Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

There has been a strong research focus on optical properties in temperate estuaries but very much less in tropical estuaries. These properties comprise light and beam attenuation dominated by suspended particulate matter, Chl a, and CDOM. Spatially and temporally distributed data on optical properties in a tropical wet and dry estuary are compared and discussed in relation to those of temperate estuaries. Sampling in the Nha Phu estuary, Vietnam, consisted of five stations on a transect from head to mouth that was sampled four times during dry conditions and three times during wet conditions between May 2006 and April 2008. Methods comprised CTD, optical measurements, and water sampling for suspended matter, Chl a, and CDOM. Results showed high light attenuation—K _d(PAR)—in wet conditions and low in dry. K _d(PAR) was highest at the estuary head and lower in the outer part. Spatial and temporal variations in K _d(PAR) were in general dominated by variations in suspended particulate matter concentrations in both wet and dry conditions. Chl a concentrations were low and showed no strong variations between wet and dry conditions. CDOM absorption coefficients were higher in wet conditions with high values at the head and lower in the central part of the estuary. The depth of the photic zone was reduced by up to 50% during wet conditions. A residence time in the estuary of 5–6 days was derived from the rate of change of K _d(PAR) after a period of heavy rain and discharge of freshwater into the estuary. This complied with a residence time of four and a half days derived from a basic physical relation. Optical properties were in general comparable to temperate estuaries in dry conditions although Chl a concentrations were lower in Nha Phu. A second distinctive point, as compared to temperate estuaries, was the episodic character with days of strong rainfall followed by longer periods of dry weather. All sampling, both wet and dry, was carried out in the dry season which implies a less definitive perception of wet and dry seasons.     

Paleolimnology of the Petén Lake district,Guatemala

The long-term impact of Maya culture on a lowland tropical watershed is assessed, using data from a 9.2 m sediment core taken from deep water (28 m) in Lake Quexil. Human population growth, estimated by the 1980 archaeological survey, is associated with a shift in the composition of the sediment to a dominance by inorganic material, the Maya clay formation, beginning ca. 3500 B.P. Increasing settlement densities are correlated with accelerated influxes of phosphorus, carbonates, and siliceous sediment. However, chemical data do not track short-term population fluctuations closely. Because much of the sediment is delivered as colluvium, and not by running water, there is a lag between terrestrial disturbance and impact on the aquatic system. As an indication of this lag, contemporary high sedimentation rates are a residual of Maya activity that virtually ceased some 300–400 years B.P. Comparison of the deep-water core with a shallow-water (7 m) section, based on palynological correlation, reveals only minor differences in proximate chemical composition. Chemical influxes are much higher at the deep-water site, however, as a consequence of sediment focusing in this hyperconical basin. Chemical analyses of soil samples from 21 test pits in the Quexil basin support the principal conclusion that bulk soil movement was the mode of nutrient transfer to the lake, following forest clearance by the Maya.     

Phosphorus in acidified lakes: The example of Lake Gårdsjön,Sweden

Supply and turnover of phosphorus was studied in an acidified lake ecosystem, Lake Gårdsjön, located in southwestern Sweden. This study included transport and budget calculations combined with field and laboratory experimental work on abiotic phosphorus chemistry and biological utilization of phosphorus. The main conclusions presented in this paper are:

- The acidification process in inland waters resulting from acid atmospheric deposition is accompanied by ‘oligotrophication’ because of reduced input of phosphorus from the drainage area, possibly due to efficient fixation of phosphorus to aluminium complexes in the B-horizon of podzol soils

- Primary productivity in acidified lakes is limited mainly by low phosphorus supply

- Algal utilization of phosphorus in acidified lakes is impaired, yielding lower biomass than could be expected from ambient phosphorus concentrations. One possible reason for this could be that enzymatic recycling of organic phosphates is prevented by high levels of aluminium in lake water.

     

Origin and production of phosphatases in the acid Lake Gårdsjön

The activity of acid phosphatases was followed for one year in Lake Gårdsjön as well as in the inlet and the outlet of the lake. A budget of the phosphatases was calculated, including an estimation of the production of phosphatases. The phosphatase activity was also measured in two basins upstream of L. Gårdsjön: the north basin and the south basin of L. Stora Hästevatten.The acid phosphatase activity was very high compared with reported alkaline phosphatase activities in other lakes. About 95% of the phosphatases in L. Gårdsjön was produced in the lake, and the production was highest in early summer.Small Chrysophyceae (< 10 µm) probably produced the majority of the acid phosphatases in the investigated lakes, and accordingly could be favoured in environments with low phosphorus supply due to their ability to produce large amounts of phosphatases.     

Specific carbonate–microbe interactions in the modern microbialites of Lake Alchichica (Mexico)

The role of microorganisms in microbialite formation remains unresolved: do they induce mineral precipitation (microbes first) or do they colonize and/or entrap abiotic mineral precipitates (minerals first)? Does this role vary from one species to another? And what is the impact of mineral precipitation on microbial ecology? To explore potential biogenic carbonate precipitation, we studied cyanobacteria–carbonate assemblages in modern hydromagnesite-dominated microbialites from the alkaline Lake Alchichica (Mexico), by coupling three-dimensional imaging of molecular fluorescence emitted by microorganisms, using confocal laser scanning microscopy, and Raman scattering/spectrometry from the associated minerals at a microscale level. Both hydromagnesite and aragonite precipitate within a complex biofilm composed of photosynthetic and other microorganisms. Morphology and pigment-content analysis of dominant photosynthetic microorganisms revealed up to six different cyanobacterial morphotypes belonging to Oscillatoriales, Chroococcales, Nostocales and Pleurocapsales, as well as several diatoms and other eukaryotic microalgae. Interestingly, one of these morphotypes, Pleurocapsa-like, appeared specifically associated with aragonite minerals, the oldest parts of actively growing Pleurocapsa-like colonies being always aragonite-encrusted. We hypothesize that actively growing cells of Pleurocapsales modify local environmental conditions favoring aragonite precipitation at the expense of hydromagnesite, which precipitates at seemingly random locations within the biofilm. Therefore, at least part of the mineral precipitation in Alchichica microbialites is most likely biogenic and the type of biominerals formed depends on the nature of the phylogenetic lineage involved. This observation may provide clues to identify lineage-specific biosignatures in fossil stromatolites from modern to Precambrian times.     

Changing Abundance of Hexagenia Mayfly Nymphs in Western Lake Erie of the Laurentian Great Lakes: Impediments to Assessment of Lake Recovery?

After an absence of 40 years, mayfly nymphs of the genus Hexagenia were found in sediments of western Lake Erie of the Laurentian Great Lakes in 1993 and, by 1997, were abundant enough to meet a mayfly‐density management goal (ca. 350 nymphs m^—2) based on pollution‐abatement programs. We sampled nymphs in western Lake Erie and Lake St. Clair, located upstream of western Lake Erie, to determine the importance of seasonal abundance and life‐history characteristics of nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly‐density management goal. Two types of density patterns were observed: (1) densities were relatively high in spring and gradually decreased through late summer (observed in Lake Erie and Lake St. Clair in 1997 and Lake St. Clair in 1999) and (2) densities were relatively high in spring, gradually decreased to mid summer, abruptly decreased in mid summer, and then increased between summer and late fall (Lake Erie and Lake St. Clair in 1998 and Lake Erie in 1999). Length‐frequency distributions of nymphs and observations of adults indicate that the primary cause for the two density patterns was attributed to failed (first pattern) and successful (second pattern) reproduction and emergence of nymphs into adults in mid summer. Gradual declines in densities were attributed to mortality of nymphs. Our results indicate that caution should be used when evaluating progress of pollution‐abatement programs based on mayfly densities because recruitment success is variable both between and within years. Additionally, the interpretation of progress toward management goals, relative to the restoration of Hexagenia populations in the Great Lakes and possibly other water bodies throughout the world, is influenced by the number of years in which consequtive collections are made.     

A study of the Werewilka Inlet of the saline Lake Wyara, Australia – a harbour of biodiversity for a sea of simplicity

Lake Wyara receives most of its water from Werewilka Creek, with the area between the two forming Werewilka Inlet which is highly variable in area, and salinity and has high habitat heterogeneity. Over 12 years, 84 species of macroinvertebrate were found in the inlet, but only 34 in the lake. Halobiont and halophilic species were the same in each, but there were many fewer salt-tolerant species in the lake and no freshwater species. The latter were excluded by salinity, but habitat homogeneity due to strong wave action in the lake seems to limit many salt-tolerant species to the inlet. Species richness in large saline lakes in inland Australia is limited by salinity, poor speciation opportunities engendered by their episodic nature, and habitat homogeneity.     

Microbial Fossils in the 2.63 Ga Jeerinah Formation,Western Australia—Evidence of Microbial Oxidation

A diamond drill core from the upper part of the Jeerinah Formation (～2.63 Ga), underlying the Hamersley Group, deposited at a time when the oxygen concentrations in the marine environment were extremely low, was examined for microbial fossils. The paper presents organo-mineral structures in the form of twisted stalks produced by bacteria being present in the laminated black carbonaceous shale sediments. These twisted stalks are organo-mineral structures produced by microaerophilic Fe(II)-oxidizing-type bacteria such as Gallionella and/or Mariprofundus that are active at very low-oxygen concentrations, thus providing evidence for oxygen being present in the marine environment at 2.63 Ga.     

Systematic of the fish Petenia splendida (Perciformes: Cichlidae) of Lake Petén Itzá, Guatemala

The Lake Petén Itzá is located in the multiple use zone of the Maya Biosphere Reserve. It belongs to the subtropical moist forest (warm) life zone, and has very important flora and fauna diversities. Among the fish species, the white fish (Petenia splendida) is of high commercial value. The main goal of the present work was to clarify the taxonomic position of the two forms of the white fish in Petén (Guatemala), and to compare it with the Usumacinta (Mexico) form, based on the collected material from 1978 and 2006 (Usumacinta), and collections made during 2008 and 2009 in the Lake Petén Itzá. Samples were obtained from 10 different locations in the lake. From the total of 57 fish specimens collected, 50 fish were selected (25 yellow form and 25 silver form); besides, 21 specimens from 10 locations of the Usumacinta river in Mexico, from the Fish Collection, FCB, UANL. A total of 36 morphometric and 16 meristic characteristics, were analyzed, and also coloration, habitat and fishing method. This study reports the P. splendida of the Lake Petén Itzá with the following characteristics: the yellow form at a depth of 0.5-1.5m with dorsal fin XIV-(XV)-XVI/11-(12)-13, the silver form at a depth of 2-3m with dorsal fin XIV-(XV)-XVI/10-(12)-13, and the Usumacinta form with a dorsal fin XIV-(XV)-XV/12-(13)-13. The discrimination analysis demonstrates a differentiation among the three analyzed populations. Some of the characteristics are the ocular diameter, the anal source-pelvic source distance and the dorsal source-anal source distance. The geographic area studied has a high diversity of fish fauna along the watershed, and it is possible to observe the anthropogenic damage, due to the overexploitation based the unapplicability of the existent regulation and the urbanization. If this situation continues it could jeopardize the survival of this emblematic specie.     

Growth rates in outbreak populations of the corallivorous gastropod Drupella cornus (Röding 1798) at Ningaloo Reef,Western Australia

Mark and recapture experiments were used to estimate the size-at-age relationship of the coral-eating gastropod Drupella cornus at Ningaloo Reef, Western Australia. Animals 15 mm long increased in length by 5.2 mm in six months at a site in an early stage of an outbreak, but by only 3.8 mm at a site within an established outbreak. Snails larger than 35 mm grew very little. Based on observed growth rates fitted to a Richards function growth equation, snails 28 mm long judged to be reproductively mature would be 2.5 to 3.5 years old, suggesting that local outbreaks represent no more than one or two generations of recruits. Indirect evidence indicates that growth is more rapid in the earlier than in later stages of outbreaking populations. The growth and timing of life-history transitions of D. cornus are not unusual among other muricid species.     

Diagenetic stoichiometry and benthic nutrient fluxes at the sediment–water interface of Lake Illawarra, Australia

Benthic flux measurements of O₂, TCO₂ and inorganic nutrients were made at three stations (seagrass beds, shallow bare sand and deep mud) in Lake Illawarra (Australia) to compare the characteristics of diagenesis and benthic biogeochemical processes for different primary producers (seagrass or microphytobenthos, (MPB)) and/or sediment types (sand or mud).Seagrass beds exhibited the highest gross primary productivity while the lowest rates occurred at the deep mud station. At the shallow bare sand station only, the gross primary production (GPP) and respiration (R) were balanced, while at the other two stations, R exceeded GPP by as much as 2 fold, indicating more organic carbon was decomposed than produced at the time of sampling. In general, nutrient fluxes displayed typical diurnal variation.Organic carbon oxidation scenarios, evaluated by either calcium carbonate dissolution or sulfate reduction models, indicated that both models can represent organic matter mineralization. The difference of estimated total carbon oxidized in this lake using the two models was small, ranging from 0.2% at deep mud station to maximum of 21% at seagrass station. In addition, N₂ flux rates (net denitrification), estimated using carbon and nitrogen stoichiometry, were of similar magnitude as the rates estimated using LOICZ budget modeling or measured using the N₂/Ar technique.Finally, a comparison of calculated diffusive fluxes and measured fluxes using incubation cores indicated that the results were of similar magnitude at the deep mud station, but the incubation cores fluxes were much higher than the calculated diffusive fluxes at the other two stations. This may have been caused by bioturbation or bioirrigation.     

Morphological and Genetic Heterogeneity of Sockeye Salmon Oncorhynchus nerka (Salmonidae) of Large Lake–River Systems in Eastern and Western Kamchatka

Journal of Ichthyology - The morphological and genetic heterogeneity of sockeye salmon Oncorhynchus nerka (from both the mixed samples and the samples collected in different periods of its mass...     

Phosphorus concentration in sediment, water and tissues of␣three submerged macrophytes of Myall Lake, Australia

Phosphorus content in sediment, water and tissues of three macrophyte species growing in Myall Lake, Australia were studied from January to November, 2004. The sites investigated were North–West (NW), North–East (NE), South–West (SW) bays and Central deep area of the lake (CL). The objective of this study was to investigate how total phosphorus (TP) in plant tissues relate to phosphorus pools and the role played by the aquatic macrophyte species under investigation in phosphorus recycling in the lake. Of the four investigated sites of the lake, TP in plant tissues were significantly higher in North–West and South–West bays compared to the rest. Najas marina had significantly higher TP content (e.g., 1.55 and 1.44 mg/g dw.; P < 0.05) for NW and SW respectively, than the other two species. N. marina is a rooted macrophyte while charophytes (C. fibrosa and Nitella hyalina) are pseudo-rooted macrophytes. Total phosphorus in the sediment and water column were significantly higher in Central deep area of the lake compared to the other three bays (P < 0.05, n 5). Soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) in sediment pore water correlated significantly with phosphorus content in the tissue of N. marina ( ; ) as well as TP in sediment (␣ and ). Using the two-compartmental uptake model, it was observed that, sediment was the main compartment through which Ni. hyalina obtained phosphorus while for the other two species, water column was the uptake route for the phosphorus. These correlations suggest that, water column and sediments are important pathways for phosphorus uptake in plants.     

The first record of the antlion Mesonemurus mongolicus Hölzel, 1970 (Neuroptera, Myrmeleontidae) in the Republic of Buryatia

The antlion Mesonemurus mongolicus Hölzel, 1970 is described for the first time for the Republic of Buryatia, where it occurs in drift sands. All the specimens were identified based on a single feature persistent in both sexes in the known populations of M. mongolicus, the presence of a wide brown spot between the antennae, which is not known in any other congener.     

Discovery of the first virus, the tobacco mosaic virus: 1892 or 1898?

Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus. Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle. Bacteria are retained by such filters, a new world was discovered: filterable pathogens. However, Ivanovski probably did not grasp the full meaning of his discovery. Beijerinck, in 1898, was the first to call 'virus', the incitant of the tobacco mosaic. He showed that the incitant was able to migrate in an agar gel, therefore being an infectious soluble agent, or a 'contagium vivum fluidum' and definitively not a 'contagium fixum' as would be a bacteria. Ivanovski and Beijerinck brought unequal but decisive and complementary contributions to the discovery of viruses. Since then, discoveries made on Tobacco mosaic virus have stood out as milestones of virology history.     

The Seasonal Aggregation of Whale Sharks at Ningaloo Reef, Western Australia: Currents, Migrations and the El Niño/ Southern Oscillation

Whale sharks, Rhincodon typus, seasonally aggregate in coastal waters off Ningaloo Reef, Western Australia. We review the oceanographic setting of the region and present evidence that such aggregations form as a result of migratory behavior associated with climatic and oceanographic processes. We utilise records of whale shark abundance collected at Ningaloo Reef from dedicated searches by boat and aircraft and from log sheets recorded by the tourism industry. Measures of whale shark abundance derived from log sheet data sets were moderately correlated with the Southern Oscillation Index and weakly correlated with coastal sea level, an index of the strength of the Leeuwin Current, and sea surface temperature over the period 1993 to 1998. Abundances of whale sharks derived from boat searches from 1983 to 1992 were also correlated with fluctuations in the Southern Oscillation Index, except during a three year period from 1988 to 1990. We conclude that, at least in some years, there appears to be a link between the abundance of aggregating whale sharks and the physical and biological oceanography of the region, with greater whale shark numbers in La Niña years. The lack of correlation in other years may be due to a combination of uneven quality of data and/or aggregations occurring in response to a complex interaction between the physical and biological oceanography of the region.     

Ecological connectivity or Barrier Fence? Critical choices on the agricultural margins of Western Australia

Western Australia's State Barrier Fence represents a continuation of colonial era attitudes that considered kangaroos, emus and dingoes as ‘vermin’. Recent plans to upgrade and extend the Barrier Fence have shown little regard for ecological impacts or statutory environmental assessment processes.     

Biomass and element pools of understory vegetation in the catchments of Čertovo Lake and Plešné Lake in the Bohemian Forest

This paper presents data on species composition, biomass, and element pools (C, N, P, Ca, Mg, Na, K, Al, Fe, Mn) of the understory vegetation of spruce forests in the catchments of lakes ?ertovo jezero (CT) and Ple?né jezero (PL) in the Bohemian Forest (?umava, Czech Republic). Calamagrostis villosa was the most abundant species in the CT catchment, while Vaccinium myrtillus was the most abundant species in the PL catchment. The catchments weighted mean (CWM) of above-ground biomass of the understory vegetation was 288 and 723 g m^?2 in the CT and PL catchments, respectively. The significant difference in the biomass between the catchments was caused by the much higher abundance of V. myrtillus in the PL catchment. The CWM of below-ground biomass of the fine roots was 491 and 483 g m^?2 in the CT and PL catchments, respectively. The respective CWM element pools of biomass in the CT and PL catchments were: C (33 and 51 mol m^?2), N (0.8 and 1.0 mol m^?2), P (24 and 34 mmol m^?2), Ca (53 and 113 mmol m^?2), Mg (24 and 41mmol m^?2), Na (3.7 and 6.5 mmol m^?2), K (83 and 109 mmol m^?2), Al (50 and 42 mmol m^?2), Fe (13.3 and 7.3 mmol m^?2), and Mn (4.2 and 8.8 mmol m^?2).     

Species composition of phytobenthos in the littoral of Lake Xolotlán (Managua)

The species composition of the phytobenthos in the littoral of Lake Xolotlán (Managua) was determined. Sampling was carried out in November 1987 (end of the rainy season) and in July–August 1988 (rainy season). Sixty-eight taxa were identified;viz. 47 Bacillariophyceae, 13 Cyanophyta and 8 Chlorophyta. The presence of diatom species likeNavicula veneta, Nitzschia amphibia andNitzschia palea indicate eutrophic conditions, high ionic concentration, alkaline conditions and intense organic pollution.