bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of a reduced‐gravity model to evaluate present and past primary productivity in the tropical open ocean
Authors: Handoh Itsuki C. , Bigg Grant R. , Inoue Masamichi
Published: June 2010

Upwelling predicted by a reduced‐gravity model is compared with remotely sensed primary productivity data through the tropical Atlantic and Pacific. The model upper layer thickness, an indicator of vertical motion, is correlated with primary productivity. We suggest that the Atlantic basin is more efficient than the Pacific in its production for the same degree of upwelling. This is a characteristic of the tropical Pacific ecological provinces being featured by low salinity in the western tropics and high nutrient, but low chlorophyll in the eastern equatorial region. A comprehensive relationship between model upper layer thickness and primary productivity is established through the tropical basins, with emphasis on the equatorial strip. Our work has implications for the application of reduced‐gravity models to estimate productivity in palaeocean studies.
Reconstructing the history of fluid flow at cold seep sites from Ba/Ca ratios in vesicomyid clam shells
Authors: Torres M. E. , Barry J. P. , Hubbard D. A. , Suess E.
Published: June 2010

Hydrogen sulfide discharge at cold seep sites is recorded as enrichment in the barium to calcium (Ba/Ca) ratio in shells of vesicomyid clams collected live from cold seeps in Monterey Canyon and the Cascadia margin. A direct relationship between increased Ba fluxes from cold seeps and Ba incorporation into shells was established for the Cascadia margin site. For the Monterey canyon site, a 2‐yr episode of high fluid flow centered on 1992 was inferred from coherent changes in the Ba/Ca profiles of three Calyptogena kilmeri shells. Comparison with precipitation and δ18O data indicates that this high‐flow period may have been driven by an increase in rainfall after the 1988–1990 California drought. High‐resolution records preserved in clam shells are shown to be useful in elucidating characteristics, history, and possible mechanisms driving fluid discharge at continental margin seeps, thus establishing their potential use as paleotracers of fluid seepage events.
Virus‐like particle distribution and abundance in sediments and overlying waters along eutrophication gradients in two subtropical estuaries
Authors: Hewson Ian , O'Neil Judith M. , Fuhrman Jed A. , Dennison William C.
Published: June 2010

Viruses are recognized as ubiquitous components of marine ecosystems; however, there has been limited study of viral abundance and its ecological role in sediments. Viral abundance was determined in both the water column and sediments of a eutrophic (Brisbane River/Moreton Bay; 27°25′S, 153°5′E) and oligotrophic (Noosa River; 26°15′S, 153°0′E) estuary in subtropical Queensland, Australia. Viruses, bacteria, and microalgae from both water column and extracted sediment samples were enumerated using SYBR Green I staining and epifluorescence microscopy. Sediment viral abundance ranged from 107 to 109 particles cm−3 of sediment, bacterial abundance ranged from 107 to 108 cells cm−3 of sediment, and microalgal abundance ranged from 104 to 105 cells cm−3 sediment. Pelagic abundances for all microorganisms were 10–1,000‐fold lower than sediment abundances. Correlations between viral abundances and suspended solids suggest that viruses sorbed to suspended material in the water column may settle out and contribute to the benthic viral population. Virus production was measured by a time course increase of viral abundance in seawater using a dilution technique. Virus production was highest in eutrophic waters of the Brisbane River, and addition of inorganic nutrients (NO3− + NH4+ + PO43− + SiO3) stimulated viral production rates at all stations by 14–52% above ambient, suggesting that inorganic nutrient availability may play a key role in aquatic viral abundance.
Climatic warming causes regime shifts in lake food webs
Authors: Scheffer Marten , Straile Dietmar , van Nes Egbert H. , Hosper Harry
Published: June 2010

Spring clear water phases caused by grazing of zooplankton on algae are among the most spectacular and well‐studied events in lake plankton dynamics. Such clear water phases are also important as windows of opportunity for recovery of aquatic vegetation and biodiversity in shallow waters. Here we use long time series from 71 shallow lakes to demonstrate that the probability of clear water phase increases with the temperature of lake water. We demonstrate that lake temperature has risen significantly over the past decades and is highly correlated with oscillations in the North Atlantic climate system. We also show a distinct climate‐related shift in the timing of clear water phases in the shallow lakes as well as in an independent set of central European lakes. Simulations with a seasonally forced plankton model confirm that temperature rise is a plausible explanation for the observed changes.
Iron uptake and physiological response of phytoplankton during a mesoscale Southern Ocean iron enrichment
Authors: Maldonado Maria T. , Boyd Philip W. , LaRoche Julie , Strzepek Robert , Waite Anya , Bowie Andrew R. , Croot Peter L. , Frew Russell D. , Price Neil M
Published: June 2010

Iron supply is thought to regulate primary production in high nitrate, low chlorophyll (HNLC) regions of the sea in both the past and the present. A critical aspect of this relationship is acquisition of iron (Fe) by phytoplankton, which occurs through a complex series of extracellular reactions that are influenced by Fe chemistry and speciation. During the first in situ mesoscale Fe‐enrichment experiment in the Southern Ocean (Southern Ocean iron release experiment [SOIREE]), we monitored the uptake of Fe by three size classes of plankton and their ensuing physiological response to the Fe enrichment. Rates of Fe uptake from both inorganic Fe (Fe′) and organic Fe complexes (FeL) were initially fast, indicative of Fe‐limitation. After Fe enrichment phytoplankton down‐regulated Fe uptake and optimized physiological performance, but by day 12 they had greatly increased their capacity to acquire Fe from FeL. The increase in Fe uptake from FeL coincided with a sixfold decrease in Fe′ that followed the production of Fe‐binding organic ligands. Phytoplankton were able to use organically bound Fe at rates sufficient to maintain net growth for more than 42 d. Adaptation to such shifts in Fe chemistry may contribute to bloom longevity in these polar HNLC waters.
Use of bomb radiocarbon to validate otolith section ages of red snapper Lutjanus campechanus from the northern Gulf of Mexico
Authors: Baker Scott Jr. M. , Wilson Charles A.
Published: June 2010

The red snapper Lutjanus campechanus is an important recreational and commercial fish species in the northern Gulf of Mexico. Management approaches have varied in part because of uncertainty of their longevity. Snapper ages have been based on presumed otolith annuli; however, this methodology has not been validated for all age classes. A recent technique to validate otolith age utilizes the increase in oceanic 14C resulting from atmospheric testing of nuclear bombs during the 1950s and 1960s. Analyses of annuli from living corals and fish otoliths from 1900 to the present have documented that elevated 14C input has occurred throughout the world's oceans. We validated otolith section age estimates through accelerator mass spectrometry analysis of bomb‐produced 14C in red snapper (otoliths) hatched before, during, and after the nuclear testing periods. Delta 14C data from the otoliths of red snapper with presumed birth dates between 1960 and 1973 clearly reflect the sharp increase in oceanic radiocarbon attributable to previous nuclear testing. Similarities between the otolith and nearby coral △14C chronologies suggest that annulus‐based age estimates of red snapper are valid on average to within 1–3 yr. In addition, this study provides the first carbonate bomb radiocarbon time series from the northern Gulf of Mexico.
Phaeocystis globosa (Prymnesiophyceae) and the planktonic food web: Feeding, growth, and trophic interactions among grazers
Authors: Tang K. W. , Jakobsen H. H. , Visser A. W.
Published: June 2010

The feeding and growth of copepods and heterotrophic protozoans when fed Phaeocystis globosa (Prymnesiophyceae) single cells were studied in the laboratory. The calanoid copepod Acartia tonsa fed on P. globosa at low clearance rates (<20 ml ind−1 d−1). P. globosa appeared to be a poor diet for A. tonsa in terms of fatty acid composition, yielding a low egg production rate (0–4.5 eggs ind−1 d−1) and an egg production efficiency (EPE; increase in egg production/increase in ingestion) close to zero, in contrast to an EPE of 35% when Rhodomonas salina (Cryptophyceae) was offered as food. Nauplii of A. tonsa feeding on P. globosa suffered higher mortality and arrested development relative to those feeding on R. salina. Among the three ciliates and two dinoflagellates tested, ingestion rates on P. globosa single cells increased with the protozoan cell size, and the growth yield in terms of biovolume ranged from 9 to 78%. We studied the trophic interactions among grazers in P. globosa‐based food chains. Gyrodinium dominans (dinoflagellate) growing on P. globosa improved the nutritional quality of P. globosa by 7.8 times for A. tonsa, such that A. tonsa feeding on G. dominans as an intermediate prey had an EPE of 35%. The ciliate Mesodinium pulex also exploited P. globosa indirectly by consuming the dinoflagellate Gymnodinium sp. as an intermediate prey. Our study showed that the trophic efficiency of a system dominated by P. globosa is dependent on the complex food‐chain structures within the planktonic food web.
Population biology and secondary production of the suspension feeding polychaete Chaetopterus cf. variopedatus: Implications for benthic‐pelagic coupling in lower Chesapeake Bay
Authors: Thompson Michelle L. , Schaffner Linda C.
Published: June 2010

Benthic suspension feeders are functionally important components of many shallow estuarine and coastal ecosystems. Their relative importance in material and energy cycling depends on physical and biological factors, of which population dynamics of individual species are a key feature. We studied the demographics and secondary production of a population of the tubicolous, suspension feeding polychaete, Chaetopterus cf. variopedatus, of southern Chesapeake Bay, Virginia, to better understand its functional role in an estuarine ecosystem. Average worm densities in the study region ranged from 30 to >1000 individuals m−2 and were greatest after the summer recruitment period. Recruitment success varied threefold between 1994 and 1995. A two‐cohort model (juveniles and adults) with seasonality best described the data. High secondary production (18 g C m−2 yr−1 in 1994, 34 g C m−2 yr−1 in 1995) was mainly due to rapid growth and maturation of new recruits during summer and tube production. An interannual difference in production was associated with the interannual difference in recruitment success. General temporal trends of primary production and worm production were similar, and the worm population required 35%–100% of the estimated annual net water column community production per m2 for this region of the estuary. Chaetopterus cf. variopedatus is an important component of the lower bay ecosystem and should be considered when modeling carbon, nutrient, and energy flow. Our results further demonstrate that temporal variations in population dynamics lead to significant temporal variability in the relative importance of benthic suspension feeder effects for ecosystem function.
Toxicity in Peridinium aciculiferum—an adaptive strategy to outcompete other winter phytoplankton?
Authors: Rengefors Karin , Legrand Catherine
Published: June 2010

Freshwater dinoflagellates may form dense blooms during winter in ice‐covered lakes. Unlike their marine counterparts, freshwater dinoflagellates are rarely considered to be potential toxin producers. Here we tested whether the winter species Peridinium aciculiferum produces a toxin(s) and investigated the potential adaptive function of that toxin, i.e., predator defense or inhibition of competitors (allelopathy). Using traditional toxicity bioassays (Artemia toxicity test and hemolytic activity assay), we detected the production of a toxic substance by P. aciculiferum cells from both the field and from laboratory cultures. Cultures deprived of phosphorus and in stationary phase showed highest toxicity. Potential predators, such as Daphnia galeata (Cladocera) and Eudiaptomus graciloides (Copepoda), were apparently not harmed by P. aciculiferum toxicity. However, the naturally cooccurring competitor Rhodomonas lacustris (Cryptophyceae) was killed by P. aciculiferum. An allelopathic substance(s) caused the cells of R. lacustris to form blisters and subsequently lyse. We concluded that our results support the hypothesis that P. aciculiferum is allelopathic, but not that toxins serve as predator defense. We therefore suggest that allelopathy may be an adaptive strategy of winter dinoflagellates, which could allow them to outcompete other phytoplankton species and thereby dominate the algal biomass.
Algal games: The vertical distribution of phytoplankton in poorly mixed water columns
Authors: Klausmeier Christopher A. , Litchman Elena
Published: June 2010

Phytoplankton often face the dilemma of living in contrasting gradients of two essential resources: light that is supplied from above and nutrients that are often supplied from below. In poorly mixed water columns, algae can be heterogeneously distributed, with thin layers of biomass found on the surface, at depth, or on the sediment surface. Here, we show that these patterns can result from intraspecific competition for light and nutrients. First, we present numerical solutions of a reaction‐diffusion‐taxis model of phytoplankton, nutrients, and light. We argue that motile phytoplankton can form a thin layer under poorly mixed conditions. We then analyze a related game theoretical model that treats the depth of a thin layer of phytoplankton as the strategy. The evolutionarily stable strategy is the depth at which the phytoplankton are equally limited by both resources, as long as the layer is restricted to the water column. The layer becomes shallower with an increase in the nutrient supply and deeper with an increase in the light supply. For low nutrient levels, low background attenuation, and shallow water columns a benthic layer occurs; for intermediate nutrient levels in deep water columns, a deep chlorophyll maximum occurs; and for high nutrient levels, a surface scum occurs. These general patterns are in agreement with field observations. Thus, this model can explain many patterns of algal distribution found in poorly mixed aquatic ecosystems.
Fluxes of semivolatile organochlorine compounds in Bow Lake, a high‐altitude, glacier‐fed, subalpine lake in the Canadian Rocky Mountains
Authors: Blais Jules M. , Schindler David W. , Sharp Martin , Braekevelt Eric , Lafreniěre Melissa , McDonald Karen , Muir Derek C. G. , Strachan William M. J.
Published: June 2010

The fluxes of several organochlorine compounds (OCs) to and from a high‐altitude lake were calculated to determine the relative contributions of rainfall, snowfall, runoff, gas absorption and volatilization, sedimentation, and outflow. Runoff inputs, particularly from a glaciated catchment, and gas absorption were major sources of many OCs. Losses by volatilization, outflow, and sedimentation were also important transport pathways for most OCs. We observed a net deposition of hexachlorocyclohexanes (HCHs) and DDT to Bow Lake by gas exchange, whereas hexachlorobenzene, chlordanes, and most polychlorinated biphenyls were seen to volatilize to the air. The insecticide lindane (γHCH), widely applied across Canada as a seed dressing in early spring, was absorbed by Bow Lake in early summer but gradually equilibrated with water as the summer progressed. This was the result of lower concentrations of γHCH in air and rising air temperatures in late summer. Results indicate that glacially derived tributary inputs are dominant sources of persistent organic pollutants to these glacier‐fed mountain lakes and that smaller contributions may derive from air‐water gas exchange. This study highlights the importance of glacial sources of OCs to mountain lakes and corroborates recent evidence of OC contamination in glacially derived aquatic systems.
Variability and control of carbon consumption, export, and accumulation in marine communities
Authors: Cebrian Just
Published: June 2010

Elucidating the extent and controls of the routes followed by primary production in marine communities (i.e., consumption by herbivores, decomposition, transportation of plant material beyond the community boundaries—referred to as export—or accumulation as biomass or detritus) is essential to understand how much and why they differ in their capacity to fuel secondary production, both within or out of the community, and in their role as sinks in the oceanic carbon budget. Here, using an extensive compilation of published reports, I compare the magnitude of these routes across and within a wide range of community types, including oceanic and coastal phytoplanktonic communities, benthic microalgal communities, coral reef algal beds, macroalgal beds, seagrass meadows, marshes, and mangroves. Furthermore, I examine whether the variability in the magnitude of these routes among and within types is associated with that in the magnitude of primary production. In general, different community types showed similar levels of consumption by herbivores and export, in spite of substantial within—type variability. On the contrary, substantial differences in detritus decomposition and accumulation were found among types: coral reef algal beds and benthic microalgal communities tended to show the highest and lowest levels of decomposition, respectively, whereas marshes and oceanic phytoplanktonic communities tended to show the largest and smallest levels of detritus accumulation. The results also identify primary production as a robust (i.e., applicable to a wide range of environmental conditions and communities) control of the variability in herbivory and decomposition among marine communities. The role of primary production as a control of export and detritus accumulation is generally minor and only restricted to coastal phytoplanktonic and benthic microalgal communities, for export, and marshes and mangroves for detritus accumulation.
Seasonal variability of the effect of coral reefs on seawater CO2 and air—sea CO2 exchange
Authors: Bates Nicholas R.
Published: June 2010

There are complex physical and biological processes controlling the exchange of carbon dioxide (CO2) between the ocean and atmosphere. In coral reef ecosystems, the balance of biological processes such as calcium carbonate (CaCO3) formation and organic carbon production can either lead to CO2 being retained in the oceanic environment (i.e., oceanic sink of CO2) or returned to the atmosphere through gas exchange (oceanic source of CO2). What remains uncertain is the fate of CO2 in reefs subject to seasonal change and the annual balance of air—sea CO2 flux in such systems. Here it is shown that the Bermuda coral reef acts as a sourc of CO2 to seawater overlying the reef. The magnitude of this source of CO2 varies seasonally in response to changes in the reef community between coral‐ and macroalga‐dominated states, reflecting changes in the net balance between calcification and organic carbon production. With knowledge of the calcification rate (~5.6 to 10.6 g CaCO3 m−2 d−1) and observed modification in seawater fCO2 by reef metabolism, rates (—0.6 to 3.3 g C m−2 d−1) and seasonal patterns of macroalgal productivity were estimated. Whether the Bermuda coral reef system acts as an oceanic sink or source of CO2 to the atmosphere not only depends on this seasonal variation, but, more importantly, depends on the pre‐existing air‐sea CO2 disequilibrium of open ocean waters surrounding the reef system. The Bermuda coral reef system serves as a useful model for understanding the fate of CO2 in other reefs, particularly those reefs changing because of environmental stress.
Contribution of absorption and scattering to the attenuation of UV and photosynthetically available radiation in Lake Biwa
Authors: Belzile Claude , Vincent Warwick F. , Kumagai Michio
Published: June 2010

Underwater ultraviolet (UV) attenuation is typically modeled using correlative relationships between UV attenuation and dissolved organic carbon (DOC) concentration or colored dissolved organic matter (CDOM) absorption. Our objective was to validate and extend a biogeooptical model of UV penetration that would take into account total absorption as well as scattering by all components of the water column. Diffuse attenuation coefficients, Kd(λ), for photosynthetically available radiation (PAR) and UV irradiance were measured using a PUV500 radiometer at 13 stations in Lake Biwa, Japan, in late summer. Absorption, a, and scattering, b, were measured at nine PAR wavelengths using an AC‐9 absorption‐attenuation meter. The average Kd(PAR) through the euphotic zone, Kdav(PAR), was estimated from the measured inherent optical properties using Kirk's equations derived from Monte Carlo simulations. The modeled Kdav(PAR) was strongly correlated with measured Kd(PAR) values (r2 = 0.998), although the model systematically underestimated measured values by ~15%. The relative contribution of absorption and scattering to UV attenuation was evaluated from measurements of the absorption coefficients, an extrapolation of b into the UV, and Kirk's equations. The UV‐absorption coefficients for CDOM and particulate matter were measured spectrophotometrically. There was a close agreement between modeled and measured Kd(UV) values (r2 ~ 0.990). The Lake Biwa data showed that particulate absorption and scattering play significant roles in UV attenuation; on average, absorption by water, CDOM, and particles contributed 1, 66, and 21% respectively to Kdav(340), while scattering by particles contributed 11%. At a turbid site (NS9) absorption by water, CDOM, and particles contributed 0.3, 40, and 36% respectively to Kdav(340), while scattering contributed the remaining 24%. The model described here integrates the effects of all absorption as well as scattering components and provides a more accurate estimate of underwater UV exposure than previous approaches based on CDOM absorption only.
Bacteriochlorophyll a in the ocean: Is anoxygenic bacterial photosynthesis important?
Authors: Goericke Ralf
Published: June 2010

Some groups of marine bacteria within the Α‐proteobacteria are capable of anoxygenic photosynthesis in oxic environments. Their primary photosynthetic pigment is bacteriochlorophyll a (BacChl a). The impact of these bacteria on flows of energy and carbon in the ocean has been difficult to ascertain in the past. Recently, however, Kolber et al. (2001) reported that such bacteria are abundant in the upper ocean and that these might contribute significantly to photosynthetically driven electron transport since measured and inferred ratios of BacChl a and chlorophyll a (Chl a) were about 0.8% in coastal environments and as high as 10% in the Eastern Tropical North Pacific. The authors suggested that the globally averaged BacChl a/Chl a ratio could be as high as 5 to 10%. To determine whether such high values are representative of other marine environments, concentrations of BacChl a were measured in samples collected in eutrophic nearshore and mesotrophic and oligotrophic offshore environments off Southern California. The average BacChl a/Chl a ratio was 1.1% in nearshore and 0.5% in mesotrophic shelf and oligotrophic offshore environments. Assuming that rates of photosynthesis scale with concentrations of photosynthetic pigments, these data suggest that the contribution of BacChl a driven anoxygenic bacterial photosynthesis to energy production in coastal eutrophic and offshore oligotrophic areas of the California current system is small, substantially smaller than the suggested global average of 5 to 10%.
The summer metabolic balance in the epilimnion of southeastern Quebec lakes
Authors: Prairie Yves T. , Bird David F. , Cole Jonathan J.
Published: June 2010

On the basis of data collected in Quebec lakes, del Giorgio and Peters (1994) and Carignan et al. (2000) have come to opposite conclusions regarding the metabolic balance between heterotrophy and autotrophy in lakes in general. In the present study, epilimnetic oxygen and carbon dioxide saturation was measured in 33 lakes from the St. Lawrence Lowlands region of Quebec to examine the extent of epilimnetic net heterotrophy (i.e., O2:CO2 balance) in lakes of different characteristics. We found that ~75% of the lakes were undersaturated with oxygen and supersaturated with CO2. There was a strong negative relationship between the departures of O2 and CO2 from saturation. What has not been noted elsewhere is that oxygen concentrations were negatively related to dissolved organic carbon (DOC) concentration, and, therefore, metabolic gas balances could be predicted from DOC; a value between 4 and 6 mg L−1 DOC corresponds to metabolic equilibrium. Because most of the lakes in del Giorgio and Peters (1994) had DOC concentrations above this threshold and most lakes in Carignan et al. (2000) were below, their apparently contradictory conclusions can be reconciled within a larger general theory. Contrary to studies elsewhere, however, we found that the degree of oxygen undersaturation increased with lake trophic status, expressed either as total phosphorus or nitrogen concentrations.
Bioavailability of DON from natural and anthropogenic sources to estuarine plankton
Authors: Seitzinger Sybil P. , Sanders R. W. , Styles Renée
Published: June 2010

Utilization of dissolved organic nitrogen (DON) from natural (forests) and anthropogenic (animal pastures, urban/suburban storm water runoff) sources (three sites per source) by estuarine plankton communities was examined in spring, summer, and fall. The proportion of DON utilized ranged from 0 to 73%. Overall, urban/suburban storm water runoff had a higher proportion of bioavailable DON (59% ± 11) compared to agricultural pastures (30% 14) and forests (23% ± 19). DON bioavailability varied seasonally; however, the seasonal pattern differed for the three sources. Bacterial production increased linearly with the amount of DON utilized across all sources and seasons; the rate of increase was approximately five times greater per micromole of N as DON used relative to dissolved inorganic N (DIN) used. Although phytoplankton production generally increased with DON addition, the increased production was not correlated with the amount of DON utilized, suggesting that a variable portion of dissolved organic matter (DOM)‐N was directly or indirectly available to the phytoplankton. This indicates that phytoplankton production is not a good measure of the amount of bioavailable DON, and measurements of the amount of bioavailable DON based on bacterial responses alone might not reflect N available to phytoplankton. Preliminary seasonal budgets of bioavailable N (DIN plus bioavailable DON) as a function of land use suggest that ~80% of the total dissolved N (TDN) from urban/suburban runoff is bioavailable, whereas a lower proportion (20–60%) of TDN is bioavailable from forests and pastures. N budgets for aquatic ecosystems based on only DIN loading underestimate bioavailable N loading, whereas total N or TDN budgets overestimate bioavailable N inputs.
Importance of acid polysaccharides for 234Th complexation to marine organic matter
Authors: Quigley Matthew S. , Santschi Peter H. , Hung Chin-Chang , Guo Laodong , Honeyman Bruce D.
Published: June 2010

In order to study the role of polysaccharides (PS) in the colloidal organic matter (COM) pool for complexing 234Th, controlled laboratory experiments were carried out to determine the chemical nature of the strong Th(IV) binding to macromolecular organic ligands (>1 kDa). The partition coefficient of 234Th between marine COM and solution, Kc, is higher than that for any known marine mineral sorbent. PS‐enriched fractions of COM had the highest partition coefficient (Kc) of any sorbent for 234Th. Kc of 234Th and other metals, including Fe, Mn, Zn, Pb, and Pu, were up to an order of magnitude higher than that for bulk COM. Most importantly, log Kc values correlated linearly with the fraction of PS‐enriched carbon (PS) of marine COM, as Kc 5 Kc(0) × 102.2PS The log Kc value of ~7.9 of the pure PS end‐member fraction was very similar to the highest values obtained for model acid PS (log Kc ~ 8). A value for the conditional stability constant for Th binding to the pure PS end member of 107.8 could be determined from a concentration of strong acid binding sites (with a pKa <=3) of 1.3 mmol g−1 COM. Through the novel use of gradient gel electrophoresis (including two‐dimensional polyacrylamide gel electrophoresis), the strong Th(IV) binding ligand was shown to be ~13 kDa in size and to have strong acidic functional groups. We propose that the observed variability of OC: 234Th ratios in suspended, and sinking matter in the ocean might be caused by the variability of PS content.
What controls the mixed‐layer depth in deep‐sea sediments? The importance of POC flux
Authors: Smith Craig R. , Rabouille Christophe
Published: June 2010

The depth of biogenic particle mixing, i.e., the mixed‐layer depth (L), is fundamental in models of organic‐matter recycling and paleoreconstructions for deep‐sea sediments. Factors postulated to control L in the oxygenated deep sea include particulate organic carbon (POC) flux, oxygen penetration into the sediment, and a balance between the downward mixing and decay of labile POC. We explore the dependence of L on biogeochemical characteristics by compiling, from 36 sites in three oceans, an internally consistent set of deep‐sea estimates of L, POC flux, biogenic mixing intensity (Db), and POC reactivity. We use excess 210Pb as a tracer for L and Db to avoid the confounding effects of tracer‐dependent mixing. We find that L, estimated from the penetration depth of excess 210Pb, varies systematically with POC flux, with an asymptotic function explaining 88% of the variance in L. Stepwise multiple regression suggests that the penetration depth of excess 210Pb (and estimated L) is much more likely to be controlled by POC flux than by (1) the sediment inventory of excess 210Pb or (2) biogenic mixing intensity (Db). In addition, L is negatively related to oxygen penetration into the sediment (r = ‐0.629) and not significantly related to predictions of L from a recent mixing/POC‐decay model. We conclude that in the food‐poor deep sea, POC flux substantially controls the size and activities of the sediment‐mixing benthos and, in turn, the thickness of the biogenic mixed layer. Thus, in contrast to previous suggestions, average mixed‐layer depth is not environmentally invariant but rather responds predictably to ecologically important parameters such as POC flux.
Factors controlling the extent of eutrophication and toxicity in sulfate‐polluted freshwater wetlands
Authors: Lamers Leon P. M. , Falla Sarah‐J. , Samborska Edyta M. , Dulken Ivo A. R. van , Hengstum Gijs van , Roelofs Jan G. M.
Published: June 2010

Increased sulfur loads originating from polluted surface water and groundwater, and from enhanced atmospheric input, are a major threat to the biogeochemical functioning and biodiversity of freshwater wetlands. Sulfate reduction, normally playing a modest role in these systems, becomes the most important biogeochemical process, inducing severe eutrophication and sulfide toxicity. In field enclosure experiments we observed striking differences between the responses of two freshwater marshes to sulfate. On one location sulfate addition resulted in strong phosphorus mobilization without sulfide accumulation, whereas high sediment sulfide concentrations, known to be toxic to wetland macrophytes, were reached in the other marsh without eutrophication occurring. The results could be explained by differences in groundwater iron discharge and nutrient contents of the peat sediments. Sulfate reduction rates appeared to be limited by either electron donor availability (first marsh) or electron acceptor availability (second marsh). The implications of these findings are explained in relation to freshwater wetland management.
Carbon sources for demersal fish in the western Seto Inland Sea, Japan, examined by δ13C and δ15N analyses
Authors: Takai Noriyuki , Mishima Yasufumi , Yorozu Akemi , Hoshika Akira
Published: June 2010

The relative importance of benthic and pelagic primary production for demersal fish and some invertebrates in the western Seto Inland Sea of Japan was examined using carbon and nitrogen stable isotope analyses. A few fishes, such as juvenile black rockfish Sebastes inermis and large Japanese anchovies Engraulis japonicus, had isotopic carbon signatures similar to pelagic particulate organic matter (−20.1 ³ 1.7‰), which indicates that their food was derived from production in the water column. However, 92% of the 401 demersal fish that were analyzed had δ13C signatures (−17.0 to −13.0‰) similar to those of benthic crustaceans, epilithic microphytobenthos, and macroalgae and unlike the signature of pelagic particulate organic matter or zooplankton. These results suggest that in the Seto Inland Sea there is not a tight coupling between pelagic primary production and the food web of demersal fishes, but rather that these fishes are dependent on carbon from benthic primary production.
Temporal decoupling of carbon and nitrogen dynamics in a mesocosm diatom bloom
Authors: Engel Anja , Goldthwait Sarah , Passow Uta , Alldredge Alice
Published: June 2010

Flows of the major biogeochemical elements (C, N, P, Si) and of transparent exopolymer particles (TEP) were traced during a bloom of a natural assemblage of marine diatoms in a mesocosm (1 m3) to determine whether the exudation and subsequent gelation of carbon‐rich phytoplankton exopolymers can account for the formation and potential export of carbon in excess of that predicted by Redfield ratios. Exponential growth of the phytoplankton community in the mesocosm extended for 10 d until nitrate concentration fell below detection and concentrations of dissolved inorganic and particulate organic nitrogen and phosphorus remained stable. Tight covariation of particulate organic elements occurred as long as nutrients were replete. But, after nitrate depletion, decoupling of carbon dynamics from that of nitrogen and phosphorus was observed, with a large flow of carbon into TEP. An uptake of 72% more dissolved inorganic carbon (DIC) than inferred from nitrate supply and Redfield stoichiometry (referred to as carbon overconsumption) occurred during the study, largely during the postbloom phase, and was almost entirely traced to the particulate organic matter (POM) pool. Marine snow (aggregates >0.5 mm) appeared at the onset of nitrate depletion and coincided with rapid increase in TEP concentrations. Elemental composition of marine snow differed from the Redfield ratio by an enrichment in carbon and a depletion in phosphorus relative to nitrogen. It is suggested that sinking of TEP‐rich marine snow could be a possible mechanism for export of carbon above calculations that are based on the Redfield stoichiometry.
Uptake of ammonium by the scleractinian coral Stylophora pistillata: Effect of feeding, light, and ammonium concentrations
Authors: Grover Renaud , Maguer Jean-François , Reynaud-Vaganay Stephanie , Ferrier-Pagès Christine
Published: June 2010

Experiments were designed to assess the uptake rates of 0.2, 1, and 5 μM ammonium by the scleractinian coral Stylophora pistillata maintained under different feeding regimes (highly fed, slightly fed, and starved) for 4–8 weeks. 15NH4 was used to follow the incorporation of nitrogen in the zooxanthellae or in the animal tissue and to calculate uptake rates. After 4 or 8 weeks, fed corals contained significantly higher concentrations of protein, chlorophyll, and zooxanthellae than starved nubbins. They also contained significantly higher amounts of carbon and nitrogen per unit surface skeleton. Results obtained showed that the algal fraction was enriched with 15N at up to 10 times the rate of the host, which suggests that the zooxanthellae are the primary site of assimilation. Uptake rates (measured in the algal fraction) varied according to the nitrogen concentration in seawater. They were ~20 times lower at 0.2 than at 1 or 5 μM 15NH4 enrichment (2–30 vs. 120–510 ng N h−1 cm−2) for both fed and starved nubbins. These rates were also affected by the feeding history of the host, because they were significantly lower for fed than for starved nubbins (analysis of variance, P < 0.005), at both high and low ammonium concentrations. On the basis of the nitrogen content of the zooxanthellae, we suggest that an external concentration of ammonium equal to 0.6 mM can sustain the growth of the zooxanthellae population.
A model of sediment transport over an intertidal transect, comparing the influences of biological and physical factors
Authors: Wood Rose , Widdows John
Published: June 2010

This paper compares modeled biotic and physical effects on intertidal sediment transport, using parameterizations that are based on laboratory and field experiments. A one‐dimensional model of an intertidal transect is constructed. The model is aligned cross shore and includes movement of water and suspended sediment. Within the model, tidal currents cause erosion, and bioturbation by the clam, Macoma balthica, alters the erodability of the bed sediment. The concentration of chlorophyll a in the surface sediment (which is an indicator of microphytobenthos density) alters the critical erosion velocity. External sediment supply is specified as an offshore suspended matter concentration. The model is applied within Spurn Bight (Humber Estuary, UK). The effects of various tide heights, biota densities, and external suspended sediment concentrations are investigated. Offshore sediment supply dominates the net deposition below midtide level, but factors affecting intertidal sediment erosion and deposition become important at higher shore levels. Changes in erosion or deposition caused by natural variation in biota densities are as large as those caused by changes in tidal range and currents over a spring‐neap cycle, or by doubling external supply. Seasonal variations in densities of stabilizing microphytobenthos can alter the magnitude of net deposition on the upper shore by a factor of two. Interannual variation in numbers of bioturbating clams can change net deposition by a factor of five. These results show that biotic influences on transport of sediment within the intertidal zone are significant and will play a role in determining sediment budgets over tidal to monthly timescales.
Reach‐scale manipulations show invertebrate grazers depress algal resources in streams
Authors: Taylor Brad W. , McIntosh Angus R. , Peckarsky Barbara L.
Published: June 2010

Experimental tools that enable manipulations of organisms at larger scales allow for comparisons of processes across multiple spatial scales and expand our ability to make predictions about ecological processes. We performed reach scale (i.e., 50 m2) manipulations of invertebrate communities in streams using a modified electroshocking technique to nondestructively remove invertebrates. In addition, we conducted a microcosm experiment (i.e., 157 cm2) with different grazer densities that enabled comparison of the strength of grazer‐algal interactions at large and small spatial scales. In high elevation headwater streams, electroshocking reduced total invertebrate abundance by 84% in a 50‐m2 reach of stream. Although mobile invertebrates recolonized the manipulated area rapidly, daily electroshocking maintained the density reduction. Electroshocking reduced the density of herbivorous invertebrates 86%, which resulted in a 57% increase in algal biomass, whereas in a stream that was not electroshocked, invertebrate density and algal biomass changed much less, only 16 and 8%, respectively. Comparison of grazer effect on periphyton between microcosm and reach‐scale experiments revealed that the per capita interaction strength of grazers on primary producers was three times greater in the reach‐scale manipulation than that observed in the microcosm experiments. Reach‐scale manipulation of invertebrate grazers in streams provides a powerful method to experimentally test patterns observed in the field at a large spatial scale, with more realism than streamside microcosms or small cages in streams.
Phytoplankton iron limitation in the Humboldt Current and Peru Upwelling
Authors: Hutchins D. A. , Hare C. E. , Weaver R. S. , Zhang Y. , Firme G. F. , DiTullio G. R. , Alm M. B. , Riseman S. F. , Maucher J. M. , Geesey M. E. , Trick C. G. , Smith G. J. , Rue E. L. , Conn J. , Bruland K. W.
Published: June 2010

We investigated phytoplankton Fe limitation using shipboard incubation experiments in the highߚnutrient South American eastern boundary current regime. Low ambient Fe concentrations (~0.1 nM) in water collected from the Humboldt and Peru Currents were supplemented with a range of added Fe levels up to 2.5 nM. Phytoplankton chlorophyll a, photosystem II photosynthetic efficiency, and nitrate and phosphate drawdown increased in proportion to the amount of Fe added. The Humboldt Current algal community after Fe additions included colonial and flagellated Phaeocystis globosa and large pennate diatoms, whereas the Peru Upwelling assemblage was dominated by coccolithophorids and small pennate diatoms. Apparent halfߚsaturation constants for growth of the two communities were 0.17 nM Fe (Humboldt Current) and 0.26 nM Fe (Peru Upwelling). Net molar dissolved Si(OH)4 : NO3- drawdown ratios were low in both experiments (~0.2ߝ0.7), but net particulate silica to nitrogen production ratios were higher. Fe limitation decreased net NO3-:PO43- utilization ratios in the Humboldt Current incubation to well below Redfield values. Phytoplankton community sinking rates were decreased by Fe additions in the Peru Upwelling, suggesting potential Fe effects on carbon export. Our results confirm that primary producers in the Peru Upwelling/Humboldt Current system can be limited by Fe, but the biological and biogeochemical consequences of Fe limitation differ from Feߚlimited California coastal upwelling waters that have been previously studied.
Peptide hydrolysis, amino acid oxidation, and nitrogen uptake in communities seasonally dominated by Aureococcus anophagefferens
Authors: Mulholland Margaret R. , Gobler Christopher J. , Lee Cindy
Published: June 2010

Elevated levels of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) are among the factors implicated in the initiation of algal blooms. However, the degree to which phytoplankton augment their autotrophic metabolism with heterotrophic uptake of organic carbon that is associated with DON is unknown. We evaluated the relative importance of peptide hydrolysis, amino acid oxidation, and amino acid uptake over a seasonal cycle in an embayment on Long Island, New York, that had high concentrations of dissolved organic matter (DOM) and a bloom of the brown tide pelagophyte, Aureococcus anophagefferens. Amino acids were a significant component (up to 50%) of the total N uptake, particularly during the late summer. About half of the associated amino acid C was also taken up. Amino acid oxidation rates were an order of magnitude lower than free amino acid uptake rates, but still supplied up to 32.5% of the NH taken up. Up to 75% of the amino acid oxidation was in the bacterial size fraction (‹1.2 μm), and rates were significantly correlated with bacterial densities. Peptide hydrolysis rates were high, and most (up to 72%) occurred in the brown tide size fraction (1.2–5 μm). The high rates of peptide hydrolysis and amino acid uptake measured in cultures of A. anophagefferens confirm that this species can readily hydrolyze peptides and take up N and C from amino acids. Laboratory findings and size‐fractionation studies in the field suggest that A. anophagefferens plays a major role in consumption of both C and N from DOM.
Diffusion and advection within and around sinking, porous diatom aggregates
Authors: Ploug Helle , Hietanen Susanna , Kuparinen Jorma
Published: June 2010

Fluid motion within and around sinking aggregates is an important factor in particle scavenging and solute exchange between sinking aggregates and the surrounding water and, hence, vertical fluxes and remineralization processes in the ocean. In the present study, we analyzed O2 uptake rates in >2‐mm porous diatom aggregates and in model aggregates impermeable to flow by measuring, on the same aggregates, the interface diffusive uptake rates with microsensors and the total (diffusive + advective) O2 uptake rate by the Winkler method. The uptake rates were measured in a flow field similar to that experienced by sinking aggregates. The ratio of total O2 uptake rate to diffusive uptake rate was 0.97 ± 0.10 (n = 14) in model aggregates impermeable to flow. In contrast, total O2 uptake was similar to or higher than diffusive uptake rate calculated from the O2 gradients at the aggregate‐water interface in 85% of all field‐sampled and roller tank diatom aggregates examined. The highest ratio of total O2 uptake rate relative to diffusive uptake rate measured in <1‐cm field‐sampled diatom aggregates was 3.91 ± 1.39 (n = 22). Hence, diffusive O2 uptake calculated from the O2 gradients in aggregates is a conservative (minimum) estimate of total O2 uptake. The estimated average fluid velocity through the cross‐sectional area of field‐sampled diatom aggregates, which could explain the measured differences in O2 uptake, ranged between 5 and 40 µm s-1. The average value was 16 µm s-1, which was equal to 1.3% of aggregate sinking velocity.
Hydrodynamics of larval settlement: The influence of turbulent stress events at potential recruitment sites
Authors: Crimaldi John P. , Thompson Janet K. , Rosman Johanna H. , Lowe Ryan J. , Koseff Jeffrey R.
Published: June 2010

We describe a laboratory investigation into the effect of turbulent hydrodynamic stresses on clam larvae in the settlement phase of the recruitment process. A two‐component laser‐Doppler anemometer (LDA) was used to measure time histories of the instantaneous turbulence structure at potential recruitment sites within reconstructed beds of the adult Asian clam, Potamocorbula amurensis. Measurements were made for two flow speeds over beds with three different clam densities and two different clam heights. We analyze the statistical effect of the turbulence on the larval flux to the bed and on the probability of successful anchoring to the substrate. It is shown that the anchoring probability depends on the nature of the instantaneous stress events rather than on mean stresses. The instantaneous turbulence structure near the bed is altered by the flow rate and the spacing and height of adult clams living in the substrate. The ability to anchor quickly is therefore extremely important, since the time sequence of episodic turbulent stress events influences larval settlement success. The probability of successful larval settlement is predicted to decrease as the spacing between adults decreases, implying that the hydrodynamics impose negative feedback on clam bed aggregation dynamics.