bluuebunny/crossref_metadata_2025 huggingface dataset:
Linking planktonic diatoms and climate change in the large lakes of the Yellowstone ecosystem using resource theory
Authors: Kilham Susan S. , Theriot Edward C. , Fritz Sherilyn C.
Published: May 2010

Resource‐based physiology of the eight important planktonic diatom species in the large lakes of the Yellowstone region can be used to explain their relative abundances and seasonal changes. The diatoms are ranked along resource ratio gradients according to their relative abilities to grow under limitation by Si, N, P, and light. Hypotheses based on resource physiology can be integrated with observations on seasonal changes in diatom assemblages to explain the present distributions of diatoms and to test the causal factors proposed to explain diatom distributions over the Holocene. Knowledge of the limnology of these lakes and process‐oriented physiology provide the basis for a more detailed interpretation of the paleorecord and a firmer basis for landscape‐level transfer functions for fine‐scale climate reconstruction.
Potential effects of climate change on ion chemistry and phytoplankton communities in prairie saline lakes
Authors: Evans J. Catherine , Prepas Ellie E.
Published: May 2010

Shallow, closed‐basin saline lakes found in semiarid areas of Canada tend to be sensitive to changes in precipitation: evaporation ratios. Historical climatic information indicates that the area is becoming increasingly arid and this trend is expected to continue under current climate‐change scenarios. The water chemistries and phytoplankton of six Alberta saline (>1 g liter‒1 total dissolved solids) lakes were studied over a 12‐yr arid period to evaluate potential chemical and biological effects of climate‐induced increases in brine conductivity. Major ion concentrations, relative proportions of major ions, chlorophyll a concentrations, and the relative importance of different phytoplankton phyla were evaluated with respect to the increasing conductivity profiles of the lakes and with respect to the range of conductivities represented in the lake series. When the data were combined, concentrations of Na+, K+, Mg2+, SO42‒, Cl‒, and alkalinity were positively correlated with conductivity and Ca2+ was negatively correlated with conductivity. The relative proportions of Na+, SO42‒, and Cl‒ increased significantly with brine conductivity (2,900–30,900 µS), and the proportions of other ions decreased. The variability of these relationships suggests that the brine compositions in some of these lakes are strongly influenced by local surface water and groundwater chemistry. Increases in conductivity were usually accompanied by decreases in Chl a concentration and a shift away from cyanophyte species in favor of chlorophytes, cryptophytes, and chrysophytes. This change in the importance of these phytoplankton phyla, which occurs at relatively low salinities (∼3,500 µS cm‒1), acts to limit phytoplankton biomass in these P‐sufficient systems by restricting the growth of nitrogen‐fixing species. Salinity‐linked shortages of nutrients other than P may account for these changes.
Effects of climate warming on fish thermal habitat in streams of the United States
Authors: Eaton John G. , Scheller Robert M.
Published: May 2010

The effects of climate warming on the thermal habitat of 57 species of fish of the U.S. were estimated using results for a doubling of atmospheric carbon dioxide that were predicted by the Canadian Climate Center general circulation model. Baseline water temperature conditions were calculated from data collected at 1,700 U.S. Geological Survey stream monitoring stations across the U.S. Water temperatures after predicted climate change were obtained by multiplying air temperature changes by 0.9, a factor based on several field studies, and adding them to baseline water temperatures at stations in corresponding grid cells. Results indicated that habitat for cold and cool water fish would be reduced by ∼50%, and that this effect would be distributed throughout the existing range of these species. Habitat losses were greater among species with smaller initial distributions and in geographic regions with the greatest warming (e.g. the central Midwest). Results for warm water fish habitat were less certain because of the poor state of knowledge regarding their high and low temperature tolerances; however, the habitat of many species of this thermal guild likely will also be substantially reduced by climate warming, whereas the habitat of other species will be increased.
Potential effects of global climate change on small north‐temperate lakes: Physics, fish, and plankton
Authors: De Stasio Bart T. , Hill David K. , Kleinhans Julie M. , Nibbelink Nathan P. , Magnuson John J.
Published: May 2010

A 10‐yr record of the thermal characteristics of four lakes at the North‐Temperate Lakes Long‐Term Ecological Research site was analyzed and used to validate simulations of lake physics with the dynamic reservoir simulation model. Simulations of cool, warm, and intermediate years were rerun with meteorology from four general circulation models with a doubling of CO2. In all simulations with doubled CO2 there is an earlier onset of stratification, increased summer epilimnetic temperature (1–7°C), and an increased intensity and longer duration of stratification. Maximum surface temperatures at times may exceed upper lethal limits of warm and cool water fish in some scenarios. Suitable thermal habitat for cold water, cool water, and warm water fish generally increases in all scenarios after climate change.

Changes in the vertical migration of Daphnia, however, are expected to vary depending on the interaction of thermal stratification and fish habitat use. In northern Wisconsin lakes with cold water planktivores, habitat overlap between fish and zooplankton is expected to decrease, while in southern Wisconsin lakes habitat overlap is expected to increase. Although most physical responses of lakes to climate change are consistent among all climate scenarios, biological responses will likely be more variable owing to the complex nature of factors determining ecological interactions in lakes.
Bacterioplankton community structure: Protists control net production and the proportion of active bacteria in a coastal marine community
Authors: del Giorgio Paul A. , Gasol Josep M. , Vaqué Dolors , Mura Paola , Agustí Susana , Duarte Carlos M.
Published: May 2010

A series of dialysis experiments was performed to study the relative importance of substrate limitation and grazing in controlling the proportion of active cells of coastal marine bacterioplankton. The grazer community was manipulated by filling dialysis bags with unfiltered water and water serially passed through 150‐, 40‐, and 0.8‐µm pore‐size filters. The total number of bacteria, the number of metabolically active cells, bacterial loss rates, and the abundances of heterotrophic nanoflagellates were measured immediately and at 3 and 6 d. Gross growth rates were similar in all treatments, suggesting that ambient nutrient concentrations set an upper limit to the maximum growth rates, whereas grazing determined the net growth rates and the final number of bacteria. Bacterial loss rates, measured as the disappearance of fluorescently labeled minicells, correlated well with the initial density of heterotrophic nanoflagellates in the different treatments. The number of active cells at the end of the experiments varied widely among treatments and reached 2.0 × 106 ml‒1, or over 55% of the total final density in dialysis bags, with little or no grazing by nanoflagellates. The final proportion of active cells was negatively correlated to both the loss rates and the initial nanoflagellate density, and it was estimated that grazing rates on metabolically active bacteria were four or more times higher than those on inactive bacteria. Heterotrophic nanoflagellates thus seemed to control bacterial density by skimming newly growing cells rather than by cropping the standing stock of bacteria.
The effect of invertebrate consumption on bacterial transport in a mountain stream
Authors: Hall Robert O. , Peredney Christopher L. , Meyer Judy L.
Published: May 2010

Although laboratory studies have shown that filter‐feeding invertebrates consume bacteria from stream water, no study has measured bacterial consumption in the field or determined system‐level removal rates of sestonic bacteria. To examine bacterial removal rates and consumption by invertebrates, we released fluorescently labeled bacteria (FLB) into a second‐order stream at Coweeta Hydrologic Laboratory, North Carolina. We performed two 1‐h releases during summer over bedrock habitat that supports many filter‐feeders. We calculated uptake length and counted FLB in the guts of seven insect taxa. Uptake length was 78 and 83 m for the two releases, which corresponded to uptake rates of 4.03 and 3.69 × 107 cells m‒2 min‒1. Simulium, a filter‐feeding blackfly larva, ingested FLB at a rate of 1.4 × 104 cells mg‒1 min‒1, 10 times the rate of other taxa. Diplectrona and Parapsyche, hydropsychid caddisfly filter‐feeders, had ingestion rates between Simulium and other taxa. Epeorus, a scraping mayfly, and Tallaperla, a shredding stonefly, also ingested FLB, presumably from cells that adhered to the substrate. Invertebrate ingestion per square meter of stream bottom was 7% of total stream uptake, with Simulium responsible for 91% of the total invertebrate ingestion. Adhesion of FLB to the substrate from the water column seemed to be more important than invertebrate consumption in this stream, and one taxon, Simulium, was responsible for most invertebrate consumption of bacteria.
Astaxanthin in Calanus pacificus: Assessment of pigment‐based measures of omnivory
Authors: Juhl Andrew R. , Ohman Mark D. , Goericke Ralf
Published: May 2010

We investigated the suitability of the pigments astaxanthin and canthaxanthin as biomarkers for measuring the contribution of microzooplankton prey to copepod diets. Identification and quantification of pigments of the marine planktonic copepod Calanus pacificus and heterotrophic protists were made using reverse‐phase HPLC with a photodiode array detector. Astaxanthin content in the body tissues of C. pacificus declined significantly within 2 h after the onset of starvation. The esterified and unesterified pigment fractions behaved differently, with the unesterified fraction initially increasing in starred animals. Tissue astaxanthin content of C. pacificus increased by 50% in 24 h when fed the cryptomonad alga Rhodomonas sp. Such rapid changes in copepod body tissue pigments in response to starvation or feeding would lead to large errors in pigment‐based measures of omnivory. Furthermore, neither astaxanthin nor canthaxanthin could be detected in any extract of six species of cultured and one species of field‐collected heterotrophic marine protists. Although a variety of carotenoids were found in protist extracts, no single pigment was common to all heterotrophic protists.
Reproductive success of “herbivorous” zooplankton fed algal and nonalgal food resources
Authors: Sanders Robert W. , Williamson Craig E. , Stutzman Paul L. , Moeller Robert E. , Goulden Clyde E. , Aoki‐Goldsmith Rika
Published: May 2010

Many species of zooplankton are traditionally considered to be herbivores despite their ability to capture nonphotosynthetic microorganisms. Several recent studies indicate that protozoa are ingested by crustacean zooplankton, but an important aspect of these trophic interactions that has generally been overlooked is the contribution of heterotrophic food organisms to growth and(or) reproduction. We conducted a series of experiments to examine the ability of two crustacean zooplankters to supplement their diets with protozoa and to utilize these foods for reproduction. The cladoceran, Daphnia pulicaria, and the copepod, Diaptomus oregonensis, both ingested bacteria, ciliates, and heterotrophic nanoflagellates in the presence of algal food. Total young produced by D. pulicaria increased in treatments with added ciliates, heterotrophic nanoflagellates, bacteria, or algae relative to the baseline level of algal food. D. oregonensis females produced abundant young only in the treatments with ciliates or extra algae. The heterotrophic flagellates were ingested at high rates by both D. pulicaria and D. oregonensis, but did not contribute significantly to reproduction in the copepod. This suggests that some foods may be utilized (vs. just ingested) differently by these two common crustaceans. Reproduction was not significantly correlated with the total amounts of carbon, nitrogen, or phosphorus ingested by D. pulicaria or D. oregonensis, suggesting that nutrient content does not sufficiently differentiate the quality of different taxa as food.
Algal recruitment from lake sediments in relation to grazing, sinking, and dominance patterns in the phytoplankton community
Authors: Hansson Lam-Anders
Published: May 2010

I assessed the importance of algal recruitment from the sediment surface to the water relative to other population variables such as grazing, growth, and sinking. In four low‐productivity lake basins, which were stratified throughout the study, 32% of the identified algal taxonomic groups exhibited recruitment, whereas the other 68% spent their entire lives in the pelagic habitat. For most species, recruitment from sediment to water occurred primarily at shallow depths (<8 m) and often increased total phytoplankton abundance by 10–50% per day. Grazing was the main loss process, reducing algal abundance by usually between 10 and 50% per day; sinking rates were usually one order of magnitude lower. Recruitment was highest in shallow water (<10 m deep); when maximum recruitment occurred below the thermocline, no relation was found between recruitment and abundance in the euphotic zone, suggesting that the thermocline functioned as a physical barrier for algal vertical migration. In three of the lakebasins, recruiting algae dominated more often than expected by chance (P < 0.05), suggesting a competitive advantage with the adaptation to perform recruitment. Successful recruitment may have a considerable impact on dominance patterns in the phytoplankton community.
Discrete dissolved and particulate proteins in oceanic waters
Authors: Tanoue Eiichiro , Ishii Masao , Midorikawa Takashi
Published: May 2010

Dissolved and particulate proteins were extracted from samples of surface seawater collected from the equatorial area, through the Indian Ocean, to the Antarctic Ocean. Dissolved proteins were also observed in waters of the equatorial Pacific. Dissolved and particulate proteins with a wide range of molecular masses were detected by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE). The particulate proteins were made up of many background proteins of overlapping molecular weight, which caused uniform staining in the gel. However, distinct bands of individual proteins with apparent molecular masses of ∼66 and 45 kDa were evident among the background proteins. Electrophoretograms of dissolved proteins were quite different from those of the particulate proteins. The dissolved background proteins were not significant, and fewer than 30 proteins were clearly visualized as major dissolved proteins. Dissolved proteins with apparent molecular masses of 48 and 37 kDa were commonly found as major proteins in all samples examined. Such molecular characteristics of dissolved and particulate proteins are consistent with previous results from the North Pacific. Thus, it appears that the processes by which specific proteins from marine organisms are transferred to and accumulated in the pools of dissolved and particulate organic matter are identical throughout the world’s oceans.
Long‐term decomposition of DOC from experimental diatom blooms
Authors: Fry Brian , Hopkinson Charles S. , Nolin Amy , Norrman Bosse , Zweifel Ulla Li
Published: May 2010

Decomposition of 13C‐labeled dissolved organic carbon (DOC) produced in two marine diatom blooms was followed for 2.5 yr with large volume (20 liter) incubations performed in the dark. The 13C tracer was used to partition decomposition dynamics of the fresh diatom‐derived DOC and the turnover of background DOC from Woods Hole Harbor. DOC from Woods Hole Harbor proved largely refractory, with DOC concentrations falling from 122 to ∼100 µM C in 2.5 yr. DOC from the diatom blooms was more labile, but was also incompletely mineralized, with 25–35% remaining after 2.5 yr. Neither nutrients nor labile carbon (dextrose) added at 1.5 yr significantly stimulated DOC mineralization. The experiments indicate that DOC produced in short‐term blooms can be surprisingly resistant to microbial attack.
A rosette system for the collection of trace metal clean seawater
Authors: Hunter Craig N. , Gordon R. Michael , Fitzwater Steve E. , Coale Kenneth H.
Published: May 2010

We designed a large‐volume rosette sampler for collecting seawater with minimal trace metal contamination. The system uses eight modified 30‐liter Go‐Flo bottles secured to a Nylon II‐coated stainless steel frame. The instrument is deployed with a dedicated winch with polyurethane‐coated, three‐conductor Kevlar hydroline. A prototype was used as part of the U.S. JGOFS Equatorial Pacific sampling program during spring and fall 1992. A redesigned model was used during the 1993 IronEx experiments and is currently being deployed in the Arabian Sea. The results of trace metal analyses collected on these cruises indicate that samples recovered are comparable to current single Go‐Flo casts.
Scavenging of 234Th and 7Be in Lake Constance
Authors: Vogler S. , Jung M. , Mangini A.
Published: May 2010

Particulate and dissolved concentrations of 234Th and 7Be, along with fluxes of total mass and particulate 234Th and 7Be into sediment traps, were measured in Lake Constance (Bodensee) from March to December 1993. During the same period, atmospheric deposition rates of 7Be and 210Pb were determined. Variations in atmospheric fluxes of 7Be and 210Pb were found to reflect variability in rainfall. The mean atmospheric flux for 7Be was 13.5 dpm cm−2 yr−1 and for 210Pb it was 0.65 dpm cm−2 yr−1. Total 234Th activities in surface water were generally high in winter and low in summer, primarily in response to the seasonality of biological activity. About 50–70% of 234Th was found in particulate form, depending on particle concentration and particle residence time. Scavenging rates for dissolved 234Th ranged from 0.14 to 0.88 d−1, having increased slightly with total particle concentration. 7Be activities in surface water exhibited large variations because of variable atmospheric input and particle flux. During periods of high biological productivity, particulate 7Be in surface water increased from ~20 to ~60% of the total 7Be concentration. The scavenging rates for dissolved 7Be(0.01−0.12 d−1) were generally lower than those for dissolved 234Th because of the lower particle reactivity of 7Be. Although the 7Be flux into sediment traps at 50 m did not differ significantly from the flux at 120 m, the 234Th flux increased with depth because of the further adsorption of water column‐produced 234Th onto sinking particles. The range of residence times for the total radionuclide inventories estimated from an irreversible scavenging model was 33–83 d for 234Th and 40–340 d for 7Be (box depth, 50 m). The residence times of both nuclides were controlled by the particle flux, which, in turn, was determined by biological productivity in the surface water.
The geochemistry of Lake Bosumtwi, a hydrologically closed basin in the humid zone of tropical Ghana
Authors: Turner Benjamin F. , Gardner L. R. , Sharp W E. , Blood E. R.
Published: May 2010

Lake Bosumtwi lies in an isolated, hydrologically closed basin formed by a meteor impact ~1 × 106 yr ago. Comparison of lake‐water samples taken in 1993 with one from 1934 shows a decrease in the concentrations of dissolved solutes, most likely owing to an estimated 13% increase in lake volume. A mass balance calculation that uses an estimate of the average chloride composition of the rainfall shows that the most recent overflow of the lake occurred within the last 3,000 yr. Evaluation of the sources and sinks of major solutes suggests that deposition of harmattan dust may be an important component of the influx of ions into the lake.

Although the lake is homogeneous with respect to major ion composition, it is stratified into an upper oxygenated layer and a lower anoxic layer, and there is an abrupt change in the concentration profiles of pH, NH4+, PO43−, NO3−, and Mn at a depth of 16 m. This chemical stratification is apparently caused by photosynthesis in the upper layer and respiration and reducing conditions below.

The stable isotopic composition of the lake water is reasonably well simulated by a simple isotope balance model for the lake. The model is used to show that the δ18O composition of the lake is relatively insensitive to changes in the water balance, but is highly sensitive to relative humidity and the isotopic composition of atmospheric moisture.
Metabolism of neutral monosaccharide constituents of storage and structural carbohydrates in natural assemblages of marine phytoplankton exposed to ultraviolet radiation
Authors: Goes Joaquim I. , Handa Nobuhiko , Taguchi Satoru , Hama Takeo , Saito Hiroaki
Published: May 2010

We used the 13C tracer technique in conjunction with gas chromatography‐mass spectrometry to examine the impact of ultraviolet radiation (UVR) on the patterns of biosynthesis and composition of monosaccharides in natural assemblages of phytoplankton photoadapting to high light intensities. Exposure to UVR resulted in a decrease in the rates of phytoplankton photosynthesis and a marked reduction in the rates of production and pool sizes of neutral monosaccharides within the storage carbohydrate fraction (operationally defined as carbohydrates soluble in hot water). In contrast, the biosynthesis of neutral monosaccharides associated with cell wall or structural carbohydrates (operationally defined as the fraction of carbohydrates insoluble in hot water) showed an increase in the presence of UVR, which, although marginal, was consistent from station to station. The decline in pool sizes of monosaccharides within the storage carbohydrate fraction was largely responsible for the decline in the overall carbohydrate content of the cells. The diminution in the rates of synthesis and pool sizes of glucose within this fraction represented one of the most significant differences compared to phytoplankton shielded from UVR. In the structural carbohydrate fraction, the synthesis of several component monosaccharides was consistently higher in phytoplankton exposed to UVR.
Size‐ascent rate relationships in positively buoyant marine diatoms
Authors: Moore J. Keith , Villareal Tracy A.
Published: May 2010

Cell size and ascent rate were measured in individual short chains (2–8 cells) and single cells of positively buoyant marine diatoms from natural populations and cultures. Maximum ascent rates for Rhizosolenia formosa, Rhizosolenia acuminata, Rhizosolenia castracanei, Rhizosolenia debyana, and Ethmodiscus rex suggest an upper limit to diatom ascent rates on the order of 7–8 m h−1. Ascent rates were weakly correlated with cell diameter, volume, and surface: volume ratio across the pooled data for all species (n = 105). Among Rhizosolenia spp., ascent rate was strongly correlated with size‐related measures. The Rhizosolenia spp. average diameter was highly correlated with average ascent rate (r2 = 0.99, n = 4). Calculated cell density was inversely related to cell diameter in Rhizosolenia spp. Cell diameter is a better predictor of ascent rate than volume in long, cylindrical cells owing to covariations of density and form resistance. The observed ascent rates are consistent with vertical migration by these large diatoms in oligotrophic seas.
Extreme supersaturation of nitrous oxide in a poorly ventilated Antarctic lake
Authors: Prisu John C. , Downes Malcolm T. , McKay Christopher P.
Published: May 2010

Lake Bonney, a permanently ice‐covered Ant‐ arctic lake, has a middepth maximum N2O concentration of 41.6 µM N (> 580,000% saturation with respect to the global average mixing ratio of N2O) in its east lobe, representing the highest level yet reported for a natural aquatic system. Atmospheric N2O over the lake was 45% above the global average, indicating that this lake is an atmospheric source of N2O. Apparent N2O production (ANP) was correlated with apparent oxygen utilization (AOU), and denitrification was not detectable, implying that nitrification is the primary source for this gas. The slope of a regression of ANP on AOU revealed that potential N2O production per unit of potential O2 consumed in the east lobe of Lake Bonney is at least two orders of magnitude greater than reported for the ocean. The maximum yield ratio for N2O [ANP/(NO2− + NO3−)] in Lake Bonney is 26% (i.e. 1 atom of N appears in N2O for every 3.9 atoms appearing in oxidized N), which exceeds previous reports for pelagic systems, being similar to values from reduced sediments. Areal N2O flux from the lake to the atmosphere is >200 times the areal flux reported for oceanic systems; most of this gas apparently enters the atmosphere through a small moat that occupies ~3% of the surface of the lake and exists for ~10 weeks in summer.
Modeling bacterial utilization of dissolved organic matter: Optimization replaces Monod growth kinetics
Authors: Vallino J. J. , Hopkinson C. S. , Hobbie J. E.
Published: May 2010

A bioenergetic model has been developed to examine growth kinetics associated with bacterial utilization of dissolved organic matter (DOM), NH4+, and NO3‒. A set of 11 metabolic reactions are used to govern the incorporation, oxidation, and N remineralization of DOM and dissolved inorganic N associated with bacterial growth. For each reaction, free energies and electron transfer requirements are calculated based on the C, H, O, and N composition of the substrates and their concentration in the environment. From these reactions, an optimization problem is constructed in which bacterial growth rate is maximized subject to constraints on energetics, electron balances, substrate uptake kinetics, and bacterial C : N ratio. The optimization approach provides more information on bacterial growth kinetics than do the Monod‐type models that are typically used to describe bacterial growth. Simulations are run to examine bacterial C yield and growth rate, N remineralization or immobilization, and substrate preferences as resource concentrations and compositions are varied. Results from the model agree well with observations in the literature, which indicate that the premise of the model, that bacteria allocate resources to maximize growth rate, may be an accurate overall description of bacterial growth. Simulations indicate that bacterial growth rate and yield are strongly correlated to the oxidation state of the labile DOM, as determined from its bulk elemental composition. Furthermore, the model demonstrates that bacterial growth cannot always be explained by a single constraint (such as the C : N ratio of substrate), since several constraints are often active simultaneously and continuously change with environmental conditions.
Nitrification in the euphotic zone as a source for nitrite, nitrate, and nitrous oxide at Station ALOHA
Authors: Dore John E. , Karl David M.
Published: May 2010

We measured chemoautotrophic bacterial nitrification rates in the lower euphotic zone at the North Pacific Time‐series Station ALOHA using low‐level chemical assays and inhibitor‐sensitive radiocarbon uptake experiments. These measurements were compared with independent nitrification rate estimates based on nitrous oxide distributions, nitrate assimilation rates based on nitrate changes during an in situ incubation, and historical estimates of nitrification and nitrate assimilation from this region. Ammonium oxidation rates ranged from 1.0 to 137.4 µmol m‒3 d‒1, and nitrite oxidation rates varied from undetectable to 138.0 µmol m‒3 d‒1. Conservative estimates of depth‐integrated euphotic zone nitrification rates from the complete three‐cruise data set were 0.69 mmol m‒2 d‒1 for nitrite oxidation and 1.64 mmol m‒2 d‒1 for ammonium oxidation. The highest nitrification rates were found below the primary nitrite maximum, suggesting a significant contribution of euphotic zone ammonium oxidation to the nitrite pool below but not within this feature. A mass balance of nitrous oxide indicates that this gas is produced within the euphotic zone at a rate of 1.68–7.94 µmol m‒2 d‒1. The nitrous oxide production rate provides an independent estimate of the total euphotic zone nitrification rate in the range of 0.34–1.59 mmol m‒2 d‒1. We estimate that the total euphotic zone nitrification rate is 47–142% of the concurrent nitrate assimilation rate, indicating that nitrification in the euphotic zone is an important source of regenerated nitrate.
Pathways of carbon oxidation in continental margin sediments off central Chile
Authors: Thamdrup Bo , Canfield Donald E.
Published: May 2010

Rates and oxidative pathways of organic carbon mineralization were determined in sediments at six stations on the shelf and slope off Concepción Bay at 36.5°S. The depth distribution of C oxidation rates was determined to 10 cm from accumulation of dissolved inorganic C in 1–5‐d incubations. Pathways of C oxidation were inferred from the depth distributions of the potential oxidants (O2, NO3‒, and oxides of Mn and Fe) and from directly determined rates of SO42‒ reduction. The study area is characterized by intense seasonal upwelling, and during sampling in late summer the bottom water over the shelf was rich in NO3‒ and depleted of O2. Sediments at the four shelf stations were covered by mats of filamentous bacteria of the genera Thioploca and Beggiatoa. Carbon oxidation rates at these sites were extremely high near the sediment surface (>3 µmol cm‒3 d‒1) and decreased exponentially with depth. The process was entirely coupled to SO42‒ reduction. At the two slope stations where bottom‐water O2 was > 100 µM, C oxidation rates were 10‐fold lower and varied less with depth; C oxidation coupled to the reduction of O2, NO3‒, and Mn oxides combined to yield an estimated 15% of the total C oxidation between 0 and 10 cm. Carbon oxidation through Fe reduction contributed a further 12–29% of the depth‐integrated rate, while the remainder of C oxidation was through SO42‒ reduction. The depth distribution of Fe reduction agreed well with the distribution of poorly crystalline Fe oxides, and as this pool decreased with depth, the importance of SO42‒ reduction increased. The results point to a general importance of Fe reduction in C oxidation in continental margin sediments. At the shelf stations, Fe reduction was mainly coupled to oxidation of reduced S. These sediments were generally H2S‐free despite high SO42‒ reduction rates, and precipitation of Fe sulfides dominated H2S scavenging during the incubations. A large NO3‒ pool was associated with the Thioploca, and the shelf sediments were thus enriched in NO3‒ relative to the bottom water, with maximum concentrations of 3 µmol cm‒3. The NO3‐ was consumed during our sediment incubations, but no effects on either C or S cycles could be discerned.
The 1991 coccolithophore bloom in the central North Atlantic. 1. Optical properties and factors affecting their distribution
Authors: Balch William M. , Kilpatrick Katherine A. , Trees Charles C.
Published: May 2010

Optical scattering and absorption were measured in the central North Atlantic Ocean during a mesoscale bloom of the coccolithophorid Emiliania huxleyi. The chlorophyll‐specific absorption was similar to previously measured levels for this species in laboratory cultures. Suspended coccoliths were responsible for ∼80% of the total backscattering in the center of the bloom, and the greatest calcite‐dependent backscattering was observed just below the base of the mixed layer. Areal maps of calcite‐dependent backscattering and reflectance were similar because of the dominance of backscattering over absorption. Calculated reflectance at 440 and 550 nm reached ∼24%, which is slightly less than what has been observed previously in Gulf of Maine blooms. Total (b) was also calculated as the difference between beam attenuation and absorption. The ratio b̃b (backscattering divided by total scattering) was ∼0.01–0.02 at 440 and 550 nm at the most turbid parts of the coccolithophore bloom (b = 1–3 m‒1). As total scattering decreased below 1 m‒1, b̃b increased. The behavior of b̃b was compared for coccolith‐dominated vs. chlorophyll‐dominated waters. Vertical profiles of calcite‐dependent scattering, combined with satellite remote sensing data, were used to assess the factors responsible for vertical transport of calcite. The subsurface peak in calcite‐dependent scattering did not result from detached coccoliths sinking but resulted either from plated coccolithophores sinking and then detaching their plates or from deep coccolithophores producing and detaching their plates in situ.
The 1991 coccolithophore bloom in the central North Atlantic. 2. Relating optics to coccolith concentration
Authors: Balch William M. , Kilpatrick Katherine A. , Holligan Patrick , Harbour Derek , Fernandez Emilio
Published: May 2010

This study summarizes the relationships between various biological and optical properties of a mesoscale coccolithophore bloom observed in the North Atlantic during June 1991. Backscattering and coccolith concentration were positively correlated. Backscattering and concentration of suspended calcite were even better correlated because atomic absorption analyses of calcite calcium were equally accurate whether calcite was attached or detached from cells, whereas it was difficult to enumerate, the numbers of coccoliths attached to cells by means of microscopy. As the bloom aged, the ratio of detached coccoliths to plated cells increased. Dilution experiments provided the most precise relationships between coccolith backscattering and coccolith abundance. The calcite‐specific scattering coefficient was estimated from measurements of beam attenuation, absorption, and calcite concentration. The contribution of coccolith backscattering to total scattering was modeled as a function of coccolith concentration and chlorophyll concentration. Even outside the coccolithophore bloom, coccoliths were responsible for 5–30% of the total backscattering. Anomalous diffraction theory was used to show that calcite‐specific scattering is the highest for 1–3‐µm spheres, which correspond to the diameters of Emiliania huxleyi coccoliths (this prediction was close to the observed values). The calcite‐specific scattering coefficients of larger calcite particles (e.g. plated coccolithophore cells, foraminifera, pteropods) would be expected to be considerably lower. These data were used to test an approach for predicting coccolith concentration from water‐leaving radiance in the blue and green wavelengths.
Description of stability and neutrally buoyant transport in freshwater lakes
Authors: Peeter F. , Piepke G. , Kipfer R. , Hohmann R. , Imboden D. M.
Published: May 2010

The concept of potential density, introduced by oceanographers to describe the vertical stability of a water column, may be inadequate if the water temperature is close to the temperature of maximum density, Tmd, where the thermal expansion coefficient changes its sign. Because Tmd decreases with increasing pressure, potential density especially fails to provide a reliable means for the analysis of the local stability of a water column in deep, cold freshwater lakes. A new quantity called “quasi‐density” is introduced. Its vertical gradient correctly describes the local stability of a water column for every water body (warm, cold, fresh, or salty). Application of this concept to field data from Lake Baikal shows that quasi‐density—in contrast to potential density—is an ideal tool to assess vertical stability. In a two‐ or three‐dimensional field of potential temperature and salinity, the “neutral surface” is defined by the direction along which an infinitesimal isentropic displacement of a water parcel is buoyancy‐free. The neutral surfaces do not define a potential; that is, there is no scalar property that is constant along the neutral surface. Isentropic transport over finite distances is not buoyancy‐free along neutral surfaces or along surfaces of constant potential density (isopycnals). We define the “neutral track” as the path along which isentropic transport of a water parcel is buoyancy‐free. In general, each water parcel defines a different neutral track. Neutral track and neutral surface are complementary concepts used to assess the potential movement of a water parcel over some distance. The latter describes the path of a water parcel that after each infinitesimal displacement completely exchanges its identity with the characteristics of its new environment, whereas the former describes a parcel that totally keeps its identity specified by potential temperature and salinity.
A qualitative study of zooplankton grazing in an oligo‐mesotrophic lake using phytoplanktonic pigments as organic markers
Authors: Quiblier‐Llobéras Catherine , Bourdier Gilles , Amblard Christian , Pepin Denise
Published: May 2010

The impact of grazing by various zooplankton fractions (calanoid copepods, cyclopoid copepods, cladocerans, and small‐sized zooplankton: 80–315 µm) on various phytoplankton groups was measured in Lake Pavin (Central Massif, France) by means of phytoplankton pigments separated by HPLC as natural organic markers. The impact of grazing was determined from April to November in the depth‐sampling layers (0–7 and 7–20 m) in which most zooplankton organisms were concentrated.

Selective grazing by consumers created spatial (vertical) and temporal variation in mortality exerted on the various phytoplankton groups. For example, the avoidance of dinoflagellates (characterized by peridinin) by most of the zooplankton organisms studied led to low grazing impacts (<280 ml liter‒1 d‒1) on this phytoplankton group during all seasons. In contrast, preferential consumption of diatoms and chrysophytes (characterized by fucoxanthin) and chlorophytes and cyanobacteria (characterized by lutein and zeaxanthin) was recorded, depending on the zooplankton fraction in question. The grazing impact exerted on these phytoplanktonic groups was much higher than that measured on dinoflagellates, reaching values of 2,300 ml liter‒1 d‒1. Grazing mostly affected diatoms and chrysophytes in the 0–7‐m layer and chlorophytes and cyanobacteria in the 7–20‐m layer; the differences between these two layers were related to the heterogeneity in the vertical distribution of both phytoplankton cells and grazing organisms.
Particle capture mechanism of the pelagic tunicate Oikopleura vanhoefleni
Authors: Luis Acuña José , Deibel Don , Morris Claude C.
Published: May 2010

Oikopleurid appendicularians use an external “house” to preconcentrate particles from seawater suspension, but their pharyngeal filter is ultimately responsible for removing. suspended particles for ingestion. Although the pharyngeal filter captures submicrometer colloids efficiently, the fluid mechanics of this process have not been investigated. Using video‐assisted microscopy, we tracked plastic beads within the pharynx of Oikopleura vanhoeffeni to analyze flow streamlines and flow rates. Impact velocities of particles range from 124 to 1,436 µm s‒1, with a mean (±SD) of 559±292 µm s‒1. Reynolds numbers for the filter fibers are of order 10‒5. Given the fiber diameters and pore sizes published earlier and our measured impact velocities, current aerosol filtration models predict particle retention spectra that do not differ statistically from those determined empirically for particles between 0.6 and 3 µm in diameter, in contrast to predictions from a simpler sieving model. We conclude that the pharyngeal filter of O. vanhoeffeni captures particles >0.6 µm in diameter by a combination of sieving and direct interception onto individual fibers. The combination of model predictions of particle capture with particle size dis.tributions from an Arctic polynya suggests that adult O. vanhoeffeni obtains 49, 29, and 18% of its ration by volume from nanoplankton (2–20 µm in diameter), microplankton (20–100 µm), and picoplankton (1–2 µm), respectively, with a possible 4% contribution from submicrometer colloids.
Free‐swimming Daphnia pulex can avoid following Stokes' law
Authors: Gorski Patrick R. , Dodson Stanley I.
Published: May 2010

The swimming behavior of Daphnia pulex was compared between two temperatures (5 and 25°C), with two acclimation protocols, using three‐dimensional video techniques. Our hypotheses, based on Stokes’ law and metabolic considerations, predicted large changes in swimming behavior. However, free‐swimming individuals did not follow Stokes’ law. They sank slower than predicted, having increased their sinking rate by ∼23% from 5 to 25°C. Anesthetized Daphnia followed Stokes’ law, showing an increase in sinking rate of 70% over the temperature range. The Q10 values of all swimming behaviors were between 0.91 and 1.11 (which are significantly less than Q10 values for metabolic rates) and were nearly uniform over a 20°C range. Our results also indicate that acclimation to different temperatures for 1 h is sufficient to minimize acclimation effects.
Feeding rates of macro‐ and microzooplankton on heterotrophic nanoflagellates
Authors: Jürgens Klaus , Wickham Stephen A. , Rothhaupt Karl Otto , Santer Barbara
Published: May 2010

Thirteen metazooplankton and three ciliate species were examined for their ability to prey on heterotrophic nanoflagellates (HNF). Grazing losses of two species of HNF, Bodo saltans (kinetoplastid) and Spumella sp. (chrysomonad), were estimated in batch experiments by the disappearance of HNF in the presence or absence of predators. Nearly all species examined caused mortality of HNF, but to different extents. Individual clearance rates ranged from a few µl ind.‒1 h‒1 with ciliates and rotifers to a few ml ind.‒1 h‒1 with daphnids. Weight‐specific clearance rates revealed that oligotrichous ciliates were the most efficient feeders on HNF, whereas differences among the filter‐feeding metazoans (rotifers, calanoid copepods, cladocerans) were relatively slight. Cyclopoid copepods had the lowest weight‐specific clearance rates and can be assumed to be inefficient grazers on HNF. Clearance rates of filter‐feeders increased significantly with body length. These rates resemble the allometric relationships of herbivorous zooplankton feeding on phytoplankton. Although four grazer species had higher feeding rates on the bodonid than on the chrysomonad flagellates, the overall clearance rate: body length relationship was independent of the HNF species.
Evaluation of the nitrogen isotope‐pairing method for measuring benthic denitrification: A simulation analysis
Authors: Middelburg Jack J. , Soetaert Karline , Herman Peter M. J.
Published: May 2010

The nitrogen isotope‐pairing method to measure sedimentary denitrification is evaluated by means of a general diagenetic model that describes the depth distribution of O2, NH4+, 14NO3‒, and 15NO3‒, among others. The model simulations demonstrate that isotope fractionation effects during denitrification can be neglected, but that nonuniform mixing of added 15NO3‒ with locally produced 14NO3‒ causes underestimation of in situ rates of denitrification. Enrichment of bottom water with 15NO3‒ concentrations above ambient levels not only results in enhanced rates of denitrification, but may also change in situ rates of coupled nitrification‐denitrification. However, the resulting rates usually deviate < 10% from in situ values, and the nitrogen isotope‐pairing method therefore remains a powerful technique to determine rates of denitrification in sediments. We argue that one should not partition denitrification into bottom‐water‐supported and nitrification‐coupled components. This partitioning causes confusion, is not required to understand sedimentary nitrogen cycling, and does not reflect a physically realizable situation.
Enzymatic analysis of riverine bacterioplankton production
Authors: Sinsabaugh Robert L. , Findlay Stuart , Franchini Paula , Fischer David
Published: May 2010

Bacterial production is the entry point for detrital macronutrients into aquatic food webs. Many factors affect productivity, but the heterogeneity of detrital substrates and the diversity of microbial communities confound simple relationships between carbon supply and growth. We tried to link the two by analyzing extracellular enzyme activities. Water samples were collected from three rivers and assayed for bacterial productivity and the activities of eight enzymes. Production varied among systems, peaking at 644, 170, and 68 µmol C liter‒1 d‒1 in the Ottawa (Ohio), Maumee (Ohio), and Hudson (New York) Rivers. Vmax values were generally correlated with productivity. The mean ratios of productivity per unit peptidase and esterase activity were similar among rivers, whereas carbohydrase and phosphatase ratios varied widely. The data were used to evaluate a model that relates productivity to carbon flow by using enzyme activities as indicators and assuming an optimum resource allocation relationship among C‐, N‐, and P‐acquiring enzymes. The data supported the model, but predictive power was low. Bacterial productivity generally increased with inorganic nutrient availability, but high levels of productivity at any specific eutrophic state required sources of both saccharides and amino acids.
Allometric scaling of compartmental fluxes of phosphorus in freshwater algae
Authors: Wen Yuan Hua , Vézina Alain , Peters Robert Henry
Published: May 2010

The time courses of uptake, distribution, and excretion of radioactive PO, were determined for 11 species of freshwater algae. Uptake of PO4 by algae was rapid, reaching a steady‐state asymptote within an hour and maintaining that maximum for at least 10 h. Uptake could be described as a biphasic exponential function. The rate constants for uptake decreased with cell volume raised to a power of ∼‒0.25, whereas the uptake rates per cell increased with cell size to a power of ∼0.75, suggesting that small cells were much more efficient at sequestering PO4. Excretion of PO4 by algae was fast during the first 10–20 min; thereafter, there was a slower prolonged loss of PO4 for the remaining period. A two‐compartment model could be convincingly fitted directly to the excretion time‐course data. Both rate constants and flux rates of PO4 excretion and intercompartmental exchanges showed a similar size‐dependency to those of PO4 uptake. The net uptake of PO4 by algae increased proportionately to cell volume raised to a normalized power of 0.75. The allometric compartment model yielded estimates for net PO4 uptake rates one order of magnitude higher than those determined by means of the Michaelis‐Menten model.
Visualization of seawater flow around morphologically distinct forms of the giant kelp Macrocystis integrifolia from wave‐sheltered and exposed sites
Authors: Hurd Catriona L. , Stevens Craig L. , Lava Bernard E. , Lawrence G. A. , Harrison P. J.
Published: May 2010

Our objective was to determine whether blades of Macrocystis integrifolia from a wave‐sheltered site possess morphological features that “trip” velocity boundary layers (VBL) from laminar to turbulent in conditions of low water motion, compared to blades from a wave‐exposed site. The movement of seawater around morphologically distinct blades of M. integrifolia from wave‐sheltered and exposed sites was visualized in a recirculating flow tank in which seawater flow was initially laminar at velocities up to 8 cm s−1. Turbulent VBLs were observed for both blade morphologies at free‐stream seawater velocities of 2 cm s−1, and at a Reynolds numbers of between 102 and 104, which is lower than that predicted from boundary layer theory. Flow around blades from a wave‐sheltered site was dominated by separation induced by large edge undulations. For the wave‐exposed morphology, the flow pattern was similar to that along a smooth, flat plate, but the observed thickness of the VBL was up to a factor of 2 greater than that predicted from laminar or turbulent boundary layer theory. There were no obvious differences in how structural features such as marginal spines and bulbs affected seawater flow around the different blade morphologies.