Open Waters Of Lake Research Articles

Microbialite Formation in Seawater of Increased Alkalinity, Satonda Crater Lake, Indonesia

ABSTRACT The crater lake of the small volcanic island Satonda, Indonesia, is unique for its red-algal microbial reefs thriving in marine-derived water of increased alkalinity. The lake is a potential analogue for ancient oceans sustaining microbialites under open-marine conditions. Current reef surfaces are dominated by living red algae covered by non-calcified biofilms with scattered cyanobacteria and diatoms. Minor CaCO3 precipitates are restricted to the seasonally flooded reef tops, which develop biofilms up to 500 µm thick dominated by the cyanobacteria Pleurocapsa, Calothrix, Phormidium, and Hyella. Microcrystalline aragonite patches form within the biofilm mucilage, and fibrous aragonite cements grow in exopolymer-poor spaces such as the inside of dead, lysed green algal cells, and reef framework voids. Cementation of lysed hadromerid sponge resting bodies results in the formation of Wetheredella-like structures. Hydrochemistry data and model calculations indicate that CO2 degassing after seasonal mixis can shift the carbonate equilibrium to cause CaCO3 precipitation. Increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium. Therefore, photosynthesis-induced cyanobacterial calcification does not occur. Instead, passive, diffusion-controlled EPS-mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place. In contrast to extreme soda lakes, the release of Ca2+ from aerobic degradation of extracellular polymeric substances does not support CaCO3 precipitation in Satonda because the simultaneously released CO2 is insufficiently buffered. Subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous, unidentified Mg-Si phase. The microstromatolites probably formed when Lake Satonda evolved from seawater to Ca2+-depleted raised-alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong CO2 degassing. The latter effect caused rapid growth of fibrous aragonite, while Mg-Si layers replaced the initially Mg-calcite-impregnated biofilms. This could be explained by dissolution of siliceous diatoms and sponge spicules at high pH, followed by Mg-calcite dissolution and Mg-silica precipitation at low pH due to heterotrophic activity within the entombed biofilms.

The dissipation, distribution and fate of a branched 14C-nonylphenol isomer in lake water/sediment systems

A single tertiary isomer which is believed to be one of the major branched isomers of the isomeric nonylphenol was synthesized for use in investigations on its metabolism and estrogenicity in aquatic organisms. The physico-chemical properties of the isomer were determined to enable the prediction of its behaviour in aquatic environments. From laboratory investigations on its dissipation and distribution in lake water, which are reported in this paper, it was found that it had a half-life of dissipation of 38.1 days and 20.1 days in an open lake water and in an open lake water/ sediment system, respectively, and to be rapidly partitioned in to sediment giving a high concentration factor of 1.76 after 28 days with an initial dose concentration of 2.52 ppm. The main dissipation route was found to occur through volatilization and co-distillation. The isomer was, however, found to be resistant to biodegradation in both the lake water and sediment, showing only a slight 9% loss (after 56 days) and 4.2% loss (after 28 days), of the 14C-residues in lake water and lake water/sediment systems, respectively, by microbial activity. Transformation to other more polar metabolites possibly by hydroxylation was also found to be minimal in both lake water and sediment samples after 14 days by HPLC analysis. After 7 days, only 2.25 and 7.4% transformation to a more polar metabolite was detected in lake water and sediment samples, respectively.

Comparison of inundation patterns among major South American floodplains

A comparative view of inundation patterns in the large floodplains of South America was derived by analysis of the 37‐GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (SMMR; Nimbus‐7 satellite, 1979–1987). The following floodplains were analyzed: (1) mainstem Amazon River floodplain in Brazil; (2) Llanos de Moxos (Beni and Mamoré rivers) in Bolivia; (3) Bananal Island (Araguaía River) in Brazil; (4) Llanos del Orinoco (Apure and Meta rivers) in Venezuela and Colombia; (5) Roraima savannas (Branco and Rupununi rivers) in Brazil and Guyana; and (6) Pantanal wetland (Paraguay River) in Brazil. The maximum areas subject to inundation in each region, which include permanent open waters of river channels and lakes, were as follows (in km2): mainstem Amazon 97,360, Moxos 92,094, Bananal 58,550, Orinoco 107,530, Roraima 16,530, and Pantanal 130,920. The duration of inundation was correlated with the maximum area inundated. Predictive relationships between flooded area and water levels in the nearby rivers allowed extension of the inundation record over nearly a century for the Amazon and Pantanal and several decades for the other floodplains. Interannual variability in the maximum extent of inundation is greatest in the Pantanal, followed by Roraima and Bananal. Based on these extended records, the long‐term mean inundation areas (in km2 and including rivers and lakes) were as follows: mainstem Amazon 46,920, Moxos 29,460, Bananal 13,110, Orinoco 34,700, Roraima 3,480, and Pantanal 34,880. This information is fundamental for hydrological, biogeochemical, and ecological studies of these floodplain‐river systems and will improve estimates of methane and other trace gas emissions to the atmosphere from these vast wetlands.

Wind information for marine weather forecasting from RADARSAT-1 synthetic aperture radar data: Initial results from the "Marine winds from SAR" demonstration project

The Canadian Ice Service (CIS), part of Environment Canada's Meteorological Service of Canada, has been a primary user of RADARSAT-1 data since its launch in November 1995. Approximately 4000 RADARSAT-1 images are received annually for ice reconnaissance work, but the appearance of dramatic atmospheric conditions imprinted on the open water of oceans and lakes has increased interest in using this data for other marine and meteorological applications. To exploit the CIS operational RADARSAT-1 data stream, a demonstration project was initiated for the winter of 2001 to deliver RADARSAT-1 ScanSAR images and derived wind products to meteorological centres in the East Coast and Great Lakes regions of Canada. Meteorologists were trained in interpreting synthetic aperture radar (SAR) imagery and how wind products are generated from SAR data. From January to April 2001, over 600 images and wind products were delivered in near real time to weather centres for use in forecast production. Feedback from meteorologists in the use of RADARSAT-1 for weather applications was positive, especially for site-specific weather forecasting in regions such as coastal or marginal ice zones, lakes, and estuaries in which scatterometer land contamination is an issue and data from other sources are sparse. Additionally, initial validations of the ocean monitoring workstation (OMW) wind products have shown promising results.

Emergence in pelagic communities

Pelagic systems, those based on the open waters of large lakes and seas, provide excellent opportunities for ecological study. This is because, the vastness of the oceans apart, pelagic ecosystems operate on short space and time scales. This affords important opportunities to study the emergence of ecosystems and the basis of striking high-order patterns of ecosystem behaviour. The essay seeks an outline of the processes by which the biologies of individual organisms - the largest functional, controlled units in the ecosystem - interact and bias the outcomes in favour of particular network structures recognised by ecologists. Populations build, communities assemble, ecosystems function but always in ways that relate to the match between the adaptations and performances of individual species and the capacities of the environments in which they find themselves. The paper attempts to discern the linkages between the biology of individual and the ways that ecosystems are put together, between organisms and organisation. Drawing on the advantages of absolutely short generation times among the producers, consumers and heterotrophs of the pelagic, I seek to sample the ascendant pathways of ecosystem synthesis, noting the energetic decisions which select for particular outcomes. However, the simple organisational state of many pelagic communities reminds us that ascendancy is frequently restrained by a scarcity of resources and tempered by the frequent intervention of abiotic factors. The presentation does not seek to prove any point about systems: it attempts to re-affirm what is known about organisational hierarchies; then, using approximate quantities, the points of bifurcation between alternative organisational structures are nominated; drawing upon suppositions about the dissipation of energy, the organisational underpinning of function at the level of the whole ecosystem is proposed. Corroboration from observations from the real world is sought throughout.

Accumulation of organic carbon in five Brazilian lakes during the Holocene

Abstract A comparative study was made of organic carbon accumulation in five lacustrine environments in Brazil (large open water lake, ponds with floating meadows and marshes). The most representative cores were used to calculate the accumulation of total organic carbon (TOC) in the sediment over the past 12,000 cal years BP. Carbon accumulation rates were determined using the TOC concentration, sediment «in situ» density, 14 C calibrated ages and the interpolated sedimentation rate (cm year −1 ) or sediment accumulation rate (g m −2 year −1 ). The C/N ratio and microscopic observations were used to characterise the sedimentary organic matter. Recent TOC accumulation in the lakes was estimated at 7–41 g m −2 year −1 by averaging the last 500 years. This variation roughly correlated with the present-day ratio of watershed area vs. lake area, indicating that nutrient input is important for the modern accumulation of organic matter. The accumulation rates were greatest in lakes with floating macrophytes. The largest lake (Dom Helvecio), with a strong thermal stratification, low primary production and low carbon accumulation, had relatively well preserved organic matter when its low watershed area/lake area ratio was considered. The general increase in carbon accumulation during the Holocene followed the expansion of lakes and the development of a wetter climate, due to a growing penetration of the Atlantic and Amazonian wet air mass over Brazil driven by insolation changes. This change in carbon accumulation was not controlled by the higher water and nutrient inputs alone, more organic matter was decomposed when lake levels were low at the beginning of the Holocene. Some lakes were also influenced by higher inputs of allochthonous organic matter during the early and middle Holocene. These inputs included high concentrations of charcoal fragments. Lake morphology and its changes as the lake level rose, as well as the nature of primary producers, strongly influenced the carbon accumulation rates. Our understanding of how climate changes are linked to changes in the lacustrine environment should not be based on measuring organic matter alone, but requires a good description of the organic matter and other limnological parameters.

Temperature variability in lake sediments

Sediment temperatures were simulated from the sediment‐water interface down to 10 m for circular lakes with surface areas of 0.2–10 km2 and maximum lake depths of 4–24 m. The calculations were made using daily weather conditions measured over 19 years (1961–1979) at three geographic locations, representing climate conditions from north to south latitudes in the central United States. A one‐dimensional sediment temperature model coupled with a year‐round lake water temperature model (MINLAKE96) was used. The models were tested against extensive water temperature and some sediment temperature data. Lake sediment equilibrium temperatures at 10 m below the water‐sediment interface were found almost equal to the annual mean temperature of the overlaying water and hence dependent on the lake temperature regime, which in turn depends on the local climate and a lake's physical characteristics (e.g., surface area As, maximum depth HMAX, and water transparency as measured by Secchi depth). The lake geometry ratio As0.25/HMAX(m−0.5) gives a good indication whether a lake will permanently stratify in summer or not, and that makes a large difference for the sediment temperature regime. Sediment temperatures at 10 m below the littoral waters of a lake are almost equal to subsurface ground (terrestrial) temperatures, regardless of the type of lake, whereas sediment temperatures at 10 m below the deepest portion of a stratified lake have a strong linear relationship with the logarithm of the lake geometry ratio. Two generalized 10‐m sediment temperature profiles were developed, one for ice‐covered lakes and the other for year‐round open water lakes. Sediment temperatures at 10 m below the sediment‐water interface at different depths of a lake can be reconstructed from the generalized profiles using Secchi depth, surface area, maximum depth, and annual mean air temperature as input. Sediment temperature at several meters depth (e.g., 10 m) below a lake bed is a useful and necessary initial condition to predict water temperature dynamics in lakes of the temperate zone and hence other water quality parameters whose kinetics are linked to water temperature.

Documenting Complex Surface Temperature Patterns from Advanced Very High Resolution Radiometer (AVHRR) Imagery of Saginaw Bay, Lake Huron

Interannual differences in nutrient concentrations, phytoplankton densities, and the dispersal of zooplankton and fish life history stages (e.g., planktonic larvae, resting eggs) in embayments often are contingent upon bay and coastal water exchange and movements. However, predicting water mass exchange is difficult in that many factors influence the circulation of waters within bays. The central theme of this contribution is that circulation phenomena derived from simple models can be identified and classified using satellite-obtained lake surface temperature maps, and the incidence of events related to gross temperature regime (season) and winds (shorter-term perturbations). To illustrate this potential, the high sampling frequency of AVHRR imagery was used to examine seasonal surface temperature patterns between Saginaw Bay and Lake Huron over a 3-year period. Linear regressions of CoastWatch IMGMAP and OCNMAP daytime sea surface temperature (SST) algorithms against shipboard bulk temperatures were highly significant, with r 2 values of 0.98 and 0.94. Synoptic reconnaissance of lake surface temperatures from AVHRR verified many previously known general seasonal events, yet provided much better spatial coverage. The thermal bar persisted in the bay for approximately 6 weeks from late April until mid-June. The combination of shallow depths and impounded river discharges caused inner bay waters to warm more rapidly than outer bay and open lake waters. A thermal gradient of 6 to 10°C persisted between the inner bay and Lake Huron waters throughout the summer. The persistence of major spatial thermal gradients restricted mixing of inner bay waters with the outer bay and open lake, whereas inner and outer bay temperatures converged during fall months, increasing the likelihood of mixing. However, frequent wind-induced effects can cause circulation reversals and move surface waters in quite complex patterns across the bay. AVHRR image classification confirms the sensitivity of inner bay waters to wind stress-related circulation, aiding interpretations of historical data sets.

Nutrient distribution in a papyrus swamp: Lake Naivasha, Kenya

Much of the permanent swamps of tropical Africa consists of monotypic stands of papyrus ( Cyperus papyrus L.). Papyrus has a high photosynthetic and productive potential due to the presence of C 4 photosynthesis. The objective of this study was to assess the nutrient status in the various compartments of a papyrus swamp which fringes Lake Naivasha, Kenya, in order to identify nutrients most likely to limit primary production. In swamp water, plant-available nitrogen was largely in the form of ammonium ions, phosphorus concentrations were higher than in the open lake water and sulphur was present in only trace amounts. The presence of C 4 photosynthesis in papyrus means that it is more efficient than C 3 species in its use of nitrogen. Plant tissue nutrient analysis suggested that there was a considerable amount of translocation of nutrients from older portions of the plant to new growth. The atomic ratio of 44N:3P:1S in papyrus suggests that sulphur is the nutrient most limiting growth of papyrus in the swamps. Calculations show that removal of large quantities of nutrients following papyrus harvesting may lead to reduced production rates in subsequent regrowth periods.

Lessons from practical application of an ecosystem approach in management of the Laurentian Great Lakes

AbstractThe Canada–United States Great Lakes Water Quality Agreement calls for the use of a systematic and comprehensive ecosystem approach (i.e. accounting for interrelationships among water, air, land, and all living things, including humans, and involving all user groups in comprehensive management) in water resource planning, research, and management. This Agreement further calls for the public to be consulted in all management actions. Remedial action plans (RAP) are being developed and implemented to restore uses in degraded areas of the Great Lakes and lakewide management plans (LaMP) are being developed and implemented to restore uses in open lake waters. These planning processes represent practical application of ecosystem approach theory. Lessons from practical experiences with Great Lakes RAP and LaMP include: an ecosystem approach can result in eliminating overlap and increasing efficiency; there can be positive effects from opening up decision‐making processes through meaningful public participation; priority should be placed on reaching agreement on problems and priorities; identification of key actions and delineation of sequencing, timeframe, and responsibilities is essential to ensure accountability; there is a need for a step‐wise approach to use restoration and demonstration of incremental progress; emphasis should be placed on planning cooperatively and sharing responsibilities for programme delivery; governments should provide resources to factilitate multi‐stakeholder decision‐making processes; spatial and temporal scale issues must be addressed; management actions should be treated as experiments; coupling of research and management has proven time and again to be cost‐ and ecosystem‐effective; and emphasis should be placed on measuring and celebrating progress for continuous improvement.

Seasonal Succession and the Strength of Intra‐ and Interspecific Competition in a Daphnia Assemblage

Species of the genus Daphnia are generalized filter—feeders and potentially strong competitors, yet several species often coexist in the open waters of lakes. We investigated the population dynamics and competitive interactions of two Daphnia species in Gull Lake, Michigan. In each of 3 yr D. pulicaria was always common, while D. galeata mendotae became abundant only in late summer. The summer invasion of D. galeata mendotae was associated with a decline in abundance of D. pulicaria in some, but not all years. Decline of D. pulicaria was strongly predicted by the loss of oxygen from deep water during summer, which resulted in greater spatial overlap between the species, and by changes in the quality of the phytoplankton resources. We employed in situ enclosures to manipulate the density of each species and quantify the intensity of intra— and interspecific competition. Repeated competition experiments demonstrated that the relative exploitative ability of species reversed from early to late summer. Strong interspecific competition was often observed, but its strength varied with juvenile or adult stage, and with season. Daphnia pulicaria juveniles were always affected strongly by interspecific effects, while D. galeata mendotae juveniles were impacted largely by intraspecific effects. The relative strength of intra— and interspecific competition on adults reversed from early to late summer for each species. The magnitude of intra— and interspecific effects on D. pulicaria adults was similar during early summer, but by late summer interspecific effects were much stronger than intraspecific effects. The reverse was true for D. galeata mendotae adults; interspecific effects greatly decreased in late summer. This seasonal shift in the nature of competitive interactions provides an explanation for seasonal succession in this Daphnia assemblage.

Physical, Chemical, and Biological Conditions Associated with the Early Stages of the Lake Michigan Vernal Thermal Front

An investigation of the thermal front in southeastern Lake Michigan during April 1988 revealed a dynamic physical, chemical, and biological environment. The front was observed approximately 4 km from the coast as a distinct gradient separating cold open-lake waters from warmer nearshore waters. Surface isotherms near the front were generally parallel to one another but skewed with respect to shore. Comparison between April 22 and 29 showed that the surface isothern pattern was modulated by wind stress. The pattern from April 29 showed signs of flow instabilities with horizontal scales of 1 km to 5 km. Surface drifter trajectories provided estimates of horizontal convergence at the fron which varied from 7×10−6 s−1 to 20×10−6 s−1. Inferred rates of downwelling, which ranged from 9.5 m d−1 to 20.7 m d−1, were sufficient to move a water parcel from the surface to the bottom in 2 to 6 d at the front. Convergent circulation was observed on both sampling dates despite contrasts in wind stress. Concentrations of chloride, soluble silica, and chlorophyll, which were always higher inshore, were 5% to 82% larger than offshore mean values. The aquatic environment just inshore of the thermal front was characterized by chlorphyll concentrations which exceeded 5.0 μg 1−1 while concentrations offshore were between 1.0 μg 1−1 and 2.0 μg 1−1. A relatively uniform vertical structure in chlorophyll concentrations in the frontal zone was consistent with the observed convergence and inferred downwelling near the front.

Survey of Pulmonate Snails of Central Minnesota. I. Lymnaeidae

ABSTRACT Aquatic snails were collected at 148 sites from various wetland habitats in central Minnesota between May and September, 1988. Ten lymnaeid species were collected, including Lymnaea palustris, L. stagnalis, L. exilis, L. caperata, L. catascopium, L. megasoma, L. (Fossaria) modicella, L. (F.) parva, L. (E.) bulimoides, and L. (F.) dalli. These species were found at 30-, 18-, 15, 12-, 11-, 7-, 20-, 9-, 1.4-, and 0.7% of the collection sites, respectively. Lymnaeids were found most frequently in still water of near neutral pH with a small particle size substrate. However, individual lymnaeid species showed great variability in habitat type selection. Lymnaea megasoma and L. exilis were found in slightly acidic water. Lymnaea catascopium was found in the deeper open water of lakes and slow moving rivers, while L. caperata and L. (Fossaria) spp. were found in temporary wetlands and mud flats. Wetland habitat reduction during the drought of 1987–1989 may have influenced distribution of the amphibious s...

The phytoplanktonic ways of life.

The adaptations of phytoplankton to life in suspension in water are considered with particular reference to hydromechanical factors ranging from molecular motion to ocean currents. The smallest phytoplankton, the picoplankton (0.2-2.0 μm), are the best adapted to the physico-chemical environment of the open waters of seas and lakes and, other things being equal, can out-compete the larger forms. The picophytoplankton are an autotrophic component in a microbial community, the ultraplankton, which also includes bacteria and flagellates up to about 20 μm in linear dimensions. This community is a highly dynamic and self-contained equilibrium system operating within a domain dominated by molecular diffusion. Within the photic zone it is limited, not by nutrient supply, but by its internal predator-prey relationships. It appears to be cosmopolitan, both in the sea and in freshwaters, to vary little either in time or space in species composition or in biomass concentration, and to contribute a minimum of organic carbon to higher trophic levels. There appears to be a fundamental divide in form and function between this and the microplankton, composed of organisms larger than about 20 μm. This community can only develop when nutrient levels are in excess of the concentrations required by the picoplankton. It is opportunistic, non-equilibrium in its dynamics, and highly variable in floristic composition and biomass concentration. Its life processes are dominated by turbulence. Nutrient supply is largely determined by turbulent eddy diffusion and movement of the organisms relative to the water mass. The microphytoplankton falls broadly into two types, one of which, exemplified by the diatoms, depends on turbulence to maintain it in the photic zone and the other, exemplified by the dinoflagellates and colony-forming cyanobacteria, relies on motility or buoyancy control to position it in a relatively stable water column so as to have best access to light and nutrients. The waxing and waning of microplankton populations is largely determined by hydrography and their floristic compositions by the interactions of the daily and seasonal rhythms of the organisms with the periodicities in the environment. In contrast to the ultraplankton microplankton species show distinct differences in biogeographical distribution. Throughout the discussion attention is drawn to the intimate relationships between the activities of phytoplankton and those of viruses, bacteria and zooplankton and the impossibility of getting a proper understanding of the physiology of the phytoplankton if they are considered in isolation. CONTENTS Summary 191 I. Introduction 192 II. Some reminders about the aqueous medium 193 III. The ideal phytoplankton organism 194 IV. Some aspects of the physiological ecology of the picoplankton 195 V. The ultraplanktonic community 197 VI. A divide in the phytoplankton 201 VII. Some aspects of the physiological ecology of the microphytoplankton 203 VIII. Small scale turbulence in the environment of phytoplankton 205 IX. Intermediate scale turbulence in the environment of phytoplankton 207 X. The effects of large scale rotational stirring 220 XI. Phytoplankton as part of a community 221 XII. Conclusions 222 References 223.

Riparian zone as a source of phosphorus for a groundwater-dominated lake

Groundwater entering Lake Bysjön in southern Sweden is somewhat higher in specific conductance and up to 20 times higher in phosphate than the mean for the lake. This leads to elevated values of both specific conductance and phosphate in lake water within a 500 m long and several meter wide strip along the shore. In areas not influenced by groundwater inflow, specific conductance and phosphorus content near the shore are close to that of open lake water. High concentrations of phosphate (up to 9 mg/l PO 4-P) in the inflowing groundwater originate from the riparian zone surrounding the lake. It is suggested that, over a long time, this ecotone has accumulated phosphorus and other nutrients that were transported from the adjacent developed areas and arable land. This phosphorus is now entering the lake, probably as a result of increased decomposition of organic matter.

Perlphyton as Indicators of Enrichment in Lake Pend Oreille, Idaho

ABSTRACT Periphyton in the littoral zone of Pend Oreille Lake, a large (383 km2, deep (Zmax — 380 m)) meso-oligotrophic lake in northern Idaho, were studied to compare with pelagic productivity and to identify areas of inshore degraded water quality. Periphyton growth was determined on artificial tiles and natural substrates at 0.5 and 1.5 m depths. Means for all measures of production on natural substrates were higher than means for artificial substrate. Indicators of biomass were higher on 0.5 m tiles than those at 1.5 m; exposed sites, however, showed less difference between depths than did the more sheltered sites. Because of inorganic interference, ash-free dry weight provided a better measure of periphyton biomass than dry weight. Significant differences existed between sites, indicating greater algal growths in developed and relatively confined bays. Cymbella was dominant on natural substrate, while Cymbella, Mougeotia, and Rhizoclonium were co-dominant on artificial substrate. Blue-green algae biomass comprised only a small part of the total biomass on either artificial or natural substrates. Periphyton biomass in Pend Oreille Lake was comparable to other lakes showing accelerated eutrophication. Despite Pend Oreille Lake's great depth and large profundal area, littoral productivity was similar to lakes more shallow in nature with higher overall productivity. In-shore water quality degradation was documented at a time when open-lake conditions indicated the lake was meso-oligotrophic. Given that changes in lake trophic status would first show up in littoral areas–compared to the relatively slow changes taking place in the phytoplankton of pelagic areas–periphyton monitoring should provide valuable refinement to in-depth limnological studies on open waters of lakes.

Dynamics of zooplankton community in enclosures of different types in a shallow eutrophic lake.

Changes in abundance and species composition of the zooplankton community in enclosures of different types in Lake Suwa were investigated and compared. Zooplankton abundance was consistently higher in tube-type enclosures (5m×5m×4.2m), which were open to the bottom sediment, than in bag type enclosures (5m×5m×3m), which had bottom sheets. In the latter enclosures, zooplankton abundance gradually decreased during the experimental period. Zooplankton community structure in the tube-type enclosure changed in a similar way to that in open lake water for eight months. Therefore, an enclosure of this type was considered to be suitable for maintaining an example of the lake ecosystem over a long period. The phenomenon of a decrease in zooplankton abundance in the bag type enclosure did not apply to the small bag enclosure (1m×1m×1m), in which zooplankton had high productivity and a littoral species, Chydorus sphaericus, predominated. This species was not found in the central zone of the large enclosures (in both the bag and tube types). The dominance of C. sphaericus in the small bag enclosure was probably due to wall effects.

Methane flux from the central Amazonian floodplain

A total of 186 methane measurements from the three primary Amazon floodplain environments of open water lakes, flooded forests, and floating grass mats were made over the period from July 18 through September 2, 1985. These data indicate that emissions were lowest over open water lakes, where flux averaged 27 plus or minus a standard error of 4.7 mg CH4 m−2 d−1(n = 41). Flux from flooded forests and grass mats was significantly higher. Emissions from flooded forests averaged 192±26.8 mg CH4 m−2 d−1(n = 90), while those from floating grass mats averaged 230±72.2 mg CH4 m−2 d−1 (n = 55). At least three transport processes contribute to tropospheric emissions: ebullition from sediments, diffusion along the concentration gradient from sediment to overlying water to air, and transport through the roots and stems of aquatic plants. Measurements indicate that the first two of these processes are most significant. Diffusive flux from flooded forests averaged 50.5±11.0 mg CH4 m−2 d−1, while that from floating mats averaged 43.7±11.8 mg CH4 m−2 d−1. Diffusive flux from open waters averaged 8.3±1.9 mg CH4 m−2 d−1. Emissions through bubbling were 168±32.2 (flooded forest), 346±128 mg CH4 m−2 d−1 (floating grasses), and 17.3±5.2 (open water). We estimate that on the average, bubbling makes up 49% of the flux from open water, 54% of that from flooded forests, and 64% of that from floating mats. If we apply our measurements to the entire Amazonian floodplain, we calculate that the region could supply up to 12% of the estimated global natural sources of methane.

Review Lecture - Picoplankton

Picoplankton consists of those organisms found in the open waters of seas and lakes which are capable of passing through a filter with 2 μm pores but not through one with 0.2 μm pores. Cells in this size range are well adapted to planktonic life in that they sink extremely slowly and are more efficient than larger forms in taking up nutrients and absorbing radiant energy. Picophytoplankton includes coccoid cyanobacteria and a variety of eukaryotic algal forms. Strains studied in the laboratory have all been found to show maximum growth at relatively low irradiances, the eukaryotic forms being more efficient than the cyanobacteria in utilizing the blue light which predominates at the bottom of the photic zone in clear oceanic waters. Oceanic strains of coccoid cyanobacteria, however, are characterized by high concentrations of phycoerythrin, which appears to function as a nitrogenous reserve as well as an accessory pigment in photosynthesis. The seasonal and spatial distribution of picophytoplankton seems explicable in terms of these physiological characteristics. Numbers of coccoid cyanobacteria have shown a striking correlation with temperature in a number of different situations. Heterotrophic bacteria are also included in the picoplankton, and a review of the information concerning them suggests that they form a highly dynamic population subsisting on dissolved organic matter liberated by living phytoplankton and zooplankton and by decomposition of dead matter. The productivity of this population in the euphotic zone approaches that of the phytoplankton. Both the picophytoplankton and the bacterioplankton are preyed on by phagotrophic flagellates. Both bacteria and flagellates are active in regeneration of mineral nutrients. Regardless of the salinity, temperature or nutrient status of the water, the numbers of heterotrophic bacteria, picophytoplankton and flagellates tend to be around 10 6 , 10 4 and 10 3 organisms per millilitre respectively. It is suggested that these populations form a basic, self-sustaining and self-regulating community in all natural waters. From present information, it seems that little of the energy which passes through this community finds its way into the larger planktonic organisms, but the role of picoplankton in recycling nutrient elements is of great importance in the marine ecosystem.

Rotifera from Australian inland waters. I. Bdelloidea (Rotifera : Digononta)

In this paper, the first of a series providing a systematic revision of all Rotifera now known from Australian inland waters, the common bdelloid rotifers are reviewed. The group is epiphytic or epibenthic in habit, but some species commonly occur in open water of billabongs, lakes and rivers, particularly in association with algal blooms. Frequent occurrence of bdelloids in plankton collections necessitates diagnostic keys to their identification. For the common species only, morphological features of taxonomic significance are described and figured to facilitate further study.