bluuebunny/crossref_metadata_2025 huggingface dataset:
The short‐term fate of fresh algal carbon in continental slope sediments
Authors: Blair Neal E. , Levin Lisa A. , DeMaster David J. , Plaia Gayle
Published: May 2010

Emplacement of a tracer mixture containing 13C‐labeled green algae on the sea floor of the continental slope offshore of Cape Hatteras, North Carolina, elicited a rapid response over 1.5 d from the dense benthic community. Certain deposit‐feeding annelids (e.g. Scalibregma inflatum and Aricidea quadrilobata) became heavily labeled with 13C as a result of ingestion of the algae. “C‐labeled organic matter was transported to a depth of at least 4–5 cm into the seabed during the 1.5‐d period, presumably as a consequence of a feeding‐associated activity. Nonlocal transport produced subsurface peaks in organic 13C at 2–3 cm. Dissolved inorganic 13C, produced by the oxidation of the labeled algae, penetrated to 10‐cm depth. The transport of highly reactive organic matter from the sediment surface at initial velocities ≥3 cm d‒1 is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations. Anaerobic processes, which are enhanced on the Cape Hatteras slope relative to adjacent areas, may be promoted by the rapid injection of reactive material into subsurface sediments. The transport, in turn, is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region.
Short‐term sedimentation pulses recorded with a fluorescence sensor and sediment traps at 9‐m depth in the Canary basin
Authors: Fischer Gerhard , Neuer Susanne , Wefer Gerold , Krause Gunther
Published: May 2010

We observed short‐term peaks in pigment fluorescence and backscattering using optical sensors combined with time‐series sediment traps at ∼900‐m depth at an oligotrophic site in the Canary Island region. These events were observed in late winter to early spring and lasted only a few hours to a few days. The events generally coincided with late winter to early spring flux maxima recorded by the traps. Surprisingly, microscopic analyses showed no evidence of sedimentation of intact phytoplankton cells during the fluorescence peaks. However, we observed well‐preserved zooplankton fecal pellets containing densely packed coccoliths and, presumably, large amounts of chlorophyll‐derived pigments.
Does flow speed also have a direct effect on growth of active suspension‐feeders: An experimental test on oysters
Authors: Lenihan Hunter S. , Peterson Charles H. , Allen Jennifer M.
Published: May 2010

The direct effects of flow velocity on growth of juvenile American oysters Crassostrea virginica (Gmelin) were tested without confounding by indirect effects of vertical mixing by measuring growth inside pipes, varying average flow over five levels (0, 0.5, 2.5, 4, and 7 cm s‒1) at each of two food concentrations. Growth increased with food concentration and increased monotonically with flow velocity over all flows tested for both food treatments. In this experiment, food concentration and flow velocity acted independently in their effects on growth, with a multiplicative term (flux) not making any significant contribution beyond the independent, additive contributions of food and flow. Thus, the apparent positive response of growth in this active suspension‐feeder to external flux of food is best interpreted as a coincidental by‐product of the action of two separate responses to the terms that comprise flux.
Trapped methane volume and potential effects on methane ebullition in a northern peatland
Authors: Fechner-Levy Elizabeth J. , Hemond Harold F.
Published: May 2010

A novel way of estimating the gas bubble volume in the floating mat sediment of a peatland was developed at Thoreau’s Bog in Concord, Massachusetts. Statistically significant relationships between the buoyancy of the floating Sphagnum mat and atmospheric pressure were observed, and these relationships were used to estimate the gas bubble volume. The mass of CH4 stored in gas bubbles is estimated to be as much as 3 times the mass of dissolved CH4, depending on the time of year. The gas bubble volume is frequently large enough to serve as a significant buffer between microbial production of CH4 and the release of CH4 to the atmosphere. Changes in atmospheric pressure, temperature, and water‐table elevation may result in modulation of the ebullitive CH4 flux. Periods of rapidly rising atmospheric pressure or equivalent pressure changes due to water‐table elevation are capable of arresting bubble volume growth, thereby halting CH4 ebullition. Periods of rapid cooling of the bog could also temporarily halt ebullition, as thermally induced contraction of bubbles and dissolution of CH4 offset bubble volume growth due to methanogenesis.
The interrelationship of copepod fecundity and mortality
Authors: Ohman Mark D. , Aksnes Dag L. , Runge Jeffrey A.
Published: May 2010

The fecundity of copepod species that carry attached eggs is commonly assessed by the egg ratio (eggs female−1), whereas the fecundity of broadcast‐spawning copepods is assessed by measures of daily per capita rates of egg production. Variability in these measures, when corrected for temperature and allometric relationships with body size of adult females, is often assumed to reflect variability in food supply in nature and to thus provide an index of food limitation of population growth and of secondary production. We show that the measured fecundity of both brooding and broadcast‐spawning copepods is affected by the mortality rate of adult females. We recognize three reproductive stages of adult female copepods: prereproductive, reproductive, and postreproductive. Mortality affects realized fecundity by shifting the relative abundance levels in these stages. Changes in mortality rates can generate substantial temporal variations in measured fecundity, even for copepods that are unlimited by ambient food supply and reproduce at physiological maximum rates. To correct for the effects of mortality on realized fecundity, precise experimental determination of the reproductive schedule of adult females is needed, along with measures of mortality rates in nature.
Modeling deep‐water renewal in Lake Baikal
Authors: Killworth Peter D. , Carmack Eddy C. , Weiss Ray F. , Matear Richard
Published: May 2010

Temperature, dissolved oxygen, nutrients, and chlorofluorocarbon‐12 data obtained from Lake Baikal are used to describe deep‐water renewal in a deep, temperate‐latitude lake. Observations are used to propose the physical mechanism governing convection and to formulate a model of deep ventilation. The key physical mechanism governing deep‐water renewal is the so‐called thermobaric instability. Because the temperature of maximum density decreases with depth, a lake can become conditionally unstable if the base of the cold mixed layer is displaced to a depth at which its temperature matches the local temperature of maximum density, thereby resulting in sinking plumes. An important consequence of this phenomenon is that deep temperate lakes such as Baikal do not completely mix twice yearly; instead, deep ventilation is episodic. A two‐dimensional model of a wind‐ and buoyancy‐driven lake shows many strong mixing events and a fairly realistic seasonal cycle, indicating that the hypothesis is physically realizable. A filling‐box model is used to deduce the annually averaged fluxes necessary to produce a steady vertical distribution of tracers as observed. Good fits are obtained to oxygen and chlorofluorocarbon distributions by this model.
Organic matter accumulation in sediments of hypersaline Mono Lake during a period of changing salinity
Authors: Jellison Robert , Anderson Robert F. , Melack John M. , Heil Darla
Published: May 2010

Finely laminated sediments of Mono Lake provide a detailed paleolimnological record of organic matter accumulation during a period of large fluctuations in salinity that resulted from climatic variation and water diversions. In sedimentary profiles representing the last 170 yr, organic carbon content of the sediments varied from 6.6 to 16.1%. The accumulation rate of organic carbon at a sedimentation rate of 0.7 cm yr−11 varied from 76 to 164 g C m−2 yr−1. The most notable change was a gradual increase in 5‐yr mean accumulation rate from 87 to 153 g C m−2 yr−1 as salinity increased from ~48 to 97 g liter−1 during the recent period of water diversions (1941–1982). Although the correlation between organic matter accumulation and salinity during the recent period may be due in part to the slow decay of organic matter under hypersaline conditions, a positive correlation between accumulation rates and estimated lake salinities at time of burial exists throughout the 170‐yr record.
Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket
Authors: Jansson Mats , Blomqvist Peter , Jonsson Anders , BergstrÖm Ann‐Kristin
Published: May 2010

Enrichment experiments with P and N were conducted in humic Lake Örträsket in northern Sweden. The composition of the microplankton community showed a dominance by bacterioplankton, followed by mixotrophic and potentially mixotrophic phytoplankton, heterotrophic nanoflagellates, and autotrophic phytoplankton. Bacterioplankton was P limited for most of the ice‐free period, and phytoplankton biomass and primary production mostly increased after enrichment with N, but not with P. The dominant group of phytoplankton, the mixotrophic flagellates, was stimulated by N but not by P, while obligate autotrophic species were stimulated only by P+N. It is suggested that N limitation in mixotrophic species is induced by grazing of P‐rich bacteria. The results suggest that primary productivity in humic lakes can be limited by N and indicate the importance of phagocytosis as a means of nutrition in phytoplankton. A link is suggested to exist in humic lakes whereby heterotrophic bacterioplankton, which use humic compounds as their principal energy source, can transfer energy and nutrients to potentially autotrophic organisms, with subsequent utilization by other components of the food web.
Measuring regeneration of dissolved phosphorus in planktonic communities
Authors: Hudson Jeff J. , Taylor William D.
Published: May 2010

We developed a technique to measure the release of dissolved phosphorus from entire or size‐fractionated plankton communities. The method involves radio‐labeling the plankton with phosphate and then competitively blocking the reassimilation of released radiolabel with 31PO4. The increase in dissolved radioactivity is then assayed. The initial ratio of 31P to radioactivity and the increase in dissolved radioactivity are used to estimate the release of dissolved phosphorus. Total (unfractionated) regeneration rates from two oligotrophic lakes had a range of 15–205 ng P liter−1 h−1. Regeneration by the <40‐µm fraction accounted for an average of 77% of the total. The results indicate that microorganisms (protists and bacteria) are the major regenerators of dissolved phosphorus in the plankton of these lakes.
Effect of food availability on the response of planktonic rotifers to a toxic strain of the cyanobacterium Anabaena flos‐aquae
Authors: Gilbert John J.
Published: May 2010

The ability of food concentration to modify the response of zooplankton to toxic cyanobacteria was examined using chronic (lifetime) toxicity tests with two rotifers, Brachionus calyciflorus and Synchaeta pectinata, and a strain of Anabaena flos‐aquae producing the alkaloid neurotoxin, anatoxin‐a. In a clone of S. pectinata, the cyanobacterium decreased both life span and lifetime fecundity to a much greater extent when the availability of food (Cryptomonas erosa) was low. Fecundity was the most sensitive parameter. In one experiment, the cyanobacterium (2.5 µg ml−1) decreased fecundity by 29% at the highest food concentration (2 × 104 cells ml−1) but by 90% at the lowest one (3 × 103 cells ml−1). In two clones of B. calyciflorus, A. flos‐aquae decreased lifespan, fecundity, and population growth rate, but there was only a tendency in one of the clones for the inhibition to be greater at lower food concentrations. The degree to which toxic cyanobacteria affect the population dynamics of susceptible zooplankton taxa in natural communities may be greatly influenced by modifying environmental factors such as food availability and temperature, especially if these factors act additively or synergistically.
Bacterial dynamics in the upper St. Lawrence estuary
Authors: Painchaud Jean , Lefaivre Denis , Therriault Jean‐Claude , Legendre Louis
Published: May 2010

The distribution of free bacteria in the St. Lawrence estuary was interpreted by means of bacterial fluxes and hydrodynamic residence times, derived from a circulation model, and growth and grazing rates, obtained from cultures. Bacterial abundances decreased exponentially along the salinity gradient, from 3.9 × 109 liter‒1 in freshwater to 0.5 × 109 liter‒1 at salinity >20. The rates of growth (0.02–0.08 h‒1) and grazing (0.01–0.09 h‒1) were strongly correlated (r = 0.82), which suggests that bacteria tended toward a state of trophodynamic equilibrium (growth ≈ grazing). However, negative bacterial fluxes obtained from the model imply that the estuary is a sink for bacteria. Results from the circulation model and the cultures show that physical processes are important controlling factors of the distribution of bacteria and point to predation as the process causing bacterial losses in the estuary. Calculations show that small imbalances between growth and grazing can account for the observed distribution. Rates of dispersion and growth and grazing are of the same order of magnitude, which shows that biological processes are nevertheless significant relative to physical processes. Although the distribution of free bacteria appears largely under hydrodynamic control, the bacterial community is characterized by significant biological rates and can experience large transformations during estuarine transit.
The relationship of solar‐stimulated natural fluorescence and primary productivity in Mexican Pacific waters
Authors: Garcia‐Mendoza Ernesto , Maske Helmut
Published: May 2010

Solar‐stimulated natural chlorophyll a fluorescence measured by upwelling radiance in the red spectral band could be a fast and noninvasive method to estimate primary production in aquatic environments if the relationship of primary production to natural fluorescence can be described as a function of easily measured environmental variables. We compared data of natural fluorescence and primary production (14C incubation for 2 h) from the California Current and the Gulf of California. The data confirm that the quantum yield ratio of fluorescence to primary production (ϕc : ϕf) is a function of in situ irradiance, but not of nutrient concentration or temperature, as has been reported in the literature. Published data from the subtropics and tropics and our data yield empirical constants that define the irradiance function of the quantum yield ratio, but variability results from ambiguity of the constant determination caused by high variance of the data. Data from the Antarctic are significantly different from the low latitude data. Below a photosynthetic rate of 300 nmol C m‒3 s‒1, our natural fluorescence data are useful as a proxy of primary production with a correlation coefficient, r2, of 0.85. Of the unexplained variance (15%), a major portion is due to the C.V. of the primary production method (9.2%). The r2 value of predicted primary production is similar to other published results, which suggests that without further information about the physiology of the phytoplankton it will be difficult to improve the quality of the primary production estimate.
Organic carbon oxidation and suppression of methane production by microbial Fe(III) oxide reduction in vegetated and unvegetated freshwater wetland sediments
Authors: Roden Eric E. , Wetzel Robert G.
Published: May 2010

High concentrations (20–75 µmol cm‒3) of amorphous Fe(III) oxide were observed in unvegetated surface and Juncus effusus rhizosphere sediments of a freshwater wetland in the southeastern United States. Incubation experiments demonstrated that microbial Fe(III) oxide reduction suppressed sulfate reduction and methanogenesis in surface sediments and mediated ≥40% of depth‐integrated (0–10 cm) unvegetated sediment carbon metabolism, compared to ≤10% for sulfate reduction. In situ CO2 and CH4 flux measurements verified that nonmethanogenic pathways accounted for ∼50% of unvegetated sediment carbon metabolism. Lower (∼10‐fold) rates of dark/anaerobic CH4 flux from experimental vegetated cores relative to unvegetated controls suggested that methanogenesis was inhibited in the Juncus rhizosphere, in which active Fe(III) oxide reduction was indicated by the presence of low but readily detectable levels of dissolved and solid‐phase Fe(II). Fe(III) oxide reduction accounted for 65% of total carbon metabolism in rhizosphere sediment incubations, compared to 22% for methanogenesis. In contrast, methanogenesis dominated carbon metabolism (72% of total) in experimental unvegetated sediment cores. The high Fe(III) oxide concentrations and reduction rates observed in unvegetated surface and Juncus rhizosphere sediments were perpetuated by rapid Fe(III) regeneration via oxidation of Fe(II) compounds coupled to O2 input from the overlying water and plant roots, respectively. The results indicate that Fe(III) oxide reduction could mediate a considerable amount of organic carbon oxidation and significantly suppress CH4 production in freshwater wetlands situated within globally extensive iron‐rich tropical and subtropical soil regimes.
The fate of marine autotrophic production
Authors: Duarte Carlos M. , Cebrián Just
Published: May 2010

The fate of photosynthetic carbon in marine ecosystems dominated by different types of primary producers was examined by compiling published reports on herbivory, autotrophic respiration, decomposition, carbon storage, and export rates as fractions of net primary production (NPP) in ecosystems dominated by different types of autotrophs (i.e. oceanic and coastal phytoplankton, microphytobenthos, coral reef algae, macroalgae, seagrasses, marsh plants, and mangroves). A large fraction (>40%) of the NPP of marine ecosystems is decomposed within the system, except for microphytobenthos (decomposition, ∼25% of NPP). Herbivory tends to be highest for microalgae (planktonic and benthic, >40% of NPP) and macroalgae (33.6 ±4.9% of NPP) and is somewhat less for higher plants. Microphytobenthos export on average a much higher proportion of their NPP than do other microalgal communities, whereas marine macrophytes, except marsh plants, export a substantial proportion (24.3–43.5% on average) of their NPP. fraction of NPP stored in sediments is 4‐fold greater for higher plants (∼10–17% of NPP) than for algae (0.4–6% of NPP). On average, ∼90% of the phytoplankton NPP is used to support local heterotrophic metabolism (i.e. grazed or decomposed). This fraction is even higher in oceanic communities. Mangrove forests, and to a lesser extent seagrass meadows and macroalgal beds, produce organic carbon well in excess of the ecosystem requirements, with excess photosynthetic carbon (i.e. export rate plus storage) in these ecosystem representing ∼40% of NPP. Extrapolation of these results to the global ocean identifies marine angiosperms, which only contribute 4% of total ocean NPP, as major contributors of the NPP stored (30% of total ocean carbon storage) and subsequently buried in marine sediments. Consideration of burial of NPP from marine angiosperms should lead to estimates of total burial of marine NPP that exceed current estimates by 15–50%.
Standing stock and dynamics of picophytoplankton in the Thau Lagoon (northwest Mediterranean coast)
Authors: Vaquer André , Troussellier Marc , Courties Claude , Bibent Bertrand
Published: May 2010

Eucaryotic picophytoplankton (PEUC), picocyanobacteria, and larger phytoplanktonic cells from the Thau Lagoon (northwest Mediterranean coast) were numbered by flow cytometry from November 1991 to February 1994. PEUC cells dominated the phytoplanktonic assemblage and exhibited seasonal dynamics. Monthly mean abundances of larger phytoplanktonic cell and PEUC were significantly correlated with temperature and solar irradiance values, with the highest correlations having been obtained for PEUC abundances. The mean abundance of total picophytoplankton (3.5 × 104 cells ml‒1) was among the highest recorded in marine waters. The dominance of picophytoplankton over larger phytoplanktonic cells (average abundance, 5 × 103 cells ml‒1) in the nutrient‐rich waters of the lagoon was related to grazing from large‐scale shellfish breeding (oyster’s ≈35,000 t), which seems to act preferentially on the largest cells. Several hypotheses, including the potential selective effect of copper, were proposed to explain the dominance of the PEUC form (average abundance, 3.4 × 104 cells ml‒1).
Photosynthetic rates derived from satellite‐based chlorophyll concentration
Authors: Behrenfeld Michael J. , Falkowski Paul G.
Published: May 2010

We assembled a dataset of 14C‐based productivity measurements to understand the critical variables required for accurate assessment of daily depth‐integrated phytoplankton carbon fixation (PP(PPeu)u) from measurements of sea surface pigment concentrations (Csat)(Csat). From this dataset, we developed a light‐dependent, depth‐resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (Pz)z) and those that control the optimal assimilation efficiency of the productivity profile (P(PBopt). The VGPM accounted for 79% of the observed variability in Pz and 86% of the variability in PPeu by using measured values of PBopt. Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in Pbopt. We developed a temperature‐dependent Pbopt model that was used in conjunction with monthly climatological images of Csat sea surface temperature, and cloud‐corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr‒1. The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing Pbopt model development on temporal and spatial, rather than the vertical, variability.
Chemical composition of biodegradable dissolved organic matter in streamwater
Authors: Volk Christian J. , Volk Catherine B. , Kaplan Louis A.
Published: May 2010

Plug‐flow biofilm reactors colonized by microorganisms in streamwater were used to measure the concentration and composition of biodegradable dissolved organic C (BDOC) in White Clay Creek. During the 4‐month study period, DOC ranged from 0.8 to 10.4 mg C liter‒1 and was, on average, composed of 75% humic substances, 13% carbohydrates, 2% amino acids, and 18% >100 kDa. The carbohydrates were predominantly polysaccharides, nearly all amino acids were present in the combined form, and most carbohydrates and amino acids were humic bound. BDOC ranged from 0.2 to 2.9 mg C liter‒1, averaged 25% of the DOC, and was composed of 75% humic substances, 30% carbohydrates, 4% amino acids, and 39% DOC >100 kDa. The carbohydrate portion of the BDOC was primarily polysaccharide or humic bound. Similarly, the amino acid portion of the BDOC was overwhelmingly present in the combined form and primarily humic bound. Glycine and aspartic acid were the dominant amino acids in White Clay Creek DOC and in the BDOC pool. Our data broaden the perspective on substrates important to microbial metabolism and energy flow in streams and provide the first direct evidence that humic substances, although largely refractory, are an important component of streamwater BDOC.
Rocky intertidal oceanography: An association between community structure and nearshore phytoplankton concentration
Authors: Menge Bruce A. , Daley Bryon A. , Wheeler Patricia A. , Strub P. Ted
Published: May 2010

On Oregon coastal rocky shores, filter‐feeders were relatively abundant and macrophytes were relatively scarce at Strawberry Hill, whereas opposite abundance patterns occurred at Boiler Bay. To determine whether nearshore oceanographic differences were associated with these patterns, we made shore‐based measurements of nutrient and Chl a concentrations. We used a three‐level nested design to identify ecologically appropriate sampling scales: “site” (10s of km), “bench” nested within site (100s of m), and “location” nested within bench (10s of m). Nutrients varied inconsistently but Chl a was consistently higher at Strawberry Hill. For Chl a, site explained ∼70% of the variance, whereas bench and location explained <20%. For nutrients, site and bench explained most of the variance, but neither was consistently more important. The data tentatively suggest that nutrient levels are weakly related to the between‐site ecological differences. In addition to the between‐site differences, Chl a changed seasonally, with maximum levels in summer. For nutrients, temporal changes were more complex, with highest levels tending to occur in late summer and autumn. No nutrient, however, was scarce enough at either site to limit phytoplankton growth, with the possible exception of nitrate in June. These results were consistent with the hypothesis that nearshore phytoplankton standing stock, a bottom‐up factor, could underlie differences in rocky intertidal community structure.
Characterization of the Ebre and Rhone estuaries: A basis for defining and classifying salt‐wedge estuaries
Authors: Ibaňez Carles , Pont Didier , Prat Narcís
Published: May 2010

River discharge is the main factor controlling the hydrologic dynamics of the Ebre and Rhone estuaries. The topography of the estuary bed also influences the extent, advance, and retreat of the salt wedge. Tides have little influence because of the low tidal range. Mean annual river discharge is close to the critical value determining the formation and breakup of the salt wedge. This is related to the fact that river flow controls the sedimentary dynamics of the estuary, including the sandbar at the mouth. When discharge is lower than the mean annual river flow, the salt wedge is established and the estuary becomes a depositional environment. With higher flows the salt wedge is washed away and erosive conditions prevail. On the basis of the conditions in which the salt wedge is formed, two types of highly stratified estuaries can be identified. In the first one, a salt‐wedge regime is established during low river flows, whereas during high flows the wedge is washed away and the estuary becomes a river. This circulation pattern corresponds to the “salt‐wedge estuary” or type 4 of the Hansen‐Rattray classification, typical of river‐dominated estuaries in microtidal seas. In the second one, a salt wedge is established during high river flows, whereas a partially mixed estuary occurs during low flows. This pattern corresponds to types 3b and 2b of the Hansen‐Rattray classification.
Acoustic and in situ measurements of freshwater amphipods (Jesogammarus annandalei) in Lake Biwa. Japan
Authors: Trevorrow Mark V. , Tanaka Yuji
Published: May 2010

During a 23‐d study of Lake Biwa, Japan (starting 23 August 1993), multifrequency inverted echo‐sounder measurements of nocturnal scattering layers in the meta‐ and epilimnion were performed at a single location. Direct samples from within this scattering layer indicated that it was composed of Jesogammarus annandalei (Crustacea: Amphipoda), with mean adult length of 8.3 mm and population densities from 4 to 50 per m3. Estimates of the scattering cross‐section for individual amphipods were extracted from echo‐amplitude probability distributions combined with volume scattering strength from a 198‐kHz sonar. Total scattering cross‐sections for adult amphipods at 88, 118, and 198 kHz were estimated as 4.3±0.9 × 10−8 m2, 8.7±1.2 × 10−8 m2, and 2.8±0.5 × 10−7 m2. These cross‐section measurements were found to be consistent with a fluid cylinder acoustic scattering model with a 1.2‐mm radius and a 9.6‐mm length. The acoustically derived population densities, sizes, and length‐to‐radius ratio were consistent with in situ amphipod samples. The amphipods exhibited a clear nocturnal migration into the lower thermocline, concentrating at depths of 15–25 m beginning after sunset (near 1830 hours local time) each day. Population densities (10‐min averaged) showed maxima of 10–30 per m3 near 2000 hours, with densities decreasing rapidly toward midnight and disappearing by approximately 0430 hours.
Whiting events: Biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton
Authors: Schultze-Lam Susanne , Schultze-Lam Susanne , Beveridge Terrance J. , Des Marais David J.
Published: May 2010

An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by ∼4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The 813C values of the dissolved inorganic C range seasonally from −9.5‰ in winter to −6.2‰ in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier δ13C value (>4%o) than does the dissolved inorganic C of the lake water owing to the cells’ preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron‐sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.
Geochemical mass balances of major elements in Lake Baikal
Authors: Callender Edward , Granina Liba
Published: May 2010

Major element mass balances for Lake Baikal are calculated with mostly previously published data for soluble fluxes and new, unpublished data for riverine suspended particulate matter chemistry. Physical transport seems to be the most important riverine process. The elements Ca, Mg, and Na seem to be very mobile in the weathering mantle and K and Si seem to be relatively mobile. A comparison of elemental input‐output budgets and mass accumulation rates (MAR) in bottom sediments shows that most major elements, except Ca, Si, and Mn, have comparable riverine particulate matter fluxes and MARs. The addition of wet atmospheric deposition fluxes results in an excess of Ca, Mg, and Na entering the lake. The additive effect of these excess inputs during a 40‐year period amounts to undetectable concentration increases in the water column. If erosion of weathered bedrock is the source of most dissolved and all particulate matter transported to the lake, theoretical elemental fluxes can be calculated with Al as the conservative element. Flux ratios (observed/theoretical) range from 0.7 to 2.2, but most fall within the acceptable range of 0.7–1.5. Major rock‐forming elements are carried by rivers as weathering products and there are minimal biogeochemical processes that modify these inputs as suspended particulate matter accumulates in the bottom sediments of the lake.
Trophic effects of sponge feeding within Lake Baikal's littoral zone. 2. Sponge abundance, diet, feeding efficiency, and carbon flux
Authors: Pile Adele J. , Patterson Mark R. , Savarese Michael , Chernykh Valeri I. , Fialkov Vladimir A.
Published: May 2010

Endemic freshwater demosponges in the littoral zone of Lake Baikal, Russia, dominate the benthic biomass, covering 44% of the benthos. We measured in situ sponge abundance and grazing and calculated sponge‐mediated fluxes of picoplankton (plankton <2 µm) for two common species, Baikalospongia intermedia and Baikalospongia bacillifera. By means of dual‐beam flow cytometry, we found retention efficiencies ranging from 58 to 99% for four types of picoplankton: heterotrophic bacteria, Synechococcus‐type cyanobacteria, autotrophic picoplankton with one chloroplast, and autotrophic picoplankton with two chloroplasts. By using a general model for organism‐mediated fluxes, we conservatively estimate that through active suspension feeding, sponges are a sink for 1.97 g C d−1 m−2, mostly from procaryotic cell types. Furthermore, grazing by these extensive sponge communities can create a layer of picoplankton‐depleted water overlying the benthic community in this unique lake.
Present‐day organic matter sedimentation on the NW Mediterranean margin: Importance of off‐shelf export
Authors: Buscail Roselyne , Germain Claire
Published: May 2010

We present an overview of the organic matter distribution in surface sediments sampled on the Gulf of Lions margin from 600 to 2,300 m depth. Surface deposits are characterized by a “fluff” layer a few millimeters to a few centimeters thick. In the underlying fine‐grained sediments, the carbonate content is high (30% DW), and the organic carbon content varies from 0.3 to 1% (DW). The highest organic carbon contents are along the axes and on the sides of the canyons (0.6–1%) and constitute midslope organic depocenters. The organic carbon content at 1,000 m depth depends on the width of the adjacent shelf. The lowest organic carbon value corresponds to the slightest declivity and, consequently, to a longer advective residence time.

In the settling sides of the axial channel of the canyons, organic carbon concentrations decrease, although sedimentation rate is constant from the upper to the lower part of the slope. This results from an increasing residence time in the water column due to the advective transfer of organic material from epicontinental zone to upper and lower slope. In the lower axes and open slopes, increasing sedimentation rates, due to sedimentary reworking and turbidity currents, dilute organic carbon with mineral grains.
The chemical budget of Lake Baikal: A review
Authors: Granina Liba
Published: May 2010

Over the past 30 yr several different estimates for the water and chemical budget of Lake Baikal have been produced. These publications are of variable quality and sometimes contradictory. However, a review of the studies indicates that it is possible to construct satisfactory estimates for a complete chemical budget of the lake.

The absence of comparable methods for the collection of suspended particulate matter has resulted in uncertain values for the suspended‐sediment budget. Data on the chemical composition of riverine suspended particulate matter are also nonexistent. As a result, none of the existing budget estimates for individual chemical elements includes this important term.
Calculating irradiance penetration into water bodies from the measured beam attenuation coefficient
Authors: Arst Helgi , Mäekivi Sirje , Lukk Toomas , Herlevi Antti
Published: May 2010

The relationships between the numerical values and spectral distributions of the downward irradiance attenuation coefficient, Kd, λ, and the beam attenuation coefficient, cλ, were investigated. Using experimental data for the Baltic Sea with Secchi disk transparency of 1.5–6 m, we obtained formulae allowing us to determine the spectra of the scattering coefficient in the range of 400–700 nm from data for the beam attenuation coefficient at 580–nm wavelength. Formulae connecting the values of the downward irradiance attenuation coefficient, the absorption coefficient, and the scattering coefficient for different illumination conditions were then used to determine the spectra of Kd, λ from measured cλ spectra. A preliminary test of this method was carried out based on experimental data from three Estonian and two Finnish lakes. The correlation coefficient between the measured and the computed (through cλ) values of Kd, λ is 0.97 and standard deviation is 0.23 m−1. This method may be useful in conditions where in situ measuring of the underwater solar radiation spectra cannot be performed because of weather conditions. Because characterization of the underwater radiation field is often a complicated and expensive procedure, our numerical method (which needs only water samples and the recording of the spectra of incident irradiance) may be useful for estimating spatial‐temporal variations of the underwater solar radiation.
Dissolved carbohydrates in streamwater determined by HPLC and pulsed amperometric detection
Authors: Gremm Thomas J. , Kaplan Louis A.
Published: May 2010

Dissolved total saccharides (DTS) and dissolved free monosaccharides (DFMS) in streamwater were determined by high‐performance liquid chromatography with pulsed amperometric detection (HPLC‐PAD). HPLC identification was verified with gas chromatography/mass spectrometry measurements. The method for DTS was improved by using a column with an anion exchange capacity of 4,500 µeq and a mobile phase of 350 mM NaOH. The detection limits for individual monosaccharides ranged from 2 to 14 nM. The average recovery for monosaccharide standards was 82% after hydrolysis, and 75% of the monosaccharides in streamwater hydrolysates were recovered following a desalting procedure. Hydrolysis of model substances showed recoveries of monosaccharides between 78 and 98%. The C.V. for a hydrolyzed stream sample was 15% for the DTS. Stream samples stored at room temperature after filtration and acidification to pH 1.1 were stable for at least 23 d. Concentrations of DTS in White Clay Creek, including sugar alcohols and amino sugars, ranged from 0.64 to 12.70 µM and accounted for 2.9–12.1% of the dissolved organic carbon pool. Neutral sugars dominated the DTS pool, and glucose and galactose were the most abundant molecules. Concentrations of DFMS ranged from 0.05 to 0.38 µM and accounted for 0.06–0.33% of the dissolved organic carbon pool.
Accumulation of degradable DOC in surface waters: Is it caused by a malfunctioning microbialloop?
Authors: Thingstad T. Frede , HagstrÖm Åke , Rassoulzadegan Fereidoun
Published: May 2010

Recent literature indicates that dissolved organic carbon (DOC) may accumulate in productive surface waters. Such accumulation will allow export of DOC to the aphotic zone by diffusion and downwelling. As an alternative to models based on low degradability, we here propose a mechanism where bacterial carbon consumption is restricted due to food web mechanisms controlling both growth and biomass of the bacteria: growth rate is kept low by bacteria‐phytoplankton competition for mineral nutrients, and biomass is kept low by bacterial predators. With such a mechanism, otherwise degradable material may accumulate and become subject both to chemical transformation and vertical transport. The steady‐states of a model describing the interactions between heterotrophic bacteria, phytoplankton, and bacterivorous protozoa is used to explore how the balance between DOC production and consumption shifts along a gradient from oligotrophy to eutrophy.
Cycling of iron, manganese, and phosphate in a meromictic lake
Authors: Hongve Dag
Published: May 2010

Lake Nordbytjernet (Southeast Norway) had up to 40 mg liter−1 dissolved iron and 67 mg liter−1 dissolved manganese in a stagnant layer. The ratio between iron and manganese loading was around 3:1, while the inventory of manganese was six times higher than for iron. High concentrations of dissolved iron occurred solely under strictly anoxic conditions, while dissolved manganese was unaffected by intrusion of oxygen during the autumnal partial circulation. Mixed potentials caused by oxidation of ferrous iron and reduction of manganic oxide or O2 controlled the redox potential values, while dissolved manganese appeared to have no influence. The following main processes controlled the sedimentation rates: fluvial supply of suspended material, precipitation of ferric hydroxide and manganese oxide from the water column, and plankton production. Sorption to ferric hydroxide in the oxic zone and reductive desorption in the anoxic zone controlled the deep water stratification of phosphorus, dissolved organic carbon, and some major cations. No similar effects were seen for manganese sedimentation. The iron sedimentation rate was enhanced in the anoxic zone due to redox coupling of iron oxidation and manganese reduction. Phosphorus was depleted in the anoxic zone during periods of substantial ferric hydroxide sedimentation. Sedimentation of manganese under anoxic conditions seemed to be governed by precipitation of carbonate and phosphate. Residence times in the lake were 0.2 yr for iron and phosphorous vs. 3.3 yr for manganese and 1.4 yr for water.
Noeffects of ambient UV radiation detected in periphyton and grazers
Authors: Hill Walter R. , Dimick Sarah M. , McNamara Amy E. , Branson Cheryl A.
Published: May 2010

The vulnerability of periphyton and grazers to current and future levels of ultraviolet radiation (UV) has important ramifications for energy flow in shallow waters. We reduced ambient UV levels in a Tennessee stream with UV‐opaque Plexiglas suspended over the stream and compared periphyton under these Plexiglas filters to periphyton under UV‐transparent polyvinylidene film. The experiments were performed three times, from autumn 1993 to summer 1994. The last experiment included a treatment with reduced snail densities, so potential interactions between grazing and UV could be identified. Periphyton biomass and photosynthesis were not significantly affected by reduced UV in any of the three experiments, indicating ambient UV effects were minor, at most. Grazing by snails (Elimia clavaeformis) tightly controlled periphyton biomass and primary production in all three experiments. Snail densities were not significantly affected by ambient UV, eliminating the possibility of a solar cascade of indirect effects. Snails may be less vulnerable to UV than are soft‐bodied grazers such as chironomids, and periphyton in southern U.S. streams may be adapted to naturally high levels of UV. The results of this study clearly imply that previous reports of UV impacts on periphyton and grazers cannot be generalized.
HFC-23 (CHF3) emission trend response to HCFC-22 (CHClF2) production and recent HFC-23 emission abatement measures
Authors: Miller B. R. , Rigby M. , Kuijpers L. J. M. , Krummel P. B. , Steele L. P. , Leist M. , Fraser P. J. , McCulloch A. , Harth C. , Salameh P. , Mühle J. , Weiss R. F. , Prinn R. G. , Wang R. H. J. , O'Doherty S. , Greally B. R. , Simmonds P. G.
Published: May 2010

Abstract. HFC-23 (also known as CHF3, fluoroform or trifluoromethane) is a potent greenhouse gas (GHG), with a global warming potential (GWP) of 14 800 for a 100-year time horizon. It is an unavoidable by-product of HCFC-22 (CHClF2, chlorodifluoromethane) production. HCFC-22, an ozone depleting substance (ODS), is used extensively in commercial refrigeration and air conditioning, in the extruded polystyrene (XPS) foam industries (dispersive applications) and also as a feedstock in fluoropolymer manufacture (a non-dispersive use). Aside from small markets in specialty uses, HFC-23 has historically been considered a waste gas that was, and often still is, simply vented to the atmosphere. Efforts have been made in the past two decades to reduce HFC-23 emissions, including destruction (incineration) in facilities in developing countries under the United Nations Framework Convention on Climate Change's (UNFCCC) Clean Development Mechanism (CDM), and by process optimization and/or voluntary incineration by most producers in developed countries. We present observations of lower-tropospheric mole fractions of HFC-23 measured by "Medusa" GC/MSD instruments from ambient air sampled in situ at the Advanced Global Atmospheric Gases Experiment (AGAGE) network of five remote sites and in Cape Grim air archive (CGAA) samples (1978–2009) from Tasmania, Australia. These observations are used with the AGAGE 2-D atmospheric 12-box model and an inverse method to produce model mole fractions and a "top-down" HFC-23 emission history. The model 2009 annual mean global lower-tropospheric background abundance is 22.8 (±0.2) pmol mol−1. The derived HFC-23 emissions show a "plateau" during 1997–2003, followed by a rapid ~50% increase to a peak of 15.0 (+1.3/−1.2) Gg/yr in 2006. Following this peak, emissions of HFC-23 declined rapidly to 8.6 (+0.9/−1.0) Gg/yr in 2009, the lowest annual emission of the past 15 years. We derive a 1990–2008 "bottom-up" HFC-23 emission history using data from the United Nations Environment Programme and the UNFCCC. Comparison with the top-down HFC-23 emission history shows agreement within the stated uncertainties. In the 1990s, HFC-23 emissions from developed countries dominated all other sources, then began to decline and eventually became fairly constant during 2003–2008. From the beginning of that plateau, the major factor determining the annual dynamics of global HFC-23 emissions became the historical rise of HCFC-22 production for dispersive uses in developing countries to a peak in 2007. Thereafter in 2007–2009, incineration through CDM projects became a larger factor, reducing global HFC-23 emissions despite rapidly rising HCFC-22 feedstock production in developing countries.
Highly time-resolved chemical characterization of atmospheric submicron particles during 2008 Beijing Olympic Games using an Aerodyne High-Resolution Aerosol Mass Spectrometer
Authors: Huang X.-F. , He L.-Y. , Hu M. , Canagaratna M. R. , Sun Y. , Zhang Q. , Zhu T. , Xue L. , Zeng L.-W. , Liu X.-G. , Zhang Y.-H. , Jayne J. T. , Ng N. L. , Worsnop D. R.
Published: May 2010

Abstract. As part of Campaigns of Air Quality Research in Beijing and Surrounding Region–2008 (CAREBeijing-2008), an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was deployed in urban Beijing to characterize submicron aerosol particles during the time of 2008 Beijing Olympic Games and Paralytic Games (24 July to 20 September 2008). The campaign mean PM1 mass concentration was 63.1±39.8 μg m−3; the mean composition consisted of organics (37.9%), sulfate (26.7%), ammonium (15.9%), nitrate (15.8%), black carbon (3.1%), and chloride (0.87%). The average size distributions of the species (except BC) were all dominated by an accumulation mode peaking at about 600 nm in vacuum aerodynamic diameter, and organics was characterized by an additional smaller mode extending below 100 nm. Positive Matrix Factorization (PMF) analysis of the high resolution organic mass spectral dataset differentiated the organic aerosol into four components, i.e., hydrocarbon-like (HOA), cooking-related (COA), and two oxygenated organic aerosols (OOA-1 and OOA-2), which on average accounted for 18.1, 24.4, 33.7 and 23.7% of the total organic mass, respectively. The HOA was identified to be closely associated with primary combustion sources, while the COA mass spectrum showed high similarity to that measured from cooking aerosol emissions. The OOA components correspond to aged secondary organic aerosol. Although the two OOA components have similar elemental (O/C, H/C) compositions, they display differences in mass spectra and time series which appear to correlate with the different source regions sampled during the campaign. Back trajectory clustering analysis indicated that the southerly air flows were associated with the highest PM1 pollution during the campaign. This result is similar to observations made in the summer of 2006, although the average PM1 concentration level for the southerly air flows is 31% lower than for the 2008 campaign. Aerosol particles in southern airmasses were especially rich in inorganic and oxidized organic species. Aerosol particles in northern airmasses contained a large fraction of primary HOA and COA species, probably due to stronger influences from local emissions. The lowest concentration levels for all major species were obtained during the Olympic game days (8–24 August 2008), possibly due to the effects of both strict emission controls and favorable meteorological conditions.