bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional comparisons of watershed determinants of dissolved organic carbon in temperate lakes from the Upper Great Lakes region and selected regions globally
Authors: Xenopoulos Marguerite A. , Lodge David M. , Frentress Jason , Kreps Timothy A. , Bridgham Scott D. , Grossman Elizabeth , Jackson Caryn J.
Published: July 2010

We analyzed how dissolved organic carbon (DOC) concentration in lakes of the North American temperate forest (Upper Great Lakes region) is related to nine catchment characteristics (lake area, lake perimeter, drainage area, ratio of drainage area to lake area, proportion of watershed occupied by wetlands, proportion of lake perimeter in wetlands, shoreline development, elevation, and watershed slope) and compared selected relationships to those from other regions across the globe. For the temperate lakes, the proportion of the lake perimeter and the proportion of the watershed occupied by wetlands were the best predictors of DOC in both univariate (r2 = 0.34 and 0.30, respectively) and multivariate regression models. Forested wetlands, in particular those with coniferous vegetation, explained the largest proportion of lake DOC variability. Wetlands with scrub‐shrubs and emergent vegetation explained very little or no variability. Secondary to wetlands, lake DOC decreased with lake area and watershed slope. When we combined the temperate lake data set with that of 10 other geographical regions of the world (ranging from subtropical to tundra), the only two variables significant in predicting DOC were proportion of wetlands in the watershed (r2 = 0.36) and lake elevation (r2 = 0.34). We conclude that regional or small‐scale DOC models likely have limited applicability in predicting DOC in other geographical areas of the world.
Phosphorus uptake by Microcystis during passage through fish guts
Authors: Lewin Wolf-Christian , Kamjunke Norbert , Mehner Thomas
Published: July 2010

Herbivorous fish feed on cyanobacteria. Digestability differs, however, between cyanobacteria species without mucous cover and mucilaginous genera such as Microcystis. The latter can pass fish guts almost undamaged, and it has been hypothesized that they can take up nutrients during gut passage. Here we tested whether live Microcystis, as food for juvenile roach labeled with 33P, indeed showed higher radioactivity after gut passage as compared to gut contents in control experiments with fish fed heated Microcystis. Microcystis showed high viability after passage through roach guts, and live colonies had a significantly higher radioactivity than dead ones. We conclude that Microcystis is protected against digestion in roach guts and can directly use the phosphorus supplied in the fish guts during passage.
Phytoplankton growth, microzooplankton grazing, and carbon cycling in marine systems
Authors: Calbet Albert , Landry Michael R.
Published: July 2010

We present an analysis of the global impact of microplanktonic grazers on marine phytoplankton and its implications for remineralization processes in the microbial community. The data were obtained by an extensive literature search that yielded 788 paired rate estimates of autotrophic growth (µ) and microzooplankton grazing (m) from dilution experiments. From studies in which phytoplankton standing stock was measured in terms of carbon equivalents, we show that the production estimate from dilution experiments is a reasonable proxy (r = 0.89) for production determined by the standard 14C method. The ratio m: µ, the proportion of primary production (PP) consumed by micrograzers, shows that microzooplankton consumption is the main source of phytoplankton mortality in the oceans, accounting for 67% of phytoplankton daily growth for the full data set. This ratio varies modestly among various marine habitats and regions, with data averages ranging from 60% for coastal and estuarine environments to 70% for the open oceans, and from ~59% for temperateߚsubpolar and polar systems to 75% for tropicalߚsubtropical regions. Given estimates for the metabolic requirements of micrograzers and assuming they consume most bacterial production, regionally averaged estimates of the protistan respiration are 35ߚ43% of daily PP for the first level of consumer or 49ߚ59% of PP for three trophic transfers. The estimated contributions of microbial grazers to total community respiration are of the same magnitude as bacterial respiration. Consequently, potential ecosystem differences in micrograzer activity or trophic structure are a large uncertainty for biogeochemical models that seek to predict the microbial community role in carbon cycling from bacterial parameters alone.
Predation efficiency in visual and tactile zooplanktivores
Authors: Sørnes Tom A. , Aksnes Dag L.
Published: July 2010

Gelatinous zooplanktivores (medusae, siphonophores, and ctenophores) and visual zooplanktivores (fish) interact through competition, predation, and commensalism. In the search for key factors governing the outcome of competition, we examined the instantaneous predation efficiency and its light dependency. The visual predator Gobiusculus flavescens and the tactile predator Bolinopsis infundibulum were used as experimental models for the two predation modes. The predation rate of G. flavescens was adequately described by Holling's curvilinear disc equation, and that of B. infundibulum was proportional to prey density. However, because of superfluous feeding, the feeding rate of B. infundibulum differed from the predation rate and approached the asymptotic limitation at high prey levels. The predation rate was reduced for G. flavescens at irradiances <5–10 µmol photons m−2 s−1, whereas light had no significant impact on the feeding pattern of B. infundibulum. Provided sufficient light, the predation rate of G. flavescens was several orders of magnitude higher than that of B. infundibulum. These results are consistent with the results of other studies, which suggests that the maximum clearance rate (Cmax) of visual and tactile predators is described by the power functions Cmax = 3.42 × 10−7 L2.94 and Cmax = 6.02 × 10−8 L1.77, respectively, where L is the length of the organisms in centimeters. We conclude that visual predation is most efficient at high visibility and low prey densities. As visibility decreases and prey density increases, the competitive efficiency of tactile predators increases.
Biogenic controls on the air—water carbon dioxide exchange in the Sundarban mangrove environment, northeast coast of Bay of Bengal, India
Authors: Biswas H. , Mukhopadhyay S. K. , De T. K. , Sen S. , Jana T. K.
Published: July 2010

The Sundarban mangrove forest (4,264 km2) constitutes about 3% of the total area of the world mangrove. We measured diurnal and seasonal variations of air—water CO2 exchange in relation to the occurrence of phytoplankton during January—December 2001. Diurnal variations of airflows showed that the minimum and maximum CO2 flux of ‐16.2 µmol m−2 h−1 and 49.9 µmol m−2 h−1, respectively, occurred during the higher sea breeze. The average ratio of dissolved inorganic nitrogen (DIN = 13.85 କ 7.19 µmol L−1) to dissolved inorganic phosphorus (DIP = 1.23 କ 0.57 µmol L−1) was 11 କ 4 and the surface water was undersaturated with respect to dissolved oxygen. The mean value of 0.1 କ 0.08 for the ratio of phytoplankton production (P) to community respiration (R) indicated that the ecosystem was heterotrophic. The saturation of dissolved carbon dioxide with respect to the atmosphere varied seasonally between 59% and 156%, with minimum levels in postmonsoon and maximum levels in premonsoon/ early monsoon (June/July). Out of the 36 genera of diatoms, 1 blue green alga, and 3 dinoflagellates that occurred throughout the year, only 6 reached bloom proportions in postmonsoon, when mangrove water was a sink of atmospheric CO2. Although 59.3% of the emitted CO2 was removed from the atmosphere by biological processes, on an annual basis, the Sundarban mangrove forest supplies 13.8 kg C ha−1 yr−1 of CO2 from water surface to the atmosphere. Even though it is important to compare all in and out fluxes, there is no direct link between CO2 emission and the later CO2 removal by biological processes.
Effects of climatic variability on the thermal properties of Lake Washington
Authors: Arhonditsis George B. , Brett Michael T. , DeGasperi Curtis L. , Schindler Daniel E.
Published: July 2010

We conducted a statistical analysis of a long‐term (1964–1998) record of intra‐ and interannual temperature fluctuations in Lake Washington, Washington. Lake Washington has experienced a warming trend, with overall increases of 1.5 (0.045°C yr−1) and 0.9°C (0.026°C yr−1), respectively, for temperature data weighted over the surface (0–10 m) and entire lake volume. This warming trend was greatest for the period from April to September and was smallest and nonsignificant for November–February. A principal‐components analysis of the long‐term mean monthly temperature time series identified two independent modes of interannual variability. The first mode represented the months of the year when the lake warms and is warmest (e.g., March–October) and explained 54% of the variability in the overall time series. The second mode represented the months when the lake cools and is coldest (November–February) and explained 24% of the variability. The March–October mode was positively correlated with interannual variability in air temperatures and the Pacific Decadal Oscillation (PDO), multivariate r2 = 0.65. The November–February mode was positively correlated with air temperature, PDO, relative humidity, solar radiation, and wind speed (r2 = 0.83). A heat budget model indicated that long‐term trends had a secondary role and interannual variability dominated, with exceptions being net long‐wave atmospheric radiation and surface‐emitted radiation, for which the long‐term trend explained ;25% and 53% of the total variance, respectively. An increase in incoming long‐wave radiation fluxes was mainly associated with the increase in minimum daily temperatures (0.06°C yr−1, r2 = 0.47), especially during the March–October mode, when the linear trend accounted for 85% of the variability.
Empirical modeling of summer lake surface temperatures in southwest Greenland
Authors: Kettle Helen , Thompson Roy , Anderson N. John , Livingstone David M.
Published: July 2010

This work presents a method to estimate mean daily lake surface water temperatures using only air temperature, theoretical clear‐sky solar radiation, and lake size. Surface water temperatures were measured at a selection of lakes in southwest Greenland during the summers of 1998–2000. The lakes are small (surface area <150 ha) with maximum depths ranging from 3.5 to 47 m. An empirical model requiring only local air temperature and theoretical clear‐sky solar radiation is developed to predict daily mean lake surface temperatures in summer for each lake. The model approximates the slow integrated response of water temperature to meteorological forcing by applying an exponential smoothing filter to air temperature. Exponential smoothing results in a 35% improvement in model fit compared with a model using unsmoothed air temperatures. The smoothed air temperatures and clear‐sky solar radiation are linearly combined to estimate the daily mean lake surface temperatures. The smoothing parameters and the three linear coefficients of the model, obtained individually for each of 15 lakes, are found to relate to lake area and maximum depth, leading to the development of a general model. With this general model it is possible to predict the summer surface temperatures at any lake in this region where local air temperatures can be estimated. Cross‐validation of the general model at each lake in turn indicated a 90% forecast skill and average standard error of prediction of 1.0°C. Examination of the daily prediction errors over time suggests a relation to strong wind events.
Marine planktonic ciliates that prey on macroalgae and enslave their chloroplasts
Authors: McManus George B. , Zhang Huan , Lin Senjie
Published: July 2010

We found two tide‐pool ciliates, Strombidium oculatum and Strombidium stylifer, that ingest ulvaceous green macroalgae and retain their chloroplasts. Sequences of the form I ribulose bisphosphate carboxylase/oxygenase (rubisco) large subunit gene (rbcL1) from chloroplasts found in the ciliates cluster with the Ulvophyceae sequences on GenBank and with those of ulvaceous macroalgae from pools in which the ciliates were collected. In addition, we have cultivated S. stylifer in vitro on filtered seawater supplemented with pieces of Enteromorpha thalli that had been treated with light and temperature shock to maximize production of reproductive unicells (swarmers). An average growth rate of 1.08 ± 0.07 SE [standard error] d‐1 was measured when S. stylifer was grown this way. Because both ciliates and the algal swarmers contain eyespots while vegetative cells in the Ulvophyceae do not, we speculate that these reproductive cells are the source of both the chloroplasts and the pigments used in the ciliates' eyespots. This ciliate will not grow in the dark and is required to ingest fresh chloroplasts every few days, making it an obligate mixotroph. Ingestion of macroalgae by ciliates constitutes an upside‐down trophic link, contrary to the usual pattern for planktonic food webs, in which production passes from very small organisms to successively larger ones. Our finding suggests that macroalgal production, heretofore believed to contribute predominantly to detrital or macroherbivore food chains, may be an important food source in the nearshore plankton and that ciliates may play an important role in this trophic pathway.
Modeling the mass balance and fate of copper in San Diego Bay
Authors: Chadwick D. B. , Zirino A. , Rivera-Duarte I. , Katz C. N. , Blake A. C.
Published: July 2010

Because of its presence in antifouling coatings, stormwater, and industrial and municipal discharges, copper is a ubiquitous contaminant in estuarine and coastal environments. We integrated a system‐wide field program with a one‐dimensional model to evaluate the overall mass balance of copper in a representative coastal harbor, San Diego Bay, California. Field results from four surveys over 1 yr showed remarkably similar distributions of total copper, with a general increase from the ocean into the Bay followed by a slight decrease in the inner Bay. Total copper concentrations ranged from 5 nmol L‐1 to nearly 60 nmol L‐1. Highest levels for both total and dissolved copper were observed during the winter. Results from a one‐dimensional model accounting for the balance of sources, flushing, and losses to the sediment illustrated the importance of accounting for losses of copper to the sediment, without which water column concentrations are overestimated by as much as a factor of five. The time scale for the loss term is on the order of 8‐10 d. The model reproduced the field measurements quite well with a loss term controlled by partitioning and settling parameters. The overall balance of total copper in the Bay appears to be split between losses to the ocean via tidal flushing and losses to the sediments via settling. Settling plays an important role in the fate of copper in the Bay, and the sediments are a key endpoint for copper.
Submarine groundwater discharge of nutrients and copper to an urban subestuary of Chesapeake Bay (Elizabeth River)
Authors: Charette1 Matthew A. , Buesseler Ken O.
Published: July 2010

We investigated the role submarine groundwater discharge (SGD) plays in the delivery of nutrients and copper to the Elizabeth River (Virginia) estuary, a major subestuary of lower Chesapeake Bay. Using an approach based on radium isotopes, we concluded that two distinct sources of groundwater were equally impacting the estuary: a surface (marsh) aquifer and deep aquifer source each with a unique 228Ra/226Ra activity ratio. Considering each of these sources, we calculated an SGD flux of 1 x 106 m3 d−1 (±10%), which represented ~6% of the SGD flux for the entire Chesapeake Bay and ~5% of the James River, a major source of freshwater to lower Chesapeake Bay. SGD‐derived dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) fluxes averaged 4.5 (±4.6) and 0.16 (±0.17) mmol m−2 d−1, respectively, and compared well with area‐normalized fluxes to Chesapeake Bay. In contrast, SGD‐derived Cu input of 730 (±390) kg yr−1 was a relatively small source of Cu (~3%) to the Elizabeth estuary given that surface water inputs, such as antifouling paints associated with naval operations, are a major component of the Cu budget for this system. These findings were in general agreement with prior studies of SGD for this region.
Limited transport and recolonization potential in shallow tidal estuaries
Authors: Lundquist Carolyn J. , Thrush Simon F. , Oldman John W. , Senior Alastair K.
Published: July 2010

Evidence of limited larval exchange and high levels of self‐recruitment in marine populations continues to accumulate, implying that marine systems are not as open as we once believed. In estuaries, some organisms with long larval periods, such as crab and bivalve species, are capable of long‐distance transport, while others, including many polychaete and gastropod species with crawling or brooded larvae, lack long‐distance larval dispersal mechanisms and may disperse as juveniles and adults. To predict transport rates and colonization potentials of macrofaunal life stages transported in the water column, we use a combined hydrodynamic and particle tracking model. We vary particle release location to investigate how different habitats (i.e., main channel, lower sandflat, high sandflat, tidal creek) will contribute to the supply of colonists in different parts of the estuary. Most particles traveled short distances and settled within their release habitat. Slightly negatively buoyant particles (corresponding to small larvae) traveled much farther than more negatively buoyant particles (corresponding to larger, heavier larvae and juveniles). Particles released from high intertidal locations had lower rates of transport and transfer among habitats compared to lower intertidal sites. Other influences on organism transport include timing of release (with respect to tide), release location within the water column, tidal range, and magnitude of freshwater flood events. In general, estuarine communities dominated by organisms with limited dispersal periods are likely to be recruitment limited and limited in their ability to reach mature community states when subject to increasing frequencies or spatial extent of disturbance.
Spatiotemporal patterns of carbon remineralization and bio‐irrigation in sediments of Casco Bay Estuary, Gulf of Maine
Authors: Green,1 Mark A. , Gulnick Jeanne D. , Dowse Nathaniel , Chapman Patience
Published: July 2010

We measured the seasonal and spatial rates of organic matter decomposition and pore‐water irrigation at four subtidal stations in Casco Bay estuary, Gulf of Maine. Organic carbon decomposition and associated flux from sediments showed strong seasonal fluctuations, with averaged highs of 44.9 (±4.9) mmol dissolved inorganic carbon (DIC) m−2 d−1 during August and lows of 8.6 (±1.6) mmol DIC m−2 d−1 during January. Apparent activation energies (Ea‐app) ranged from 61 (±5.5) to 83 (±14.5) kJ mol−1 in the 0–1 and 2–3 cm layers of sediments, respectively, which reflects a decrease in carbon reactivity with depth. Spatial differences in surface Ea‐app correlate with C:N ratios in pore water, with lowest Ea‐app levels at stations with lowest C: N; ratios, which is consistent with the remineralization of recently formed organic matter. In addition, there was a significant time‐dependent change in the transport mechanism between sediments and overlying water. Br2 tracer experiments, comparison of flux estimates, and diagenetic transport‐reaction models all independently showed that transport increases significantly because of the activities of benthos during spring, summer, and fall, when rates are ~3 times higher than simple diffusion alone. Biologically enhanced transport resulted from the high density of benthos (≫1.0 mm, ~7,000 m−2), with the nephtyid polychaete Aglaophamus neotenus and the spionid polychaete Prionospio steenstrupi being most abundant. The polychaete Owenia fusiformis and the burrowing, deposit‐feeding amphipod Casco bigelowi were also important. These results further confirm the importance of understanding seasonal variability in both carbon degradation and the influence of benthic organisms in controlling material exchange between sediments and water in estuarine systems.
Decrease in molecular weight of photosynthetic products of marine phytoplankton during early diagenesis
Authors: Hama Takeo , Yanagi Katsumi , Hama Junko
Published: July 2010

Changes in the size and neutral aldose (NAld) composition of phytoplankton photosynthetic products during the early diagenetic process were experimentally examined using 13C as a tracer. Most (94.7%) of the photosynthetically produced (P−) organic carbon (OC) was found to be particulate organic carbon (POC) after a 12‐h light incubation. An increase in the concentration of P‐dissolved organic carbon (DOC) was found after the shift to the dark incubation, probably due to a leakage of cellular constituents. An increase in the concentration of P‐DOC was mainly due to an increase in the high molecular weight (HMW: ≫10 kDa) fraction that reached its maximum concentration on day 3 and then declined at a relatively high rate. The change in the concentration of the low molecular weight (LMW: ≪10 kDa) DOC fraction was less marked than that in the HMW fraction, and the rate of decrease was much slower, indicating a more biorefractory nature of P‐LMW DOC. P‐dissolved carbohydrates (DCHO) accounted for 38% and 50% in P‐HMW DOC and P‐LMW DOC, respectively, after a 12‐h light incubation. The concentration of P‐LMW DCHO showed a rapid decrease in the early stage of the dark incubation, whereas the concomitant increase in the concentration of P‐LMW dissolved noncarbohydrate (DnonCHO) was noticed. The decrease in the contribution of CHO was noticed both in P‐POC and P‐HMW DOC fractions, but the decline rates were slower than that in P‐LMW DOC fraction. On day 60, the remaining P‐OC accounted for 4.6% of photosynthetic material originally produced. The distribution of the size fractions of the remaining P‐OC on day 60 (POC, 14%; HMW DOC, 22%; LMW DOC, 64%) indicates that phytoplankton photosynthetic products were rapidly degraded to the less bioreactive LMW DOM during early diagenesis. The present results indicate that the annual global ocean production rate of semilabile DOC with lifetimes exceeding 2 months is 1.91 PgC yr−1.
Outer‐membrane siderophore receptors of heterotrophic oceanic bacteria
Authors: Armstrong Evelyn , Granger Julie , Mann Elizabeth L. , Price Neil M.
Published: July 2010

Pathogenic gram‐negative bacteria use specific receptors to transport ferric siderophore complexes across their outer membrane during iron (Fe)‐limited growth. Receptors such as these have not yet been characterized in oceanic heterotrophic bacteria. We examined four species of γ‐proteobacteria for the presence of Fe‐siderophore receptors with the use of a nondenaturing polyacrylamide gel electrophoresis binding assay and the siderophore ferrioxamine B (FB) labeled with 55Fe. Small‐subunit rRNA sequence analysis assigned these bacteria to the genera Pseudoalteromonas and Alteromonas. Two oceanic species, Pseudoalteromonas haloplanktis (Neptune) and Alteromonas macleodii (Jul88), which were shown previously to transport and assimilate Fe bound to FB during growth, synthesized an outer‐membrane FB receptor under Fe‐limiting conditions. Only low concentrations of the receptors were detected in these bacteria when they were grown with high concentrations of Fe. The FB receptor of P. haloplanktis (Neptune) had an apparent molecular mass of 79 kDa and an externally oriented binding site. The molecular mass of the receptor of A. macleodii (Jul88) was 100 kDa. No FB receptors were detected by our methods in two coastal species, Pseudoalteromonas rubra (LMG1) and Pseudoalteromonas piscicida (PWF3). P. haloplanktis (Neptune) and A. macleodii (Jul88) also bound 55Fe‐ferrichrome, a trihydroxamate siderophore like FB. Binding assays conducted with 115 nmol L−1 55Fe‐FB in the presence of increasing concentrations of desferrioxamine B showed a progressive decrease in the amount of 55Fe‐FB bound by the receptor protein, suggesting strong affinity of the receptor for the Fe‐free siderophore. Our results provide the first demonstration of Fe‐siderophore receptors in oceanic heterotrophic bacteria.
Autochthonous versus allochthonous carbon sources of bacteria: Results from whole‐lake 13C addition experiments
Authors: Kritzberg Emma S. , Cole Jonathan J. , Pace Michael L. , Granéli Wilhelm , Bade Darren L.
Published: July 2010

Organic substrates for pelagic bacteria are derived from dissolved organic carbon (DOC) in the water column. DOC is a heterogeneous mixture of molecules, some of which are imported from the watershed (allochthonous DOC) and others that are produced by autotrophs within the system (autochthonous DOC). We examined the importance of autochthonous versus allochthonous DOC in supporting the growth of pelagic bacteria by manipulating the 13C content of autochthonous sources in a whole‐lake experiment. NaH13CO3 was added daily to two small forested lakes for a period of 42 d, thereby strongly labeling autochthonous primary production. To obtain bacterial carbon isotopes, bacteria were regrown in vitro in particle‐free lake water and in situ in dialysis tubes; little difference was found between the two methods. The contribution of autochthonous versus allochthonous carbon to the bacterial biomass was estimated by applying a two‐member mixing model using a 13C of −28‰ as the allochthonous end member. The autochthonous end member, which varied over time, was estimated indirectly by several approaches. The bacterial biomass consisted of 35–70% allochthonous carbon. This result confirms the often‐stated hypothesis that autochthonous carbon alone does not support bacterial production. On the other hand, autochthonous DOC was preferentially utilized relative to terrestrial DOC. On the basis of 13C measurements, only 13% of the DOC standing stock was of recent autochthonous origin, but it supported 30–65% of bacterial production.
Effects of Microcystis aeruginosa and purified microcystin‐LR on the feeding behavior of Daphnia pulicaria
Authors: Ghadouani Anas , Pinel-Alloul Bernadette , Plath Klaus , Codd Geoffrey A. , Lampert Winfried
Published: July 2010

We investigated the mechanisms behind the negative effects of cyanobacteria on zooplankton by comparing the effects of Microcystis aeruginosa single cells, colonies, and toxins on the feeding behavior of Daphnia pulicaria in three independent experiments. The animals were fed a mixture of Scenedesmus supplemented by increasing proportions (0, 20, 50, 80, 100%) of Microcystis or concentrations (0, 50, 500, 5,000 ng ml−1) of purified microcystin‐LR. The changes in feeding behavior, as indicated by the appendage beat, mandible or labrum movement rates were evaluated by a direct observation method that coupled video recording and computerized image analysis. Daphnia responded in a different manner to the presence of single cells and colonies. In the case of the single cells, the mandibular movement rate (MMR) declined more than appendage beat rate (ABR), suggesting that Daphnia have the ability to discriminate between Microcystis and Scenedesmus. Colonies, on the other hand, produced a typical feeding interference response: the animals increased their labral rejection rate (LRR) and showed starvation signs. LRR increased in the presence of both unicellular and colonial Microcystis. In both cases, the changes in MMR and ABR were rapidly reversible and hence unlikely to be caused by intoxication from the presence of cellbound microcystins. In contrast, the addition of purified microcystin‐LR at the concentration of 5,000 ng ml−1 produced a nonreversible impairment of Daphnia feeding behavior.
Oxidative coupling during gut passage in marine deposit‐feeding invertebrates
Authors: Giessing Anders M. B. , Mayer Lawrence M.
Published: July 2010

We tested for oxidative coupling of phenolic materials, including organic contaminants and tyrosine, in gut fluid from marine deposit‐feeding invertebrates. A phenolic metabolite (pyrenol) of a polycyclic aromatic hydrocarbon (PAH), which can arise during accumulation by deposit‐feeding invertebrates, was found to participate in oxidative coupling reactions to organic matter in gut fluid. Gut fluid from four species of marine deposit‐feeding invertebrates (three polychaetes and one holothuroid) catalyzed oxidative coupling of pyrenol (1‐hydroxypyrene) in rough proportion to their enzyme activity and dissolved organic matter levels. Nereis virens gut fluid also catalyzed coupling of tyrosine monomers to form dityrosine, a common marker of oxidative damage in proteins. An antioxidant enzyme activity, similar to that of heme peroxidase and capable of oxidative coupling, was tentatively identified in gut fluid from N. virens by protein precipitation, dye decolorization assays, and enzyme inhibitor studies. Unaltered N. virens gut fluid had high total oxyradical scavenging capacity, indicating the presence of fast‐acting antioxidants. Oxidative coupling of PAHs will reduce subsequent bioavailability, toxicity, and transport of these compounds in marine environments. Furthermore, oxidative coupling of PAHs represents a hitherto overlooked sink for organic contaminants in marine sediments and suggests a biological mechanism for formation of aquatic humic material.
Black carbon in estuarine and coastal ocean dissolved organic matter
Authors: Mannino Antonio , Rodger Harvey H.
Published: July 2010

We measured black carbon (BC) in ultrafiltered, high‐molecular weight dissolved organic matter (UDOM) in surface waters of Delaware Bay, Chesapeake Bay, and the adjacent Atlantic Ocean (U.S.A.) to investigate the importance of riverine and estuarine dissolved organic matter (DOM) as a source of BC to the ocean. BC was 5‐72% of UDOM‐C (27 ± 17%), which corresponds to 8.9 ± 6.5% of dissolved organic carbon (DOC), with higher values in the heavily urbanized midbay region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of Delaware Bay suggest that the elevated levels of BC in surface water UDOM originate from localized sources, possibly from atmospheric deposition or release from resuspended sediments. BC in UDOM made up 4–7% of the DOC in the coastal Atlantic Ocean, revealing that river‐estuary systems are important exporters of colloidal BC to the ocean. The annual flux of BC from Delaware Bay UDOM to the Atlantic Ocean was estimated at 2.4 x 1010 g BC yr−1, supporting the hypothesis that the DOC pool is an important contributor of BC to the ocean.
Variations in the mass‐specific absorption coefficient of mineral particles suspended in water
Authors: Babin Marcel , Stramski Dariusz
Published: July 2010

We examined the light‐absorption properties of various samples of mineral particles suspended in water, which included pure mineral species (quartz, calcite, illite, kaolinite, and montmorillonite) and natural particulate assemblages such as desert dust originating from different locations in the Sahara. The absorption coefficient was measured in the spectral region from ultraviolet (UV) to near‐infrared on particle suspensions, using a special measurement geometry that reduced the scattering error to a very small level. The concentrations of the total mass of particles in suspension, as well as the mineralogical and elemental composition of particulate samples, were also determined. For the samples of pure mineral species with negligible contamination with iron, absorption was undetectable in the visible spectral region. All of the examined natural assemblages of mixed mineral species showed a significant content of iron (5–29% by weight), and all these samples exhibited significant absorption in the UV and blue‐green (400–550 nm) spectral regions. The spectral shape of absorption was similar to that determined on pure iron hydroxide suspension, with some spectral features (shoulders and changes in slope) superposed onto a general increase of absorption toward short wavelengths in the UV. The mass‐specific absorption coefficient of the mineral samples, a*m(λ), obtained by normalization of the absorption coefficient to the dry‐mass concentration of particles, *m showed a significant positive correlation with Fe content. No such relationship was found for other elements present in particles. The range of a*m(λ) values covered more than an order of magnitude (from <0.1 to <1 m2 g−1 near 400 nm), but the normalization of absorption coefficient to iron concentration led to a considerable reduction in variability among the samples. The iron‐specific absorption coefficient, a*Fe(λ), varied from <1 to 4 m2 (g Fe)−1 near 400 nm for the natural mixtures of mineral species. Although iron was a major pigmenting agent, its concentration could explain only part of variability observed in the absorption properties of mineral particles.
Evidence for a residual postglacial founder effect in a highly dispersive freshwater invertebrate
Authors: Freeland Joanna R. , Rimmer Vivien K. , Okamura Beth
Published: July 2010

In the northern hemisphere, glacial periods have had profound and lasting effects on the population genetics of numerous species, with founder effects often persisting for many generations in formerly glaciated regions. We found an unusual example of this in the freshwater bryozoan Cristatella mucedo, which showed regional differences in haplotype diversity with relatively low levels of haplotype diversity in northern Europe compared to central/southern Europe despite previous evidence for frequent dispersal between C. mucedo populations. Such contradictions between high dispersal and low gene flow have now been reported in several other freshwater taxa and may be attributed to persistent founder effects following colonization of sites by a few individuals whose efficient reproduction leads to rapid population growth. Alternatively, selection may determine which genotypes can thrive in northerly locations, or it may be that C. mucedo has undergone cryptic speciation. Future work on adaptive genomic regions is required before we can understand how gene flow, local adaptation, and speciation influence the current distribution patterns of bryozoans and other freshwater invertebrates.
Diel variation of molybdenum and iron in marine diazotrophic cyanobacteria
Authors: Tuit Caroline , Waterbury John , Ravizza Gregory
Published: July 2010

Measurements of Mo:C and Fe :C ratios in cultured cells of two N2‐fixing cyanobacteria, Crocosphaera watsonii strain WH8501 and Trichodesmium erythraeum strain IMS101, agree with estimated metal : carbon ratios based on growth rate and the metal use efficiency of the nitrogenase enzyme. Crocosphaera, a single‐celled nocturnal N2 fixer, showed two‐ to eightfold increases in Mo and Fe cellular concentrations in response to nitrogen fixation activity. Mo required for N2 assimilation can account for almost the entire Mo pool measured in the cells, implying that Crocosphaera synthesizes its entire nitrogenase pool de novo each night. In contrast, cultures of Trichodesmium, a filamentous, diurnal N2‐fixing cyanobacterium, did not show diel variations in Mo or Fe carbon ratios or in cellular metal concentrations. Trichodesmium appears to maintain an internal pool of Mo. In Trichodesmium cultures, Mo concentrations were up to 30% higher than needed to support measured N2 fixation. Trichodesmium colonies collected from the field had Mo:C ratios 10‐fold larger than those measured in culture, far in excess of what is needed to fix N2 at rates normally measured in the field, despite equivalent Fe :C ratios (66 ± 39 [field samples] and 87 ± 64 [cultures] µmol mol−1). The average Fe :C ratio measured in N2‐fixing Crocosphaera (16 ± 11 µmol mol−1) was equivalent to theoretical estimates of Fe demand based on nitrogenase requirements (13 ± 5 µmol mol−1). These results demonstrate the extremely efficient use of Fe by these organisms and provide support for the use of theoretical estimates of Fe :C ratios to calculate biological Fe demand for N2 fixation.
The demise of the marine cyanobacterium, Trichodesmium spp., via an autocatalyzed cell death pathway
Authors: Berman-Frank Ilana , Bidle Kay D. , Haramaty Liti , Falkowski Paul G.
Published: July 2010

We present experimental laboratory evidence and field observations of an autocatalyzed, programmed cell death (PCD) pathway in the nitrogen‐fixing cyanobacterium Trichodesmium spp., which forms massive blooms in the subtropical and tropical oceans. The PCD pathway was induced in response to phosphorus and iron starvation as well as high irradiance and oxidative stress. Transmission electron microscopy revealed morphological degradation of internal components including thylakoids, carboxysomes, and gas vesicles, whereas the plasma membranes remained intact. Physiologically stressed cells displayed significantly elevated endonuclease activity and terminal d‐UTP nick‐end labeling. Nucleic acid degradation was concordant with increased immunoreactivity to human caspase‐3 polyclonal antisera and enhanced cleavage of a caspase‐specific substrate, DEVD. Caspase activity was positively correlated with mortality and was inhibited by the irreversible caspase inhibitor Z‐VAD‐FMK. A search of the Trichodesmium erythraeum genome identified several protein sequences containing a conserved caspase domain structure, including the histidine‐ and cysteine‐containing catalytic diad found in true caspases, paracaspases, and metacaspases. Induction of PCD by caspase‐like proteases in a bacterial photoautotroph with an ancient evolutionary history requires a reassessment about the origins and roles of cell death cascades. This process is a previously unappriciated mortality mechanism that can lead to the termination of natural Trichodesmium blooms and that can influence the fluxes of organic matter in the ocean.
Interactive regulation of dissolved copper toxicity by an estuarine microbial community
Authors: Dryden Christina L. , Gordon Andrew S. , Donat John R.
Published: July 2010

Cultured marine microorganisms under copper stress produce extracellular compounds having a high affinity for copper (copper‐complexing ligands). These ligands are similar in binding strength to those found in natural waters, but few studies have examined the relationship between copper, copper‐complexing ligand concentrations, and natural microbial populations. A series of in situ experiments in the Elizabeth River, Virginia, revealed that an intact estuarine microbial community responded to copper stress by production of extracellular, high‐affinity copper complexing ligands. The rate of ligand production was dependent on copper concentration and resulted in a reduction of the concentration of free cupric ions, Cu2+, by more than three orders of magnitude during a 2‐week period in one experiment. We believe that this interactive response to copper stress represents a feedback system through which microbial communities can potentially buffer dissolved Cu2+ ion concentrations, thereby regulating copper bioavailability and toxicity.
Extreme13 C enrichments in a shallow hypereutrophic lake: Implications for carbon cycling
Authors: Gu Binhe , Schelske Claire L. , Hodell David A.
Published: July 2010

An analysis of stable carbon isotope (δ13C) ratios in Lake Apopka, Florida, reveals extreme 13C enrichments of dissolved inorganic carbon (DIC) pools in the water column and sediment pore water of this shallow polymictic and hypereutrophic lake. The sediment pore water had high averageδ13C of DIC (26.4‰), DIC (8.37 mmol L−1), and methane (CH4) concentrations (1.23 mmol L−1). The extreme 13C enrichment in the sediment pore‐water DIC pool is attributed to methanogenesis, which produces 13C‐rich carbon dioxide (CO2) and 13C‐poor CH4 during the bacterial fermentation of organic matter. The δ13C in the water‐column DIC pool ranged from 5‰ to 13‰ with an average of 9.0‰. The flux‐weighted δ13C from the DIC due to external loading and sediment respiration was estimated as −12‰, whereas the δ13C from particulate organic carbon (POC) due to water‐column production was −13‰. The 13C enrichment in the water column is attributed directly to the diffusion and advection of isotopically heavy DIC from the sediment and to the isotopic fractionation by phytoplankton photosynthesis and is attributed indirectly to the removal of isotopically light CH4 by ebullition and organic matter by sedimentation and outflow. Atmospheric invasion and sedimentation were the most important source and sink, respectively, in the carbon mass balance. CH4 oxidation, atmospheric invasion, anaerobic respiration, and sedimentation are the important flux terms affecting the isotopic mass balance. A combination of shallow water depth, frequent wind mixing, anoxic sediments with high rates of methanogenesis, high phytoplankton productivity, and lack of external loading dominated by terrestrial carbon led to the 13C enrichment of the water‐column DIC pool in Lake Apopka.
Controls of δ13C‐DIC in lakes: Geochemistry, lake metabolism, and morphometry
Authors: Bade Darren L. , Carpenter Stephen R. , Cole Jonathan J. , Hanson Paul C. , Hesslein Raymond H.
Published: July 2010

We investigated δ13 carbon (C)‐dissolved inorganic carbon (DIC) values in 72 lakes from diverse regions using literature data as well as new measurements for 32 lakes. δ13C‐DIC varied broadly among lakes from ~31 to +2.6‰. This variation of surface‐water δ13C‐DIC among lakes is greater than the seasonal variation within most lakes. Several statistical models account for a large portion of the interlake variation and indicate that geochemical (e.g., DIC, pH, alkalinity) and morphometric (area) variables are important, whereas biological (e.g., gross primary productivity [GPP], respiration [R], chlorophyll a) variables are generally not significant. A process‐based model including gas exchange with the atmosphere, inorganic carbon speciation, and ecosystem metabolism was also constructed. The model provides a reasonable fit to the data for lakes, in which respiration exceeded GPP (heterotrophic lakes; 75% of lakes sampled). Lakes for which GPP exceeded respiration (autotrophic) were not fit well by the process‐based model. The data and models indicate that metabolism creates substantial variation in δ13C‐DIC around the potential δ13C‐DIC that is set by geochemical factors of the watershed.
Synchrony in relationships between the North Atlantic Oscillation and water chemistry among Sweden’s largest lakes
Authors: Weyhenmeyer Gesa A.
Published: July 2010

The North Atlantic Oscillation (NAO) is commonly presented as an easy and reliable index that can be used to study climatic effects on aquatic ecosystems. Here, the NAO winter index (NAOW) was applied to determine effects of winter climate changes on 13 water chemical variables measured monthly at 16 sites in Sweden’s three largest lakes (Vänern, Vättern, and Mälaren). The NAOW strongly affected meteorological, physical, and consequently also chemical conditions. Significant relationships were numerous in Sweden’s three largest lakes, but they exhibited little agreement among lakes and even across a lake. Synchronous relationships between the NAOW and water chemistry among lake sites were restricted to variables closely linked to surface‐water temperature (i.e., reactive silica and pH in May). The weaker the association of a lake variable with water temperature, the weaker the mean NAOW signal on the variable over the 16 lake sites. The results of this study might facilitate the prediction of lake ecosystem responses to future changes in the weather over a large region.
Nutrient cycling in a strongly acidified mesotrophic lake
Authors: Jiří Kopáček , Brzákova Martina , Hejzlar Josef , Nedoma Jiří , Porcal Petr , Vrba Jaroslav
Published: July 2010

In contrast to the well‐known nutrient transformations in circumneutral lakes, acidified water bodies may exhibit significant changes in nutrient cycling due to changes in their chemistry and biology. In‐lake cycles of carbon (C), nitrogen (N), and phosphorus (P) were evaluated in the strongly acidified Plesné Lake (Central Europe). The lake tributaries had high concentrations of dissolved organic C (DOC), inorganic N, and total phosphorus (TP), resulting in annual averages of 644, 52, and 0.72 µmol L−1, respectively. Because of the absence of fish and largely reduced zooplankton, Plešne’ Lake has a “simplified” food web. The mass balance of nutrients was based on the major external inputs (tributaries and atmospheric deposition), internal sources and transformations (primary and bacterial production, biological decomposition of sedimenting seston and sediments), sedimentation, and outputs. External inputs of total organic C (TOC), total N (TN), and TP into Plesné Lake were 7,244, 864, and 8.6 mmol m−2 yr−1, respectively. Net primary production of particulate C (Cpart) and extracellularly released DOC were 3,205 and 613 mmol m−2 yr−1, respectively. Bacterial Cpart and total inorganic C production were both 1,518 mmol m−2 yr−1. Of the total internal and external inputs of TOC, TN, and TP, the in‐lake processes removed 4,551 (50% respiration, 40% sedimentation, and 10% photooxidation), 211 (74% sedimentation and 26% denitrification), and 4.6 (100% sedimentation) mmol m−2 yr−1, respectively. Compared to circumneutral lakes, nutrient cycling differed as follows: (1) Liberated orthophosphate from sedimenting seston was converted from a liquid to a particulate phase by colloidal aluminum (Al) in the hypolimnion and deposited. Similar abiotic P immobilization with Al removed 1.6 mmol m−2 yr−1 from the whole‐water column, thus reducing by ~20% the pool of potentially bioavailable P and contributing to a severe P limitation of biomass. (2) The cessation of nitrification due to long‐term water acidification led to an atypical situation in which the lake became a net source of NH4+ (30 mmol m−2 yr−1) because dissimilative liberation of NH4+ exceeded its assimilation.
Millennial‐scale relationships of diatom species richness and production in two prairie lakes
Authors: Rusak James A. , Leavitt Peter R. , McGowan Suzanne , Chen Gemai , Olson Olaf , Wunsam Sybille , Cumming Brian F.
Published: July 2010

Insight into the causes and consequences of changes in aquatic biodiversity requires an improved understanding of the nature of the relationships between species richness and ecosystem function over a much longer temporal perspective than we currently possess. We used high‐resolution paleoecological records from two prairie lakes to show that diatom species richness (as fossil frustules) was negatively correlated (r2 = 0.09–0.24, p < 0.001) with diatom production (as fossil pigments) during the past 2,000 yr. By comparing analyses from intervals of fresh and saline waters, we demonstrate that these significant richness‐production relationships arose during freshwater periods (r2 = 0.13–0.45, p < 0.001) and could be eliminated (r2 < 0.02, p > 0.1) by abiotic disturbances such as droughts. Procrustes analyses of the concordance of species change within freshwater communities and the change in richness‐production relationships through time revealed that shifts in diatom community composition could have a large influence in determining the negative relationship between richness and production. Finally, significant correlations (r2 = 0.09–0.24, p < 0.0001) between past diatom species richness and ratios of stable isotopes (primarily δ15N) suggested that C and N biogeochemical cycles are also linked to changes in algal biodiversity. Taken together, these analyses suggest that the ongoing disruption of climate and biogeochemical systems by humans may obscure the relationship between aquatic biodiversity and ecosystem function in the future.