was quantified with a short-term test for the inhibition of photosynthesis. The communities were established in a continuous flow of natural seawater through microcosms with or without added Irgarol. The selection pressure from Irgarol resulted in an altered species composition and an inducted community tolerance to Irgarol. Moreover, there was a very high diversity in the psbA gene sequences in the periphyton, and the composition of psbA and D1 fragments within the communities was dramatically altered by increased Irgarol exposure. Even though tolerance to this type of compound in land plants often depends on a single amino acid substitution (Ser₂₆₄→Gly) in the D1 protein, this was not the case for marine periphyton species. Instead, the tolerance mechanism likely involves increased degradation of D1. When we compared sequences from low and high Irgarol exposure, differences in nonconserved amino acids were found only in the so-called PEST region of D1, which is involved in regulating its degradation. Our results suggest that environmental contamination with Irgarol has led to selection for high-turnover D1 proteins in marine periphyton communities at the west coast of Sweden.     

Periphyton production and grazing by chironomids in Alderfen Broad, Norfolk

The standing crops of periphyton were measured on dead Typha stems and glass rods in a small, eutrophic lake from February to November. Chironomid larvae were also counted on the Typha stems; very few were present on the glass rods. The standing crop of periphyton on the Typha stems fell from 1.8 mg cm⁻² in early April to nearly zero in November. On the glass rods the periphyton reached a peak of 1.93 mg cm⁻² in late May and 1.94 mg cm⁻² in July, thereafter falling to a steady level of 1.6 mg cm⁻². The population of chironomids showed a peak in late May and then declined. The alimentary canals of chironomids collected fromTyphastems contained diatoms and filamentous algae so it appeared that chironomids were grazing down the periphyton. Chironomids moved on to theTyphastems in spring and returned to the mud in autumn. The periphyton is a richer source of essential amino acids than the mud, so that a movement from mud to reedstems in spring may increase the rates of growth and metamorphosis of the larvae. A crude production estimate gave a net primary production of periphyton of 170 mg dry wt m⁻² day⁻¹; the periphyton, however, would have contained bacteria and many small animals as well as algae.     

Periphyton analysis for the evaluation of water quality in running waters of Greece

Based on a microfloristic analysis of periphyton, a selected ecological method of evaluating water quality, independent of saprobic systems is applied to a chosen section of running water in the springs of Levadia, Greece. The graphic representation of the results and an estimation of the degree of pollution is given. A simple method for the quantitative evaluation of the biocoenose of epilithic algae is additionally developed.     

Nematodes in Meiobenthos and Periphyton of the Rybinsk Reservoir (Review)

This paper presents data on changes in the taxonomic composition and abundance of nematodes in meiobenthos and periphyton of the Rybinsk Reservoir in the long term. The species composition of roundworms in bottom communities is significantly richer and their number is manyfold higher than among fouling organisms. These differences are determined by the different habitat conditions at the bottom and hard substrate surfaces in the water column. In modern anthropogenically disturbed zones of various waterbodies, the biocenotic and functional roles of nematodes depend to a larger extent on food availability than on some other environmental factors limiting the development of worms. Roundworms, living under a wide range of ecological conditions, are one of the key groups of invertebrates critical for preserving aquatic life under anthropogenic stresses.