bluuebunny/crossref_metadata_2025 huggingface dataset:
>Dissolved inorganic carbon sources for epipelic algal production: Sensitivity of primary production estimates to spatial and temporal distribution of 14C
Authors: Vadeboncoeur Yvonne , Vadeboncoeur David M.
Published: May 2010

Estimates of epipelic algal primary production using 14C are sensitive to whether the presumptive source of dissolved inorganic carbon (DIC) is the overlying water, the interstitial water, or both. To determine the source of DIC, we compared 14C uptake among intact sediment cores exposed to different 14C ratios between interstitial and overlying water. In addition, we evaluated the effect of varying time between addition of 14C and light incubation (preincubation time) and the effect of photosynthetic uptake on final distribution of 14C. Both preincubation time and photosynthetic uptake affected final 14C distribution, but the magnitude of the photosynthesis effect was larger. Estimates of primary production ranged between 50 and 200 mg C m−2 h−1, depending on the presumed DIC source and whether we accounted for differential photosynthetic depletion of 14C and DIC. Using nonlinear regression, our best estimate of epipelic production was 114 mg C m‐2 h‐1, and the fraction of DIC sequestered from overlying water was 0.5 (R2 = 0.84). Similar assessments should be applied in other systems for accurate 14C estimates of epipelic algal production.
Photochemical reactivity of dissolved lignin in river and ocean waters
Authors: Opsahl Stephen , Benner Ronald
Published: May 2010

The photochemical reactivity of dissolved lignin and photobleaching of dissolved organic matter (DOM) were examined in riverine and open‐ocean water samples. Approximately 75% of the total dissolved lignin in Mississippi River water was lost during 28 d of incubation in sunlight, mostly due to photooxidation. The remaining fraction of dissolved lignin was much less susceptible to photooxidation. About 90% of the dissolved lignin in river water was present as high‐molecular‐weight (HMW, >1,000 Dalton) DOM. However, after exposure to sunlight, about 80% of the remaining lignin was present as low‐molecular‐weight (LMW, <1,000 Dalton) DOM. An absolute increase in concentration of LMW lignin provided direct evidence for the phototransformation of macromolecular DOM to smaller molecules. The composition of riverine dissolved lignin also changed dramatically during photooxidation. The abundance of syringyl relative to vanillyl phenols decreased twofold, while concentrations of vanillic acid relative to vanillin, (Ad/Al)v, increased fourfold. The increase in (Ad/Al)v was found exclusively in the photooxidized LMW DOM. The photochemically altered composition of riverine dissolved lignin was consistent with the composition of oceanic dissolved lignin, The dissolved lignin in HMW DOM from the equatorial Pacific Ocean was highly resistant to photooxidation. These findings suggest that photochemical reactions play a prominent role in determining the composition and reactivity of terrigenous DOM in the ocean,
Sediment nutrient dynamics on the South Atlantic Bight continental shelf
Authors: Marinelli Roberta L. , Jahnke Richard A. , Craven Deborah B. , Nelson James R. , Eckman James E.
Published: May 2010

Continental shelf sediments on the South Atlantic Bight (SAB) consist of relict sands that, at depths ranging from 14–45 m, fall within the photic zone and are sites in which significant rates of benthic primary production are observed. Thus, SAB seafloor sediments are a source of organic matter to the shelf system and are possibly a sink for nutrients regenerated within the sediments. We have investigated the nutrient dynamics in SAB shelf sediments along two transects (off the coasts of Georgia and Florida) as part of a study that addresses the significance of benthic primary production in terms of overall shelf biogeochemistry. Sandy sediments were sampled with a newly designed corer that permits retention of pore water in highly permeable sands and thus avoids commonly encountered “washout” problems. Nutrient (ammonium, silicate, nitrate + nitrite, and phosphate) distributions from sediments along both transects show substantial variation in concentration magnitudes and profile shapes over short horizontal spatial scales (meters). Laboratory experiments and numerical models of diagenetic processes in these sediments suggest that (1) pore‐water advection, driven by current flows over wave ripples and bioturbational features, is likely an important transport process in promoting nutrient exchange in these porous sands (more so than irrigation), and (2) reaction rates in SAB sediments are rapid and are comparable to those in nearshore muddy habitats. In spite of this variation and the apparently high rates of advective transport, time series measurements show a gradual increase in depth‐integrated nutrient concentrations at one station along the Georgia transect from the spring through the fall. This increase is probably related to elevations in temperature and metabolic rates in sediments during the warmer summer months.

Measured oxygen and nutrient fluxes across the sediment‐water interface in paired transparent “light” chambers and opaque “dark” chambers did not conform to trends observed in shallow water systems, where oxygen is typically evolved and nutrients are consumed in the light (versus oxygen that is consumed and nutrients that are evolved in the dark). The absence of measurable or consistent fluxes on the SAB shelf is likely the result of low concentrations of nutrients in both the water column and the upper sediment layers. However, rapid regeneration rates in sediments and generally higher nutrient concentrations in deeper sediment layers suggest that sediments are an important source of the nutrients that fuel benthic primary production. Although ammonium is rapidly produced in these oxic sands, nitrate concentrations are uniformly low, and measurable nitrate generally appears in the oxic sedimentary layers. The absence of high nitrate concentrations in the suboxic or anoxic zone suggests that denitrification may not be an important process in SAB shelf sediments.
A mini drivepoint sampler for measuring pore water solute concentrations in the hyporheic zone of sand‐bottom streams
Authors: Duff John H. , Murphy Fred , Fuller Chrsistopher C. , Triska Frank J. , Harvey Judson W. , Jackman Alan P.
Published: May 2010

A new method for collecting pore‐water samples in gravel streambeds is presented. We developed a mini drivepoint solution sampling (MINIPOINT) technique to collect pore‐water samples at 2.5‐cm vertical resolution. The sampler consisted of six small‐diameter stainless steel drivepoints arranged in a 10‐cm‐diameter circular array. In a simple procedure, the sampler was installed in the streambed to preset drivepoint depths of 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 cm. Sampler performance was evaluated in the Shingobee River, Minnesota, and Pinal Creek, Arizona, by measuring the vertical gradient of chloride concentration in pore water beneath the streambed that was established by the uninterrupted injection to the stream for 3 d. Pore‐water samples were withdrawn from all drivepoints simultaneously. In the first evaluation, the vertical chloride gradient was unchanged at withdrawal rates between 0.3 and 4.0 ml min− but was disturbed at higher rates. In the second evaluation, up to 70 ml of pore water was withdrawn from each drivepoint at a withdrawal rate of 2.5 ml min−1 without disturbing the vertical chloride gradient. Background concentrations of other solutes were also determined with MINIPOINT sampling. Steep vertical gradients were present for biologically reactive solutes such as DO, NH4+, NO3−, and dissolved organic C in the top 20 cm of the streambed. These detailed solute profiles in the hyporheic zone could not have been determined without a method for close interval vertical sampling that does not disturb natural logic mixing between stream water and groundwater.
From algal competition to animal production: Enhanced ecological efficiency of Brachionus plicatilis with a mixed diet
Authors: Sommer Ulrich
Published: May 2010

The food ‐chain transmission of mineral nutrient effects to zooplankton production via phytoplankton competition was studied by two ‐stage experiments with a mixed phytoplankton assemblage from the Indian Ocean and the rotifer species Brachionus plicatilis. Phytoplankton species composition was steered by nutrient competition in the first stage of the cultures. High atomic Si:N ratios (>1:1) in the medium resulted in diatom dominance, and low ones resulted in flagellate dominance. Medium Si:N ratios (0.3–0.6:1) resulted in even mixtures of both types of algae. The phytoplankton assemblage resulting from competition was used as food for Brachionus. An even mixture between diatoms and flagellates in the food resulted in higher Brachionus production than one sided food mixtures.
How important are rare species in aquatic community ecology and bioassessment?
Authors: Cao Yong , Williams Dudley D. , Williams Nancy E.
Published: May 2010

We examined the effects of excluding rare species on the comparison of species richness. A river benthic data set and a randomization resampling procedure were used to show the importance of this consideration in aquatic bioassessment in particular. The data set was manipulated by deleting species at three levels of rarity as defined by occurrence frequency: once in all 24 replicates from each of three sites, no more than twice, and no more than five times. We focused on differences in species richness because many other bioassessment metrics are dependent on species richness and species composition. Species abundance patterns at the three sites were very different, with many more rare species at the least impacted site than at the more impacted sites. As sample size increased, the diffcrcnces in species richness among the three sites markedly increased in the original data set. However, the exclusion of rare species at the same level of rarity substantially reduced species richness at the least impacted site but had little effect on the most impacted site. This result led to a serious underestimation of the differences in species richness among the sites in terms of both absolute numbers and species loss percentages. Deleting rare species can damage the sensitivity of community‐based methods to detect ecological changes; rare species are critical for bioassessment.
Enhancement of new production in the northeast subarctic Pacific Ocean during negative North Pacific index events
Authors: Wong C. S. , Whitney F. A. , Matear R. J. , Iseki K.
Published: May 2010

We examined interannual variability in the 1965–1990 winter‐summer differences in surface nitrate (ΔNO3) in the northeast subarctic Pacific Ocean (Station P, 50°N, 145°W). Increases in ΔNO3, of 30–70% above the mean value occurred during four events (1969, 1971‐1972, 1979, 1983). The ΔNO3 time series was highly correlated (r = 0.86) with the spring‐summer nitrate utilization rate from 1970 to 1980. The ΔNO3 time series was negatively correlated with the North Pacific index (NPI) (r = ‐0.72) and positively correlated with solar radiation in the spring (r = 0.48) and summer (r = 0.46). A simple ecosystem model forced with observed incident solar radiation and mixed‐layer depth during the spring‐summer period predicted increases in export production that were 50% of the observed increase for 1970–1972 and 1977–1979. Comparison between the ΔNO3 and sedimenting particulate organic nitrogen (PON) showed that the high ΔNO3 event of 1983 was associated with a dramatic increase in PON fluxes. A simple ecosystem model underpredicts observed interannual variations in export production, and this result combined with the observed PON fluxes suggests that a combination of increased phytoplankton production and increased f ratio produced the observed increase in ΔNO3. The increase in f‐ratio implies a change in the community structure of the phytoplankton during the elevated ΔNO3 events that appears connected to changes in the NPI.
Effects of phytoplankton blooms on the cycling of manganese and iron in coastal waters
Authors: Schoemann V. , de Baar H. J. W. , de Jong J. T. M. , Lancelot C.
Published: May 2010

The development of intense plankton blooms during spring controls the concentrations of dissolved Mn and Fe in eutrophic shallow coastal waters of the North Sea. Proliferation of diatoms, Phaeocystis colonies, and Noctiluca was accompanied by changes of particulate and dissolved Mn and Fe in the water column. The latter parameters were measured simultaneously with relevant physical, chemical, and biological variables at two sites in the coastal waters of the Southern North Sea, in 1993 at one site and in 1994 at both sites. Removal of dissolved Fe and particulate Fe, Mn, and Al occurred during the inception of the spring bloom. This could be due to biological uptake, adsorption of abiotic particles onto settling phytoplankton cells, or ingestion of abiotic particles by zooplankton during grazing, with subsequent settling of fecal pellets. We also observed a seasonal increase of dissolved Mn and Fe and progressive changes in the composition of the particulate Mn and Fe in the water column after peaks in spring diatom and Phaeocystis blooms. This can be explained by the following sequence of events. The organic matter produced during the spring phytoplankton blooms is degraded by the heterotrophic organisms in the water column and the sediment. This leads to anoxic conditions near the surficial layer in the shallow coastal sediments. First, Mn oxides and then Fe oxides are used as oxidants for the degradation of organic matter, resulting in the reduction and dissolution of Mn and Fe. Dissolved Mn and Fe diffuse to the oxic overlying water and are partly adsorbed or precipitated on the suspended particulate matter, The other part remains in solution longer because of a decrease in the oxidation rate. This decrease results from a lowering of both the pH from 8.6 to 8.1 and the oxygen concentrations from 378 to 204 µM in the water column due to the activity of heterotrophs in the water column and sediment. Noctiluca could also be responsible for the reduction of Mn and Fe associated with bacteria and phytoplankton, Overall, the seasonal evolution of dissolved and particulate Mn and Fe is consistent with the successive autotrophic and heterotrophic activities.
Effect of gas bubbles on the diffusive flux of methane in anoxic paddy soil
Authors: Rothfuss Franz , Conrad Ralf
Published: May 2010

The emission of CH4 from paddy soil is driven by CH4 concentration gradients in the submerged soil. CH4 concentration gradients between anoxic methanogenic and oxic methanotrophic soil layers were measured in paddy soil microcosms by using gas diffusion probes with a spatial resolution of 1 mm. The CH4 emission rate was measured by placing a microcosm into a chamber containing an atmosphere of either synthetic air (80% N2, 20% 02) or N2. The CH4 flux was 1.6 ± 5.4 nmol cm−2 d−1 under synthetic air and 288 ± 10 nmol cm−2 d−1 under N2. The difference between the oxic and the anoxic CH4 fluxes was due to CH4 oxidation. The vertical CH4 concentration gradients indicated CH4 oxidation at 2–3 mm depth. Below this depth CH4 concentrations increased steadily to about 10 mm depth, below which accumulation of gas bubbles was observed. The diffusive flux calculated by Fick's first law from the linear part of the gradient was 166 ± 14 nmol cm−2 d−1. Obviously, the flux calculated from molecular diffusion was smaller than the flux that was actually measured under N2. An important condition for the use of Fick's law is that the slope of the gradient used for the calculation is taken in the direction where the slope is steepest. This direction is not necessarily identical with the vertical direction if CH4 concentrations also change in horizontal direction. Measurement of horizontal and vertical CH4 profiles demonstrated that the gradients had a three‐dimensional structure. The reason for this structure was that the isopleths of identical CH4 concentrations followed the uneven surface of the gas bubble layer as the main direct source for the CH4 diffusion gradients. We conclude that gas bubbles do not only directly cause a CH4 flux by ebullition but also indirectly affect the diffusional flux of CH4 in soil or sediment. When the diffusive CH4 flux was calculated from the concentration gradient at 6–8 mm depth, it was larger (224 ± 70 nmol cm−2 d−1) than from that at 3–5 mm depth (125 ± 86 nmol cm−2 d−1). Thus, a transport process in addition to molecular diffusion seemed to be active in the upper soil layers, possibly bioirrigation.
Exopolymer production by intertidal epipelic diatoms
Authors: Smith David J. , Underwood Graham J. C.
Published: May 2010

Epipelic diatoms are motile, the locomotive force being generated by the extrusion of carbohydrate‐rich exopolymers (EPS). Production rates of EPS, colloidal (water‐soluble) carbohydrates, and glucan (a photosynthetic storage product of diatoms) were investigated in axenic cultures, in sediments under laboratory conditions, and in the field. In stationary‐phase axenic monocultures of Cylindrotheca closterium, Navicula perminuta, and Nitzschia sigma, EPS concentrations significantly increased during darkness. EPS concentrations in darkness corresponded to decreases in glucan concentration. Glucan concentrations increased significantly in illuminated cultures, Identical patterns of concentration changes were observed in intact diatom‐dominated sediments. Inorganic 14C incorporation was used to determine rates of production and flux of photoassimilates through the different carbohydrate fractions in intact sediments. Biofilms exhibited endogenous rhythms of primary and carbohydrate production under laboratory conditions in the absence of tidal influence and under constant illumination (200 µmol m−2 s−1). Maximum production (27.7 mg C m−2 h−1) occurred during periods when sediments would have been emersed had they remained in the field, with 8.0, 3.0, and 0.8% of photoassimilates being incorporated into colloidal‐S, glucan, and EPS, respectively. Higher rates of primary production were measured under natural illumination (617 µmol m−2 s−1) in the field (82.7 mg C m−2 h−1), but the maximum incorporation into colloidal‐S, glucan, and EPS was similar (10.9, 2.8, and 1.0%, respectively). Pulse experiments revealed that 14C initially incorporated into glucan was subsequently reallocated into EPS. Increases in labeled EPS occurred up to 4 h after 14C incorporation, coinciding with periods of migratory activity linked to impending tidal immersion. Production of EPS by epipelic diatoms therefore appears to be closely linked to migratory rhythms, During periods of photosynthesis, assimilated carbon is stored as intracellular glucan, as well as being utilized to produce EPS. A number of stimuli increase the production of EPS: dim light, darkness, and migration linked to tidal immersion. Such increases in EPS production can be met either by increasing the allocation of photoassimilated carbon from current photosynthesis or by reallocating an internal carbon source. This short‐term variability in EPS production has implications for our understanding of estuarine carbon budgets and biogenic stabilization of sediments.
Relationship between microcystin production and cell division rates in nitrogen‐limited Microcystis aeruginosa cultures
Authors: Orr Philip T. , Jones Gary J.
Published: May 2010

Analysis of changes over time in microcystin content of nitrogen‐limited Microcystis aeruginosa (Kützing) Lemmermann batch cultures (strain MASHOl‐A19) showed that net microcystin production was limited to the phase of growth when cell concentration was increasing. The net microcystin production rate decreased as the specific cell division rate (µc) decreased, but, more importantly, the specific toxin production rate (µMCYST) decreased at an identical rate to that of µc when the culture became nitrate‐limited. The actual size of the microcystin pool (total culture microcystin concentration) increased while cells were dividing, then remained constant or decreased only slightly during the stationary and death phases, even when the cultures were severely nitrate‐starved. These findings demonstrate conclusively that the processes of cell division and microcystin production are tightly coupled under nitrogen‐limited cell division. Our findings suggest that microcystin production is controlled by environmental effects on the rate of cell division, not through any direct effect on the metabolic pathways of toxin production. Reevaluation of data presented by others shows this to be the case for two other cyanobacterial species producing nine different microcystins over a wide range of environmental variables. We believe these relationships now provide a unifying view of environmental control of microcystin production in hepatotoxic cyanobacteria. We conclude that there is a direct linear correlation between cell division and microcystin production rates in all microcystin‐producing cyanobacteria regardless of the environmental factor that is limiting cell division. We also conclude that microcystin is not a secondary metabolite, as is currently thought, but that it displays many of the attributes of essential intracellular nitrogenous compounds in toxigenic cyanobacteria.
Current meters for measurement of low‐speed velocities in ice‐covered lakes
Authors: Glinsky Alexander
Published: May 2010

Two current meters for measurement of low‐speed currents in ice‐covered lakes, a “drag‐wire” current meter (DWCM) and an acoustic current meter (ACM), are presented. The recording range is 0.1–20 mm s−1 for the DWCM and 0.2–70 mm s−1 for the ACM. The accuracy, obtained from laboratory calibration, is ±30% of the velocity reading and ± 10° for direction for the DWCM and ±40% of the velocity reading and ± 10° for direction for the ACM. Comparison of the two devices in the field and between simultaneous DWCM recordings and drogue observations, performed in a wind‐protected hole in the ice, showed reasonable agreement.
A new method to measure the terminal velocity of small particles: A demonstration using ascending eggs of the Atlantic menhaden (Brevoortia tyrannus)
Authors: Cambalik John J. , Checkley David M. , Kamykowski Daniel
Published: May 2010

A new method, incorporating video, motion analysis, and a novel experimental apparatus, was used to measure the terminal velocity of particles. The method facilitated the investigation of treatment effects and maximized the number of measurements For each replicate, thus improving the statistics for a population of particles. The eggs of the Atlantic menhaden (Brevoortia tyrannus) were used to demonstrate the method by investigating the effects of salinity and stage of development on their ascent rate. Egg ascent rate was greatest at intermediate salinity (36.5‰) and decreased in the late stage of embryonic development. We estimate eggs at oceanic salinities (>35.5‰) in nature to ascend at 0.19–0.25 cm s−1.
Measuring gross uptake of 15N‐labeled nitrogen by marine phytoplankton without particulate matter collection: Evidence of low 15N losses to the dissolved organic nitrogen pool
Authors: Slawyk Gerd , Raimbault Patrick , Garcia Nicole
Published: May 2010

Present 15N tracer techniques allowing indirect estimates of gross uptake of dissolved inorganic nitrogen (DIN) from measurements of DIN net uptake and DIN loss to the dissolved organic nitrogen (DON) pool (DIN gross uptake = DIN net uptake + DIN loss) require collection by filtration of particulate organic nitrogen (PON). We introduce a simple and reliable method that avoids this filtration step and permits direct determination of DIN gross uptake. The method involves (1) collection after 15N tracer addition and incubation of a 300‐ml sample, (2) removal of initial DIN, (3) conversion of total organic nitrogen (PON + DON) to DIN, (4) recovery of formed DIN, and (5) quantification of mass and 15N enrichment of initial and formed DIN. Gross uptake rates obtained in parallel from experiments without particulate matter collection (WOPMC) and with particulate matter collection (WIPMC) were in good agreement (R2 = 0.99) with values ranging from about 0.2 nM h−1 (open ocean) to 200 nM h−1 (culture). Variation in gross uptake rate in a set of five replicate samples, processed using both the WOPMC and WIPMC methods, was less than 7%. Losses of DIN to the DON pool were found to be negligible in laboratory cultures and represented on average only 15% of gross DIN uptake in the open ocean. Experimental considerations suggest that high DIN losses (≥50% of gross DIN uptake) to the DON pool are unlikely for healthy and actively growing cells and probably are limited to dying cells loosing their organic nitrogen content during postbloom situations (cell lysis) and/or during sloppy feeding by zooplankton (cell rupture).
Viruses in Antarctic lakes
Authors: Kepner Raymond L. , Wharton Robert A. , Suttle Curtis A.
Published: May 2010

Water samples collected from four perennially ice‐covered Antarctic lakes during the austral summer of 1996–1997 contained high densities of extracellular viruses. Many of these viruses were found to be morphologically similar to double‐stranded DNA viruses that are known to infect algae and protozoa. These constitute the first observations of viruses in perennially ice‐covered polar lakes. The abundance of planktonic viruses and data suggesting substantial production potential (relative to bacterial secondary and photosynthetic primary production) indicate that viral lysis may be a major factor in the regulation of microbial populations in these extreme environments. Furthermore, we suggest that Antarctic lakes may be a reservoir of previously undescribed viruses that possess novel biological and biochemical characteristics.
Nitrate uptake and diffusive nitrate supply in the Central Atlantic
Authors: Planas Dolors , Agustí Susana , Duarte Carlos M. , Granata Tim C. , Merino Martín
Published: May 2010

The latitudinal variation (35° to 28°N) in the rate of diffusive nitrate supply across the thermocline and the associated variation in the uptake rate of nitrate and ammonium in the Central Atlantic was studied. The calculated diffusive nitrate flux showed a sharp latitudinal gradient, with the lowest nitrate supply (0.00037 μmol m−3 d−1) in the South Atlantic subtropical gyre and the highest values (23.5 μmol m−3 d−1) between the Equator and 15°N. The uptake rate of nitrate was inhibited at high irradiance at most stations. Both nitrate and ammonium uptake rates were lowest (about 3 and 10 umol m−3 d−1, respectively) at the southern end of the transect and increased (about 20 and 55 μmol m−3 d−1, respectively) towards the Equator, with this increase being much greater for ammonium than for nitrate uptake. The f‐ratio was highest (≈0.4) just south of the Equator and lowest (≈0.03) at the southern end of the transect. The slope between total uptake rate of dissolved inorganic nitrogen and gross primary production, calculated from O2 ‐based measurements, in surface waters (4.72 ± 1.54) was somewhat lower, but not significantly so, than the expected C/N ratio of 6.6. The average uptake rate of nitrate did not differ significantly from the average estimated diffusive supply of nitrate to the biogenic layer over the Central Atlantic. However, the nitrate uptake rate increased as the ⅓ power of the diffusive nitrate flux to the biogenic layer. As a result, nitrate uptake far exceeded (by up to 100‐fold) the nitrate flux to the biogenic layer in the stations where the supply of nitrate was lowest. The excess nitrate uptake averaged 0.65 ± 0.24 mmol NO3 m−2 d−1 (range, 0.05–1.9 mmol NO3 m−2 d−1), which must be supplied through atmospheric deposition and other perturbation events. This excess nitrate uptake is relatively large compared to the diffusive supply in the most unproductive areas, where external nitrate inputs fuel the new production. In contrast, these sources of nitrate are far less significant where high diffusive fluxes suffice to maintain high nitrate uptake rates.
Selective feeding on natural phytoplankton by Calanus finmarchicus before, during, and after the 1997 spring bloom in the Norwegian Sea
Authors: Meyer‐Harms Bettina , Irigoien Xabier , Head Robert , Harris Roger
Published: May 2010

Selective feeding by the calanoid copepod Calanus finmarchicus was investigated during a 3‐month study in spring 1997 at a permanent station in the Norwegian Sea (Sta. M, 66°N, 02°E). Phytoplankton biomass increased from 317 ng chlorophyll a (Chl a) liter−1 in the prebloom phase to 2,095 ng liter−1 during the bloom and declined after the bloom to 1,260 ng Chl a liter−1. In the prebloom phase, clearance rates of C. finmarchicus females were between 22 and 100 ml copepod−1 d−1, while during the bloom, they ranged from 75 to 92 ml copepod−1 d−1, with a decline in the postbloom phase (41 ml copepod−1 d−1). After the phytoplankton bloom, the C. finmarchicus population was dominated by copepodid stages CIV and CV, with clearance rates ranging from 7 to 23 ml copepod−1 d−1. Grazing rates of adult females on the phytoplankton standing stock were low in the prebloom phases (5–23 Chl a copepod−1 d−1, respectively), increased during the bloom from 82 to 219 ng Chl a copepod−1 d−1, and declined after the bloom (64 ng Chl a copepod−1 d−1 for adult females and 7–27 ng Chl a copepod−1 d−1 for copepodid stages CIV and CV). C. finmarchicus showed a selection for diatoms throughout the study period and for dinoflagellates, before and after the spring bloom, despite the low concentration of both groups in the pre‐ and postbloom phases. During the postbloom period, no differences were observed in the selective feeding behavior of the copepodid stages compared to the adults. The contribution of diatoms to the overall phytoplankton biomass was 8 and 14% in the pre‐ and postbloom periods, respectively, while dinoflagellates were ≦3%. Haptophytes (dominated by Phaeocystis pouchetii) and cryptophytes were ingested according to their abundance. Avoidance of cyanobacteria (Synechococcus spp.), pelagophytes, and “green algae” was observed throughout the study period.
Physical constraints of chemoreception in foraging copepods
Authors: Moore Paul A. , Fields David M. , Yen Jeannette
Published: May 2010

The small‐scale spatial and temporal dynamics of phycosphere‐sized chemical signals entrained within the feeding current of copepods is quantified here by combining flow visualization techniques with electrochemical technology (IVEC‐10). Using the 30‐μm electrochemical probe sampling at 50 Hz and the velocity gradients created by two marine copepods, we evaluated how odor deformation improves the potential for remote chemoreception. Our data show that when shear is strong, as found in the feeding current of an omnivore, Pleuromamma xiphias, elongation of the chemical signal is greater than that found for an odor signal entrained in the low‐shear feeding current of a carnivore, Euchaeta rimana. Furthermore, within the feeding current of a single species, E. rimana, certain areas provided greater potential for remote chemoreception. These results support the hypotheses that chemical signals are deformed by the feeding current and that the feeding current structure enhances signal detection. The deformation of the odor field within the laminar feeding current provides a leading edge that gives a chemosensitive copepod early warning of an approaching odor source. By sensing the leading edge, a copepod could have a few hundred milliseconds to reorient itself with respect to the odor source. Advance warning improves the probability of successful behavior in response to signal sources such as prey, predators, and mates.
Redfield behavior of carbon, nitrogen, and phosphorus depletions in Antarctic surface water
Authors: Hoppema Mario , Goeyens Leo
Published: May 2010

Inspired by the recent debate about anomalous nutrient utilization ratios in the surface oceans, we calculated depletions of total carbon dioxide, nitrate, and phosphate for the surface layer of the western Weddell Sea in summer. The depletion ratios, which incorporate all changes over a period of about 3 months starting from the onset of the vegetative season, essentially follow the classical Redfield model. We argue that reliable Redfield ratios can only be obtained when the time interval over which the nutrient utilization ratios are determined is comparable to the length of the vegetative season. Nutrient depletions are perfectly suitable to obtain reliable nutrient consumption ratios. We have good reason to believe that in the surface waters of the Antarctic, as they are nutrient replete, the nutrient consumption ratios comply with the classical Redfield values.
Growth rates of copepods in the southern Benguela upwelling system: The interplay between body size and food
Authors: Richardson Anthony J. , Verheye Hans M.
Published: May 2010

Copepod growth rates were estimated from shipboard measurements of egg production of adult female Calanus agulhensis, Calanoides carinatus, Nannocalanus minor, and Centropages brachiatus and molting rates of juvenile stages (N6–C5) of C. agulhensis. Data were obtained during austral spring and summer of 1989–1995 in the southern Benguela upwelling system. While maximum growth rates showed less than a threefold decline over the body‐size range examined (525–2,763‐µm total length), probably owing to allometric considerations, mean growth rate decreased by one order of magnitude, suggesting limitation of growth rate by an environmental factor. Most of this decline in mean growth rate was attributable to food limitation of large copepods. Frequency distributions of growth rate under low food densities were severely skewed toward slow growth rate for large copepods, whereas they were more symmetric for smaller copepods. In contrast, at high food concentrations, the frequency distributions had a high degree of symmetry for all copepods. These frequency distributions were interpreted in terms of a probabilistic model describing the encounter rate of copepods with suitably sized food particles. The effect of food limitation on growth rate was evaluated by regressing the coefficient of variation of growth rate against body size. A strong positive relationship was found (r2 = 0.94, P < 0.001), indicating that small copepods were always growing well, whereas the growth rate of large copepods was more variable. It is suggested that this difference is a consequence of the ability of small copepods to consume small particles, which are present at a relatively constant background density.
Absorption efficiencies and biochemical fractionation of assimilated compounds in the cold water appendicularian Oikopleura vanhoeffeni
Authors: Bochdansky Alexander B. , Deibel Don , Rivkin Richard B.
Published: May 2010

Using 68Ge:14C dual‐labeling, we investigated the absorption efficiency of diatom carbon for the cold water appendicularian Oikopleura vanhoeffeni. The absorption efficiency of bulk carbon (mean = 67%) was not influenced by body size or ingestion rate. For the first time for a pelagic tunicate, food and feces were fractionated into their major biochemical constituents (i.e., low‐molecular‐weight compounds, lipid, protein, and polysaccharide), allowing calculation of absorption efficiencies for each fraction. Low‐molecular‐weight compounds and proteins were pref‐erentially absorbed over lipids and polysaccharides. However, predicted C:N ratios of the fecal pellets of O. vanhoeffeni were in the lower range of C:N ratios reported for zooplankton feces. The results are relevant for modeling biogeochemical cycles because pelagic tunicates contribute greatly to vertical particulate organic carbon flux.
Seasonal change in the optical properties of the permanent ice cover on Lake Bonney, Antarctica: Consequences for lake productivity and phytoplankton dynamics
Authors: Fritsen Christian H. , Priscu John C.
Published: May 2010

Geophysical and ecological dynamics within lakes of the McMurdo Dry Valleys, Antarctica, are controlled by the presence of permanent ice covers. Despite the importance of the permanent ice cover, there have been no studies that have examined specific couplings between changes in the geophysical properties of the ice covers and dynamic ecological processes within the underlying water column. Herein we present seasonal irradiance and primary production data from Lake Bonney, Taylor Valley, and we show that the phenomena of “ice whitening” is caused by changes in the scattering properties within the upper meter of the ice column and that the timing and extent of this phenomena exerts a predominant constraint on primary production and overall phytoplankton dynamics.
Population biology of a failed invasion: Paleolimnology of Daphnia exilis in upstate New York
Authors: Hairston Nelson G. , Perry Linda J. , Bohonak Andrew J. , Fellows Meghan Q. , Kearns Colleen M. , Engstrom Daniel R.
Published: May 2010

Viable diapausing eggs of Daphnia exilis, a species within the Daphnia similis species complex, occur in sediments of Onondaga Lake, New York. The discovery of this species, which otherwise occurs exclusively in temporary saline ponds in southwestern North America, represents a range extension of 1,000 km. 210Pb‐dating of the sediments containing diapausing eggs indicates that D. exilis was present in Onondaga Lake between the mid‐1920s and the early 1980s. The species' introduction, successful colonization, and subsequent disappearance from the water column correspond temporally with distinct events in the history of industrial activity along the shores of the lake and with the paleoecological record of this activity deposited in Onondaga Lake sediments. Only the most recently deposited diapausing eggs (late 1970s to early 1980s) hatch during laboratory incubation; older eggs may not be viable because of toxic concentrations of mercury pollution in older sediments. The D. exilis eggs that have hatched have had strikingly low genetic (allozyme) variation in comparison with the variation documented for populations in the southwestern United States by Hebert and Finston (1993). Exploration of various invasion scenarios through simulated introduction of genotypes from the southwestern United States suggests that a single genotype established the D. exilis population in Onondaga Lake. These observations document the ecological and microevolutionary patterns associated with an invasion by an exotic crustacean that currently persists only in the sediment egg bank.
Carbon fixation by phytoplankton in high Arctic lakes: Implications of low temperature for photosynthesis
Authors: Markager Stiig , Vincent Warwick F. , Tang Evonne P.Y.
Published: May 2010

Photosynthesis vs. irradiance relationships were determined for phytoplankton communities from seven lakes in the Canadian high Arctic, including ultraoligotrophic Char Lake, nutrient‐enriched Meretta Lake, and two meromictic lakes. The derived photosynthetic parameters were low for all samples, with a mean (±SD) light‐saturated photosynthetic rate (PmB) of 0.46 (±0.28) g C g−1 chlorophyll a (Chl a)h−1 and a mean αB(light‐limitation parameter) of 1.23 (±0.56) g C g−1 Chl a m2 mol−1. The saturation irradiance (EΚ) ranged from 50 to 196 μmol quanta m−2 s−1 and was positively correlated with mean irradiance for the water column. Quantum yields for photosynthesis in the Arctic lake phytoplankton were also low (mostly <10 mmol C mol−1 quanta). An intersystem comparison of αB and PmB values with literature data for algae from other cold environments showed that the photosynthetic parameters for phytoplankton in Arctic and Antarctic lakes are three‐ to sixfold lower than for marine algae, ice algae, and cultures over the same low‐temperature range. This may be the result of more severe nutrient stress in high latitude lakes relative to polar marine environments and to the persistence of nonactive pigments in cold freshwaters.
Bio‐optical properties of the marine diazotrophic cyanobacteria Trichodesmium spp. II. A reflectance model for remote sensing
Authors: Subramaniam1 Ajiit , Carpenter Edward J. , Falkowski Paul G.
Published: May 2010

The spatial and temporal distribution of Trichodesmium in the world's oceans is highly variable and can potentially be assessed using satellite imagery. Distinguishing these organisms from other phytoplankton in the upper ocean using remotely sensed information, however, requires an optical model that uniquely characterizes Trichodesmium. Here, we parameterize a standard remote‐sensing reflectance model using measured values of Trichodesmium's inherent optical properties, namely the spectral dependence of the chlorophyll‐specific optical absorption cross‐sections and the spectral dependence of the chlorophyll‐specific backscatter cross‐sections. Values for the chlorophyll‐specific absorption cross sections are described in the previous paper. We calculated the spectral chlorophyll‐specific backscattering cross‐section (b*b) from measurements of the chlorophyll‐specific volume‐scattering function and the spectral backscatter coefficients. b*b was 0.0027 m2 (mg chlorophyll a [Chl a])−1 at 436 nm and 0.002 m2 (mg Chl a)−1 at 546 nm; these cross‐sections are approximately one order of magnitude higher than those for "typical" phytoplankton. The optical model revealed that the combination of high backscatter, absorption, and fluorescence could be used to distinguish moderate to high concentrations (>1 mg Chl m−3)of Trichodesmium from other phytoplankton. The model also predicted that surface scum blooms of Trichodesmium would have high reflectance in the near infrared. The high reflectance feature of surface Trichodesmium blooms was used in conjunction with sea truth and data from the advanced very high resolution radiometer (AVHRR) to map a 300,000‐km2 Trichodesmium bloom off the Somali Coast in May 1995. The nitrogen fixed by this bloom was estimated to be 9.4 × 108 gN d−1. These results demonstrate the potential of using remote‐sensing techniques in the estimation of nitrogen fixation and the contribution of nitrogen fixation to global biogeochemical processes.
Oxygen and carbon dioxide mass balance for the estuarine‐intertidal marsh complex of five rivers in the southeastern U.S.
Authors: Cai Wei‐Jun , Pomeroy Lawrence R. , Moran Mary Ann , Wang Yongchen
Published: May 2010

We measured dissolved O2 concentrations, pCO2 values, and respiratory rates in five estuaries of the southeastern U.S. in October 1995 and July 1996. In the low‐salinity sections of the coastal plain rivers, dissolved O2 saturation states were typically only 50%, while pCO2 values were over 4,000 matm. Respiratory rates measured concurrently in estuarine water averaged 8 and 23 mmol m−3 d−1 in October 1995 and July 1996, but they showed little variability either within or among the five estuaries. Benthic chamber incubations in the adjacent intertidal marshes indicated fluxes of 30–40 mmol m−2 d−1 and 50–120 mmol m−2 d−1 for O2 and total dissolved inorganic carbon (DIC), respectively. For the Satilla River estuary, simple calculations revealed that neither respiratory activity in estuarine waters and sediments nor any other within‐estuary process (not including the intertidal marsh system) was sufficient to account for the observed O2 concentrations and pCO2 values. Dissolved oxygen concentrations in four other southeastern U.S. estuaries fit the same general pattern as the Satilla, and likewise, within‐estuary processes could not explain observed gas concentrations. Measured O2 concentrations, pCO2 values, pelagic respiratory rates, and benthic fluxes were used to construct a mass‐balance model, focusing on the influence of the extensive intertidal marshes on O2 and CO2 mass balance and water‐atmosphere gas exchange in the five estuaries. Results indicate that respiratory activity in the sediments and overlying water of the marshes during high tide leaves a signal that is funneled back to the estuary during ebb tide and can account for the estuarine gas concentrations and fluxes. Both experimental and modeling approaches argue that the intertidal marshes of the southeastern U.S. export considerable amounts of inorganic respiratory products to the estuaries and that “outwelling” of organic matter to the estuaries is a minor process by comparison. The DIC exported to the coastal ocean, however, is only a small fraction of the total gas mass flow between the marsh, estuary, and atmosphere.
Radiocarbon in marine bacteria: Evidence for the ages of assimilated carbon
Authors: Cherrier Jennifer , Bauer James E. , Druffel Ellen R. M. , Coffin Richard B. , Chanton Jeffrey P.
Published: May 2010

It is generally accepted that marine bacteria utilize labile, recently produced components of bulk dissolved organic matter. This interpretation is based largely on indirect measurements using model compounds and plankton‐derived organic matter. Here, we present an assessment of the relative proportions of modern and older dissolved organic carbon (DOC) utilized by marine bacteria. Bacterial nucleic acids were collected from both estuarine (Santa Rosa Sound, FL) and open‐ocean (eastern North Pacific) sites, and the natural radiocarbon signatures of the nucleic acid carbon in both systems were determined. Bacterial nucleic acids from Santa Rosa Sound were significantly enriched in radiocarbon with respect to the bulk DOC and were similar to the radiocarbon signature of atmospheric CO2 at the time of sampling, indicating that these bacteria exclusively assimilate a modern component of the estuarine bulk DOC. In contrast, bacterial nucleic acids from the oceanic site were enriched in 14C relative to the bulk DOC but depleted in 14C with respect to modern surface dissolved inorganic carbon (DIC) and suspended particulate organic carbon (POCsusp). This suggests that open‐ocean bacteria assimilate both modern and older components of DOC. The distinct radiocarbon signatures of the nucleic acids at these two sites (i.e., +120 ± 17‰ estuarine vs. −34 ± 24‰ oceanic) demonstrate that natural 14C abundance measurements of bacterial biomarkers are a powerful tool for investigations of carbon cycling through microbial communities in different aquatic systems.