bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioturbation and bioirrigation extend the open exchange regions in permeable sediments
Authors: Volkenborn N. , Polerecky L. , Hedtkamp S. I. C. , van Beusekom J. E. E , de Beer D.
Published: November 2010

Large‐scale experimental exclusion of lugworms (Arenicola marina) from 400 m2 intertidal fine sand revealed significant effects of their bioturbation and bioirrigation on sediment characteristics, benthic infauna composition, and the dominant mineralization and benthic‐pelagic exchange processes in the sediment. Absence of lugworms resulted in sediment clogging with organic‐rich fine particles, an eightfold decrease in sediment permeability, low oxygen penetration depths, and accumulation of reduced mineralization products in the pore water. The sand flat inhabited by lugworms had low fine‐particle and chlorophyll contents and low sulfide and nutrient concentrations in the pore water. The effects were not limited to the vicinity of lugworm burrows but extended throughout the entire sediment down to ~20‐cm depth. Sediments with the lugworm shared the characteristic of low‐organic, advection‐driven permeable sand rather than of muddy, diffusion‐dominated sediments in the absence of lugworms. Areal oxygen uptake rates depended strongly on hydrodynamic conditions: under calm conditions, sedimentary oxygen uptake was slightly higher at the exclusion site. Experimental flushing using controlled hydrodynamic conditions showed that oxygen uptake at the lugworm site would be higher during more dynamic conditions (e.g., storms) due to significantly deeper oxygen penetration permitted by higher sediment permeability. Our results indicate an interactive effect of bioturbating organisms and hydrodynamics on water‐sediment exchange processes and highlight the importance of benthic infauna for sedimentary processes even in physically dominated systems.
Controls on spatial and temporal variation of nutrient uptake in three Michigan headwater streams
Authors: Hoellein Timothy J. , Tank Jennifer L. , Rosi-Marshall Emma J. , Entrekin Sally A. , Lamberti Gary A.
Published: November 2010

We measured whole‐stream uptake of ammonium (NH4+), nitrate (NO3−), and phosphate (as soluble reactive phosphorus [SRP]) in two reaches of three forested headwater streams eight times from May 2003 to April 2004 (n = 46 measurements per nutrient type). We also measured factors that could affect uptake, including ambient nutrient concentrations, whole‐stream metabolism, and organic matter standing stocks. In all three streams, we measured the highest rates of NH4+ and NO3− uptake velocity (Vf) during the spring. Low ambient NH4+ concentrations limited NH4+ uptake (U) in two streams. In one stream, when ambient NO3− concentrations increased during summer, NO3− Vf decreased. Temporal patterns of SRP Vf varied among streams, but were unrelated to variability in ambient SRP concentration. However, in all three streams, seasonal variation in SRP Vf was strongly influenced by heterotrophic metabolism (as measured by community respiration; State Creek r = 0.81, p = 0.03; Shane Creek r = 0.89, p < 0.01; Walton Creek r = 0.91, p < 0.01). Although heterotrophic processes typically dominate in forested headwater streams, we found that variability in nutrient uptake among streams was also explained by variables related to autotrophic activity (i.e., proportion coverage of large inorganic substrata and gross primary production). We suggest that the unexpected influence of autotrophy in this study was a result of stream sampling frequency, which included winter and spring—seasons not typically sampled. Our study demonstrates that examining nutrient uptake across streams and during different seasons can provide insight into factors controlling nutrient uptake parameters.
Flooding and arsenic contamination: Influences on ecosystem structure and function in an Appalachian headwater stream
Authors: Lottig Noah R. , Maurice Valett H. , Schreiber Madeline E. , Webster Jackson R.
Published: November 2010

We investigated the influence of flooding and chronic arsenic contamination on ecosystem structure and function in a headwater stream adjacent to an abandoned arsenic (As) mine using an upstream (reference) and downstream (mine‐influenced) comparative reach approach. In this study, floods were addressed as a pulse disturbance, and the abandoned As mine was characterized as a press disturbance. We further addressed chronically elevated As concentrations as a ramp disturbance, in which disturbance intensity was ramped by increasing proximity to the As source. Stream ecosystem structure and biogeochemical functioning were characterized monthly over a period ranging from July to December 2004. Influence of the press disturbance was evident in the mine‐influenced reach, where As concentrations (254 ± 39 µg L−1) were more than 30 times higher than in the reference reach (8 ± 1 µg L−1). However, in almost all cases the presence of the abandoned As mine appeared to exert little influence on reach‐scale measures of ecosystem structure and function (e.g., organic matter [OM] standing crops, phosphorus [P] uptake). Conversely, floods significantly influenced OM standing stock in both study reaches. Interactions between press and pulse disturbances influenced P uptake in the mine‐influenced reach. Within the mine‐influenced reach, P uptake across a gradient of As concentrations correlated with Michaelis‐Menton models of enzyme kinetics in the presence of a competitive inhibitor. These results indicate that As competitively inhibits P uptake by microbial assemblages.
Frequent regime shifts in trophic states in shallow lakes on the Boreal Plain: Alternative "unstable" states?
Authors: Bayley S. E. , Creed I. F. , Sass G. Z. , Wong A. S.
Published: November 2010

Shallow lakes are known to exhibit alternative states in their biotic structure. Lakes dominated by submersed aquatic vegetation (SAV) are ‚‚clear,’’ while lakes dominated by algae (high concentrations of chlorophyll a [Chl a]) are ‚‚turbid.’’ The roles of total phosphorus (TP) and SAV in defining these alternative states were examined for up to 6 yr in 24 naturally eutrophic shallow lakes (12.4‐670.4 µg TP L−1) with variable SAV cover (0–100%) on the western Boreal Plain in Alberta, Canada. Clear lakes had <18 mg Chl a L−1. Sixty‐seven percent of lakes were clear in any given year, but individual lakes did not remain clear over consecutive years. While 29% did not switch, 71% of lakes were unstable, with 57% switching states once and 14% switching more than once. To increase the temporal and spatial scale of analysis, we used Landsat Thematic Mapper satellite imagery (1984‐ 2003) to classify clarity for up to 20 yr in 82 naturally eutrophic shallow lakes. Approximately 80% of lakes were unstable, with 7% switching once and more than 73% switching 2–9 times. Only 20% of lakes were stable and clear. Switches in lake clarity were related to TP but were also dependent on the abundance of SAV. For lakes with high SAV, the TP threshold for the transition from clear to turbid was 275 µg TP L−1, while for lakes with low SAV, the TP threshold was 50 µg TP L−1. Given the harsh winter conditions, including lakes with ice depths of up to 0.7 m and anoxia leading to winterkill of aquatic communities, these systems are strongly abiotically regulated and lack mechanisms that maintain a lake in a stable state.
Caveats on the use of paleolimnology to infer Pacific salmon returns
Authors: Hobbs William O. , Wolfe Alexander P.
Published: November 2010

The ability of paleolimnology to reconstruct historical sockeye salmon (Oncorhynchus nerka) abundance was assessed at Fraser Lake, an important nursery lake in the interior of British Columbia (BC), Canada. Multiple sediment proxies of lake production, as well as nitrogen and carbon stable isotopes, all portray relatively complacent stratigraphies, despite well‐monitored changes in salmon returns over the most recent 60 years. The separation of autochthonous from total sediment organic matter did not clarify the identification of the nitrogen isotopic fingerprint of marine‐derived nutrients (MDN). Slight shifts in diatom assemblages are better interpreted as responses to either early human activities in the catchment or post‐Little Ice Age climate warming. The low proportion of MDN in the lake's annual budget (3% N and 7% P) is the probable reason their influence is not expressed in lake sediments. Thus, paleolimnology is incapable of providing unequivocal inferences concerning historical salmon abundances in Fraser Lake, in contrast to lakes from southern Alaska, where the same techniques have yielded unambiguous results. Sediment MDN proxies, together with catchment characteristics and escapement data, were collated for an additional nine sockeye nursery lakes spanning southern Alaska to southern BC. Primary production and biogeochemical cycling in Alaskan nursery lakes appears largely driven by MDN from sockeye returns, whereas BC lakes are more strongly influenced by allochthonous organic matter and lake‐water residence times. Alaskan lakes possess the limnological features that are prerequisite for meaningful salmon reconstructions using paleolimnology, while lakes from southern BC do not. This does not suggest that MDN are unimportant in southern BC lakes but rather that they are not readily disentangled from other factors that shape the paleolimnological record.
The lost generation of Calanus pacificus: Is the diatom effect responsible?
Authors: Pierson James J. , Frost Bruce W. , Leising Andrew W.
Published: November 2010

An apparent mismatch between periods of high reproduction (spring) and high copepodite abundance (autumn) has been observed for the copepod Calanus pacificus in Dabob Bay, Washington, U.S.A. This persistent pattern leads to a lost generation of progeny that are produced in spring but do not recruit to the juvenile and adult populations, and this is likely due to a combination of factors including advective losses, predation mortality, and nonviability of progeny. Here we test the hypothesis that observed detrimental effects of diatoms on the viability of copepod embryonic and naupliar stages (the diatom effect) are the primary reason for the observed patterns of reproduction and abundance. Furthermore, we test how assumptions about egg production rate and naupliar viability can affect calculations of copepod recruitment. To test these hypotheses, we developed a numerical model to quantitatively explore how certain parameters may have affected the population of C. pacificus population in Dabob Bay. Predation mortality was the most significant contributor to population losses, while advective losses and naupliar viability were of lesser importance, and the model results were more sensitive to parameterization of naupliar viability than egg production rate. Although brief instances of low naupliar viability caused a 25‐30% reduction in cumulative stage I copepodite abundance over time when compared with the assumption of persistent high naupliar viability, the lost generation of C. pacificus in Dabob Bay is likely due to predation mortality, not the diatom effect.
Infochemical‐mediated trophic interactions between the rotifer Brachionus calyciflorus and its food algae
Authors: Verschoor Antonie M. , Zadereev Yegor S. , Mooij Wolf M.
Published: November 2010

We studied how chemicals obtained as filtrates from algal monocultures (algal chemicals) and from rotifer cultures with or without algae (rotifer chemicals) affected feeding rates of the rotifer Brachionus calyciflorus on its food algae, both directly and indirectly (through chemical‐induced changes in algal morphology). Algal chemicals had a strong stimulating effect on the feeding rate of B. calyciflorus, but these effects were counteracted by rotifer chemicals. In functional response experiments, rotifer chemicals lowered maximum ingestion rates and had strong effects on assimilation rates and assimilation efficiencies of B. calyciflorus, probably due to the release of unspecific (auto)toxic metabolites. Furthermore, rotifer chemicals induced colony formation in the food alga Scenedesmus obliquus. Above the optimum particle size for ingestion by B. calyciflorus, larger algal colony sizes increased the food‐handling time, thus lowering ingestion and assimilation rates. Through their effects on trophic interactions, infochemicals may play a role in structuring and the functioning of aquatic food webs.
Initial conditions mediate the interaction between Daphnia and bloom‐forming cyanobacteria
Authors: Sarnelle Orlando
Published: November 2010

To assess whether Daphnia populations in eutrophic lakes can increase when bloom‐forming cyanobacteria dominate the phytoplankton assemblage and whether such an increase can result in strong suppression of phytoplankton biomass, I created contrasting initial conditions (high Daphnia pulicaria, low cyanobacteria vs. low D. pulicaria, high cyanobacteria) via fish manipulation in large enclosures, then removed fish from some enclosures and subsequently monitored zooplankton and phytoplankton abundance for 48 days. After being released from fish predation, D. pulicaria was apparently able to reduce cyanobacteria and total phytoplankton biomass to very low levels despite the fact that the phytoplankton assemblage was initially composed of about 90% Microcystis aeruginosa, a species that has inhibited Daphnia growth and reproduction in many laboratory studies. Thus, it appears possible for Daphnia to graze down an established bloom of cyanobacteria. In contrast, in enclosures where fish were never present, M. aeruginosa was eventually able to increase from low levels despite initially high D. pulicaria biomass. As a result, the apparent effect of D. pulicaria on M. aeruginosa at the end of the experiment was very different across enclosures with different initial conditions.
A standard protocol for stable isotope analysis of zooplankton in aquatic food web research using mass balance correction models
Authors: Smyntek Peter M. , Teece Mark A. , Schulz Kimberly L. , Thackeray Stephen J.
Published: November 2010

Stable isotope analysis has become a crucial tool for aquatic food web ecologists, but a lack of methodological standardization hinders comparisons between studies. One methodological inconsistency in stable isotope food web research is the decision whether to extract lipids before stable isotope analysis. The depletion in zooplankton stable carbon isotope values (δ13C) due to fatty acid content and the accuracy of mathematical correction models designed to predict this depletion were examined for a range of zooplankton species from nine lakes of diverse size and productivity. Large differences of up to 5% observed between δ13C values of nonextracted and lipid‐extracted zooplankton samples correlated with zooplankton fatty acid content. A mass balance δ13C correction model for fatty acid content using atomic C:N ratios and directly measured δ13C values of fatty acids accurately predicted (R2 = 0.95) lipid‐extracted δ13C values for both copepod and cladoceran zooplankton. Researchers should use mass balance lipid corrections as an efficient method to eliminate bias in comparisons of zooplankton and fish δ13C values and allow their results to be more easily compared with other studies.
Scaling of phytoplankton photosynthesis and cell size in the ocean
Authors: Maraóón Emilio , Cermeóo Pedro , Rodríguez Jaime , Zubkov Mikhail V. , Harris Roger P.
Published: November 2010

We have determined the scaling relationship between photosynthesis rate and cell size in natural phytoplankton assemblages of contrasting marine environments. We found that phytoplankton photosynthesis in the ocean does not scale as the L‐power of cell size, but scales approximately isometrically with cell size, indicating that a single model cannot predict the metabolism‐size relationship in all photosynthetic organisms. The scaling relationship between cellular chlorophyll a content and cell size is also isometric. Taxonomical changes along the size spectrum may explain the deviation of phytoplankton photosynthesis from the general allometric rule. The size scaling exponent for photosynthesis is significantly higher (1.14) in coastal productive waters than in the oligotrophic open ocean (0.96), which provides a physiological basis to explain the dominance of larger cells in nutrient‐rich environments. The size scaling exponent for phytoplankton abundance is significantly less negative in coastal productive waters (–0.90) than in the oligotrophic open ocean (–1.25). The observed size scaling relationships imply that carbon fixation per unit volume decreases with cell size in oligotrophic waters, whereas the opposite occurs in productive ones. By controlling the metabolism‐size scaling relationship, nutrient supply plays a major role in determining community size structure and the energy flow through the pelagic ecosystem.
Influence of light and temperature on Prochlorococcus ecotype distributions in the Atlantic Ocean
Authors: Zinser Erik R. , Johnson Zackary I. , Coe Allison , Karaca Erdem , Veneziano Daniele , Chisholm Sallie W.
Published: November 2010

In a focused analysis of Prochlorococcus population structure in the western North Atlantic, we found that the relative abundances of ecotypes varied significantly with depth and, at seasonally stratified locations, with degree of vertical mixing. More limited regional variation was observed (e.g., Sargasso Sea, Gulf Stream, continental slope, and equatorial current), and local patchiness was minimal. Modeling of a combined North and South Atlantic data set revealed significant, independent effects of light and temperature on ecotype abundances, suggesting that they are key ecological determinants that establish the different habitat ranges of the physiologically and genetically distinct ecotypes. This was in sharp contrast with the genus Synechococcus, whose total abundance was related to light but did not vary in a predictable way with temperature. Comparisons of field abundances with growth characteristics of cultured isolates of Prochlorococcus suggested the presence of ecotypespecific thermal and light adaptations that could be responsible for the distinct distribution patterns of the four dominant ecotypes. Significantly, we discovered that one “low‐light‐adapted” ecotype, eNATL2A, can thrive in deeply mixed surface layers, whereas another, eMIT9313, cannot, even though they have the same growth optimum for (low) light.
Molecular assessment of phosphorus and iron physiology in Trichodesmium populations from the western Central and western South Atlantic
Authors: Webb Eric A. , Jakuba Rachel Wisniewski , Moffett James W. , Dyhrman Sonya T.
Published: November 2010

Trichodesmium is capable of responding to low phosphorus (P) and low iron (Fe) concentrations through the induction of alkaline phosphatase (AP) activity (an enzyme that hydrolyzes inorganic phosphate from phosphomonoesters) and the IdiA protein (an iron deficiency protein that putatively binds iron), respectively. We monitored AP activity and IdiA expression as molecular diagnostics of P and Fe stress in Trichodesmium field samples on a transect from the western central to the western South Atlantic and compared the expression of these markers with physical, chemical, and N2 fixation measurements. Trichodesmium AP activity was detected at many stations, whereas IdiA expression was not. Incubation additions of inorganic P at one station resulted in a loss of AP activity and an increase in N2 fixation. Our data suggest that P, and not Fe, is the constraining factor limiting Trichodesmium N2 fixation along most of the transect. These results support previous modeling efforts predicting that diazotrophs in this region are P‐stressed and further validate the use of molecular diagnostics of nutritional physiology, in concert with more traditional approaches, for identifying constraints on marine N2 fixation.
Trichodesmium in the western Gulf of Mexico: 15N2‐fixation and natural abundance stable isotopic evidence
Authors: Holl Carolyn M. , Villareal Tracy A. , Payne Christopher D. , Clayton Tonya D. , Hart Cassandra , Montoya Joseph P.
Published: November 2010

Surface aggregations of the diazotrophic cyanobacterium Trichodesmium were encountered at nearly every station along a 300‐km transect in the northwestern Gulf of Mexico during July 2000. 15N2‐fixation rate measurements for all treatments and locations ranged from 1.3 X 10−4 nmol N trichome−1 h−1 to 2.6 X 10−2 nmol N trichome−1 h−1, with a mean of 3.4 X 10−3 ± 7.6 X 10−4 nmol N trichome−1 h−1 (mean ± SE, n = 45). Trichodesmium C‐fixation, measured by the incorporation of 13C, ranged from 1.3 X 10−2 nmol C trichome−1 h−1 to 4.5 X 10−1 nmol C trichome−1 h−1, with a mean of 1.2 X 10−1 ± 9.3 X 10−2 nmol C trichome−1 h−1 (mean ± SE, n = 44). Both 15N2‐fixation and 13C‐fixation rates attenuated with decreasing light intensity from a maximum at 50% surface intensity. Areal Trichodesmium 15N2‐fixation rates, based on a 10‐h N2‐fixation day, enumerated vertical trichome abundance and corrected for estimated in situ light intensity ranged from 47.2 mmol N m−2 d−1 to 118.6 mmol N m−2 d−1, with a mean of 84.5 ± 17.7 mmol N m−2 d−1 (mean ± SE, n = 4). The light natural abundance isotopic signatures of dissolved inorganic nitrogen, particulate nitrogen, and zooplankton nitrogen within these surface populations are consistent with our limited biological rate measurements and indicate that recently fixed N is moving into the food chain to promote secondary production in these nutrient‐impoverished waters. Although our sample size was relatively small, natural abundance isotope data indicate that as much as 60% of macrozooplankton C and N was derived from Trichodesmium in the oligotrophic regions of the Gulf of Mexico.
Zinc, cadmium, and cobalt interreplacement and relative use efficiencies in the coccolithophore Emiliania huxleyi
Authors: Xu Yan , Tang Degui , Shaked Yeala , Morel François M. M.
Published: November 2010

We investigate the interreplacement of Zn, Cd, and Co in the cosmopolitan coccolithophore Emiliania huxleyi by examining its growth rate, cellular metal quotas, and cellular metal uptake rates under different combinations of Zn, Cd, and Co concentrations in the medium. Co and Zn can fully replace each other, except perhaps for small individual requirements that are met by minute metal concentrations supplied as contaminants. Zn is used at 75% efficiency by E. huxleyi compared with Co. In contrast, Cd can only partially replace Zn or Co and is used at 66% efficiency compared with Co. Up to 50% of the cellular Zn or Co can be replaced by Cd, once the minimum cellular Zn or Co requirement is fulfilled. The limitation by Zn, Cd, and Co and the interreplacement of the three metals occurs over a range of unchelated metal concentrations, 0.2‐5 pmol L−1, that is relevant to surface oceanic waters. Based on our laboratory results and the published metal concentrations in surface oceanic waters, we calculate that interreplacement of Zn, Cd, and Co should occur in regions where Zn is highly depleted.
Direct and indirect effects of burrowing crab Chasmagnathus granulatus activities on erosion of southwest Atlantic Sarcocornia‐dominated marshes
Authors: Escapa Mauricio , Minkoff Darío R. , Perillo Gerardo M. E. , Iribarne Oscar
Published: November 2010

Using field measurements and field experiments, we investigated the effect of a dominant Southwest Atlantic intertidal burrowing crab, Chasmagnathus granulatus, on the inland growth of tidal creeks and creek genesis in salt marshes. By burrowing intensively on marsh sediments, this crab changed sediment physical parameters, such as penetrability, water content, and shear strength, which are related to sediment resistance to erosion. There were positive relationships between crab density and activities occurring in the creek heads and creek growth rates. Field experiments show that the presence and activity of C. granulatus and the presence of their burrows enhance the growth rates of tidal creeks, promoting marsh erosion. When crabs were present, these creeks grew faster than did creeks in which crabs were excluded. Furthermore, the interaction (disturbance and herbivory) between crabs and the dominant halophyte marsh plant, Sarcocornia perennis, generate circular depressions that accumulate standing water (salt pans), which in turn facilitates the creation of new creeks in the marsh surface, which evolve, to a greater extent, into fully functional tidal creeks because of colonization by crabs, which in turn further enhances creek growth rates. These direct and indirect effects of crabs on marsh erosion provide strong evidence of the importance of bioturbation and biological processes to the erosion and geomorphology of marshes.
Change in filter‐screen morphology and depth selection: Uncoupled responses of Daphnia to the presence of filamentous cyanobacteria
Authors: Bednarska Anna , Dawidowicz Piotr
Published: November 2010

In many eutrophic lakes, ability to cope with filamentous cyanobacteria is crucial to Daphnia fitness, as the filaments can reduce food intake by interference with food‐particle retention. Two basic mechanisms were proposed to explain food collection by Daphnia: mechanical sieving, in which filtering appendages act as sieves, and direct interception, in which appendages act as paddles and water does not pass through. As was recently suggested, both mechanisms may be active, and their relative importance is determined by the Reynolds number on filtering appendages. Mechanical sieving seems particularly sensitive to the interference from filamentous cyanobacteria, which can clog the meshes while passing through the filtering chamber. We therefore hypothesized that in the presence of filaments, Daphnia minimizes the interference with filtration by decreasing the Reynolds number on the filters and by thus reducing the relative importance of sieving. To test this hypothesis, we examined the responses of nine clones of the Daphnia longispina group to the presence of nontoxic, filamentous cyanobacteria. The presence of cyanobacteria triggered in Daphnia responses of both behavioral (descending to deep, cold waters) and morphological nature (decreased intersetal and intersetular distances in the filtering apparatus). Both responses led to a decrease in the Reynolds number on the filters. Moreover, the two responses were inversely correlated: individuals with larger meshes descended to colder strata than did those with smaller meshes. These modifications of phenotype are regarded as adaptive, since they allow for minimized filamentinduced interference with the filtration process.
Escape strategies in co‐occurring calanoid copepods
Authors: Burdick Daniel S. , Hartline Daniel K. , Lenz Petra H.
Published: November 2010

We show how four co‐occurring calanoid copepod species modulate their responses to two contrasting hydrodynamic stimuli. Species‐specific patterns in escape behavior included quantitative differences in performance to each stimulus type. Using high‐speed video, we compared escape reactions in Acartia hudsonica, Centropages hamatus, Tortanus discaudatus, and Temora longicornis. Responses to a flow field created by a suction tube involved reorientation away from the source of suction followed by a series of vigorous power strokes. Responses to brief computer‐controlled hydrodynamic stimuli had short latencies (a few milliseconds) and consisted of a reorientation followed by a few pereiopod power strokes. Two species responded to this stimulus with higher escape speeds. The other two species gave a larger response to the suction stimulus by producing long escape trajectories. Each species perceived the magnitude of the threat in a different way and employed a different strategy in the escape response.
Biogeochemistry of the Dumai River estuary, Sumatra, Indonesia, a tropical black‐water river
Authors: Alkhatib M. , Jennerjahn T. C. , Samiaji Joko
Published: November 2010

The biogeochemistry of the Dumai River estuary in eastern Sumatra, Indonesia, was studied in order to obtain information on the sources, transformation, and fate of organic matter. Between October and December 2003, water, total suspended matter (TSM), and sediments were sampled along a salinity gradient during four campaigns, and plants and soils were collected from the catchment. Water samples were analyzed for dissolved inorganic nutrients and dissolved organic carbon (DOC). The concentrations of organic carbon (Corg) and total nitrogen (N) and the stable carbon (δ13Corg) and nitrogen (δ15N) isotope distributions were determined in TSM, sediments, plants, and soils. The pH as well as the concentrations of dissolved inorganic nutrients and TSM were very low in the river and increased toward the sea. A maximum DOC concentration of 5,050 µmol L−1 was measured in the river, and concentrations decreased toward the sea. Low‐gradient relief and a dense vegetation cover, and hence little weathering and erosion, appear to be responsible for low river loads of dissolved nutrients and TSM in this black‐water river. Leaching from extensive peat soils in its catchment may account for the high DOC content of the Dumai River. Peat swamps drained by numerous small rivers are estimated to cover 3.3 X 104 km2 in eastern Sumatra, suggesting that leaching of DOC may be a significant source of carbon to the adjacent coastal seas. A comparison with “normal” rivers shows that black‐water rivers can export similar amounts of DOC from catchments that are orders of magnitude smaller. Thus, export from small black‐water rivers may be quantitatively more significant for the global DOC input into the ocean than previously thought.
Lipids from stomach oil of procellariiform seabirds document the importance of myctophid fish in the Southern Ocean
Authors: Connan Maëlle , Cherel Yves , Mayzaud Patrick
Published: November 2010

We investigated the relative importance of myctophid fish and Antarctic krill in the diet of adult flying seabirds of the Southern Ocean. The main prey of short‐tailed shearwaters Puffinus tenuirostris (P. ten.), white‐chinned petrels Procellaria aequinoctialis (P. aeq.), blue petrels Halobaena caerulea (H. cae.), thin‐billed prions Pachyptila belcheri (P. bel.), and Antarctic prions Pachyptila desolata (P. des.) were mostly deduced from the lipid analysis of adult stomach oils. More than 97% of the 125 analyzed oils mainly consisted of wax esters (WEs) and triacylglycerols (TAGs) (>70% of total lipids). WE fatty alcohol (FAlc), WE fatty acid (FA), and TAG‐FA profiles clearly segregated P. aeq. from P. ten., with smaller, but still significant, differences among the three other petrel species. P. aeq. and P. ten. therefore preyed on distinct prey species, whereas H. cae., P. bel., and P. des. had a more similar diet, but still with some prey differences. Comparisons between FAlc and FA patterns of oils with those of potential prey species showed that >93% of FAlc and FA patterns of oil WEs had a high probability of resemblance with the myctophid signatures, and similar results were obtained with the TAG fractions. Almost no stomach oil fit the lipid patterns of subantarctic and Antarctic euphausiids, including those of the WE‐rich Thysanoessa macrura and the TAG‐rich Antarctic krill Euphausia superba. This study thus demonstrates for the first time the importance of myctophids in the nutrition of adult flying seabirds breeding in subantarctic islands and foraging in Antarctic waters during the austral summer.
History of mercury inputs to Minnesota lakes: Influences of watershed disturbance and localized atmospheric deposition
Authors: Engstrom Daniel R. , Balogh Steven J. , Swain Edward B.
Published: November 2010

The history of mercury (Hg) inputs to 55 Minnesota (U.S.A.) lakes was reconstructed from 210Pb (lead‐210)‐ dated sediment cores to determine if erosion of soils from agriculture and urbanization contributes a significant loading of Hg to lakes, and whether lakes near Hg‐emitting facilities receive appreciable local atmospheric deposition. Modern (1994–1997) Hg accumulation and Hg flux ratios (modern : preindustrial) increase significantly with the percentage of watershed area under urban or agricultural land‐use. Both past and modern Hg accumulation rates are strongly correlated with the flux of total aluminum (Al), a tracer for soil erosion. Modern Hg accumulation rates are substantially higher in the Minneapolis‐St. Paul metropolitan area and in agriculturally dominated south‐central Minnesota than in the forested northeastern part of the state, largely because of erosional inputs of soil‐bound Hg from disturbed catchments. Modern Hg loading from direct atmospheric deposition is also greater in the metropolitan region than in the rural areas of south‐central or northeastern Minnesota. However, some of the excess loading to urban lakes may also be a legacy of formerly high Hg deposition to urban watersheds. A decline in local Hg emissions from peak levels in the 1970s coupled with reduced erosional inputs has cut Hg loading to many metro‐area lakes by more than half.
Ecophysiology of a Mono Lake picocyanobacterium
Authors: Budinoff Charles R. , Hollibaugh James T.
Published: November 2010

We isolated an unusual picocyanobacterium (strain MLCB) from alkaline, hypersaline Mono Lake, California. The organism blooms (~5.0 X 107 cells L−1) in late summer. It has very low population densities in the photic zone through spring and summer (<105 cells L−1) but maintains a significant population (107‐108 cells L−1) in anoxic, sulfidic waters below 25 m year‐round during meromictic periods. Complete turnover of the lake resulted in a significant (>90%) loss of the deep‐water population that could not be attributed to simple dilution. The deep‐water population returned to its previous concentration by the following autumn. The organism is phycoerythrin rich, does not contain phycourobilin, and is not capable of complementary chromatic adaptation. Phylogenetically, our isolate groups with marine Synechococcus, Prochlorococcus, and Cyanobium genera. Salinity tolerance of our strain was compared to select members of the Cyanobium and showed that strain MLCB was the most halotolerant, capable of growing at 10% salinity, compared to limits of 0‐6% for the other strains tested.
Ammonium uptake and growth limitation in marine phytoplankton
Authors: Sunda William G. , D. Ransom Hardison
Published: November 2010

We used continuous culture techniques and a sensitive fluorescence method to quantify relationships among ammonium (NH4+) concentration, cellular NH4+ uptake rates, and growth rate limitation for five marine algal species ranging in diameter from 3 to 11 µm. The growth rate of two high‐nutrient‐requiring coastal diatoms, Thalassiosira weissflogii and Thalassiosira pseudonana, were limited at NH4+ concentrations <90‐100 nmol L−1, while those of low‐nutrient‐adapted species, the oceanic coccolithophore Emiliania huxleyi, the coastal pelagophyte Aureoumbra lagunensis, and the coastal trebouxiophyte Nannochloris atomus, were limited at concentrations <30‐40 nmol L−1. In the nitrogen‐limited cyclostats, the residence times of dissolved ammonium were extremely short (4‐12 min at chlorophyll a levels of 20‐30 µg L−1), and these short times had to be taken into account to obtain accurate NH4+ measurements. Ammonium and nitrate concentrations in stratified surface ocean waters (3‐15 nmol L−1) fall within the range that substantially limited algal growth rates in our experiments, providing evidence for nitrogen limitation in these waters. Ammonium uptake rates and associated specific growth rates were much lower for T. weissflogii (10‐11 µm in diameter) than for the other smaller (3.1– 4.5 µm in diameter) species under ammonium limitation owing to the limits imposed by NH4+ diffusion to the cell surface. Diffusion per unit of cell volume varies with the inverse square of the cell diameter and, thus, greatly restricts growth of large‐celled species under NH4+ limitation. The resultant selection of small‐celled algal species in ammonium‐limited ocean waters should promote rapid grazing and nutrient cycling and minimum nutrient loss via settling of intact cells and zooplankton fecal material.
Viruses as mortality agents of picophytoplankton in the deep chlorophyll maximum layer during IRONAGES III
Authors: Baudoux Anne-Claire , Veldhuis Marcel J. W. , Witte Harry J. , Brussaard Corina P. D.
Published: November 2010

We report viral‐induced mortality rates of the picoeukaryotic (two size classes) and prokaryotic (cyanobacteria Prochlorococcus and Synechococcus) phytoplankton during a cruise in the oligotrophic subtropical northeastern Atlantic (October 2002). A dilution assay, simultaneously estimating viral lysis and microzooplankton grazing, was applied around the deep chlorophyll maximum (DCM) at six stations. For the smallest picoeukaryotes (group I), viral lysis was responsible for 50‐100% of the total cell losses, with rates ranging from 0.1 to 0.8 d−1. Viral lysis rates were positively linked to the abundance and contribution of large genome‐sized (180–225 kb) putative algal viruses. In contrast, the prokaryotic picophytoplankton did not seem to be controlled by viral lysis. For Synechococcus, microzooplankton grazing dominated, with rates between 0.1 and 0.25 d−1 (comparable to those for the eukaryotic algae). For Prochlorococcus, both viral lysis and microzooplankton grazing rates were very low (0–0.1 d−1). Overall, the total carbon production by the picophytoplankton community was balanced by the combined losses due to viral lysis and microzooplankton grazing. Viral lysis released 0.1‐0.3 µg of picophytoplanktonic C L−1 d−1, which comprised 21% of the total carbon production by picophytoplankton.
Effects of progressive oxygen depletion on sediment diagenesis and fluxes: A model for the lower St. Lawrence River Estuary
Authors: Katsev Sergei , Chaillou GwÉnaëlle , Sundby Bjørn , Mucci Alfonso
Published: November 2010

We applied a diagenetic model to examine the effects of a decadal‐timescale progressive decrease in bottomwater oxygen concentration on sediment geochemistry and fluxes across the sediment‐water interface. The model was calibrated using geochemical data acquired over the last 30 yr in the lower St. Lawrence River Estuary (Canada), where the bottom‐water oxygen concentration has been decreasing at an average rate of 1 µmol L−1 yr−1 over the past 70 yr. Benthic fluxes calculated from the model are comparable to fluxes derived from shipboard sediment incubations. By propagating the model forward in time and allowing the oxygen concentration to decrease further at 1 µmol L−1 yr−1, we predict changes in the distributions and fluxes of iron, manganese, phosphorus, nitrogen, and sulfur. As the oxygen concentration decreases, the concentrations and distributions of reactive phases in the sediment change at an accelerating pace. Fluxes of reduced substances out of the sediment increase, reactive iron and manganese oxide phases become depleted, and the sediment becomes progressively enriched in iron sulfides. A notable exception is the efflux of phosphate, which remains invariant. At the study site, these changes are likely to become measurable within the next 20 yr. Model results are sensitive to the effects of decreasing oxygen concentrations on the benthos, the response of which we represent by two different approximations of the bioturbation and bioirrigation formulations: a gradual decrease and a threshold type decrease. The principal obstacle to reliable predictions of how sediments will respond is the lack of knowledge about the response of bioturbation and bioirrigation to decreasing oxygen in bottom waters.
Coral cavities are sinks of dissolved organic carbon (DOC)
Authors: de Goeij Jasper M. , van Duyl Fleur C.
Published: November 2010

We studied the removal of dissolved organic carbon (DOC) by coral cavities of 50‐250 dm3 at a depth range of 5‐17 m along the coral reefs of Curaçao, Netherlands Antilles, and the Berau area, East Kalimantan, Indonesia. We found significantly lower DOC concentrations in cavity water compared with ambient reef water. On average, DOC concentrations in cavity water were 15.1 ± 6.0 µmol L−1 (Curaçao) and 4.0 ± 2.4 µmol L−1 (Berau) lower than in reef water. When the cavities were closed, DOC concentrations in the cavities declined by 22% ± 8% and 11% ± 4% in Curaçao and Berau, respectively, within 30 min. This corresponded to average DOC removal rates per cavity surface area of 342 ± 82 mmol C m−2 d−1 in Curaçao and 90 ± 45 mmol C m−2 d−1 in Berau. Bioassays showed that bacterioplankton are not responsible for this DOC removal by coral cavities. DOC fluxes exceeded bacterioplankton carbon (BC) fluxes into cavities by two orders of magnitude. On average BC fluxes per cavity surface area were 3.6 ± 1.3 mmol C m−2 d−1 (Curaçao) and 1.9 ± 1.3 mmol C m−2 d−1 (Berau area). The net DOC removal per square meter of cryptic surface likely exceeded the gross primary production per square meter of planar reef area. We conclude that coral cavities and their biota are net sinks of DOC and play an important role in the energy budget of coral reefs.
Possible effects of downwelling on the recruitment of coral reef fishes to the Eilat (Red Sea) coral reefs
Authors: Ben-Tzvi Ofer , Kiflawi Moshe , Gildor Hezi , Abelson Avigdor
Published: November 2010

We compared water current measurements with data on the recruitment of reef fishes to a coral reef in Eilat, Red Sea for two consecutive recruitment seasons. There was a clear correlation between the daily number of recruits and the magnitude of the downwelling flow, suggesting that an increase in offshore (near bottom) flow induces higher recruitment. The higher recruitment may be the result of larval swimming against the flow. Although the exact mechanism explaining this correlation is unclear, it may involve odor transport from the reef by the downwelling currents, which reaches competent larvae in deeper water and directs them to potential settlement sites.
Zinc isotope fractionation during high‐affinity and low‐affinity zinc transport by the marine diatom Thalassiosira oceanica
Authors: John Seth G. , Geis Robert W. , Saito Mak A. , Boyle Edward A.
Published: November 2010

We have measured the isotopic fractionation of zinc (Zn) during uptake by the marine diatom Thalassiosira oceanica cultured at a range of free Zn2+ concentrations representative of the natural range from coastal and oligotrophic regions of the ocean. Harvested cells were rinsed with either plain seawater or a wash designed to remove adsorbed extracellular metals. Unwashed cells had much higher levels of Zn and were isotopically heavier than the media, indicating a positive isotope effect for extracellular Zn adsorption. Internalized Zn, measured in washed cells, was isotopically lighter than the media. The magnitude of Zn isotope fractionation changed with free Zn2+ concentration, corresponding to a switch on the part of T. oceanica between the predominance of high‐ and low‐affinity Zn transport pathways. The total isotope effect for uptake (δ66Zn) was ‐0.2% for high‐affinity uptake at low Zn concentrations and ‐0.8% at the highest Zn concentrations, where low‐affinity uptake is dominant. To our knowledge, this is the first study to describe a physiological basis for biological metal isotope fractionation during transport across the cell membrane. Similar high‐ and low‐affinity Zn transport pathways are common among marine phytoplankton, suggesting that the processes described here are an important factor in natural marine Zn isotope variations.
High abundance and dark CO2 fixation of chemolithoautotrophic prokaryotes in anoxic waters of the Baltic Sea
Authors: GÜnter Jost , Zubkov Mikhail V. , Yakushev Evgeniy , Labrenz Matthias , JÜrgens Klaus
Published: November 2010

We determined the abundance and distribution of chemolithoautotrophic prokaryotes in the redoxcline in two basins (Gotland Deep, Landsort Deep) of the central Baltic Sea by combining dark CO2 fixation measurements with flow cytometric cell sorting. Maximum CO2 fixation rates were recorded in sulfidic waters about 20 m below the chemocline. Flow cytometric analyses of deoxyribonucleic acid (DNA)‐stained bacterioplankton revealed the existence of at least five different prokaryotic clusters in water samples collected below the chemocline. Dark CO2 fixation in these clusters was determined by flow cytometric sorting after anoxic incubations with NaH14CO3 tracer. Two clusters, representing about 30% of total prokaryotes, were responsible for 65% to 100% of the total dark fixation. Calculated cell‐specific CO2 fixation rates in the two basins ranged from 3.5 to 24.7 fg C cell−1 d−1 and suggested that these clusters are dominated by chemolithoautotrophic prokaryotes. Mean cell‐specific fixation rates reached more than 10 fg C cell−1 d−1 in most cases, indicating relatively high growth rates (doubling times 1‐2 d) of chemolithoautotrophic prokaryotes. Our results provide the first evidence of such high cell‐specific CO2 uptake and abundance of chemolithoautotrophic prokaryotes in a pelagic marine environment. However, the identity of the organisms as well as the mechanisms fueling CO2 dark fixation in the anoxic zone remain unknown.
Rates and regulation of anaerobic ammonium oxidation and denitrification in the Black Sea
Authors: Jensen Marlene M. , Kuypers Marcel M. M. , Gaute Lavik , Thamdrup Bo
Published: November 2010

We performed incubation experiments with 15N‐labeled nitrogen compounds to investigate the vertical distribution of pathways of N2 production through the suboxic zone of the central Black Sea and the impact of oxygen and sulfide on the anammox process. Anammox rates increased with depth through the upper suboxic zone and reached a maximum of ~11 nmol N2 L−1 d−1 at the sharp interface between nitrate and ammonium, below which rates decreased toward the depth of sulfide accumulation. Heterotrophic denitrification was not detected, and therefore anammox was the prevailing sink for fixed nitrogen in the central Black Sea. In incubations with low oxygen concentrations, anammox activity was only partially inhibited, with a decrease in anammox rates to ~70% and 50% of the anoxic level at ~3.5 and ~8 µmol L−1 O2, respectively, and complete inhibition at ~13.5 µmol L−1 O2. Thus, the anammox process is not constrained to anoxic marine waters. This increases the volume of the major open‐ocean oxygen‐deficient zones, where anammox is potentially active, which has important implications for the contribution of anammox to the marine nitrogen cycle. We observed an inhibitory effect of micromolar sulfide concentrations on anammox activity, indicating that the vertical and likely horizontal distribution of active anammox bacteria is constrained to nonsulfidic water layers, which may explain the absence of the process in sulfidic basins with no suboxic zone.