bluuebunny/crossref_metadata_2025 huggingface dataset:
A seasonal cycle in the carbon‐isotope composition of organic carbon in the Sanaga River, Cameroon
Authors: Bird Michael I. , Giresse Pierre , Ngos Simon
Published: May 2010

We report measurements of the carbon‐isotope composition (δ13C value) of particulate organic carbon (POC) in the suspended sediment load of the Sanaga and Mbam Rivers, Cameroon. The results demonstrate that there is a seasonal cycle in δ13C value of 3.3%0 (−26.6 to −23.3%0) in the Sanaga River and 5.9%0 (−27.1 to −21.2%0) in the Mbam River that is directly related to seasonal changes in the discharge of the rivers. During periods of high discharge, δ13C values of POC are high, reflecting an increase in the proportion of POC derived from C, plants, including C4‐derived carbon transported overland by wet season rains from savanna regions in the catchment hinterland. During periods of low discharge, the δ13C values of POC are low, reflecting derivation of the carbon primarily from C4 plants growing close to the riverbanks. Results suggest that the prime determinant of POC δ13C values in tropical rivers that carry a significant suspended sediment load is the δ13C value of the catchment vegetation.
Photoadaptive response during the development of a coustal Antarctic diatom bloom and relationship to water column stability
Authors: Moline Mark A.
Published: May 2010

The raio of the xanthophylll pigments diadinoxanthin and diatoxanthin to chlorophyll a [(DD+DT}:Chl a] was used as a photoadaptive index during the development of a large Antarctic diatom bloom. This index was found to track fluctuations in the incident solar irradiance and the in situ light field over a 3 order magnitude change in the water column biomass. Depth profiles of the (DD+DT}:Chl a ratio showed that the upper mixed layer, assessed by physical data, was in fact stable over the course of the month. Diel experiments conducted over the same period showed a delayed (5–8 h) response of the DD+DT pool to the instantaneous Qpar (400–700 nm) irradiance. These time series results illustrate the potential use of xanthophyll pigmnents in assessing phytoplankton light histories and the degree of water column stability.
Colonization of diatom aggregates by the dinoflagellate Noctiluca scintillans
Authors: Tiselius Peter , Kiørboe Thomas
Published: May 2010

Abundance and vertical distribution of the dinoflagellate Noctiluca scintillans were studied during a diatom bloom in the Benguela current. Video observations showed the occurrence of abundant Chaetoceros spp. aggregates colonized by N. scintillans. The diatom aggregates were formed by regular coagulation of diatom cells and not by mucus feeding behavior of N. scintillans. N. scintillans can be positively buoyant, and estimates of encounter rates between N. scintillans and diatom aggregates during ascent demonstrates that this mechanism is sufficient to account for the observed colonization. The attached N. scintillans were feeding on the diatoms in the aggregates, as revealed by food vacuole content. In the particular environment studied, N. scintillans appeared not to depend on aggregate feeding since shipboard experiments showed that clearance rates (10–20 µl h−1) on unaggregated cells were sufficient to account for the high growth rates measured (up to 0.7 d−1).
Sedimentary record of sources and accumulation of organic matter in Pyramid Lake, Nevada, over the past 1,000 years
Authors: Meyers Philip A. , Tenser Gabrielle E. , Lebo Martin E. , Reuter John E.
Published: May 2010

We have examined the organic matter contents of two 210Pb‐dated cores of sediment from Pyramid Lake for consequences of the historic environmental and limnological changes that have occurred since modem settlement of this region began in the 1850s. Agricultural diversion of Truckee River water has diminished the volume of this saline, terminal lake by one‐fourth since 1905. Organic C:N ratios, organic d13C values, and terrigenous:aquatic n‐alkane ratios indicate that the proportion of land‐derived organic matter in sediments has decreased as river flow has decreased. Algal productivity also appears to have decreased since 1930. Some prehistorical variations in the delivery of organic matter are evident in older sediments. Elevations in the proportion of land plant wax and in C:N ratios in sediments deposited A.D. 1200–1400 suggest that contributions of land‐derived organic matter were enhanced at this time. Proportions of biomarker n‐alkanes indicate that grasses were more important than trees and shrubs as the dominant source of land plant waxes during this period, suggesting an interlude of regionally wetter climate.
Copepod mortality induced by fluctuating levels of natural ultraviolet radiation simulating vertical water mixing
Authors: Zagarese Horatio E. , Cravero Walter , Gonzalez Pablo , Pedrozo Fernando
Published: May 2010

The effect of fluctuating ultraviolet radiation levels on the copepod Boeckella gracilipes was investigated in Lake Escondido (Patagonia, Argentina). The animals were incubated either at fixed depths or rotating in in situ plankton wheels of different diameters. The observed mortality was significantly higher in rotating treatments. Static incubations can be used to predict the mortality of vertically moving B. gracilipes, providing that the doses of UVA and UVB are known. The results suggest that under moderate wind conditions, the plankton of shallow lakes are exposed to potentially damaging levels of solar radiation, even in relatively turbid waters.
Metal‐rich concretions on the roots of salt marsh plants: Mechanism and rate of formation
Authors: Sundby Bjørn , Vale Carlos , Caçador Zsabel , Catarino Fernando , Madureira Maria-João , Caetano Miguel
Published: May 2010

The roots of the vascular plant Spartina maritima, growing in the saltmarshes of the Tagus Estuary, Portugal, are surrounded by tubular concretions whose diameter can reach >0.2 cm. Concretions are also found scattered within the sediment matrix in and below the root zone. The concretions comprise 4% (DW) of the sediment and contain 11.7 ± 1.6% iron compared to 4.9 ± 0.3% iron in the sediment in which they are found. They are formed by the precipitation of iron oxides in the pores between the sediment grains; this has filled about one‐sixth of the originally available pore space. To produce the concretions, the plants have extracted 0.25% Fe from the anoxic bulk sediment and concentrated it into the oxidized microenvironment surrounding each root. A mass‐balance model using cylindrical geometry shows that the observed concretion density can be produced by a network of roots with 1‐cm spacing. The space between the roots limits the amount of Fe that is available to a given root and thus determines the size of the individual concretion. Field observations and mathematical modeling show that plants can produce concretions on their roots in the space of a few weeks. The rhizoconcretions are 5–10 times enriched in Cd, Cu, Pb, and Zn with respect to the sediment surrounding them, and the smaller diameter concretions are more enriched than the larger ones. The preferential enrichment of the smaller diameter concretions, which was not observed for Fe and Mn, is independent of depth in the sediment for Cd and Cu; however, for Zn and Pb, the preferential enrichment is most pronounced within the upper trace metal‐contaminated sediment layer. The rhizoconcretions have acquired their load of metals via diffusion from the surrounding sediment. In the case of Fe and Mn, the concentration gradient that drives the diffusion is maintained by the precipitation of insoluble oxides. In the case of Cd, Cu, Zn, and Pb, the mechanism that maintains a concentration gradient toward the surface of the root is not know, but our data show that S. maritima is capable of mobilizing trace metals dispersed in reducing anoxic estuarine sediment and concentrating them into the distinct oxidized microenvironments that surround the roots.
Dissolved gas dynamics in perennially ice‐covered Lake Fryxell, Antarctica
Authors: Hood E. M. , Howes B. L. , Jenkins W. J.
Published: May 2010

We use the concentrations of noble gases (He, Ne, and Ar), helium isotopes, and tritium to characterize the mechanisms and rates of ventilation for Lake Fryxell, Antarctica, as well as the physical processes controlling dissolved gases. The upper oxic zone is ventilated on timescales of several decades. The anoxic bottom waters are weakly ventilated, with a turnover time of ∼3,800 years. In the upper euphotic zone, helium and neon are greatly undersaturated with respect to solubility equilibrium with the atmosphere, whereas argon is greatly supersaturated owing to equilibrium partitioning of the gases between ice, water, and air inclusions in the ice. In the bottom waters, the inert dissolved gas concentrations may be remnants of a near‐desiccation event that occurred ∼2,000 years B.P., consistent with current paleoclimatic theories.
The spatial information preservation method: Sampling the nanoscale spatial distribution of microorganisms
Authors: Krembs Christopher , Juhl Andrew R. , Strickler J. Rudi
Published: May 2010

It has been hypothesized that plankton patchiness exists on scales of tens to hundreds of micrometers (nanoscale patchiness). Current sampling methods disrupt the spatial pattern on this scale and therefore cannot detect nanoscale patchiness. We describe a method that allows the collection of microorganisms and other particles without destroying their relative spatial distribution. Our spatial information preservation (SIP) method is based on rapidly freezing a small sample of water. The three‐dimensional particle distribution captured in the ice is preserved in two dimensions as a projection on a microscope slide. Experiments were conducted on the extent of particle movement during freezing and removal of ice from around the particles, as well as the potential for cell loss during these procedures. The exneriments demonstrate that microorganisms can be collected quantitatively with sufficient preservation of their spatial distribution to resolve nanoscale patchiness.
In situ depletion of phytoplankton by an azooxanthellate soft coral
Authors: Fabricius Katharina , Yahel Gitai , Genin Amatzia
Published: May 2010

The in situ removal of phytoplankton by the soft coral Dendronephthya hemprichi was investigated by taking small‐scale measurements of chlorophyll concentrations around colonies on a reef of the northern Red Sea. The chlorophyll concentration downstream of a 0.75‐m‐deep colony thicket was depleted by 6.4% (± 1.4% SE) compared with the water upstream. Neighboring organisms are thus exposed to water that is significantly depleted of phytoplankton. A 0.75 × 0.1 × 0.1‐m passage of actively feeding colonies removed 34 mg of carbon per day from the water, equivalent to ~1.3 times their respiratory carbon demand. Rates of algae intake were also estimated by determining the decrease in gut fluorescence in starved colonies. The in situ depletion technique showed a three‐ to sixfold greater sensitivity compared with the gut fluorescence technique, and should be preferred as a technique for estimating feeding rates.
Reversibility of acidification of mountain lakes after reduction in nitrogen and sulphur emissions in Central Europe
Authors: Kopáček Jiří , Hejzlar Josef , Stuchlík Evžien , Fott Jan , Veselý Josef
Published: May 2010

The reversal of water acidification has been recently indicated by both empirical data and experiments. The world's largest whole‐ecosystem “experiment” involving ~30% and ~40% reduction in nitrogen and sulfur emissions, respectively, has occurred in Central Europe due to the political and economic changes in the postcommunist countries since 1989. Parallel decreases in deposition rates of SO42−, NO3−, and NH4+ have resulted in a rapid reversal in hydrochemistry of acidified lakes in the Šumava Mountains and the High Tatra Mountains. Concentrations of SO42− and NO3− in lakes were reduced by 11–14 and 13–32 mmol m−3, respectively, between the late 1980s and middle 1990s. Leaching of calcium, magnesium, and aluminum from the watersheds decreased while lake water pH and alkalinity increased. The immediate decline in NO3− concentrations after reduced nitrogen emissions has suggested a rapid reversibility of nitrogen saturation of the mountainous ecosystems in response to decreased amounts of nitrogen deposition.
Recycling of organic matter in Antarctic sediments: A transect through the polar front in the Southern Ocean (Indian Sector)
Authors: Rabouille Christophe , Gaillard Jean‐Francois , Relexans Jean‐Claude , Tréguer Paul , Vincendeau Marie‐Anne
Published: May 2010

Sediments from the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1. The first porewater distributions of O2 and NO3= and organic carbon data in the solid phase in this part of the ocean were used to model the recycling of organic matter in sediments. The data are described by a model containing two types of degradable organic matter with distinct reactivities. We estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average C : N ratio of 7. We estimate that particulate organic carbon fluxes deposited at the sediment‐water interface range between 0.2 and 0.8 mol C m−l y−l, with two peaks near the Polar Front and the Subantarctic Front. The flux 01 organic carbon deposited at the sediment‐water interface is unusually high and represents ˜10–20% of estimated primary production. From these findings, we conclude that production in the pelagic zone of this region is strongly linked to deposition and recycling in the sediment.
RNA content of copepods as a tool for determining adult growth rates in the field
Authors: Saiz Enric , Calbet Albert , Fara Angela , Berdalet Elisa
Published: May 2010

We propose a method to determine growth rates of adult copepods based on their nucleic acid contents. We investigated the suitability of this method on the marine copepod Acartia gruni in a range of food concentrations and temperatures. There was a good linear relationship between growth rate (estimated as egg production) and RNA contents of the adult copepods. The slope of the relationship was dependent on temperature. We also built a multiple regression model to predict egg production rates of A. grani as a function of RNA contents and temperature. This method allows very intensive field sampling and does not require incubations onboard. Samples are preserved frozen and analyzed in the laboratory using a very sensitive fluorometric technique that allows working with small numbers of individuals of the desired species.
Storage lipids of the copepod Calanus Jinmarchicus from Georges Bank and the Gulf of Maine
Authors: Miller Charles B. , Morgan Cheryl A. , Prahl Fredrick G. , Sparrow Margaret A.
Published: May 2010

Storage lipids of fifth copepodites (C5) of Calanus finmarchicus from Georges Bank and the Gulf of Maine were quantified from video images and by Iatroscan (thin‐layer chromatography with flame‐ionization detection, FID). Oil withdrawn from the oil sac by micropipette was pure wax ester (WE); triacylglycerols (TAG) were elsewhere in the body. Video images indicated more WE than could be demonstrated by Iatroscan. This was due to greater FID response to pure, commercially available waxes with low levels of unsaturation than to mixtures of mostly polyunsaturated wax in C. finmarchicus. A revised calibration scheme uses both WE and TAG purified in bulk by silica gel chromatography from C. finmarchicus itself. Use of quadratic calibration curves allowed analysis of single specimens, showing the individual variability of lipid class composition. C5 collected in April–July, while presumably storing lipid for the resting stage, showed a nearly constant level of TAG, ˜17 µg ind.−1, whereas WE amounts varied from nearly 0 to >300 µg ind.−1. There appears to be a TAG quota that is filled before WE accumulates significantly and that is usually not exceeded. Many C5 collected in February and March had very high amounts and fractions of TAG. This likely results from transformation of stored WE to TAG in preparation for egg production.
Endomycorrhizae of isoetids along a biogeochemical gradient
Authors: Wigand C. , Andersen F. O. , Christensen K. K. , Holmer M. , Jensen H. S.
Published: May 2010

Endomycorrhizae of aquatic plants may be important in phosphorus uptake and carbon exchange in lakes, but the environmental controls on mycorrhizal distribution are not known. We examined biogeochemical variables that were correlated with aquatic endomycorrhizae of isoetid‐type macrophytes in an oligotrophic, softwater lake. Endomycorrhizal infection was greatest in the shallow stations with high sediment redox potential and lowest in the deeper stations where there was low redox potential and high sediment organic content and porewater P levels. There was a significant 0. = +0.93, P < 0.05) positive correlation between percentage of hyphal infection of the roots and a root ergosterol (a specific fungal sterol) index determined per root mass. Fungal vesicle infection was also positively correlated with the root ergosterol index, although not significantly (r = +0.76, P = 0.14). Furthermore, the root ergosterol index was significantly correlated with plant rosette density (r = +0.97, P < 0.03. An increase in rosette density of isoetids increases the number of lacunae transporting oxygen to the roots, perhaps increasing fungal infection. The root ergosterol index was also significantly (P < 0.05) correlated with sediment redox status, porewater phosphate, solid phase iron‐bound P, exchangeable inorganic P, and inorganic adsorbed P There were no significant correlations between above‐ or belowground biomass or porewater NH4+ with the root ergosterol index, and porewater DOC was weakly correlated (P = 0.08) with the ergosterol index. Isoctid‐type plants are common in oligotrophic softwater lakes, and knowledge of environmental variables that are associated with endomycorrhizae will facilitate in management and restoration of these types of submersed vegetation.
A new device for studying benthic invertebrate recruitment
Authors: Whitlatch Robert B. , Osman Richard W.
Published: May 2010

An automated larval settlement sampler has been designed and tested in the field to examine the effects of environmental conditions on the recruitment of epifaunal and infaunal benthic invertebrates. The sampler (1) exposes substrates to settling larvae at four discrete levels of naturally varying environmental conditions (e.g. different tidal states, current speeds, light regimes), (2) repeatedly exposes substrates over a period (2–8 weeks) sufficient to accumulate measurable numbers of recruits, and (3) maintains unexposed substrates in an environment that does not result in unnatural levels of mortality. Preliminary field trials indicate that the device was effective in assessing recruitment responses of epifaunal invertebrates to diurnal variations in light level and infaunal invertebrates to variations in tidal state.
Determination of dissolved vanadium in natural waters by flow injection analysis with colorimetric detection
Authors: Shiller Alan M. , Mao Lunjin , Cramer Jeramé
Published: May 2010

A flow injection technique for the determination of dissolved vanadium in natural waters has been developed. The technique utilizes the vanadium‐catalyzed oxidation of Bindschedler's green leuco base by bromate with tiron and tartrate as reaction activators. The reaction product is quantified colorimetrically. A chelator column of immobilized 8‐hydroxyquinoline reduces matrix effects but can be eliminated if samples with a constant matrix are being analyzed. By using the chelator column, 1 ml of sample can be analyzed in < 10 min with a detection limit of 0.2 nM. The method has been used successfully for the determination of dissolved vanadium in river and estuarine waters.
Submicrometer particles in northwest Pacific coastal environments: Abundance, size distribution, and biological origins
Authors: Yamasaki Akiko , Fukuda Hideki , Fukuda Rumi , Miyajima Toshihiro , Nagata Toshi , Ogawa Hiroshi , Koike Isao
Published: May 2010

Submicrometer particles (SMP) are suggested to be a critical component for organic matter transitions in seawater, but little is known about variations and controls of SMP in coastal systems. We examined vertical and horizontal distributions of SMP (0.4–l µm in equivalent spherical diameter as measured by a resistive pulse particle counter) and biological variables (chlorophyll a concentration, abundance of bacteria, and heterotrophic nanoflagellates) in northwest Pacific coastal environments, The abundance and total volume of SMP in the upper 200 m varied in the range of 5 × 104−3 × 107 particles ml−1 and 4 × 103−3 × 106 µm3 ml−1, respectively. Over a large trophic gradient (Chl a, 0.02–4 µg liter−1), the total volume of SMP was strongly positively correlated with Chl a concentration (r = 0.90, P < 0.0001, n = 47) and with other microbial variables (r = 0.84–0.90) consistent with a hypothesis that SMP dynamics are closely related to microbial food‐web processes. Notably, size distribution of SMP in upper waters often exhibited a distinctive peak at a size range of 0.6–0.7 µm, which was most pronounced in productive nearshore waters and became less evident with depth and with distance from the shore. A sonication experiment revealed that the 0.6–0.7‐µm particles are primarily nonliving. We hypothesize that SMP, particularly the 0.6–0.7‐µm component, are directly produced by biological processes. Our data suggest that SMP are a highly reactive and abundant component of detrital colloids and play important roles in material cycles within coastal systems.
Phytoplankton distribution and grazing near coral reefs
Authors: Yahel Gitai , Post Anton F. , Fabricius Katharina , Marie Dominique , Vaulot Daniel , Genin Amatzias
Published: May 2010

Depletion of phytoplankton cells and pigments over coral reefs was studied in the Gulf of Aqaba, Red Sea,
during 1994–1996. Phytoplankton abundance and chlorophyll (Chl) a concentrations were 15–65% lower near the
reefs than in the adjacent open waters. The decrease in chlorophyll near the reef was typically associated with an
increase in the concentration of its degradation products, the pheopigments. The steepest slope of these cross‐shore
gradients occurred within 1–3 m above bottom. More than 50% of the variation in the extent of the chlorophyll
gradients, but not of pheopigments, could be explained by the advection of water during 2 h preceding the transect
and by the concentration of Chl a in the open water. No cross‐shore gradients were observed at a sandy‐bottom
site without reef. Eukaryotic phytoplankton (<5 pm) contributed >70% of the total depleted carbon near the reef
during winter, while the cyanobacterium Synechococcus (1 pm) contributed the largest share in summer. The proportions
of different taxa in depleted fractions were similar to those in ambient waters, indicating no size selectivity.
Direct measurements of phytoplankton removal rates were made in water passing through a unique 5‐m‐long
perforated reef, dominated by herbivorous soft corals. The waters downstream of that reef were strongly depleted
of phytoplankton (10 to >36%, or 32 to >100 ng Chl a liter−1). When converted to carbon fluxes, these rates greatly exceeded reported values of carbon input to coral reefs via zooplankton predation. Phytoplankton grazing
is an important component of benthic‐pelagic coupling in coral reefs.
Linking nitrogen in estuarine producers to land‐derived sources
Authors: McClelland James W. , Valiela Ivan
Published: May 2010

It is clear that anthropogenic nitrogen inputs from watersheds to estuaries stimulate eutrophication. It has been difficult, however, to explicitly link anthropogenic N entering estuaries to N found in estuarine producers. To explore this link, we compared stable isotope ratios of N in groundwater and producers from the Waquoit Bay watershedestuary system, Cape Cod, Massachusetts. The δ15N values of groundwater nitrate within the Waquoit Bay watershed increase from −0.9‰ to + 14.9‰ as wastewater contributions increase from 4 to 86% of the total N pool. As a result, the average δ15N of dissolved inorganic nitrogen (DIN, nitrate + ammonium) received by different estuaries around Waquoit Bay increases from +0.5‰ to +9.5‰. This increase is strongly correlated to increases in δ15N of eelgrass, macroalgae, cordgrass, and suspended particulate organic matter. The increase of all producers examined in Waquoit Bay with increasing δ15N of DIN in groundwater demonstrates a tight coupling between N contributed to coastal watersheds and N used by primary producers in estuaries. The ability to identify effects of increasing wastewater N loads on δ15N of estuarine producers may provide a means to reliably identify incipient eutrophication in coastal waters.
The role of sunlight in the removal and repair of viruses in the sea
Authors: Wilhelm Steven W. , Weinbauer Markus G. , Suttle Curtis A. , Jeffrey Wade H.
Published: May 2010

We investigated the in situ destruction rates of marine viral particles as well as the decay rates of infectivity for
viral isolates along an ~400‐km transect from oligotrophic offshore waters to productive coastal waters in the Gulf
of Mexico. Light‐mediated decay rates of viral infectivity averaged over the solar day ranged from 0.7 to 0.85 h−1 in surface waters at all stations and decreased with depth in proportion to the attenuation of UVB (305 nm). The destruction rates of viral particles also decreased with depth, although the rates of particle destruction were only 22–61% of infectivity when integrated over the mixed layer. The rates of viral particle destruction indicated that at three of four stations 6–12% of the daily bacterial production would have to be lysed in order to maintain ambient viral concentrations. At the fourth station, where there was a dense bloom of Synechococcus spp. and the mixed layer was shallower, 34–52% of the daily bacterial production would have to be lysed. A comparison of the difference between destruction rates of viral particles and infectivity integrated over the depth of the mixed layer implies that host‐mediated repair must have restored infectivity to 39–78% of the sunlight‐damaged viruses daily. The calculated frequency of contacts between viral particles and bacterial cells that resulted in infection (contact success) ranged from ~18 to 34% in offshore waters, where the frequency of contacts between viruses and bacteria was much lower, to ~1.0% at the most inshore station, where contact rates are much higher. This suggests that in offshore waters bacterial communities are less diverse, and that there is less selection to be resistant to viral infection. This paper provides a framework for balancing viral production, destruction, and light‐dependent repair in aquatic
viral communities.
Adaptive feeding behavior of Duphnia magna in response to short‐term starvation
Authors: Plath Klaus
Published: May 2010

Feeding behavior of Daphnia has been intensely studied, yet the generally observed behavior of maximal feeding
at low food concentrations contradicts the predictions of optimal foraging theory. To explore this inconsistency, 1
investigated the behavioral feeding response of Daphnia magna through direct observation of thoracic filtering
appendage beat rates at low food concentrations. I observed animals that were subjected to either varying starvation
periods or to different food concentrations prior to the experiments. Starvation led to a behaviorally mediated
decrease in appendage beat rate, which depended on the food concentration at which the daphnids were cultured.
Starved daphnids consistently showed an almost immediate increase in their appendage beat rate once food was
added, irrespective of the length of the starvation period (from 1 to 3 d). Therefore, the initial decrease in appendage
beat rate displayed by animals during starvation could not have been caused by the deprivation of energy (exhaustion)
alone. Furthermore, the food conditions under which the animals were cultured influenced the behavioral
response. After 1 h of starvation, animals cultured at high food level showed no behavioral response to the addition
of food, while animals cultured at low food level increased their appendage beat rate significantly. The results of
this study contradict the maximal feeding strategy and highlight problems of the optimal foraging strategy.
Excretory products of mobile epifauna as a nitrogen source for seaweeds
Authors: Taylor Richard , Rees T. Alwyn V.
Published: May 2010

The potential for excretory product of mobile epifauna to be source of nitrogen for seaweeds was investegated for the fucalean alga Carpophyllum plumosum var. capillifolium at Matheson Bay, northeastern New Zealand.The epifauna excreted an average of 1.5–2.1 times as much nitrogen as the plants were using. A comparison of rates at which the plants took up ammonium with turnover rates of water in the bed indicated that the plants could derive, on average, up to 79% of the nitrogen they required for growth from ammonium excreted by epifauna. This value was estimated under the assumption that ammonium excreted was instantaneously diluted into the water mass surrounding the entire bed. In nature, the availability of ammonium to the individual host seaweed should be greater owing to hydrological processes that restrict water flow around the plant.
Transparency of Antarctic ice‐covered lakes to solar UV radiation
Authors: Vincent Warwick F. , Rae Rowena , Laurion Isabelle , Howard‐Williams Clive , Priscu John C.
Published: May 2010

Depth profiles of solar ultraviolet radiation (UVR), photosynthetically available radiation (PAR), and related variables were measured beneath the thick, permanent ice cover of four lakes in the McMurdo Dry Valleys (77°S, 162°E). These lakes span a range of phytoplankton concentrations (0.1–10 μg Chl a liter−1) but receive little input of chromophoric dissolved organic matter (CDOM) from their barren, polar desert catchments. The diffuse attenuation coefficients for downwelling radiation (Kd) in the upper water column of the lakes were at or below those for clear natural waters elsewhere, with minimum values in Lake Vanda of 0.080 (305 nm), 0.055 (320 nm), 0.036 (340 nm), 0.023 (380 nm) and 0.034 (PAR) m−1. The attenuation lengths (l/Kd) for these lakes and for a set of high latitude lakes in the northern hemisphere (tundra and boreal forest catchments) showed a close log‐log relationship with dissolved organic carbon (DOC) concentrations (r2 ≥ 0.90; n = 20); dry valley lakes were at the high transparency end of this polar‐subpolar continuum. Phytoplankton exposure to UVR relative to PAR is known to rise steeply with decreasing DOC in the concentration range 2–4 g m−3; the addition of the dry valley lakes data shows the continuation of this upward, markedly nonlinear trend at lower DOC concentrations. Calculation of the biologically effective UVR dosage rate for the upper phytoplankton community of Lake Vanda indicated that sufficient UVR penetrates through the 3.5‐m‐thick lake ice to cause inhibition of algal growth. These results show that polar desert lakes are optical extremes in terms of their water‐column transparency to UVR, and that their dilute, mostly autochthonous CDOM offers little protection against the ultraviolet‐B radiation flux that is continuing to increase over the polar regions.
Seasonal variation in the regulation of phytoplankton by nitrogen and grazing in a salt‐smarsh estuary
Authors: Lewitus Alan J. , Koepfler Eric T. , Morris James T.
Published: May 2010

In North Inlet, a tidally dominated salt‐marsh estuary near Georgetown, South Carolina, the summer chlorophyll
maximum correlates with an annual peak in ambient NH4+ concentration. This relationship suggests that phytoplankton population growth during the summer bloom is limited by factors other than nutrient supply, because
NH4+ is the major inorganic nitrogen source available to phytoplankton in North Inlet, and phosphorus should not be limiting (N:P is generally ~7). We tested the hypothesis that phytoplankton population growth during the bloom
was controlled by grazing. Natural samples were incubated in treatments designed to differentiate between nutrient
and grazing effects, and time‐course changes in total phytoplankton biomass and phototrophic community composition
were followed. Marked seasonal differences were observed in the relative contribution of pica‐, nano‐, or
microplankton to phytoplankton community biomass, as well as the mechanisms controlling phytoplankton population
growth. During the summer bloom, phototrophic picoplankton (mostly Synechococcus spp.) and nanoplankton
(mostly flagellates) were relatively abundant, and phytoplankton population growth was unaffected by NH4+ addition, but was greatly stimulated by dilution that reduced microzooplankton grazing pressure. During the winter,
when diatoms dominated the phytoplankton, the response to dilution was relatively minor, while NH4+ addition
significantly stimulated the growth of various phytoplankton groups and total chlorophyll. The results indicate a
seasonal transition in microbial food‐web trophic structure and regulation in North Inlet estuary. During the summer,
microzooplankton grazing is an important factor regulating phytoplankton population growth during the nanoflagellate‐
prevalent bloom, whereas in the winter, a diatom‐dominated community is limited by nutrient supply.
Atmospheric exchange of carbon dioxide in a low‐wind oligotrophic lake measured by the addition of SF6
Authors: Cole Jonathan J. , Caraco Nina F.
Published: May 2010

Many freshwater lakes are supersaturated in CO2 with respect to the atmosphere. This concentration gradient implies a net flux of CO2 from the water to the air. The actual rate of gas exchange is governed by both this
concentration gradient and the gas transfer coefficient, k. To directly measure k, we added the chemically and
biologically inert gas, sulfur hexaflouride (SF6), to the epilimnion of Mirror Lake, New Hampshire, a small (15 ha),
low‐wind softwater lake. k was independent of wind speed over the 50‐d summer stratification period and averaged 2.65 ± 0.12 cm h−1 (95% CI; normalized to a Schmidt number of 600); k800, was better correlated to precipitation events than it was to wind speed. Our data support the idea that gas exchange across the air‐water interface is largely independent of wind at low wind speeds. The surface water of Mirror Lake was persistently supersaturated in CO, with respect to the atmosphere. During a 3.5‐‐year period the partial pressure of CO2 in the surface waters of the lake averaged 726 ± 39 µatm (95% CI) and showed substantial seasonal variation (360–2,000 patm). Diel and day‐to‐day variation in CO2 were very small compared to the CO2 pool. We combined our estimates of k with weekly measurements of the partial pressure of CO2 to estimate CO2 gas exchange in the lake. Mirror Lake released from 26 to 50 g C m−2 to the atmosphere each year, depending on the method of calculating k. Atmospheric CO2 exchange is a large term in the C economy of the lake—the most conservative gas flux estimate is about four times as large as outflow plus seepage of total dissolved inorganic carbon and 1.5 times as large as the export of dissolved organic C from the lake.
Selective predation by the mosshead sculpin Clinocottus globiceps on the sea anemone Anthopleura elegantissima and its two algal symbionts
Authors: Augustine Leon , Muller-Parker Giséle
Published: May 2010

The mosshead sculpin Clinocottus globiceps (Girard, 1857) feeds on the sea anemone Anthopleuru elegantissima that contains two different algal endosymbionts, zooxanthellae and zoochlorellae. During laboratory feeding experiments, the sculpin selectively fed on the tentacles of zooxanthellate anemones over those of zoochlorellate and algae‐free anemones. Zoochlorellae passed through the fish gut unharmed while zooxanthellae were degraded. The productivity of zooxanthellae in the fish feces (0.20 ± 0.13 pg C cell−1 h−1) was significantly lower (93% less) than that of zooxanthellae freshly isolated from anemones (3.14 ± 0.52 pg C cell−1 h−1), whereas the productivity of fecal zoochlorellae was the same as that of freshly isolated zoochlorellae (1.21 ± 0.15 pg C cell−1 h−1). The chlorophyll content (Chl a and c) of zooxanthellae was reduced by 50% after passage through the fish gut while the chlorophyll content of zoochlorellae (Chl a and b) did not change. Selective predation on zooxanthellate anemones confers several ecological advantages to zoochlorellate anemones and to zoochlorellae, most notably predator avoidance and dispersal of viable zoochlorellae that may serve as a source of symbionts for other anemones. By influencing the outcome of predator‐prey interactions involving their hosts, symbiotic algae may have broader ecological roles in benthic communities than previously described.
El Niño, ice cover, and Great Lakes phosphorus: Implications for climate warming
Authors: Nicholls K. H.
Published: May 2010

Phosphorus concentrations in a 19‐year record of the Lake Huron outflow (Laurentian Great Lakes of North America) were negatively correlated with the extent of Great Lakes winter ice cover. The highest phosphorus concentrations (2–3 times higher than normal) occured during 1983,1987, and 1992 in response to strong El Niño‐related moderation of winter air temperatures. The 1983 winter air temperature anomaly of +2.5°C (the mildest winter in the record) is well within the output of predicted temperature increaces by general circulation models for the Great Lakes basin under a 2× CO2 climate warming scenario. Lake data from strong El Niño years, when contrasted with other years having near‐normal winter temperatures and ice cover, can thus serve to identify some previously unanticipated impacts of global warming on lake water quality. I suggest that global warming may have important implications for eutrophication control in the Great Lakes.
Fecal pellets from a dense aggregation of suspension‐feeders in a stream: An example of ecosystem engineering
Authors: Wotton Roger S. , Malmqvist Björn , Muotka Timo , Larsson Kristina
Published: May 2010

Blackfly larvae (Diptera: Simuliidae) are “allogenie ecosystem engineers” that capture fine particulate and dissolved matter from suspension and egest much larger fecal pellets. We investigated the effects of blackfly larvae on organic matter transport at 25 sites along a small stream that flowed 500 m from a lake to the sea. Blackfly density was high upstream (>6 × 105 ind. m−2) and the numbers of fecal pellets in suspension rose markedly downstream from the blackfly aggregation. A total of 1.6 × 109 fecal pellets (biomass 3.2 kg C d−1) were discharged to the sea each day and 8.0 × 108 pellets (biomass 1.6 kg C d−1) were lost from suspension. Sedimenting pellets were available to the benthic microbial and invertebrate communities.
δ13C composition of primary producers and role of detritus in a freshwater coastal ecosystem
Authors: Keough Janet R. , Hagley Cynthia A. , Ruzycki Elaine , Sierszen Michael
Published: May 2010

Stable‐isotope ratio signatures of primary producers in a coastal wetland and in adjacent offshore waters of western Lake Superior indicated that phytoplankton are the primary source of carbon for the grazing food web of this ecosystem. This study outlines the possible roles of other autotrophs in this regard. Isotopic signatures of macrophytes reflected their life‐form‐associated constraints on diffusion of inorganic carbon. Data indicated that differences between wetland and lake phytoplankton may be explained by the isotopic signatures of their dissolved inorganic carbon (DIC) sources. Results of an in situ experiment showed that respiration associated with macrophyte decomposition is capable of enriching surrounding water with significant amounts of 13C‐depleted DIC and lowering the net δ13C ratio of DIC in water in lowturbulence situations. The δ13C ratio for wetland phytoplankton may be depleted relative to pelagic algae because the fixed carbon is derived from decomposing detritus.
The effects of ultraviolet‐B radiation on freshwater invertebrates: Experiments with asolar simulator
Authors: Hurtubise Robin D. , Havel John E. , Little Edward E.
Published: May 2010

There is concern that decreases in stratospheric ozone will lead to hazardous levels of ultraviolet‐B (UV‐B) radiation at the Earth's surface. In clear water, UV‐B may penetrate to significant depths. The purpose of the current study was to compare the sensitivity of freshwater invertebrates to UV‐B. We used a solar simulator, calibrated to match local ambient solar radiation, to expose five species of freshwater invertebrates to enhanced levels of UV‐B radiation. UV‐B measurements in a eutrophic pond revealed that 10% of the irradiance penetrated to 30‐cm depth and 1% to 57‐cm depth. The irradiance at the upper 5–20 cm was comparable to levels used in the simulator. Median lethal dose (LD50) values were determined for the cladocerans Ceriodaphnia reticulata, Scapholeberis kingii (two induced color morphs), and Daphnia magna; the ostracod Cyprinotus incongruens; and the amphipod Hyalella azteca. Among the species, 96‐h LD50 estimates were quite variable, ranging from 4.2 to 84.0 µW cm−2. These estimates indicated S. kingii to be highly sensitive and H. azteca, C. reticulata, and D. magna to be moderately sensitive, whereas the ostracod C. incongruens was very tolerant to UV‐B radiation. Overall, this study suggests that, in shallow ponds without physical refuges, UV‐B radiation would have the strongest effects upon cladocerans and amphipods occurring in the water column, whereas ostracods would be better protected.
Development of a subsurface chlorophyll maximum at the entrance to the Gulf of Finland, Baltic Sea
Authors: Kononen Kaisa , Hällfors Seija , Kokkonen Marjaana , Kuosa Harri , Laanemets Jaan , Pavelson Juss , Autio Riitta
Published: May 2010

Horizontal, vertical, and temporal variability of chlorophyll a (Chl a), stratification, currents, and pelagial biology (phytoplankton, size‐fractionated primary productivity and Chl a, ciliates, picocyanobacteria, bacterial production) were followed at the entrance to the Gulf of Finland during a 12‐day cast study in July–August 1994. The study was carried out during weak wind conditions when hydrodynamic activity was minimal and when an intense blooming of diazotrophic cyanobacteria Aphanizomenon flos‐aquae (Linné) Ralfs, Anabaena lemmermannii Richter, and Noduluria spumigena Mertens was in its decaying phase. The property conservation equation was used to differentiate the contributions of physical and biological processes to the local Chl a changes in the layer above the thermocline. Subtraction of the Chl a change due to physical processes, mainly advection, gave a biologically induced mean decrease of 0.18 mg Chl a m−3 d−1. Sampling data confirmed the calculated decrease and revealed the basin‐wide character of the phenomenon. The observed plankton dynamics showed that the pelagial system was “top‐down” controlled and that about half the decrease of Chl a was due to a size‐specific grazing of ciliates on the dominating flagellates Chrysochromulina spp. 2–5 µm and Ochromonas spp. 7–8 µm in the upper layer. The grazers were confined to the layer above the thermocline, while the flagellates inhabited both the thermocline and the layer above. This led to the formation of a subsurface Chl a maximum in the thermocline.
Resource competition in a discrete environment: Why are plankton distributions paradoxical?
Authors: Siegel David A.
Published: May 2010

For nearly all natural waters, planktonic organisms will be distributed discretely in the fluid mechanical sense. This means that the dynamics of planktonic ecosystems occur among discrete particles, not continuous scalar fields. This idea was first suggested by Hurlburt (1990) as an explanation for the paradox of the plankton. However, the discrete nature of organism distributions has many important implications for the interpretation and modeling of planktonic ecosystems. In particular, mass conservation relationship approaches to the modeling of planktonic populations (i.e., resource competititon and its result, competitive exclusion) will not be valid for all natural conditions. A microscale model of competition among individual phytoplankton cells was used to investigate the role of discreteness on phytoplankton competitition for a single, limiting nutrient substrate. This scaling analysis demonstrates that rates of competitition should increase with cellular abundance and phytoplankton size. For a typical eutrophic planktonic ecosystem (relatively large cell abundances and cell sizes), resource competitition among individual phytoplankters appears to be likely. However, for oligotrophic conditions (low cell abundances and small cells), rates of competitive displacement should be greatly reduced. The microscale competition model does not predict that the final outcome of competition will differ from resource competition theory when evaluated over thousands of division cycles. However the time required for this outcome to occur may be so long that other processes, such as episodic nutrient inputs, imposed diel cycles, and specialization of the grazer assemblage, are likely to have a dominant role in determining the species composition of an oligotrophic phytoplankton community. This seeming violation of the principle of competitive exclusion occurs because nutrient competition in oligotrophic environments is governed by interactions among discrete individuals rather than entire populations. Discreteness in plankton distributions also creates an ecological subgrid scale (SGS) problem that must be solved as part of most mathematical descriptions of plankton population dynamics. Approaches towards solution of the ecological SGS problem are suggested; however, a great deal of theoretical and experimental work remains.
Measurement of solar‐stimulated fluorescence in natural waters
Authors: Hu Chuanmin , Voss Kenneth J.
Published: May 2010

The oceanic Fraunhofer line discriminator (OFLD), designed to measure the solar ‐stimulated inelastic scattering in the ocean, has been deployed in various types of water in Florida Bay and the Dry Tortugas to measure Fraunhofer lines and oxygen‐absorption lines near 689 nm in the solar spectrum. The line‐filling principle and previous work enable us to partition the measured light into elastic, Raman scattering, and fluorescence components. We show that in optically deep, oligotrophic water, where chlorophyll a (Chl a) concentration is as low as 0.1 mg m−3, fluorescence near 689 nm was still measurable by the OFLD. In moderately eutrophic shallow waters, where Chl a concentration ranges from 0.2 to 0.8 mg m−3, the fluorescence from either Chl a or dissolved organic matter in the water column was found to be a negligible component of the total light field due to the additional light reflected from the bottom. We also include measurements of the solar ‐stimulated fluorescence for benthic surfaces, such as brain coral, and have found these to be saturated under normal solar illumination.