bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of microbial Fe(III) oxide reduction in freshwater wetland sediments
Authors: Roden Eric E. , Wetzel Robert G.
Published: June 2010

The kinetics of microbial amorphous Fe(III) oxide reduction was investigated in sediments from a freshwater wetland in north central Alabama, USA. Fe(III) oxide concentrations decreased exponentially with time during anaerobic incubation of sediment slurries and homogenized surface sediments. Rates of organic carbon mineralization (ΣCO2 + CH4 accumulation) did not change markedly during the course of Fe(III) oxide reduction, which indicated that the exponential decline in Fe(III) oxide concentration over time resulted primarily from Fe(III) limitation rather than a decrease in organic matter decay rate. Initial rates of Fe(III) oxide reduction were linearly correlated with initial Fe(III) oxide concentrations in experiments with mixtures of Fe(III)‐rich and Fe(III)‐depleted sediment slurries. Similar results were obtained in experiments with sediment from various depth intervals in the upper 3 cm of freshly collected cores. These findings provide explicit evidence that microbial Fe(III) oxide reduction rates are first order with respect to amorphous Fe(III) oxide concentration in the wetland sediment. The observed first‐order relationship between Fe(III) oxide concentration and reduction rate is consistent with established models of surface area‐controlled mineral transformation. An experiment in which Fe(III) oxide‐rich sediment slurries were amended with different amounts of labile organic matter demonstrated a direct correlation between first‐order Fe(III) reduction rate constants and initial rates of organic carbon mineralization. These results provide empirical support for existing approaches to modeling organic matter decay‐dependent Fe(III) oxide reduction kinetics in sediments.
Seasonal variations in uptake and in situ regeneration of nitrogen in mangrove waters
Authors: Dham Vivek V. , Heredia Anjali Menezes , Wafar Sayeeda , Wafar Mohideen
Published: June 2010

Seasonal changes of uptake of nitrogenous nutrients (NH4+, NO3−, NO2−, and urea) and regeneration (NH4+ and NO2− production) in the plankton fraction of a mangrove ecosystem on the west coast of India were investigated. Nitrate was the major fraction of assimilable N (72%), followed by NH4+ (16%), NO2− (6%), and urea (6%). Changes of nutrient concentrations followed clear seasonal cycles and were mainly regulated by in situ biological processes. The plankton took up NO3− and NH4+ in more or less equal proportions (39 and 44% respectively), followed by urea (11%) and NO2− (6%). Seasonal patterns of uptake were distinct, with a dominance of NO3− and NO uptake in the postmonsoon, followed by a dominance of NH4+ and urea uptake in the premonsoon. The high and prolonged use of NO3− at the beginning of the productive season was due to a strong allochthonous supply of NO3−, dominance of microplankton, and low NH4+ regeneration rates. Heterotrophs may take up all four nutrients and could account for half of the annual total N uptake. Ammonium and NO2− regeneration rates were among the highest known from nearshore waters and showed clear seasonal patterns. Production and use of NH4+ were closely coupled. Nitrite production rates were related to NH4+ production rates in a rectangular‐hyperbolic fit. Nitrogen balance analyses showed that proximity to mangrove vegetation enhanced the flux rates, noninclusion of nitrification may lead to an overestimation of new production by 30%, and regeneration in the plankton fraction provided about 40% more N than was assimilated.
Nutrients and organic matter in a glacial river—floodplain system (Val Roseg, Switzerland)
Authors: Tockner Klement , Malard Florian , Uehlinger Urs , Ward J. V.
Published: June 2010

Nutrient and organic matter dynamics were evaluated for a glacial river—floodplain system in the Swiss Alps (Val Roseg). Glacial melt water was the primary source of particulate organic and inorganic matter; hillslope groundwater was richest in DOC and SiO2; and pulses in dissolved nitrogen were identified during spring snowmelt. Calculations of temporal coherency revealed that hydrological processes within the catchment—floodplain complex controlled nutrient and organic matter species along the main channel; however, local hydrological and/or biogeochemical processes played a major controlling role in most floodplain channels. DON and NO3−N were the only variables that were in average significantly correlated across all sampling sites. Comparisons of measured concentrations and concentrations based on a two end member mixing model indicated that the floodplain served as a major sink for particulate phosphorous and suspended matter but was never a source for nutrients or organic matter. Annual area‐specific export rates from the Val Roseg catchment were 7.6 kg ha−1 yr−1 for TOC (47% DOC), 4.3 kg for TP (98% particulate phosphorus), and 4.1 kg for TN (78% NO3−N).
Determination of apparent quantum yield spectra for the formation of biologically labile photoproducts
Authors: Miller William L. , Moran Miller , Sheldon Wade M. , Zepp Richard G. , Opsahl Stephen
Published: June 2010

Quantum yield spectra for the photochemical formation of biologically labile photoproducts from dissolved organic matter (DOM) have not been available previously, although they would greatly facilitate attempts to model photoproduct formation rates across latitudinal, seasonal, and depth‐related changes in spectral irradiance. Apparent quantum yield spectra were calculated for two coastal environments from the southeastern United States using postirradiation bacterial respiration as a measure of total labile photoproduct formation and a cutoff filter method to model spectral dependence. As has been the case for previously studied classes of DOM photoproducts (i.e., dissolved inorganic carbon, CO, and H2O2), ultraviolet (UV)‐B irradiance was significantly more efficient at forming labile photoproducts (i.e., compounds readily assimilated by marine bacterioplankton) than UV‐A and visible irradiance. Calculations of DOM photoproduct formation in southeastern U.S. coastal surface waters indicate a formation ratio for biologically labile photoproducts :CO of 13 : 1. The slope of a natural log plot of the apparent quantum yield spectrum obtained for biologically labile photoproducts was similar to that for CO (0.028 nm−1 vs. 0.034 nm−1). Modeled kinetic rates therefore indicate that the production ratio of these photoproduct classes is approximately maintained despite variations in the solar spectrum that occur with depth in a water column or distance from shore. Application of the apparent quantum yield to coastal regions worldwide predicts an annual formation rate of biologically labile photoproducts in coastal waters of 206 × 1012 g C.
Effects of temperature, nitrogen, and light limitation on the optical properties of the marine diatom Thalassiosira pseudonana
Authors: Stramski Dariusz , Sciandra Antoine , Claustre Hervé
Published: June 2010

A series of laboratory experiments were conducted to examine the optical properties of the marine diatom Thalassiosira pseudonana for a broad range of growth rates (µ from 0.22 to 2 d−1) under temperature‐, nitrogen‐, and light‐limited conditions. The effects of temperature and nitrogen limitation on spectral absorption cross‐sections expressed on a per cell basis, σa(λ), were similar. With the reduction in growth rate, σa at a light wavelength λ = 674 nm showed an equivalent decrease regardless of whether the cells were limited by temperature or nitrogen. The effect of growth irradiance was distinctively different, since σa increased with light limitation. The chlorophyll a (Chl a)—specific absorption coefficient showed the opposite trends than those of σa. These patterns resulted primarily from the acclimative strategies of T. pseudonana involving an increase in Chl a content in response to light limitation and a decrease in Chl a under temperature and nitrogen limitation. The scattering cross‐sections, σb(λ), and carbon‐specific scattering coefficients, b*c(λ), were generally not a strong function of growth rate with the exception of lower values of b*c for light‐limited cells. While T. pseudonana exhibited some changes in cell size, variations in the refractive index had the major influence on cell optical properties. The imaginary part of the refractive index (at λ = 674 nm) showed a strong correlation with intracellular Chl a concentration, and the real part of the refractive index (at λ = 660 nm) was correlated with the intracellular carbon concentration. Our results indicate that integrated studies of the effects of various environmental factors such as light, nutrients, and temperature are needed to adequately describe optical variability in phytoplankton.
The influence of food quality (P :C ratio) on RNA:DNA ratio and somatic growth rate of Daphnia
Authors: Vrede Tobias , Persson Jonas , Aronsen Grete
Published: June 2010

Growth experiments with juvenile Daphnia galeata were performed to investigate how fast their RNA:DNA ratio responds to changes in food quality, the relationship between RNA:DNA ratio and somatic growth rate, and the effect of food quality (P :C ratio) on the RNA:DNA ratio. RNA and DNA concentrations in individual daphnids were measured with a single‐dye (RiboGreen) fluorometric method. Algae were cultured in chemostats and different P :C ratios were obtained by altering the dilution rate and the P content of the medium. The RNA:DNA ratio of the daphnids responded within 5 h to differences in food quality. The RNA:DNA ratio was highly correlated with the somatic growth rate (r2 = 0.94), and the RNA:DNA ratio increased with increasing food P :C ratio below a threshold P :C ratio (by atoms) of approximately 0.005 (C : P ≈ 200). The response in RNA:DNA ratio to changes in food quality is rapid and consistent with previously reported patterns for somatic growth rate. This enables shortterm experiments that reduces the problems with keeping both food quantity and quality constant during incubation. Analysis of zooplankton RNA:DNA ratios in short‐term experiments has a potential for addressing questions about when and where food quantity, quality, or both limit zooplankton growth in nature.
Influence of temperature on Cd accumulation by species of the biomonitor Chaoborus
Authors: Croteau Marie-Noële , Hare Landis , Tessier André
Published: June 2010

We exposed larvae of several species of the phantom midge Chaoborus to the trace metal cadmium (Cd) to determine whether Cd accumulation rates varied with ambient temperature. Because this predator is known to accumulate its Cd mainly from food rather than from water, we presented the Cd in food, that is, Cd‐rich copepods taken from a lake near a metal smelter. Rates of Cd accumulation by larvae of Chaoborus americanus, C. flavicans, and C. punctipennis were measured at three temperatures (5, 14, and 228C) covering the seasonal range encountered by these animals. The rates at which all species accumulated Cd increased with temperature. To explain these results, we fit our experimental data to a bioaccumulation model that allowed us to estimate Cd assimilation efficiency, Cd‐efflux rate, and larval growth rate. Temperature‐related changes in Cd accumulation rates were best explained by changes in the rate at which Chaoborus larvae ingested prey as well as the efficiency with which they assimilated Cd from their food. Neither the rate of larval growth nor the rate at which larvae lost Cd was influenced by temperature. Extrapolations of our laboratory results to the field suggest that our model results provide a realistic representation of the processes involved in Cd accumulation by larvae of this common aquatic insect.
The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschiamultiseries and Pseudo‐nitzschia australis
Authors: Maldonado Maria T. , Hughes Margaret P. , Rue Eden L. , Wells Mark L.
Published: June 2010

Toxigenic pennate diatoms of the genus Pseudo‐nitzschia produce domoic acid (DA), the neurotoxin linked to amnesic shellfish poisoning. We investigated how Fe and Cu affect growth and DA production by P. multiseries and P. australis clones isolated from Monterey Bay, California. Growth rates of these species could be inhibited by both Fe limitation (pFe 20.5, µ = 50% ³max) and Cu toxicity (pCu 10.5, 00B5 =5 30−50% ³max). The rate of DA production during the exponential phase was a significant inverse function of cellular growth rates (P < 0.02). Voltammetric measurements of dissolved DA‐equivalents in short‐term experiments indicated that the cellular production of DA increased from ~5 amol DA cell−1 h−1 under optimal growth conditions to ~40 amol DA cell−1 h−1 under Fe‐deficient conditions and ~105 amol DA cell−1 h−1 under Cu‐stressed conditions. The DA was released to the medium under metal stress conditions, with intracellular DA concentrations decreasing relative to nonstressed cells. Fe uptake rates by P. multiseries were slow compared to other marine diatoms in the absence of dissolved DA but were enhanced threefold (P < 0.03) by adding DA to the medium. DA addition also partially alleviated toxic Cu conditions. Our findings suggest that DA production during exponential growth of these two toxigenic Pseudo‐nitzschia species is directly induced by Fe‐deficient or Cu stress conditions and that 95% of this DA is actively released into the medium. Changing trace metal conditions in coastal waters therefore may have a profound effect upon intracellular DA concentrations and thereby influence the toxic effect of these harmful bloom events.
Contribution of entrainment and vertical plumes to the winter cascading of cold shelf waters in a deep lake
Authors: Fer Ilker , Lemmin Ulrich , Thorpe S. A.
Published: June 2010

Observations made from vertical moorings of thermistors and current meters are used to analyze the relative contribution of the entrainment of overlying water and the cold plumes convecting from the surface to the cascade of dense shelf waters down the sides of Lake Geneva. Assuming a steady state and ignoring the effects of the Earth’s rotation, a simple model was introduced and 25 individual slugs of gravity currents were analyzed. The average drag coefficient, which includes the effects of friction on the slope and the interface between the gravity current and the ambient water, is found to be equal to CD = (4.6 ± 1.5) × 10−3. The volume flux in the gravity current increases with downslope distance—a consequence of both the entrainment of water into the gravity current and the supply of cold water from the plumes. Entrainment was found to be, on average, 1.9 ± 0.9 times the contribution of vertical plumes, suggesting that the latter may be important in the dynamics of the cascade.
Temporal, spatial, and taxonomic patterns of crustacean zooplankton variability in unmanipulated north‐temperate lakes
Authors: Rusak J. A. , Yan N. D. , Somers K. M. , Cottingham K. L. , Micheli F. , Carpenter S. R. , Frost T. M. , Paterson M. J. , McQueen D. J.
Published: June 2010

We quantified the spatial and temporal variability of crustacean zooplankton abundance at annual time steps with 261 lake‐years of data from 22 lakes in three regions of central North America. None of these lakes had been experimentally manipulated. Using a nested three‐way analysis of variance, we apportioned variance among years, regions, lakes, and their interactions for 10 functional groups and 4 larger taxonomic aggregates. We proposed that relative variation in the abundance of zooplankton would be greatest among regions and lakes and least among years. We also explored how variability differed among functional groups and changed with taxonomic aggregation. Spatial sources of variation dominated the analysis, but a large interaction between lakes and years indicated that time cannot be ignored. Regional variation was half that found among lakes. Relative variance components differed widely among functional groups, which indicates that species will differ in their response to environmental controls and sensitivity to perturbation. Total explained variation also differed widely among zooplankton and decreased with increasing aggregation of taxa. Whether choosing ecological indicators or designing experiments and monitoring programs, these results clearly show that large‐scale temporal and spatial variability will be an important consideration.
Assimilation and retention of selenium and other trace elements from crustacean food by juvenile striped bass (Morone saxatilis)
Authors: Baines Stephen B. , Fisher Nicholas S. , Stewart Robin
Published: June 2010

Estimates of the assimilation and retention of trace elements from food by fish are useful for linking toxicity with the biogeochemical cycling of these elements through aquatic food webs. Here we use pulse‐chase radiotracer techniques to estimate the assimilation and retention of Se and four trace metals, Ag, Am, Zn, and Cd, by 43‐ and 88‐d‐old juvenile striped bass, Morone saxatilis, from crustacean food. Brine shrimp nauplii, Artemia franciscana, or adult copepods, Acartia tonsa, were fed radiolabeled diatoms and then fed to juvenile striped bass. Assimilation efficiencies (AEs ± SD) for 43‐d‐old fish were 18 ± 2%, 6 ± 1%, 23 ± 4%, 33 ± 3%, and 23 ± 2% for Ag, Am, Cd, Se, and Zn, respectively. For 88‐d‐old fish, the AEs were 28 ± 1%, 42 ± 5%, and 40 ± 5% for Cd, Se, and Zn, respectively. The higher AEs in the older fish may result from longer gut passage times for larger fish. The 44‐d‐old fish excreted 5 ± 0.8%, 4 ± 2.0%, 7 ± 0.3%, 9 ± 0.4%, and 1.3 ± 0.9% of the Ag, Am, Cd, Se, and Zn, respectively, they ingested from food per day, whereas the 88‐d‐old fish excreted 3 ± 1.0%, 8 ± 0.5%, and 3 ± 0.5% of the assimilated Cd, Se, and Zn per day, respectively. Predictions of steady state Se concentrations in juvenile striped bass tissues made using a biokinetic model and the measured AE and efflux rates ranged from 1.8 to 3.0 mg Se g−1 dry wt for muscle tissue and 6.8 to 11.6 mg Se g−1 dry wt for gut tissue. These predictions agreed well with average values of 2.1 and 13 mg Se g−1 dry wt measured independently in North San Francisco Bay, where elevated Se concentrations are of concern. The model results imply that the planktonic food web, including juvenile striped bass, does not transfer Se as efficiently to top consumers as does the benthic food web.
Relative importance of carbon sources for macroinvertebrates in a Rocky Mountain stream
Authors: McCutchan James H. Jr. , Lewis William M. Jr.
Published: June 2010

Estimates of carbon sources, as determined from ratios of stable isotopes, were used in conjunction with estimates of secondary production to determine the relative contribution of algal carbon to macroinvertebrate production across a gradient of elevation in a Rocky Mountain stream (North St. Vrain Creek, Colorado). The relative contribution of algal carbon to macroinvertebrate production was then compared to the relative availability of algal carbon. Although algal production accounted for less than 2–40% of the combined sources of organic matter to North St. Vrain Creek, the relative contribution of algal carbon to annual macroinvertebrate production ranged from approximately 40% at a subalpine site to nearly 80% at a more open site in the foothills. Thus, the proportional contribution of algal carbon to consumer production greatly exceeded the relative availability of algal carbon in North St. Vrain Creek. Despite the disproportionate importance of algal carbon to consumers, most macroinvertebrates in North St. Vrain Creek used some vascular plant carbon.
Larval distributions in inner‐shelf waters: The roles of wind‐driven cross‐shelf currents and diel vertical migrations
Authors: Garland Elizabeth D. , Zimmer Cheryl Ann , Lentz Steven J.
Published: June 2010

To determine how physical processes and biological behaviors influence larval dispersal on the inner shelf, time series of larval concentrations were quantified during August 1994, on the Outer Banks of North Carolina, U.S.A. Zooplankton pumps, moored in 21 m of water at 3.2, 8.7, and 12.2 m above bottom, collected larvae every 3 h for 3 weeks. Physical variables and larvae were sampled at similar time and space scales. Larval concentrations were typically 102–104 m−3 for polychaetes, bivalves, and gastropods and 10–102 m−3 for brachyuran crab zoeae. There were two dominant scales of variability, 3–6 h and 2–10 d. The high‐frequency signal is partially explained by diel vertical migrations—nocturnal ascent and daytime descent. This pattern would allow larvae to feed in subthermocline waters while avoiding visual predators. Low‐frequency variations tracked with water temperature. Highest concentrations of worm larvae occurred in cool (upwelled) water and of crab zoeae in warm (downwelled) water. At least two larval groups comprised the clam and snail time series, one with fairly high abundances in cool water and the other with peak concentrations in warm water. Wind‐driven cross‐shelf transport is the most plausible explanation for these low‐frequency fluctuations. For example, dense patches of worm larvae overlying parental habitat (offshore muds) would be carried shoreward in cool, upwelling flows. In contrast, brachyuran zoeae in nearsurface waters would descend at the coast during downwelling and, together with larvae aloft nearshore sediments, be transported seaward below the thermocline. Thus advected by strong along‐shore and weaker cross‐shelf currents, larvae zigzag up and down the coast. Vertically traversing the water column while they feed and grow, larvae ultimately seek a suitable habitat in which to settle.
Copper toxicity and cyanobacteria ecology in the Sargasso Sea
Authors: Mann Elizabeth L. , Ahlgren Nathan , Moffett James W. , Chisholm Sallie W.
Published: June 2010

The closely related cyanobacteria Synechococcus and Prochlorococcus have different distributions in stratified water columns in the northern Sargasso Sea. The abundance of Synechococcus is relatively uniform with depth, but Prochlorococcus cell numbers are low within shallow mixed layers and high in and below the thermocline. Because free cupric ion (free Cu2+) concentrations are high (up to 6 pM) in shallow mixed layers and lower in deeper water, there is an inverse relationship between Prochlorococcus densities and the free Cu2+ concentration. We explored the possibility of a causal underpinning for this relationship by examining the relative copper sensitivities of Prochlorococcus and Synechococcus in cultures and field populations. Prochlorococcus isolates from both the highߚ and lowߚlight adapted ecotypes were inhibited at free Cu2+ concentrations that had no effect on Synechococcus. However, the highߚlight adapted strains were more copper resistant than their lowߚlight adapted counterparts. When copper was added to Prochlorococcus from environments where the in situ free Cu2+ was low (in deeply mixed water columns and below the mixed layer in stratified conditions), net growth rates were substantially reduced and cells arrested in the G1 and early S phases of the cell cycle. Prochlorococcus in shallow mixed layers were less sensitive to copper and were probably members of the copperߚresistant highߚlight adapted ecotype. Synechococcus were relatively copper resistant across a range of environments in the Sargasso Sea. These observations are consistent with our hypothesis that copper plays a role in cyanobacteria ecology in the Sargasso Sea.
Wind‐induced plume and bloom intrusions into Willapa Bay, Washington
Authors: Curtis Roegner G. , Hickey Barbara M. , Newton Jan A. , Shanks Alan L. , Armstrong David A.
Published: June 2010

The physical oceanography and chlorophyll distribution in Willapa Bay and the adjacent coastal ocean were measured during an upwelling‐downwelling wind cycle in late May 1999. Coastal conditions were determined shipboard during two sets of five cross‐shelf transects conducted 4 d apart, and instrument moorings simultaneously recorded wind velocity in the nearshore zone and biophysical water properties within Willapa Bay. The results demonstrate that estuarine physical oceanography and chlorophyll concentrations were determined by processes occurring in the nearshore ocean, and these in turn were forced by variation in wind stress. At the start of the study period, southerly winds produced downwelling conditions that forced the Columbia River plume against the coast, and low salinity water was advected into Willapa Bay. This water was relatively low in chlorophyll (<2 mg m-3). As the winds switched to an equatorward direction, coastal upwelling ensued and the Columbia plume was replaced by cold, salty water nearshore. A phytoplankton bloom exceeding 10 mg m-3 was generated on the shelf with its core located 10 to 40 km from the estuarine mouth. The upwelling‐favorable winds then relaxed, and the bloom was apparently advected across the shelf to the coast and subsequently into Willapa Bay, where instruments recorded pulses of chlorophyll entering the estuary on flood tides. Weak downwelling conditions were prevalent for the next several days, and the Columbia River plume returned to the coast where it mixed with the chlorophyll‐enriched waters in the nearshore before entering the estuary. These results demonstrate that primary productivity generated in coastal waters can be transported to estuaries, where it is likely an important yet episodic food source for estuarine organisms.
Deviating vertical distribution and increased conspicuousness of parasitized Calanus
Authors: Torgersen Thomas , Karlsbakk Egil , Kaartvedt Stein
Published: June 2010

Abnormally colored yellow and red Calanus spp. occurred in the Oslofjord (southeast Norway) in late summer. These specimens were infected with an extensive parasitic growth consisting of large branched hyphae‐like tubes filled with spores. This parasite has previously been referred to as Ichthyosporidium sp. (now Ichthyophonus, Ichthyosporea), and suspected to be a stage in the life cycle of the fish pathogen Ichthyophonus hoferi. This assumption was not supported by our examination. Infected copepods were virtually confined to the upper meter, while distribution of the uninfected specimens was much deeper. We argue that the change in color and distribution is induced by the parasite, facilitating nearsurface, visual predation, dispersal of spores, and, hence, increasing transmission to new hosts.
Origin of salinity variations in Florida Bay
Authors: Swart P. K. , Price R.
Published: June 2010

This note presents a method of distinguishing the source of freshwater that causes reductions in salinity in the coastal environment of South Florida. This technique, which uses the δ18O and δD of the water, allows for differentiation of the freshwater derived from precipitation as opposed to runoff, because surface waters in the Everglades have been highly evaporated and therefore have elevated δ18O and dD values relative to precipitation. A time series of monthly δ18O and δD values of surface waters, collected from stations in Florida Bay between 1993 and 1999, has shown that, during this time, the major source of freshwaters causing depressions in the salinity in the western portion of Florida Bay was derived from precipitation rather than from the runoff of water from the Everglades. In the eastern portion of Florida Bay, close to the boundary between peninsular Florida and the Bay, the proportion of freshwater derived from precipitation drops steadily, reaching <10%. This method not only allows differentiation between the sources of freshwater but can, in a temporal sense, ascertain the effectiveness of water management practices on the salinity of the estuarine ecosystems of South Florida.
Ultrasonic in situ measurements of density, adiabatic compressibility, and stability frequency
Authors: Gräfe Holger , Boehrer Bertram , Hoppe Niels , Müller Stefan C. , Hauptmann Peter
Published: June 2010

An in situ density profile has been measured with an ultrasonic density probe in the mining lake Merseburg‐Ost 1b. From the acquired measurements of sound speed and acoustic impedance, the important physical properties of in situ density and adiabatic compressibility could be calculated. It was also shown that these two properties sufficed to determine the stability frequency, which hence becomes a directly observable physical magnitude. Measurements of all magnitudes are presented. Currently the accuracy only suffices to provide new insight in the density structure of natural water bodies in cases of unusual composition of dissolved substances. However, as all required data are acquired in situ and density is measured directly, i.e., without need of empirical formulations (“equations of state”), the ultrasonic approach has the potential to become a reliable reference for density measurements in limnic waters, when chemical conditions are complex or spatial or temporal variation of dissolved substances becomes relevant for the stability of the water column.
The volume scattering function of natural bubble populations
Authors: Zhang Xiaodong , Lewis Marlon , Lee Michael , Johnson Bruce , Korotaev Gennady
Published: June 2010

The volume scattering function (VSF) of natural bubble populations is (1) determined from Mie scattering theory, (2) measured by a newly designed volume scattering meter in the laboratory, and (3) inferred from field observations of the VSF. The laboratory measurements have confirmed our theoretical prediction in that (1) bubbles of sizes that have been recorded in situ in the surface ocean (>10 μm) show elevated scattering for angles between 60° and 80° and (2) the organic coatings on the bubble surface will increase the scattering in the backward hemisphere but little change the scattering in the forward directions, including the critical angles. An optimization analysis is applied to the measurement of the VSF in coastal waters, and the results suggest the potential existence of submicron bubbles that are coated with organic film. The bubble population thus determined, which has a negligible contribution to the total scattering (5%), accounts for 40% of the total backscattering that has been observed in situ. The extension of the bubble size distribution to smaller sizes than can presently be measured by direct techniques will alter the shape of derived phase function in general but will result in rather small changes to the backscattering ratio (<20%) as long as the slope of the size distribution is small, because most of the changes are in the forward (<10°) direction. However, the prominent peak in the VSF at the critical angle observed for larger bubbles is strongly reduced by the inclusion of the small sizes, and the backscattering ratio is increased by a factor of two for distributions that varies as the −4 power of size. Because these bubbles contribute strongly to scattering at large angles, these results have significant implications for the remote observation of the color of the sea.
Colored dissolved organic matter and dissolved organic carbon exclusion from lake ice: Implications for irradiance transmission and carbon cycling
Authors: Belzile Claude , Gibson John A. E. , Vincent Warwick F.
Published: June 2010

Thick ice cover is a feature of cold‐temperate, polar, and alpine lakes and rivers throughout much of the year. Our observations from Canadian lakes and rivers across the latitudinal gradient 46–80°N show that their overlying ice contains low concentrations of dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) relative to the underlying waters. The CDOM exclusion factor (water/ice) ranged from 1.4 to 114 and was typically greater than twice the exclusion factor for inorganic solutes. Application of synchronous fluorescence analysis to lake ice samples and experimentally frozen lakewater indicated that only less complex, lower molecular weight molecules were retained within the ice. Consistent with this analysis, DOC‐specific absorption showed that the DOC in the ice was generally less colored than that in the underlying waters. The reduced CDOM absorption within the ice allowed relatively high ultraviolet (UV) transmission despite the elevated scattering within the ice and resulted in UV diffuse attenuation coefficients up to eight times lower in the ice than in the underlying waters. This relatively low attenuation by the ice would cause organisms trapped near the surface by inverse stratification to experience high UV exposure prior to ice breakup. The ice exclusion effect gives rise to a concentrated zone of CDOM and DOC that is likely to favor heterotrophic and mixotrophic processes and influence biogeochemical interactions.
Changes in primary productivity and chlorophyll a in response to iron fertilization in the Southern Polar Frontal Zone
Authors: Gervais Frank , Riebesell Ulf , Gorbunov Maxim Y.
Published: June 2010

EisenEx—the second in situ iron enrichment experiment in the Southern Ocean—was performed in the Atlantic sector over 3 weeks in November 2000 with the overarching goal to test the hypothesis that primary productivity in the Southern Ocean is limited by iron availability in the austral spring. Underwater irradiance, chlorophyll a (Chl a), photochemical efficiency, and primary productivity were measured inside and outside of an iron‐enriched patch in order to quantify the response of phytoplankton to iron fertilization. Chl a concentration and photosynthetic rate (14C uptake in simulated in situ incubations) were measured in pico‐, nano‐, and microphytoplankton. Photochemical efficiency was studied with fast repetition rate fluorometry and xenon‐pulse amplitude modulated fluorometry. The high‐nutrient low‐chlorophyll waters outside the Fe‐enriched patch were characterized by deep euphotic zones (63–72 m), low Chl a (48–56 mg m-2), low photosynthetic efficiency (Fv/Fm ~ 0.3), and low daily primary productivity (130–220 mg C m-2 d-1). Between 70 and 90% of Chl a was found in pico‐ and nanophytoplankton. During the induced bloom, Fv/Fm increased up to ;0.55, primary productivity and Chl a reached the maximum values of 790 mg C m-2 d-1 and 231 mg Chl a m-2, respectively. As a consequence, the euphotic depth decreased to ~41 m. Picophytoplankton biomass hardly changed. Nano‐ and microphytoplankton biomass increased. In the first 2 weeks of the experiment, when the depth of the upper mixed layer was mostly ≪40 m, primary productivity was highly correlated with Chl a. In the third week, productivity was much lower than predicted from Chl a, probably because of a reduction in photosynthetic capacity as a consequence of increased physical variability in the upper water column. These results provide unequivocal evidence that iron supply is the central factor controlling phytoplankton primary productivity in the Southern Ocean, even if the mixing depth is ≫80 m.
The influence of ammonium, nitrate, and dissolved oxygen concentrations on uptake, nitrification, and denitrification rates associated with prairie stream substrata
Authors: Kemp Melody J. , Dodds Walter K.
Published: June 2010

Substrata samples were collected from Kings Creek on Konza Prairie Biological Station (Manhattan, Kansas) and incubated with varying levels of ammonium (NH4+), nitrate (NO3−), and dissolved oxygen (O2) to examine the response of nitrogen (N) uptake and transformation rates. Substrata collected were fine benthic organic matter (FBOM), coarse benthic organic matter, filamentous green algae, bryophytes, suspended particulate organic matter, and epilithic diatoms. Nitrification and denitrification were estimated by use of the nitrapyrin and acetylene inhibition methods, respectively. Ammonium uptake demonstrated Michaelis‐Menten kinetics, with the highest maximum rates (Vmax) associated with filamentous green algae (5.90 mg N gdm−1 d−1) and epilithic diatoms (4.96 mg N gdm−1 d−1). Nitrate uptake did not saturate at the highest NO3− addition (25 µg N L−1) above ambient when associated with FBOM. Overall, maximum uptake rates of NH4+ were 10‐fold higher than for NO3−. Nitrification response to increasing NH4+ concentrations was highly variable, depending on the substrata type. Nitrification was lowest under low O2 conditions, being undetectable when NO3− was added but not when NH4+ was added. Denitrification increased linearly with NO3− concentration when associated with epilithic diatoms and FBOM but became saturated at ~20 µg N L−1 above ambient concentrations when associated with filamentous green algae. Samples purged with N2 gas had the highest rates of denitrification. We predicted stream ecosystem rates using equations derived from the experimental data and substrata mass estimates measured in the field. Substantial temporal variability was predicted in uptake (0–1,300 mg NH4+−N m−2 d−1; 0–5.2 mg NO3−−N m−2 d−1), nitrification (0–35 mg NH4+−N m−2 d−1), and denitrification (0–130 µg N2O‐N m−2 d−1) as due to natural variation in water column NH4+, NO3−, and O2 concentrations.
Fine‐scale mapping of land‐derived nitrogen in coral reefs by δ15N in macroalgae
Authors: Umezawa Yu , Miyajima Toshihiro , Yamamuro Masumi , Kayanne Hajime , Koike Isao
Published: June 2010

We measured the C/N ratio and Δ15N values of two brown macroalgae δl Padina spp. and Dictyota sp., which are distributed over all the subtropical fringing reefs of the Ryukyu Islands, Japan— to evaluate the feasibility of these algae as indicators of the terrestrial nitrogen load to the reef. The correlations between the distance from the shoreline and algal C/N ratio and surrounding NO concentrations were not clear, although their average values among the reefs seemed to indicate differences in nitrogen loadings from the land. The Δ15N values of these algae, on the other hand, linearly or curvilinearly decreased from 18‰ to 12‰ with increasing distance from the shoreline, indicating the difference in nitrogen sources available to macroalgae. The slope of the decline among eight study areas had different characters, which seemed to depend on the residence time of reef seawater and the fluxes of terrestrial nitrogen. Using Δ15N values of brown algae as an indicator, we confirmed that primary producers, such as macroalgae on the reefs, assimilated land‐derived nitrogen and successfully evaluated time‐integrated effects of terrestrial nitrogen on coral reef algae, which had been missed by conventional monitoring of the water column nutrients.
Comparative analysis of energy allocation to tissue and skeletal growth in corals
Authors: Anthony Kenneth R. N. , Connolly Sean R. , Willis Bette L.
Published: June 2010

In aquatic invertebrates that form exoskeletons, the partitioning of energy between skeletal and tissue growth is an important tradeoff, especially under resource limitation or physiological stress. Here, we provide the first comparative analysis of energy investment into tissue and skeleton in corals. We develop a mathematical growth model based on colony geometry, tissue mass and quality (enthalpy), and predicted cost of calcification. For hemispherical colonies, the model predicts greater investment in tissue at small sizes, but a shift to skeletal‐dominated growth at colony sizes greater than 5–14 cm radius, depending on tissue mass and quality. A similar transition occurs in branches, but is a function of radius and length. An experimental study to assess the impact of resource (light) limitation and physiological stress (sediment load) on energy partitioning in small hemispherical colonies (Goniastrea retiformis Lamarck) and branches (Porites cylindrica Dana) showed that tissue mass and quality varies greatly over small increments in colony or branch size. In particular, allocations to tissue growth varied tenfold (from positive to negative) more across sediment treatments than did allocations to skeletal growth. A model of energy acquisition versus loss (scope for growth) indicated that tissue growth is more responsive to resource variation and physiological stress than skeletal growth. These results suggest that (1) skeletal and tissue growth rates are weakly correlated across environmental conditions, and that (2) variation in tissue properties is a better proxy for coral health or stress than skeletal growth.
Inorganic nitrogen assimilation by picoplankton and whole plankton in a coastal ecosystem
Authors: Rodrigues Rubina M. N. V. , Williams Peter J. le B.
Published: June 2010

NH4+ and NO3− seasonal uptake by the phytoplankton and <2−µm communities were investigated in the Menai Strait using 15N tracer techniques. Based on O2‐determined primary production and DIN metabolism measurements, five phases were defined: (1) prebloom (before April), (2) primary net autotrophic (April and May), (3) net heterotrophic (June), (4) secondary net autotrophic (July and August), and (5) regenerative (remainder of calendar year). The inorganic N nutrition of phytoplankton and <2–µm organisms was NO3−−based in spring and NH4+ ‐based in summer and autumn, reflecting varying ambient concentrations of these nutrients superimposed on a general preference for NH4+ by both communities. The percent contribution of picoplankton to the total NH4+ uptake was higher than to nitrate (seasonal averages of 50 ± 14% and 32 ± 24%, respectively). The contribution of the <2–µm size fraction was lowest during both net autotrophic phases (4–13%) and highest during the net heterotrophic, prebloom and regenerative phase (70–84%). A strong correlation between percent NH4+ and NO3− assimilation by the <2–µm size fraction and bacteria abundance between May and July suggests significant bacterial uptake at this time. Bacterial DIN utilization was estimated by correcting uptake rates by the <2−µm fraction, for picophytoplankton presence. During the primary net autotrophic phase, inferred bacterial uptake constituted 13 and 34% of total NO3− and NH4+ uptake, respectively. In the net heterotrophic phase, it amounted to ca. 70% of the total DIN uptake, with no differences between nutrients. Competition between bacteria and phytoplankton for depleted DIN could have contributed to the phytoplankton bloom termination.
Diel variations in Prochlorococcus optical properties
Authors: Claustre Hervé , Bricaud Annick , Babin Marcel , Bruyant Flavienne , Guillou Laure , Le Gall Florence , Marie Dominique , Partensky Frédéric
Published: June 2010

Prochlorococcus is an important component of phototrophic biomass in oligotrophic areas. In such systems, diel variations in optical properties have been reported. In order to better understand these natural variations, the optical (absorption, attenuation, and scattering) and biochemical (carbon and pigment) properties of an axenic clone of Prochlorococcus, PCC 9511, grown in a turbidostat set under light conditions that simulated those found near the ocean surface, were monitored every 2 h for several consecutive days. All optical parameters showed pronounced diel patterns except the divinyl‐chlorophyll a (Dv‐Chl a) specific absorption coefficient at 676 nm, a*(676), which remained stable (0.019 m2 mg Dv‐Chl a21). The diel oscillations of the Dv‐Chl a specific absorption coefficient at 440 nm, a*(440) (43% increase between sunrise and sunset), were essentially governed by variations in the zeaxanthin to Dv‐Chl a ratio (52% increase of this ratio between sunrise and sunset). The scattering cross section at 555 nm, σb(555), showed oscillations with the largest amplitude (182% increase between sunrise and sunset). Finally, the carbon‐specific attenuation coefficient at 660 nm, cc*(660) (1.04 m2 gC−1) is less than half that of the other algal groups. This estimation, together with the diel fluctuations in cc*(660) highlighted in the present study, is discussed in the context of using in situ measurements of optical properties to infer biogeochemical stocks (vegetal or detrital biomass) or processes (primary production).
Complex interactions of climatic and ecological controls on macroalgal recruitment
Authors: Lotze Heike K. , Worm Boris
Published: June 2010

Little is known about the cumulative effects of multiple (.2) environmental controls on species performance and interactions in aquatic ecosystems. We asked how changes in climatic (temperature, ultraviolet radiation) and ecological controls (nutrients, grazing) affect recruitment of the green macroalga Enteromorpha intestinalis, which forms destructive algal blooms in coastal ecosystems worldwide. We designed factorial laboratory experiments to analyze the recruitment response to (1) single and combined effects of nutrient enrichment, grazing pressure, and grazer species composition and (2) the cumulative effects of ultraviolet (UV) radiation, temperature, nutrients, and grazing. Recruitment of E. intestinalis increased exponentially with nutrient enrichment. Grazers could control algal recruitment until a nutrient threshold was reached depending on grazer species composition. Snails (Littorina littorea) had strong negative effects on recruit density, whereas amphipods (Gammarus oceanicus) had weak grazing effects and favored algal recruitment through excretion when nutrient supply was low. Temperature and nutrients both enhanced algal recruitment but also the effects of grazers, which led to a significant three‐way interaction among these factors. Similarly, effects of UV radiation depended on grazer presence and temperature. When grazers were absent, UV radiation reduced recruitment at 11 and 17°C but enhanced recruitment at 5°C. No effects were seen in the presence of grazers. Our results indicate that multiple human influences, such as climate change, eutrophication, and food web alterations, have interdependent effects and the potential for synergistically enhancing the development of macroalgal blooms in coastal ecosystems.
Kinetic isotope effect and characterization of form II RubisCO from the chemoautotrophic endosymbionts of the hydrothermal vent tubeworm Riftia pachyptila
Authors: Robinson Jonathan J. , Scott Kathleen M. , Swanson S. Todd , O'Leary Marion H. , Horken Kempton , Tabita F. Robert , Cavanaugh Colleen M.
Published: June 2010

It has been hypothesized that the δ13C values of chemoautotrophs at deep‐sea hydrothermal vents, which cluster in two groups around −11‰ and −30‰, are due to variation in isotopic discrimination by different forms of RubisCO. The most enriched δ13C values are from the vestimentiferan tubeworm Riftia pachyptila, whose bacterial endosymbionts provide essentially all of its organic carbon via CO2 fixation by a form II RubisCO. The kinetic parameters of purified R. pachyptila symbiont RubisCO were determined to assess the degree to which the δ13C values of tubeworm biomass are due to isotopic fractionation during CO2 fixation by this enzyme. Like most form II enzymes, the KCO2 is high, at 240 mmol L−1, whereas the CO2/O2 specificity factor (Ω) is low, at 8.6. The ε value, which is proportional to the degree of isotopic discrimination by the enzyme, was determined to be 19.5‰, lower than that for form I RubisCO. This low ε value supports the hypothesis that the degree of isotopic fractionation during CO2 fixation appears to be an important influence on the δ13C values of R. pachyptila biomass. Our results indicate that it is necessary to consider RubisCO ε values in interpreting δ13C values from autotrophs.