bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in winter air temperatures near Lake Michigan, 1851‐1993, as determined from regional lake‐ice records
Authors: Assel Raymond A. , Robertson Dale M.
Published: May 2010

Records of freezeup and breakup dates for Grand Traverse Bay, Michigan, and Lake Mendota, Wisconsin, are among the longest ice records available near the Great Lakes, beginning in 1851 and 1855, respectively. The timing of freezeup and breakup results from an integration of meteorological conditions (primarily air temperature) that occur before these events. Changes in the average timing of these ice‐events are translated into changes in air temperature by the use of empirical and process‐driven models. The timing of freezeup and breakup at the two locations represents an integration of air temperatures over slightly different seasons (months). Records from both locations indicate that the early winter period before about 1890 was ∼1.5°C cooler than the early winter period after that time; the mean temperature has, however, remained relatively constant since about 1890. Changes in breakup dates demonstrate a similar 1.0–1.5°C increase in late winter and early spring air temperatures about 1890. More recent average breakup dates at both locations have been earlier than during 1890–1940, indicating an additional warming of 1.2°C in March since about 1940 and a warming of 1.1°C in January–March since about 1980. Ice records at these sites will continue to provide an early indication of the anticipated climatic warming, not only because of the large response of ice cover to small changes in air temperature but also because these records integrate climatic conditions during the seasons (winter‐spring) when most warming is forecast to occur. Future reductions in ice cover may strongly affect the winter ecology of the Great Lakes by reducing the stable environment required by various levels of the food chain.
Methyl chloride (CH3Cl) production in phytoplankton cultures
Authors: Tait V. K. , Moore R. M.
Published: May 2010

Unialgal nonaxenic cultures of seven species of phytoplankton, including both warm‐ and cold‐water organisms, were examined under halocarbon‐clean conditions for the production of CH3Cl. Incubations of all species showed CH3Cl increases significantly greater than in the control medium. The magnitude of increase varied with the phytoplankton species present and in some cases also with growth stage. Longer time series showed that CH3Cl continued to increase after the death of all the phytoplankton cells. Although direct production as a by‐product of phytoplankton metabolism cannot be ruled out earlier in the time series, indirect chemical and (or) biotic reaction of algal‐associated organic matter is required to explain this continued increase. Characterization of the role of bacteria in both pre‐ and postsenescent stage CH3Cl production will require comparable experiments carried out under axenic conditions.
Diel vertical migration by Daphnia longispina in a Spanish lake: Genetic sources of distributional variation
Authors: King Charles E. , Miracle Maria R.
Published: May 2010

Individuals of many zooplankton species undergo diel vertical migration in which they move toward the surface after sunset and return to deeper waters at dawn. However, even when vertical migration can be clearly demonstrated by mapping the distributions of individuals at noon and midnight, at any given time the population is usually scattered over a broad range of depths. This paper focuses on a major potential source of the variance associated with depth distributions.

We have used electrophoretic analysis of isozymes to identify “clones” of Daphnia longispina in a Spanish lake. In September 1991, two clones constituted 55% of the individuals collected at noon and midnight on each of two successive days. While both displayed significant diel vertical migration, one clone was consistently located deeper in the water column than the other clone. Our results constitute the first demonstration from a field study of Daphnia that a single population is genetically subdivided into groups having different patterns of diel vertical migration. Intrapopulational genetic variation for vertical migration patterns may explain a significant portion of the variability in the depth distributions of zooplankton populations.
Contribution of metazoan plankton to the cycling of nitrogen and phosphorus in Lake Biwa
Authors: Urabe Jotaro , Nakanishi Masami , Kawabata Keiichi
Published: May 2010

To clarify the contribution of metazoan plankton to N and P fluxes in Lake Biwa, we examined particle elimination, net production, and nutrient release rates simultaneously with primary production from June to November 1992. Throughout the study period, the zooplankton eliminated 70% of the elements fixed as particulate forms by primary producers. However, because the N: P ratio of the seston was higher than that of the zooplankton on most dates, the zooplankton selectively accumulated P from seston with higher efficiency, while a larger fraction of N was released to maintain elemental balance. As a result, the mass ratio of N to P released by the zooplankton changed markedly from 19 to 123 according to the magnitude of deviation in the N:P ratio of seston from that of the zooplankton. On average, the zooplankton released 50% of N but only 15% of P fixed by primary production during the study period. The results demonstrate that whether zooplankton act as source or sink for a bioelement depends on the relative abundance of that element in both the food and the zooplankton. In Lake Biwa, the zooplankton can promote P limitation for phytoplankton by fixing a large fraction of the P in the system into their own mass and recycling a substantial amount of the N to a dissolved form.
Sources of nitrogen and phosphorus supporting the growth of bacteria and phytoplankton in an oligotrophic Canadian shield lake
Authors: Sterner Robert W. , Chrzanowski Thomas H. , Elser James J. , George Nicolas B.
Published: May 2010

We used a dilution gradient technique to determine the relative importance of N and P derived from the dissolved pool, storage, and recycling by planktonic consumers to the growth of bacteria and algae in an oligotrophic lake. Recycling was the dominant source of N for both algae and bacteria and the dominant source of P for bacteria. However, storage was an important source of P for algae early in the year, but P recycling was a dominant source for algae late in the year. Models of nutrient flux in the microbial and classic food webs must be combined in a manner consistent with the integrated nature of these fluxes.
Estimation of phosphorus release rates from natural zooplankton communities feeding on planktonic algae and bacteria
Authors: Vadstein Olav , Brekke Oddmund , Andersen Tom , Olsen Yngvar
Published: May 2010

Phosphorus release rates from Daphnia galeata, the dominant metazoan, were estimated in eutrophic Lake Nesjøvatn during summer by applying our previously published mass balance model. For both juveniles (2.0 µg C ind.−1) and adults (6.6 µg C ind.−1), three different estimates of P release were made by two different parametrizations and by considering the importance of ingestion of detrital particles. As a basis for estimates of P release, clearance rates of algae and bacteria were determined as well as a thorough characterization of the food compartments.

The specific release rate of P varied between 0.16 and 1.18 µg P mg C h−1 for juveniles and between 0.06 and 0.96 for adults, independent of estimate. These release rates are considerably lower than those obtained by previously published models. Most of the observed variation was due to variation in the P content of the food, thus emphasizing the importance of including this variable in studies of P release from zooplankton. Calculations of rates of population P release suggest that D. galeata contributed <⅓ of the P requirements of algae and bacteria.
Effects of products released by Aphanizomenon flos‐aquae and purified saxitoxin on the movements of Daphnia carinata feeding appendages
Authors: Haney James F. , Sasner John J. , Ikawa Miyoshi
Published: May 2010

Experiments were run to determine the effect of filtrate from incubated Aphanizomenonflos‐aquae on the thoracic appendage beat rate and frequency of postabdominal rejections by Daphnia carinata. Comparisons were made between the response to Aphanizomenon filtrate and to purified saxitoxin (STX). The short‐term response pattern to the filtrate included an immediate 30–50% depression of thoracic appendage beat rate and elevation of postabdominal rejection rate followed by slowly decreasing thoracic appendage beat rate and increasing postabdominal rejection rate during the 10‐min exposure. Animals recovered to pretreatment activity rates in <5 min. A similar response was observed in STX, except that Daphnia began to recover immediately from the thoracic appendage beat rate inhibition. Animals recovered to ∼60% of pretreatment activity after 1–2 h in Aphanizomenon filtrate, whereas in STX they returned to pretreatment activity levels after ∼ 1 h of exposure to the neurotoxin. Water from a lake with a winter bloom of A. flos‐aquae produced the same pattern of thoracic appendage beat rate and postabdominal rejection rate response as seen with the cultured Aphanizomenon. A comparison of responses to STX and the Aphanizomenon filtrate indicates the effect on D. carinata is through chemosensory stimulation rather than neuromotor inhibition.
Dynamics of dissolved organic carbon in a coastal ecosystem
Authors: Zweifel Ulla Li , Wikner Johan , Hagström Åke , Lundberg Erik , Norrman Bosse
Published: May 2010

In the Bothnian Sea, there was a marked seasonal variation of dissolved organic C (DOC) in 1990–1992, with a large increase in DOC concentrations in summer at two stations. The accumulation of DOC at the coastal station persisted for 5 months, reaching peak values 24–31% above the mean winter value (288 µM). At the offshore station DOC concentrations were elevated throughout the water column in July, reaching 14% above the mean winter value (291 µM). The DOC concentration at the coastal station was significantly correlated to water flow in an adjacent river, suggesting that the source of the summer DOC increase was largely explained by riverine input. Bioassays indicated that a large portion (22–99%) of the introduced DOC was degradable by bacteria after inorganic nutrients were added. A negative correlation between DOC and phosphate concentration was also found, suggesting that the system was P deficient in summer. The accumulation of DOC in summer was thus possibly caused by slow bacterial degradation due to phosphate deficiency and transient accumulation of refractory DOC. An annual C balance at the coastal station indicated an insufficient supply of C from phytoplankton production to support the C demand of the system; at the offshore station the budget was close to balanced. The results suggest that riverine DOC had a major impact on coastal DOC dynamics and that it was partly used in the microbial food web in the bay.
Plant pigments as biomarkers of high‐molecular‐weight dissolved organic carbon
Authors: Bianchi Thomas S. , Lambert Corey , Santschi Peter H. , Baskaran M. , Guo Laodong
Published: May 2010

We used plant pigments as tracers of high‐ molecular‐weight dissolved organic C (HMW DOC) (<0.2 µm and > 1,000 Da). Water samples were collected from four stations along a transect on cruises in June 1992 and January 1993 in the Gulf of Mexico. Samples were also collected from three stations on the continental shelf of Cape Hatteras for comparison. Chlorophylls a and b were at detectable levels in HMW DOC; concentrations of the carotenoids zeaxanthin and fucoxanthin in HMW DOC indicated that cyanobacteria, prochlorophytes, and diatoms contributed to the total HMW DOC pool across the continental margin in the gulf. The extremely low concentrations of pheopigments (except for chlorophyllide) in particulate organic C and HMW DOC suggested that direct exudation from phytoplankton and sloppy feeding by zooplankton were the major mechanisms of release. However, significant and selective pigment loss, due to light and thermal degradation in the reservoir, did occur in the absence of any cooling or light‐shielding precautions. This study demonstrated that pigments can be used to acquire qualitative information on the sources of HMW DOC and to gain insight on its relative age—based on pigment turnover.
On the chlorophyll a retention properties of glass‐fiber GF/F filters
Authors: Chavez Francisco P. , Buck Kurt R. , Bidigare Robert R. , Karl David M. , Hebel Dale , Latasa Mikel , Campbell Lisa , Newton Jan
Published: May 2010

Extensive comparisons of the retention properties of glass‐fiber GF/F and 0.2‐µm membrane filters show that these two filter types retain equivalent amounts of Chl a. The experiments conducted were in the open ocean waters of the Pacific Ocean, from 46°N to 28°S, including waters from the equatorial divergence, the low latitude subtropical gyres, and higher latitudes. These results contradict a recent report that suggests that in some cases GF/F filters underestimate chlorophyll concentration by 4‐fold when compared with 0.2‐µm membrane filters. The data set also allowed examination of latitudinal gradients in integrated chlorophyll. Previously observed latitudinal gradients in the North Pacific were present but were much weaker than those found in the South Pacific.
Spatio‐temporal patterns in the diel vertical migration of the copepod Metridia lucens in the northeast Atlantic derived from the Continuous Plankton Recorder survey
Authors: Hays Graeme C. , Warner Andrew J. , Proctor Catherine A.
Published: May 2010

The archived data set collected over a 45‐yr period (1948–1992) by Continuous Plankton Recorders (CPRs) towed in near‐surface waters was used to investigate the diel vertical migration of the copepod Metridia lucens in the northeast Atlantic (47–63°N and 10–30°W). Although the CPR sampling intensity was uniform during the day and the night, M. lucens was caught predominantly in samples collected at night, consistent with a normal diel vertical migration pattern involving movement from greater depth during the day to shallower depths at night. The length of time spent near the surface varied seasonally and was closely correlated (r2 = 0.80) with seasonal change in length of night. The residual variation in length of time spent at the surface was nonrandom, with more time being spent at the surface in spring before the onset of the spring bloom, and less time being spent at the surface in autumn, than that predicted from the length of night at these periods. The timing of this enhanced near‐surface occupation in spring varied with latitude, occurring a mean of 3.4 d later per degree of latitude.
Biological production of form aldehyde in the marine environment
Authors: Nuccio Joseph , Seaton Pamela J. , Kieber Robert J.
Published: May 2010

We investigated biological production of low‐molecular‐weight (LMW) carbonyl compounds (e.g. formaldehyde, acetaldehyde, propanal, and glyoxal) in axenic unialgal phytoplankton cultures of Skeletonema costatum and Heterocapsa pygmaea and in several natural plankton assemblages collected at a coastal location in southeastern North Carolina. Of the compounds studied, formaldehyde was the only LMW carbonyl produced by the biota with the exception of a single natural assemblage which also produced propanal. Similar patterns of biological production and utilization of formaldehyde were observed during these culture experiments. Concentrations in filtrates increased while chlorophyll a concentrations remained relatively low, then declined as the organisms began their exponential growth phase. These oscillations in formaldehyde concentration suggest biota are both generating and using formaldehyde concurrently. In situ depth profiles provided additional information regarding the turnover of formaldehyde. Concentrations were relatively high at the surface and decreased to a minimum near the chlorophyll maximum, below which no consistent trends in formaldehyde concentration were observed. This study is the first known report of biological production of a LMW aldehyde in the marine environment.
Nitrate uptake rates in a coastal upwelling regime: A comparison of PN‐specific, absolute, and Chl a‐specific rates
Authors: Dickson Mary-Lynn , Wheele Patricia A.
Published: May 2010

PN‐specific, absolute, and Chl a‐specific nitrate uptake rates were measured during two upwelling seasons and one winter off Oregon. Although PN‐specific and absolute uptake rates showed no dependence on nitrate concentration, Michaelis‐Menten kinetics applied when the uptake rates were normalized to Chl a. Chl a‐specific nitrate uptake rates were saturated when nitrate concentrations were > 5 M. Uptake rates decreased in response to either low nitrate concentrations or when extremely high phytoplankton biomass caused shading. PN‐ and Chl a‐specific uptake rates were similar when Chl a concentrations were ≥ 4 µg liter−1 and phytoplankton N comprised most of the PN (particulate organic N) pool. When Chl a was <4 µg liter−1, however, phytoplankton N accounted for only 20–30% of the PN, and estimated phytoplankton‐specific uptake was 5‐fold greater than PN‐specific uptake rates. These results suggest that observed temporal changes in PN‐specific nitrate uptake rates reflect variations in phytoplankton biomass rather than changes in phytoplankton‐specific activity.
Changes in oxygen consumption at the sediment‐water interface formed by settling seston from the Elbe estuary
Authors: Kemer M. , Gramm H.
Published: May 2010

A new laboratory device was used to study microbial processes within a ∼ 1‐mm layer of aggregated seston material during different seasons. The conditions below and above this sediment‐water interface were simulated, and the concentrations of plant nutrients and oxygen were controlled. Nitrification occurred in the layer only at oxygen concentrations > 1.5–2 mg liter−1. Heterotrophic processes followed zero‐order kinetics with respect to oxygen; thus, anoxic conditions were reached within the seston layer at depths of 800–1,400 µm. Oxygen consumption rates in the heterotrophic layer differed as much as 10‐fold, and values were highest at the oxic‐suboxic interface in the layer due to production of dissolved organic C by fermentation. Nitrification accounted for 100% of the total O2 consumption in the layer during the first 20 h. Thereafter, an increase in the oxygen flux into the layer by factors as high as 2–9 was due to initiation of heterotrophic processes. About 120 h after settling, the aggregated seston material became refractory to aerobic microbial degradation. The observed short‐term succession of microbial autotrophic and heterotrophic O2 consumption in aggregated seston material might control environmental conditions both at the sediment‐water interface and in flocs in the open water.
Concentration of mercury species in relationship to other site‐specific factors in the surface waters of northern Wisconsin lakes
Authors: Watras Carl J. , Morrison Kenneth A. , Host Jodi S. , Bloom Nicolas S.
Published: May 2010

To investigate relationships between mercury speciation and site‐specific factors in temperate freshwaters, we measured the concentration of seven Hg species along with 18 environmental variables in the surface waters of 23 northern Wisconsin lakes during spring and fall. The lakes spanned relatively wide gradients in Hg (0.15–4.8 ng liter −1) and methylmercury (MeHg: 0.04–2.2 ng liter− 1). Over the range of measured variables, Hg and McHg were most strongly correlated with each other (r2 = 0.83–0.88) and with dissolved organic C (DOC) (r2 = 0.64–0.92). Multiple regression models containing DOC and a (DOC × pH) interaction term accounted for 85–90% of the variability in Hg and MeHg between lakes.

Observed differences between lakes reflected internal cycling processes and external transport pathways. Internally, high DOC and low pH favored Hg methylation and retention over Hg evasion across the air‐water interface. Externally, watershed mapping suggested that the cotransport of DOC, Hg, and MeHg from riparian wetland was also a potentially important process. Observed seasonal differences indicated a 30% increase in MeHg across lakes during summer due to internal or external processes.

The effects of DOC on bioaccumulation may be twofold and antagonistic. Although waterborne Hg and MeHg increased with DOC, seston‐water partition coefficients tended to decrease, indicating disproportionately more Hg in the dissolved phase. These observations are consistent with previous data on bioaccumulation factors for zooplankton and fish.
Microbial nutrient limitation in prairie saline lakes with high sulfate concentration
Authors: Waker Marley J. , Robarts Richard D.
Published: May 2010

Most of the lakes on the Canadian prairies are saline (>3 g liter −1 salt). Sulfate ions are relatively more abundant in these lakes than anywhere else in the world. Studies indicate that some of these lakes do not conform to empirical models which link chlorophyll a to spring total phosphorus concentration. A suite of tests, including nutrient enrichment bioassays, sestonic and protein to carbohydrate ratios, alkaline phosphatase activity, and 32P‐turnover times were used to test microbial nutrient limitation in three prairie saline lakes. Although the concentration of soluble reactive P (SRP) was high (9–31 µg liter−1) in two of the lakes, little was available for microbial growth. Bacteria were responsible for 84 and 53% of the32P uptake in these two lakes. Production of high levels of alkaline phosphatase by the phytoplankton in one lake appears to keep their intracellular stores of P replete and PN : PP ratios in the P‐sufficient range. Striking differences were noted when our data from saline lakes were compared to data from freshwater lakes. Our saline lakes were P‐deficient at SRP concentrations <31 µg liter−1, while freshwater lakes were P‐deficient at SRP concentrations <1 µg liter−1 . High concentrations of dissolved organic C, pH, and ionic composition in saline lakes appear to play a role in the availability of P.
Continuous measurement of CO2 for estimation of air‐water fluxes in lakes: An in situ technique
Authors: Sellers Patricia , Hesslein Raymond H. , Kelly Carol A. Kelly
Published: May 2010

Three parameters must be known to use the thin boundary‐layer model (or other bulk transfer models) for CO2 flux between water and air: the concentration of dissolved CO2, CO2(aq), the concentration of CO2 in the air immediately above the water, CO2(atm), and the wind velocity, which is used to determine the appropriate transfer coefficient. These parameters change hourly and from day to day in a nonlinear fashion, so the frequency of measurements is an important factor in determining the accuracy of flux estimates for any period. To achieve a high frequency measurement, we developed a self‐contained, solar‐powered, in situ sampling system that continuously measures and records CO2(aq), CO2(atm), and windspeed. Unique to this technique is an underwater in situ equilibration chamber (ISEC). The ISEC was tested in a shallow wetland pond in which changes in both CO2(aq) and CO2(atm) were large. The data obtained showed that large errors may result from extrapolating flux calculations made from short‐term data (e.g. daily) to longer time periods.
The influence of lake morphometry on sediment focusing
Authors: Blais Jules M. , Kalff Jacob
Published: May 2010

Sediment focusing is a process whereby water turbulence moves sedimented material from shallower to deeper zones of a lake. Sediment focusing occurs in lakes in both the erosional (coarse‐grained sediments) and the transportational zone with the latter characterized by discontinuous sedimentation and resuspension. The zone of accumulation is defined as the zone where sedimentation is final (i.e. no resuspension) and where there is no further sediment focusing. A geochemical tracer (Pb) was used to trace sediment focusing patterns in 12 lakes of different morphometries. The area occupied by the zone of accumulation is predicted from the mean basin slope (α'p) with 86% of the variance explained. Only in large, exposed lakes in which turbulence from waves is more severe are the resulting sediment distributions more erratic. This study is the first to provide a general model of sediment focusing patterns among lakes.
Seepage exchange in an Amazon floodplain lake
Authors: Lesack Lance F. W.
Published: May 2010

Exchange of water between the lake and the surrounding groundwater system was computed for a permanent lake on the central Amazon floodplain (Lake Calado) from an empirical seepage model incorporating 240 direct measurements of seepage from the lakebed and seasonal changes in lake stage and morphometry. Seepage rates varied with the daily rate of change in stage height and inversely with depth of the lakebed from the water surface. Since the hypsometric characteristics of the lake are well known, overall seepage for the 1983–1984 water year was estimated by integrating the product of seepage rate per unit area for a given rate of stage change and depth of lakebed with the representative area of lakebed at a given depth as each varied over the annual cycle, then integrating the daily rates of seepage over time. The volume of seepage outflow over the rising‐water period (4 × 106 m3) is plausible if the rate of groundwater flow is constrained by the hydraulic conductivities expected for the soils. The 10‐m annual change in water level and the potential movement of floodwaters into deeply weathered tropical soils, beyond the silt and clay deposits immediately adjacent to the main‐stem river channel, represent conditions that are particularly conducive to seepage exchange and are representative of a significant number of lakes on the Amazon floodplain.
Effects of acid washing on stable isotope ratios of C and N in penaeid shrimp and seagrass: Implications for food‐web studies using multiple stable isotopes
Authors: Bunn S. E. , Loneragan N. R. , Kempster M. A.
Published: May 2010

We investigated the effects of acid washing on the carbon and nitrogen composition and stable isotope ratios of C and N in shrimp (Metapenaeus spp.) and seagrass (Enhalus acoroides). Acid washing did not affect the mean δ13C ratios for juvenile Metapenaeus moyebi and resulted in only an ecologically insignificant change (0.3‰) in mean δ13C ratios for larger Metapenaeus bennettae. In contrast, acid washing increased the mean δ15N signatures of shrimp tissue (∼ 3‰) and decreased that of seagrass (∼1.8‰) to a degree that may confound the interpretation of food webs. The increase in %C and %N in both shrimp and seagrass after acid washing suggests that the changes in isotope ratios are due to loss of molecules comparatively low in C and N. Treating samples by acid washing also resulted in an increase in the variation among individuals for both δ15N and δ13C, which would lead to a loss of statistical power for testing differences between species, sites, or seasons.
A biochemical index of duration of the molt cycle for planktonic Crustacea based on the chitin‐degrading enzyme, chitobiase
Authors: Espie Patrick J. , Roff John C.
Published: May 2010

The activity of chitobiase over an entire molt cycle was measured in Daphnia magna; it increased by 5‐fold from intermolt to premolt (when animals are in apolysis). Duration of the entire molt cycle increased about 3‐fold with a decrease in temperature from 25 to 6°C, but increased by <2‐fold over an 80‐fold difference in food concentration. There was a strong (r2 = 0.95) linear relationship between chitobiase activity and duration of the molt cycle, as modulated by food concentration, in asynchronous populations of D. magna. The relationship between chitobiase activity and duration of the molt cycle, as modulated by temperature, was also highly significant (r2 = 0.77) but nonlinear. The relationship between chitobiase activity and temperature is also nonlinear (r2 = 0.67). Asignificant linear relationship between chitobiase activity and duration of the molt cycle was also found for a natural population of Daphnia rosea (r2 = 0.88). Regressions of enzyme activity with body size and glucosamine content for three species of Daphnia indicate that differences exist between species. Chitobiase activity is an index of the proportion of animals in apolysis in a population. Because this proportion changes as a function of food concentration, but apparently not as a function of temperature, chitobiase activity is a measure of the duration of the molt cycle as limited by food concentration.
Bacterial ectoenzymes in marine waters: Activity ratios and temperature responses in three oceanographic provinces
Authors: Christian James R. , Karl David M.
Published: May 2010

Ectoenzymatic hydrolysis is a crucial first step in bacterial utilization of polymeric dissolved organic matter (DOM). Variation in the relative activities of different enzymes can indicate seasonal and geographic variation in the mode of bacterioplankton nutrition. We found that relative activities of leucine aminopeptidase and β‐glucosidase in seawater varied significantly among three oceanic regions: the subtropical North Pacific, the equatorial Pacific, and the Southern Ocean. The temperature responses of these enzymes also vary significantly among these three regions, suggesting distinct bacterial phenotypes with distinct isozymes. Our results suggest a latitudinal trend in bacterial carbon and nitrogen utilization, with significant synthesis of cell constituents from glucose and ammonium in equatorial waters but little such de novo synthesis in Antarctic waters. The observed patterns have important implications for the parameterization of secondary production and nutrient regeneration in global production models and for understanding the role of DOM in global carbon and nitrogen fluxes.
Primary production and phytoplankton in Lake Kinneret: A long‐term record (1972‐1993)
Authors: Berman T. , Stone L. , Yacobi Y. Z. , Kaplan B. , Schlichter Al. , Nishri A. , Pollingher U.
Published: May 2010

The long‐term (22 yr) record of primary production in Lake Kinneret, Israel, has been examined, together with chlorophyll and microscopically determined algal biomass, in order to discern whether there have been any significant changes in these parameters during this period. During the period 1972 through 1993, annual averages have ranged from 1,223 to 2,311 mg C m−2 d−1 for primary production, from 127 to 246 mg m−2 for chlorophyll, and from 39.3 to 98.5 g m−2 for algal wet weight. The annual peak of these parameters was in April–May. Over 22 yr, variability in primary productivity was more closely related to changes in chlorophyll than to changes in algal biomass. No evidence was found for consistently increasing long‐term trends in primary production, chlorophyll concentrations, or algal wet weight biomass from 1972–1993. Although the annual and semiannual averages of algal biomass were significantly higher in the past 11 yr than those in the previous decade, this pattern could arise from a long‐term cyclical but self‐compensating trend. The extended record indicates that despite population growth and intense economic development around the lake and in its catchment area, there has been no extreme eutrophication of Lake Kinneret from 1972 to 1993. We suggest that this relative resiliency of the Kinneret ecosystem is due to high ambient levels of alkalinity, calcium, and pH in the lake water acting to limit phosphorus availability, which in turn restricts the outgrowth of phytoplankton.
Competition of copper and zinc for strong ligands in a eutrophic lake
Authors: Xue HanBin , Kistler David , Sigg Laura
Published: May 2010

Free aquo copper ion and zinc ion concentrations were determined in water samples from eutrophic Lake Greifen by means of ligand exchange with catechol and cathodic stripping voltametry (for Cu) and ligand exchange with EDTA and anodic stripping voltametry (for Zn). The ratios of total dissolved Zn (10–40 nM) to dissolved Cu (7–20 nM) were [Zn]: [Cu] = 0.5–3 in samples taken at different seasons of a year; the ratios of the free aquo ion concentrations [Zn2+] : [Cu2 +] were ∼ 106. pCu was in the range of 14.5–15.9 and pZn 8.6–9.5 at different times and depths. The release of Zn from electrochemically inert complexes upon addition of Cu suggested direct competition of Cu and Zn for ligands in all lake‐water samples examined. The selectivity of the natural ligands for Cu over Zn was evaluated as the conditional constant for the reaction Cu2+ + ZnL1 = Zn2 + CuL1; K = (1.4±0.9) × 106 (average in the euphotic zone; pH 8). These highly selective ligands are probably of biological origin.
Fiber‐optic oxygen microsensors, a new tool in aquatic biology
Authors: Klimant Ingo , Meyer Volker , Kühl Michael
Published: May 2010

A new fiber‐optic oxygen microsensor (microoptrode) based on dynamic fluorescence quenching has been developed to measure oxygen gradients in marine sediments and microbial mats. The microoptrodes are fabricated by immobilizing an oxygen‐quenchable fluorophore at the tapered tip of an optical fiber. A special optoelectronic system has been designed to measure oxygen with these microoptrodes. It is based on small and cheap optical components and can easily be miniaturized for field applications. In contrast to oxygen microelectrodes, the new oxygen microoptrodes are easy to make, do not consume oxygen, and show no stirring dependence of the signal. In addition, they show excellent long‐term stability and storage stability. Hydrogen sulfide, carbon dioxide, and other relevant chemical parameters do not interfere with the measurement. Oxygen profiles in marine sediments obtained from measurements with microoptrodes show good correlation to profiles measured with oxygen microelectrodes.
Biomass, production, and specific growth rate of bacterioplankton and coupling to phytoplankton in an oligotrophic lake
Authors: Coveney Michael F. , Wetzel Robert G.
Published: May 2010

Production of bacterioplankton and phytoplankton was analyzed in oligotrophic Lawrence Lake, Michigan, over a 2‐yr period. Variables examined were temperature, bacterial numbers and biovolumes, bacterial production and specific growth rates (µ), phytoplanktonic biomass and production, and alkaline phosphatase activity. Algal and bacterial production varied similarly on temporal and spatial scales; some differences in vertical patterns were evident during summer stratification. Values for µ ranged from 0.2 d‒1 during winter to 2.6 d‒1 in midsummer. Decreases in specific growth rates of bacteria coincided with the onset of heavy CaCO3 precipitation and with increased alkaline phosphatase activities. µ was close to predicted maximal values during periods of mixing but was depressed in upper layers during summer. Temperature showed significant bivariate rank correlations with all variables. With temperature controlled, µ did not show significant partial correlations with algal chlorophyll or production, consistent with a minor role of dissolved organic carbon from phytoplankton for bacterial growth. Low and high estimates of bacterioplanktonic production over 2 yr exceeded that of phytoplankton by factors of 1.33 and 3.35. Net metabolism in the pelagic zone was heterotrophic, a state likely maintained by littoral macrophytic and periphytic production. Apparent coupling between phyto‐ and bacterioplankton stemmed mainly from similar responses of each component to common regulating factors rather than from direct metabolic links.
The significance of nonviable eggs for Daphnia population dynamics
Authors: Boersma Maarten , Vijverberg Jacobus
Published: May 2010

Egg mortality was studied in populations of Daphnia galeata, Daphnia cucullata, and the hybrid between these species. In Tjeukemeer, a shallow eutrophic lake in the Netherlands, egg mortality in daphnids manifested itself as an apparent increase in the frequency of eggs in the early developmental stages. Close examination of these eggs revealed that many of them stopped their development. Egg mortality was observed during a 1‐month period in autumn 1990 and for about 2 months in spring 1991. The percentage of females carrying nondeveloping eggs averaged 20% (SD = 11%) in the 1990 period and 35% (SD = 20%) in spring 1991, resulting in an average reduction of the birth rate of 0.043 (SD = 0.027) and 0.040 (SD = 0.030). The maximum incidence of nondeveloping eggs was as high as 70%. Because it is difficult to recognize nondeveloping eggs, little is known about the cause of this arrested development. Our results suggest that food quantity was not an important factor and that egg mortality was caused by nutritional deficiency of the lake seston in certain periods of the year. Egg mortality can have serious consequences for the population development of daphnids, and it might be a more common phenomenon than is supposed. An analysis of zooplankton population dynamics is essential to properly assess the viability of eggs, since ignoring egg mortality will cause both birth and death rates to be overestimated.
Bacterial carbon metabolism in the Amazon River system
Authors: Benner Ronald , Opsahl Stephen , Chin-Leo Gerardo , Richey Jeffrey E. , Forsberg Bruce R.
Published: May 2010

Bacterial abundance and production and community respiration were measured at several mainstem and tributary stations in November‐December 1988, April–May 1990, and August–September 1991 in a 1,950‐km reach of the Amazon River between Vargem Grande and Obidos, Brazil. Bacterial abundances averaged 1.1 × 109 cells liter‒1 in the mainstem during the three cruises, and rates of heterotrophic bacterial production and community respiration averaged 1.16 µg C liter‒1 h‒1 and 0.61 µM O2 h‒1, respectively. Bacterial production and respiration were carbon limited in the mainstem, indicating that the bulk of the relatively abundant particulate and dissolved organic matter was of limited bioavailability. Spatial variability in measured parameters was minimal even though tributary and mainstem stations included waters with distinct physical and chemical features. Blackwater and whitewater rivers supported similar bacterial abundances and rates of bacterial production and respiration. Strong seasonal patterns of variability were evident; maximal bacterial growth rates and minimal respiration rates were measured during high water stages of the hydrograph. Estimates of bacterial growth efficiencies ranged from 4 to 55%, with consistently higher values measured during high water. It appeared that enhanced bacterial growth efficiencies during periods of high water resulted from increased bioavailability of substrates derived from the extensive varzea (floodplain).
Flow‐dependent herbivory and growth in zooxanthellae‐free soft corals
Authors: Fabricius Katharina E. , Genin Amatzia , Benayahu Yehuda
Published: May 2010

The diet of Dendronephthya hemprichi and three other abundant soft corals in the northern Red Sea consists mainly of phytoplankton, a food source so far unknown for cnidarians. We present a carbon budget for this species, synthesizing field data on somatic growth, food intake, and respiration. In situ rates of phytoplankton uptake and addition of polyps were affected in a similar and nonlinear fashion by flow, with optimal values observed at ∼15 cm s‒1 . The size of polyps increased with increasing flow between 1 and 32 cm s‒1. Zooplankton capture was selective for weakly swimming bivalve and gastropod larvae and contributed <5% to the corals’ carbon demand for growth and respiration and about two to three orders of magnitude less than the carbon gained by phytoplanktivory. The ability of octocorals to feed on phytoplankton is probably related to the narrowly spaced pinnules on their tentacles as well as morphological and behavioral adaptations to living in strong flow. The utilization of phytoplankton, which has nearly an order of magnitude higher biomass than zooplankton, is probably the principal mechanism allowing an azooxanthellate cnidarian to be highly productive in oligotrophic reef waters.
Modeling and interpreting element ratios in water and sediments: A sensitivity analysis of post‐Chernobyl Ru : Cs ratios
Authors: Hilton J. , Rigg E. , Davison W. , Hamilton‐Taylor J. , Kelly M. , Livens F. R. , Singleton D. L.
Published: May 2010

When elements are simultaneously added to lakes, experimentally or by accident, their ratios in the water phase and in bottom sediments can change with time due to differential partitioning between solution and suspended particles or sediments. A number of equations are developed to show the change of ratio with time in water and sediments assuming simultaneous pulse inputs followed by a range of combinations of loss processes from solution (i.e. hydraulic losses, sorption to particles followed by settling, and diffusion into the sediments). The pattern of events is discussed both for pulse events with specific limiting assumptions and for combined continuous and pulse inputs. The models show that elemental ratios in sediments are generally less sensitive indicators of differential partitioning than are elemental ratios in water. For lakes with long residence times, the long‐term elemental ratio in the sediments does not differ from that in the initial spike to the water column, but for short residence times, it is directly dependent on the ratio of either partition or diffusion coefficients.

The models are used to interpret Ru : Cs ratios measured in the water and sediments of Esthwaite Water subsequent to the pulse input of Chernobyl fallout. The ratios can be explained by assuming nuclides were lost either by flushing and sorption or by flushing, sorption, and diffusion. The process combination of flushing and diffusion is incompatible with the observed constant ratios.
Marine algae‐a source of trichloroethylene and perchloroethylene
Authors: Abrahamsson K. , Ekdahl A. , Collén J. , Pedersén M.
Published: May 2010

Our results show the natural production of two olefins, trichloroethylene and perchloroethylene, by various marine macroalgae and a microalga. We found significant difference in the ability of the algae to produce these compounds. The production rates for trichloroethylene varied between 0.022 and 3,400 ng g‒1 fresh wt (FW) h‒1 and were generally higher than those for perchloroethylene (0.0026–8.2 ng g‒1 FW h‒1). The two subtropical algae, Asparagopsis taxiformis and Falkenbergia hillebrandii, showed the highest formation rates. One axenic marine red microalga, Porphyridium purpureum, was also tested and it could also produce trichloroethylene and perchloroethylene. The measured rates suggest that the emission of trichloroethylene and perchloroethylene from the oceans to the atmosphere may be of such a magnitude that it cannot be neglected in the global atmospheric chlorine budget.
A dye‐binding assay for the spectrophotometric measurement of transparent exopolymer particles (TEP)
Authors: Passow U. , Alldredge A. L.
Published: May 2010

Large transparent exopolymer particles (TEP) are found abundantly in the ocean and play an important role in many fields of marine ecology. Quantification of TEP by light microscopy, however, is labor‐intensive and slow. Here we introduce a simple, semiquantitative method to determine the concentration of TEP colorimetrically. In this method TEP are first stained with alcian blue. The dye complexed with TEP is then redissolved and measured spectrophotometrically. Several independent tests of the method show that the concentration of TEP measured spectrophotometrically compares well with parallel light microscope counts. Fractionation experiments confirm that TEP are not generated as an artifact of filtration. Field data show that the concentration of TEP in different oceanic environments ranges from 10 to 500 µg liter‒1 xanthan equivalent depending on season, depth, and plankton community composition.
Natural photolysis by ultraviolet irradiance of recalcitrant dissolved organic matter to simple substrates for rapidbacterial metabolism
Authors: Wetzel Robert G. , Hatcher Patrick G. , Bianchi Thomas S.
Published: May 2010

Whole leachate and humic and fulvic acid fractions of dissolved organic matter (DOM) released from senescent littoral aquatic plants were exposed to varying spectra of ultraviolet radiation as well as natural UV of sunlight over different periods of time. Examination of the DOM by solid‐state 13C nuclear magnetic resonance and pyrolytic gas chromatography‐mass spectrometry before and after photolysis revealed only subtle changes to the bulk DOM. However, the DOM exposed to natural UV radiation showed immediate stimulation of and sustained bacterial growth. Chemical analyses by high performance liquid chromatography (HPLC) of the small organic fractions generated by photolysis of humic substances showed marked, progressively increasing release of numerous small fatty acids, particularly acetic, formic, citric, pyruvic, and levulinic, among others. Use of radiolabeled humic substances demonstrated that these small compounds photolyzed from the humic substances were readily metabolized by the bacteria.
Cobalt and zinc interreplacement in marine phytoplankton: Biological and geochemical implications
Authors: Sunda William G. , Huntsman Susan A.
Published: May 2010

Zinc is used extensively in the metabolism of higher organisms; cobalt's usage is minimal. We found an unusual pattern of requirement for these metals in marine phytoplankton in which the cyanobacterium Synechococcus bacillaris needed Co but not Zn for growth, the coccolithophore Emiliania huxleyi had a Co requirement that could be partly met by Zn, and the diatoms Thalassiosira pseudonana and Thalassiosira oceanica had Zn requirements that could be largely met by Co. These results indicate that Co and Zn can replace one another metabolically in the eucaryotic species. Associated with this replacement, there was up to a 700‐fold increase in cellular Co uptake rates with decreasing Zn ion concentration, indicating that Zn should have a major influence on biological scavenging of Co. This hypothesis is consistent with Zn and Co distributions within the oceanic nutricline which show Co depletion only after Zn has become depleted. Zn ion concentrations and Co : Zn ratios vary widely in the ocean, and these variations could influence the relative growth of diatoms and coccolithophores, with potential effects on global carbon cycles.
Expression of form I and form II Rubisco in chemoautotrophic symbioses: Implications for the interpretation of stable carbon isotope values
Authors: Robinson Jonathan J. , Cavanaugh Colleen M.
Published: May 2010

Invertebrate‐chemoautotroph symbioses, in which the bacterial partner provides an internal source of autotrophically fixed carbon for its host, fall into two main groups based on previously reported stable carbon isotope ratios: those with δ13C = ‒27 to ‒35‰ (referred to as the ‒30‰ group) and those with δ13C = ‒9 to ‒16‰ (referred to as the ‒11‰ group). The δ13C values of the ‒30‰ group resemble those of free‐living chemoautotrophic bacteria, suggesting the role of the symbionts in the nutrition of the bivalves; there is presently no satisfactory explanation for the δ13C values of the ‒11 ‰ group. Immunological and enzyme inhibition data are presented demonstrating that the CO2‐fixing enzyme expressed in representatives of the ‒11‰group is a form II ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), while a form I Rubisco is expressed in the ‒30% symbioses. Previously reported in vitro determinations on purified Rubisco show that the form II enzyme from free‐living bacteria has a smaller kinetic isotope effect with respect to CO2 than does form I. Thus, the 13C‐enriched stable carbon isotope signature observed in the intact ‒11% symbioses appears to be at least partially due to this diminished enzymatic discrimination.