bluuebunny/crossref_metadata_2025 huggingface dataset:
The disappearance of the long term meromictic stratification of the Dead Sea
Authors: Steinhorn Iiana
Published: April 2010

Following a lowering of its surface level by 3.5–4 m, the water of the Dead Sea turned over in February 1979, ending a long period of stratification. The “classic” structure (a salinity gradient at a depth of 30–40 m separating the surface layers, through a transitional zone, from a “fossil” water spreading from 60 to 80 m to the bottom 320 m) was replaced by a reduction of the salinity difference between surface and deep waters from 25 g kg−1 in 1960 (50 g kg−1 in 1864) to 3 g kg−1 in 1975, and to <0.1 g kg−1 in 1978, and by a series of deepenings of the interface between the fossil waters and the upper, seasonally variable layers, from about 80‐m depth in 1975 to 180 m in 1978. The “eroded” deep waters maintained their original properties (mean salinity 275.8 g kg−1, mean potential temperature 21.34°C, mean density 1.2334 g cm−3, and tritium content 0.1 TU). In February 1979 the entire water column was essentially homogeneous and stable (Brunt‐Väisälä frequency 5.8 × 10−4 s−1), with temperature, salinity, and density somewhat higher than those of the former deep waters.

The successive deepenings and the complete overturn were caused when the surface (10–25 m) layers cooled during autumn and winter from 37° to 18°C, and, following each dry year, reduced their excess salinity (3 g kg−1) by vertical mixing to a greater depth than in the previous winter. The meromixis of the Dead Sea is ectogenic, caused by freshwater inflow over hypersaline deep layers. The imbalance between the effects of salinity and temperature changes on the density of the water column, and variations (both natural and artificial) in amount and timing of the inflow rate, cause the seasonal changes of the water column to be nonrepetitive; the cumulative extreme development of this is an overturn.
Mixed layer dynamics in a lake exposed to a spatially variable wind field1
Authors: Imberger Jörg , Parker Geoffrey
Published: April 2010

Field measurements are described detailing the formation of frontal structures in the surface mixed layer near the entrance of an embayment in a medium‐sized lake. The observed evolution of the fronts is interpreted in terms of three well defined dynamical regimes. The first, differential heating, is defined as the variable heat capture due to decreased surface heat losses and warmer surface water in the sheltered embayments. The second, variable deepening of the mixed layer, is induced by a sudden increase in wind speed in the open central areas of the lake, with only minimal mixing in the sheltered parts of the lake. The third is the horizontal gravitational motion driven by the horizontal density gradients set up by the active deepening of the mixed layer in the exposed parts of the lake. Although detailed wind data were not available, observations of the temperature and salinity fields show the existence of fronts in lakes and strongly suggest the importance of the above mechanisms in determining the horizontal variability of these fields in the surface mixed layer of medium‐sized lakes.
Stream‐dwelling copepods: Their life history and ecological significance1
Authors: O'Doherty Erin Claire
Published: April 2010

The stream‐dwelling harpacticoid copepod Bryocamptus zschokkei was reared in the laboratory at 3.5°, 10°, 15°, 18°, and 20°C with naturally conditioned leaf disks as a food source. Egg and naupliar development rates were fastest at 18°C.

A complete life table experiment was conducted at 18°C. Females were longer‐lived than other copepods and produced eggs continuously until death. The intrinsic rate of natural increase (r) and the net reproductive rate (Ro) were found to be lower than those of most copepods. Reproduction is probably continuous throughout the year in the stream, since animals reproduced in the laboratory at the extreme temperatures experienced by the natural population. Since most copepods reproduce seasonally, the annual intrinsic rate of increase of B. zschokkei may be comparable to those of other copepods.
Selective predation by the carnivorous marine copepod Euchaeta elongata: Laboratory measurements of predation rates verified by field observations of temporal and spatial feeding patterns1,2
Authors: Yen J.
Published: April 2010

The size of copepod prey strongly influenced dietary selectivity by Euchaeta elongata. Adult females (4.2‐mm prosome length) showed highest predation rates on adult copepod prey 650– 1,000 µm long and on intermediate sized copepodid stages of Calanus pacificus. Selective feeding curves of copepodid stages IV and V of E. elongata showed a slight shift toward smaller prey. The prosome length of the primary prey was 70% the length of the second basipodal segment of the maxilliped for CIV, CV, and adult females of E. elongata. In both single and multispecies experiments at two concentrations, predation rates of adult female E. elongata seemed to be invariably focused on prey 650–1,000 µm long. Because E. elongata can consume adults of small copepod prey and the young copepodid stages of large copepod prey, it causes mortality of the entire copepod assemblage. Apparent recognition of a preferred prey, Pseudocalanus spp., and the nonpreferred cyclopoids seems to depend partly on their activity patterns. Thus, although size is an important determinant of dietary selectivity, species‐specific behavioral differences can also influence feeding rates.

Variations in predatory feeding activity on copepod prey were closely related to diel vertical migrations of E. elongata. The number of adult females with ingested prey began to increase soon after sunset, when the predatory copepod entered the surface layers containing prey of the preferred size, thus corroborating the selective feeding pattern observed in the laboratory. The timing of the migrations coincided well with sunset (ascent) and sunrise (descent) in winter, spring, and summer.
Pathways of photosynthetic carbon assimilation in sea‐ice microalgae from McMurdo Sound, Antarctica1
Authors: Palmisano Anna C. , Sullivan Cornelius W.
Published: April 2010

Although sea‐ice microalgae share a low temperature, ice‐associated environment, their patterns of 14C assimilation into proteins, polysaccharides, lipids, and small molecular weight metabolites suggest that the physiological ecology of surface, bottom congelation, and platelet ice communities should be considered separately.
Flux comparisons between sediments and sediment traps in the eastern tropical Pacific: Implications for atmospheric C02 variations during the Pleistocene1
Authors: Dymond Jack , Lyle Mitchell
Published: April 2010

Regeneration rates of labile elements and biogenic components were measured at two sites in the Guatemala Basin by comparing fluxes of material caught in sediment traps to fluxes of that preserved in the sediments. From 95 to 99% of the N, P, organic C, CaCO3, opal, and Br reaching the sea floor are regenerated at the two sites. For elements bound largely in refractory phases (e.g. Al, Sc, Ti, and Fe), the particle‐associated flux to the bottom is within 20% of the accumulation rate in the sediment.

The two MANOP sites, about 800 km apart, have similar fluxes of organically associated N, P, and C, reflecting similar and relatively high primary productivity. There is a marked contrast in the opal/carbonate fluxes which leads to differences in CO2 cycling at the two locations. At least 95% of the total particulate organic carbon and >97% of the total particulate phosphate are regenerated at <1,500‐m depth in the oceans. In contrast, much of the CaCO3 is destroyed at the sea floor. By a simple three‐box ocean model we show that the recycling and storage depths of organic C, CaCO3, and P can be important factors in the control of the CO2 content of the atmosphere. We suggest that Pleistocene CO2 variations were due in part to global increases in upwelling during glacial periods with synchronous increases in total oceanic productivity and differences in diatom vs. carbonate productivity.
The diurnal mixed layer1
Authors: Imberger J.
Published: April 2010

Fine‐scale measurements and temperature gradient microstructure data are used to describe the diurnal energetics of the mixed layer in the Wellington Reservoir in Western Australia. The data covered a morning period of solar heating, a period of severe wind mixing induced by an afternoon sea breeze, and a period of pure penetrative convection extending through most of the night. The Wedderburn number (W) ranged from a value of 0.02 at the start of the heating phase to a value of about 10 at the end of the convective period. During the intermediate strong wind period the value of W remained about 0.1; the surface wind stress induced a strong tilt of the isotherms at the base of the mixed layer. The other main parameter, the ratio of the Monin‐Obukhov length to the depth of the mixed layer, ranged from about 5.0 during the morning down to 0.005 at the end of the convective period. The full range of mixed‐layer deepening processes could thus be analyzed.

A simple one‐dimensional integral mixed‐layer model was applied to assess the importance of the temporal terms in diurnal simulations and to verify the values of the energy conversion efficiencies used in such models. Overall, the model performed extremely well; however, the results showed the need to develop parameterizations for the energetics of billowing induced by large shears across the base of the mixed layer and for the mixing accompanying upwelling.
Wind‐forced motions in stratified lakes and their effect on mixed‐layer shear
Authors: Monismith Stephen G.
Published: April 2010

The solution for the response of a rectangular, n‐layered, stratified lake to an arbitrarily varying (in time) wind stress is presented. The case n = 3 is considered in detail. For a three‐layered lake the response is made up of the individual responses of one external and two internal modes. When the upper layer is shallow relative to the other two layers, the mixed‐layer shear is due almost entirely to the slower, second‐mode response. Moreover, the upper interface can tilt quite severely while the lower interface remains nearly flat. Calculations based on the three‐layer model are compared with measurements made in Wellington Reservoir, Western Australia.
The fate of planktonic primary production1
Authors: Forsberg Bruce R.
Published: April 2010

The carbon dynamics of phytoplankton communities in six different lakes were investigated. In each lake carbon‐specific rates of production (b) and loss (d) were highly correlated and closely balanced through most of the year. As a result carbon‐specific growth rates were usually very low and carbon standing crop was relatively stable between sampling dates. Major fluctuations in algal biomass occurred only when the production‐loss balance was significantly perturbed. The frequency of these perturbations and the seasonal variability of b and d differed between lakes. The most consistent pattern was found in the low altitude lakes of the temperate zone, where b and d were highest in summer and lowest in winter. Values were also low during the spring and fall mixing periods when perturbations in the production‐loss balance caused major peaks in carbon standing crop. The fate of primary production varied significantly between lakes. In most of the lakes considered the majority of carbon fixation was consumed in metabolic processes. However, in Lake Wingra a large part of the production was apparently lost through grazing and sedimentation. Differences in the average values of b, d, and % metabolic loss between lakes appeared to depend on the combined loss rate due to sinking and grazing. These results suggest a general pattern of carbon dynamics similar to that found in steady state continuous cultures.
Phosphorus deposition from the epilimnion of Onondaga Lake1
Authors: Wodka Martin C. , Effler Steven W. , Driscoll Charles T.
Published: April 2010

The downward flux of inorganic and organic fractions of phosphorus from the epilimnion of calcium‐rich, hypereutrophic, Onondaga Lake was determined over 7 months in the water and in sediment traps. Material was collected in sediment traps for short and long periods (average of 4 and 14 days) throughout the study. A linear relationship between overlying concentrations of particulate phosphorus and downward flux (mg P m−2 d−1) of phosphorus was only weakly supported (significant at the 99.5% confidence level, r2 = 0.156). About 30% of the phosphorus deposited was in inorganic form. The time‐averaged flux of particulate phosphorus (45.4 mg P m−2 d−1) was greater than any values in the literature for other systems. The substantial contribution of inorganic phosphorus to total phosphorus deposition and the large magnitude of the overall downward flux may be attributed to oversaturation with respect to the solubility of calcite in the epilimnion of the lake, which facilitates the sedimentation of phosphorus with calcite and may also enhance the settling of phytoplankton cells. A comparison of the sediment trap data with annual mass balance calculations suggests that phosphorus settling across the metalimnion cycles vertically on the average about three times before it is exported from the lake or incorporated into the sediments.
Obtaining life table data from cohort analyses: A critique of current methods1
Authors: Hairston Nelson G. , Twombly Saran
Published: April 2010

Methods for estimating zooplankton instar development rates and survivorships from cohort analyses are often based on two equations that are correct only under limited and ecologically unrealistic conditions. We derive more general forms of the two equations and show that, using them, development times and survivorships cannot both be calculated from the information available in a single cohort analysis.
Anaerobic methane oxidation rates at the sulfate‐methane transition in marine sediments from Kattegat and Skagerrak (Denmark)1
Authors: Iversen Niels , Jorgensen Bo Barker
Published: April 2010

Concomitant radiotracer measurements were made of in situ rates of sulfate reduction and anaerobic methane oxidation in 2–3‐m‐long sediment cores. Methane accumulated to high concentrations (>1 mM CH4) only below the sulfate zone, at 1 m or deeper in the sediment. Sulfate reduction showed a broad maximum below the sediment surface and a smaller, narrow maximum at the sulfate‐methane transition. Methane oxidation was low (0.002–0.1 nmol CH4 cm−3 d−1) throughout the sulfate zone and showed a sharp maximum at the sulfate‐methane transition, coinciding with the sulfate reduction maximum. Total anaerobic methane oxidation at two stations was 0.83 and 1.16 mmol CH4 m−2 d−1, of which 96% was confined to the sulfate‐methane transition. All the methane that was calculated to diffuse up into the sulfate‐methane transition was oxidized in this zone. The methane oxidation was equivalent to 10% of the electron donor requirement for the total measured sulfate reduction. A third station showed high sulfate concentrations at all depths sampled and the total methane oxidation was only 0.013 mmol m−2 d−1.

From direct measurements of rates, concentration gradients, and diffusion coefficients, simple calculations were made of sulfate and methane fluxes and of methane production rates.
Seawater filtration: Particle flow and impaction considerations
Authors: Johnson B. D. , Wangersky P. J.
Published: April 2010

In filtration of seawater, adsorption of substances dispersed at sizes smaller than the filter pore dimension can result in major error. This error may be particularly severe for pore sizes approaching the 0.45‐µm delineation between dissolved and particulate.

A model based on diffusion in forced convection and interception predicts that, under typical conditions for filtration of seawater, a large portion of materials dispersed at sizes smaller than the filter pore dimension will interact with the filter pore wall. However, the fraction of these interacting materials that adsorb must be a function of many variables, both physical and surface chemical.
Sinking characteristics of dinoflagellate cysts1
Authors: Anderson Donald M. , Lively John J. , Reardon Ellen M. , Price Carl A.
Published: April 2010

This study reports the first direct measurements of the density and sinking rates of marine dinoflagellate cysts. Gyrodinium uncatenum, Gonyaulax tamarensis, and Scrippsiella trochoidea cysts had densities of 1.14, 1.24, and 1.32 g cm−3. No significant difference between cultured and natural cyst density was observed. Measured settling velocities ranged from 0.008 to 0.013 cm s−1 (6–11 m d−1). Settling rates calculated using the measured densities and reasonable assumptions about shape and orientation during descent were within 10–20% of measured sinking rates, confirming that cyst sinking can be described by a modification of Stokes’ law for nonspherical particles in a viscous medium. The three types of cysts examined are more dense and fall faster than most vegetative phytoplankton cells. Removal of an outer layer of short calcite spines from S. trochoidea cysts reduced both cell density and radius by 7% and the sinking rate by 37%. The faster settling velocity of the spiny cyst is not considered a general effect common to all ornamented cysts but presumably applies only to those with numerous short spines or processes. Morphological features can thus markedly affect the rate of cyst deposition, but the adaptive significance of surface ornamentation remains unknown.
Relative feeding rates on free and particle‐bound bacteria by freshwater macrozooplankton1
Authors: Schoenberg Steven A. , Maccubbin Alexander E.
Published: April 2010

Feeding suspensions of equivalent particle spectra were assembled with either free‐living (< 1.0 µm) or attached bacteria specifically labeled with [3H]thymidine. Clearance (ml ind−1 d−1) of attached bacteria was 3–29 × that of free bacteria for the cladocerans Acantholeberis, Chydorus, and Eubosmina. Pseudosida and Ceriodaphnia showed weaker discrimination or no selection, indicating a lower size threshold for filtration in these species. Feeding suspensions composed of isolated free bacteria yielded significantly higher or lower estimates of grazing than free bacteria with the full complement of particles, depending on species. Relative clearance (attached : free) tended to increase with body size within a species and varied for different particle environments. Bacteria associated with large particles may increase detrital energy flow to consumers in eutrophic environments.
Wave forces on intertidal organisms: A case study1
Authors: Denny Mark W.
Published: April 2010

Breaking waves impose large forces on intertidal organisms, and these forces are important in structuring wave‐swept communities. Here a telemetry system is used to continuously record wave forces at an exposed site; the interpretation of one such record is presented as a case study of the nature of wave forces. For waves with a breaking height of 2–4 m, water velocities of at least 8 m s−1 and accelerations of at least 400 m s−2 are present near the substratum. The forces imposed on organisms by these flows depend on the size and shape of the organism. For a limpet (Collisella pelta) an average force is about 0.6 N, a maximum about 3 N. The magnitude and direction of wave forces are unpredictable in both time and space over periods of seconds to hours, although predictability is possible over longer periods. A quantitative exposure index, based on an organism’s ability to withstand wave forces, shows that various organisms exposed to the same flow are at widely varying risks. No impact forces were observed during this study.
Microzone formation: Its role in the enhancement of aquatic N2 fixation1
Authors: Paerl Hans W.
Published: April 2010

Cyanobacterial‐bacterial aggregates form internal microenvironments (microzones) having metabolic and redox conditions distinct from those of ambient planktonic and benthic marine and freshwater habitats. Low turbulence accompanied by adequate supplies of dissolved organic matter (DOM) favored the formation of microzones. Increases in cyanobacterial and possibly bacterial N2 fixation potentials paralleled the development of microzones, while increased turbulence and DOM deprivation greatly reduced both microzone formation and N2 fixation potentials. Among North Carolina nearshore marine and freshwater systems examined, the formation and maintenance of microzones were shown to override both trace metal and phosphorus availability as factors regulating magnitudes of N2 fixation. The degree to which development of microzone‐scale symbiotic cyanobacterial‐bacterial interactions occur in aquatic habitats in part determines the extent to which N2 fixation can meet nitrogen demands in nitrogen‐depleted waters.
Chaoborus‐induced shifts in the morphology of Daphnia ambigua1
Authors: Hebert Paul D. N. , Grewe Peter M.
Published: April 2010

A simple filtration procedure allows the isolation of a factor from Chaoborus spp. which induces morphological change in Daphnia ambigua Scourfield. Neonate morphology is unaffected by exposure to the compound, but adults develop both a large helmet and pronounced spinescence along the carapace margin. The term chemomorphosis is proposed to describe cases in which morphological variation is induced by an exogenous chemical agent.
Measurement of the Mueller matrix for phytoplankton1
Authors: Fry E. S. , Voss K. J.
Published: April 2010

Measurement of the light‐scattering Mueller matrix of phytoplankton cultures resulted in a characteristic Mueller matrix much like that of seawater.
Eutrophication and the rate of denitrification and N20 production in coastal marine sediments
Authors: Seitzinger Sybil P. , Nixon Scott W.
Published: April 2010

Large (13 m3, 5 m deep) microcosms with coupled pelagic and benthic components were used to measure the effect of nutrient loading and eutrophication in coastal marine ecosystems on the rates of benthic denitrification (N2) and N2O production. After 3 months of daily nutrient addition, average denitrification rates ranged from about 300 µmol N m−2 h−1 in the sediments of the control microcosm to 880 in the most enriched microcosm. which received 65 times the nutrient input of the control. Increases in the production of N2O were more dramatic and increased by a factor of about 100, from 0.56 µmol N m−2 h−1 in the control to 51 in the most enriched microcosm. Although there was a clear increase in the denitrification rate in the more eutrophic systems, the amount of fixed nitrogen removed was a constant or progressively smaller fraction of the nitrogen input. Even in the most enriched microcosm, at least 16% of the N input was removed by denitrification.
Molybdenum in the Northeast Pacific Ocean1
Authors: Collier Robert W.
Published: April 2010

The concentration of dissolved molybdenum has been determined in several profiles from the Northeast Pacific Ocean. The salinity‐normalized concentration is essentially constant in all open‐ocean samples (107 nM, 1σ = 2.5 nM). The dissolved distribution is not significantly affected by biological cycling.
Production of heterotrophic bacteria inhabiting macroscopic organic aggregates (marine snow) from surface waters1
Authors: Alldredge Alice L. , Cole Jonathan J. , Caron David A.
Published: April 2010

Macroscopic detrital aggregates, known as marine snow, are a ubiquitous and abundant component of the marine pelagic zone. Descriptions of microbial communities occurring at densities 2–5 orders of magnitude higher on these particles than in the surrounding seawater have led to the suggestion that marine snow may be a site of intense heterotrophic activity. We tested this hypothesis using incorporation of [3H]thymidine into macromolecules as a measure of bacterial growth occurring on marine snow from oceanic waters in the North Atlantic and from neritic waters off southern California.

Abundances of marine snow ranged from 0.1 to 4.3 aggregates liter−1. However, only 0.1–4% of the bacteria in the water occurred in association with marine snow. Mean thymidine incorporation per cell on aggregates was generally equal to or lower than that of bacteria found free‐living in the surrounding seawater, indicating that attached bacteria were not growing more rapidly than free‐living bacteria. Bacteria inhabiting aggregates were up to 25 times larger than free‐living forms. Thus, the contribution of these attached bacteria to total bacterial production in surface waters was low but occasionally significant, ranging from 3 to 26% and averaging 8 ± 7%
Sources of carbon and sulfur nutrition for consumers in three meromictic lakes of New York State1
Authors: Fry Brian
Published: April 2010

The trophic importance of bacterioplankton as a source of carbon and sulfur nutrition for consumers in meromictic lakes was tested using stable carbon (δ13C) and sulfur (δ34S) isotopic measurements. Studies in three lakes near Syracuse, New York, showed that most consumers ultimately derive their C and S nutrition from a mixture of terrestrial detritus, phytoplankton, and littoral vegetation, rather than from bacterioplankton. Food webs in these meromictic lakes are thus similar to those in other lakes that lack dense populations of bacterioplankton.
An experimental investigation of a flagellate‐ciliate‐copepod food chain with some observations relevant to the linear biomass hypothesis
Authors: Sheldon R. W. , Nival P. , Rassoulzadegan F.
Published: April 2010

Predation by copepods (Euterpina acutifrons) on ciliates (Lohmanniella spiralis) and by ciliates on flagellates was followed during a 12‐day experiment in a small enclosed ecosystem (100 liters). For a period of about 4 days the three populations seemed to exist in a state of quasi‐equilibrium with growth balanced by predation. During this time, material transfer from prey to predator was taking place with an efficiency of 30–40%.
Isolation of viable uncontaminated Chlorella from green hydra1
Authors: McAuley P. J.
Published: April 2010

Symbiotic Chlorella isolated from green hydra by simple techniques of homogenization and centrifugation have been found to be contaminated with comparatively large amounts of animal debris. Additional washing with sodium dodecyl sulfate (SDS) removed virtually all contaminating host protein from the Chlorella without affecting its viability.
Relation between biomass and body weight of plankton in a steady state oceanic ecosystem1
Authors: Rodriguez Jaime , Mullin Michael M.
Published: April 2010

In the size range from 10−4 to 103 µg (carbon) body weight, the biomass of plankton in the euphotic layer of the North Pacific Central Gyre decreases as an allometric function of body weight. Even in a steady state ecosystem such as that analyzed here, there is variability in space and time; this suggests that one must be careful in extrapolating the relation to less predictable marine areas. In obtaining dynamic information from biomass spectra, one must distinguish changes due to the flow of energy within the spectrum (growth, predation, reproduction) from changes due to emigration from or immigration into the spectrum of the particular area sampled, such as those due to the diel vertical migration of macrozooplankton in the largest size classes.
Bacterivory in seawater studied with the use of inert fluorescent particles1
Authors: McManus George B. , Fuhrman Jed A.
Published: April 2010

Fluorescent pigments were used to study the uptake of bacteria‐sized particles by laboratory and field populations of heterotrophic nanoplankton. With membrane filtration these particles can be made to mimic the natural bacterioplankton size distribution. Uptake was roughly linear for 20–40 min, and leveled off after that, with the number of particles per cell remaining constant for at least several hours. Photosynthetic nanoplankton did not take up the particles in significant numbers. Experiments with a small nonpigmented flagellate indicated some selection against the particles in favor of ingestion of unicellular cyanobacteria, but this may have been based on the size of the particles rather than quality. Preliminary field experiments indicated that nonpigmented nanoplankton was responsible for virtually all of the grazing on bacterioplankton, with microzooplankton playing a minor role.
On the reactivity of metals for marine phytoplankton
Authors: Fisher Nicholas S.
Published: April 2010

The concentration of metals by marine phytoplankton, assessed for diverse species in laboratory culture experiments with radiotracer methodology and taken together with literature values for other metals, was analyzed in light of geochemical models describing particle surface chemistry. Concentration factors vary among the metals from ≃0 to ≃106, and there are only modest differences (less than an order of magnitude) among algal species for any particular metal. Regression analyses show that, at equilibrium, the logs of the concentration factors are exponentially related (P < 0.001) to solubility products of metal hydroxides and to cytotoxicity and are linearly related (P < 0.001) to the log of the mean oceanic residence times (years) of the metals. It would appear that concentration factors and toxicity of metals in marine phytoplankton and oceanic residence times of metals can be predicted to within an order of magnitude from the chemical literature.
The relationships of sex size ratio and season to mating intensity in some calanoid copepods1
Authors: DeFrenza Joe , Kirner Robert J. , Maly Edward J. , van Leeuwen Henry C.
Published: April 2010

Samples of four species of calanoid copepod were analyzed to obtain the sex size ratios and the percentage of females carrying a clutch or spermatophore. A multiple regression model was developed to determine if the percentage of successfully mated females was related to either season or sex size ratio. Three of the species had peaks in sexual activity when sex size ratios approached the mean ratios observed in nature, but the fourth did not exhibit such a peak. Three species appeared most sexually active in summer months; the fourth was more sexually active during the colder months. We hypothesize that characteristic sex size ratios promote successful copulation and that co‐occurrence of species of similar size is more likely if there are temporal differences in sexual activity.
Algal growth response to particle‐bound orthophosphate and zinc
Authors: Kuwabara James S. , Davis James A. , Chang Cecily C. Y.
Published: April 2010

Dissolved nutrient concentrations in natural waters may at times be controlled by interactions between particulate and solution phases. Effects of Zn [0–1 µM total Zn(II)] and orthophosphate (8–12 µM total P) additions on growth indices for the chlorophyte Selenastrum capricornutum Printz were examined in a synthetic growth medium containing 50 mg liter−1 colloidal titania. Over the Zn(II) concentration range used, detrimental growth and yield effects were observed. Addition of P to a synthetic growth medium (S‐3) increased stationary phase cell density, but had minimal effect on growth rate and duration of lag phase. Presence of TiO2 particles in culture media significantly reduced Zn and P dissolved fractions. Although adsorbed Zn and P were less available to Selenastrum, desorption of both solutes increased their availability. Rapid desorption of Zn(II) from TiO2 particles served in effect to buffer Zn2+ free ion concentration, until Zn became partitioned primarily with the algal fraction as cell concentration approached stationary phase density. Although phosphate desorption from TiO2 in nonbiological systems was negligible, Selenastrum was able to scavenge some P initially adsorbed onto TiO2. Accurate primary productivity predictions in nature may therefore require an understanding of equilibrium and reaction rates involved in the partitioning of nutrients and toxic substances between dissolved and particulate phases.
Absorption and scattering coefficients in Irondequoit Bay1
Authors: Weidemann A. D. , Bannister T. T.
Published: April 2010

Profiles of scalar, downwelling, upwelling, and spectral irradiance were measured on 37 dates in 1982–1983. Values of the attenuation coefficient K were 0.8–1.2 m−1, and the reflectance R was 0.03–0.06. By Kirk’s method, the absorption and scattering coefficients a and b were found to be 0.44–0.83 and 1.8−5.0 m−1. Also measured were turbidity, chlorophyll, and absorption spectra of dissolved yellow substances and of particles. Independent estimates of a, as the sum of absorption components, were in reasonable agreement with values obtained by Kirk’s method. For particles, the average value of the Chl‐specific absorption coefficient ka was ~0.008–0.010 m2 mg−1 Chl. Values of the Chl‐specific scattering coefficient kb were usually ~0.05–0.10 m2 mg−1 Chl; values were higher (~0.12) when gas‐vacuolate cyanobacteria were present.
Diel nucleic acid synthesis and particulate DNA concentrations: Conflicts with division rate estimates by DNA accumulation1
Authors: Winn C.D. , Karl D.M.
Published: April 2010

The diel rate of microbial nucleic acid synthesis and the concentration of particulate DNA were measured at various locations in the oligotrophic Pacific Ocean. Net synthesis of RNA and DNA was observed over 24‐h periods at all locations investigated, but the actual rate sometimes varied with time of day. It is concluded that whenever possible, daily rates of synthesis should be determined from a series of consecutive incubations conducted over a complete 24‐h period. In addition, nonreplicating DNA comprised 75–90% of the total particulate DNA at the locations investigated. These results appear to preclude the use of light‐dependent DNA accumulation as a measure of phytoplankton growth rate in the oligotrophic oceans.
Nitrogen metabolism of the eutrophic Delaware River ecosystem1
Authors: Lipschultz Fredric , Wofsy Steven C. , Fox Lewis E.
Published: April 2010

A comprehensive investigation of the nitrogen cycle in the Delaware River was carried out using 15N tracers to measure rates for important transformations of nitrogen. Daily, depth‐averaged 15N rates for the principal inorganic nitrogen species were consistent with rates derived from longitudinal profiles of concentration in the river.

The data indicated that nitrification was a rapid, irreversible sink for NH4+, with export of the product NO3− from the study area. Utilization of NO3− by primary producers was negligible, owing to low irradiance levels and to high NH4+ concentrations.

The oxygen sag near Philadelphia was found to result from oxygen demand in the water column, with only minor benthic influence. Reaeration provided the major oxygen input. Nitrification accounted for about 1% of the net oxygen demand near Philadelphia but as much as 25% farther downstream.
Dissolved humic substances of the Amazon River system1
Authors: Ertel John R. , Hedges John I. , Devol Allan H. , Richey Jeffrey E. , Ribeiro Maria de Nazaré Góes
Published: April 2010

Aquatic humic and fulvic acids from nine mainstem and seven major tributary sites in the Amazon River Basin are characterized by their elemental and lignin phenol compositions. Combined humic substances represent 60% of the riverine dissolved organic carbon (DOC), with fulvic to humic acid (FA : HA) ratios in the mainstem averaging 4.7±1.0. All dissolved humic and fulvic acids have clearly recognizable lignin components at levels (8 and 3% of the carbon) suggesting a predominantly allochthonous source. Lignin compositional characteristics are dominated by diagenetic transformations, which include preferential loss of methoxylated structural units and oxidative degradation of lignin side chains. Fulvic acids have consistently lower lignin levels, lower lignin phenol methoxylation, higher acid : aldehyde ratios, and higher C: N ratios than coexisting humic acids, all indicative of greater aerobic degradation of the fulvic acid fraction. An extreme example of lignin degradation is seen in the Rio Negro humic and fulvic acids, which differ significantly in lignin and elemental compositions from other blackwater tributary and mainstem samples.

Over most of the mainstem humic and fulvic acids behave conservatively. However, downstream of the Rio Negro confluence, humic acids appear to be selectively adsorbed onto fine suspended particles. Approximately 25 and 40% of the total fluxes of lignin and of carbon are represented in the dissolved humic substances. The annual flux of dissolved, chemically recognizable lignin in the Amazon River at Obidos is calculated to be 1.2 × 1011 g yr−1.
Net community production and hypolimnetic nutrient regeneration in a Michigan lake1
Authors: Lehman John T. , Naumoski Trajče
Published: April 2010

Net community oxygen production in Third Sister Lake, Michigan, was calculated from concentration gradients, eddy diffusion, and gas flux at the lake surface. The trophogenic zone extended on average to 4.5 m from April to August. Vertical flux of dissolved P provided negligible support for the productivity during this time. Stoichiometries for biomass production from inorganic N and P were inferred from enclosure experiments and from vertical profiles. N and P accumulated in the hypolimnion at a ratio of 24 : 1 by atoms, whereas ratios in the algae averaged 9.5 : 1. On the basis of areal rates of nutrient remineralization and the oxygen budget, most of the net community production from April to August could be assigned to the open water rather than to the littoral region. Littoral production processes are relatively isolated from the open water in this small, sheltered lake during the time of thermal stratification.
Changes of phosphorus and nitrogen concentration and of phytoplankton in enriched lake enclosures1
Authors: Istvánovics Vera , Vörös Lajos , Herodek Sándor , Tóth, László G. , Tátrai István
Published: April 2010

Enclosures isolating 17 m3 water with the underlying sediments in the mesotrophic area of Lake Balaton were used to simulate the main processes taking place in its hypertrophic area. In an enclosure with both P and N added the production and the biomass of phytoplankton increased immediately. Algae rapidly took up the added nutrients, transporting a third of the loadings from the water to the sediments and supplying a large amount of organic substrate for denitrification. As a result of N loss from the system, Aphanizomenon flos‐aquae formed a second bloom. In an enclosure with only N added the production and the biomass of algae remained similar to those in the open water. NO3− accumulated in the water for a long time. In an enclosure with only P added the algal production and biomass showed a moderate increase, followed by an outburst of A. flos‐aquae. PO43− accumulated in the water during the first part of the experiment and was used up during the second.
A numerical analysis of hypolimnetic nitrogen and phosphorus transformations in Lake Rotoiti, New Zealand: A geothermally influenced lake
Authors: Priscu John C. , Spigel Robert H. , Gibbs Max M. , Downes Malcolm T.
Published: April 2010

Measurements of chlorophyll, oxygen, and particulate and dissolved forms of nitrogen and phosphorus made over a year were used in a one‐dimensional diffusion model to calculate rates of generation or loss of these substances in the hypolimnion of Lake Rotoiti, New Zealand. During summer stratification the hypolimnion was always a sink for chlorophyll, particulate nitrogen (PN), particulate phosphorus (PP), and dissolved oxygen. The order of decomposition was chlorophyll >PP >PN. The hypolimnion was a source for NH4+ and dissolved reactive phosphorus (DRP), whereas dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) showed no distinct seasonal trends. N2O reached 8,800% of air saturation just before the hypolimnion became anaerobic. At this time, the hypolimnetic N2O pool comprised about 13% of the total dissolved inorganic nitrogen pool. Diffusion of dissolved inorganic nitrogen (DIN) and DRP from the hypolimnion to the epilimnion could increase mean epilimnetic concentrations during summer stratification by 0.10 mg DRP m−3 d−1 and 0.34 mg DIN m−3 d−1. The ratio of DIN : DRP supplied to the epilimnion was 3.4 (by weight), which would exacerbate DIN deficiency in this lake.
Dynamics of gut pigment in the copepod Temora longicornis and the determination of in situ grazing rates
Authors: Wang Rong , Conover Robert J.
Published: April 2010

Gut fluorescence attributable to algae eaten by an herbivorous zooplankter should be a function of chlorophyll consumption minus loss of pheopigments in defecation. The amount of chlorophyll ingested, as determined in a laboratory grazing experiment, minus the gut pigment content at the end in the grazers, should equal chlorophyll defecated and should also provide a calibration for the determination of evacuation rate in filtered seawater. The kinetics of gut filling and emptying in Temora longicornis have been studied at different food concentrations. Neither is constant with time. Filling rate is positively correlated with food concentration but gut pigment content may be maximal at lower concentrations when food supply is presumably still limiting. Evacuation rates, while not constant, are independent of initial gut chlorophyll content or food concentration in the experimental environment over a range from 0.5 to 8 mm3 liter−1 of Coulter Counter volume. Ingestion rates determined from gut pigment concentration and gut clearance time and those determined from filtration rate were directly correlated (slope = 1) but showed a systematic difference apparently caused by undetected loss of gut pigment. An improved method for determining in situ grazing rates from gut pigment measurements is proposed.
The measurement of bacterial chlorophyll and algal chlorophyll a in natural waters
Authors: Caraco N. , Puccoon A. H.
Published: April 2010

Several groups of chlorophyll‐bearing photosynthetic organisms often coexist in anoxic waters. Because of the close similarity between the absorbance spectra of chlorophyll a (in cyanobacteria and algae) and the chlorophylls of green sulfur bacteria (Chl‐GSB) it is difficult to distinguish these two groups of organisms where they co‐occur.

We have developed a simple method to measure both chlorophyll a and Chl‐GSB and used it in a meromictic coastal pond. In anoxic bottom waters Chl‐GSB was the major pigment present (averaging 20 mg m−3), but chlorophyll a accounted for from 5 to > 50% of the total pigment present throughout the year. Without our method large errors in calculated Chl‐GSB and chlorophyll a concentrations would have resulted.
Determination of hydrogen sulfide in seawater using flow injection analysis and flow analysis1
Authors: Sakamoto‐Arnold Carole M. , Johnson Kenneth S. , Beehler Carl L.
Published: April 2010

Flow injection analysis (FIA) and flow analysis (FA) were used to automate the colorimetric determination of hydrogen sulfide by the methylene blue method. A low‐sensitivity FIA manifold for concentrations up to 200 µM H2S had a detection limit of 1.2 µM. A high‐sensitivity FIA manifold for concentrations up to 75 µM H2S had a detection limit of 0.12 µM. The C.V. was <1% at concentrations >10 M. Sulfide standards were calibrated by colorimetric measurement of the excess triiodide ion remaining after reacting sulfide with iodine. The FIA method was tested onboard ship with samples from the Galapagos hydrothermal vents and compared with results obtained in situ using FA.
Response of the marine diatom Thalassiosira weissflogii to iron stress1
Authors: Harrison Gail I. , Morel F. M. M.
Published: April 2010

The coastal diatom Thalassiosira weissflogii responds to iron limitation with decreasing growth rate, decreasing quotas of cellular iron, and increasing rates of maximum short term uptake. Growth response to steady iron limitation can be modeled according to the equations of Droop and Monod. The cellular iron quota varies from about 2 to 25 × 10−5 mol iron per liter‐cell with increasing iron; the half‐saturation constant for growth, Kµ, is 1.1 × 10−21 M (free ferric ion). In contrast, the half‐saturation constant for iron uptake, Kp, is about 3 × 10−19 M; the maximum iron uptake rate (ρmax) is increased several‐fold under iron limitation, resulting in a potential short term uptake rate that is a few hundred times the steady state rate. At a fixed concentration of free manganese ion, the cellular manganese quota is increased several‐fold in iron‐limited cultures compared to iron‐sufficient cultures.
Utilization of inorganic and organic nitrogen by bacteria in marine systems1
Authors: Wheeler Patricia A. , Kirchman David L.
Published: April 2010

The relative contribution of various inorganic and organic forms of nitrogen to the nitrogen requirements of picoplankton was examined with 15N tracers. Size fractionation was used to measure uptake by <1‐µm size microorganisms, and inhibitors of protein synthesis were used to separate procaryotic from eucaryotic nitrogen uptake. Picoplankton utilized mainly ammonium and amino acids and only negligible amounts of nitrate and urea. Nearly all amino acid uptake was by procaryotes, while both procaryotes and eucaryotes utilized ammonium. About 78% of total ammonium uptake was by procaryotes, and a significant portion of this was due specifically to heterotrophic bacteria. Regeneration of ammonium was correlated with eucaryotic rather than procaryotic activity. Ammonium accounted for at least 20–60% of the summed ammonium plus amino acid utilization by bacteria. The results suggest that a significant portion of ammonium uptake in the euphotic zone was by heterotrophic bacteria rather than solely by phytoplankton. This may invalidate the use of the Redfield C : N ratio for estimating rates of nitrogen assimilation in the euphotic zone from carbon assimilation rates.
Reciprocal interactions between roach, Rutilus rutilus, and zooplankton in a small lake: Prey dynamics and fish growth and recruitment1
Authors: Cryer Martin , Peirson Graeme , Townsend Colin R.
Published: April 2010

Recruitment success of roach varied dramatically between 1979 and 1982 in Alderfen Broad, a small lake in eastern England. When fry were abundant (in 1979 and 1981, but not in 1980 or 1982) the summer zooplankton became sparse and was dominated by copepods and rotifers. In years of good recruitment, as each of the preferred cladoceran prey species entered the diet of underyearling roach, its density dropped dramatically. Mean size of Daphnia hyalina and Ceriodaphnia quadrangula also declined significantly during these seasons. The results of enclosure experiments indicate that the link between roach recruitment and zooplankton dynamics is causal. Older roach also feed to a significant extent on zooplankton, but the 0+ age group exerted the greatest influence. The abundant underyearling roach in years of good recruitment showed poor growth, as a result of depression of their prey populations. Older fish also grew poorly in these years and were then less fecund in the following season. The evidence indicates that there may be a 2‐year cycle in roach recruitment, and we describe the unusual circumstances in Alderfen which may be responsible.