bluuebunny/crossref_metadata_2025 huggingface dataset:
Methane input and evasion in a hardwood forest stream: Effects of subsurface flow from shallow and deep pathway
Authors: Jones Jeremy B. , Mulholland Patrick J.
Published: May 2010

Streams are typically supersaturated and emit methane to the atmosphere. Much of this gas appears to be imported from groundwater and riparian zones, where anoxia and methane production are common. We investigated how methane evasion and the concentration in groundwater discharge varied between five stream sections with differing rates of groundwater discharge along the east fork of Walker Branch in eastern Tennessee. Evasion and groundwater concentration were determined from measurements of methane in surface water in conjunction with coinjection of conservative solute and volatile gas tracers. Methane in surface water was supersaturated, varying from 0.67 to 1.56 µg CH4 liter−1, which translates to concentrations 17.6–41.4 times greater than those at atmospheric equilibrium. Methane evasion rates ranged from 0.4 to 13.2 mg CH4 m−2 d−1. Differences in methane concentration and evasion were related to variation in subsurface discharge and concentration in groundwater. All study sections gained flow, although the rate of subsurface discharge into the second study section (section 2) was particularly low. Furthermore, the specific conductance of groundwater flowing into section 2 averaged only 82.3 µS cm−1, compared with 110–125 µS cm−1 in the other study sections, indicating that groundwater discharge was derived from riparian soils as opposed to deeper flow from fractured bedrock. The mean concentration of 549.2 µg CH4 liter−1 in subsurface water flowing into section 2 was notably greater than in the other sections, where average groundwater concentration ranged from 158.9 to 376.2 µg CH4 liter−1. Our results suggest that subsurface flow from riparian soils appears to be the major source of methane to streams, although deeper bedrock flow also supplies methane at a lower concentration to surface waters.
Oxygen and hydrogen isotope systematics of Lake Baikal, Siberia: Implications for paleoclimate studies
Authors: Seal Robert R. , Shanks Wayne C.
Published: May 2010

We interpret oxygen and hydrogen isotope data for water samples from Lake Baikal, Siberia, its tributaries and other local rivers, and local precipitation in terms of the known water budget for the modern lake in order to gain insight into past limnological and climatic processes that influenced the lake. Lake Baikal is remarkably uniform in its isotopic composition δ18O = −15.8 ± 0.2‰; δD = −123 ± 2‰) and lies slightly to the right of the global meteoric water line, which suggests significant evaporation. Water is supplied to the lake by over 300 rivers and streams. The oxygen isotope values (δ18O) of the rivers in the Baikal catchment range from −13.4 to −21.2‰. The hydrogen isotope values (δD) for the same area range from −103 to −156‰. Both these ranges generally conform to the global meteoric water line. The weighted average isotopic composition of input to the lake (rivers plus precipitation) is −15.2‰ for δ18O and −116‰ for δD, values higher than those of the modern lake. Therefore, the isotopic composition of the modem lake cannot be related to the modern input through simple evaporation. Instead, modeling of the isotopic mass balance of the lake suggests that inputs (precipitation and influx from rivers) and outputs (evaporation and outflow) are not at a steady‐state equilibrium under current climate conditions. We found previous input to the lake had lower δ18O and δD values than modern input, which reflects cooler climates in the past compared with modern conditions. Under constant climate conditions, steady‐state conditions are not expected to be reached by the lake for at least 700 yr because of its large size and the long residence time of water in the lake.
The role of dissolved organic matter release in the productivity of the oligotrophic North Pacific Ocean
Authors: Karl David M. , Hebel Dale V. , Björkman K. , Letelier R. M.
Published: May 2010

Based on a long‐term set of observations and measurements at a station in the subtropical North Pacific Ocean, it now appears that contemporaneous rates of primary production in low‐nutrient open ocean regions and perhaps in the ocean as a whole may be greater than had been considered in field studies conducted in previous decades. Data collected at the Hawaii Ocean Time‐Series (HOT) Station ALOHA from October 1988 to July 1997 indicate that daytime particulate organic carbon (POC) production, based on 12‐h 14C in situ incubations, averages 472 mg C m−2 d−1 (SD = 125 mg C m−2 d−1; n = 70). This carbon production rate is two‐ to three‐fold greater than most of the pre‐1980 estimates. We present evidence that particulate production rates may have been overestimated by up to 30% as a result of 14C‐labeled dissolved organic carbon (14C‐DOC) adsorption onto glass fiber filters. More importantly, when one considers the 14C‐DOC that is produced but not adsorbed onto the filters, gross primary production rates (14C‐POC plus 14C‐DOC) in the subtropical North Pacific Ocean may approach 1 g C m−2 d−1. We hypothesize that the large flux of 14C‐DOC may be a manifestation of decade‐scale habitat changes resulting from variations in climate. The balance between POC and DOC production will ultimately influence the structure of the food web, especially the interactions of phytoplankton and heterotrophic bacterial populations, and the mechanisms and rates of carbon sequestration by the biological pump.
Abundance and properties of dissolved organic matter in pore waters of a freshwater wetland
Authors: Chin Yu‐Ping , Traina Samuel J. , Swank Cathleen R. , Backhus Debera
Published: May 2010

The abundances, molecular weights, molar absorptivities, and polydispersities of sediment pore water dissolved organic matter (DOM) and ferrous iron, Fe(II), were measured from three sites within a freshwater wetland (Old Woman Creek) adjacent to Lake Erie. DOM concentrations (expressed as organic carbon) increased with depth. Number‐average molecular weight, weight‐average molecular weight, and molar absorptivities (at 280 nm) also increased with depth up to 5 cm and remained relatively constant below this depth. These properties are indicative of the respective changes in the size of the DOM constituents and the number of aromatic moieties present. Moreover, a strong correlation was observed between Fe(II) and DOM, which suggests that both constituents coaccumulate in these pore fluids, It is hypothesized that reductionof iron oxides coated with organic matter releases both DOM and Fe(II). Increases in the molecular weights and molar absorptivities of the DOM constituents suggest that the “sorbed” component released by iron oxide dissolution is composed of larger and more aromatic molecules. The molecular‐weight data also suggest that much of the refractory organic carbon in the interstitial waters comprises smaller‐than‐expected polymeric molecules. Thus, the release of the sorbed organic materials during the reductive dissolution of the oxide phases in anoxic sediments coupled with the selective preservation of refractory organic components may play an important role in both the DOM‐mediated fate of pollutants and the cycling of carbon in wetlands.
Influence of an infaunal bivalve on the erosion of an intertidal cohesive sediment: A flume and modeling study
Authors: Willows Robert I. , Widdows J. , Wood R. G.
Published: May 2010

A model was developed to describe the erosion of a cohesive sediment within an annular flume. The model relates the rate of resuspension of sediment per unit area to the difference between the amount of sediment available for resuspension from the bed and the amount already resuspended into the water column. The rate of erosion also depends on the excess free‐stream near‐bed current velocity above a critical threshold velocity. The basic five parameter model describes 96% of the variation in suspended sediment concentration within the flume, where natural sediment is exposed to increments in current velocity (up to 43 cm s−1, equivalent to a shear stress of 1.5 Pa) in the absence of macrofauna. The addition of a small clam, Macoma balthica, to the experimental system led to increased levels of resuspension at all velocities. This effect increased asymptotically with Macoma population density and could be modeled using two additional parameters. Complete analysis of the resulting seven‐parameter model showed that the effect of the fauna was confined solely to the amount of sediment available for resuspension.

Field data supported the laboratory‐determined functional relationship between Macoma density and the quantity of sediment resuspended at environmentally realistic maximum current velocities and provided field‐based parameter estimates for modeling the erosion of in situ sediment. Using predicted flood and ebb tidal current velocities along a 3.5‐km transect normal to the shore, we determined the potential impact of Macoma on the amount of sediment resuspended over a single tidal inundation. We estimate that natural densities of Macoma increase the amount of sediment resuspended, at our sites above midtidal shore level, by 0.42 kg m−2 per tide.

We suggest that experimental flume studies, which can include field deployments, combined with this parametersparse model of fauna1 impact on sediment resuspension provide a straightforward means of quantifying the complex effects of biotic components on rates of sediment erosion.
The trophic dynamics of riverine bacterioplankton: Relationships among substrate availability, ectoenzyme kinetics, and growth
Authors: Foreman C. M. , Franchini P. , Foreman R. L.
Published: May 2010

The role of dissolved organic matter (DOM) in the trophic dynamics of aquatic systems is difficult to study. One approach is to focus on the activity of the extracellular enzyme systems that heterotrophic bacteria use to obtain nutrients from DOM. These data are easy to acquire, but difficult to interpret, because we lack general models that relate these activities to the two sides of the trophic reaction: the DOM pool and bacterial production. To address this gap, we collected water samples from the Maumee River on nine dates from May 1996 through November 1996. The water was filtered and placed in bottles to which a variety of substrates were added (final concentration 20 µM unless otherwise noted): ammonium, leucine, albumin (1 mg liter−1), glucose, cellobiose, starch (1 mg liter−1), vanillin, and tannin (2 mg liter−1). After 20 h at ambient river temperature, respiration, productivity, growth efficiency, and the activities of α‐glucosidase, β‐glucosidase, leucine aminopeptidase, phosphatase, and esterase were measured. The glucosidases were the most responsive enzymes, followed by phosphatase and peptidase. Saccharide and albumin additions produced the largest increases in production and growth efficiency. Phenolic amendments generally depressed growth efficiency. The results suggest that production was primarily carbon limited: Peptides appeared to be a major component of the diet, but high productivities were associated with the availability of saccharides. During the summer, production appeared to be fueled by lysates and exudates generated through the microbial loop. Lower ratios of productivity (e.g., enzyme activity and positive metabolic responses to phenols) suggested that allochthonous carbon may have been important during spring and autumn.
Voltammetric determination of elemental sulfur in pore waters
Authors: Wang Feiyue , Tessier André , Buffle Jacques
Published: May 2010

We describe a new simple, reliable, and sensitive method that employs square‐wave cathodic stripping voltammetry (SWCSV) for the measurement of dissolved elemental sulfur, S(0), in pore waters. The method, which requires only small pore‐water samples (~1.5 ml), shows a linear relationship over three orders of magnitude (~10−9−10−6 Eq S liter−1) between peak current or peak area and S(0) concentration; the practical detection limit (3 × 10−9 Eq S liter−1) is below that required for most pore waters. Experiments carried out over a wide range of pH (2.5–11.5) indicate that peak current and peak potential vary with pH and that thiosulfate, sulfite, and thiols (and probably humic substances) would not interfere with the determination of S(0) over this pH range; interference from sulfide is easily removed by acidifying and bubbling with N2. The slopes (nA/Eq S liter−1) obtained by standard additions of S(0) to pore‐water samples containing 10 mg liter−1 dissolved organic carbon were not statistically different from the slopes of calibration curves, indicating that fouling effects due to natural organic matter should be minimal. Porewater concentration profiles obtained at an anoxic site of a Shield lake indicate that S(0) concentrations were greater than those predicted from equilibrium with orthorhombic sulfur.
Consequences of pelagic food‐web changes during a long‐term lake oligotrophication process
Authors: Manca M. , Ruggiu D.
Published: May 2010

Changes in the pelagic communities of Lago Maggiore (Italy) during 1983–1995, when the lake underwent a process of oligotrophication caused by a gradual phosphorus abatement, were analyzed. Events in the plankton after a large increase of Bythotrephes longimunus starting in 1988 were strikingly similar to those in Lake Michigan after the initial Bythotrephes cederstroemii invasion. They included a decrease in numbers of Daphnia, assumed to be caused by Bythotrephes predation, and an increase in the body size of Daphnia. In Lago Maggiore, these changes took place with a stable fish stock. As Lehman initially found in Lake Michigan, herbivory did not constrain the maximum phytoplankton biomass. However, a significant negative correlation (P < 0.01) existed between Daphnia and phytoplankton cell numbers over the whole long−term period. It is concluded that, although chlorophyll and biovolume changes are dependent on phosphorus reduction, the observed increase in cell numbers of phytoplankton and the decrease in average cell size may depend not only on phosphorus decline but also web during lake oligotrophication.
A dual sheath flow cytometer for shipboard analyses of phytoplankton communities from the oligotrophic oceans
Authors: Cavender‐Bares Kent K. , Frankel Sheila L. , Chisholm Sallie W.
Published: May 2010

Flow cytometry has been used to study phytoplankton since the early 1980s. Because of the wide range of cell sizes and concentrations that occur in natural samples, multiple instrument configurations have been required to characterize pico‐, ultra‐, and nanophytoplankton. Lengthy changeover times between configurations have made synoptic analyses of phytoplankton communities extremely cumbersome and therefore rare. To overcome this problem, we have added dual‐sheath capability and adjustable optics to a commercially available flow cytometer. These additions expand the instrument's capabilities during routine operation. The dual‐sheath cytometer can characterize both the submicron picoplankter Prochlorococcus at sample flow rates of 10 µl min−1 and, after a 1‐min changeover, ultraphytoplankton and nanophytoplankton at sample flow rates >1 ml min−1. These capabilities make possible real‐time analysis of phytoplankton size spectra at sea.
Elevated production of dimethylsulfide resulting from viral infection of cultures of Phaeocystis pouchetii
Authors: Malin Gillian , Wilson William H. , Bratbak Gunnar , Liss Peter S. , Mann Nicholas H.
Published: May 2010

The effects of viral lysis on dimethyl sulfide (DMS) and particulate and dissolved dimethylsulfoniopropionate (DMSP) concentrations were studied in batch cultures of Phaeocystis pouchetii infected with a strain‐specific viral isolate. After 20 h, DMS concentration had increased by fourfold over the levels observed in the control cultures, and this increased to eightfold 45 h after addition of viral particles. The results suggest that viral lysis of DMSP‐containing phytoplankton cells should be considered alongside autolysis, grazing, and bacterial activity as a process that can influence DMS concentrations in seawater. Further research will be necessary to determine the importance of viruses in the biogeochemical DMS cycle in the natural environment.
Influence of microalgal biomass on absorption efficiency of Cd, Cr, and Zn by two bivalves from San Francisco Bay
Authors: Lee Byeong‐Gweon , Louma Samuel N.
Published: May 2010

The bioavailability to clams (Potamocorbula amurensis and Macoma balthica) of Cd, Cr, and Zn from suspended particulate material (SPM) collected during a phytoplankton bloom was compared to bioavailability from SPM dominated by resuspended sediments. Bioavailability was also compared among mudflat sediments amended with different levels of living benthic microalgae. Bioavailability was defined by absorption efficiencies determined using pulse‐chase protocols, modified for studying natural particle assemblages. The partitioning of Cd and Zn to particles (Kd) increased as the microalgae biomass (Chl a) increased in the particle assemblages; partitioning of Cr was less affected by the algal biomass. The clams fed particle assemblages enriched with microalgae absorbed Cd and Zn with significantly greater efficiency than did the clams fed algae‐poor particles. This was partially explained by the greater occurrence of Cd and Zn in the cytosolic fraction of the particle assemblages that were microalgae enriched, as well as by the efficient absorption of cytosolic material by the clams. Among metals, Zn was most efficiently absorbed by both clams, and Cr the least. M. balthica absorbed Zn more efficiently from all types of food particles (39–82%) than did P. amurensis (13–50%). P. amurensis absorbed Cd with greater efficiency from the bloom SPM (44–48%) than did M. balthica (13–21%), but the two clams absorbed Cd similarly from benthic microalgae (26‐51%). The addition of microalgae to complex natural particle assemblages clearly affected the bioavailability of associated metals, so studies using sediments (or suspended particulate material) that do not include a realistic living food component could underestimate metal bioavailability from particle ingestion.
Interactive effects of external manganese, the toxic metals copper and zinc, and light incontrolling cellular manganese and growth in a coastal diatom
Authors: Sunda William G. , Huntsman Susan A.
Published: May 2010

Manganese is a fundamental component of the photosystem 11 reaction center, and thus its requirement should be linked to light utilization. High levels of Cu and Zn antagonize Mn nutrition by inhibiting cellular Mn uptake. Experiments were conducted to examine the interactive effects of Mn, the toxic metals Cu and Zn, and light on cellular Mn, chlorophyll a (Chl a), and specific growth rate in Thalassiosiru pseudonana. Cu and Zn inhibition of growth rate occurred only at. low Mn ion concentrations, an effect that was independent of light intensity and was totally accounted for by inhibition of Mn uptake by these metals. Cells grown at growth‐limiting low light intensities contained high levels of Mn and Chl a, which are needed for the synthesis of additional photosynthetic units during low‐light acclimation. This additional Mn was not provided by higher cellular Mn uptake rates, since these rates were the same in light‐saturated and light‐limited cells. However, because steady‐state cell Mn is equal to the uptake rate divided by the specific growth rate, the cells were able to accumulate the additional Mn needed for acclimation once light limitation caused growth rate to decline, a inherent negative feedback relation. In seawater, Mn and Cu may interact with light in controlling algal growth rate, since the free ion concentration of both metals is influenced by iight within the euphotic zone.
Solute transport in sediments by freshwater infaunal bioirrigators
Authors: Matisoff Gerald , Wang Xiaosong
Published: May 2010

Laboratory experiments using the radionuclide 22Na as a solute tracer were conducted in microcosms containing the freshwater chironomid larvae Coelotanypus sp. and Chironomus plumosus and the mayfly larvae Hexagenia limbata to determine the exchange of solutes between sediments and overlying water. Three different mathematical models of transient solute transport in bioturbated sediments were applied to the data to evaluate which best quantified solute exchange and to determine how that exchange varied with fauna1 type and density. Although all three species of larvae constructed burrows and irrigated them, the larger H. limbata frequently abandonded their burrows and vigorously burrowed the sediment. As a result, an enhanced diffusion model, in which the solute diffusion coefficient is higher in the bioturbated zone than in unmixed sediments, best described the data for the larger H. limbata. The enhanced diffusion model generally underestimated solute transport by smaller H. limbata, C. plumosus and Coelotanypus sp. larvae because it did not account for the effects of burrow irrigation, Both the cylindrical burrow model and the nonlocal exchange model with a constant value of the exchange coefficient in the mixed layer described the transport processes well, presumably because the smaller H. limbata, C. plumosus, and Coelotanypus sp. maintained and actively irrigated their burrows. At natural bottom fauna1 densities, C. plumosus induced the greatest exchange of solutes between sediment and overlying water, followed by the small H. limbata, the large and medium H. limbata, and Coelotanypus. However, H. limbata enhanced the flux by about an order of magnitude more than did C. plumosus and by about a facior of 20 times that of Coelotanypus on an individual basis.
Hydrologic influence on methane and carbon dioxide dynamics at two north‐central Minnesota lakes
Authors: Striegl Robert G. , Michmerhuizen Catherine M.
Published: May 2010

Annual emissions of (CH4 + CO2) to the atmosphere were proportional to net hydrologic inputs of C, mostly by groundwater, at two lakes in the Shingobec River watershed in north‐central Minnesota. Williams Lake (WL), a closed basin lake near the top of the watershed, had a hydraulic residence time of 2–4 yr and groundwater exchange of about +2 mol dissolved inorganic carbon (DIC) and −0.1 mol dissolved organic carbon (DOC) m−2 lake area yr−1. The Shingobee River flows through Shingobee Lake (SL) that had a hydraulic residence of 0.3–0.4 yr and received net groundwater plus surface‐water inputs of +5.3 to +7.3 mol DIC and fewer than + 1.3 mol (DOC + particulate organic carbon) m−2 yr−1. Approximately 60–80% of net annual C input to SL was from groundwater. Lake storage of CH4 and CO2 was greatest in late winter, with maximum emissions to the atmosphere immediately following ice melt. The lakes emitted CH4 continuously during open water, having annual losses of −1.6 mol CH4 m−2 yr−1 at WL and −1.9 mol CH4 m−2 yr−1 at SL. Although the WL epilimnion was CO2 depleted throughout summer, net annual CO2 exchange with the atmosphere was near zero because springtime emission offset summertime uptake. CO2 supersaturation resulted in emission of −8.0 mol CO2 m−2 yr−1 at SL.
Prediction of annual and seasonal phosphorus concentrations in stratified and polymictic lakes
Authors: Nürnberg >Gertrud K.
Published: May 2010

Phosphorus (P) concentrations in lakes arc summarized and reported in different ways. Annual whole lake P (Pann), epilimnetic summer P (Pepi), and mixed water column P during fall turnover after summer stratification (Pfall) were investigated with data from up to 150 lakes. Differences between P averages are caused by temporal variation in thermal stratification and the size of internal P sources. To predict various P averages in specific lake types, I combined a P retention model that predicts annual retention due to sedimentation (Rpred) with external and internal load estimates (Lext, Lint) in a steady‐state, P mass balance approach.

Retention of internal and external loads in stratified and polymictic lakes can be predicted by the same model, Rpred = 15/(18 + qs), where qs is annual water load (m yr−1). However, lakes with chemically enhanced P coprecipitation (e.g., with calcium) are an exception. P averages can be predicted in stratified lakes, as
urn:x-wiley:19395590:media:lno19984371544:lno19984371544-math-0001although Pepi is overestimated in lakes with oxic hypolimnia. P concentrations can be approximately predicted in polymictic lakes as
urn:x-wiley:19395590:media:lno19984371544:lno19984371544-math-0002
Glycine betaine uptake, retention, and degradation by microorganisms in seawater
Authors: Kiene Ronald P. , Williams Lynn P. Hoffmann
Published: May 2010

The uptake of nanomolar levels of methyl‐14C‐glycine betaine (GBT) was studied in surface water samples from the Gulf of Maine, Mobile Bay, and the Gulf of Mexico. At all locations, 14C‐GBT was rapidly taken up into particulate material (>0.2 µm). Formalin treatment, autoclaving, or prefiltration of water through 0.2‐µm membranes completely inhibited 14C‐GBT uptake, indicating the process was biologically mediated, probably by bacteria. During the first several hours of uptake, >80% of the label found in particulates was recovered as untransformed 14C‐GBT This fraction diminished over longer incubations but never fell below 16%, indicating some longer term storage of GBT in microorganisms. Respiration of the added label to 14CO2 was typically <5% of the total uptake during 5–10‐min incubations but increased to approximately 40–60% after 24–48 h. Increasing the salinity of an estuarine water filtrate culture from 14 to 25 or 35 resulted in greater retention of 14C‐GBT in particulates and less production of 14CO2, suggesting that GBT may be used as an osmolyte by microorganisms. Uptake, retention, and degradation patterns were similar in <0.8‐µm filtrates and whole seawater, and size fractionation experiments showed that most GBT uptake was by organisms of <1 µm, suggesting bacteria as the microbes most likely responsible for GBT uptake. Uptake rates followed Michaelis‐Menten kinetics with saturation at <20 nM added GBT in most cases and Kt + Sn values ranging from 1.2 to 49 nM. Turnover times for Sn were short, ranging from 0.52 to 11 h. Vmax values ranged from 0.39 to 44 nmol liter−1 h−1, and Vmax could be increased by enriching <1.0‐µm filtrates for 48 h with 100 µM glucose or acrylate. GBT uptake displayed temperature optima from 20°C to 30°C, with optima close to the in situ temperature on the day of sample collection. Together, the results indicate that nanomolar levels of GBT are rapidly scavenged by seawater microorganisms for use as an osmolyte or carbon and energy source. The relative proportion of retention vs. degradation is likely to depend on the composition of the microbial community and environmental factors such as osmotic stress and the availability of alternative osmotic or carbon and energy substrates.
Trophic ecology of massive shrimp aggregations at a Mid‐Atlantic Ridge hydrothermal vent site
Authors: Polz Martin F. , Robinson Jonathan J. , Cavanaugh Colleen M. , Van Dover Cindy L.
Published: May 2010

The source of nutrition of shrimp that form giant aggregations at Mid‐Atlantic Ridge hydrothermal vents was explored by a combination of different molecular techniques. These animals have been hypothesized either to graze on the free‐living, surface microbial community or to feed off epibiotic bacteria growing on their exoskeleton. Stable isotope compositions of potential food sources, consumer tissues, and gut contents suggest that the shrimp derive most of their carbon and nitrogen from the epibionts. However, probing of nucleic acids extracted from shrimp guts points to the existence of a gut microflora that is isotopically similar but genetically distinct from the epibionts. Carbon dioxide fixation experiments were carried out to compare the magnitude of potential primary productivity of the different nutritional sources of the shrimp. Relatively low and comparable rates were observed for both the free‐living community and the epibionts but activity associated with gut preparations was surprisingly high. These high CO2 fixation rates in the gut may be indicative of a nutritional relationship between the shrimp and their gut microflora. Overall, the data indicate a nutritional symbiosis of the shrimp with their epibionts and possibly also with a separate gut microflora.
Field study on currents in a shallow, ice‐covered lake
Authors: Malm Joakim , Bengtsson Lars , Terzhevik Arkady , Boyarinov Pjotr , Glinsky Alexander , Palshin Nikolaj , Petrov Michail
Published: May 2010

A field study on current structure and circulation characteristics in Lake Vendyurskoe, a small, shallow, icecovered lake in Karelia, Russia, is presented. The current velocity magnitudes were generally found to be small. The most pronounced currents had an oscillating character, with velocity amplitudes on the order of millimeters per second. The oscillation period, obtained from spectral density calculations, corresponded to that of a barotropic uninodal seiche. The seichelike nature of the current oscillations was supported by the results from analysis of icelevel fluctuations, giving identical periods and a phase shift of one‐fourth the period between the two types of oscillations.

Mean currents measured during the winter were on the order of millimeters per second. Because Lake Vendyurskoe does not have any significant river inflow or outflow during winter, the most probable cause of these currents is horizontal temperature (pressure) gradients. Scaling analysis indicated that these currents are geostrophic. This was supported by theoretical estimates, based on observed horizontal temperature gradients, being of the same order as the observed currents. The mean current velocities increased considerably after spring convection from <1 to several millimeters per second.
Isotopic composition of nitrate in the central Arabian Sea and eastern tropical North Pacific: A tracer for mixing and nitrogen cycles
Authors: Brandes Jay A. , Devol Allan H. , Yoshinari T. , Jayakumar D. A. , Naqvi S. W. A.
Published: May 2010

The δ15N composition of nitrate and N2 gas was measured in the eastern tropical North Pacific (ETNP) and central Arabian Sea (AS) suboxic regions. The δ15N of nitrate increased from 6‰ at 2,500 m to 15‰ at 250–350 m in both regions, while the δ15N of N2 concurrently decreased from 0.6‰ to 0.25‰. The denitrification isotopic fractionation factor (εdenit) for each region was estimated using both advection‐reaction and diffusion‐reaction models. Values for εdenit in the ETNP ranged from 25 ± 2 (advection‐reaction) to 30 ± 3 (diffusion‐reaction). Values for εdenit in the central AS varied from 22 ± 3 (advection‐diffusion) to 25 ± 4 (reaction‐diffusion) using a starting nitrate isotopic composition of 6‰ but were indistinguishable from calculated values from the ETNP when an initial value of 5‰ was employed. Based upon the model results, an average global εdenit of 27 ± 3 is proposed for marine suboxic water columns. Isotopic enrichment of nitrate in oxic waters beneath the active denitrification regions was observed and indicates the presence of significant cross‐isopycnal ventilation at depth. The isotopic composition of nitrate decreased above 250 m to −80 m, and this pattern is hypothesized to be caused by the input of isotopically light nitrogen from nitrogen fixation in the euphotic zone. A simple isotopic mass balance indicates that a significant percentage of primary productivity in the central AS may be fueled by nitrogen fixation.
Diurnal signals in vertical motions on the Hebridean Shelf
Authors: Rippeth Tom P. , Simpson John H.
Published: May 2010

In this paper, we consider the interpretation of measurements of vertical velocity and backscatter signal intensity, made using an acoustic doppler current profiler (ADCP) mounted on the seabed, at a position on the Hebridean Continental Shelf. The existence of vertically migrating scatterers is inferred from both the backscatter signal intensity and vertical velocity data, which indicate migration rates of 2–3 cm s−1, and shows consistency between the displacement deduced from the vertical velocity and the observed movement of scatterers from the near bed to the near‐surface regions, evident in temporal variations in the backscatter signal intensity. Independent evidence that the observed vertical velocities are largely due to movements of the acoustic scatterers relative to the water is obtained through comparison of the ADCP vertical velocity data with vertical velocities inferred from the movement of the thermocline. The close phase locking between the motion and sunset and sunrise times has led us to interpret the signal in terms of the diel vertical migration of zooplankton. Although no biological samples were collected during this study, previous surveys of the area have identified species of copepod and euphausiid that are known to migrate. The 12 d of data available show an initial period, when there was a strong vertical migration signal, and a later period, during which the signal was not clear. By combining the observed vertical and horizontal velocity components in a particle tracking model, it is demonstrated that the change in the migration signal may be a result of the advection of the patch of migrating zooplankton away from the ADCP, during the later part of the observational period.
High spatial resolution measurements in lake sediments with PVC based liquid membrane ion‐selective electrodes
Authors: Müller Beat , Buis Kerst , Stierli Ruth , Wehrli Bernhard
Published: May 2010

Ion‐selective liquid membrane electrodes for Ca2+, CO32−, NH4+, NO3−, NO2−, and pH have been miniaturized and their characteristics evaluated in view of their application in sediment pore water of lakes. PVC membranes were prepared in polyethylene pipette tips with an end diameter of 0.6 mm. This is a simple method to produce inexpensive disposable ion‐selective electrodes for various applications. Detection limits were 1 µM for Ca2+, CO32−, NH4+, and NO3−, and 10 µM for NO2−. The pH sensor was linear in the pH range of 4–11. Selectivities for Ca2+, CO32− and pH are high enough for the application in seawater. The sensors for NH4+, NO3−, and NO2− in their low concentration range experience interferences from K+, SO42+, and HCO3−, respectively, in lake pore water. Reproducibility in pure solutions is between 20.2 and 20.6 mV, The applicability of the miniaturized sensors are demonstrated in measurements of concentration gradients across the sediment‐water interface in sediment cores of several lakes.
Ingestion and digestion of an autotrophic picoplankter, Synechococcus, by a heterotrophic nanoflagellate, Bode saLtans
Authors: Dolan John R. , Šimek Karel
Published: May 2010

We investigated the process of digestion and estimated ingestion from digestion rate and food vacuole content in a planktonic freshwater bacterivore. Digestion was examined in feeding and nonfeeding Bodo flagellates previously exposed to Synechococcus and in “naive” flagellates. Digestion of Synechococcus by Bodo was estimated for flagellates in different growth phases. Food vacuole contents declined exponentially, and digestion rate was relatively constant, averaging about 1% food vacuole content min−1 at 22°C, regardless of feeding history or growth phase. There was close agreement among ingestion rates based on digestion rate and rates estimated from the disappearance or direct uptake of Synechococcus. We also examined ingestion of Synechococcus by Bodo. Ingestion was similar in cells of different growth phases and in the presence or absence of fluorescent microspheres. In contrast, in the presence of Synechococcus, microspheres were ingested at lower rates in late‐exponential‐phase cells and not at all in mid‐ and late‐stationary‐phase flagellates. Results of a preliminary experiment with marine Synechococcus and mixed marine flagellates gave results similar to those obtained with Bodo in terms of an exponential decline in average cell contents and a digestion rate of about 1% cell contents h−1. Our results suggest that food vacuole content can be used to estimate ingestion of autotrophic picoplankton by heterotrophic nanoflagellates.
Annual average abundance of heterotrophic bacteria and Synechococcus in surface ocean waters
Authors: Li W. K. W.
Published: May 2010

Global abundance of marine bacteria was investigated at the annual climatological scale. In surface waters of diverse marine habitats, the annual average abundances of heterotrophic bacteria and the photosynthetic cyanobacterium Synechococcus are directly related to annual average temperature below 14°C. Notably, average nitrate concentrations at the surface are never high where the temperature is above 14°C. These results suggest that, over the course of a year, temperature is the dominant factor affecting bacterial growth and loss in colder waters. Other factors, such as substrate supply, may be important in warmer waters.
Evidence for a clade‐specific temporal and spatial separation in ribulose bisphosphate carboxylase gene expression in phytoplankton populations off Cape Hatteras and Bermuda
Authors: Paul John H. , Pichard Scott L. , Kang Jordan B. , Watson Gregory M. F. , Tabita F. Robert
Published: May 2010

The factors affecting the regulation of photosynthetic carbon fixation in diverse phytoplankton populations are not yet understood. To this end, we have measured the expression of the gene (rbcL) for the major carbon fixation enzyme, ribulose‐1,5‐bisphosphate carboxylase/oxygenase, in coastal phytoplankton populations off Cape Hatteras and in oligotrophic oceanic picoplankton near Bermuda. Using gene probes specific for the cyanobacterial/chloro‐phytic clade and the chromophytic clade (diatoms, chrysophytes, prymnesiophytes, and others) of Form I rbcL genes (“cyano” and “chromo” probes, respectively), we have measured rbcL messenger ribonucleic acid (mRNA) levels in size‐fractionated coastal waters, in a decktop diel incubator and a Lagrangian drifter study, and in vertical profiles in stratified, oligotrophic ocean water. In coastal waters influenced by estuarine plumes, an equal distribution of carbon fixation between the picoplankton and the micro/nannoplankton occurred, with cyano rbcL mRNA coinciding with Synechococcus counts in the <1‐μm fraction, with the majority of the chromo rbcL mRNA expression occurring in the larger sized phytoplankton fraction. In profiles of oligotrophic oceanic waters, the cyano rbcL mRNA was found in the upper water column (∼50‐m depth) and coincided with peaks in Synechococcus counts. The chromo rbcL mRNA was concentrated at the subsurface chlorophyll a (Chl a) maximum (∼85 m) and corresponded to red‐fluorescing cell counts, thought to be picoeucaryotes and diatoms. Photosynthetic carbon fixation and RUBISCO enzyme activity encompassed both cyano and chromo rbcL mRNA peaks, suggesting a near equal contribution to carbon fixation in the water column by these two phytoplankton clades. Both decktop diel incubator studies and a Lagrangian drifter study in coastal waters indicated cyano rbcL transcription in the morning and chromophytic rbcL transcription in the late afternoon/early evening. Thus, the two major clades of RUBISCO‐containing phytoplankton occupy separate niches in time, space, and cell size in the waters off Cape Hatteras. The factors determining such clade‐specific niches may include efficiency of nutrient utilization, differences in relative carboxylase/oxygenase activity (τ values) of cyano (Form IB) and chromophytic (Form ID) RUBISCOs, and differences in pigment composition/adaptation to light regimes. Additionally, we propose that chromo rbcL mRNA may be indicative of new production, whereas cyano rbcL mRNA correlates with recycled production in stratified, oligotrophic oceanic environments.
The response of photosynthetic absorption coefficients to irradiance in culture and in tidally mixed estuarine waters
Authors: Culver Mary E. , Perry Mary Jane
Published: May 2010

The accuracy of models for primary production and light propagation depends on correct assignment of absorption to photosynthetic pigments. The phytoplankton absorption coefficient is comprised of two components: photosynthetic and photoprotective absorption coefficients. A method based on the fluorescent excitation of chlorophyll a is used to quantify the photosynthetic absorption coefficient for phytoplankton grown in culture and sampled from Puget Sound, Washington. The difference spectrum between total phytoplankton and photosynthetic absorption should be equivalent to photoprotective absorption. For cultures, the difference spectra exhibit peaks near 460 and 490 nm and broad‐band absorption between 400 and 450 nm. However, for field samples an additional pronounced peak is observed around 440 nm, similar in shape to the chlorophyll a Soret peak. If the 440‐nm peak were associated with photosystem I chlorophyll a, the photosynthetic absorption coefficient will be underestimated by <15% for these samples. Variability in both coefficients is predictable as a function of irradiance. The photosynthetic coefficient varies inversely with growth irradiance, and the photoprotective coefficient varies directly with irradiance. This direct relationship with irradiance accounts for much of the variability in the spectral shape of the total phytoplankton absorption coefficient. The ratio of the photosynthetic absorption coefficient to the total phytoplankton absorption coefficient increases as a function of decreasing irradiance for cultures and for field samples collected from stratified regions of the water column. This ratio is a photoadaptive parameter that can serve to integrate physiological response to irradiance and has the potential to provide estimates of mixed layer dynamics.
The ecology of Paraphysomonas imperforata based on studies employing oligonucleotide probe identification in coastal water samples and enrichment cultures
Authors: Lim Ee Lin , Dennett Mark R. , Caron David A.
Published: May 2010

The geographical distribution and seasonal abundance of the cosmopolitan heterotrophic flagellate Paraphysomonas imperforata in several coastal waters was examined using species‐specific oligonucleotide hybridization probes which target small subunit ribosomal RNA. P. imperforata was found to occur in several coastal environments, but at very low abundances (typically <50 cells ml−1). The seasonal abundance of P. imperforata examined at one sampling site remained consistently low and constituted no more than 1% of the total nanoplankton at any time during a 17‐month sampling period. In contrast to the low abundances observed in natural water samples, P. imperforata frequently dominated heterotrophic enrichment cultures prepared from these same samples, comprising up to 98% of the total nanoplankton. Based on these findings, we conclude that P. imperforata is an opportunistic species capable of growing rapidly to high abundances when prey concentrations are high. Water and enrichment temperature as well as the temperature tolerance range of P. imperforata appear to have played a role in the seasonal differences observed in P. imperforata dominance. Experiments with enrichment cultures indicated that the absolute abundances of P. imperforata in the water samples and the activity of consumers of nanoplankton also influenced the degree to which P. imperforata dominated the heterotrophic nanoplankton assemblages of enrichment cultures. Seasonal changes in water temperature might also affect these latter factors, and, as a consequence, indirectly influence the ability of P. imperforata populations to dominate enrichments. Our results support the notion that enrichment cultivation of heterotrophic flagellates, and perhaps incubations in general, can select for species such as P. imperforata that may not be representative of nanoplanktonic protists that numerically dominate natural assemblages.
Bacteria—protist interactions and organic matter degradation under P‐limited conditions: Analysis of an enclosure experiment using a simple model
Authors: Thingstad T. F. , Havskum H. , Kaas H. , Nielsen T. G. , Riemann B. , Lefevre D. , Williams P. J. le B.
Published: May 2010

An enclosure experiment was performed in the brackish layer of a Norwegian fjord, a system where both phytoplankton and bacterial growth have previously been hypothesized to be phosphorus (p) limited. All enclosures had a succession pattern characterized by an initial autotrophic phase with positive net community production, increasing phytoplankton primary production, and chlorophyll, followed by a heterotrophic phase with decline in primary production, negative net community production, increased community respiration, bacterial production, and biomass. Daily additions of phosphate increased the amplitudes of both the autotrophic and the heterotrophic phases of this succession. Because no stimulating effect of glycine addition on bacterial production or on community respiration was observed, the delay in bacterial response could not easily be explained as a delay in production or availability of carbon substrates for the bacteria. An alternative hypothesis is that bacterial production is regulated by a combination of P‐limited bacterial growth rate and predatory control of bacterial biomass. A simple numerical model based on this hypothesis was able to reproduce the main features of the observed pattern of succession.
First evidence of some dinoflagellates reducing male copepod fertilization capacity
Authors: Ianora A. , Miralto A. , Buttino I. , Romano G. , Poulet S. A.
Published: May 2010

Evidence is presented that hatching failure in Temora stylifera eggs can depend on poor sperm quality. Three dinoflagellate diets, Prorocentrum micans, Gymnodinium sanguinium, and Gonyaulax polyedra, significantly modified spermatophore production and reduced the fertilization capacity of male sperm after 6–12 d of continuous feeding. Two other diets, the dinoflagellate P. minimum and the prymnesiophycean Isochrysis galbana, had no effect on hatching success, which remained high (>;89%) and stable with time. A reduction in fertilization capacity was neither due to maternal effects nor to male age since hatching success returned to normal upon the introduction of freshly caught wild males or males conditioned with a good diet such as P. minimum for the same length of time as couples fed with the poor diets, P. micans, G. sanguinium, and G. polyedra. Confocal microscope images of unhatched eggs colored with a nucleus‐specific fluorescent dye confirmed that these eggs had not been fertilized. Experiments with Calanus helgolandicus females, which did not require reinsemination and which were fed the same diets that induced hatching failure in T. stylifera, showed no change in hatching success with time.
An optical oxygen sensor and reaction vessel for high‐pressure applications
Authors: Stokes M. D. , Somero G. N.
Published: May 2010

We describe a simple hyperbaric chamber and optical oxygen probe (optrode), which is based on the dynamic fluorescent quenching of a ruthenium metal complex, that can be used to measure changes in oxygen concentration in either aqueous or gaseous media. Initial experiments illustrate the utility of this robust form of sensor. The optrode showed a typical response time of ≪10 s, a linear temperature response with greater fluorescent quenching at lower temperatures, and was unaffected by pressures as great as 34.4 mPa (340 atm). Yeast cultures measured at 27.8 mPa (275 atm) showed an up to ninefold decrease in respiration rate compared to cells at 1 atm. The oxygen optrode is a simple and rugged device that appears exceptionally well suited for experimentation under conditions in which polarographic electrodes or conventional chemical analysis is difficult, e.g., at high or variable pressures.