bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissolution from a liquid CO2 lake disposed in the deep ocean
Authors: Fer Ilker , Haugan Peter M.
Published: July 2010

The dissolution from a liquid CO2 lake source located at a flat ocean bottom at 3,000 m depth is investigated. Using the unsteady, two‐dimensional advection‐diffusion equation, temporal and spatial distribution of CO2 dissolved from the source of 500 m length and of unit span is sought in a domain of 20 km horizontal and 200 m vertical extent. Different cases were run with uniform longitudinal speed and constant horizontal and vertical diffusion coefficients and with vertical profiles of velocity and diffusivity derived from turbulent boundary layer theory. Each case was run with and without a hydrate film at the interface between the seawater and the liquid CO2. The properties of the hydrate film are modeled using a capillary permeation model. The computations show that the presence of a hydrate layer retards the dissolution rate by a factor of 2.7 when the density effects due to the increase of CO2 concentration as a result of the dissolution are neglected. However, the strong, stable stratification above the hydrate layer, as a consequence of the increase in density of seawater enriched by CO2, suppresses the vertical mixing considerably and reduces the sensitivity to hydrate. The dissolution rate is found to be 0.1 m yr𢀒1 for realistic vertical profiles of longitudinal velocity (order of 5 cm s𢀒1) and diffusivity. However, during conditions of a benthic storm (20 cm s𢀒1), the dissolution rate reaches 1.6 m yr𢀒1.
Horizontal transport and dispersion in the surface layer of a medium‐sized lake
Authors: Stocker Roman , Imberger Jörg
Published: July 2010

Lagrangian GPS drifter experiments, carried out in the surface layer of stratified Lake Kinneret (Israel), are presented. Differential kinematic properties and Lagrangian statistics were calculated and used to estimate the dominant mechanisms for horizontal dispersion. On time scales smaller than a few internal wave periods, internal waves lead to strong divergence and convergence events, causing instantaneous apparent horizontal growth rates that were larger, by up to an order of magnitude, than the actual mean dispersion coefficient. It is shown that the internal wave field modulated the vorticity field so as to satisfy conservation of potential vorticity. On time scales larger than a few internal wave periods, unbounded horizontal shear dispersion was of the same order as the actual mean observed dispersion coefficient (Kxy = 17.1 m2 s−1), while vertical shear dispersion was negligible.
Photolysis and the dimethylsulfide (DMS) summer paradox in the Sargasso Sea
Authors: Toole Dierdre A. , Kieber David J. , Kiene Ronald P. , Siegel David A. , Nelson Norman B.
Published: July 2010

Apparent quantum yields and rates of dimethylsulfide (DMS) photolysis were determined from Sargasso Sea seawater with the goal of assessing the extent to which photoreactions affect the unusually elevated upper ocean concentrations of DMS during the summer, the so‐called DMS summer paradox. Apparent quantum yields determined with monochromatic radiation decrease exponentially with increasing wavelength and indicate that DMS photolysis is driven by ultraviolet (UV) radiation. The relative spectral partitioning differs between samples collected from the surface mixed layer (15 m) and from the chlorophyll a maximum (80 m), presumably because of differences in chromophoric dissolved organic matter (CDOM) quality (e.g., apparent degree of bleaching). Quantum yields are also temperature dependent, and an approximate doubling of photolysis rates occurs for a 20°C increase in temperature. The significance of DMS photolysis to upper ocean sulfur budgets is explored using a multiyear (1992–1994) DMS time series, concurrent irradiance determinations and temperature profiles, and estimates of CDOM absorption. Depth‐integrated, mixed‐layer DMS photolysis rates peak in the summer (15–25 µmol m−2 d−1) and decline to ,1 µmol m−2 d−1 in the winter. These rates correspond to specific turnover rates of ~0.29 d−1 in the summer and > 0.02 d−1 in the winter. Seasonal changes in solar radiation, temperature, and DMS concentrations drive the 30‐fold differences in photolysis rates, overshadowing differences caused by photosensitizer (CDOM) quantity or quality (21–35%). These results demonstrate that although photolysis is not the primary driver of the summer paradox, it makes an important contribution to the time‐depth pattern of DMS concentrations observed in the Sargasso Sea.
Evaluating the influence of macrophytes on algal and bacterial production in multiple habitats of a freshwater wetland
Authors: Stanley Emily H. , Johnson Mark D. , Ward Amelia K.
Published: July 2010

Algal 14C uptake and bacterial 3H leucine incorporation were measured over 20 months to assess the influence of macrophytes on the spatial distribution and magnitude of microbial production and the relative importance of algae versus macrophytes to whole‐system energy flow in a southeastern U.S. wetland. Algal and bacterial production were determined for water column and plant‐, sediment‐, and wood‐surface microhabitats in four zones defined by aquatic vascular plant composition: no macrophyte, floating leaved (Nymphaea odorata), heterophyllous (Proserpinaca palustris), or emergent macrophyte (Juncus effusus) zones. We combined production data with detailed habitat measurements to estimate production at meter‐squared and whole‐wetland scales and compared microbial C fixation to concurrently determined rates of macrophyte production. Production on plant surfaces was significantly lower than on wood and benthic sediments in all zones. At a meter‐squared scale, 79% of algal production and 74% of bacterial production occurred on sediments, with epiphytes contributing ,6% to both algal and bacterial rates. With the exception of phytoplankton in the Nymphaea zone and bacteria on Juncus zone sediments, production in the water column or on plant or sediment surfaces did not significantly differ among macrophyte zones. Thus, plant type did not affect the spatial distribution of microbial activity except in the Juncus marsh, where the limited area and volume of water per square meter reduced production at larger spatial scales. However, the magnitude of bacterial production was influenced by macrophytes, as bacterial carbon demand greatly exceeded the amount supplied by algal production. At the whole‐ecosystem scale, macrophytes overwhelmed algal production, which accounted for only 4–10% of total wetland C fixation.
Enhanced phosphorus accumulation efficiency by the pelagic community at reduced phosphorus supply: A lake experiment from bacteria to metazoan zooplankton
Authors: Teubner Katrin , Crosbie N. D. , Donabaum K. , Kabas W. , Kirschner A. K. T. , Pfister G. , Salbrechter M. , Dokulil M. T.
Published: July 2010

The effects of experimentally reduced total phosphorus concentrations (TP) from 2.4 to 0.6 µmol L−1 on plankton community in a shallow lake were evaluated from the proportion between dissolved reactive P (DRP), dissolved nonreactive P (DOP) and particulate organic P (POP), and the stoichiometry among particulate organic carbon (POC), nitrogen (PON), and POP. In both triple ratios, DRP:DOP:POP and POC:PON:POP, we used POP as a key component to indicate shifts between P fractions and between nutrients in particulate organic matter. The enhanced P accumulation by the planktonic assemblage by 14% at reduced P supply was achieved by two steps, in the first year mainly at the expense of DOP and in the second year by DRP. The evidence that this increase of %POP of TP reflects the adaptive P utilization of the organisms under low P supply was substantiated by significant relationships between P fractions and changes in the community. A higher %POP of TP was associated with higher specific alkaline phosphatase activity and with tighter coupling between producers and consumers respectively—that is, driven from both the nutrient‐producer and the producer‐consumer interface. A lowered %DOP of TP was significantly related to smaller overall loss rates for the carbon pool of bacteria and algae, whereas %DRP of TP was correlated to the decrease of the biomass of most organism groups. Stoichiometric shifts toward a P‐rich assemblage under low TP have been justified by compositional shifts from N‐rich cyanobacteria to P‐rich eukaryotic algae and bacteria. The shifts toward POP in both triple ratios strongly indicated that the plankton community acted as a sink for phosphorus under reduced total pool size.
Measurements of phosphate affinity constants and phosphorus release rates from the microbial food web in Villefranche Bay, northwestern Mediterranean
Authors: Tanaka Tsuneo , Rassoulzadegan Fereidoun , Thingstad T. Frede
Published: July 2010

Using 32>P, uptake and transfer of phosphorus in the microbial food web were studied in surface water from Villefranche Bay (northwestern Mediterranean) from September to December 2001. During the study, the thermocline gradually declined and vertical mixing started, leading to a transition from a nutrient‐depleted period to a nutrient‐replete period. Before vertical mixing started, the orthophosphate turnover time ranged from 1 to 5 h. Orthophosphate uptake was dominated by the 0.6–2 µm size fraction (mean, 70%), where the cyanobacteria biomass was dominant. The estimated affinity constants for bacteria, cyanobacteria, and autotrophic nanoflagellates ranged from 0.001 to 0.028, 0.047 to 0.103, and 0.002 to 0.032 L nmol P−1 h−1 during the period, with relatively short (> 5 h) orthophosphate turnover times. These results suggest that cyanobacteria were superior for orthophosphate uptake among osmotrophs. For cyanobacteria and autotrophic nanoflagellates, the mean affinity constants were almost at the theoretical maximum predicted by diffusion‐limited uptake. On the basis of a cold‐chase technique, release rates of dissolved 32P from labeled particles were > 0.5% h−1, which corresponds to a turnover time of the particulate fraction up to three orders of magnitude greater than that of orthophosphate. Although a net loss of 32P occurred in the 0.2–0.6 and 0.6–2 µm fractions, a net increase in the <2 µm fraction suggested P transfer to the larger size fraction by predation. Viruses did not contribute significantly to 32P release from bacteria during the study period.
Experimental studies on the accumulation of polonium‐210 by marine phytoplankton
Authors: Stewart Gillian M. , Fisher Nicholas S.
Published: July 2010

Bioaccumulation of polonium‐210 (t1/2 = 138 d) in marine phytoplankton can introduce this naturally occurring radioisotope into food chains, where it accounts for most of the radiation dose to marine organisms and to human consumers of seafood. Moreover, this isotope could be useful as a tracer of the flux of organic matter in ocean surface waters. We performed laboratory experiments with eight algal species representing six algal divisions to quantify the uptake, cellular partitioning, and retention of 210Po by algae. Biological uptake was unaffected by temperature or light, and volume concentration factors (VCFs) for these algal species ranged between 0.5 and 3.0 × 104. Interspecific differences in VCFs could be explained by considering the surface area to volume ratios of the cells and cellular protein content. Once associated with the cells, between 30 and 60% of the total cellular 210Po was in the cytoplasm of the different species. 210Po was not irreversibly bound to the cells but displayed a biological half‐life of ~23 d. Because 210Po associates appreciably with organic matter inside cells, unlike other particlereactive nonessential metals, it could have promise as a tracer of sinking organic matter in the ocean.
A shallow scattering layer: High‐resolution acoustic analysis of nocturnal vertical migration from the seabed
Authors: Kringel Keli , Jumars Peter A. , Holliday D.V.
Published: July 2010

Using bottom‐mounted, high‐frequency, inverted echo sounders (the Tracor acoustic profiling system) to examine acoustic backscattering every 2 min in 50‐cm range bins above the seabed, we recorded strong, remarkably regular, nightly migrations of organisms from ≥0.5 m above the seabed to the upper pelagic layers over a period of 6 d in July—August 1995. Population migration speeds on ascent versus descent (mean ± 1 SD) were not significantly different when estimated from the mode (or leading/trailing edge) of the population and were 0.59 ± 0.24 cm s−1 in ascent (0.96 ± 0.25 cm s−1 leading edge) and 0.67 ± 0.13 cm s−1 on descent (0.78 ± 0.14 cm s−1 trailing edge). The SD in start times of the ascent over the six nights was only 3 min, and that in the times of the completion of the descent was 7 min. Emergence began after and reentry was completed before downwelling irradiance at photosynthetically active wavelengths 1 m above bottom reached 0.5 X 10−6 µmol quanta cm−2 s−1. Migrators increased column scattering strength at 265 kHz by a factor of 14. Emergence‐trap samples and nighttime plankton tows suggested that the migrating population was dominated by mysids, mostly Neomysis kadiakensis. Our acoustic results suggest that emergence is much more prevalent and important in coastal and estuarine environments than trapping and net sampling can reveal and hence that this important component of benthic‐pelagic coupling requires additional attention both in measurements and in theoretical treatments.
Cryptic coloration and mirrored sides as camouflage strategies in near‐surface pelagic habitats: Implications for foraging and predator avoidance
Authors: Johnsen Sönke , Sosik Heidi M.
Published: July 2010

Mirrored and colored surfaces are common adaptations for crypsis in pelagic habitats. Although highly successful when optimized for a particular situation, either may become less successful if it is then viewed in a different situation. In this study we examine the relative robustness of these two strategies by determining how visible an organism becomes when viewed under optical conditions different from those under which the camouflage is optimal. Underwater radiance distributions were calculated using inherent optical properties measured in coastal waters 80 km off the coast of New Hampshire. These radiance distributions were then used to calculate optimally cryptic diffuse and specular reflectance spectra as a function of depth, solar elevation, viewing angle, and azimuth. Then the visibilities of organisms cryptic in one situation viewed in a different situation were calculated, using the Atlantic Cod, Gadus morhua, as the viewer. In contrast to benthic organisms, pelagic organisms cryptic under one set of optical conditions were quite visible under a different set, particularly when viewed from a different azimuth. The crypsis afforded by mirrored surfaces was generally more robust than that resulting from colored surfaces. However, because mirrored surfaces could never be perfectly cryptic when viewed in the azimuth of the sun, neither strategy clearly outperformed the other. In general, crypsis by colored or mirrored surfaces was not robust in nearsurface water, which may help explain both the predominance of transparent species in near‐surface pelagic habitats and the vertical migration of many colored and mirrored species. The results also show that three common foraging strategies—circling, crepuscular activity, and driving prey toward the surface—all increase the visibility of cryptically colored or mirrored prey.
Photoinhibition in shallow‐water colonies of the coral Stylophora pistillata as measured in situ
Authors: Winters Gidon , Loya Yossi , Röttgers Rüdiger , Beer Sven
Published: July 2010

Continuous pulse amplitudeߚmodulated (PAM) fluorescence measurements were performed in situ under natural irradiances for colonies of the coral Stylophora pistillata growing in shallow (2 m) and deeper (11 m) waters of the Red Sea. The effective quantum yield (ΔF/F′m ) showed a diurnal pattern inversely related to that of the incident downwelling photosynthetically available radiation (PAR), but this pattern was skewed for the shallow colonies such that the values were always lower in the afternoon than during morning hours when measured at similar irradiances. Accordingly, the relative photosynthetic electron transport rate (rETR, = ΔF/F′m × incident PAR) for those colonies also showed lower values in the afternoons than in the mornings at equal irradiances. The rETRs also saturated well before maximal midday irradiances occurred. At the same time, nonphotochemical quenching (NPQ, measured as [Fm ‐ F′m ]/F′m ) was higher in the afternoons than during the mornings under similar incident PAR values. These results indicate an afternoon loss in photosynthetic capacity from photoinhibition. Such photoinhibition was not apparent during the course of the day in the corals growing in deeper water. The latter also showed no saturation of photosynthesis at the highest incident PAR values at noon (which were approximately a third of those at the shallower site). In addition, the shallow‐growing corals showed significantly lower maximum quantum yields (ΔF/F′m measured during nighttime, equivalent to Fv/Fm) than the deeper growing ones. This is most likely caused by an additional, more chronic, photoinhibition in the shallow‐growing corals but could also be due to some form of photoacclimation or to factors other than light.
Lysogeny and virus‐induced mortality of bacterioplankton in surface, deep, and anoxic marine waters
Authors: Weinbauer Markus G. , Brettar Ingrid , Höfle Manfred G.
Published: July 2010

Lysogeny (bacteria containing inducible prophages) and lytic viral infection (bacteria in a lytic stage of infection) were investigated at the community level in contrasting marine environments such as estuarine versus offshore waters, surface versus deep waters, and oxic versus anoxic waters in the Mediterranean and Baltic Seas. The frequency of lysogenic cells (FLC) in bacterioplankton communities ranged from not detectable to 84% as estimated by prophage induction due to mitomycin C, and highest values were typically found in deep waters (800–2,000 m). Transmission electron microscopy based estimates of virus‐induced mortality of bacterioplankton (VMB) ranged from a few percent to 71%, and highest values were found in anoxic waters of the Baltic Sea. FLC and the frequency of infected cells (FIC) were related in form of a negative power function indicating that environments exist where one of the two viral life strategies prevails. Across all investigated environments, FLC was negatively related to bacterial abundance and production, whereas FIC showed a positive relationship with viral and bacterial parameters. FIC was higher and FLC was lower in moderately productive estuarine and offshore surface waters than in less productive mesopelagic and deep waters. Thus, lysogeny seems to be a survival strategy at low host abundance and activity, whereas high host abundance and activity seems to favor the lytic life cycle. The key process for the prevalence of lytic infection compared to prophage replication at high host abundance could be competition due to outnumbering. Between 11% and 88% (average, 35%) of the bacteria contained a functional (lytic or lysogenic) viral genome.
Phytoplankton production in a large, regulated river: A modeling and mass balance assessment
Authors: Sellers Tim , Bukaveckas Paul A.
Published: July 2010

Phytoplankton production in riverine systems is regulated by hydrologic processes and coupled optical dynamics, which determine the light dosages experienced by phytoplankton during transit within a defined reach. We used data on river stage, discharge, and channel geomorphometry to model changes in light availability experienced by phytoplankton during transit within a 122‐km navigational pool of the Ohio River. Whole‐pool estimates of phytoplankton production were derived from photosynthesis‐irradiance relationships and modeled values of light availability.
Hydrologic and hydraulic control of macrophyte establishment and performance in streams
Authors: Riis Tenna , Biggs Barry J. F.
Published: July 2010

Macrophytes play a key role in many unshaded lotic ecosystems, but little is known of the factors controlling their presence, abundance, and composition. Macrophyte abundance, diversity, and composition were studied in 15 New Zealand streams to test the hypotheses that the presence and development of macrophytes in lotic systems is primarily controlled by the hydrologic regime (frequency of high‐velocity flood events) and that the interflood spatial distribution and performance of taxa in more stable systems is strongly influenced by local hydraulic conditions (depth/velocity/sediments). Both hypotheses were supported by our results. We found that the abundance and diversity of macrophytes decreased as flood disturbance frequency increased (r2 = 0.52, P = 0.002 for abundance; r2 = 0.53, P = 0.022 for diversity) and that vegetation was absent in streams with more than ~13 high‐flow disturbances per year. An experiment in an ecohydraulics flume identified that the main mechanism causing these effects was not stem breakage at high water velocity but probably uprooting associated with bed sediment erosion. We found that plants with high propagule production constituted a greater proportion of the vegetation in more flood disturbed streams than in stable streams, suggesting that this species trait is important for the maintenance of macrophyte communities in flood prone streams. Distinct velocity, depth, and substrate particle size habitat preferences were displayed by four common species in the study streams. None of the macrophytes showed overlapping preferences for all three habitat variables, suggesting coexisting of the species in streams by physical niche separation. These results significantly expand our understanding of the role of flow regimes in determining lotic ecosystem structure and functioning.
Distribution of particulate, colloidal, and dissolved mercury in San Francisco Bay estuary. 1. Total mercury
Authors: Choe Key-Young , Gill Gary A. , Lehman Ronald
Published: July 2010

Surface water samples were collected from the San Francisco Bay estuary in September‐October 2000 (low flow) and March 2001 (high flow). Total mercury (Hg) concentrations were measured in unfiltered, filter‐passing (<0.45 µm), colloidal (1 kDa‐0.45 µm), and dissolved (<1 kDa) fractions. Particulate Hg was the dominant phase (88 ± 7%, n = 29) in unfiltered water. Suspended particulate matter (SPM) explained most particulate Hg concentrations in the northern reach. A significant portion of filter‐passing Hg was associated with colloidal Hg, accounting for 38 ± 18% (n = 9) in the fall and 57 ± 10% (n = 12) in the spring. Seasonal variability of the filter‐passing Hg concentration observed in the upper estuary was attributed to the temporal change in the riverine colloidal Hg. The strong correlation observed between Hg and organic carbon in the filter‐passing fraction indicates that organic material is an important transport medium of Hg in San Francisco Bay. Assessment of various forms of the particle‐ water distribution coefficient revealed that Hg was preferentially associated with SPM during the low flow period but that colloidal material played as important a role in Hg phase speciation as SPM during the high flow condition. A steady‐state nonconservative estuarine mixing model suggested that the northern reach had an internal source of colloidal Hg in September‐October, possibly from resuspended sediments, and a sink of colloidal Hg within the estuary in March 2001.
Distribution of particulate, colloidal, and dissolved mercury in San Francisco Bay estuary. 2. Monomethyl mercury
Authors: Choe Key-Young , Gill Gary A.
Published: July 2010

The phase speciation and estuarine behavior of monomethyl mercury (MeHg) were determined in surface waters of the San Francisco Bay estuary in September‐October 2000 (low flow) and March 2001 (high flow). Colloidally associated MeHg was isolated using a cross‐flow ultrafiltration technique with a nominal molecular weight cutoff of 1 kDa. Filter‐passing MeHg was 57 ± 18% of the MeHg in unfiltered water in the fall and 39 ± 12% in the spring. Colloidal MeHg averaged 34 ± 11% of the filter‐passing MeHg in the fall and 56 ± 15% in the spring. Significantly higher particle‐water partition coefficients were observed between colloidal and dissolved MeHg (log Kc = 5.6 ± 0.3, n = 21) compared with those between particulate and dissolved MeHg (log KP = 4.9 ± 0.5, n = 21), which suggests that MeHg is preferentially associated with colloidal material. Strong correlations of MeHg with organic carbon content in the filter‐passing, colloidal, and dissolved fractions confirmed the importance of organic matter in the MeHg cycle. Both absolute and relative (as a percentage of Hg) MeHg concentrations were highest in the river water end‐member under both flow regimes, which suggests that riverborne MeHg is the major source of MeHg introduced to the estuary. A nonconservative estuarine mixing model suggests that significant amounts of colloidal and dissolved MeHg are removed in the estuary under both flow regimes, standing in marked contrast to Hg, which had a source within the estuary under the low flow condition.
Atmospheric deposition of inorganic phosphorus in the Levantine Basin, eastern Mediterranean: Spatial and temporal variability and its role in seawater productivity
Authors: Markaki Z. , Oikonomou K. , Kocak M. , Kouvarakis G. , Chaniotaki A. , Kubilay N. , Mihalopoulos N.
Published: July 2010

Total and dissolved inorganic phosphorus (IP) was measured in both rainwater and aerosol samples collected from two remote coastal areas: on the island of Crete (Greece) and at Erdemli (Turkey). Particle size distributions of P, as well as total deposition were also measured. Wet and dry deposition of dissolved inorganic phosphorus (DIP) from Crete are compared with simultaneously obtained dissolved inorganic nitrogen (DIN) and with productivity data from the literature. Our results indicate that (1) in both wet and dry deposition, the DIN/DIP molar ratio ranges between 63 and 349, exceeding by a factor of up to 22 the N/P ratio observed in seawater (ranging from 25 to 28) and (2) atmospheric deposition of DIP could reasonably account for a significant part of the new production (up to 38%) observed during the summer and autumn period (i.e., when water stratification is at its maximum).
On the relative constancy of iodate and total‐iodine concentrations accompanying phytoplankton blooms initiated in mesocosm experiments in Antarctica
Authors: Truesdale VictorW. , Kennedy Hilary , Agusti Susana , Waite TimJ.
Published: July 2010

The integrated iodate and total‐iodine concentrations accompanying accelerated growth of natural phytoplankton in eight 14‐m deep mesocosm experiments did not vary significantly. Growth was induced by the addition of nutrients, while light irradiance was controlled by neutral density screens. These measures resulted in a range of particulate organic carbon concentrations of between 13 and 220 µmol L−1, that is, covering some that are well in excess of blooms generally found in the natural environment. This, together with most earlier results obtained from phytoplankton culturing and much hydrographic survey, is used as an opportunity to question whether phytoplankton growth can be the cause of iodate reduction in seawater.
Metabolic and structural response of hyporheic microbial communities to variations in supply of dissolved organic matter
Authors: Findlay Stuart E. G. , Sinsabaugh Robert L. , Sobczak William V. , Hoostal M.
Published: July 2010

Hyporheic sediment bacterial communities were exposed to dissolved organic matter (DOM) from a variety of sources to assess the interdependence of bacterial metabolism and community composition. Experiments ranged from small‐scale core perfusions with defined compounds (glucose, bovine serum albumin) to mesocosms receiving natural leaf leachate or water from different streams. Response variables included bacterial production, oxygen consumption, extracellular enzyme activity, and community similarity as manifest by changes in banding patterns of randomly amplified polymorphic DNA (RAPD). All DOM manipulations generated responses in at least one metabolic variable. Additions of both labile and recalcitrant materials increased either oxygen consumption, production, or both depending on background DOM. Enzyme activities were affected by both types of carbon addition with largest effects from the labile mixture. Cluster analysis of RAPD data showed strong divergence of communities exposed to labile versus recalcitrant DOM. Additions of leaf leachate to mesocosms representing hyporheic flowpaths caused increases in oxygen consumption and some enzyme activities with weaker effects on production. Community structure was strongly affected; samples from the leachate‐amended mesocosms clustered separately from the control samples. In mesocosms receiving water from streams ranging in DOC (0.5–4.5 mg L−1), there were significant differences in bacterial growth, oxygen consumption, and enzyme activities. RAPD analysis showed strongest clustering of samples by stream type with more subtle effects of position along the flowpaths. Responses in community metabolism were always accompanied by shifts in community composition, suggesting carbon supply affects both functional and structural attributes of hyporheic bacterial communities.
Hypolimnetic oxidation rates in Lake Superior: Role of dissolved organic material on the lake's carbon budget
Authors: McManus James , Heinen Erik A. , Baehr Matthew M.
Published: July 2010

On average, the water column of Lake Superior is undersaturated with respect to dissolved oxygen and supersaturated with respect to carbon dioxide during the summer‐stratified period. On the basis of temporal changes in water column dissolved oxygen, we calculate rates of oxygen consumption that range from 0.19 to 0.75 mmol m−3 d−1. These rates are a factor of 5–10 times larger than can be supported by the particulate carbon settling rates and benthic oxygen consumption rates. In addition, on the basis of the limited information available, dissolved allochthonous carbon inputs are insufficient to account for the calculated rates of carbon oxidation. Rates of nitrate and total CO2 ΣCO2) production are 0.019 ± 0.012 and 0.13 ± 0.06 mmol m−3 d−1, respectively, and are consistent with the oxidation of a dissolved organic component that is similar in composition (C :N ratio) to the settling particulate material. Previously published estimates of total primary production were smaller but similar in magnitude to our integrated water column respiration rates. We interpret the observed imbalance between particulate carbon delivered to the deep lake and the calculated rate of carbon oxidation to be the result of the decomposition of dissolved organic carbon that appears to have both an autochthonous and an allochthonous component.
Quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in Lake Baikal, Siberia
Authors: Ryves David B. , Jewson David H. , Sturm Michael , Battarbee Richard W. , Flower Roger J. , Mackay Anson W. , Granin Nikolai G.
Published: July 2010

Endemic planktonic diatoms are a major component of Lake Baikal sediments during interglacial periods. To investigate how these diatom assemblages are altered during sediment formation, quantitative plankton monitoring (1995–1998) was integrated with sediment trapping over 2 yr (1996–1997) in Baikal's southern basin (depth ~1,400 m). The traps consisted of both open (~6 monthly) and sequential (~2 weekly) collectors deployed throughout the water column. Sedimentation was seasonal, with diatom species composition, valve abundance, and total dry massreflecting changes in the planktonic communities. Sedimented assemblages were transmitted largely intact to the deepest traps (~1,300–1,390 m); some compositional blurring occurred from differential sinking rates and dissolution of diatom valves. A rapid mass flux event of Aulacoseira skvortzowii and A. baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d−1 and dry mass fluxes >5 g m−2 d−1. Although dissolution was evident for all species, more delicate taxa were preferentially affected (e.g., A. skvortzowii vegetative cells and fine Synedra species), whereas Nitzschia acicularis valves were almost entirely dissolved within the water column. Comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment, with sedimentary diatom accumulation rates being only about 1% of trap deposition and plankton production rates. Dissolution was significant in explaining 5–30%
Allochthonous organic carbon decreases pelagic energy mobilization in lakes
Authors: Jansson Mats
Published: July 2010

Over the past decade, it has been shown that unproductive lakes worldwide are net heterotrophic because bacterial respiration of allochthonous organic carbon (AOC) makes community respiration exceed primary production. Net heterotrophy means that aquatic systems are net sources of
A Synechococcus serotype is found preferentially in surface marine waters
Authors: Toledo Gerardo , Palenik Brian
Published: July 2010

In marine ecosystems, gradients of light, temperature, and nutrients occur horizontally (coastal to offshore) and vertically. The extent to which microorganisms acclimate or speciate in response to these gradients is under active investigation. Strain isolation data (e.g., site or depth), environmental DNA clone libraries, and preliminary physiology experiments have indicated that marine Synechococcus strain CC9605 might be adapted to the surface oligotrophic ocean. In the present work, we used an immunofluorescent approach to detect the CC9605 serotype in the California Current during September 1998. At two offshore stations, samples were collected along vertical profiles. The relative abundance of the CC9605 serotype was significantly higher in shallow depths within the mixed layer than in deeper depths at the two stations, with maximum values (± standard deviation) of 10.3% ± 6.4 and 28.7% ± 9.5. Surface samples along an offshore‐inshore transect showed higher abundance in the most oligotrophic site (8% v 3), compared with almost 1% inshore, but one coastal site also had high relative abundance of the CC9605 serotype (7% ± 0.5). These data indicate that Synechococcus strains are not uniformly distributed and that some strains, such as CC9605, are more abundant in the mixed layer of the euphotic zone than below the mixed layer.
Growth rates of coastal phytoplankton from time‐series measurements with a submersible flow cytometer
Authors: Sosik Heidi M. , Olson Robert J. , Neubert Michael G. , Shalapyonok Alexi , Solow Andrew R.
Published: July 2010

Our understanding of the dynamics of phytoplankton communities has been limited by the space and timescales associated with traditional monitoring approaches. To overcome some of these limitations, we have developed a submersible flow cytometer (FlowCytobot) that is designed for extended autonomous monitoring of phytoplankton abundance, cell size, and pigmentation. FlowCytobot was moored on the seafloor from late July to October 2001 at the Long‐term Environmental Observatory study site off the coast of New Jersey, and water samples from 5 m depth were pumped continuously through the instrument. Analysis of cells' optical properties revealed distinct populations of Synechococcus and cryptophytes, as well as an assemblage of other pico‐ and nanophytoplankton of mixed taxonomy. For each of these groups, dramatic variations in cell concentration were observed within the sampling period. Diel variations in cell scattering, which are indicative of changes in cell size, were consistent with patterns of cell growth during the light period and cell division late in the day. We developed a size‐structured matrix population model that accommodates simultaneous growth and division and then used the model and size distribution data from FlowCytobot to estimate daily specific growth rates for Synechococcus; these estimates are independent of cell concentration and do not include mortality. The results show that a dramatic autumn decline in the concentration of Synechococcus can be attributed to a decrease in the specific growth rate rather than to effects of physical transport processes or trophic interactions.
Production and partitioning of organic matter during simulated phytoplankton blooms
Authors: Wetz Michael S. , Wheeler Patricia A.
Published: July 2010

Few studies have examined the partitioning of organic matter in upwelling systems, despite the fact that these systems play a key role in carbon and nitrogen budgets in the ocean. We examined the production and partitioning of phytoplankton‐derived organic matter in deck incubations off Oregon during the upwelling season. During exponential growth of the phytoplankton, ≥78% of total accumulated organic matter was in particulate (POM) form. This suggests that dissolved organic matter (DOM) is a small fraction of primary production during the exponential growth of coastal phytoplankton blooms. After nitrate depletion, carbon‐rich (C :N ≥ 16) DOM accumulated in incubations dominated by the diatom Chaetoceros sp., accounting for 38% (±8.5%) of accumulated total organic carbon (TOC) and 24% (±8%) of accumulated total organic nitrogen (TON). However, in a bloom dominated by the diatom Leptocylindrus minimus, a relatively smaller amount of DOM accumulated, accounting for only 15% of accumulated TOC and 7% of accumulated TON. On the basis of measured concentrations of nitrate and accumulated TOC, ~70%–157% more carbon was fixed than would be predicted by Redfield stoichiometry (referred to as "excess carbon fixation"), with 20%–69% of the excess carbon fixation occurring after nitrate depletion. The accumulation of carbon‐rich DOM and excess carbon fixation suggests that nitrate assimilation (i.e., new production) might not equate to net production of POM in coastal upwelling systems.
The uptake of silica during the spring bloom in the Northeast Atlantic Ocean
Authors: Brown Louise , Sanders Richard , Savidge Graham , Lucas Cathy H.
Published: July 2010

A full understanding of the biogeochemical cycling of silica in the North Atlantic is hampered by a lack of estimates of silica uptake by phytoplankton. We applied the 32Si radiotracer incubation technique to determine silica uptake rates at 10 sites during the UK‐(Natural Environment Research Council) Faroes‐Iceland‐Scotland hydrographic and environmental survey (FISHES) cruise in the Northeast Atlantic, May 2001. Column silica uptake rates ranged between 6 and 166 mmol Si m−2 d−1; this data set was integrated with concurrent hydrographic, chemical, and primary productivity data to explain these changes in silica uptake in terms of the progress of the spring bloom. In order to interpret data covering a relatively large spatial and temporal scale, we used mean photic zone silica concentration as a proxy time‐series measure of diatom bloom progression. Both absolute and specific silica uptake rates were highest at dissolved silica concentrations >2 µmol L−1. Si and C uptake were vertically decoupled at those stations where surface silica was strongly depleted. Absolute primary productivity was not strongly correlated with dissolved silica concentrations, owing to either exhaustion of silica at diatom‐dominated stations or to dominance of the community by other phytoplankton. Silica uptake as a function of increased substrate concentration was linear up to 25 µmol L−1; we consider some possible reasons for the nonhyperbolic response.
Diminished efficiency in the oceanic silica pump caused by bacteria‐mediated silica dissolution
Authors: Bidle Kay D. , Brzezinski Mark A. , Long Richard A. , Jones Janice L. , Azam Farooq
Published: July 2010

Previous laboratory findings indicated that marine bacteria accelerate biogenic silica (bSiO2) dissolution rates in the sea by degrading the organic coating surrounding diatom frustules and exposing the underlying silica to chemical attack by undersaturated seawater. We examined the effectiveness of bacterial activity in facilitating in situ bSiO2 dissolution during a diatom bloom in Monterey Bay, California, following moderate upwelling. Inhibition of bacterial activity with antibiotics and protease inhibitors reduced specific bSiO2 dissolution rates (Vdis) at five of six stations, with a reduction of 44 ± 27% (mean ± SD, n = 6, range 22–91%) over 24 h. Reduced Vdis in inhibitor treatments corresponded with reductions in abundance, production, and proteolytic activity of attached bacteria. Dissolution rates were highly correlated with protease activity integrated from the surface down to the depth where each dissolution was measured, suggesting that increased Vdis with depth in the upper 20–80 m of the ocean is caused by the progressive removal of organic matter from frustules during sinking. Facilitation of bSiO2 dissolution by in situ bacterial assemblages varied between stations and was likely influenced by the physiological condition of resident diatom assemblages. Denaturing gradient gel electrophoresis and 16S rRNA gene sequencing of bacteria colonizing in situ diatom assemblages confirmed previous findings that specific bacterial phylotypes (Cytophaga/Flavobacteria/Bacteriodes; a and g subclasses of Proteobacteria) mediate bSiO2 dissolution.
Fish facilitate wave resuspension of sediment
Authors: Scheffer Marten , Portielje Rob , Zambrano Luis
Published: July 2010

The resuspension of sediment by waves or currents is a major cause of turbidity in many shallow waters. Here we show that bottom‐feeding fish greatly facilitate this process by reducing the erosion resistance of the sediment. We use a fish‐removal experiment from a large Dutch lake to show that the absence of fish makes sediment resistant to wind effects, and we use controlled lab experiments to demonstrate that the effect of fish can be explained by the characteristic hole‐punching behavior used in the search for food. Undisturbed sediment in the laboratory consolidated rapidly. The critical water velocity needed for resuspension roughly doubled in 2 weeks. However, the acquired erosion resistance could be virtually eliminated by holes corresponding to only 2% of the sediment area. An analysis of a model based on our experimental results suggested that benthivorous fish may prevent sediment consolidation that, in the absence of fish, would sufficiently stabilize the sediment during a quiet period to resist wave resuspension during subsequent windy periods. Our results imply that, even in exposed shallow lakes that are turbid because of wind resuspension, a temporary reduction of fish stock may work as "shock therapy"to restore an alternative stable clear‐water state.
The role of submerged macrophyte beds in phosphorus and sediment accumulation in Lake Memphremagog, Quebec, Canada
Authors: Rooney Neil , Kalff Jacob , Habel Catherine
Published: July 2010

The relationships between long‐term (~115‐year) phosphorus and sediment accumulation and submerged macrophyte biomass were determined both within a submerged macrophyte bed and among beds in Lake Memphremagog, Quebec, Canada. Strong relationships between present submerged macrophyte biomass and littoral‐zone sediment and phosphorus accumulation rates both within and among macrophyte beds yielded simple models for estimating long‐term littoral‐zone accumulation rates. Mean sediment particle size at the depth of maximum submerged macrophyte biomass, estimated from water content, was comparable with the mean particle size in profundal zone of Lake Memphremagog, suggesting that energy environments differ little between vegetated littoral zones and profundal zones. The mean total sediment‐accumulation rate of 1.2 mm yr−1 in the macrophyte beds was indistinguishable from average profundal rates of sediment accumulation in North American lakes. Although dense beds accumulated twice as much bulk sediment per unit area (g m−2 yr−1) compared with their profundal counterparts, phosphorus accumulation per unit bulk sediment in macrophyte beds with a biomass of 1,000 g m−2 (wet weight) was one sixth that measured in profundal sediments, pointing to large postdepositional losses of sedimented phosphorus (>70%) from macrophyte beds. Finally, extrapolation of the present results to five nearby lakes suggests, based on still‐limited data, that, in lakes in which half of the sediment surface is colonized by submerged macrophytes, the littoral zone accounts for roughly one third of whole‐lake phosphorus and two thirds of whole‐lake bulk sediment accumulated annually.
A comparison of egg‐bank and long‐term plankton dynamics of two Daphnia species, D. hyalina and D. galeata: Potentials and limits of reconstruction
Authors: Jankowski Thomas , Straile Dietmar
Published: July 2010

Resting eggs of planktonic organisms from datable sediment cores are increasingly used to reconstruct historical information on the abundance, size, genetic composition, and microevolution of planktonic organisms. All of these studies have relied on the (up to now) mostly untested assumption that the resting egg bank in sediment will indeed allow an accurate reconstruction of past populations. Here we test the performance of the egg bank to reconstruct historical data of the Daphnia population of Lake Constance, which was thoroughly investigated throughout the past century. We show that it is possible to reproduce the variability in the abundance, size, and genetic composition of Daphnia galeata within a period of ~2 decades. Furthermore, resting egg data allowed us to reconstruct the timing of the invasion of D. galeata into Lake Constance. However, the egg bank did not reconstruct (1) the dynamics of the native Daphnia species of Lake Constance, D. hyalina, and (2) the relative importance of the two Daphnia species. We present evidence that the latter is caused by differences in the sexually reproductive activity between the two species. The failure to reconstruct the long‐term dynamics of D. hyalina in the lake is most probably due to a change in the frequency and timing of sexual activity during the course of eutrophication.
Effect of the brittle star Amphiura filiformis (Amphiuridae, Echinodermata) on oxygen flux into the sediment
Authors: Vopel Kay , Thistle David , Rosenberg Rutger
Published: July 2010

O2 plays a key role in early sedimentary diagenetic processes, but the effect of most macrofaunal species on the pathways and rates of supply of O2 into the seabed are not well known. We investigated the effect of the ophiuroid Amphiura filiformis, one of the dominant macrobenthic species on soft bottoms in the northeast Atlantic, at depths of ~15–100 m, in a laboratory environment. We determined how the presence of the ophiuroid changed the total O2 uptake of macrofauna‐free sediment by combining measurements from a microcosm approach and an approach that uses microelectrodes and a flushed aquarium. We suggest that natural populations of A. filiformis can account for 80% of the total flux of O2 into the soft bottom. At least 67% of this portion is due to the diffusion of O2 across additional sediment‐water interfaces excavated by the brittle star.