bluuebunny/crossref_metadata_2025 huggingface dataset:
Settlement of a marine tube worm as a function of current velocity: Interacting effects of hydrodynamics and behavior1
Authors: Pawlik Joseph R. , Butman Cheryl Ann
Published: May 2010

Settlement experiments were conducted with larvae of Phragmatopoma lapidosa californica (a reef‐building sabellariid polychaete) in turbulent flume flows (near‐surface velocities of 5, 10, 15, 20, 25, 30, and 35 cm s−1) over a hydrodynamically smooth bed. Boundary shear velocities spanned the critical shear velocity for initiation of particle motion and for suspended‐load transport of passive larval mimics. Larvae were allowed one pass over a sediment array with two treatments: tube sand, a natural inducer of metamorphosis, and noninductive sand. Delivery of larvae to the array was the result of interactions between the flow regime and larval behavior. At intermediate flows (15, 20, and 25 cm s−1), where numbers of metamorphosed juveniles and total animals (larvae + juveniles) in the array were maximal, larvae tumbled along the flume bottom, as did the passive larval mimics. At slower flows, larvae actively left the bottom and swam into the water, passing over the array. At the fastest flows, hydrodynamics alone may have reduced settlement because larvae, like the mimics, were eroded from the bed and carried as suspended load over the array or because enhanced turbulent mixing distributed larvae more evenly in the water, thus reducing their concentration close to the bed. Once delivered to the substratum, behavioral responses to chemical cues were ultimately responsible for metamorphosis; in all flows, >96% of metamorphosed juveniles were in the tube sand, whereas most unmetamorphosed larvae were in noninductive sand.
Field evaluation of a valved sediment trap
Authors: Peterson M. L. , Hernes P. J. , Thoreson D. S. , Ifedges J. I. , Lee C. , Wakeham S. G.
Published: May 2010

An internally valved sediment trap designed to isolate sinking particulate matter from free‐swimming animals, temporally subsample particle flux, and minimize washout of solid and dissolved material is described. The trap is controlled by a single microprocessor capable of supporting multiple traps as well as other instrumentation on a single array. Test deployments of valved and nonvalved control traps, along with three other conventional cylindrical trap designs, were undertaken during a series of six 1‐week experiments in Dabob Bay, Washington. Treated traps containing biocide‐spiked (HgCl2 or Formalin) bottom brine layers (80‰ NaCl brine), brine layers alone, and only seawater (untreated) were deployed on multitrap arrays.

Fluxes of material >850 µm in size (almost exclusively large zooplankton) caught in biocide‐ and brine‐treated valved traps were reduced by an average of 88% relative to non‐valved control traps; all other open traps collected >850‐µm fluxes equivalent to controls. The type of treatment had a significant effect on the >850‐µm mass flux, with Formalin‐treated traps >HgCl2 ∼ NaCl brine ≫ untreated. Fluxes of <850‐µm material were reduced in treated valved traps and averaged 39% less than fluxes caught in VERTEX‐style particle interceptor traps. Organic C: total N ratios were higher in material caught in valved traps than in all other types, primarily due to reduced nitrogen fluxes. Reduced fluxes of the primarily autochthonous biochemicals (pigments, amino acids, and lipids) measured by valved relative to control traps indicate significant exclusion (>80%) of zooplankton <850 µm from valved traps.
Vertical distributions and susceptibilities to vertebrate predation of the marine copepods Metridia lucens and Calanus pacificus
Authors: Bollens Stephen M. , Osgood Kenric , Frost Bruce W. , Watts Sidney D.
Published: May 2010

We present results of a 2‐yr field study of the vertical distributions and diel vertical migrations (DVM) of Metridia lucens Boeck in Dabob Bay, Washington, and compare them to previous findings for co‐occurring Calanus pacificus Brodsky. M. lucens was found deeper than C. paciftcus, both day and night, and always exhibited DVM behavior, whereas C. pacificus exhibited more variable migration behavior, occasionally occurring in the surface layer in the daytime. These results led us to test the hypothesis that M. lucens exhibits greater avoidance of the well‐lit surface layer than C. pacificus because the former is more susceptible to predation by planktivorous fish. A 2‐yr field study of the diet and ambient prey fields of planktivorous fish in Dabob Bay indicated that 31 of 39 species/size classes of fish exhibited greater electivity for C. pacificus than M. lucens. A series of laboratory experiments corroborated these findings by showing juvenile Pacific herring to exhibit a highly statistically significant preference for C. pacificus over M. lucens. On the basis of both studies we reject the hypothesis that M. lucens is more susceptible to visual predation than C. pacificus and we conclude that the deeper distribution and greater avoidance of surface waters of M. lucens must be due to some other factor.
Lack of endogenous rhythmicity in Daphnia diel vertical migration
Authors: Loose Carsten J.
Published: May 2010

A population of Daphnia Galeata × hyalina was induced to perform diel vertical migration (DVM) by the addition of fish‐kairomones to a large plankton tower. Vertical profiles of zooplankton abundance were measured every 12 h. When the tower was covered to shield the water column from the light, DVM ceased, and vertical distributions were not statistically different from the night profiles that had been observed before the tank was covered. This result suggests that endogenous rhythms do not trigger DVM, but that a change in light intensity must occur.
The assimilation ofelements ingested by marine planktonic bivalve larvae
Authors: Reinfelder John R. , Fisher Nicholas S.
Published: May 2010

The assimilation efficiencies of nine elements were measured in planktonic bivalve mollusc larvae (oysters, Crassostrea virginica, and hard clams, Mercenaria mercenaria) fed uniformly radiolabeled phytoplankton cells (Isochrysis galbana) in order to test whether the “liquid” digestion strategy observed in marine copepods operates in other planktonic herbivores with gut morphologies different from that of crustacean zooplankton. Of the elements studied (Ag, Am, C, Cd, Co, P, S, Se, and Zn), americium was assimilated the least by both the larval oysters (7.9%) and clams (2.6%), while selenium was assimilated with the highest efficiency by the larvae (oysters, 97%; clams, 100%). Assimilation efficiencies were directly related to the fraction of each element present in the cytoplasm of the ingested algae. Like copepods, bivalve larvae have short gut passage times and assimilate only the easily mobilized, cytoplasmic fraction of ingested phytoplankton cells. The cytoplasmic fraction of some elements (Se, Zn, and Cd) and of protein in I. galbana increased inversely with algal growth rate. Larvae feeding on senescent cells would therefore be expected to assimilate proportionately more of these elements and protein than when feeding on rapidly dividing cells.
Sustained fecundity when phytoplankton resources are in short supply: Omnivory by Calanus finmarchicus in the Gulf of St. Lawrence
Authors: Ohman Mark D. , Runge Jefrey A.
Published: May 2010

Despite low ambient concentrations of phytoplankton, Calanus finmarchicus sustained relatively high rates of egg production (11–45 eggs female−1 d−1) in the open waters of the Gulf of St. Lawrence in late June–early July. These rates were comparable to egg production rates observed in high‐chlorophyll waters of the lower St. Lawrence estuary. Contrary to classical, linear food‐chain models, variations in egg production of C. finmarchicus were therefore not predictable from variations in standing stocks of autotrophic cells. Egg production rates were independent of the concentration of chlorophyll in situ, the abundance of autotrophic microplankton cells, in situ gut fluorescence, and the rate of ingestion of autotrophic particles. Heterotrophic microplankton—including ciliates and dinoflagellates presumed to be heterotrophic—constituted a disproportionate fraction of the ration of C. finmarchicus in the open Gulf of St. Lawrence, despite their relatively low cell densities. Evidence suggests that heterotrophic microplankton frequently provided a prey resource sufficient for net lipid synthesis as well as for egg production.
Microorganisms as food resources at deep‐sea hydrothermal vents
Authors: Van Dover Cindy Lee , Fry Brian
Published: May 2010

We used stable isotopes of carbon and nitrogen to examine the diversity of microbial populations consumed as foods at deep‐sea hydrothermal vents. Invertebrate consumers at Gorda and Juan de Fuca Ridge vent sites had variable carbon isotope compositions, implying the use of more than one microbial food resource. δ13C values for consumer invertebrates at Gorda ranged between −13.2‰ (polynoid polychaete) and −43.7‰ (limpet); within Gorda microhabitats, δ13C compositions of invertebrate species were also not uniform, differing by as much as 8–19‰. At the Juan de Fuca site, δ13C values showed a wide range (−14.6 to − 33.9‰) for nine invertebrate species collected from a dense community colonizing the surface of a sulfide flange. Carbon isotope differences between tubeworm symbioses and consumer invertebrates within microhabitats suggest that these symbioses may play a minor role as nutritional resources in vent food webs. Nitrogen isotope compositions of consumer species from vents were consistently depleted in 15N relative to animals collected away from vents. δ15N compositions of some vent individuals are among the lowest measured in any organism (<−10‰) and likely reflect relatively abundant supplies of inorganic nitrogen compounds used by microbial populations at vents.
Organic content and bacterial metabolism in amorphous aggregations of the northern Adriatic Sea
Authors: Müller‐MNiklas Gerald , Stefan Schuster , Kaltenböok Elisabeth , Herndl Gerhard J.
Published: May 2010

The “successional stage” of marine aggregates from formation to final decay was investigated in the northern Adriatic Sea in summer 1991. In marine snow, bacterial biomass and production rates increased exponentially and in gellike aggregates (GEA — considered as late‐stage marine snow) reached values 2–3 orders of magnitude higher than in ambient water. Specific growth rates of marine snow‐associated bacteria (0.31–1.76 d−1) were similar to ambient water bacteria; however, they were significantly lower in GEA (0.08–0.31 d−1). Concentrations of dissolved free amino acids (DFAA) in aggregates were up to 80 µM. Despite these high concentrations of DFAA, the organic C: N ratio increased significantly over the 3 months of the investigation period, ranging from 6.7 to 17.3 and indicating that refractory substances accumulate in aging aggregates. This notion is also supported by the ratio of α‐glucosidase activity to β‐glucosidase activity, which declined from ambient water (α‐glue : β‐glue = 1.7) to marine snow and GEA (α‐glue : β‐glue = 0.51). Extracellular enzymatic activity calculated on a per cell basis was similar for ambient water and marine snow‐attached bacteria, but significantly lower rates were obtained for GEA. These data indicate that GEA become an increasingly poor habitat for bacterial growth. The relation between hydrolysis rate and substrate uptake does not support the hypothesis of a loose coupling between hydrolysis and uptake in marine snow‐attached bacteria.
Export of carbon, nitrogen, and major ions from three tropical montane watersheds
Authors: McDowell William H. , Asbury Clyde E.
Published: May 2010

Annual exports of suspended sediment, dissolved and particulate C and N, dissolved N and P, and major cations and anions were measured in three montane tropical rain forest watersheds in Puerto Rico during 1983–1986. Organic C was primarily exported in the form of DOC, and DOC export (33–94 kg ha−1 yr−1) was similar to values in larger tropical watersheds with similar runoff. Particulate and dissolved organic N accounted for 60–70% of the 4–9 kg ha−1 yr−1 of total N exported. Export of base cations and rates of weathering varied with bedrock geology in the three watersheds. Concentrations of suspended sediment, particulate C and N, and DOC increased as a function of discharge in all three streams. NH4, NO3−, SO42−, and K+ concentrations showed little or no response to variations in discharge; Na+, Ca2+, Mg2, Cl −, HCO3−, and SiO2 all decreased at high flows. After removing the effects of discharge, residual NO3− concentrations in each stream were inversely related to estimated rates of leaf fall. On a watershed basis, export and accumulation of N in biomass were greater than precipitation inputs, suggesting that unmeasured inputs (8–16 kg ha−1 yr−1) were large.
Acetate concentrations and oxidation in salt‐marsh sediments
Authors: Hines Mark E.
Published: May 2010

Acetate concentrations and rates of acetate oxidation and sulfate reduction were measured in Spartina alterniflora sediments in New Hampshire and Massachusetts. Pore water extracted from cores by squeezing or centrifugation contained >0.1 mM acetate and in some instances >1.0 mM. Pore water sampled nondestructively contained much less acetate, often <0.01 mM. Acetate was associated with roots, and concentrations varied with changes in plant physiology. Acetate turnover was very low whether whole‐core or slurry incubations were used. Radiotracers injected directly into soils yielded rates of sulfate reduction and acetate oxidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a substantial percentage of sulfate reduction. These results differ markedly from data for unvegetated coastal sediments where acetate levels are low, oxidation rate constants are high, and acetate oxidation rates greatly exceed rates of sulfate reduction. The discrepancy between rates of acetate oxidation and sulfate reduction in these marsh soils may be due to the use of substrates other than acetate by sulfate reducers or to artifacts associated with measurements of organic use by rhizosphere bacteria.
Age, viability, and vertical distribution of zooplankton resting eggs from an anoxic basin: Evidence of an egg bank
Authors: Marcus Nancy H. , Lutz Robert , Burnett William , Cable Peter
Published: May 2010

Seabed cores to a sediment depth of 24 cm were obtained by divers from an anoxic basin in the Pettaquamscutt estuary. The cores were processed to determine the age, viability, and vertical distribution of zooplankton resting eggs in the bottom sediments. Zooplankton eggs were found throughout the upper 24 cm. Copepod nauplii emerged from sediments as deep as 22 cm that were incubated in the laboratory. Based on 210Pb analyses of the sediments, we calculated that the viable eggs ranged in age from <1 yr in the surface layers of the seabed to >40 yr in the deepest portions. These data provide conclusive evidence for the existence of an egg bank.
Primary production of prochlorophytes, cyanobacteria, and eucaryotic ultraphytoplankton: Measurements from flow cytometric sorting
Authors: Li William K. W.
Published: May 2010

A partitioning of ultraphytoplankton primary production among prochlorophytes, cyanobacteria, and eucaryotic algae was made by shipboard flow cytometric sorting of 10C‐labeled cells. Aggregate primary production was derived from the sum, over all three ultraplankton groups, of the product of cell abundance and cell‐specific rate of 14C uptake which ranged from 0.03 to 4 fg C cell−1 h−1 for prochlorophytes and 0.2 to 10 fg C cell−1 h−1 for cyanobacteria. Results indicated that the dominant primary producer was not necessarily the numerical dominant nor necessarily the group with the highest cell‐specific rate of 14C uptake. Generally, eucaryotic ultraphytoplankton are dominant because of their high cell‐specific rate of 14C uptake and in spite of their relatively low abundance. Less often, it seems, procaryotic picoplankton may dominate in spite of their low cell‐specific rate of 14C uptake because of their high abundance.
The fate of the missing 15N differs among marine systems
Authors: Bronk Deborah A. , Glibert Patricia M.
Published: May 2010

In nitrogen uptake studies with 15N tracer techniques, a common observation is that the 15N label added at the start of the experiment is not fully recovered at the end of the experiment in the particulate and dissolved N pools measured. We have made direct measurements of the 15N content of the traditionally measured NH4+ and particulate N pools, as well as the dissolved organic N (DON) and bacterial pools in studies conducted in Chesapeake Bay, the Caribbean Sea, and the Choptank River (a subestuary of Chesapeake Bay). We found that the fate of the “missing 15N” differs from eutrophic to oligotrophic waters and is dependent on the length of incubation, the dissolved inorganic N substrate used, and the length of time the sample was contained before the 15N uptake experiment. In general, it appears that it is more important to include the 15N that enters the DON and bacterial pools to achieve a 15N mass balance in more oligotrophic ecosystems and when longer (>1 h) incubations are used.
A comparative study of the ecosystem dynamics of four fiords
Authors: Ross Alex H. , Gurney William S. C. , Heath Michael R.
Published: May 2010

In this paper we develop our previously published strategic simulation model of a sea‐loch into a quantitatively testable form. This formulation includes the effects of phytoplankton self‐shading, aggregation by zooplankton to areas of high phytoplankton density, and a representation of temperature‐dependent energy allocation in zooplankton. We confront the model with datasets from four contrasting Scottish and Irish sea‐lochs. After further extension to incorporate variations in the vertical distribution of phytoplankton, driven by vertical mixing and grazing pressure, the model provides a quantitatively acceptable fit to all four datasets. We illustrate the “top‐down” nature of the control operating in these systems by formulating a three‐state variable model, describing only the biotic components of the system. This simplified model produces the same quality of fit to the appropriate data as its progenitor.
Stable isotopes of oxygen and hydrogen in the Truckee River–Pyramid Lake surface‐water column. 1. Data analysis and extraction of paleoclimatic information
Authors: Benson L. V.
Published: May 2010

The δ18O content of streamflow discharge entering Pyramid Lake is a simple mixture of isotopically enriched Lake Tahoe discharge and isotopically depleted snowmelt. The δ18O value of Pyramid Lake water varies continuously, as isotopically depleted water evaporates from the epilimnion and isotopically depleted water enters the lake as streamflow discharge and on‐lake precipitation. In a normal water year, the δ18O of Pyramid Lake surface water varies seasonally because the components of the hydrologic balance in the Pyramid Lake system are seasonally shifted. The problem of isotopic and thermal heterogeneity can be minimized by analyzing carbonates that integrate the annual variance in δ18O, form in an environment in which temperature is relatively invariant, and are not subject to recrystallization after deposition.
Stable isotopes of oxygen and hydrogen in the Truckee River–Pyramid Lake surface‐water system. 2. A predictive model of δ18O and 182H in Pyramid Lake
Authors: Hostetler S. W. , Benson L. V.
Published: May 2010

A physically based model of variations in δ18O and δ2H in Pyramid Lake is presented. For inputs, the model uses measurements of liquid water inflows and outflows and their associated isotopic compositions and a set of meteorological data (radiative fluxes, air temperature, relative humidity, and windspeed). The model simulates change of lake volume, thermal and isotopic stratification, evaporation, and the isotopic composition of evaporation. A validation of the model for 1987–1989 and 1991 indicates that it can reproduce measured intra‐ and interannual variations of δ18O and δ2H. Three applications of the model demonstrate its ability to simulate longer term responses of δ18O to change in the hydrologic balance and hydrologic characteristics (opening and closing) of the lake.
Cladoceran body size and vulnerability to copepod predation
Authors: Gliwicz Z. Maciej , Umana Gerardo
Published: May 2010

We examined species‐related and age‐ related mortality caused by a predaceous copepod (Acanthocyclops robustus) in five closely related cladocerans representing a wide spectrum of body size. Animals of all five species from clonal cultures were exposed for 1, 2, or 4 d in medium from a copepod‐infested enclosure that either did or did not contain natural densities of Acanthocyclops adults and copepodites (40–50 copepods liter−1). In each of the five species, the 1‐d‐old neonates were most, and adults least, vulnerable to the copepods. Small‐bodied Daphnia cucullata and Ceriodaphnia reticulata remained vulnerable until maturation, but the susceptibility of large Daphnia magna drastically decreased in 3‐ and 5‐d‐old animals, and 7‐d‐old adults were immune to copepod predation.
Limitation of water hyacinth by nitrogen in subtropical lakes of the Paraná floodplain (Argentina)
Authors: Carignan Richard , Neiff Juan José , Planas Dolors
Published: May 2010

Low (0.1–0.7 µmol liter−1) dissolved inorganic nitrogen concentrations are common in the floodplain lakes of the Paraná River, where the water hyacinth (Eichhornia crassipes) is the major primary producer. We tested the hypothesis that N supply could limit production of E. crassipes during the growth season by adding NH4+ or PO43− during 1 month to large in situ enclosures. Those enclosures amended with N produced twice as much biomass as the controls and P‐treated enclosures. The low and limiting N content (1.3% AFDW) of the control and P‐treated plants provide a first diagnostic value for N deficiency in the field for E. crassipes. N limitation in these lakes may be attributable to high P supply from Andean rivers, high losses of macrophyte N during floods, and the unstable nature of floodplain lakes.
A sound scattering layer in a freshwater reservoir
Authors: Jones Ian S. F. , Xie Jishi
Published: May 2010

A near‐surface sound scattering layer has been observed in a freshwater reservoir with a 200 kHz echosounder over the last 5 yr. Net sampling revealed that Chaoborus is the cause of the strong 200‐kHz sound scattering in this layer. With 50‐kHz sound, this layer cannot be distinguished from the background. Recent acoustic measurements have determined the target strength of a single Chaoborus larva and the frequency response of backscattering from Chaoborus in the reservoir so that an acoustic estimation of the Chaoborus population can be made. This population estimate is compared with simultaneous net‐sampling estimates.
Regional pattern of riverine dissolved organic carbon in the Amazon drainage basin of Bolivia
Authors: Guyot Jean Loup , Wasson Jean Gabriel
Published: May 2010

Dissolved organic carbon (DOC) was analyzed at 11 hydrometric stations and 41 Andean and lowland sites in the upper Rio Madeira drainage basin where anthropogenic alteration is low. The two regions, Andes and Llanos, behave very differently. Mean DOC is 2.2 mg liter−1 (range, 1.2–4.2 mg liter−1) in the Andes and 5.7 mg liter−1(range, 4.8–7.4 mg liter−1) in the Llanos. DOC enrichment may occur rapidly as Andean rivers enter the Llanos. The specific DOC export is correlated with the watershed forested area in the Andes but not in the Llanos. Specific DOC yield for a given water runoff is 3 times higher in the Llanos. Regionalization seems important for predicting DOC dynamics in such a large basin.
Effects on the benthic diffusive boundary layer imposed by microelectrodes
Authors: Nøhr Glud Ronnie , Gundersen Jens Kristian , Revsbech Niels Peter , Jørgensen Bo Barker
Published: May 2010

Oxygen microgradients and fluxes were studied in a 0.3–0.6‐mm‐thick diffusive boundary layer (DBL) of aquatic sediments by the use of O2 microelectrodes with sensing tips of 5 µm. One microelectrode was introduced vertically from above while another was introduced along the same vertical axis from below, thus penetrating up through the sediment. Microelectrodes introduced from below did not alter the DBL, but those introduced from above reduced its thickness by 25–45%. The effect was detected even when the microsensor tip was situated >1 mm above the sediment surface. The reduction of the DBL resulted in steepening the O2 gradient. In typical coastal sediments, the microelectrode thereby increased the diffusive O2 flux by 8%; in a highly sulfidic sediment the increase was 59%.
Use of diffusion samplers in oligotrophic lake sediments: Effects of free oxygen in sampler material
Authors: Carignan Richard , St‐Pierre Sylvie , Gachter Rene
Published: May 2010

In the anoxic sediments of an oligotrophic lake, acrylic pore‐water diffusion samplers conditioned by a 30‐d exposure to N2 before use gave pore‐water concentration profiles of total Fe, Fe2+, dissolved reactive P, and SO42− that were significantly different from those obtained with samplers in which only the aqueous dissolved O2 had been removed by bubbling for 18 h with N2. The differences in concentrations are attributable to the loss of substantial amounts of O2 by the plastic material and reaction of the liberated O2 with reduced porewater constituents. Laboratory tests show that acrylic in equilibrium with atmospheric O2 can store up to 1.6% (vol/vol) of O2 that will be slowly lost (halftime, ∼5.7 d) once exposed to an anoxic environment. Oxygen solubility at 23°C is highest in polycarbonate (3.7%) and Teflon (2.8%) and lowest in high‐density polyethylene (0.6%) and polyvinylidene fluoride (0.8%). Samplers made of such materials should not be exposed to atmospheric O2 for more than a few hours.
Origins and processing of organic matter in the Amazon River as indicated by carbohydrates and amino acids
Authors: Hedges John I. , Cowie Gregory L. , Richey Jeffrey E. , Quay Paul D. , Benner Ronald , Strom Mike , Forsberg Bruce R.
Published: May 2010

Aldose, amino acid, and elemental compositions were determined for flux‐weighted samples of coarse (>63 µm) and fine (<63 µm) particulate organic material and ultrafiltered (>1,000 Daltons) dissolved organic matter collected at three sites along the Brazilian Amazon River and six of its major tributaries. Concentrations of total organic C (TOC) were relatively uniform (550±100 µM) at all sites, with DOC comprising the major (50–100%) component. An average of 77% of the total DOC was isolated by ultrafiltration.

The greatest compositional differences observed in the Amazon River system were among the coarse, fine, and dissolved organic fractions. All coarse particulate fractions were nitrogen‐poor (atomic C : N = 21) and exhibited stable carbon isotope, aldose, and amino acid compositions similar to those of angiosperm tree leaves. Coarse particulate organic materials, although the least degraded of the three fractions, had lost appreciable carbohydrate and had immobilized excess nitrogen of apparent bacterial origin. Fine particulate materials were more nitrogen‐rich (C : N = 9) than coarse counterparts and had lower total aldose yields and glucose percentages. Fine particles gave greater total yields of amino acids, characterized by high ratios of basic vs. acidic components. Coexisting dissolved organic materials recovered by ultrafiltration were nitrogen‐poor (C : N = 27–52) and yielded the lowest amounts of aldoses, among which deoxy sugars were concentrated. Dissolved fractions gave extremely low yields of amino acids in mixtures that were enriched in nonprotein components and in acidic vs. basic molecules. These yield and composition patterns are consistent with a “regional chromatography” model in which highly degraded leaf material is solubilized and then partitioned between soil minerals and water during transport to the river, resulting in suspended fine particulate organic materials of soil origin that are nitrogen‐rich and coexisting dissolved organic substances that are nitrogen‐poor.
Patterns in planktonic P:R ratios in lakes: Influence of lake trophy and dissolved organic carbon
Authors: del Giorgio Paul A. , Peters Robert H.
Published: May 2010

A comparative analysis of planktonic metabolism in 20 southern Québec lakes was carried out to test the hypothesis that planktonic P : R ratios reflect gradients of both nutrient enrichment and dissolved organic carbon (DOC). Mean epilimnetic phytoplankton photosynthesis ranged from 8 to 377 mg C m−3 d−1, and the amount of C respired by the plankton in excess of phytoplankton photosynthesis ranged from 30 to 86 mg C m−3 d−1 . Plankton community respiration was 2–8 times greater than phytoplankton photosynthesis in all oligotrophic and mesotrophic lakes during the growing season, and this imbalance narrowed toward the more productive lakes. P : R ratios were positively related to chlorophyll and total P concentration, and inversely related to water color and DOC concentration. The strong influence of DOC on planktonic P : R ratios was almost exclusively due to its depressing effect on phytoplankton photosynthesis; DOC had no statistical effect on respiration. The calculated DOC loading for these lakes suggests that organic C loss through epilimnetic respiration in excess of phytoplankton photosynthesis is comparable to the estimated DOC loss within the lakes and that summer plankton metabolism could be supported by external DOC inputs in most lakes. The highly significant intercept of the respiration to production relationship, 27 mg C m−3 d−1, may indicate the baseline metabolism supported by external sources of C that occurs in these temperate lakes. Estimates of respiratory CO2 production from the pelagial of these lakes range from 11 to 60 mmol CO2 m−2 d−1, depending on lake trophy and DOC concentration. These estimates suggest that the planktonic metabolism of allochthonous DOC probably constitutes a major source of CO2 in lakes.
Enrichment and purification of Chaoborus kairomone from water: Further steps toward its chemical characterization
Authors: Tollrian Ralph , von Elert Eric
Published: May 2010

Predatory larvae of the genus Chaoborus release a chemical compound (kairomone) into the water which induces morphological changes, as antipredatory defenses, in daphnids. We present a method for enriching the active compounds released by the larvae directly from their aquatic environment by sorbent extraction. We developed a fast microscale bio‐test based on Daphnia pulex morphological response to the kairomone to obtain new information about the kairomone’s chemical nature. Carboxyl and hydroxyl groups are essential for kairomone activity. The kairomone can be characterized as a low‐molecular weight, non‐olefinic hydroxy‐carboxylic acid. Separation by reversed‐phase HPLC yields only one active fraction. The kairomone can be purified by anion exchange and HPLC. This is the first time a kairomone, which is sensed by Daphnia, has been enriched from water by sorbent extraction technology. This technique of enrichment offers the possibility of following seasonal kairomone concentrations in natural environments.
Sediment oxygen profiles in a super‐oxygenated antarctic lake
Authors: Wharton Robert A. , Meyer Michael A. , McKay Christopher P. , Mancinelli Rocco L. , Simmons George M.
Published: May 2010

Perennially ice‐covered lakes are found in the McMurdo Dry Valleys of southern Victoria Land, Antarctica. In contrast to temperate lakes that have diurnal photic periods, antarctic (and arctic) lakes have a yearly photic period. An unusual feature of the antarctic lakes is the occurrence of O2 at supersaturated levels in certain portions of the water column. Here we report the first sediment O2 profiles obtained using a microelcctrode from a perennially ice‐covered antarctic lake. Sediment cores collected in January and October 1987 from Lake Hoare in Taylor Valley show oxygenation down to 15, and in some cases, 25 cm. The oxygenation of sediments several centimeters below the sediment‐water interface is atypical for lake sediments and may be characteristic of perennially ice‐covered lakes. There is a significant difference between the observed January and October sediment O2 profiles. Several explanations may account for the difference, including seasonality. A time‐dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photoperiod and benthic primary production in sediments overlain by a highly oxygenated water column.
Mesoscale variability in nitrogen uptake rates and the f‐ratio during a coastal phytoplankton bloom
Authors: Vézina Main F.
Published: May 2010

The proportion of the biological nitrogen demand met by nitrate (f‐ratio) is a strong candidate for a biogeochemical parameter to relate primary production to the oceanic organic carbon flux, the latter being a potential global carbon sink. There is a controversy over whether f can be related to spatial and temporal variations in NO3− concentration for the purposes of estimating carbon fluxes. I report measurements of NO3− and NH4+ uptake rates and of the f‐ratio taken during a coastal phytoplankton bloom and address the problem of mesoscale f‐ratio variability. The results reveal two distinct behaviors of the f‐ratio depending on light level: at the 50% level, f is nonlinearly related to ambient NO3− concentration; at the 10 and 1% light levels, f is not related to NO3 concentration but is instead related to variations in the stratification in the NO3− profile. There seems to be a “two‐track” biological system in the euphotic zone: a shallow food web that quickly incorporates new NO3− supplies and a deep food web that responds more slowly to a varying supply. New production tends to be higher near the surface than deeper, which is opposite the vertical structure generally proposed for NO3−‐limited systems. The implication is that NO3−‐based algorithms to predict f may not work over the full three‐dimensional NO3− field.
Detrital bedrock elements as tracers of settling resuspended particulate matter in a coastal area of the Baltic Sea
Authors: Blomqvist Sven , Larsson Ulf
Published: May 2010

Particulate matter settling out of the trophogenic layer was collected in sediment traps at five stations during 5 yr in a coastal area of the Baltic Sea. Al, Fe, and Ti in the intercepted matter were inferred to be due mainly to the presence of fine‐grained bedrock detritus and were used as markers to calculate the proportion of primary settling matter and resuspended sediment in the collected matter. Considerable variations within and between years, seasons, and nearby stations were found for gross sedimentation rate and for the ratio between primary settling matter and resuspended sediment. This pattern also applied to organic C. A predominance of primary settling matter was recorded mainly in spring. Resuspended matter was a large component in the annual budget for all years and stations. In fact, the resuspended portion commonly exceeded 50%, and periods without resuspension seem to occur rarely or never in the investigated area.
Morphological constraints in the piscivore‐planktivore interaction: Implications for the trophic cascade hypothesis
Authors: Hambright K. David
Published: May 2010

Results are presented from a 3‐yr, replicated pond study examining how differential planktivore vulnerability can influence planktivore responses to piscivory and ultimately plankton responses via cascading effects. Without piscivores, planktivory from a multispecies planktivore assemblage (fathead minnow Pimephales promelas and pumpkinseed sunfish Lepomis gibbosa) produced the well‐documented plankton responses. Chaoborus densities, zooplankton biomass, and cladoceran and copepod mean body sizes were reduced, and chlorophyll concentrations and gross primary production were enhanced. With piscivores, levels of planktivory were depressed due to elimination of the highly vulnerable minnow and a shift in the size structure of the relatively less vulnerable sunfish toward larger, benthivorous sizes. Hence, zooplankton biomass and cladoceran and copepod mean body sizes were increased, and chlorophyll concentrations and gross primary production were reduced. However, juvenile sunfish remained abundant in ponds containing piscivores, so Chaoborus densities remained low and small cladocerans (Bosmina and Ceriodaphnia) were abundant. Moreover, Daphnia biomass, mean body size, and number of days present during the final year in these ponds were negatively correlated with small sunfish biomass, indicating that piscivory did not simply cancel out the effects of planktivory.
The biogeochemistry of hydrogen sulfide: Phytoplankton production in the surface ocean
Authors: Walsh Russell S. , Cutter Gregory A. , Dunstan William M. , Radford‐Knoery Joël , Elder Jennifer T.
Published: May 2010

Hydrogen sulfide can exist in oxic waters in the form of a dissolved gas, dissociated ions, dissolved metal sulfide complexes, and particulate metal sulfides. The sum of the dissolved species is termed total dissolved sulfide (TDS). In addition to the hydrolysis of carbonyl sulfide, it has been speculated that phytoplankton may produce TDS. We present results from preliminary culture studies which demonstrate that phytoplankton produce TDS and particulate acid‐volatile sulfide (pAVS). The phylogenetic order of TDS + pAVS production (per unit cell volume) for the oceanic species examined is Synechococcus sp. > Emiliania ≈ Pyramimonas obovata > Thalassiosira oceanica. Moreover, TDS and pAVS production increases when the concentrations of uncomplexed trace metals in culture media are also increased, suggesting metal detoxification via the formation of metal sulfide complexes.
Thermal structure of lakes varying in size and water clarity
Authors: Mazumder Asit , Taylor William D.
Published: May 2010

The epilimnion depth of lakes is related both to lake size, which affects wind‐induced mixing, and to water clarity, which affects the depth over which solar radiation heats the water. Here we attempt to isolate the relative importance of these two variables by examining lakes that have changed in water clarity with time (between years), by examining nearby lakes of comparable size, and by partitioning a large number of lakes into subsets with a restricted range in size or Secchi depth. Overall, results indicate that both lake size and water clarity are important determinants of epilimnion depth, but the absolute effect (indicated by slope) of Secchi depth is approximately constant in small (<12.5 km2) as well as large lakes and the Laurentian Great Lakes, while its relative importance (indicated by r2) appears to be restricted to the small lakes.
Development of a new method for direct measurement of pCO2 in natural waters
Authors: Che Guangwei , Ilmberger Johann
Published: May 2010

A new direct measurement method for pCO2 in water samples is presented. The technique is based on the fact that the dissolved CO2 in a water sample is able to diffuse through the wall of a thin silicon rubber tubing, whereas the dissolved ions remain. The CO2 passing through the wall is equilibrated with the deionized water flowing inside the tubing, and its electric conductivity is measured by a conductivity flow cell afterward.

Laboratory experiments on 255 CO2 standard samples with pCO2 varying from 300 to 30,000 ppmv show a mean CO2 exchange ratio R across the silicon rubber membrane of 0.95, with SD = ±0.04. For pCO2 in the 40–300 ppmv range (40 CO2‐standard samples), a mean exchange ratio R = 0.93±0.09 has been determined. The detection limit of this method is 0.6 µM (∼18 ppmv at 25°C).
Prey consumption and predatory effects of an invertebrate predator (Bythotrephes: Cladocera, Cercopagidae) based on phosphorus budgets
Authors: Burkhardt Stefen , Lehman John T.
Published: May 2010

Phosphorus excretion rates, ingestion efficiency, and P content of Bythotrephes at different developmental stages are used to estimate predation rates indirectly from metabolic needs. A growth model is developed to predict P content and weight of this invertebrate planktivore throughout its life. P consumption required to complete one parthenogenic life cycle of the predator is estimated from metabolic rates and weight measurements of individual instars. Based on P requirements and prey stoichiometry, empirical ingestion efficiency of 59%, and assimilation efficiency of 85%, each Bythotrephes consumes the equivalent of 14 Daphnia per day on average and can inflict mortality equal or greater in magnitude to Daphnia recruitment rates during midsummer in offshore waters of Lake Michigan, particularly when predator population abundance exceeds 400 individuals m−2.
Determination of phytoplankton crops by top‐down and bottom‐up mechanisms in a group of English lakes, the West Midland meres
Authors: Moss Brian , McGowan Suzanne , Carvalho Laurence
Published: May 2010

Twenty‐four lake basins formed in glacial drift ranged in maximum depth from 1.5 to 31 m and were characterized by generally low inorganic N concentrations and very high total P concentrations. The high P values were in some cases related to farm effluent pollution but in many others, despite annual mean values up to 1.46 mg liter−1, appear natural and due to the local mineralogy.

For the entire group, there were no significant relationships between mean growth season chlorophyll a concentration and any measured chemical, morphometric, or zooplankton variable. When the group was divided on the basis of maximum depth and presence or absence of thermal stratification in summer into a shallow group (<3 m) and a deep group (>3 m), strong inverse correlation was obtained between chlorophyll a and cladoceran abundance in the shallow group and strong direct correlation with inorganic N in the deep group. Grazer control in the shallow group is probably linked with the dominance of submerged macrophytes and the refuges they provide for grazers. Some of the controversy presently surrounding the relative importance of top‐down vs. bottom‐up control of phytoplankton populations may thus be removed if consideration is given to the morphometry of the lakes.
Seasonality of stable carbon isotopes within the pelagic food web of Lake Kinneret
Authors: Zohary Tamar , Erez Jonathan , Gophen Moshe , Berman-Frank Ilana , Stiller Mariana
Published: May 2010

Seasonal variations in the carbon isotope composition of components of the pelagic food web in Lake Kinneret were recorded and compared with those recorded for bulk plankton from the lake in the early 1970s. Individual planktonic components as well as bulk plankton were isotopically lightest shortly after overturn in January and heaviest in May, after the peak of the annual bloom of the dinoflagellate Peridinium gatunense. The range of δ13C values observed over an annual cycle and the annual and seasonal means varied considerably between taxa. Within the primary producers, P. gatunense (range, −23.2 to −17.9‰) was significantly 13C‐enriched relative to concurrent nanoplankton (−27.4 to −19.0‰). Zooplankton δ13C showed indistinct taxon‐specific differences but greater seasonal variation (−33.8 to −19.8%) than any phytoplankton component examined. Adult fish exhibited smaller δ13C variability than the planktonic components. End‐member isotope compositions confirmed the linkages nanoplankton → zooplankton → Kinneret sardines, and Peridinium → Sarotherodon galilaeus. Likely grazing of zooplankton on isotopically heavy Peridiniopsis spp. in spring and on a yet undetected light component in winter were implicated. The data demonstrate that the δ13C of bulk particulate organic matter samples provides only a simplified view of a complex picture of δ13C dynamics within the pelagic food web of a freshwater system.
Coupling of near‐bottom pelagic and benthic processes at abyssal depths in the eastern North Pacific Ocean
Authors: Smith K. L. , Kaufmann R. S. , Baldwin R. J.
Published: May 2010

A time‐series site was established in the eastern North Pacific Ocean to study the coupling between near‐bottom pelagic and benthic processes at abyssal depths in an area with well‐documented seasonality in surface water productivity. Particulate total mass (PTM), particulate organic C (POC), particulate total N (PTN), and particulate calcium carbonate [P(CaCO3)] fluxes were measured from sediment trap collections at 600 and 50 m above bottom from February 1990 to October 1991 (606 d). The sea floor at 4,100 m was concurrently monitored with a time‐lapse camera over a 386‐d period from July 1990 to July 1991. During this study, in situ measurements of sediment community oxygen consumption (SCOC) were made and surface sediment samples collected seasonally with a free‐vehicle grab respirometer. PTM, POC, PTN, and P(CaCO3) fluxes exhibited a strong seasonal signal, with episodic peaks from spring through fall and lows in winter. SCOC increased sharply between winter and summer, coinciding with spring peaks in particulate fluxes. Detrital aggregates appeared on the sea floor in pulses over a 6‐month period from July to December 1990, coinciding with periods when particulate fluxes were elevated but delayed ∼1.5 months after the initial peaks in particulate flux. Mobile epibenthic megafauna monitored with time‐lapse photography consisted primarily of holothuroids and echinoids and were twice as active when detrital aggregates were observed on the sea floor as during the rest of the year. Our results show a temporal relationship between the flux of particulate matter entering the benthic boundary layer, the arrival and residence of detritus on the sea floor, and the activity of the sediment community and mobile epibenthic megafauna.
Chlorophyll concentration effects on asymptotic optical attenuation
Authors: Francisco P. W. , McCormick N. J.
Published: May 2010

The concentration of chlorophyll in seawater has a significant effect on the asymptotic exponential decay coefficient and, in some cases, the eigenfunction of the radiative transfer equation that describes the asymptotic behavior of the angular dependence of the radiation at large depths. Calculations were performed for wavelengths ranging from 400 to 700 nm and for chlorophyll concentrations of 0.01–10 mg m−3. The coefficients monotonically increase with increasing concentration, but not with increasing wavelength. Values at different wavelengths can vary by as much as a factor of four for concentrations of 1 mg m−3 or greater. The eigenvalues calculated with the Henyey‐Greenstein model for scattering anisotropy are in close agreement with those obtained with the delta‐Eddington model. Suggestions from this investigation may be helpful when using “asymptotic closure” theories for estimating optical properties of water from vector irradiance and scalar irradiance data.
hresholds for growth in Daphnia magna with high and low phosphorus diets
Authors: Sterner Robert W. , Robinson Judy L.
Published: May 2010

Algae that have a low growth rate with a low mineral content are inferior foods for Daphnia growth, but these foods are not inferior for maintenance metabolism. The C per unit volume of low‐growth‐rate algal food necessary for zero body growth was similar to that of high‐growth‐rate food. Maintenance metabolism requires mainly energy, while body growth requires other essential substances; thus, they are separate influences of food quality.