bluuebunny/crossref_metadata_2025 huggingface dataset:
Inducing User Cooperation in Peer-to-Peer Television
Authors: Fokker Jenneke , Ridder Huib de , Westendorp Piet , Pouwelse Johan
Published: May 2010

Television and the Internet have proven to be a popular combination for both broadcasters and viewers. Because of this popularity they are increasingly facing the consequences of central bottlenecks, which could be overcome by taking a different approach: Peer-to-Peer (P2P) technology. However, P2P systems can only be successful with as much cooperation among as many users as possible. This chapter explains how this cooperation is hard to enforce, and how inducing it might be more successful. Relevant psychological theories are listed that can be used to induce this user cooperation, along with possible applications of cooperation inducing mechanisms for Peer-to-Peer Television (P2P-TV) systems. The authors aim to provide practical criteria along which these mechanisms can be evaluated on their contribution to social activity in P2P-TV systems.
Online Video as a Social Activity
Authors: Weisz Justin D.
Published: May 2010

Online video is one of the Internet’s most popular services. In addition to entertainment, it can provide a social experience. This chapter describes several design decisions related to incorporating a live chat feature alongside online video, and how these decisions could influence the entertainment and social dimensions of the viewing experience. Two laboratory studies explore issues of distraction, entertainment and sociability when integrating live chat with online video. Surprisingly, these studies show that despite being distracting, chat with video can be enjoyable and sociable. Researchers and practitioners need to explore the generality of this finding both for different genres of content and interaction media and for small and large viewing audiences. The chapter concludes by looking at new models for online video and chat and the implications of those models on sociability.
Molybdenum assimilation by cyanobacteria and phytoplankton in freshwater and salt water
Authors: Cole Jonathan J. , Lane Judith M. , Marino Roxanne , Howarth Robert W.
Published: May 2010

We measured the uptake rate of molybdate and related kinetic parameters for nine taxa of cyanobacteria and for the natural phytoplankton communities of six freshwater lakes containing planktonic N2‐fixing cyanobacteria. Molybdate uptake followed saturation kinetics and was competitively inhibited by both tungstate and sulfate. Tungstate inhibited molybdate uptake in a nearly mole‐for‐mole fashion; inhibition constants (Ki) were in the same concentration range (10–30 nM) as the half‐saturation constants for molybdate uptake (Km). Sulfate also inhibited molybdate uptake, but this inhibition was much less specific. The Ki for sulfate was in the mM range—three orders of magnitude above the Km for molybdate uptake. Despite these high Ki values, however, sulfate can be an important inhibitor of molybdate uptake in many natural waters as sulfate concentrations are usually some 4–6 orders of magnitude greater than molybdate concentrations. At ambient sulfate and molybdate concentrations in most freshwater lakes, molybdate uptake would be inhibited by 1–5% due to sulfate. In marine and estuarine systems this inhibition would be 15–20% and in some saline lakes could be >70%.
Near‐bed turbulence and hydrodynamic control of diffusional mass transfer at the sea floor
Authors: Dade W. Brian
Published: May 2010

A simple closure scheme for turbulent transport yields mean‐velocity and dissolved‐substance concentration profiles just above and solute fluxes across a sediment‐water interface underlying uniform, steady flow. In the case of near‐bed turbulence characterization, this approach retains both turbulent and viscous terms in expressions for important structural aspects of the near‐bed regions of turbulent boundary layers. Moreover, a modified turbulent kinetic energy balance is used to define eddy viscosity in the viscous‐dominated region of flow very near the bed. In the case of characterization of mass distribution and diffusional transfer rate, the approach partitions important factors that control mass transfer rate: nearbed turbulent transport, interfacial‐flux boundary condition, and reaction kinetics. Diffusive sublayers overlying smooth beds exposed to typical deep‐sea conditions are predicted to be ∼ 1 mm thick, a result in agreement with the sublayer thickness observed in situ and the inferred thickness used in many hydrodynamic models. One application of the new closure scheme indicates that typical biogenic roughness in fine‐sediment marine environments enhances solute exchange rates threefold over those expected for a smooth bed. This increase is due to enhanced turbulent transport in the vicinity of the rough bed and occurs in spite of viscous ponding of “dead water” among roughness elements.
A strategic simulation model of a fjord ecosystem
Authors: Ross Alex H. , Gurney William S. C. , Health Michael R. , Hay Steven J. , Henderson Eric W.
Published: May 2010

We formulate a strategic simulation model of a fjordic ecosystem, paying careful attention to consistency of spatial and temporal scales. Our model incorporates all the major physical and biological elements of the system but is simple enough to allow unambiguous identification of the mechanisms underlying its behavior. Despite this simplicity the model is capable of semiquantitative agreement with the observed behavior of the Killary Harbor ecosystem over the 1981 season.

The key conclusion from our analysis of the model is that because of the very high rates of tidal and freshwater flushing in Scottish sea‐lochs, the persistence of such systems is ultimately determined by the balance of nutrient import and export in a manner analogous to a laboratory chemostat. Except at the peak of the spring bloom, inorganic nitrogen supply exceeds biological demand, so that primary production is controlled by physical factors (temperature and irradiance) and the activities of higher trophic levels. The size of the spring phytoplankton bloom is mainly determined by the dynamics of the following zooplankton bloom and is thus strongly influenced by the overwintering success of zooplankton inside the system as well as zooplankton immigration from the sea.
Zooplankton feeding ecology: A cinematographic study of animal‐to‐animal variability in the feeding behavior of Calanus finmarchicus
Authors: Turner Jeferson T. , Tester Patricia A. , Strickler J. Rudi
Published: May 2010

Cinematography of the feeding behavior of five adult female Calanus finmarchicus revealed considerable individual variation in time allocation to three types of behavior: “slow swim,” in which only feeding appendages were moving, “jump,” in which first antennae and posterior swimming legs were moving, and “break,” in which no appendages were moving. Filming was done at three different concentrations of unialgal cultures and in filtered seawater. Animal‐to‐animal variation within given food concentrations was significant (α = 0.01, t‐test). The significant differences (α = 0.01, Cochran’s Q‐test) in mean responses to different food concentrations were complicated by high individual animal variability within food concentrations. Behavioral transitions per minute, and durations of individual periods of slow swimming and break were similarly variable. There was no relation between time spent feeding and concentration of food. We conclude that cinematographic techniques can precisely determine behavioral time allocation, but that sufficient replication must be performed.
Mechanisms of suspension feeding in bivalves: Resolution of current controversies by means of endoscopy
Authors: Ward J. E. , MacDonald B. A. , Thompson R. J. , Beninger P. G.
Published: May 2010

Controversy concerning the mechanism of suspension feeding in bivalves centers around whether particle capture and transport on the gills (ctenidia) is accomplished via mucociliary or hydrodynamic action. Evidence for and against these fundamentally different processes has been based on examinations of isolated feeding structures and dissected specimens, techniques that may produce artifactual data owing to the trauma associated with the procedures. In the present study, in vivo observations of the ctenidia of undisturbed bivalves, made with a fiber‐optic endoscope and video image‐analysis system, revealed that the two mechanisms are not mutually exclusive. Both mucociliary and hydrodynamic mechanisms function concurrently at different sites on the ctenidia, thereby minimizing particle loss and optimizing particle transport efficiency. The importance of mucus in the normal feeding process of bivalves is confirmed. These findings refute results of previous studies that used surgically invasive techniques and emphasize the importance of making observations on morphologically intact specimens.
Fish foraging behavior changes plankton‐nutrient relations in laboratory microcosms
Authors: Flamarique I. Novales‐ , Griesbach S. , Parent M. , Cattaneo A. , Peters R. H.
Published: May 2010

To demonstrate that the effects of higher trophic elements on plankton in laboratory aquaria are not simple top‐down or bottom‐up processes, we measured phosphorus and chlorophyll concentrations in replicated month‐old aquaria undergoing one of five permutations involving three fish species, Daphnia pulex, and algae. Goldfish (Carassius auratus) extirpated the Daphnia and produced the highest observed algal and nutrient levels. Daphnia persisted with armored catfish (Plecostomus hypostomus) but algal levels were still high, even though total P concentrations of the water were lower. Angelfish (Pterophyllum scalare) cropped all the Daphnia, but only moderate levels of algae resulted, apparently because these fish regenerate sedimented nutrients less effectively. Aquaria with neither fish nor Daphnia supported even less algae, although total P concentration was not reduced. Finally, the water in aquaria with Daphnia, but no fish, had the lowest levels of both chlorophyll and total P. These gross changes were accompanied by shifts between the two dominant algal genera, seemingly because higher levels of nutrient regeneration favor Scenedesmus over Monoraphidium. Apparently, higher trophic elements affect lower ones directly, from above by modifying predation pressure and from below by changing the quantity and quality of regenerated nutrients, and indirectly by modulating competition within the plankton and between plankton and periphyton.
Coupling of microbial fermentation and respiration processes in an intertidal mudflat of the Elbe estuary
Authors: Kerner M.
Published: May 2010

In laboratory experiments, the consumption of terminal electron acceptors was studied under defined redox conditions during different seasons. Under oxic conditions oxygen together with nitrate and Mn was reduced. Under suboxic conditions nitrate reduction occurred simultaneously with Mn and ferric Fe reduction and the fermentation of organic matter. Over an annual cycle, maximum reduction rates were found in early summer. These were 24.71 for oxygen, 1.13 for Mn(IV) and 3.33 µmol g−1 d−1 for Fe(III). In winter, the respective rates decreased 3.4‐, 4.7‐, and 9.2‐fold. Nitrate reduction remained constant from July to November at about 5.62 µmol g−1 d−1 and decreased 2.8‐fold by February. The production of CO2 due to fermentation of organic substances was the same magnitude as that for oxygen respiration in summer. When fermentation processes stopped at the end of summer, nitrate respiration out‐competed Fe and Mn reduction for organic substrate. These results indicate that even great differences in free energy do not prevent coexistence of different respiration processes in the same sediment layer. Microbial reduction rates in the sediment appear to depend on organic matter of low molecular weight which is produced during fermentation.
Rare earth tagging methods for the study of larval dispersal by marine invertebrates
Authors: Levin Lisa A. , Huggett Douglas , Myers Philip , Bridges Todd , Weaver Jack
Published: May 2010

Rare‐earth elements (REEs) are proposed as a label for invertebrate larvae (clams, barnacles, and polychaetes) and passive larval mimics (polystyrene spheres) to be used in field studies of larval dispersal. Different elements, their uptake levels, retention times, and effects on larval survivorship were examined to assess suitability of REEs as larval tags. Lu, Sm, and Eu were selected for labeling work based on extremely low levels in natural plankton and seawater and due to the high sensitivity of neutron activation analysis to these elements. Adequate label retention occurs on time scales of hours to days in both larvae and microspheres. Combined use of Eu‐labeled microspheres and Lu‐ and Sm‐labeled larvae in release‐recapture mode offers a highly sensitive method for studying trajectories and behavior of larvae in natural settings. However, dilution factors may limit experimentation to small and intermediate spatial scales (meters to kilometers) in the field.
Carbon dynamics and sources in the Parani River
Authors: Depetris Pedro J. , Kempre Stephan
Published: May 2010

The Paraná River was sampled and analyzed for carbon and mineral concentrations at the Paraná‐Santa Fe (Argentina) cross‐section (∼600 km above the mouth) between March 1981 and November 1984. Within this period, the Paraná was affected by an extraordinary flood caused by the 1982 El Niño/ Southern Oscillation (ENSO) climatic anomaly. Under such conditions, with a flow 75% higher than the long‐term mean, the river exported a total organic C (TOC) load of 8.43 Tg yr−1(3.0 g m−2 yr−1) of which 89% was accounted for by dissolved organic C (DOC) and the remainder by particulate organic C (POC). Under normal hydrological conditions, however, the Paraná has a TOC load that is roughly half of that determined during the ENSO‐triggered flood (4.43 Tg yr−1, 1.6 g m−2 yr−1), but with a very different DOC: POC ratio (63 : 37).

In July–August 1985 the Paraná was sampled along a reach of over 1,300 km. At the time of sampling, the Paraguay River supplied ∼68% of the POC load, 59% of the labile particulate load (LPOC), and 71% of the DOC entering the middle reach of the Paraná. Carbohydrates in LPOC appear to become more abundant than amino acids in the lower reaches, probably due a significant input from the floodplain of the Paraná.
A dynamic model for wave‐induced light fluctuations in a kelp forest
Authors: Wing Stephen R. , Leichter James J. , Denny Mark W.
Published: May 2010

We formulated a dynamic model with linear wave theory to predict the effects of wave height, wave length, and water depth on modulation of the local surface cover in a Macrocystis pyrifera canopy. This model was incorporated into a general model for attenuation of photosynthetically active radiation (PAR) in a M. pyrifera forest with particular emphasis on light reaching understory algae. The model predicts that the period of fluctuations of PAR on the bottom matches that of the dominant wave period and that the amplitude of irradiance peaks is increased by positive local surface areal stain during the trough of a wave. Field measurements of instantaneous irradiance and surface elevation and simultaneous video recording of the surface canopy allowed investigation of these predictions. Cross‐correlation analysis on irradiance and surface elevation measurements showed a significant negative correlation between surface elevation and PAR reaching the understory. This correlation cannot be attributed to the decrease in light‐path length alone, but can be explained by the change in M. pyrifera surface cover. Measured changes in instantaneous fractional canopy cover exceeded theoretically predicted values by a factor of as much as 3. Consequently, the intensities of light flecks exceeded predictions. A combination of mechanisms, as well as assumptions of the model, may explain the deviation between the magnitudes of predicted and measured fluctuations in canopy cover and light. The dominant period of ocean swells is typically in the range of 5–20 s, and light flashes with these periods have been shown to effect significant gains in light utilization efficiency by certain algae.
Dark fixation of 14C: Variations related to biomass and productivity of phytoplankton and bacteria
Authors: Li W. K. W. , Irwin B. D. , Dickie P. M.
Published: May 2010

In various North Atlantic sites, the rate of dark 14C fixation by microbial plankton was significantly correlated with the rate of light 14C fixation, with the rate of bacterial [3H]thymidine incorporation, and with chlorophyll biomass. For plankton sampled near the sea surface (<5 m) and at the depth of the maximum light 14C fixation, the median value for the ratio of dark to light fixation was only 1%. At the depth of the subsurface chlorophyll maximum where less light was available, the median value for this ratio was still quite low at 7%. Our results confirm early claims that generally in the oceans, including oligotrophic regions where plankton biomass is low, dark 14C fixation is high in relation to light fixation only at depths where photosynthesis is severely limited by light. We infer that direct 14C fixation by both bacteria and phytoplankton are significant processes that contribute to measured 14C fixation in opaque bottles during 12 h dawn‐to‐dusk incubations.
Vertical distribution and transport of molybdenum in a lake with a seasonally anoxic hypolimnion
Authors: Magyar B. , Moor H. C. , Sigg L.
Published: May 2010

Distribution and trends of Mo concentrations in the seasonally anoxic Lake Greifen were investigated over 15 months. Mo in water samples and settling particles was determined by catalytic adsorption polarography and inductively coupled plasma mass spectrometry. Mo concentrations in the epilimnion were usually homogeneous at −0.48 µg liter−1. A significant decrease with depth was found during the stratification period. The lowest Mo concentrations (0.31 µg liter−1) were found in the presence of H2S near the sediment. A vertical flux of particle‐bound Mo of 1.1–4.6 µg m−2 d−1 was found. The Mo concentration‐depth profiles result from a combination of different transport mechanisms that are compared by computer model calculations.
Potential role of fish predation and natural populations of zooplankton in structuring a plankton community in eutrophic lake water
Authors: Christoffersen Kirsten , Riemann Bo , Klysner Annette , Søndergaard Morten
Published: May 2010

During April to September, plankton community structure was monitored in large enclosures (60 m3) in the presence and absence of planktivorous fish. Weekly sampling included inorganic nutrients, oxygen, pH, and transparency as well as biomass of phytoplankton, bacteria, heterotrophic flagellates, rotifers, and macrozooplankton. In fishless enclosures, concentrations of inorganic nutrients and transparency were higher than in enclosures with fish, whereas oxygen, pH, and biomasses of phytoplankton, picoplankton and rotifers were lower. As an average for the entire period, Chl a was 14 µg liter−1 in the enclosures without fish and 46 µg liter−1 in enclosures with fish. Macrozooplankton biomass was significantly lower in enclosures with fish than in enclosures without fish. Averaged over the entire period macrozooplankton biomass was 625 µg C liter−1 in enclosures with fish and 1,149 µg C liter−1 in those without fish. Cladocerans dominated the macrozooplankton community in fishless enclosures and controlled the biomass of bacteria and heterotrophic flagellates. The rotifer community was depressed in enclosures without fish, which probably was a combined effect of mechanical interference with Daphnia and food competition. The initial buildup of a high macrozooplankton biomass and the dominance of cladocerans in the enclosures without fish, prevented cyanobacteria from forming large colonies. In contrast, cyanobacteria (Microcystis, Aphanizomenon, and Anabaena) bloomed in the enclosures with fish. The observed changes in the plankton communities support the theory of cascading trophic interactions.
Individual and population level consequences of an algal epibiont on Daphnia
Authors: Allen Yvonne C. , De Stasio Burt T. , Ramcharan Charles W.
Published: May 2010

In spring 1990 an algal epibiont (Synedra cyclopum var. incisa) infested cladocerans and copepods in Lake Mendota, Wisconsin. Daphnia pulicaria and Daphnia galeata mendotae were particularly infested (mean maximum diatom density, 22,900 cells animal−1). Laboratory experiments revealed that infested Daphnia had greater sinking and filtering rates than uninfested animals. Respiration rates were not significantly different between the two groups. Field‐collected animals were counted and scored for degree of infestation, number of eggs, and total body size. Abundance of both adult and immature Daphnia increased only after the epibiont no longer infested Daphnia. Clutch size was not significantly different between infested and uninfested Daphnia, but death rates were higher during the period of infestation. This increased mortality is attributed to added stress on individuals caused by the epibiont, demonstrating the translation of physiological effects into population level consequences.
Resuspension of sediment by focused groundwater in Lake Banyoles
Authors: Casamitjana X. , Roget E.
Published: May 2010

Resuspension of sediment by subterranean springs occurs in karstic, multibasin Lake Banyoles, Spain. The sediment at the bottom of one of the basins was consolidating when intrusion of groundwater caused resuspension. Here, the lutocline rose nearly 20 m over 10 months. During this episode temperature profiles, sediment size distributions, bulk density, and settling rates showed that the jet‐generated turbulence produced strong mixture in the central core of the conic depression forming the basin. Data from another basin where the sediment was always in suspension are presented for comparison. Here, the stratification in density and settling rate of the particles suggest sorting out of the aggregates, with the largest flocs occupying the deepest parts of the basin.
Lack of coupling between heterotrophic nanoflagellates and bacteria: A general phenomenon across aquatic systems?
Authors: Gasol Josep M. , Vaque Dolors
Published: May 2010

The literature proposes that bacterial abundance (BA) and heterotrophic nanoflagellates abundance (HNFA) are positively related across different aquatic systems, suggesting a strong resource control of HNFA and predatory control of BA. To test this proposed pattern, we collected published and unpublished data and analyzed trends across lakes, rivers, marine, and benthic samples. BA varied between 105 and 1011 cells ml−1, while HNFA ranged from 102 to 106 cells ml−1. The relationship was stronger in systems with low bacterial abundances and weaker in the most bacteria‐rich systems. When data were averaged per study or per system we detected a trend with trophy, with highest HNFA in benthic systems followed by lakes and coastal areas of the sea, and lowest abundances in rivers and the open ocean. This relationship was improved in lakes, where cladoceran abundance was negatively related to HNFA. The effect of cladocerans was stronger in lakes where Daphnia spp. dominated. The weak pattern observed between BA and HNFA across systems suggests that several factors (resources, predators, environment, etc.) are acting differently on BA and HNFA. Changes in population abundances of bacteria and heterotrophic nanoflagellates are mainly determined by nutrient supply and grazing, and also by complex trophic interactions with numerous feedbacks. Empirical relationships between BA and HNFA across systems can only partially explain these changes in terms of predator‐prey dependence.
Lead isotopic disequilibria between plankton assemblages and surface waters reflect life cycle strategies of coastal populations within a northeast Pacific upwelling regime
Authors: Flegal A. Russell , Garrison David L. , Niemeyer Sidney
Published: May 2010

Stable lead isotopic compositions (204Pb, 206Pb, 207Pb, 208Pb) were determined for net plankton samples from a northeast Pacific upwelling regime, following a study that revealed pronounced isotopic composition differences in seawater within that regime. Lead isotopic ratios of the plankton were positively correlated with those of the seawater. Both evidenced the predominance of two sources of industrial Pb (North American and Asian aerosols) in northeast Pacific surface waters, which substantiated the postulate that essentially all (>90%) of the Pb in the northeast Pacific biome derives from anthropogenic emissions. However, the isotopic compositions of plankton and seawater collected concurrently from the same locations were often markedly dissimilar. The isotopic disequilibria are attributed
The stoichiometry of carbon, nitrogen, and phosphorus in particulate matter of lakes and oceans
Authors: Hecky R. E. , Campbell P. , Hendzel L. L.
Published: May 2010

The mean carbon, nitrogen, and phosphorus contents of particulate material for 51 lakes or lake basins, extending from arctic to tropical climatic regions, including small lakes as well as the largest lakes in the world, indicate that Redfield ratios are the exception rather than the rule in freshwater. The C : P and N : P ratios are more variable for lake particles but generally higher than marine particles, and the mean molar C : N, C : P, and N : P ratios are substantially higher than the Redfield ratio of 106 : 16: 1. On average, lower C : N, C : P, and N : P ratios occur in subarctic lakes while higher ratios occur in the tropics and in temperate, oligotrophic lakes on the Canadian Shield. In shield lakes with long residence times (>6 months) the high ratios of C : N, C : P, and N : P do not originate from streamborne or atmospherically deposited particles but arise from in‐lake processes. Regression analysis demonstrates that small lakes are generally more N and P deficient than large lakes. In freshwaters, particulate composition ratios imply that a wide variety of conditions exists in lakes, including N and P deficiency, as well as N and P sufficiency. In the Experimental Lakes Area of Canada, independent physiological nutrient status indicators generally agree with the status indicated by seston ratios. The relative uniformity of marine C : N : P composition (compared to lakes) at the Redfield ratio suggests that marine plankton cannot be as severely, or as frequently, limited by N and P as lake plankton. Consequently, the paradigm of N limitation in the oceans requires qualification. Based on particulate composition, it is more correct to say that ocean plankton is not as N and P deficient as lake plankton.
Nutrient chemistry of the water column of Lake Tanganyika
Authors: Edmond J. M. , Stallard R. F. , Craig H. , Craig V. , Weiss R. F. , Coulter G. W.
Published: May 2010

Lake Tanganyika shows permanent thermal stratification with deep‐water temperatures that have been stable over the period of observation (since 1939). The lake is anoxic below ∼150‐m depth. In general the nutrients show Redfield behavior save in the deep waters of the northern basin where large excesses of phosphate and ammonia are present. Bacterial disproportionation of organic material probably plays an important role in producing these excesses. Inorganic desorption from fluvial detritus is also a possible source of excess phosphate in deep waters. The oxic‐anoxic boundary at ∼150 m is a sink for all forms of fixed nitrogen. Thus the nutrient budget of the lake probably involves fixation of nitrogen in the surface layer in addition to substantial inputs from rainfall and runoff, with the phosphate supplied by vertical mixing. Because these processes are in approximate balance under present conditions, the productivity of the lake must be very sensitive to changes in climatic forcing.
An estimate of CO2 flux in Lake Nyos, Cameroon
Authors: Nojiri Yukihiro , Kusakabe Minoru , Tietze Klaus , Hirabayashi Jun‐ichi , Sato Hiroaki , Sano Yuji , Shinohara Hiroshi , Njine Thomas , Tanyileke Greg
Published: May 2010

An outburst of lethal gas from Lake Nyos, Cameroon, killed more than 1,700 people on 21 August 1986. The surveys carried out so far indicate that a considerable portion of the CO2 dissolved in the lake was released to the atmosphere and asphyxiated the people. We revisited the lake in December 1988. The conductivity‐temperature‐depth profiler (CTD) measurements and chemical analysis of the lake water revealed that temperature, total dissolved solids (TDS), and CO2 content of the bottom water increased in parallel fashion, especially in the bottom layer, during the preceding 25 months. The result supports the view that CO, is being supplied to the lake bottom in the form of warm, CO2‐charged, mineralized water. From the increments of temperature and CO2, during the period, fluxes of heat and CO2, were estimated to be 0.43 MW and 1.0 Mmol yr−1. The CO2 flux is large enough to saturate the lake’s hypolimnion within ∼30 yr. In the 1988 survey, the very bottom layer of the lake was estimated to be close to saturation with CO2. Using the CO2‐TDS‐Si relationship and temperature dependence of the solubility of amorphous silica, we estimated the chemical composition of the warm, mineralized water; these estimates suggest the existence of a CO2‐saturated fluid below the sedimentary cover.
Landscape linkages between geothermal activity and solute composition and ecological response in surface waters draining the Atlantic slope of Costa Rica
Authors: Pringle Catherine M. , Rowe Gary L. , Triska Frank J. , Fernandez Jose F. , West John
Published: May 2010

Surface waters draining three different volcanoes in Costa Rica, ranging from dormant to moderately active to explosive, have a wide range of solute compositions that partly reflects the contribution of different types of solute‐rich, geothermal waters. Three major physical transport vectors affect flows of geothermally derived solutes: thermally driven convection of volcanic gases and geothermal fluids; lateral and gravity‐driven downward transport of geothermal fluids; and wind dispersion of ash, gases, and acid rain. Specific vector combinations interact to determine landscape patterns in solute chemistry and biota: indicator taxa of algae and bacteria reflect factors such as high temperature, wind‐driven or hydrologically transported acidity, high concentrations of various solutes, and chemical precipitation reactions. Many streams receiving geothermally derived solutes have high levels of soluble reactive phosphorus (SRP) (up to 400 µg liter−1), a nutrient that is typically not measured in geochemical studies of geothermal waters. Regional differences in levels of SRP and other solutes among volcanoes were typically not significant due to high local variation in solute levels among geothermally modified streams and between geothermally modified and unmodified streams on each volcano. Geothermal activity along the volcanic spine of Costa Rica provides a natural source of phosphorus, silica, and other solutes and plays an important role in determining emergent landscape patterns in the solute chemistry of surface waters and aquatic biota.
Geochemical and hydrologic controls on the composition of surface water in a high‐elevation basin. Sierra Nevada, California
Authors: Williams Mark W. , Brown Aaron D. , Melack John M.
Published: May 2010

Hydrologic, mineralogic, and soil data are used to determine the sources and geochemical controls on the composition of surface water in the Emerald Lake watershed (ELW), a high‐altitude basin located in the southern Sierra Nevada. The solute composition of stream waters at the ELW can be divided into three periods: snowpack runoff, a transition period in summer as snowpack runoff decreases and little precipitation occurs, and a low‐flow period from late summer through winter. Each period has different geochemical controls on the solute composition of surface waters. During snowpack runoff ∼50% of stream flow was from direct surface runoff and ∼50% of stream flow was return flow from subsurface reservoirs. Hydrologic residence time of subsurface water at maximum snowpack runoff was measured directly with a 6LiBr tracer and varied from 9 to 20 h. Three independent measurements show that the acidity in snowpack runoff was neutralized by cation exchange in soils and talus. Discharge from soil reservoirs was the primary source of stream flow during the summer transition period when the composition of stream flow was congruent with the stoichiometry of plagioclase weathering. Processes occurring below the soil zone exerted the dominant geochemical controls on the composition of stream waters during the period of low flow, with preferential weathering of the anorthite component of plagioclase in subsurface rock and further weathering of kaolinite to gibbsite.
Vertical mixing in a shallow, eutrophic lake: Possible consequences for the light climate of phytoplankton
Authors: MacIntyre Sally
Published: May 2010

Profiles of temperature‐gradient microstructure are used to define the size and location of mixing regions, the intensity of turbulence, and the potential exposure of phytoplankton to fluctuating irradiance in a shallow, turbid, productive lake. The part of the water column which was mixing tended to be subdivided into two regions with different dynamics, one in which the turbulence was active and one in which it was constrained by buoyancy. Generally the upper layer, which ranged from 0.3 to 1.5 m deep, was actively mixing. Energy dissipation rates were on the order of 10−7 m2 s−3, vertical eddy diffusivities ranged from 10−3 to 10−5 m2 s−1, and overturns mixed on a time scale of minutes. Phytoplankton could become well mixed before turbulent transport within overturns ceased and, while the wind persisted, were likely to experience continuous fluctuations in irradiance. In one of the largest overturns, phytoplankton could circulate between the 90% light level and the 5% light level in 3–4 min. Where buoyancy affected turbulence, energy dissipation rates ranged from 10−9 to 10−7 m2 s−3 and vertical eddy diffusivities from 10−7 to 10−4 m2 s−1. Mixing times based on these diffusivities exceeded π/N, the time scale for turbulent transport, indicating overturns would mix only partially. Phytoplankton could still experience large fluctuations in irradiance, but the fluctuations probably were not continuous.
Phytoplankton competition in Plußsee: A field test of the resource‐ratio hypothesis
Authors: Sommer Ulrich
Published: May 2010

During a 10‐month study in Plußsee Si, N, and light were found as potentially limiting resources for phytoplankton growth rates. Therefore, three ratios of essential resources (Si : N, Si : light, N : light) and one ratio of substitutable resources (nitrate : ammonium) were compared to changes in species composition to test the hypothesis that the seasonal change of phytoplankton species composition was a response to changing resource ratios. The relationship was analyzed by a rank correlation analysis between the relative contribution of individual species to total biomass and resource ratios. Allowance was made for time lags between changes in resource ratios and changes in relative biomass. Of 16 species, 14 showed a significant response to at least one resource ratio. Time lags ranged from 0 to 6 weeks. Most species seemed to be favored either by minimal or maximal ratios; optimal ratios in the middle of the range were rare.
Relationships between resource ratios and phytoplankton species composition during spring in five north German lakes
Authors: Makulla Alexandra , Sommer Ulrich
Published: May 2010

Phytoplankton species composition and the availability of potentially limiting resources were investigated in five northern German lakes (Suhrer See, Kellersee, Behler See, Plußsee, and Krummsee) during spring 1988. Species composition was related to resource ratios to test Tilman’s resource‐ratio hypothesis. The clearest results were obtained for Aulacoseira spp. Both the time‐courses within the lakes and the comparison among the lakes suggest a strong tendency of this genus to become dominant at high Si : light ratios. Fragilariaceae occupied the next position on the Si: light gradient. Such conditions permitted them to become important even when Si : P ratios were quite low. With the onset of stratification diatoms were replaced by flagellates.
Food‐web responses to species invasion by a predatory invertebrate: Bythotrephes in Lake Michigan
Authors: Lehman John T. , Cáceres Carla E.
Published: May 2010

Several developments in the offshore plankton community accompanied the invasion of Bythotrephes cederstroemi Schoedler (Crustacea: Cladocera: Cercopagidae) into Lake Michigan. A native predatory cladoceran, Leptodora kindti, became significantly reduced in abundance and biomass in the presence of Bythotrephes. The offshore Daphnia assemblage, which had consisted of three species before the arrival of Bythotrephes, was reduced to dominance by only D. galeata mendotae. Abundances of Daphnia species exhibited reciprocal relationships to Bythotrephes abundance in both space and time. The surviving Daphnia populations offshore exhibited altered daytime vertical distributions which reduced spatial overlap with the invading predator. Model calculations indicate that energetic requirements by Bythotrephes equaled or exceeded replacement production by Daphnia during midsummer of the first years of species invasion. Decreases in midsummer Daphnia biomass did not produce significant increases in midsummer algal biomass, measured as particulate chlorophyll a. Instead, physical mixing depth and epilimnetic temperature, a correlate of the intensity of density stratification, exhibited the strongest statistical relationship to Chl a over the years studied.
Feeding, growth, and behavior of the thecate heterotrophic dinoflagellate Oblea rotunda
Authors: Strom Suzanne L. , Buskey Edward J.
Published: May 2010

Laboratory experiments were performed to determine the growth and grazing capabilities of Oblea rotunda, a pallium‐feeding dinoflagellate. Although Oblea can feed and grow on a wide range of phytoplankton species, the highest observed growth rates (~1 doubling d−1) were supported by the large diatom Ditylum brightwellii. Functional and numerical response curves, obtained with the green alga Dunaliella tertiolecta and D. brightwellii as foods, were typical in form of those obtained previously for other planktonic protozoans. Ditylum, however, consistently supported higher rates of growth and grazing than Dunaliella. Gross growth efficiencies for Oblea were relatively high. A chemosensory response to phytoplankton exudates was observed during motion analysis of swimming behavior; no response to mechanical cues was evident. Long‐term behavioral responses to different phytoplankton species or concentrations were not observed. The wide range of food species available to Oblea suggests that size‐ or taxon‐based parameterizations of such grazers in food‐web models may be inadequate to describe actual grazing interactions.
Predator‐induced phenotypic plasticity in Daphnia pulex: Life history and morphological responses to Notonecta and Chaoborus
Authors: Black A. Ross
Published: May 2010

Results from a laboratory life‐table study show Daphnia pulex has a unique set of rapidly induced responses to waterborne chemicals from each of two predator species. Additionally, Daphnia exhibits a unique set of induced responses when simultaneously exposed to both predators. Daphnids possessed neck teeth and experienced delayed maturity when exposed to waterborne chemicals released from larvae of the phantom midge Chaoborus americanus. Possessing the Chaoborus‐induced phenotypic plasticity was not associated with a lower population growth rate relative to that in the control treatment. When exposed to waterborne chemicals released from the backswimmer Notonecta undulata, D. pulex exhibited an unexpected assemblage of responses. The Notonecta‐induced phenotypic plasticity included rapid juvenile growth to a large size at first reproduction, little growth beyond maturity, and high reproductive output. Simultaneous exposure to chemical cues from Notonecta and Chaoborus resulted in a life history and morphologies that agreed with predicted life history and morphological responses of Daphnia that had been simultaneously exposed to large‐ and small‐size selective predators.
Arsenic cycling in eutrophic Lake Greifen, Switzerland: Influence of seasonal redox processes
Authors: Kuhn Annette , Sigg Laura
Published: May 2010

The arsenic cycle was investigated over 1.5 yr in a eutrophic Swiss lake with a seasonally anoxic hypolimnion. Arsenate, As(V), was predominant throughout the entire water column when the lake was well‐mixed in winter. During summer stratification, arsenate disappeared in the epilimnion and was replaced by arsenite, As(III), but in the anoxic hypolimnion As(V) remained the dominant species. Reduction of As(V) in the hypolimnion occurred only late in the stagnation phase, in the presence of sulfide. The dominant redox reactions of inorganic As in the epilimnion were biologically mediated reduction by phytoplankton in summer and oxidation of As(III) by Mn oxides in fall. Approximately 50% of total dissolved As in the epilimnion and hypolimnion was refractory to the direct hydride generation method. The composition of particles, collected regularly in sediment traps, indicated that Fe oxides were the main scavengers for inorganic As. Nevertheless sedimentation was only a minor sink of inorganic As.
Solar UV‐light penetration and photodegradation of humic substances in peaty lake water
Authors: De Haan H.
Published: May 2010

The in situ photodegradation of aquatic humic substances by underwater UV light (300–400 nm) in peaty lake water was studied. The photodegradation of aquatic humic substances (HS) occurred at depths where UV light with wavelengths <320 nm can penetrate. The daily photodegradation rate of aquatic HS under a cloudless summer sky in the northern Netherlands appeared to be of the same order of magnitude as that of the mean daily pelagic photosynthetic fixation of dissolved inorganic C in typically oligotrophic humic lakes. However, the measured UV degradation of aquatic HS on a yearly basis is small compared to the approximate annual primary production of temperate lake phytoplankton (8%) and submerged macrophytes (3%) under fertile conditions. The measured UV‐light‐driven HS degradation implies a higher turnover of organic C in humic lakes than believed so far.
A simple model for predicting the date of spring stratification in temperate and subtropical lakes
Authors: Demers Eric , Kalff Jacob
Published: May 2010

The date of onset of spring stratification in northern hemisphere lakes is predictable from mean annual air temperature. The prediction is further improved by also considering lake surface area (surrogate of wind exposure) and by the ratio (R) of lake surface area to mean depth, with R reflecting aspects of lake morphometry and heat storage capacity. Mean annual air temperature and R together explain 68% of the variance in the date of onset of stratification in a combined 70‐lake data set from North America, Europe, and Asia. Nearly identical fractions were explained when the lakes were separated into dimictic and warm monomictic data sets. The remaining unexplained variation is probably largely attributable to interyear variation in weather, but also to unexamined differences in regional wind strength, local protection from winds, lake shape, and lake turbidity, as well as differences in the intervals at which temperature profiles were taken.
A method to determine the contribution of bacteria to phosphate uptake by aerobic freshwater sediment
Authors: Sinke Anja J.C. , Cottaar Francis H.M. , Keizer Peer
Published: May 2010

An extraction method to determine the contribution of bacterial processes to phosphate uptake of aerobic freshwater sediment was tested on Fe hydroxyphosphate that was either synthesized or formed under in situ conditions and a pure culture of Acinetobacter 210A. A mild extraction with H2SO4 solubilized the entire Fe hydroxyphosphate fraction but did not extract bacterial phosphate.

Phosphate uptake of randomly sampled surface layers of the sediment of Lake Loosdrecht was considerable, ranging from 11 to 138 µmol g−1 on a dry weight basis. The contribution of bacterial processes ranged from 12 to 32%. Addition of an easily degradable substrate, such as acetate, to the sediment stimulated the uptake of phosphate and augmented the biologically bound phosphate fraction. The results indicated that growing bacteria play a considerable role in phosphate uptake by aerobic sediment.
Vertical structure of productivity and its vertical integration as derived from remotely sensed observations
Authors: Zaneveld J. Ronald V. , Kitchen James C. , Mueller James L.
Published: May 2010

A method for predicting oceanic productivity from remotely sensed diffuse attenuation (488 nm) and surface chlorophyll concentration is presented. The method uses a climatological approach which consists of applying a set of regressions for each region and season to yield the depth of the chlorophyll maximum, the exponential slope of the chlorophyll profile, and the depths of various irradiance levels from the remotely sensed diffuse attenuation coefficient at 488 nm. These parameters, combined with the remotely sensed surface chlorophyll concentration and a model of quantum efficiency vs. irradiance, yield a vertical profile of productivity. This profile can be numerically integrated or directly integrated piecewise with a logarithmic approximation for the quantum efficiency model and a piecewise linear relationship of total irradiance and irradiance at 488 nm. The results favorably compare with productivity profiles calculated from direct measurements of chlorophyll and irradiance for a meridional transect of the North Pacific Ocean.
Inherent optical properties of the ocean: Retrieval of the absorption coefficient of chromophoric dissolved organic matter from fluorescence measurements
Authors: Hoge Frank E. , Vodacek Anthony , Blough Neil V.
Published: May 2010

The quantitative relationship between the absorption and fluorescence emission of chromophoric (colored) dissolved organic matter (CDOM) has been determined along five cruise tracks in the western North Atlantic Ocean, the Gulf of Mexico, and Monterey Bay, and includes Gulf Stream, Loop Current, slope, shelf, and coastal waters. We present a protocol for the determination of CDOM fluorescence that will allow both interlaboratory comparisons and the calibration of airborne fluorescence measurements. This protocol is based on the use of the water Raman signal as an internal radiometric standard and quinine sulfate as an external standard. This study demonstrates that when an appropriate and consistent procedure is used to standardize fluorescence measurements, the fluorescence per unit absorption exhibits surprisingly little variation for diverse waters. The maximum variability observed between all sites was 36% and within the western North Atlantic the variability was only 12%. Algorithms are presented for retrieval of the absorption coefficient of CDOM at 355 and 337 nm from shipboard or airborne measurements of the water‐Raman‐normalized fluorescence emission resulting from 355‐ and 337‐nm excitation.
A spectrally averaged model of light penetration and photosynthesis
Authors: Anderson Thomas R.
Published: May 2010

A model was developed which predicts the daily photosynthesis of a vertical pigment profile divided into a number of homogeneous layers. A spectral model (irradiance divided into a large number of wavebands) was used to derive simple empirical equations for calculating spectrally averaged values of two parameters — the vertical light attenuation coefficient and the chlorophyll‐specific absorption of algae— for each layer as a function of its pigment content and position in the water column. The empirical equations are not dependent on the layer depths chosen, i.e. the same equations can be used for any given set of depths. The spectrally averaged parameters can be used with analytic integrals to give a computationally rapid and accurate result. The model is therefore ideally suited for general circulation models.