bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleo‐indicators and water quality change in the Charlotte Harbor Estuary (Florida)
Authors: Turner R. E. , Rabalais N. N. , Fry B. , Atilla N. , Milan C. S. , Lee J. M. , Normandeau C. , Oswald T. A. , Swenson E. M. , Tomasko D. A.
Published: July 2010

We reconstructed water quality changes for 1800 to 2000 in Charlotte Harbor (Florida), a shallow subtropical estuary, by using a suite of biological and geochemical proxies in dated sediments collected in the region of a present day, midsummer hypoxic zone. The declining freshwater loading into the estuary from 1931 to the 1980s is not the probable causal agent encouraging the appearance or expansion of a hypoxia zone (measuring up to 90 km2 in summer). Rather, the reconstructed trends in nitrogen loading indicate increased phytoplankton production has likely caused a decline in bottom water oxygen concentrations. Sedimentary biogenic silica (BSi), carbon, nitrogen, and phosphorus concentrations increased concurrently with known or inferred changes in nutrient loadings. There were direct relationships between phytoplankton pigments and BSi, heavier δ34S with increased carbon loading, and sequestration of P, Al, and Fe as carbon loading increased. The results from the sediment analyses and the results from mixing models using C:N ratios and δ13C suggest an estuarine system that is responsive to increased carbon loading from the nitrogen‐limited phytoplankton community and whose sediments are becoming increasingly anoxic as a result. The present nitrogen loading is about three times above that prior to the 1800s, suggesting that without management intervention the anticipated doubling of the watershed’s population from 1990 to 2020 will greatly increase the nitrogen loading to this estuary and will lead to much higher amounts of phytoplankton biomass and accumulation and exacerbate hypoxic conditions.
Evidence for a delayed response of riverine phosphorus exports from increasing agricultural catchment pressures in the Lough Neagh catchment
Authors: Foy R. H. , Lennox S. D.
Published: July 2010

Total phosphorus (TP) exports from the rivers draining into Lough Neagh increased between 1974 and 2000 despite lower TP inputs to the rivers from point sources. Over this period annual diffuse exports of dissolved reactive P (DRP) increased by 238%, from 17 to 57 kg P km−2 with an annual rate increase of 1.6 ± 0.3 kg P km−2 yr−1. Dissolved unreactive P exports increased by 0.4 ± 0.2 kg P km−2 yr−1, but particulate P exports did not increase. Annual exports of these three P fractions were positively correlated with annual runoff. The catchment of Lough Neagh has experienced an intensification of agriculture, with phosphorus inputs of manures and fertilizers to agricultural land increasing from 1,176 kg P km−2 yr−1 in 1925 to 3,823 kg P km−2 yr−1 in 2000. However 85% of this increase predated 1975. Increasing DRP exports after 1974 were better correlated with increasing soil P, and 70% of the increase in P accumulation by soils since 1925 occurred after 1974. Land use remained stable after 1974 with a historically low component of arable (>5%) and a dominance of grassland (<63%). The principal decade of intensification was in the 1940s, but this coincided with a greater arable component of land use. This period predated the increase in diffuse DRP exports. Intensively managed grasslands appear to be vulnerable to high DRP exports, reflecting surface application of manures, accumulation of soil P at the surface, and the creation of bypass flow pathways that facilitate the loss of P from soil to water.
Top down control from the bottom: Regulation of eutrophication in a large river by benthic grazing
Authors: Caraco N. F. , Cole J. J. , Strayer D. L.
Published: July 2010

We use a 15‐yr record from a 100‐km stretch of the tidal, freshwater Hudson River to examine the controls of phytoplankton biomass. Across years, seasonal mean chlorophyll a (Chl a) and maximum Chl a varied by approximately 15‐fold, with mean growing‐season Chl a as high as 24 mg L−1 and maximum Chl a as high as 120 mg L−1. For 3 of the 15 yr the river would be classified as eutrophic on the basis of lake standards for Chl a. Year‐toyear variation in Chl a was not closely related to either nutrients (phosphorus or nitrogen concentrations) or hydrologic flow. Annual variation in grazing by the invasive zebra mussel (Dreissena polymorpha) explained 90% of the variation in mean Chl a; however, the maximum Chl a reached during the growing season was not significantly related to grazing and, even with high grazing, blooms of phytoplankton that contained high proportions of potentially toxic cyanobacteria occurred. Further, zebra mussels decreased dissolved oxygen concentrations even while increasing production of submersed aquatic vegetation. The results from the Hudson add to a growing literature that suggests that ecosystem changes linked with high phytoplankton biomass depend on a diverse range of system characteristics as well as whether phytoplankton are controlled by top‐down or bottom‐up mechanisms
Is phosphorus retention in autochthonous lake sediments controlled by oxygen or phosphorus?
Authors: Moosmann Lorenz , Gächter René , Müller Beat , Wüest Alfred
Published: July 2010

Eutrophication of various lakes on the Swiss Plateau was targeted in the 1980s by reducing external nutrient loading and installing aeration/oxygenation systems. For five eutrophic lakes, three of which have been artificially oxygenated and aerated for almost 20 yr, phosphorus (P) balances were established using input, water‐column inventory, export via the outlet, and sediment core data. To separate the effects of aeration/oxygenation from the effects of P‐input reduction, two measures of P retention were determined—the ratio of net sedimentation to input and the ratio of net sedimentation to gross sedimentation. A comparison among the five lakes shows that, presently, P retention does not differ significantly between lakes with aeration/oxygenation and lakes with an anoxic hypolimnion, whereas retention at times of maximum P concentrations in the 1970s and 1980s was significantly lower compared with retention in today’s moderately eutrophic lakes. This is in agreement with the finding that net sedimentation in all lakes remained relatively constant between 280 and 950 kg km−2, independent of their P concentration. It is shown that constant net sedimentation is likely to prevail as long as P concentrations remain above a critical value of around 40 mg m−3. Constant net sedimentation indicates that permanent deposition of P is limited by the sediment's binding capacity. Oxic conditions in the hypolimnion do not necessarily increase this capacity because redox‐dependent P species may still be released within the anoxic bulk sediment and diffuse back into the water column. To characterize the P retention capacity of anoxic sediments, we suggest that the P burial rate be determined from dated sediment cores rather than from input/output balances.
An empirical model describing the seasonal dynamics of phosphorus in 16 shallow eutrophic lakes after external loading reduction
Authors: Jensen Jens Peder , Pedersen Asger Roer , Jeppesen Erik , Søndergaard Martin
Published: July 2010

Based on monthly mass balances on 7–8 yr of data from 16 shallow (mean depth: 1‐10 m), eutrophic, unstratified, or only temporarily stratified Danish lakes, we developed a simple empirical model relating the seasonal variation in lake total phosphorus (TP) concentrations to external loading, accumulated phosphorus in the sediment, hydraulic retention time, and water temperature. The aim was to describe the early recovery phase following an external loading reduction, i.e., when internal phosphorus loading is high, and to include seasonal dynamics. We calibrated a common set of model parameters for all 16 lakes and lake‐specific estimates of the exchangeable phosphorus pool in the sediment (Ps). Estimated annual mean TP deviated on average 12% from observed values in the 16 lakes. Moreover, the estimated seasonal dynamics and trend following the external loading reduction closely mimicked the observed pattern. The model was successfully tested on nine of the lakes for which data were available for an additional 7‐yr period. The results suggest that TP in the sediment does not provide an adequate description of the exchangeable P pool. In Lake Arreskov, which has shifted from a turbid to a clear‐water state following fish kill and biomanipulation, the model significantly overestimated TP, indicating that the model is inadequate for describing seasonal dynamics during the shift from a turbid to a clear‐water state. Although simple, the empirical model predicts reasonably well the seasonal dynamics of TP following a P‐loading reduction in a variety of shallow turbid lakes.
Fate of peptidoglycan in an intertidal sediment: An in situ 13C‐labeling study
Authors: Veuger Bart , van Oevelen Dick , Boschker Henricus T. S. , Middelburg Jack J.
Published: July 2010

We investigated the fate of peptidoglycan, a bacterial cell wall component, in sediment by 13C‐labeling the bacterial community of an intertidal mudflat and subsequently tracing the fate of 13CC in D‐alanine (D‐Ala, a bacterial biomarker specific for peptidoglycan), bacteria‐specific phospholipid‐derived fatty acids (PLFAs, specific for cell membranes of living bacteria), and total hydrolysable amino acids (THAAs, representing bulk proteinaceous material) over a 4.5‐month period in situ. Results showed a relatively slow loss of 13C from D‐Ala (half lives of 20–67 d) compared with that from bacteria‐specific PLFAs (half lives of 13–33 d) during the sampling period and a relatively strong retention of 13C in D‐Ala compared with the other compounds after 4.5 months. This provides direct in situ evidence for relative accumulation of peptidoglycan during reworking and degradation of bacterial biomass in sediments. Degradation also resulted in compositional changes of the [13C]THAA pool, including increased relative abundances of glycine, serine, and proline.
Modeling vertical excursions of the redox boundary in sediments: Application to deep basins of the Arctic Ocean
Authors: Katsev Sergei , Sundby Bjørn , Mucci Alfonso
Published: July 2010

A diagenetic reaction‐transport model was used to simulate how the sediment redox boundary migrates in response to persistent or episodic changes in the deposition flux of degradable organic matter and the concentration of oxygen in the overlying bottom water. The position of the redox boundary is represented by the depth of oxygen penetration. The simulations reveal that the position of the redox boundary in organic‐poor sediments, such as those in the deep basins of the Arctic Ocean, is highly sensitive to the flux of organic matter: relatively small and/or brief increases in that flux can cause the redox boundary to migrate rapidly from deep within the sediment to within a few centimeters of the sediment‐water interface. Reoxidation of the sediment column after such an event can take years. Redox fluctuations can redistribute solid‐phase manganese within the sediment column and produce multiple concentration peaks in its depth profile on a decadal time scale. Manganese peaks observed in sediment cores from the deep basins of the Arctic Ocean do not necessarily correspond to the position of the redox boundary during previous climatic periods or reflect historical changes in manganese deposition rates. The model supports the hypothesis that the recent decrease in the Arctic ice cover has increased the flux of organic matter to the seafloor and moved the redox boundary close to the sediment‐water interface. The presence of iron sulfides at depths significantly below the bioturbated layer suggests that either the Arctic sediments have been anoxic for millennia, or iron and sulfate are reduced at these depths by dissolved organic matter diffusing downward from the bioturbation zone.
Advective relief of CO2 limitation in microphytobenthos in highly productive sandy sediments
Authors: Cook Perran L. M. , Røy Hans
Published: July 2010

Following field observations of increased photosynthesis at increased rates of sediment flushing in sandy sediments, we conducted a series of laboratory experiments to elucidate the mechanism behind these observations. Column experiments in which water was pumped though sand at rates ranging from 0 to 613 L m−2 d−1 showed that carbon (C) fixation, as measured using carbon‐14 (14C) incorporation, increased from 6.4 to 8.6 mmol m−2 h−1 with increasing rates of flushing. Bottle incubations showed that the addition of inorganic nutrients [ammonium ion (NH4+), inorganic phosphate (HPO4−), silicic acid Si(OH)4] did not stimulate C fixation over short‐term incubations. Microprofiles of pH showed that the pH within the photic zone increased to 8.9, reducing free carbon dioxide (CO2) concentrations to ~0.5 µmol L−1. Further bottle incubations, where pH and total inorganic carbon (TCO2) were manipulated, showed that high pH (9.6) did not affect photosynthesis if free CO2 was present at concentrations of 10 µmol L−1, suggesting a direct effect of low free CO2 concentrations. 14C fixation profiles at a resolution of 100 µm recorded by b‐radiation imaging showed that while the depth specific maximum rates of C fixation were the same under both diffusive and advective (flushed) conditions, the integrated rates of photosynthesis were highest under flushed conditions because of a thickening of the photosynthetic zone. We conclude that advective pore‐water transport can enhance benthic photosynthesis in shallow permeable sand sediments by counteracting CO2 limitation.
Relative importance of CO2 recycling and CH4 pathways in lake food webs along a dissolved organic carbon gradient
Authors: Lennon Jay T. , Faiia Anthony M. , Feng Xiahong , Cottingham Kathryn L.
Published: July 2010

Terrestrial ecosystems export large quantities of dissolved organic carbon (DOC) to aquatic ecosystems. This DOC can serve as a resource for heterotrophic bacteria and influence whether lakes function as sources or sinks of atmospheric CO2. However, it remains unclear as to how terrestrial carbon moves through lake food webs. We addressed this topic by conducting a comparative lake survey in the northeastern U.S. along a gradient of terrestrial‐derived DOC. We used naturally occurring carbon stable isotopes of CO2, particulate organic matter (POM), and crustacean zooplankton, as well as gas measurements and culture‐independent assessments of microbial community composition to make inferences about the flow of terrestrial carbon in lake food webs. Stable isotope ratios of POM and zooplankton decreased with DOC and were often depleted in 13C relative to terrestrial carbon, suggesting the importance of an isotopically light carbon source. It has been proposed that the incorporation of biogenic methane (CH4) into plankton food webs would account for such trends in stable isotope ratios, but we found weak evidence for this hypothesis, on the basis of relationships of CH4, methanogenic archaebacteria, and methanotrophic bacteria in our lakes. Instead, our results are consistent with the view that phytoplankton increase their use of heterotrophically respired CO2 with increasing concentrations of terrestrialderived DOC. The effect of this CO2 recycling can be detected in the stable isotope composition of crustacean zooplankton, suggesting that the direct transfer of terrestrial DOC inputs to higher trophic levels may be relatively inefficient.
Spectral diversity of phycoerythrins and diazotroph abundance in tropical waters
Authors: Neveux Jacques , Tenírio Marcio M. B. , Dupouy CÉcile , Villareal Tracy A.
Published: July 2010

Phycoerythrin (PE) spectral diversity was investigated in eastern tropical Australian waters and around New Caledonian and Fijian archipelagos. Colony sorting of filamentous cyanobacteria revealed slight differences in the PE excitation spectrum of Trichodesmium thiebautii and T. erythraeum. Spectra of PE from Katagnymene spiralis and Richelia intracellularis were examined for the first time. PE spectra of filamentous cyanobacteria (Trichodesmium, Katagnymene, and Richelia) showed a broader phycoerythrobilin (PEB) band than those of Synechococcus. The influence of PE Trichodesmium on the global spectrum of PE in natural waters was clearly visible at various stations. The PEB band was large at the surface and narrower at increased depth, suggesting a shift of the cyanobacterial community from a dominance of diazotrophic filamentous cyanobacteria to small Synechococcus. Size fractionation of water samples confirmed this. A good linear relationship was observed between PE concentration in the >10‐µm cellular‐size fraction and the abundance of filamentous cyanobacteria expressed by either trichome numbers, total trichome surface area, or total trichome volume. PE in the >10‐µm fraction is a useful tool for rapidly quantifying filamentous cyanobacteria. Neither diel variations nor photoacclimation significantly influenced the PE fluorescence excitation spectra in T. thiebautii and T. erythraeum. Using this method, we identified green colonies of filamentous cyanobacteria in deep waters (50–120 m) of the Coral Sea with a novel high‐phycourobilin PE. While morphologically similar to Trichodesmium, it possesses distinctive photosynthetic responses and could be a new species.
Effect of pH on growth, cell volume, and production of freshwater ciliates, and implications for their distribution
Authors: Weisse Thomas , Stadler Peter
Published: July 2010

We investigated the effect of pH on growth, cell volume, and production of the freshwater ciliates Urotricha farcta, U. furcata, and U. castalia in laboratory cultures with Cryptomonas sp. as food. Overall, pH had a significant, species‐specific effect on all parameters investigated. The food alga, Cryptomonas sp., showed a wide pH tolerance, with positive growth rates between pH 4.4 and pH 9.65. Among the ciliates, U. farcta was the most pH‐tolerant and U. castalia was the most pH‐sensitive species, with positive growth being confined to pH 6.5‐8.2. The pH optimum was derived from cellular production rates. The pH optima of the three ciliate species were shifted; their production rates peaked at pH 4.4‐5.3 (U. farcta), pH 5.9‐7.3 (U. furcata), and pH 6.8‐7.9 (U. castalia). The pH effect on growth and survival of the ciliates was minor at circumneutral and moderately alkaline pH values, relative to the effect of temperature and food measured in earlier experiments. The widths of the pH tolerances of the ciliates were positively related to the widths of their temperature niches and to their natural distributions. U. farcta and U. furcata were characterized as euryoecious species, with broad pH and temperature tolerances and ubiquitous distribution; U. castalia is a rare, stenoecious species, requiring specific pH and temperature conditions.
Nitrogen fixation and release of fixed nitrogen by Trichodesmium spp. in the Gulf of Mexico
Authors: Mulholland Margaret R. , Bernhardt Peter W. , Heil Cynthia A. , Bronk Deborah A. , O'Neil Judith M.
Published: July 2010

During a 3‐yr study in the Gulf of Mexico, we measured dinitrogen (N2) fixation and nitrogen (N) release by Trichodesmium and compared these rates with water column N demand and the estimated N necessary to support blooms of Karenia brevis, a toxic dinoflagellate that severely affects the West Florida shelf. Net and gross N2 fixation rates were compared in simultaneous incubations using δ15N2 uptake and acetylene reduction, respectively. The difference between net and gross N2 fixation is assumed to be an approximation of the rate of N release. Results demonstrate that Trichodesmium in the Gulf of Mexico are fixing N2 at high rates and that an average of 52% of this recently fixed N2 is rapidly released. Calculations suggest that observed densities of Trichodesmium can provide enough N to support moderately sized K. brevis blooms. Based on other studies where δ15N2 and acetylene reduction were compared directly, it appears that N release from Trichodesmium is common but varies in magnitude among environments. In addition, carbon (C) and N‐based doubling times for Trichodesmium vary among studies and environments. Comparing gross N2 fixation and C fixation directly, C‐based doubling times exceeded N‐based doubling times, which suggests an imbalance in elemental turnover or a failure to fully quantify Trichodesmium N use.
Flexible elemental stoichiometry in Trichodesmium spp. and its ecological implications
Authors: White Angelicque E. , Spitz Yvette H. , Karl David M. , Letelier Ricardo M.
Published: July 2010

We conducted laboratory experiments to assess the bioelemental plasticity of cultures of Trichodesmium IMS101 under phosphorus (P)‐replete, P‐restricted, and light‐limited conditions. The results reveal a high degree of stoichiometric flexibility. Specifically, Trichodesmium IMS101 is capable of growth with carbon (C) : nitrogen (N) : P ratios of C585±56 : N90±10 : P1, approximately six times higher than would be predicted by the Redfield reference ratio (C106 : N16 : P1), thus signifying low cellular P quotas relative to C and N. Luxury consumption of P occurs rapidly after periods of prolonged P restriction, under both light and dark conditions, resulting in substantial increases in P quotas and reductions of C : N : P ratios (C96±8 : N16±1 : P1). Comparisons of laboratory culture data to our field observations from the Northwest Atlantic and the North Pacific indicate that, while natural populations of Trichodesmium exhibit persistently low P content relative to C and N (C290±15 : N53±3 : P1), the highest and lowest C : P and N : P ratios recorded in the laboratory are rarely observed in nature. We have also performed laboratory experiments intended to simulate the energetic and nutritional extremes that would occur as naturally migrating populations of Trichodesmium sink out of the euphotic zone into P‐rich regions of the upper disphotic zone. The duration of dark survival for this isolate is on the order of 3‐6 d, after which time cells are unable to recover from light deprivation. This finding provides a constraint on the temporal scale of vertical migration.
Photosynthetic performance of benthic microbial mats in Lake Hoare, Antarctica
Authors: Vopel Kay , Hawes Ian
Published: July 2010

We measured in situ photosynthesis of benthic microbial mats at various depths in Lake Hoare, a permanently ice‐covered lake of the McMurdo Dry Valleys, Antarctica, using oxygen (O2) microelectrodes. We further investigated the vertical distribution and activity of pigments in the microbial mats using an imaging pulseamplitude‐ modulated fluorometer. Microbial mats to at least 16.6‐m water depth are net producers of O2 during the summer period. Net O2 production ranges from 100‐500 µmol m−2 h−1 at incident downwelling irradiances of photosynthetically active radiation (PAR) of 1.0‐4.6 µmol quanta m−2 s−1. Photosynthesis of mat‐forming cyanobacteria and diatoms occurs at all lake depths at or close to maximum efficiency. We measured absorption by the pigment arrays at a single water depth and, by assuming that absorption is water‐depth invariant, we estimated an area‐specific maximum community quantum yield of 0.073 mol carbon per mol photons. A community compensation irradiance of 0.1 µmol quanta m−2 s−1 was estimated, reflecting extreme shade acclimation. These results confirm estimates previously derived from laboratory gas‐exchange measurements and imply that even minor changes in the intensity of the incident downwelling irradiance of PAR caused by, for example, changes in the transparency of the ice cover or the optical properties of the water column can significantly alter rates of benthic carbon fixation. In situ measurements were confined to mats with flat surfaces. Laboratory measurements at the surface of mats with pinnacled surfaces revealed a complex small‐scale chemical structure at the mat‐water interface.
Prey‐specific encounter rates and handling efficiencies as causes of prey selectivity in ambush‐feeding hydromedusae
Authors: Hansson Lars Johan , Kiørboe Thomas
Published: July 2010

We examined the foraging process in the jellyfish Sarsia tubulosa feeding on three types of prey: cirripede nauplii, cypris larvae, and Acartia tonsa copepodites. Clearance rate was used as measure of prey selectivity. To estimate maximal clearance rate (Fmax), we used a predictive encounter model with input parameters quantified from video observations. Both encounter rate and handling efficiency were important in determining Fmax. Encounter volume rate was three times higher for cirripede nauplii than for copepodites, but sequential handling was 10 times more efficient for copepodites than for cirripede larvae. Two critical steps in the postcapture feeding process—capture of encountered prey with the tentacle, and mouth attachment to the captured prey—created a clear selectivity for copepods over barnacle larvae. Predicted values were close to laboratory measurements of Fmax, and for cirripede nauplii also to field‐estimated Fmax. We suggest that species‐specific handling efficiency is the main factor creating trophic niche separation in the large functional group of ambush‐feeding hydromedusae.
The ecological distribution and comparative photobiology of symbiotic dinoflagellates from reef corals in Belize: Potential implications for coral bleaching
Authors: Warner Mark E. , LaJeunesse Todd C. , Robison Jennifer D. , Thur Rebecca M.
Published: July 2010

The photobiology and distribution of dinoflagellates in the genus Symbiodinium was investigated for eight common reef coral species over a depth range of 1‐25 m on a coral reef in Belize. The genetic identification of symbionts using polymerase chain reaction‐denaturing gradient electrophoresis of the internal transcribed spacer 2 region revealed marked differences in host specificity and depth zonation for certain symbiont types. Each host taxon was found to associate with a limited subset of symbionts that exist in the region. Intraspecific variation was greatest at the shallower sites (1‐8 m), where as many as five distinctive symbionts were distributed among a single host population (e.g., Montastraea faveolata). At depth (15‐25 m), variation from colony to colony was minimal, where one algal type associated with most or all the colonies of a species. The maximal photochemical efficiency and light‐acclimated efficiency of photosystem II (PSII) were determined by active chlorophyll fluorescence and used to assess potential differences in photosynthetic potential. Under normal ambient conditions, little or no physiological differences were noted among different symbionts occurring in the same species of coral at a particular depth, yet interspecific differences in PSII efficiency were noted between coral species at the same depth. Short‐term bleaching experiments showed that symbionts B1 and C7 within M. faveolata experienced a higher degree of thermally induced photoinhibition relative to A4a symbionts in Porites astreoides. The differential patterns of PSII inactivation observed within M. faveolata could be explained by the presence of different symbiont populations within this coral. Differences in in situ maximum excitation pressure on PSII between symbionts within some corals may provide a predictive measure of how different species of coral or individual colonies with different symbionts would respond to natural thermal stress events.
Dimethyl sulfide triggers search behavior in copepods
Authors: Steinke Michael , Stefels Jacqueline , Stamhuis Eize
Published: July 2010

The oceans are nutritionally dilute, and finding food is a major challenge for many zooplanktonic predators. Chemodetection is necessary for successful preycapture, but little is known about the infochemicals involved in the interaction between herbivorous copepods and their phytoplankton prey. We used females of Temora longicornis to investigate chemodetection of dimethyl sulfide (DMS) in this calanoid copepod and quantified its behavioral response to plumes of DMS using video‐microscopy in combination with laser‐sheet particle image velocimetry (PIV). Slow injection of a 1‐µmol L−1 DMS plume into the feeding current resulted in a characteristic behavioral pattern (“tail‐flapping”), a redirection of flow equivalent to 30% of the average current velocity, and changes in the location of flow‐induced vortices. In free‐swimming individuals, this likely results in somersault‐type movements that are associated with search behavior in copepods. In comparison to seawater controls, DMS injections significantly increased the average number of tail‐flaps per copepod during the first 2 s after exposure to DMS gradients. Our results demonstrate that copepods can detect and react to plumes of DMS and suggest that this biogenic trace gas can influence the structure and function of pelagic foodwebs.
Molecular analysis of picocyanobacterial community structure along an Arabian Sea transect reveals distinct spatial separation of lineages
Authors: Fuller Nicholas J. , Tarran Glen A. , Yallop Marian , Orcutt Karen M. , Scanlan David J.
Published: July 2010

We investigated the community structure of Synechococcus and Prochlorococcus along a transect in the Arabian Sea during September 2001. The transect spanned contrasting oceanic conditions, allowing investigation of the effects of both horizontal and vertical environmental gradients over relatively large spatial scales on picocyanobacterial population structure. We applied previously developed oligonucleotide probes specific for different Prochlorococcus ecotypes and Synechococcus clades by hybridization to ‘oxygenic phototroph’ 16S ribosomal DNA polymerase chain reaction amplicons. Flow cytometry data showed that, in general, the picocyanobacterial community was dominated by Prochlorococcus in the southern oligotrophic waters and by Synechococcus in the northern mesotrophic waters. Molecular analysis of these picophytoplankton communities, however, revealed more specific spatial separation of lineages along the transect, with Prochlorococcus in southern surface waters being dominated by the high light‐adapted ecotype, while low light‐adapted (LL) ecotypes were confined to deeper waters below the surface‐mixed layer. Interestingly, between Sta. 2 to 4, the LL genotype MIT9303 appeared to be partitioned at the very base of the euphotic zone, beneath other LL genotypes. Most of the central and northern parts of the transect were dominated by Synechococcus genotypes of the clade II lineage. A significant exception was in the mesotrophic upwelling region, where genotypes representative of clades V/VI/ VII dominated. Members of the recently discovered clades IX and X were found in subsurface samples in warm, coastal waters. We propose that discrete differences, both horizontally and vertically, in a suite of environmental parameters along the transect provide optimal growth conditions for specific genotypes in a particular patch of water, giving rise to distinct spatial compartmentalization of picocyanobacterial lineages.
Spatial and temporal patterns of mineralization rates and oxygen distribution in a permeable intertidal sand flat (Sylt, Germany)
Authors: Werner Ursula , Billerbeck Markus , Polerecky Lubos , Franke Ulrich , Huettel Markus , van Beusekom Justus E. E. , de Beer Dirk
Published: July 2010

Oxygen distribution and benthic mineralization rates were investigated in a permeable intertidal sand flat (permeability: 3.9 x 10‐11 m2) in a transect from the low toward the high waterline. At all stations, oxygen penetrated several millimeters to centimeters into the sediments during inundation because of pore‐water advection. The wave‐ and current‐driven deep oxygen penetration caused high oxygen consumption rates (OCRs) and high aerobic mineralization rates at all stations. Because oxygen penetration was enhanced during inundation, 71‐90% of the daily oxygen consumption took place in that period. OCRs and sulfate reduction rates (SRRs) changed with inundation time of the stations, emphasizing the importance of pore‐water advection for benthic mineralization: OCRs were elevated at the lower flat in summer (lower flat 131‐187; middle and upper flat 64‐108 mmol C m‐2 d‐1). SRRs increased sharply from the high to the low waterline during all seasons (e.g., in summer: lower flat 18‐40; middle flat 8.8‐9.4, upper flat 0.5‐4 mmol C m‐2 d‐1). A one‐dimensional model of the advective organic matter supply to the sediment could only explain a fraction of the organic carbon required for benthic mineralization. This suggests that either transport of particles via the seawater is more efficient than the one‐dimensional concept can explain or that additional carbon was supplied through other sources (e.g., benthic photosynthesis). Mineralization rates were higher in summer than in winter. Only in summer did sulfate reduction contribute ≫20% to total mineralization.
Copepod biodiversity as an indicator of changes in ocean and climate conditions of the northern California current ecosystem
Authors: Hooff Rian C. , Peterson William T.
Published: July 2010

We evaluated copepod taxonomic diversity as a potential biological indicator of ocean conditions in the northeast Pacific Ocean using data collected biweekly between May 1996 and December 2004 and from 1969 to 1973 and 1983 off Newport, Oregon. During the summer, low copepod biodiversity is accompanied by high biomass, with the opposite patterns prevailing in the winter. High biodiversity, and associated low biomass, is also observed during the summers of major El Nino events (1983, 1997‐1998) and during years when the Pacific Decadal Oscillation is in a positive phase. From 1996 to the present, seasonally adjusted monthly anomalies of taxa richness and the Shannon‐Weiner diversity index were compared to hydrographic and meteorological variables and to basin‐wide climatological indices. Correlations of biodiversity with physical variables were strongest during the summer months for the Multivariate El Nino/Southern Oscillation Index, temperatures at a water depth of 50 m, and the Pacific Decadal Oscillation. During a 4‐year cool period (1999‐2002), biodiversity was low, likely a result of the increased transport of coastal subarctic waters into the northern California current. In recent years (2002‐2005), however, there has been a dramatic increase in biodiversity. These increases may be attributable to the influence of a weak El Nino event in 2003; yet, high biodiversity persisted through the summer of 2005 and at times was higher than during the strongest El Nino events of the 20th century (1983 and 1997‐ 1998). Our analyses suggest that changes in source waters, driven by remote basin scale forcing and not local environmental events, cause interannual‐to‐decadal variations in copepod biodiversity in the northern California current.
Distribution of the thiols glutathione and 3‐mercaptopropionic acid in Connecticut lakes
Authors: Hu Haiying , Mylon Steven E. , Benoit Gaboury
Published: July 2010

The spatiotemporal chemical characteristics of the water column in Linsley Pond, a freshwater lake in Connecticut, were studied from just before its stratification in April through the fall turnover in December. Two low‐molecular‐weight thiols, glutathione and 3‐mercaptopropionic acid (MPA), were detected at nanomolar concentrations in the water column. GSH was detected (average concentrations were ca. 5 nmol L−1 in the particulate phase and ca. 3 nmol L−1 in the dissolved phase) in surface and near‐surface waters only and covaried with chlorophyll a. Both particulate and dissolved MPA were measured in the oxic and anoxic regions. In the metalimnion, MPA concentrations were greater than in the oxic water layers above. At times, the MPA concentrations in the metalimnion were as high as those found in the anoxic hypolimnion. The MPA present at different depths in the Linsley Pond water column is most likely produced through dissimilar mechanisms. Throughout the water column, MPA may be a product of the metabolic degradation of sulfur‐containing organic compounds; however, in the hypolimnetic waters, dissolved sulfide may play an important role in MPA formation through abiotic nucleophillic addition to unsaturated functionalities in dissolved organic matter. Parallel laboratory experiments were performed to assess the importance of MPA in copper speciation. The results confirmed that despite nanomolar levels in Linsley Pond, MPA does not play an important role in copper speciation. A survey of six additional lakes in Connecticut was made for detectable thiols. Only MPA was detected in four of these lakes, and its distribution was similar to that in Linsley Pond.
Responses of fish communities in five north temperate lakes to exotic species and climate
Authors: Willis Theodore V. , Magnuson John J.
Published: July 2010

Exotic species invasions and climatic variation that occurred in north central Wisconsin provided the opportunity to contrast influences of climate and invasive species in shaping fish community dynamics in five Wisconsin lakes from 1981 to 2001. Year (passage of time) was positively correlated (r > 0.9) with invasive species. Year, invasive species, and climatic variables were the principal determinants of fish community dynamics according to redundancy analysis (RDA). The same invasive species negatively affected the same general group of species in different lakes; benthic invertivores declined in lakes invaded by crayfish, Orconectes spp., and pelagic zooplanktivores declined in lakes invaded by rainbow smelt, Osmerus mordax. Micropterus dolomieu, Pimephales notatus, and Notropis volucellus increased in abundance in lakes invaded by crayfish. When year was included in RDAs as a covariable (partial RDA), fish community changes in three lakes did not differ significantly from ordinations of Monte Carlo simulated data; for two lakes, growing season length and lake productivity were significant explanatory variables under the reduced model. The resulting shifts in the fish community might represent declines in those species that used resources similar to the invading crayfish and smelt or were eaten by the invading smelt. Subsequent community compensation might have occurred, with other species increasing in response to the declines in species affected directly by the invasive species.
Comparison of UV irradiances from Aura/Ozone Monitoring Instrument (OMI) with Brewer measurements at El Arenosillo (Spain) – Part 2: Analysis of site aerosol influence
Authors: Cachorro V. E. , Toledano C. , Antón M. , Berjón A. , de Frutos A. , Vilaplana J. M. , Arola A. , Krotkov N. A.
Published: July 2010

Abstract. Several validation studies have shown a notable overestimation of the clear sky ultraviolet (UV) irradiance at the Earth's surface derived from satellite sensors such as the Total Ozone Mapping Spectrometer (TOMS) and the Ozone Monitoring Instrument (OMI) with respect to ground-based UV data at many locations. Most of this positive bias is attributed to boundary layer aerosol absorption that is not accounted for in the TOMS/OMI operational UV algorithm. Therefore, the main objective of this study is to analyse the aerosol effect on the bias between OMI erythemal UV irradiance (UVER) and spectral UV (305 nm, 310 nm and 324 nm) surface irradiances and ground-based Brewer spectroradiometer measurements from October 2004 to December 2008 at El Arenosillo station, with meteorological conditions representative of the south-west of Spain. The effect of other factors as clouds, ozone and the solar elevation over this intercomparison were analysed in detail in a companion paper (Antón et al., 2010). In that paper the aerosol effects were analysed making only a rough evaluation based on aerosol optical depth (AOD) information at 440 nm wavelength (visible range) without applying any correction. Here, the correction of the OMI UV data is proposed based on a detailed study about the determination of absorbing aerosols provided by AERONET data. Because of the difficulty to have reliable data about absorbing aerosol properties at many sites, first we consider AOD, Angstrom exponent and also OMI-Aerosol Index for this determination, but finally single scattering albedo (SSA) from AERONET was used since it represents a much more precise information. An aerosol correction expression was applied to the OMI operational UV data using two approaches to estimate the UV absorption aerosol optical depth, AAOD. The first approach was based on an assumption of constant SSA value of 0.91. This approach reduces OMI UVER bias from 13.4 to 8.4%. Second approach uses daily AERONET SSA values reducing the bias only to 11.6%. Therefore we have obtained a 37% and 12% of improvement, respectively. Similar results were obtained for spectral irradiances at 305 nm, 310 nm and 324 nm, where for 324 nm the OMI bias is reduced from 10.5 to 6.98% for constant SSA and to 9.03% for variable SSA. Contrary to what was expected, the constant SSA approach has a greater bias reduction than variable SSA, but this is a reasonable result according to the discussion about the reliability of SSA values. Our results reflect the level of accuracy that may be reached at the present time in this type of comparison, which may be considered as satisfactory taking into account the remaining dependence on other factors. Nevertheless, improvements must be accomplished to determine reliable absorbing aerosol properties, which appear as a limiting factor for improving OMI retrievals.
Electromagnetic oscillations of the Earth's upper atmosphere (review)
Authors: Khantadze A. G. , Jandieri G. V. , Ishimaru A. , Kaladze T. D. , Diasamidze Zh. M.
Published: July 2010

Abstract. A complete theory of low-frequency MHD oscillations of the Earth's weakly ionized ionosphere is formulated. Peculiarities of excitation and propagation of electromagnetic acoustic-gravity, MHD and planetary waves are considered in the Earth's ionosphere. The general dispersion equation is derived for the magneto-acoustic, magneto-gravity and electromagnetic planetary waves in the ionospheric E- and F-regions. The action of the geomagnetic field on the propagation of acoustic-gravity waves is elucidated. The nature of the existence of the comparatively new large-scale electromagnetic planetary branches is emphasized.
WRF model and ASAR-retrieved 10 m wind field comparison in a case study over Eastern Mediterranean Sea
Authors: Miglietta M. M. , Zecchetto S. , De Biasio F.
Published: July 2010

Abstract. In Synthetic Aperture Radar (SAR) imagery, signatures of coherent atmospheric structures, due to sea surface roughness modulation by surface winds, are usually well detected. In the present study, the wind field derived from the Envisat Advanced SAR (ASAR) sensor has been analyzed and compared with those simulated with a regional atmospheric model in a case study over an area located in the eastern Mediterranean Sea, extending southward and eastward of Crete island. This is a region subject to complex wind patterns, due to the interaction of the almost steady northerly Etesian wind with the orography of the islands in the region. The ASAR Wide Swath Mode images provide datasets at resolutions exceptionally high compared to model data, appropriate for investigating the mesoscale phenomena on the marine atmospheric boundary layer and to retrieve the surface wind field. The latter has been obtained with a methodology based on the 2-D Continuous Wavelet Transform, suitable to isolate the backscatter patterns on the base of energy and scale considerations. Numerical simulations with the Weather Research and Forecasting (WRF) model have been performed using three 2-way nested domains, the inner one covering the area of interest with a resolution of 1 km. Several simulations, using different diffusion and boundary layer parameterization schemes, have been performed in a case study corresponding to mountain lee waves detected in the ASAR image. The 10 m winds resulting from the numerical experiments have been compared to those retrieved from the ASAR, both quantitatively and qualitatively, in order to analyze the correspondence of observed and simulated wind structures.
Temporal and spatial changes of radon concentration in borehole water (Little Carpathians Mts., Slovakia)
Authors: Smetanová I. , Holý K. , Müllerová M. , Polášková A. , Túnyi I.
Published: July 2010

Abstract. The 222Rn activity concentration in ground water from four boreholes was investigated from January 2006 to June 2008. The boreholes are situated in the region of the Astronomical and Geophysical Observatory in Modra-Piesok (Little Carpathians Mts., 40 km NW from Bratislava, Slovakia). Three boreholes have been drilled in Lower Triassic quartzite. Another borehole has been drilled in granodiorite of the Modra massif in which the quartzite is folded. Temporal and spatial differences in radon concentration were observed. Significant short-term variations were noticed in all boreholes. Precipitation caused the changes of water level and strongly affected the values of 222Rn activity concentration in less deep boreholes. The measured activities in boreholes ranged approximately over 1–240 kBq/m3.
The RISKMED project: philosophy, methods and products
Authors: Bartzokas A. , Azzopardi J. , Bertotti L. , Buzzi A. , Cavaleri L. , Conte D. , Davolio S. , Dietrich S. , Drago A. , Drofa O. , Gkikas A. , Kotroni V. , Lagouvardos K. , Lolis C. J. , Michaelides S. , Miglietta M. , Mugnai A. , Music S. , Nikolaides K. , Porcù F. , Savvidou K. , Tsirogianni M. I.
Published: July 2010

Abstract. This paper presents RISKMED, a project targeted to create an Early Warning System (EWS) in case of severe or extreme weather events in the central and eastern Mediterranean and specifically in southern Italy, northwestern Greece, Malta and Cyprus. As severe or extreme weather events are considered, cases when the values of some meteorological parameters (temperature, wind, precipitation) exceed certain thresholds, and/or a severe weather phenomenon (thunderstorm, snowfall) occurs. For an accurate weather forecast, selected meteorological models have been operated daily, based on a nesting strategy using two or three domains, providing detailed forecasts over the above mentioned areas. The forecast results are further exploited for the evaluation and prediction of human discomfort and fire weather indices. Finally, sea wave models have also been operating daily over the central and eastern Mediterranean Sea. In case a severe or extreme weather event is forecasted within the next 48 or 72 h for selected target areas (sub-regions defined by their morphological and population characteristics), the local authorities and the public are informed via a user-friendly graphic system, the so-called RISK MAP. On the web page of the Project ( http://www.riskmed.net ), additional information is provided about the real-time values of some meteorological parameters, the latest satellite picture and the time and space distribution of lightning during the last 24 h. The RISKMED project was financed by the EU and th Ministries of National Economy of Greece, Italy, Malta and Cyprus, in the frame of INTERREG IIIB/ARCHIMED programme.