bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescent response of the red tide dinoflagellate Lingulodinium polyedrum to laminar and turbulent flow
Authors: Latz Michael I. , Rohr Jim
Published: May 2010

While it is universally accepted that plankton continually experience a dynamic fluid environment, their sensitivity to the features of the surrounding flow field at the relevant length and time scales of the organism is poorly characterized. The present study uses bioluminescence as a tool to understand how the red tide dinoflagellate Lingulodinium polyedrum (= Gonyaulax polyedra) responds to well‐characterized hydrodynamic forces present in fully developed laminar and turbulent pipe flow. The response of L. polyedrum to hydrodynamic stimulation was best characterized by wall shear stress; at similar values of wall shear stress, the response was similar for laminar and turbulent flows. The response threshold occurred in laminar flow at a wall shear stress of approximately 0.3 N m−2. At these low flow rates, video analysis of the velocity of flash trajectories revealed that responding cells were positioned only near the pipe wall, where local shear stress levels were equal to or greater than threshold. For cell concentrations ranging over four orders of magnitude, threshold values of wall shear stress were restricted to a narrow range, consistent with an antipredation function for dinoflagellate bioluminescence. For laminar flows with above‐threshold wall shear stress values ≤= 1 N m−2, mean bioluminescence increased with wall shear stress according to a power (log–log) relationship, with the slope of the power function dependent on cell concentration. The increase in bio‐luminescence within this range was due primarily to an increasing population response rate and, to a lesser extent, an increase in maximum flash intensity per cell and the increased flux of organisms with higher flow rates. For wall shear stress levels > 1 N m−2, the maximum intensity per cell remained approximately constant with increasing wall shear stress, even as the flow transitioned from laminar to turbulent, and the smallest turbulent length scales became less than the average cell size.
Decomposition dynamics of six salt marsh halophytes as determined by cupric oxide oxidation and direct temperature‐resolved mass spectrometry
Authors: Klap Vincent A. , Louchouarn Patrick , Boon Jaap J. , Hemminga Marten A. , van Soelen Jos
Published: May 2010

This paper presents the results of a comparative study on the aerobic decomposition of six salt marsh plant species over a period of 2 yr. In addition to ash‐free dry weight (AFDW) determination and elemental analysis (C and N), two analytic methods have been applied to obtain insight into the decomposition dynamics of lignin in the various plant tissues. The analytic methods are (1) cupric oxide (CuO) oxidation followed by gas chromatography—mass spectrometry (GC‐MS) and (2) direct temperature‐resolved mass spectrometry (DT‐MS).

AFDW losses could generally be well described by double exponential relations with time. Carbon‐to‐nitrogen ratios increased during the initial stages of decomposition and decreased again afterward. For five of the six plant species, a correlation between initial lignin content and AFDW loss was observed. Decay dynamics of lignin denoted a rapid relative increase during the first weeks of field exposure, followed by stabilizing contents over the next 2 yr. CuO oxidation data indicate the establishment of a stable “lignin endmember” within 1–2 months. DT‐MS data, on the contrary, showed continuous modification of the lignin polymer throughout the duration of the experiment.

Evidence was found for the incorporation of (presumably) microbial N‐acetylglucosamine in the complex residue produced upon decomposition. Combination of CuO oxidation and DT‐MS data suggested that lignin degradation products became attached to the original macromolecular material and could still be identified as lignin‐derived material. The data support a humification mechanism via condensation of small degradation products instead of the selective preservation of certain biomacromolecules (like lignin).
Bioavailability of wetland‐derived DON to freshwater and marine bacterioplankton
Authors: Stepanauskas Ramūnas , Leonardson Lars , Tranvik Lars J.
Published: May 2010

Access to bioavailable nitrogen often limits primary production in marine and freshwater ecosystems. Around 70% of nitrogen transported by rivers worldwide consists of dissolved organic nitrogen (DON), but its bioavailability has been poorly investigated. To assess the potential bacterial growth on DON, we developed a bioassay employing natural DON and bacterial inocula in medium manipulated to make N the limiting nutrient. We analyzed the bacterial utilization of the high‐molecular‐weight fraction of DON isolated by ultrafiltration from three wetlands in South Sweden throughout the year. The bioavailability of low‐molecular‐weight and bulk DON was also analyzed in one of the wetlands, where inorganic nitrogen concentration was sufficiently low and did not interfere with bioassays. The bioavailability of bulk DON in the latter wetland varied from 2% to 16%, suggesting that DON is an important nitrogen source for the biota of coastal waters. DON may be the dominant input of bioavailable nitrogen during summer, when nitrate concentrations in rivers decrease and DON bioavailability increases. Marine bacterioplankton assimilated a substantially larger fraction of DON than did freshwater bacterioplankton, on average by a factor of 2.4. This finding indicates that the susceptibility of DON to bacterial mineralization increases as it is transported from freshwaters into saline environments.
Ice break‐up on southern Lake Baikal and its relationship to local and regional air temperatures in Siberia and to the North Atlantic Oscillation
Authors: Livingstone David M.
Published: May 2010

The calendar date of ice break‐up on southern Lake Baikal has been recorded uninterruptedly since 1869. A strong trend to earlier thawing up to around 1920 (1 d per 3.3 yr) is followed by the lack of any significant trend thereafter. For the period 1931–1994, the timing of break‐up is related to local surface air temperatures integrated over periods of 1–3 months. Although highest unimodal correlations are with the 3‐month mean air temperature, a bimodal relationship between break‐up and air temperature exists at shorter integration times, with break‐up date being related not only to the air temperature prevailing during thawing (April) but also to that prevailing during the time of ice formation, when air temperatures are lowest (February). High frequency (interannual) fluctuations in the timing of break‐up appear to be influenced mainly by the air temperatures prevailing during thawing, and low‐frequency (interdecadal) fluctuations by those prevailing during ice formation. Whereas correlations with April air temperatures are always significant, those with February air temperatures are only significant during the latter part of this century, i.e., after cessation of the tendency toward earlier thawing.
A comparison of chlorophyll/nutrient dynamics at two survey sites near South Georgia, and the potential role of planktonic nitrogen recycled by land‐based predators
Authors: Whitehouse M. J. , Priddle J. , Brandon M. A. , Swanson C.
Published: May 2010

There is an apparent mismatch between the high carbon demand of seals and seabirds breeding on the subantarctic island of South Georgia and the overall low primary production measured in the waters that surround the island. However, average phytoplankton production values may not be completely representative, and local systems may exist where primary production is considerably higher. Here, we examine the distribution of phytoplankton and nutrients along with physical oceanographic variables measured during two mesoscale surveys of two sites adjacent to South Georgia (January 1996 and December 1996–January 1997). Chlorophyll a concentrations were consistently higher (by up to an order of magnitude during one cruise) at the western end of the island (maximum >30 mg m−3). Surface phosphate and silicate at times appeared to have been depleted to particularly low levels (<0.8 and <2 mmol m−3, respectively), whereas nitrate concentrations remained relatively high throughout the two surveys (∼14–30 mmol m−3). However, ammonium, a crucial reduced nitrogen source for South Georgia phytoplankton, was plentiful and widespread in the upper mixed layer during both surveys (maximum >3 mmol m−3). An examination of upper mixed layer nutrient dynamics showed an apparent shortfall in phytoplankton use of nitrate‐nitrogen compared with silicate and phosphate at the western end of the island, where ammonium‐nitrogen use appeared greatest.

The western end of subantarctic island of South Georgia is noted for its large numbers of breeding Antarctic fur
seals, Arctocephalus gazella, and macaroni penguins, Eudyptes chrysolophus, (∼2.6 × 106 and ∼5.4 × 106 individuals, respectively). As land‐breeding endotherms, these animals have high metabolic costs, and they recycle dietary nitrogen rapidly. Furthermore, because they take krill advected into their foraging range and return frequently to their colonies to feed pups and chicks, they concentrate nutrients close to the land. We evaluated the relationship between the preferential use of reduced nitrogen by phytoplankton and its production and concentration by the landbased predators (a minimum of 1 × 107 mol N d−1 in January for the colonies in the study area). We examined the predators’ potential for the redistribution of plankton nitrogen in an on‐shelf environment where currents were relatively sluggish and encompassed retentive, eddy‐like structures, which might have facilitated more stable conditions for phytoplankton growth.
A novel approach for estimating ecosystem production and respiration in estuaries: Application to the oligohaline and mesohaline Hudson River
Authors: Swaney Dennis P. , Howarth Robert W. , Butler Thomas J.
Published: May 2010

Most estimates of metabolism in estuaries are based on water samples incubated in bottles. Such approaches may severely underestimate rates of both gross primary production (GPP) and respiration for a variety of reasons, including reduced turbulence, unnatural light fields, respiration of 14C‐labeled organic matter, and altered grazer communities. These problems may be particularly intense in turbid and deeply mixed estuaries. The measurement of metabolism from in situ changes in dissolved oxygen (DO) concentration over a diel time period offers a potential solution to these problems, but complicated patterns of water advection and mixing in estuaries have limited the use of such open‐water approaches. Here, we describe a method of using diel changes in oxygen concentrations in the oligohaline and mesohaline Hudson River estuary to estimate GPP, whole‐ecosystem respiration (ER), and net ecosystem production (NEP). For this approach, concentrations of DO at any given time for several stations are described as a function of salinity and depth, providing a surface in the three‐dimensional space of oxygen, depth, and salinity. The change in this “response surface” for oxygen over time, once corrected for atmospheric exchange, allows the estimation of metabolism rates. The regression procedures used allow an estimate of the standard error associated with the metabolism measures. For the mesohaline Hudson River estuary, these standard errors are reasonably small. Similarly, any potential errors associated with the estimation of atmospheric exchange in oxygen are small for the Hudson. The technique should be useful for estimating GPP, NEP, and ER in other partially mixed estuaries without the biases associated with incubations in bottles.
Phytoplankton phosphorus limitation and food quality for Bosmina
Authors: Schulz Kimberly L. , Sterner Robert W.
Published: May 2010

Recent studies have demonstrated that Daphnia, a cladoceran (anomopod) zooplankton species with a high phosphorus content, can become P limited when fed algae deficient in phosphorus. Bosmina is another common anomopod zooplankter, but its body has a lower percentage of P than does that of Daphnia, and Bosmina might therefore be less susceptible to P mineral limitation. To test for this hypothesized interspecific difference in nutrition, Bosmina and Daphnia were raised on two food types: P‐deficient or P‐sufficient Scenedesmus acutus in two concentrations (0.2 or 1.0 mg C L−1). As predicted by its lower P content, Bosmina growth and fecundity were not affected by the P content of algal food, even though P‐deficient food caused significant declines in these life history parameters for Daphnia. Results suggest that Bosmina has a lower P requirement than does Daphnia and that Bosmina may process phosphorus more efficiently or be better able to survive losses in body P content. The outcome of competition between Bosmina and Daphnia therefore might shift in favor of low‐P‐content zooplankton such as Bosmina under conditions of seston P mineral limitation.
Chemoreception in a marine cryptophyte: Behavioral plasticity in response to amino acids and nitrate
Authors: Lee Eunjung S. , Lewitus Alan J. , Zimmer Richard K.
Published: May 2010

The behavioral responses of Chroomonas sp. to ammonium, nitrate, and 19 individual amino acids were examined by computer‐assisted video motion analysis. Cells were cultured with either glycine or nitrate as the sole nitrogen source. Relative to seawater, rates at which glycine‐grown cells stopped and turned were significantly reduced in response to 10−6 and 10−7 M glutamate, methionine, alanine, and aspartate. This response was akin to the tumbling behavior (chemotaxis) displayed by flagellated bacteria. When cultured in nitrate, Chroomonas sp. did not react to amino acids and ammonium but did significantly reduce stopping and turning in response to 10−6 M nitrate. These results are the first to demonstrate chemoreception in any cryptophyte species. Because Chroomonas sp. commonly lives in habitats where light and inorganic nutrients are limiting, behavioral mechanisms that maximize use of both amino acids and nitrate would seem particularly adaptive.
Bacterial utilization of dissolved glucose in the upper water column of the Gulf of Mexico
Authors: Skoog Annelie , Biddanda Bopaiah , Benner Ronald
Published: May 2010

Several aspects of bacterial glucose assimilation and bacterial production (BP) were investigated over 2 d in the upper 300 m of the Gulf of Mexico. Glucose concentrations ranged from 2 to 15 nM in surface seawater; glucose utilization rates were 1–3 nM d−1 in the upper 150 m of the water column and 0.02–0.8 nM d−1 in deeper water (150–300 m). Turnover of glucose and bacteria were similar and were in the range of 0.01–0.4 d−1. Measured glucose assimilation rates imply that glucose supports ∼5–10% of the observed BP in surface waters. The limiting factors for bacterial glucose utilization varied with depth. Glucose assimilation seemed to be limited by availability of inorganic N in the chlorophyll maximum. Additions of nitrate or ammonium had similar effects on glucose assimilation. BP was limited by C below and above the chlorophyll maximum. Additions of high‐molecular‐weight (HMW) dissolved organic matter (DOM) decreased bacterial glucose uptake rates, indicating that substances competing with glucose assimilation were derived from HMW DOM extracellularly. Thus, the measurement of free glucose assimilation appears to integrate bacterial utilization of combined glucose and indicates that many of the free sugars in seawater may be derived from polymers. The higher glucose assimilation rates achieved with inorganic nutrient additions indicate that bacterial degradation of C‐rich organic matter (OM) could vary between ocean regions with varying inorganic nutrient concentrations.
Ultraviolet‐B radiation stimulates shikimate pathway‐dependent accumulation of mycosporine‐like amino acids in the coral Stylophora pistillata despite decreases in its population of symbiotic dinoflagellates
Authors: Shick J. M. , Romaine-Lioud S. , Romaine-Lioud S. , Ferrier-Pagès C. , Gattuso J.-P.
Published: May 2010

Colonies of Stylophora pistillata maintained for four years in indoor aquaria in the near absence of ultraviolet radiation (UVR) contained only small amounts (<5 nmol mg−1 protein) of 10 identified mycosporine‐like amino acids (MAAs, which act as UV sunscreens), the largest number reported in any organism. The concentrations of most MAAs increased linearly or exponentially when colonies were exposed to ultraviolet‐A (UVA) and ultraviolet‐B (UVB) for 8 h d−1 in the presence of photosynthetically active radiation (PAR). Total MAA concentration reached 174 nmol mg−1 protein after 30 d, with palythine and mycosporine−2 glycine constituting more than half of the final total. UVB specifically stimulated MAA accumulation: after 15 d, MAA levels in colonies exposed to PAR alone and to PAR and UVA did not differ (7 and 5 nmol MAA mg−1 protein, respectively), while those in colonies exposed to PAR and UVA + UVB were significantly higher (28 nmol mg−1 protein). Glyphosate, an inhibitor of the shikimate pathway, eliminated or reduced the UV‐induced accumulation of most MAAs during 7 d of exposure, providing the first experimental evidence of their synthesis via this pathway in a coral symbiosis. Densities of zooxanthellae in colonies of S. pistillata, Acropora sp., and Seriatopora hystrix exposed to UVR for 15 d were only one‐third of those in control colonies unexposed to UVR. This net decrease in the number of zooxanthellae in the corals (bleaching) occurred despite UV stimulated increases in algal cytokinesis and in the host cell‐specific density of zooxanthellae in hospite, increases that apparently destabilized the symbiosis and caused expulsion of the zooxanthellae.
Atmospheric input of nitrogen and phosphorus to the Southeast Mediterranean: Sources, fluxes, and possible impact
Authors: Herut Barak , Krom Michael D. , Pan Gang , Mortimer Robert
Published: May 2010

Estimates of the sources and wet deposition fluxes of inorganic nutrients (PO43−, NO3−, NO2−, NH4+) have been made using a long‐term wet atmospheric deposition measurement at three sites along the Mediterranean coast of Israel. The nutrient composition in rainwater indicated a dominant anthropogenic source for NO3− and NH4+ and a continental, natural, and anthropogenic, rock/soil source for PO43−. The calculated long‐term dissolved inorganic N (IN) and inorganic P (IP) fluxes were 0.28 and 0.009 g m−2 yr−1 to the coastal zone and estimated as 0.24 and 0.008 g m−2 yr−1 to the Southeast (SE) Mediterranean, with a possible increasing pattern of the annual dissolved IN fluxes. Concentration of total and seawater leachable IP (LIP) from dust was examined on 20 Whatman 41 filters collected during 1996. The mean total IP concentration in dust was 0.13 ± 0.11% (geomean = 0.09%), with a mean of 387 ± 205 μg IP per g of dust leached by seawater. LIP from dust varies between 6 and 85% (mean of 38%) of the dry total IP. Dust of desert‐type (Saharan) events exhibited lower LIP solubility in seawater (∼25%, median) than air masses of European origin (∼45%, median). The calculated ratio of wet deposition to total (wet and dry) deposition here of 0.2 showed the importance of dry deposition of P in the SE Mediterranean basin compared to atmospheric inputs into the northwestern basin. The total IP and seawater LIP fluxes from dry deposition were estimated as 0.04 and 0.01 g m−2 yr−1, respectively. Atmospheric inputs of bioavailable N and P represent an imbalanced contribution to the new production of 8–20 and 4–11%, respectively, and reinforce the unusual N:P ratios (∼27) and possible P limitation in the SE Mediterranean.
Dissolved organic phosphorus in the coastal ocean: Reassessment of available methods and seasonal phosphorus profiles from the Eel River Shelf
Authors: Monaghan E. J. , Ruttenberg K. C.
Published: May 2010

Methods for quantifying total dissolved phosphorus (TDP) were reevaluated. High‐temperature ashing/hydrolysis (Ash/Hydrol.) and Acid Persulfate methods were examined for their ability to quantitatively convert a range of organic‐P compounds to orthophosphate. The Ash/Hydrol. method recovered on average 99% of organic‐P compounds tested, including phosphonates (compounds with C‐P bonds). Contrary to concerns voiced in prior studies, we found no P loss due to volatilization in seawater samples. Poor recovery by the Acid Persulfate method was observed for two compound classes: phosphonates and phospholipids. The Ash/Hydrol. method is recommended for routine TDP analyses.

The hydrolysis of dissolved organic phosphorus (DOP) during the phosphomolybdate‐blue reaction and the subsequent overestimation of dissolved inorganic phosphorus (DIP) have long been a concern. Extent of hydrolysis of standard DOP compounds was evaluated both during this reaction and over long‐term acidified (pH 1.0)/refrigerated and unacidified/frozen storage. Eleven of 12 compounds tested hydrolyzed <2% during the phosphomolybdate‐blue reaction. Phospholipid, phosphosugar, and nucleotide mono‐ and diphosphate standards stored acidified/refrigerated over 2.5 months were <5% hydrolyzed; compounds with higher energy phosphate bonds (e.g., phosphocreatine) hydrolyzed to a greater extent. A natural seawater sample showed no hydrolysis over 80 d, however, suggesting that refrigerated storage of acidified samples is a viable option.

Seasonal DOP profiles from the Eel River Shelf quantified by the Ash/Hydrol. and Acid Persulfate methods yielded comparable results, indicating that the DOP pool at this site did not contain significant phospholipids or phosphonates, which are underrecovered by the Persulfate method. Recoveries using a third method, Nitrate Oxidation, were on average 7% lower. Surface‐water DOP exceeded DIP in summer and was apparently related to biological productivity, underscoring the need to include organic species when evaluating nutrient limitation and creating nutrient budgets.
Lead binding to metal oxide and organic phases of natural aquatic biofilms
Authors: Nelson Yarrow M. , Lion Leonard W. , Shuler Michael L. , Ghiorse William C.
Published: May 2010

The role of the composition of surface‐coating materials in controlling trace metal adsorption in aquatic environments was investigated using natural biofilms that developed on glass slides in three New York State lakes and a water𠄃supply well. Adsorption isotherms were obtained for Pb binding to each of the biofilms in solutions with defined Pb speciation at 25°C and pH 6.0, with Pb concentrations ranging from 0.2 to 2.0 μM. Adsorption isotherms for Pb binding to laboratory‐derived metal oxides and surrogate organic materials were determined under the same conditions. These isotherms, combined with characterization of natural biofilm composition, were used to estimate the relative contributions of the organic and metal oxide surface‐coating constituents by assuming additivity of adsorption to discrete adsorbing phases. Cells of a diatom (Navicula peliculosa), a green alga (Chlorella vulgaris), the bacterium Leptothrix discophora, and extracellular polymer of the bacterium Burkholdaria cepacia were tested as laboratory analogs for the organic phase of the biofilms. Amorphous Fe oxyhydroxide, γAl2O3, and a laboratory‐derived biogenic Mn oxyhydroxide were used as laboratory surrogates for biofilm minerals. The sum total of predicted Pb binding to the defined surrogates accounted for at least 90% of the total observed Pb binding in the three lake biofilms and 60% of that observed for the well biofilms. For the lake biofilms, Pb adsorption to Fe and Mn oxides was significantly greater than that estimated for organic materials. The use of biogenic Mn oxide as a model component resulted in an estimated Pb adsorption to Mn oxyhydroxides in the lake biofilms up to four times greater than that estimated for Fe oxyhydroxide. Estimated Pb binding by Al oxide was negligible for all four biofilms. These results suggest that Fe and biogenic Mn oxides exert the greatest influence on Pb adsorption in oxic freshwater environments at pH 6.0.
Copper‐induced release of complexing ligands similar to thiols by Emiliania huxleyi inseawater cultures
Authors: Leal M. Fernanda C. , Vasconcelos M. Teresa S. D. , van den Berg Constant M. G.
Published: May 2010

Marine microalgae (Emiliania huxleyi) were grown in seawater enriched only with nitrogen and phosphorus, without control of free metal concentrations using synthetic chelators. Complexing ligands and thiol compounds were determined by cathodic stripping volt–ammetry. Copper was added to these cultures, and ligands were produced in response to the copper addition. Parallel measurements of thiols showed that glutathione and other unidentified thiols (electrochemically similar to thioacetamide) were produced by the algae at rates and concentrations similar to those of the complexing ligands. Smaller amounts of thiols were produced when ligands including thiols were added to the culture. The results indicate that thiols can account for a major part or most of the copper–complexing ligands produced by these algae. Furthermore, a feedback mechanism exists in which the production of thiol–type complexing ligands is controlled by the free copper concentration, production already being stimulated by an increase of [Cu2+] from 0.4 to 1.5 pM. Incubations with added exudates, thiols, and salicylaldoxime (SA) showed much reduced copper toxicity even though copper uptake was increased by the exudates and the SA.
Cadmium sources and exchange rates for Chaoborus larvae in nature
Authors: Munger Catherine , Hare Landis , Tessier André
Published: May 2010

Although freshwater insects are known to accumulate trace metals in the laboratory from both water and food, the relative importance of metal sources for these animals, as well as the rate at which they take up and eliminate their metal, has not been measured in nature. We describe a novel in situ approach that allowed us to determine that trophic transfer is the main source of cadmium for larvae of a common lake‐dwelling animal, the phantom midge Chaoborus punctipennis. We transferred C. punctipennis larvae from a low‐cadmium to a high‐cadmium lake, where they were exposed in 64‐μm‐mesh mesocosms to the prevailing high‐Cd concentrations in water and to various quantities of prey collected from the Cd–rich lake. Our experimental design ensured exposure of C. punctipennis larvae to realistic Cd concentrations in water and in a natural mixture of prey types. Our results indicate that larvae take up their Cd mainly from prey. Thus models of metal dynamics and effects on these invertebrates are likely to be more realistic if they include food as a metal source. Using the same mesh mesocosm design, we also determined that C. punctipennis larvae transferred from a high‐Cd to a low‐Cd lake lost their Cd slowly. Combining our information on Cd uptake and loss from C. punctipennis allowed us to model Cd exchange between this insect and its surroundings.
Critical depth and critical turbulence: Two different mechanisms for the development of phytoplankton blooms
Authors: Huisman Jef , van Oostveen Paul , Weissing Franz J.
Published: May 2010

A turbulent diffusion model shows that there are two different mechanisms for the development of phytoplankton blooms. One of these mechanisms works in well‐mixed environments and corresponds to the classical critical depth theory. The other mechanism is based on the rate of turbulent mixing. If turbulent mixing is less than a critical turbulence, phytoplankton growth rates exceed the vertical mixing rates, and a bloom develops irrespective of the depth of the upper water layer. These results demonstrate that phytoplankton blooms can develop in the absence of vertical water‐column stratification.
Landcover changes and δ13C composition of riverine particulate organic matter in the piracicaba river basin (southeast region of brazil)
Authors: Martinelli Luiz A. , Ballester Maria Victoria , Krusche Alex V. , Victoria Reynaldo L. , de Camargo Plinio B. , Bernardes Marcelo , Ometto Jean P. H. B.
Published: May 2010

Assuming the paradigm that catchment vegetation is the main source of particulate organic matter (POM) to rivers, the main objective of this study was to determine what the proportion of original C3 carbon from the forest had already been replaced by C4 carbon from sugar cane and pasture in the rivers of the Piracicaba Basin. In order to achieve this objective, we first produced a detailed landcover map using Landsat5‐TM images, and then we measured the carbon stable isotopic composition of the particulate riverine organic matter (δ13C‐POM) in seven sites along the major rivers and in two sites along a small creek. Sugar cane and pasture (C4 plants) covered almost 60% of the basin area, while silviculture, mostly of other crops, citrus, and forest that are C3 plants, covered 35%. Isotopic studies conducted in large pristine tropical rivers of South America and of Africa have shown that catchment vegetation is the main source of carbon in suspended POM. Our study demonstrates that relatively recent changes (70–80 yr ago) in landcover in the Piracicaba River Basin have already affected the composition of the riverine POM. Therefore, as in natural ecosystems, the vegetation (allochthonous source) plays an important role in the composition of the riverine POM in agricultural systems such as the Piracicaba River Basin. This control can be supported by the good correlation between cumulative area of the basin covered with C4 plants and the δ13C of the riverine POM. However, our study, differently from others, also shows that, during the low water period, in situ processes, such as primary production, may be an important source of carbon to the riverine POM.
Effects of nutrients versus herbivores on reef algae: A new method for manipulating nutrients on coral reefs
Authors: Miller M. W. , Hay M. E. , Miller S. L. , Malone D. , Sotka E. E. , Szmant A. M.
Published: May 2010

There has been much discussion and some controversy regarding the role of nutrient enrichment versus other factors, such as altered rates of herbivory, in the degradation of coral reef ecosystems. The resolution of this controversy has been hampered by the lack of manipulative field studies testing the effects of ecologically relevant levels of nutrient enrichment on coral reef communities. We present a new method for adding ecologically relevant levels of nutrients to experimental substrates on coral reefs. The method elevates nutrients for sustained periods of time (>41 d without replenishment of nutrients) and allows for testing interactions of nutrients and altered levels of herbivory. Results from an offshore reef in Key Largo, Florida, show strong effects of excluding large herbivorous fishes, negligible effects of nutrient enrichment–;or effects that are opposite of predictions, and no interaction between nutrient levels and herbivory in affecting algal abundance. Patterns observed for this reef did not confirm predictions of previously proposed models that frondose macroalgal or crustose algal abundance would be enhanced with nutrient enrichment or that dominance of filamentous turfs would be greater in unenriched conditions. In contrast to previous predictions, the abundance of larger macroalgae at this site was not increased by elevating nutrients above predicted threshold response levels of 1.0 µM for total inorganic nitrogen or 0.10 µM for soluble reactive phosphate. Also conflicting with some models, filamentous, nitrogen‐fixing cyanobacteria were enhanced, rather than suppressed, by nutrient enrichment.
Bacterioplankton turnover of dissolved free monosaccharides in a mesotrophic lake
Authors: Bunte Christoph , Simon Meinhard
Published: May 2010

Concentrations and bacterioplankton uptake of dissolved free monosaccharides (DFCHO) in relation to bacter‐ioplankton production and phytoplankton biomass were studied in mesotrophic Lake Constance, Germany, from August 1995 to December 1996. Concentrations of total DFCHO, measured by high‐performance liquid chroma‐tography (HPLC) and pulsed amperometric detection, ranged from <20 to 440 nM and exhibited pronounced spatiotemporal variations. Enhanced concentrations of DFCHO were often associated with the breakdown of phy‐toplankton blooms and periods of low phytoplankton growth. Bacterial uptake rates of DFCHO were also enhanced during such events, as well as at peaks of bacterioplankton production (BP). Ratios of uptake of DFCHO/BP, however, indicated that DFCHO concentrations were relatively more important as substrates during periods of low bacterial growth than during phases of intense bacterial growth. Ratios of bacterial uptake of DFCHO/BP from spring to fall ranged from 0.22 to 0.39 in the layer 0–10 m, from 0.17 to 0.56 at 20 m, and from 0.22 to 0.46 at 50 m, respectively. Glucose, galactose, and mannose dominated the DFCHO pool and constituted ∼55 to ∼70 mol%. The analysis of individual turnover times of five DFCHO concentrations from August to November 1995 at 3, 10, and 50 m revealed that the glucose pool turned over most rapidly, followed by galactose and mannose. Glucosamine and fructose always exhibited substantially longer turnover times. Comparisons to previous studies show that DFCHO concentrations are of similar significance for bacterioplankton growth as dissolved free amino acids (DFAA), even though temporal uptake patterns of both substrates are different.
Max Planck Institute for Limnology, P.O. Box 165, 24302 Plön, Germany
Authors: Wiltshire Karen Helen , Lampert Winfried
Published: May 2010

It is known that the zooplankter Daphnia induces colonies in the alga Scenedesmus. As Daphnia grazes on Scenedesmus, it has been postulated that colony formation represents an algal defense mechanism. This induction of Scenedesmus coenobia/colonies by Daphnia could be associated with a substance exuded by the animals that acts as a specific infochemical (kairomone) for Scenedesmus. However, the chemical nature of such a substance is still unknown. Because coenobia can be formed in the absence of Daphnia kairomone, as a result of different N concentrations in the algae and media, we checked different nitrogen excretory products of Daphnia as potential candidates. In this paper we test the hypothesis that ammonia and urea excreted by zooplankters (Daphnia) may induce coenobia formation in Scenedesmus. Using experiments with dialysis separation of Daphnia and algae we show that one of the excretory products of zooplankters, urea, can induce colony formation in Scenesdesmus, whereas ammonia has no effect. Although the effect of urea on coenobia formation may simply be a nutrient effect, this does not exclude the possibility that it results in grazing protection of the algae. Hence, urea produced by zooplankton may serve as a colony inducer to algae.
Brine shrimp larval photoresponses involved in diel vertical migration: Activation by fish mucus and modified amino sugars
Authors: Forward, Richard B. , Rittschof Dan
Published: May 2010

Photoresponses involved in the descent phase of nocturnal diel vertical migration of brine shrimp (Artemia franciscana) naupliar larvae were measured in a laboratory system that mimicked the underwater angular light distribution. The test hypothesis was that kairomones from fish that activate photoresponses involved in DVM include degradation products of polysaccharides in their external mucus. Studies focused on the glycosaminoglycans heparin, chondroitin sulfate A, and hyaluronic acid and their repeating disaccharide units. Active molecules were identified by their activation of the descent photoresponse. Mucus from the mummichog (Fundulus heteroclitus) activated photoresponses at concentrations down to 10−5 g wet weight of mucus L−1 . Water that had previously contained this species had (1) active molecules that were <10 kDa in size, (2) polysaccharides in the >10‐kDa, ≪30‐kDa fraction that could be acted upon by heparinase and chondroitinase to produce active molecules, and (3) enzymes in the >30‐kDa, <100‐kDa fraction that acted on heparin and chondroitin sulfate polysaccharides to produce active molecules. The repeating disaccharide subunits of heparin, chondroitin sulfate A, and hyaluronic acid‐induced photoresponses. The disaccharide subunit of hyaluronic acid was the most potent disaccharide, as it activated photoresponses at concentrations as low as 10−9 M. Tests with different subunits found that compounds with the most potent biological activity were disaccharides with either a sulfamino or acetylamino group on carbon 2 of the hexoseamine. Collectively, the results support the hypothesis and indicate that enzymatic degradation products of sulfated and acetylated fish mucus can serve as kairomones.
Feeding selection of heterotrophic marine nanoflagellates based on the surface hydrophobicity of their picoplankton prey
Authors: Monger Bruce C. , Landry Michael R. , Brown Susan L.
Published: May 2010

Theory suggests that variation in the attractive solvation force associated with cell‐surface hydrophobicity can significantly affect contact rates among small cells in aqueous environments and consequently may influence rates and selective impacts of marine nanoflagellate grazers feeding on picoplankton assemblages. To investigate this hypothesis, we assayed the natural range in hydrophobic characteristics of subtropical picoplankton from the oligotrophic subtropical Pacific (Station Aloha, 22°45'N, 158°W) and mesotrophic Kaneohe Bay, Hawaii, using hydrophobic interaction chromatography (HIC) in conjunction with analytical flow cytometry. Variability in a relative index of cell‐surface hydrophobicity (HIC index) for heterotrophic bacteria, Prochlorococcus and Synechococcus, exhibited some consistent spatial patterns. The HIC index for Prochlorococcus at Station Aloha varied about three‐fold, being consistently more hydrophobic in the upper 80 m of the water column and dropping abruptly below this depth. Heterotrophic bacteria were more hydrophobic near the surface and decreased slightly, but steadily, with increasing depth. The hydrophobicity of heterotrophic bacteria steadily increased along a Kaneohe Bay transect extending from oligotrophic to mesotrophic conditions. In experiments involving nanoflagellates grazing on laboratory cultures of Prochlorococcus, cell cultures exhibiting the highest HIC indices were grazed upon at the highest rates. An additional experiment involving mixtures of Prochlorococcus cells exhibiting high and low hydrophobicities showed that the average hydrophobicity of the uningested prey mixture was driven progressively toward lower hydrophobicity as the more hydrophobic cells were selectively removed through time. If these laboratory grazing results hold in nature, the rate at which picoplankton cells are cleared from suspension by nanoflagellates could vary by as much as twofold due solely to natural variation in cell surface hydrophobicity.
Photosynthesis and the dynamics of oxygen consumption in a microbial mat as calculated from transient oxygen microprofiles
Authors: Epping Eric H. G. , Khalili Arzhang , Thar Roland
Published: May 2010

A new method is presented to determine the rates of oxygen consumption, net oxygen metabolism (defined as photosynthesis minus oxygen consumption), and gross photosynthesis at high vertical resolution in benthic photo‐trophic communities. The rates of oxygen consumption and of net oxygen metabolism as a function of depth and time are calculated from the dynamics in oxygen concentration, as measured with oxygen microsensors during light‐dark cycles, by numerically solving the general non‐steady state diffusion‐reaction equation. The results, as obtained for a temperate intertidal microbial mat, strongly suggest that the vertical distribution and the dynamics in oxygen consumption are controlled by the supply of both oxygen and oxidizable substrates from different sources. The depth distribution of gross photosynthesis, as obtained by the cycling procedure, showed reasonable agreement with the photosynthesis profile, as measured with the conventional light‐dark shift method prior to the light‐dark cycling experiment, thus supporting the applicability of the method.
Diffusive boundary layers, photosynthesis, and respiration of the colony‐forming plankton algae, Phaeocystis sp
Authors: Ploug Helle , Stolte Willem , Epping Eric H. G. , Jørgensen Bo Barker
Published: May 2010

Diffusive boundary layers, photosynthesis, and respiration in Phaeocystis colonies were studied by the use of microelectrodes for oxygen and pH during a bloom in the Barents Sea, 1993, and in the Marsdiep, Dutch North Sea, 1994. The oxygen microenvironment of a Phaeocystis colony with a mean diameter of 1.4 mm was mapped from 346 O2 measurements and showed gradients of oxygen concentration in the water phase up to 1 mm distance from the colony surface. The effective diffusive boundary layer was 0.4–0.9 mm thick. Oxygen concentrations inside colonies reached 180% of the bulk water, and pH increased up to 0.4 units when measured in light at saturating intensities (>90 µmol photons m−2 s−1 ). The respiration in the dark was low, resulting in a 6% lowering in oxygen concentration and 0.04 units lowering in pH inside colonies, compared to the bulk water phase. Such colonies were net heterotrophic communities at light intensities up to 10 µmol photons m−2 s−1. A week later, colonies were net heterotrophic at light intensities up to 80 µmol photons m−2 s−1. The effective diffusion coefficient for oxygen in the gelatinous colonies was not significantly different from that in sea water.
Diffusive boundary layers of the colony‐forming plankton alga Phaeocystis sp.— implications for nutrient uptake and cellular growth
Authors: Ploug Helle , Stolte Willem , Jørgensen Bo Barker
Published: May 2010

The impact of colony formation on cellular nutrient supply was calculated for Phaeocystis in a turbulent environment using a diffusion‐reaction model. The model included diffusive boundary layer as predicted by Sherwood numbers in mass transfer to a sphere. Literature values for nutrient uptake (Vmax , Km ) of single cells and colonies and the size dependence of cell numbers in colonies were used in the model. Colony formation was shown to decrease nutrient uptake by Phaeocystis cells because of the presence of diffusive boundary layers with concentration gradients surrounding the colonies. At diffusion limitation, this concentration gradient was reflected by an apparently higher half‐saturation constants for nutrient uptake, KM , for colonial cells compared with that for single cells. The diffusion limited supply of inorganic nitrogen and orthophosphate from the bulk water phase with concentrations of 2 and 0.2 µM, respectively, was sufficient to support nutrient demands for 1 cell doubling in colonies in 6–10 h, respectively, at a shear rate of 0.1 s−1 . The same nutrient concentration levels could theoretically support nutrient demands of single cells for one cell doubling within 2–3 h. It was concluded that the lower grazing pressure in the size class of colonies relative to that of single free‐living cells may be more important for colony formation than nutrient concentrations.
Preferential recycling of nutrients—the ocean's way to increase new production and to pass nutrient limitation?
Authors: Thomas Helmuth , Ittekkot Venugopalan , Osterroht Christoph , Schneider Bernd
Published: May 2010

Uptake of atmospheric CO2 by the oceans and the export of carbon into deeper waters via the biological CO2 pump is driven by the production of particulate organic matter (POM). The elemental ratios of carbon, nitrogen, and phosphorus within POM follow Redfield ratios, suggesting that the concentrations of dissolved inorganic carbon (DIC) and nutrients decrease during new production corresponding to these ratios. Subsequently, new production and the efficiency of the biological CO2 pump are usually estimated using Redfield ratios. However, our observations in the Baltic Sea and obser‐vations elsewhere show significantly greater decreases in DIC during the productive season than that predicted from the decline in nutrients with reference to Redfield ratios. Using new DIC, nutrient, and oxygen data from the Baltic Sea, we discuss this discrepancy and provide evidence that preferential recycling of nutrients fuels the productive community with nutrients. Limiting nutrients are preferentially recycled and become available for new production. These findings derived from hydrochemical bulk data confirm the picture of the microbial loop but question the common description of new production and nutrient limitation. Finally, we argue for a carbon‐based efficiency estimate of the biological CO2 pump probably exceeding significantly nutrient‐based estimates.
Aerosol-induced changes of convective cloud anvils produce strong climate warming
Authors: Koren I. , Remer L. A. , Altaratz O. , Martins J. V. , Davidi A.
Published: May 2010

Abstract. The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. Small human-induced perturbations to cloud characteristics via aerosol pathways can create a change in the top-of-atmosphere radiative forcing of hundreds of Wm−2. Here we focus on links between aerosol and deep convective clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting that the aerosol environment in each region is entirely different. The tops of these vertically developed clouds consisting of mostly ice can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing. We find that increased aerosol loading is associated with taller cloud towers and anvils. The taller clouds reach levels of enhanced wind speeds that act to spread and thin the anvil clouds, increasing areal coverage and decreasing cloud optical depth. The radiative effect of this transition is to create a positive radiative forcing (warming) at top-of-atmosphere. Furthermore we introduce the cloud optical depth (τ), cloud height (Z) forcing space and show that underestimation of radiative forcing is likely to occur in cases of non homogenous clouds. Specifically, the mean radiative forcing of towers and anvils in the same scene can be several times greater than simply calculating the forcing from the mean cloud optical depth in the scene. Limitations of the method are discussed, alternative sources of aerosol loading are tested and meteorological variance is restricted, but the trend of taller clouds, increased and thinner anvils associated with increased aerosol loading remains robust through all the different tests and perturbations.
Technical Note: Automatic river network generation for a physically-based river catchment model
Authors: Birkinshaw S. J.
Published: May 2010

Abstract. SHETRAN is a physically-based distributed modelling system that gives detailed simulations in time and space of water flow and sediment and solute transport in river catchments. Standard algorithms for the automatic generation of river channel networks from digital elevation data are impossible to apply in SHETRAN and other similar models because the river channels are assumed to run along the edges of grid cells. In this work a new algorithm for the automatic generation of a river channel network in SHETRAN is described and its use in an example catchment demonstrated.