bluuebunny/crossref_metadata_2025 huggingface dataset:
The coupling of nitrification and denitrification in two estuarine sediments1,2
Authors: Jenkins Mark C. , Kemp W. Michael
Published: April 2010

Nitrification and denitrification in estuarine sediments were measured by 15N isotopic tracer techniques at two stations in the Patuxent River estuary for April and August. A close coupling of the two processes was demonstrated directly from the evolution of labeled N2 following 15NH4+ amendments during spring experiments: >99% of the added 15NH4+ which was oxidized to 15NO3‒ was subsequently reduced to 15N‐labeled N2 during 48‐h incubations, suggesting that the two reactions were occurring in close proximity to one another. In contrast, this coupled nitrification‐denitrification was decreased by two orders of magnitude in the summer, even though the capacity for denitrification (N2 production from NO3‒ enrichment) remained similar to spring levels. This pattern of sharply seasonal nitrification was corroborated with measurements of bacterial relative abundance. Indirect evidence suggests low redox conditions (and reduced O2 concentrations) as the possible cause of decreased summertime nitrification. Ambient rates of nitrification‐denitrification were inferred from 15N experiments in these sediments. Estimated springtime rates of about 77–89 µmol N·m‒2·h‒1 are similar to previously reported values for denitrification supported by NO3‒ diffusion from overlying water to coastal sediments.
A headspace technique for oxygen measurements in deep‐sea sediment cores1
Authors: Sørensen Jan , Roger T. , Wilson S.
Published: April 2010

A headspace analysis technique is described for shipboard measurement of O2 in deep‐sea sediments. A subsample of a core is equilibrated with helium in a closed vial and a gas sample is taken for gas chromatographic determination of O2. Air contamination, bubble formation, and microbial activity are minimized by careful design of procedures, rapid handling, and storage in the cold. The results are in agreement with a parallel series of O2 measurements in porewaters collected by in situ filtration at the sea bottom. The technique is particularly useful in diagenetic studies of the sediments as oxygen can be determined in samples from the same core used for determination of all other diagenetically active chemical species.
The asphyxiation technique: An approach to distinguishing between molecular diffusion and biologically mediated transport at the sediment—water interface
Authors: van der Loeff Michiel M. Rutgers , Anderson Leif G. , Hall Per O. J. , Iverfeldt Åke , Josefson Alf B. , Sundby BjÅrn , Westerlund Stig F. G.
Published: April 2010

On the assumption that lack of oxygen will cause the activity of benthic infauna to cease and thereby limit solute transport to that accomplished by molecular diffusion, we have measured the flux of dissolved silicate across the sediment‐water interface of sediments incubated in situ under parallel benthic flux chambers. In one chamber the oxygen concentration was allowed to go to zero, and in the other the oxygen and pH remained at ambient values.

As long as oxygen was present in the chambers, the measured summer and fall fluxes were 2– 10 times those calculated from porewater profiles assuming one‐dimensional molecular diffusion. The differences in fluxes predicted from the densities of macrobenthos at two different sites agree well with the flux measurements. After oxygen depletion, the silicate fluxes decreased and approached the values calculated on the basis of molecular diffusion. In one experiment the ratio between the oxic and anoxic fluxes was nearly identical to the ratio between the effective diffusion coefficient, as measured under oxic conditions using 22Na as a tracer, and the whole‐sediment molecular diffusion coefficient. In winter (‒1°C) measured and calculated Fickian fluxes agreed closely, indicating a negligible effect of benthos on solute transport.
Small‐scale nutrient patchiness: Some consequences and a new encounter mechanism1
Authors: Scavia Donald , Fahnenstiel Gary L. , Davis Judith A. , Kreis Russell G.
Published: April 2010

Semicontinuous cultures of Lake Michigan algal assemblages were run at 0.15·day‒1 dilution rates under P limitation for 41 days. In control cultures, nutrients were supplied to the entire culture once per day. In patch cultures, 10% of the cultures received a high concentration 10‐min pulse each day. Patch and control cultures received equal nutrient flux and achieved equal biomass levels; however, their species composition was different. Patch cultures were dominated by the filamentous blue‐green alga Schizothrix calcicola and control cultures were dominated equally by S. calcicola, Nitzschia acicularis, and a group of phytoflagellates. These results, as well as shifts in subdominants, demonstrate the effect of small‐scale, short term nutrient patches on species composition. Similar patch and control unialgal cultures revealed lower cell nutrient quotas for patchy cultures.

Microvideographic observations of Daphnia magna suspended in three concentrations of Chlamydomonas sp. allowed quantification of rates at which algal cells were collected, swept close by, and released via bolus rejection or outwashing of unpacked cells. Outwashing release rates of presumably unharmed cells increased from 31 to 71% of the collection rate as food concentration increased. It appears that algal outwashing is a significant mechanism for eliminating excess food. An important implication is the potential algal nutritional consequence of this very close nondestructive encounter.
Primary production and grazing in freshwater and intertidal reaches of a coastal stream, Southeast Alaska
Authors: Murphy Michael L.
Published: April 2010

During summer 1981, primary production of periphyton and grazing by macroinvertebrates were measured in Porcupine Creek, a small stream in Southeast Alaska. The intertidal reach was in a meadow primarily of sedge (Carex sp.); the freshwater reach was in a mature forest of western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis). Daily net primary production was 50% greater in the intertidal reach (mean = 486 mg C·m‒2) than in the freshwater reach (mean = 324 mg C·m‒2). In the freshwater reach, periphyton had high biomass (mean = 7.8 g C·m‒2; 95% C.I. = 4.9–10.7 g C·m‒2) and low production: biomass ratio (0.04), and shade of the forest canopy limited primary production. In the intertidal reach, periphyton had low biomass (mean = 2.0 g C· m‒2; 95% C.I. = 1.3–2.7 g C·m‒2) and high production: biomass ratio (0.24), and grazing macroinvertebrates limited primary production by reducing the biomass of periphyton. Mean daily net primary production in the intertidal reach could supply about 3.8 kcal·m‒2·d‒1 and satisfy 200% of the daily energy requirement for maintenance and activity of the population of macroinvertebrates in the reach, primarily the isopod Gnorimosphaeroma oregonensis and amphipods Paramoera columbiana and Eogammarus confervicolus. Autochthonous primary production by periphyton is probably the dominant source of energy in summer for secondary producers in the intertidal reach of Porcupine Creek.
Responses of phytoplankton to experimental nutrient enrichment in an Amazon floodplain lake1
Authors: Setaro Frank V. , Melack John M.
Published: April 2010

Natural algal populations in 4‐, 10‐, and 800‐liter enclosures were fertilized to ascertain to what extent ammonium, nitrate, or phosphate enrichment changed phytoplankton abundance and physiology in an Amazon floodplain lake (Lake Calado). When water was rising and was between 8 and 11 m (March–May 1982), algal abundance ranged from 13–24 µg Chl a liter−1 and epilimnetic NH4+, NO3−, and PO43− concentrations were usually <0.3 µM. Chlorophyll increased over the control by 60–265% in the P treatment, 5–40% in the N treatments, and 75–270% in the N+P treatments after about 5 days. In three of the four experiments, increases in chlorophyll after addition of phosphate alone were significantly greater (P < 0.05) than after additions of nitrate or ammonium alone. Increases in net photosynthesis and in particulate C and N concentrations corroborated the chlorophyll data. Deficiency indices (ammonium‐enhanced dark 14C fixation, N and P uptake rates, and sestonic N:P ratios) implied that the phytoplankton were impoverished with respect to nitrogen and phosphorus; nutrient enrichment relieved this condition but deficiency often returned after a few days. When water depth was falling and was between 7 and 2 m (September–November 1982) algal abundance ranged from 4 to 15 µg Chl a·liter−1, turbidity increased, and epilimnetic inorganic N and P were usually <0.3 µM. During September both N and P additions increased algal standing crop, whereas in early October enrichment with N increased abundance substantially (P < 0.05) above that after P addition. The physiological evidence indicated that the lake was N‐deficient during September; in October neither N nor P deficiency was discernible except for slight alkaline phosphatase activity.
Carbon and hydrogen isotopic composition of bacterial methane in a shallow freshwater lake
Authors: Woltemate I. , Whiticar M. J. , Schoell M.
Published: April 2010

Hydrogen and carbon isotopes measured in biogenic gas from a shallow freshwater lake indicate the acetate‐reduction pathway to be responsible for over 70% of the methanogenesis in these sediments. Methane δD was strongly depleted (up to 307‰) relative to the associated formation water (ca. −25‰ vs. SMOW) and was similar to fermentation methane from sewage sludge digesters. Although the methane δ13C ranged from −52‰ to −61‰, relative to the porewater CO2 it had a consistent fractionation about αc = 1.05. With the combination of H isotopes, we can interpret previously ambiguous methane δ13C values (−50 to −60‰) as being of biogenic origin.
Above‐ and belowground emergent macrophyte production and turnover in a coastal marsh ecosystem, Georgia1
Authors: Schubauer J. P. , Hopkinson C. S.
Published: April 2010

Seasonal patterns of aboveground plant mass and the depth distribution of live roots, rhizomes, and dead belowground organic matter were measured for Spartina alterniflora and Spartina cynosuroides in Georgia tidal marshes. Peak live aboveground biomass was 1.6 × higher for S. cynosuroides than for S. alterniflora. Live biomass was 2.4 × more belowground than aboveground for S. cynosuroides and 1.7 × for S. alterniflora. Rhizomes made up 76 and 87% of live belowground biomass during the year. Mirrored patterns of biomass accumulation and loss in above‐ and belowground tissues during the year suggest the importance of seasonal storage and redistribution of organic matter.

Belowground production was measured with a technique that partially accounts for midseason decomposition. Total plant production was estimated to be 7,620 g dry mass·m−2·yr−’ for S. alterniflora and 7,708 for S. cynosuroides. Belowground production was roughly 1.6 × aboveground production. Turnover rates for belowground live material were 1.42 · yr−1 for S. cynosuroides and 3.22·yr−1 for S. alterniflora. The fate of root and rhizome material, including the extent to which such material enters the estuarine or nearshore food webs, is not clear.
Productivity and utilization of the seagrass Halodule wrightii and its attached epiphytes1
Authors: Morgan Mark D. , Kitting Christopher L.
Published: April 2010

Epiphytic algae growing attached to shoalgrass (Halodule wrightii) blades accounted for nearly half of the aboveground live biomass and primary productivity of two seagrass meadows in southern Texas from June–December 1980. They also accounted for the major fraction of recognizable diet material of common seagrass meadow macroinvertebrates, such as grass shrimp (Palaemonetes), crabs (Callinectes), snails (Anachis and Bittium), and amphipods (Cymadusa). Significant shading of seagrass by epiphytes did not appear evident at the light intensities normally encountered by these populations. The passage of Hurricane Allen near the area in early August 1980 did not seem to have a major impact on the seagrass meadow, despite wind gusts of 150 kph and storm tides of +3 m.
The other side of cyclomorphosis: Why Daphnia lose their helmets
Authors: Riessen Howard P.
Published: April 2010

While the possession of a helmet ap pears to be advantageous to many species of Daphnia as an antipredator device in summer, the fact that this structure is absent in spring suggests that during this time its formation is disadvantageous. Both helmeted and round‐headed individuals of Daphnia retrocurva occur simultaneously in Heney Lake, Quebec, in late May. Round‐headed individuals have significantly larger clutch sizes than do helmeted ones of the same carapace length at this time. The reproductive disadvantage of being helmeted seems to select for the round‐headed form in spring, when food levels are high and predation pressure is low.
High phytoplankton growth and production rates in oligotrophic Hawaiian coastal waters1
Authors: Laws E. A. , Redalje D. G. , Haas L. W. , Bienfang P. K. , Eppley R. W. , Harrison W. G. , Karl D. M. , Marra J.
Published: April 2010

Plankton biomass, material fluxes, e.g. 14C uptake, and specific growth rates are related quantities. In the course of comparing various methods of measuring these properties in September 1982 off Oahu, Hawaii, we found specific growth rates of 1–2·d−1. Such rates approach the maximum expected values observed in laboratory cultures.
Organic matter diagenesis in freshwater sediments: The alkalinity and total CO2 balance and methane production in the sediments of Lake Washington1,2
Authors: Kuivila Kathryn M. , Murray James W.
Published: April 2010

The interstitial water chemistry of Lake Washington sediments collected with an in situ sampler was studied. The depth where the sulfate concentration reaches a low background value appears to delineate a transition within the sediments above and below which profiles of total CO2, alkalinity, methane, and ammonium are linear, suggesting zones dominated by diffusion separated by a narrow zone of reaction.

A stoichiometric model is used to identify the increase of alkalinity with depth in the interstitial waters. Ammonium production, followed by iron reduction, makes the largest contribution to this increase; about 30–40% is due to ammonia that has been produced but subsequently adsorbed by the sediments. The measured and calculated ammonia exchange constants agree well.

The C:N ratio of the decomposing organic matter increases systematically, from 3.9 at 5 cm to over 14 at 50 cm. The organic matter being decomposed becomes nitrogen‐poor with age.

Flux calculations for the lake‐sediment system show good agreement between the flux of carbon to the sediments and the sum of the diffusive loss from the sediments of CH4 and total CO2 and the permanent burial in the sediments. About a fourth of the detrital rain of carbon is recycled to the lake as a diffusive flux of CO2 and CH4.
Microbial mediation of Mn(II) and Co(II) precipitation at the O2/H2S interfaces in two anoxic fjords1
Authors: Tebo Bradley M. , Nealson Kenneth H. , Emerson Steven , Jacobs Lucinda
Published: April 2010

We studied the potential for bacterial catalysis of Mn(II), Co(II), and Fe(III) precipitation at the O2/H2S interfaces in Saanich Inlet, British Columbia, and in Framvaren Fjord, Norway. In Saanich Inlet the interface is below the photic zone, but in Framvaren Fjord it is within the region of significant light penetration. Biological catalysis of metal removal was measured as the binding of radioactive isotopes as a function of time in the presence and absence of poisons which do not measurably interfere with the solution chemistry of manganese. In a region just above the oxic/ anoxic interface in Saanich Inlet, the binding of Co(II) and Mn(II) was inhibited by the bacterial poisons, but Fe(III) precipitation was not. Measurements of the oxidation state of the particulate material indicated a slightly higher Mn(IV):Mn(II) ratio in the region of dissolved Mn(II) precipitation, confirming that manganese was being oxidized and not simply bound. In both fjords, binding was either stronger or more rapid under air saturation than under conditions of oxygen limitation, suggesting that O2 is the electron acceptor during manganese oxidation. In Framvaren Fjord a threefold increase in Mn(II) concentration [to 10 µM Mn(II)] severely inhibited both Mn(II) and Co(II) binding. A 25‐ to 250‐fold increase in Co(II) concentration [to 0.18 or 1.8 µM Co(II)], on the other hand, completely inhibited Co(II) binding, but the highest concentration inhibited Mn(II) binding by only 40%. The results suggest microbial mediation of Co(II) and Mn(II) precipitation in these environments and that the mechanisms of these processes are not the same.
Survival of Cyclops abyssorum tatricus (Copepoda, Crustacea) in alpine lakes stocked with planktivorous fish1
Authors: Gliwicz Z. Maciej , Rowan Marc G.
Published: April 2010

Results of field sampling and experiments suggest a strategy enabling Cyclops abyssorum tatricus to be the sole crustacean survivor in alpine lakes stocked with brook char. Reproductive pattern and population spatial distribution, egg resistance to char digestive enzymes, as well as the absence of cladocerans which would otherwise compete with Cyclops nauplii for scarce food resources, all ensure the survival of this planktonic crustacean.
Visual factors in Daphnia feeding
Authors: Young Stephen , Taylor Victoria A. , Watts Elaine
Published: April 2010

The beating rate of Daphnia filter limbs is responsive to changes in light field distribution, but not to overall light intensity changes. To account for this we suggest that Daphnia uses a method of visual estimation to assess the ambient concentration of suspended food particles.
Asplanchna‐induced polymorphism in the rotifer Keratella slacki1
Authors: Gilbert John J. , Stemberger Richard S.
Published: April 2010

Asplanchna releases into its environment a filterable factor which induces eggs of Keratella slacki to develop into individuals with slightly larger (≈ 15%) bodies, considerably longer (≈ 30%) anterior spines, much longer (≈ 130%) right posterior spines, and sometimes short, left posterior spines not otherwise present. The Asplanchna‐induced morph is much less susceptible to Asplanchna predation than the noninduced morph, its long spines making it about two times less likely to be captured after being attacked and about five times less likely to be ingested after being captured. The pronounced asymmetry of the posterior spines may minimize the cost of spine production without sacrificing protection.
The conductivity‐density‐salinity‐chlorinity relationships for estuarine waters1
Authors: Millero Frank J.
Published: April 2010

The relative conductivity and density of estuarine waters formed by mixing “world” river water with standard seawater have been determined. The results are used to examine the conductivity‐density‐salinity‐chlorinity relationships of estuarine waters of known composition with seawater diluted with pure water (i.e. the new International Equation of State and Practical Salinity Scale). The maximum difference between the true salinity and the value derived from conductivity was 0.047 in dilute solutions; the maximum density difference between the measured and calculated values was 35 × 10−6 g·cm−3. These results are compared with measurements of waters from the St. Lawrence estuary.
234Th:238U disequilibria within the California Current1
Authors: Coale Kenneth H. , Bruland Kenneth W.
Published: April 2010

Profiles of dissolved and particulate 234Th were determined at several stations within the California Current. Modeling of the disequilibria between the 234Th and 238U within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging (τd varies from 6 to 50 days), the particle residence time (τp varies from 2 to 20 days), and the particulate 234Th flux exiting the surface layer. The model‐derived, first‐order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production. Particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present. Model‐derived particulate 234Th fluxes are in good agreement with direct measurements by sediment traps.
The distribution and abundance of phototrophic ultraplankton in the North Atlantic1,2
Authors: Murphy L. S. , Haugen E. M.
Published: April 2010

We compared the vertical distribution and abundances of procaryotic chroococcoid cyanobacteria (Synechococcus) and eucaryotic phototrophic ultraplankton at 50 stations in the North Atlantic. At 34 of these stations, cells were also separated by filter‐size fractionation, permitting comparison of the distribution of size classes with the distribution of pigment types. Both eucaryotic ultraplankton and cyanobacteria have subsurface numerical maxima. In vertically stable water, cyanobacterial abundance peaks at about the 1% light level and that of the eucaryotic ultraplankton at about the 0.5% light level. Cyanobacterial abundance decreases with northerly increasing latitude, and this decrease correlates with decreasing temperature. The eucaryotic assemblage is numerically dominated by the ultraplankton. The numbers of the ultraplankton generally range one order of magnitude less than the cyanobacteria, but they may equal or exceed cyanobacteria at depth and in northerly latitudes.
The geochemistry of manganese in the northeast Pacific Ocean off Washington1,2
Authors: Jones Carolyn J. , Murray James W.
Published: April 2010

Water collected along a transect normal to the coast of Washington was analyzed for dissolved (<0.4 µm) and total dissolvable manganese (TDM). The vertical profiles exhibit the same general features observed elsewhere in the Pacific, but a horizontal section of the transect shows that concentrations increase markedly toward the continental margin. A surface maximum, ranging from 0.57 nmol kg−1 in offshore waters to 5.24 over the continental slope, is probably due to fluvial inputs, especially from the Columbia River. Another possible source is the upwelling of manganese‐enriched bottom water over the shelf. Horizontal gradients are also observed in the oxygen minimum as manganese concentrations decrease from 4.75 nmol kg−1 near the continental slope to 0.71 in open ocean water. Porewater and solid phase data suggest that manganese is being actively remobilized under reducing conditions in the slope sediments and is diffusing into the overlying seawater at a rate sufficient to balance losses by vertical mixing and particulate scavenging. Two stations on opposite sides of the Juan de Fuca Ridge have deep concentration maxima that are almost certainly due to injections of hydrothermal vent fluid along the ridge.
The sea‐surface microlayer: Fate and residence times of atmospheric metals1
Authors: Hardy J. T. , Apts C. W. , Crecelius E. A. , Fellingham G. W.
Published: April 2010

Deposition of atmospheric particles provides a major source of metals to the world’s oceans. Before entering the water column these metals must pass through the sea‐surface microlayer (upper 50 µm)—a boundary with unique physical, chemical, and biological properties. A model, derived from laboratory microcosm studies, is used to predict the behavior of six metals under two conditions of biotic enrichment and wind mixing and three atmospheric deposition rates. Mean residence times of metals in the microlayer are 1.5–15 h. Maximum predicted enrichments (microlayer/water metals concentrations) are Pb > Cu > Zn > Ag > Ni > Mn. Predicted Pb enrichments with a 3.6 m s−1 wind are 130, 60, and 2 for urban, rural coastal, and oceanic environments. These predicted enrichments agree well with mean microlayer metal enrichments measured in the field.
The prediction of cladoceran grazing rate spectra1
Authors: McCauley Edward , Downing John A.
Published: April 2010

Reanalysis of published observations on the ingestion of artificial particles by cladocerans confirmed the statistical significance of particle size selection in situ. Three statistical approaches were tested to seek a framework for a general theory of cladoceran particle size selection: the algebraic continuous model, the algebraic discrete model, and the distributional model. The first two approaches can predict the shape of grazing rate: particle size spectra but make biased predictions. The last approach, in which equations are used to predict the parameters of the negative binomial distribution which mimics grazing rate spectra, makes fairly precise (r2 = 0.67) and unbiased predictions. Improvement of this kind of model is suggested as a step toward quantification of the role played by zooplankton in the dynamics of phytoplankton communities.
Effects of sampling technique on measurements of porewater constituents in salt marsh sediments1
Authors: Howes Brian L. , Dacey John W. H. , Wakeham Stuart G.
Published: April 2010

We examined the effect of three methods of porewater extraction on the measured concentrations of seven porewater constituents in vegetated salt marsh sediments. Porewater extraction by standard core sectioning followed by squeezing or centrifuging was compared with two less destructive methods of water collection. The core sectioning technique significantly increased the concentration of total dissolved organic carbon and dimethylsulfide presumably due to root damage by cutting. Sampling technique did not appear to influence interstitial salinity or concentrations of dissolved inorganic carbon, dissolved ammonium, soluble sulfides, and dissolved sulfate as long as proper precautions were taken to prevent the loss of reduced compounds.
A rapid and sensitive automated determination of phosphate in natural waters1
Authors: Fernández J. A. , Niell F. X. , Lucena J.
Published: April 2010

The malachite green micromethod for determination of inorganic phosphate has been automated for use in natural waters. It shows very good reproducibility. The molar absorptivity was 120,000 cm–1 mol (PO43−)−1 liter−1, six times more sensitive than the method of Murphy and Riley. The sometimes very important interferences from silicate and arsenate are easily removed.
The atmospheric correction and measurement of chlorophyll concentration using the coastal zone color scanner1
Authors: Guan Fumin , Peláez José , Stewart Robert H.
Published: April 2010

The Coastal Zone Color Scanner on the Nimbus‐7 satellite produces images of the sea in five colors (bands) of light, and these can be used to measure chlorophyll concentrations in the water, to visualize chlorophyll patterns, and to observe how these patterns change through time. However, 80–90% of the light observed by the instrument comes from the atmosphere, and removing this air light is difficult and usually requires considerable processing of the data. We describe here a new method to remove the influence of air light that is accurate, independent of external information, and requires far fewer computations than previous methods. This procedure should facilitate the use of CZCS data in biological oceanography, especially by investigators who may not have access to large computers and elaborate atmospheric correction procedures.

The technique has been tested by comparing ship and satellite estimates of chlorophyll; the comparison shows very good agreement. In addition, a comparison of sequential chlorophyll images shows that the technique produces stable chlorophyll estimates under changing atmospheric conditions.
Growth‐irradiance relationships in phytoplankton1
Authors: Falkowski Paul G. , Dubinsky Zvy , Wyman Kevin
Published: April 2010

The steady state growth rates of three species of marine phytoplankton, Thalassiosira weisflogii, Isochrysis galbana, and Prorocentrum micans, were followed in turbidostat culture. At each growth irradiance, photosynthesis and respiration were measured by following changes in oxygen. Together with measurements of optical absorption cross sections, cellular chlorophyll, carbon and nitrogen, and excretion rates as well as knowledge of the quantum flux, the quantum requirement for growth (1/ϕµ) and photosynthesis (1/ϕp) were calculated. Our results suggest that variations in growth rate caused by changes in irradiance may be related to changes in respiration rates relative to growth as well as changes in optical absorption cross sections for a given species. Interspecific differences in growth rate at a given irradiance are not related to changes in respiration however, but are primarily attributable to differences in optical absorption cross sections normalized to chlorophyll a and differences in chlorophyll: carbon ratios.
Nutrient internal cycling and the trophic regulation of Green Lake, Wisconsin1
Authors: Stauffer Robert E.
Published: April 2010

Algal nutrients (Si, N, P) and dissolved oxygen were studied in Green Lake, Wisconsin, in 1971– 1972, and in 1978–1980 following a reduction of about 35% in total external P loading in December 1976.

Despite oxic conditions, there is more P in the hypolimnion than would be expected from the dissolved oxygen and from classical Redfield stoichiometry. Because of a metalimnetic dissolved oxygen minimum in late summer, the calculation and interpretation of the hypolimnetic oxygen deficit is affected by turbulent transport of dissolved oxygen.

Vertical fluxes of P into the mixed layer are important in late spring and early summer, but, owing to metalimnetic P depletion, negligible between mid‐July and mid‐October. Vertical transport of Si into the mixed layer is negligible in summer and early fall compared with inputs from the land drainage basin.

Although P is high at spring turnover, epilimnetic concentrations of P are low and Secchi transparency is high by mid‐to‐late summer. These seasonal changes are caused by sedimentation of P and low seasonal inputs from the drainage basin. This P is recovered in the hypolimnion and recirculated throughout the lake at fall overturn. It causes silica limitation of the diatom bloom each succeeding spring.

The total P content of Green Lake and its seasonal partition among the layers were remarkably stable between 1971 and spring 1980, despite the reduction in external loading in 1976. The hypolimnetic oxygen deficit also showed no significant change between the first and eighth decades of this century.
A box corer for studying metabolism of epipelic microorganisms in sediment under in situ conditions1
Authors: Carlton Richard G. , Wetzel Robert G.
Published: April 2010

The device described here permits sampling of a combined sediment and overlying water volume of about 29 liters (cross‐sectional area >700 cm2) with minimal disturbance of sediment structure. Vertical microprofiles of oxygen concentration measured in littoral sediments before (in situ) and after sampling with the box corer showed good agreement. These data are compared with oxygen microprofiles measured in pelagic sediments sampled with the box corer and kept in a laboratory under in situ conditions. Oxygen production by epipelic algae exposed to very low quantum flux resulted in marked diurnal phasing of oxygen above and within the sediments.
Nitrogenous nutrient uptake, primary production, and species composition of phytoplankton in the Carmans River estuary, Long Island, New York1
Authors: Carpenter Edward J. , Dunham Susan
Published: April 2010

Uptake of NH4+, NO3−, and urea was measured at four stations in a small temperate‐zone estuary over a 10‐month period. Considering all four stations, NO3− accounted for 45% of all N taken up, followed by NH4+ (43%) and urea (12%). Nitrogen uptake was highly temperature‐dependent (r = 0.82), and an exponential relationship was apparent. Recycling was very important as a source of nitrogen, and mean NH4+ pool turnover times were rapid, ranging from 4.3 to 6.8 h in the lower estuary in summer. PN turnover times in the lower estuary were also rapid, averaging 28.8 h in summer and being as short as 3.1 h in July and August.

An analysis of N uptake using the relative preference index (RPI) indicated that NH4+ was the preferred nutrient. However, high NO3− concentrations appeared to override the repressive effect of NH4+ concentrations on nitrate reductase, and NO3− uptake was significant even at relatively high NH4+ concentrations. Urea uptake did not appear to be affected by NH4+ concentration.
Factors controlling phosphorus limitation in stream sediments1
Authors: Klotz R. L.
Published: April 2010

Factors influencing the phosphorus limitation of benthic microorganisms were determined for four streams (two agricultural and two forested) in central New York State over an annual cycle. Phosphorus limitation was measured biweekly as specific alkaline phosphatase activity (APA) of sediment samples. Analysis of variance showed the forested streams (sites 2 and 4) to have significantly different sediment APA from the agricultural streams (sites 1 and 3), the higher APA for the forested sites indicating greater phosphorus limitation. Stream total reactive phosphorus concentrations showed no relationship with watershed type, with mean annual values of 10.5 and 6.0 µg liter−1 for agricultural sites 1 and 3 and 4.1 and 9.6 for forested sites 2 and 4. With all sites grouped together, sediment APA had a low correlation with stream water phosphate (r = 0.184, n = 73). Phosphorus sorption isotherms showed sediments from agricultural streams to have higher phosphate sorption indices than forested sites and to sorb rapidly large amounts of phosphorus. This resulted in higher available phosphorus content for the agricultural sediments and lower sediment APA.
In situ twilight grazing rhythm during diel vertical migrations of a scattering layer of Calanus finmarchicus1
Authors: Simard Yvan , Lacroix Guy , Legendre Louis
Published: April 2010

A scattering layer of Calanus finmarchicus was sampled every 90 min during 48 h in the lower St. Lawrence estuary. Grazing activity (phytoplankton pigments in the gut) and the percentage of recently and nonrecently fed copepods (from observation of food in the gut) were monitored in two strata (0–30 m and 30–100 m). Phytoplankton was restricted to the upper stratum. A bimodal twilight grazing rhythm was observed: the first feeding period, in the upper stratum, begins after sunset; it is followed by the “midnight sinking” in the deeper stratum (2–3 h), during which the gut content is evacuated; after this, the animals return to the upper stratum for a second meal, before the dawn descent. In both migrations, there was a dynamic interchange of individuals between the two strata, which masked the fact that all the copepods migrated to the upper stratum and that a dawn rise actually happened. The feeding time in the warmer surface water was very short. Feeding ceased rapidly even if phytoplankton concentration was low. A large increase in the number of migrants did not change the feeding patterns. Results support the hypothesis that the behavior of C. finmarchicus during the central phase of vertical migrations in late summer is closely linked to an in situ grazing rhythm.
Production of fishes in a subtropical blackwater ecosystem: The Okefenokee Swamp1
Authors: Freeman Byron J. , Freeman Mary C.
Published: April 2010

Secondary production by the three dominant fishes inhabiting an acidic macrophyte marsh in the Okefenokee Swamp was 171 kg wet wt ha−1 yr−1. Production was estimated by the instantaneous growth rate and size‐frequency methods. The size‐frequency method gave higher, presumably more accurate, estimates because it is not affected by nonsynchronous cohort development; also, densities of small, undersampled, individuals could be back‐calculated from densities in larger size classes. This estimated production exceeds many values reported for stream and river habitats. It is suggested that such blackwater dystrophic habitats are more productive than previously thought.
Relationships between primary production and ii radiance in coral reef algal communities1
Authors: Carpenter Robert C.
Published: April 2010

Shallow water algal turf communities are the major primary producers on coral reefs. High rates of primary production are maintained despite extremely high light intensities and exposure to ultraviolet wavelengths. The relationships between the light intensity and primary production in these assemblages are typical of algae adapted to a high light environment [low α (initial slope), high Ik (saturating light intensity), and high Ic (compensation point light intensity)]. Seasonal variations in algal standing crop due to herbivory and daylength result in some characteristic photoadaptive changes in a, Ik, and Ic, and changes in Pnetmax rate s (maximum net photosynthetic rate achieved at light saturation) on both a chlorophyll a and an areal basis. Exposure to UV wavelengths results in significantly higher respiration rates but no changes in α, Pnetmax, or Ik, when compared with these parameters for the same algal communities incubated at the same light intensities without UV wavelengths. The apparent lack of photoinhibition in these algae allows calculation of the daily integrated production from the P vs. I parameters. This integrated production is highest in July (3.1 ± 0.2 g C m−2 d−1) and is reduced by 30% from this maximum in December (2.1 ± 0.1 g C m−2 d−1).
Estimating release rates of phosphorus from zooplankton: Model and experimental verification1
Authors: Olsen Yngvar , Østgaard Kjetill
Published: April 2010

The flux of phosphorus in a zooplankton‐phytoplankton system is described by a simple compartment model, with differential equations for grazing, growth an d reproduction of animals, and release and recycling of P. The mean release rates from zooplankton for a given period are derived for cases restricted to animals feeding on algae at densities above the incipient limiting food concentration. The model is used to analyze short term incubaton experiments with Daphnia pulex feeding on Scenedesmus sp. and Daphnia longispina feeding on Rhodomonas lacustris in dim light. When food organisms were saturated with P, total rele ase rates were in the range 1.1–1.5 µg P (mg dry wt)−1 h−1 in accordance with a maximalexcretion rate of 0.8 µg P (mg dry wt)−1 h−1 predicted by the model of Peters. Phosphorus‐starved phytoplankton, containing less P, gave much lower release rates, about 0.05 µg P (mg dry wt)−1 h−1, only 10% of the excretion rate predicted by the model of Peters.
Cyclomorphosis of Daphnia pulex spined morphs1
Authors: Havel John E.
Published: April 2010

Chaoborus‐induced spined phenotypes of Daphnia pulex were present at frequencies > 80% in two Wisconsin ponds during summer 1983 but were rare earlier in the year, even though predaceous instars of Chaoborus americanus were common. Laboratory induction experiments with one clone revealed that the proportion of Daphnia juveniles which bore the Chaoborus‐induced spines (% SM) was a positive function of both temperature and Chaoborus density, and C. americanus from different times of year could induce high percentages of spined morphs. For both ponds, clonal descendants of Daphnia isolated during the spring were less sensitive to a standard Chaoborus treatment than descendants of summer Daphnia. The results suggest that the changing frequency of spined rnorphs in the field was due in part to a shift of Daphnia populations, one unresponsive and another responsive to the Chaoborus factor. Phenotypic plasticity to environmental factors may also influence the distribution of morphs in the field.
Modes of algal capture by the freshwater copepod Diaptomus sicilis and their relation to food‐size selection1,2
Authors: Vanderploeg Henry A. , Paffenhöfer Gustav‐Adolf
Published: April 2010

High‐speed motion pictures (500 frames s−1) of tethered Diaptomus sicilis feeding in suspensions of Chlamydomonas spp. of three different sizes at three different concentrations (0.3, 1.0, and 3.0 mm3 liter−1), showed two modes of feeding: a passive mode in which algae flowed into the space between the left and right second maxillae and an active mode in which the second maxillae or second maxillae plus maxilliped made large amplitude flaps to bring in the cell. Cells ≤4 µm in diameter were always captured passively, and cells ≥6 µm were captured both actively and passively. Active captures were 18% of total captures for the medium‐sized (6 µm) algae and 36% for the large (12 µm) algae. During passive captures, algae usually flowed through the space between the left and right second maxillae rather than being caught on the setules; thus, the leaky‐sieve model of particle retention does not apply for passive captures by D. sicilis. Except for brief interruptions to actively capture a large alga nearby, the second maxillae of D. sicilis oscillated continuously at low amplitude at all times during feeding, in marked contrast to the marine copepods Eucalanus and Paracalanus that vibrated their second maxillae to enhance capture in monocultures of small algae but not large algae. These observations explained both the shape of the curve of selectivity vs. particle size for D. sicilis and its relative invariance. Analyses of feeding mechanisms and the water currents around Diaptomus showed that, in contrast to Eucalanus and Paracalanus, Diaptomus is specialized for capturing small particles, which may be a more important food in freshwater than in marine environments.
Mass mortality of fish and invertebrates associated with a bloom of Hemidiscus hardmannianus (Bacillariophyceae) in Parangipettai (southern India)
Authors: Subramanian A. , Purushothaman A.
Published: April 2010

A bloom of Hemidiscus hardmannianus (Bacillariophyceae) in the estuarine and neritic waters of Parangipettai (southern India) was associated with heavy mortality of fishes and invertebrates.
Phototrophic sulfur bacteria in two Spanish lakes: Vertical distribution and limiting factors1
Authors: Guerrero R. , Montesinos E. , Pedrós‐Alió C. , Esteve I. , Mas J. , van Gemerden H. , Hofman P. A. G. , Bakker J. F.
Published: April 2010

The anaerobic zones of Lakes Cisó and Vilar (Banyoles karstic area, NE Spain) had mass developments of purple sulfur bacteria during summer 1982. In Lake Vilar, Chromatium spp. was dominant (up to 92% of the microbial biovolume). In Lake Cisó, the predominant microorganisms were Chromatium spp. (up to 71%) and another purple sulfur bacterium forming aggregates (20%).

The bacterial layer could be divided according to the physiological state of the cells into a top part of maximal specific activity, a peak of maximal abundance, and a bottom part of inactive cells. The bacteria in the peak were predominantly limited by light; sulfide, phosphate, and acetate were not limiting in the middle of the day. The light limitation started at the depth having the maximal concentration of cells; the top of the layer appeared to be sulfide‐limited. Specific contents of photopigments, elemental sulfur, and reserve polymers decreased from the top to the bottom of the bacterial layer. These phenomena point to the crucial role of light in the development of layers of phototrophic bacteria in stratified lakes.
The role of eopepod fecal pellets in the deposition of diatoms in Lake Tanganyika1
Authors: Haberyan Kurt A.
Published: April 2010

Fecal pellets from a 16,000‐year sediment core from southern Lake Tanganyika account for over 40% of all diatom deposition and about 30% of total bulk sedimentation. Comparison of diatoms inside pellets with those in the surrounding sediment indicates that small, blunt species like Fragilaria brevistriata and Gomphonema clevei are preferentially ingested by grazing copepods. Long, fragile species like Nitzschia spiculum are strongly avoided. Filamentous Melosira spp. seem to be an important food of copepods.

This grazing selectivity, coupled with the enhanced sinking rates and preservation of fecal pellets, could distort the fossil diatom record. Relative diatom abundances in pelletized, nonpelletized, and pooled stratigraphies indicate that pellets actually cause shifts of <4% of total diatom abundance in Lake Tanganyika. Even with selective grazing, F. brevistriata and G. clevei are rare in sediments (<2% of all diatoms).
Carbon: pheopigment ratios of zooplankton fecal pellets as an index of herbivorous feeding1
Authors: Downs Jan Newton , Lorenzen Carl J.
Published: April 2010

A simple model using carbon to pheopigment ratios (C:Ph) to estimate the fraction of carbon derived from recently ingested phytoplankton was used on fecal pellets from laboratory‐fed Calanus pacificus and field zooplankton and on sediment trap material from Dabob Bay, Washington. During the grazing season of herbivorous macrozooplankton, fecal pellets from laboratory‐fed C. pacificus have C : Ph ratios of 7–13, yielding calculated copepod assimilation efficiencies (AE%) of 77%. Diapausal copepods produce pellets with higher C : Ph ratios (24–33) and yield lower calculated AE% (46%), suggesting reduced digestive enzyme activities at this time. On the basis of measurements of field phytoplankton C : Chl and estimates of field copepod assimilation efficiencies, the C : Ph ratio of fecal pellets from exclusively herbivorous field copepods ranges from 11 to 18. Higher values (25–29) found from naturally feeding copepods indicate a significant amount of omnivory, carnivory, or both. The amount of the total organic carbon flux out of the euphotic zone in Dabob Bay resulting from herbivorous feeding was quantified. Its magnitude was directly related to the primary productivity and the seasonal grazing pattern of C. pacificus, averaging 36% when grazers are actively feeding and 9% when many are in diapause. On an annual basis, 31% of the carbon flux out of the surface layer in Dabob Bay is derived from ingested or sunken phytoplankton cells.
Inhibition of Daphnia by Oscillatoria in Lake Washington1
Authors: Infante Aida , Abella Sally E. B.
Published: April 2010

The hypothesis of Edmondson and Litt concerning the inhibition of Daphnia by Oscillatoria in Lake Washington was tested in experiments with cultures. Growth and reproduction of Daphnia pulicaria and Daphnia thorata were reduced by increasing concentrations of Oscillatoria agardhii from 0 to 400 filaments ml−1 in the presence of adequate amounts of Cryptomonas as food. Cryptomonas reproduction also was inhibited by Oscillatoria, by an undetermined mechanism. The results are consistent with the idea that the scarcity of Daphnia in Lake Washington during the 10‐year period before 1976 was related to high concentrations of O. agardhii.
Collection of large and small food particles by Bosmina1
Authors: Bleiwas Agnes H. , Stokes Pamela M.
Published: April 2010

The rate of collection by Bosmina of large and small food particles was measured with 14C‐labeled algae and checked by visual observation. Bosmina collected and ingested a large alga, Cosmarium, about six times faster than a small one, Chlorella. This is consistent with the observation of DeMott and Kerfoot that Bosmina has two modes of feeding: small‐particle filtering and large‐particle grasping.
Micromethod for lipids in aquatic invertebrates1
Authors: Gardner Wayne S. , Frez William A. , Cichocki Elizabeth A. , Parrish Christopher C.
Published: April 2010

Microtechniques with disposable,

calibrated, capillary pipets were developed to measure amounts and classes of lipids in individual Lake Michigan benthic invertebrates. After lipids from an animal were partitioned into 100 µl of extraction solvent and purified, measured portions were weighed with an electrobalance. Lipids in some samples were also characterized by thin layer chromatography with flame ionization detection (TLC‐FID). The extraction method was calibrated gravimetrically with cod liver oil and evaluated with a dry, ground fish sample. Lipid content was proportional (r = 0.99) to fish tissue dry weight over the range of 0.3–13 mg. TLC‐FID measurements correlated well (r = 0.98) with gravimetric analysis for portions of extracts of individual amphipods (Pontoporeia hoyi) and oligochaetes (Stylodrilus heringianus). TLC‐FID analysis indicated that <5% of the measured gravimetric weights was due to the inclusion of nonlipid material in the extracts.