Pulse Events Research Articles

Analysis of single-walled carbon nanotubes using spICP-MS with microsecond dwell time

Although catalytic metal nanoparticle (NP) impurities in carbon nanotube (CNT) structures are undesirable in a manufacturing context, they can be used as proxies to detect CNTs by single particle inductively coupled plasma–mass spectrometry (spICP-MS). The use of 100μs dwell times, a recent advancement for spICP-MS, increases resolution between pulse events and reduces background signal, improving the detection of low metal-content CNTs. Serial filtration supports the assertion that metal NPs, containing yttrium in this study, are primarily incorporated in CNT structures and remain bound to the tubes throughout analysis. Analysis of both acid-digested and suspended CNTs confirmed that CNTs are fully ablated in the plasma and that all residual metals are ionized. This result, combined with good agreement with UV–Vis spectroscopy analysis, indicates that spICP-MS can provide quantitative CNT mass analysis. Though Nanoparticle Tracking Analysis (NTA) was less accurate than spICP-MS when counting Au-PVP NPs, it gave higher particle number concentrations than spICP-MS for CNTs. The likely undercounting of CNTs by sp-ICPMS is ascribed to the heterogeneous distribution of yttrium NPs among CNTs, and the small diameter of many yttrium NPs (~15nm), nearing their detection limit. Despite this limitation, its sensitivity and elemental specificity make spICP-MS a powerful nanometrology method for environmental exposure assessment of CNTs. To illustrate this capability, CNT association with Daphnia magna was measured at μg/L CNT concentrations. After 48hours of exposure to a CNT suspension, 3.48±0.32% of CNTs were taken up by D. magna adults. This simple and direct application of spICP-MS to detect CNTs in organisms can be applied to toxicological investigations to help understand potential bioaccumulation of CNTs in aquatic ecosystems.

Spatial Autocorrelation and its Relationships with Community Dynamics, Soil and Site quality factors: A study from Arid desert with Different Magnitudes of Resource Pulses

Spatial autocorrelation (SAc) is a useful descriptor for horizontal assemblage of plant. Most of the spatial autocorrelation studies have focused on the measurement of spatial dependency, however majority of them did not addressed the three major attributes, a. how spatial autocorrelation changes with different temporal events, b. how the spatial autocorrelation information can be use to predict other community variables and c. what are the underlying factors associated with patterns of autocorrelation. Objectives of the present study encompasses temporal changes in spatial autocorrelation under different pulse events (pulse, rain; inter-pulse, winter; and non-pulse, summer) in arid plant communities and factors associated with spatial autocorrelation. During different temporal events both Moran's I and Geary's C indices showed positive and significant spatial autocorrelation however, the strength of autocorrelation was subsequently decreased from pulse to nonpulse events. Regression analysis revealed that community, soil and site quality factors influenced the patterns and strength of spatial autocorrelation. Among the soil factors, organic carbon, electric conductivity and the available phosphorus were identified as the significant controlling factors for SAc. Community indices like diversity, richness, evenness, dominance and Community Maturity Index were also associated with spatial autocorrelation. Within such specific set of environmental heterogeneity (arid region), species richness form 6 to 9 were identified as threshold limit for positive autocorrelation. Among site quality parameters percent bare surface area and species composition of climax species can be use as predictor's for changes in spatial autocorrelation specifically in arid region.

Reduced salinity increases susceptibility of zooxanthellate jellyfish to herbicide toxicity during a simulated rainfall event

Accurately predicting how marine biota are likely to respond to changing ocean conditions requires accurate simulation of interacting stressors, exposure regimes and recovery periods. Jellyfish populations have increased in some parts of the world and, despite few direct empirical tests, are hypothesised to be increasing because they are robust to a range of environmental stressors. Here, we investigated the effects of contaminated runoff on a zooxanthellate jellyfish by exposing juvenile Cassiopea sp. medusae to a photosystem II (PSII) herbicide, atrazine and reduced salinity conditions that occur following rainfall. Four levels of atrazine (0ngL−1, 10ngL−1, 2μgL−1, 20μgL−1) and three levels of salinity (35 ppt, 25 ppt, 17 ppt) were varied, mimicking the timeline of light, moderate and heavy rainfall events. Normal conditions were then slowly re-established over four days to mimic the recovery of the ecosystem post-rain and the experiment continued for a further 7 days to observe potential recovery of the medusae. Pulse-amplitude modulated (PAM) chlorophyll fluorescence, growth and bell contraction rates of medusae were measured. Medusae exposed to the combination of high atrazine and lowest salinity died. After 3 days of exposure, bell contraction rates were reduced by 88% and medusae were 16% smaller in the lowest salinity treatments. By Day 5 of the experiment, all medusae that survived the initial pulse event began to recover quickly. Although atrazine decreased YII under normal salinity conditions, YII was further reduced when medusae were exposed to both low salinity and atrazine simultaneously. Atrazine breakdown products were more concentrated in jellyfish tissues than atrazine at the end of the experiment, suggesting that although bioaccumulation occurred, atrazine was metabolised. Our results suggest that reduced salinity may increase the susceptibility of medusae to herbicide exposure during heavy rainfall events.

Patterns of herbaceous species richness and productivity along gradients of soil moisture and nutrients in the Indian Thar Desert

For the temperate vegetation community, herbaceous biomass and species richness relationship has been eminent as a humpback response hypothesis. This appraised higher level of herbaceous richness at an intermediate level of biomass. However, no such study has been made in the sultry parched ecosystem. Hence, in the present study this kinship have been explored in the Indian hot, arid desert using three distinct seasonal events. Different community and soil parameters were quantified during different pulse events by following the touchstone methods. Based on dominant herbs, selected grazing lands were categorized under sub-climax stage, where 30, 24 and 18 species were recorded during pulse (rain), inter-pulse (winter) and non-pulse (summer) events, respectively. ANOVA analysis blabs significant variations in herbaceous biomass and in different soil components that brought by events, sites as well as by their interactions. Kaiser-Meyer-Olkin test and Bartlett test of spehericity proves the worthiness of factorial analysis used in this study. Result substantiates that unimodal relationship between herbaceous richness and biomass hold true in the Indian arid Thar Desert. Herbaceous biomass ranging from 101.77 to 123.5 gm−2 supports the maximum herbaceous richness with combination of different pulse events. Relationships of soil components and grazing intensity with richness and biomass were illustrated.

Combination effects of pyrethroids and neonicotinoids on development and survival of Chironomus riparius

Standard ecotoxicological risk assessments are conducted on individual substances, however monitoring of streams in agricultural areas has shown that pesticides are rarely present alone. In fact, brief but intense pulse events such as storm water runoff and spray drift during application subject freshwater environments to complex mixtures of pesticides at high concentrations. This study investigates the potential risks to non-target aquatic organisms exposed to a brief but intense mixture of the neonicotinoid pesticides imidacloprid and thiacloprid and the pyrethroid pesticides deltamethrin and esfenvalerate, compared to single substance exposure. All four of these pesticides have been detected in surface waters at concentrations higher than benchmark values and both classes of pesticides are known to exert adverse effects on non-target aquatic organisms under single substance exposure scenarios. First instar midge larvae of the non-target aquatic organism, Chironomus riparius, were exposed to combinations of these four pesticides at 50% of their LC50 (96h) values in a 1h pulse. They were then reared to adulthood in uncontaminated conditions and assessed for survival, development time and fecundity. Our results show that the risk of disruption to survival and development of non-target aquatic organisms under this scenario is not negligible on account of the significant increases in mortality of C. riparius found in the majority of the pesticide exposures and the delays in development after pyrethroid exposure. While none of the deleterious effects appear to be amplified by combination of the pesticides, there is some evidence for antagonism. No effects on fecundity by any of the pesticide treatments were observed.

Turbulence effects on broadband pulses propagating near the ground

Broadband sound pulses (such as from gunfire and explosions) distort randomly as they propagate through atmospheric turbulence. Recently, a general theory was formulated to describe the statistical moments, including the mean and space-time coherence, of such signals propagating along line-of-sight paths (Ostashev et al., J. Acoust. Soc. Am. 136(5), 2414–2431 (2014)). This presentation focuses on some practical issues related to the physical interpretation of the theoretical predictions for the moments, such as what the theory predicts for pulse signals and turbulence regimes of typical interest, and how the behavior of individual pulse events is reflected in the averages that can be compared directly to the theory. In particular, we examine the conditions when the scattering is dominated by pulse wander (variations in arrival time) and when is it dominated by pulse spread (broadening of the energy in the impulse). Conversion of real-valued signals to analytic signals, and the averaging of these represent...

Determination of equilibrium electron temperature and times using an electron swarm model with BOLSIG+ calculated collision frequencies and rate coefficients

AbstractElectromagnetic pulse (EMP) events produce low‐energy conduction electrons from Compton electron or photoelectron ionizations with air. It is important to understand how conduction electrons interact with air in order to accurately predict EMP evolution and propagation. An electron swarm model can be used to monitor the time evolution of conduction electrons in an environment characterized by electric field and pressure. Here a swarm model is developed that is based on the coupled ordinary differential equations (ODEs) described by Higgins et al. (1973), hereinafter HLO. The ODEs characterize the swarm electric field, electron temperature, electron number density, and drift velocity. Important swarm parameters, the momentum transfer collision frequency, energy transfer collision frequency, and ionization rate, are calculated and compared to the previously reported fitted functions given in HLO. These swarm parameters are found using BOLSIG+, a two term Boltzmann solver developed by Hagelaar and Pitchford (2005), which utilizes updated cross sections from the LXcat website created by Pancheshnyi et al. (2012). We validate the swarm model by comparing to experimental effective ionization coefficient data in Dutton (1975) and drift velocity data in Ruiz‐Vargas et al. (2010). In addition, we report on electron equilibrium temperatures and times for a uniform electric field of 1 StatV/cm for atmospheric heights from 0 to 40 km. It is shown that the equilibrium temperature and time are sensitive to the modifications in the collision frequencies and ionization rate based on the updated electron interaction cross sections.

Wetting and Drying Variability of the Shallow Subsurface Beneath a Snowpack in California's Southern Sierra Nevada

In recent years, regions such as the western United States have been projected to have drastically changing snow and soil moisture conditions in mountainous regions. The importance of subsurface flow during snowmelt for groundwater recharge and streamflow has long been known. This study was conducted to investigate the variability of soil wetting and drying dynamics within a network of soil moisture sensors beneath a seasonally persistent snowpack in California's southern Sierra Nevada. Data were analyzed to quantify the persistence of soil moisture, the rate of change in soil moisture, and vertical gradients of soil moisture during the 2009, 2010, and 2011 water years at varying elevations (1750–2000 m), aspects (north, south, and flat), and canopy conditions (open, drip edge, and under canopy). Results from this study demonstrated snowmelt water moving through a wetted shallow region of the soil in most locations, while other locations displayed drier conditions in the top layers of soil and higher rates of soil moisture change deeper within the soil. This occurred at various depths within the top 1 m of soil, displaying high variability across the catchment and under different canopy conditions. More than 1400 pulse events above a rate of change in water content of 0.06 cm cm−1 d−1 were observed, with many >0.10 cm cm−1 d−1. Average numbers of pulse events per year ranged from 1 to 18, with a median of 4.3 for all sensors. The lower elevation sensors averaged 6.0 wetting events per year reaching at least 60‐cm depth and the upper sensors averaged 4.7, with standard deviations among elevation and aspect clusters ranging from 2.5 to 3.0 for upper elevation sites and 2.9 to 3.2 for lower elevation sites. This demonstrates the high variability of the wetting and drying dynamics of the top 1 m of soil at the sub‐hillslope scale. These results have implications for groundwater recharge, plant production, and streamflow response in a changing climate.

Seasonal differences and response to a tropical storm reflected in diatom assemblage changes in a southwest Florida watershed

Because estuaries are dynamic on many temporal scales, it is difficult to differentiate long-term shifts from those resulting from erratic pulse events like severe storms. Diatoms are abundant and diverse in estuaries, and may characterize these dynamics across relevant time scales. The climate of south Florida is subtropical, with dry winters and wet summers that may also harbor tropical storms and cyclones. We investigated whether these repeated seasonal drivers of change in estuaries differ from the influence of tropical cyclones on planktonic and benthic diatom assemblages. Diatom assemblages and environmental parameters were measured in the Charlotte Harbor watershed of southwest Florida to identify differences between the wet and dry seasons and changes that occurred following Tropical Storm Debby in 2012. Indicator taxa that were significantly affiliated with each season and post-storm conditions were identified. Diatom assemblages across the watershed were similar in wet and dry seasons, but differences increased following the tropical storm. The reduction in community dispersion following the storm was pronounced in each of the major drainages of the estuary. There were spatially-distinct responses of diatoms to environmental changes driven by the storm. These results suggest that past storm activity could be detected using diatoms preserved in estuarine sediments using both single indicator-species as well as community approaches.

Transforming the ASDEX Upgrade discharge control system to a general-purpose plasma control platform

The ASDEX Upgrade Discharge Control System DCS is a modern and mature product, originally designed to regulate and supervise ASDEX Upgrade Tokamak plasma operation. In its core DCS is based on a generic, versatile real-time software framework with a plugin architecture that allows to easily combine, modify and extend control function modules in order to tailor the system to required features and let it continuously evolve with the progress of an experimental fusion device. Due to these properties other fusion experiments like the WEST project have expressed interest in adopting DCS.For this purpose, essential parts of DCS must be unpinned from the ASDEX Upgrade environment by exposure or introduction of generalised interfaces. Re-organisation of DCS modules allows distinguishing between intrinsic framework core functions and device-specific applications. In particular, DCS must be prepared for deployment in different system environments with their own realisations for user interface, pulse schedule preparation, parameter server, time and event distribution, diagnostic and actuator systems, network communication and data archiving.The article explains the principles of the revised DCS structure, derives the necessary interface definitions and describes major steps to achieve the separation between general-purpose framework and fusion device specific components.

Assessment of stand types for phosphorus acquisition and internal utilization efficiency in a desert plant Blepharis sindica (T. Andres.)

Impact of stand types (monoculture and polyculture) on phosphorus acquisition efficiency and their subsequent internal utilization efficiency were determined at species level, in a seratonious arid endangered plant, Blepharis sindica. At pure stand phosphorus acquisition efficiency (PAE) was recorded higher during pulse event (rain) while at mixed stand it was recorded more during non-pulse event (summer). This indicates that at pure stand this species rapidly full-fill their P demand during high soil P availability (pulse event), but at mixed stand due to presence of other life forms this species have adjusted their P acquisition efficiency during non-pulse (low soil P), when other associate probably not able to do this. Ordination analysis shows lack of correlation between PAE and PUTIL, indicates that selection of one of these should not affect the other. Regression analysis between P variables and community factors revealed that at species level dominance of B. sindica reflects with its higher P acquisition efficiency; however as the community diversity (Richness, Shannon and Weaver index and evenness) increases the P internal utilization and PUE were inhibited. Thus it can be concluded that both P internal utilization and PUE of B. sindica are largely influenced with temporal factors (Increase and decrease of community diversity during pulse and non-pulse events, respectively). This plant achieved their effective nutrient use through temporal partitioning, through which it full-fill their P requirements during low resource availability (non-pulse event). Both soil organic carbon and carbon to nitrogen ratio supports PAE in linear fashions. Similarly soil pH also monotonically supports PAE, while soil organic carbon monotonically inhibits QUTIL. The greater nutrient uptake and uptake efficiency in a pure stand reflects narrow niche width of B. sindica and hence it can be conclude that the impact of life-form diversity on nutrient use efficiency is not a static phenomenon.

A succession of theories: purging redundancy from disturbance theory.

The topics of succession and post-disturbance ecosystem recovery have a long and convoluted history. There is extensive redundancy within this body of theory, which has resulted in confusion, and the links among theories have not been adequately drawn. This review aims to distil the unique ideas from the array of theory related to ecosystem change in response to disturbance. This will help to reduce redundancy, and improve communication and understanding between researchers. We first outline the broad range of concepts that have developed over the past century to describe community change in response to disturbance. The body of work spans overlapping succession concepts presented by Clements in 1916, Egler in 1954, and Connell and Slatyer in 1977. Other theories describing community change include state and transition models, biological legacy theory, and the application of functional traits to predict responses to disturbance. Second, we identify areas of overlap of these theories, in addition to highlighting the conceptual and taxonomic limitations of each. In aligning each of these theories with one another, the limited scope and relative inflexibility of some theories becomes apparent, and redundancy becomes explicit. We identify a set of unique concepts to describe the range of mechanisms driving ecosystem responses to disturbance. We present a schematic model of our proposed synthesis which brings together the range of unique mechanisms that were identified in our review. The model describes five main mechanisms of transition away from a post-disturbance community: (i) pulse events with rapid state shifts; (ii) stochastic community drift; (iii) facilitation; (iv) competition; and (v) the influence of the initial composition of a post-disturbance community. In addition, stabilising processes such as biological legacies, inhibition or continuing disturbance may prevent a transition between community types. Integrating these six mechanisms with the functional trait approach is likely to improve the predictive capacity of disturbance theory. Finally, we complement our discussion of theory with a case study which emphasises that many post-disturbance theories apply simultaneously to the same ecosystem. Using the well-studied mountain ash (Eucalyptus regnans) forests of south-eastern Australia, we illustrate phenomena that align with six of the theories described in our model of rationalised disturbance theory. We encourage further work to improve our schematic model, increase coverage of disturbance-related theory, and to show how the model may link to, or integrate with, other domains of ecological theory.

N<sub>2</sub>O, NO, N<sub>2</sub> and CO<sub>2</sub> emissions from tropical savanna and grassland of northern Australia: an incubation experiment with intact soil cores

Abstract. Strong seasonal variability of hygric and thermal soil conditions are a defining environmental feature in northern Australia. However, how such changes affect the soil–atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still not well explored. By incubating intact soil cores from four sites (three savanna, one pasture) under controlled soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emissions were very low (<7.0 ± 5.0 μg NO-N m−2 h−1; <0.0 ± 1.4 μg N2O-N m−2 h−1) or in the case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μg N m−2 h−1) and relatively small N2O pulse emissions (max: 5.8 ± 5.0 μg N m−2 h−1) were recorded following soil wetting, but these pulses were short lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was generally dominated by N2 emissions (82.4–99.3% of total N lost), although NO emissions contributed almost 43.2% to the total atmospheric nitrogen loss at 50% SM and 30 °C ST incubation settings (the contribution of N2 at these soil conditions was only 53.2%). N2O emissions were systematically higher for 3 of 12 sample locations, which indicates substantial spatial variability at site level, but on average soils acted as weak N2O sources or even sinks. By using a conservative upscale approach we estimate total annual emissions from savanna soils to average 0.12 kg N ha−1 yr−1 (N2O), 0.68 kg N ha−1 yr−1 (NO) and 6.65 kg N ha−1 yr−1 (N2). The analysis of long-term SM and ST records makes it clear that extreme soil saturation that can lead to high N2O and N2 emissions only occurs a few days per year and thus has little impact on the annual total. The potential contribution of nitrogen released due to pulse events compared to the total annual emissions was found to be of importance for NO emissions (contribution to total: 5–22%), but not for N2O emissions. Our results indicate that the total gaseous release of nitrogen from these soils is low and clearly dominated by loss in the form of inert nitrogen. Effects of seasonally varying soil temperature and moisture were detected, but were found to be low due to the small amounts of available nitrogen in the soils (total nitrogen <0.1%).

Acoustic behaviors in Hawaiian coral reef fish communities

Coral reef fish communities often include hundreds of sympatric species which are of great inter- est to reef conservation and fisheries managers. Long- term acoustic monitoring of fish sounds can be used to infer periodic reproductive activity and changes in pop- ulation abundance. However, limited records of sound production by coral reef species have precluded the ap- plication of acoustic monitoring at the population or community levels. We used rebreather and digital acoustic/ video techniques to produce a sound library for fishes on coral reefs of west Hawai'i Island, HI, USA. We documented 85 sounds produced by 45 (47%) of the 96 resident species that were associated with agonistic interactions and resource defense, reproduction, nest defense, feeding, and vigilance behaviors. Most non- feeding sounds consisted of single or trains of pulse events <100 ms long that were distributed across a spectrum of <100 to 1000 Hz with the majority of peak frequencies between 100 and 300 Hz. Agonistic sounds created during competitive interactions over food, space, or nest brood resources were identified for dam- selfishes, surgeonfishes, butterflyfishes, and trigger- fishes, among others. Reproductive sounds associated with courtship, spawning, or nest defense were pro- duced by damselfishes, goatfishes, butterflyfishes, par- rotfishes, and surgeonfishes, as well as wrasses and Moorish idols. The distinct adventitious feeding sounds recorded for some parrotfishes and triggerfishes oc- curred in a higher frequency band (2�6 kHz) and may be useful indicators of feeding activity and rates of reef bioerosion. This is the first study to characterize the spe- cies-specific behavior soundscape that can be applied to acoustic monitoring of a coral reef fish community.

Climate change and climatic events: community-, functional- and species-level responses of bryophytes and lichens to constant, stepwise, and pulse experimental warming in an alpine tundra

We experimentally imposed three different kinds of warming scenarios over 3 years on an alpine meadow community to identify the differential effects of climate warming and extreme climatic events on the abundance and biomass of bryophytes and lichens. Treatments consisted of (a) a constant level of warming with open top chambers (an average temperature increase of 1.87 °C), (b) a yearly stepwise increase of warming (average temperature increases of 1.0; 1.87 and 3.54 °C, consecutively), and (c) a pulse warming, i.e., a single first year pulse event of warming (average temperature increase of 3.54 °C only during the first year). To our knowledge, this is the first climate change study that attempts to distinguish between the effects of constant, stepwise and pulse warming on bryophyte and lichen communities. We hypothesised that pulse warming would have a significant short-term effect compared to the other warming treatments, and that stepwise warming would have a significant mid-term effect compared to the other warming treatments. Acrocarpous bryophytes as a group increased in abundance and biomass to the short-term effect of pulse warming. We found no significant effects of mid-term (third-year) stepwise warming. However, one pleurocarpous bryophyte species, Tomentypnum nitens, generally increased in abundance during the warm year 1997 but decreased in control plots and in response to the stepwise warming treatment. Three years of experimental warming (all treatments as a group) did have a significant impact at the community level, yet changes in abundance did not translate into significant changes in the dominance hierarchies at the functional level (for acrocarpous bryophytes, pleurocarpous bryophytes, Sphagnum or lichens), or in significant changes in other bryophyte or lichen species. The results suggest that bryophytes and lichens, both at the functional group and species level, to a large extent are resistant to the different climate change warming simulations that were applied.

The effect of seasonality on the structure of rotifers in a black-water shallow lake in Central Amazonia.

Rotifers have often been used as indicators of sudden changes in physical and chemical features of the aquatic environment. Such features vary greatly during flood pulse events in small lakes connected to major floodplains. However, few are the studies that investigate the consequences of the flood pulse in rotifer species composition, abundance, richness and diversity, especially in Amazonian lakes. We analyzed samples from a small blackwater lake of an "igarapé" connected permanently to the Negro river, in Central Amazonia. Samples were taken twice a year for two years, comprising flooding and receding periods of the flood pulse. Rotifer abundance increased significantly after draught events, and electrical conductivity and turbidity were intrinsically related to such variation. Species composition also changed from flooding to receding periods. Some taxa, such as Brachionus zahniseri reductus and Lecane remanei were restricted to receding periods, while Brachionus zahniseri, Brachionus gillardi and Lecane proiecta were only present during flooding. A shift in the composition of rotifer families was observed from one period to another, showing the effect of renewing waters of the flood pulse. These results suggest that the flood pulse acts as a driving force and stressing condition, considerably altering rotifer community dynamics, either changing species composition or decreasing abundance.

Onset of the spring bloom in the northwestern Mediterranean Sea: influence of environmental pulse events on the in situ hourly-scale dynamics of the phytoplankton community structure.

Most of phytoplankton influence is barely understood at the sub meso scale and daily scale because of the lack of means to simultaneously assess phytoplankton functionality, dynamics and community structure. For a few years now, it has been possible to address this objective with an automated in situ high frequency sampling strategy. In order to study the influence of environmental short-term events (nutrients, wind speed, precipitation, solar radiation, temperature, and salinity) on the onset of the phytoplankton bloom in the oligotrophic Bay of Villefranche-sur-Mer (NW Mediterranean Sea), a fully remotely controlled automated flow cytometer (CytoSense) was deployed on a solar-powered platform (EOL buoy, CNRS-Mobilis). The CytoSense carried out single-cell analyses on particles (1–800 μm in width, up to several mm in length), recording optical pulse shapes when analyzing several cm3. Samples were taken every 2 h in the surface waters during 2 months. Up to 6 phytoplankton clusters were resolved based on their optical properties (PicoFLO, Picoeukaryotes, Nanophytoplankton, Microphytoplankton, HighSWS, HighFLO). Three main abundance pulses involving the 6 phytoplankton groups monitored indicated that the spring bloom not only depends on light and water column stability, but also on short-term events such as wind events and precipitation followed by nutrient pulses. Wind and precipitation were also determinant in the collapse of the clusters' abundances. These events occurred within a couple of days, and phytoplankton abundance reacted within days. The third abundance pulse could be considered as the spring bloom commonly observed in the area. The high frequency data-set made it possible to study the phytoplankton cell cycle based on daily cycles of forward scatter and abundance. The combination of daily cell cycle, abundance trends and environmental pulses will open the way to the study of phytoplankton short-term reactivity to environmental conditions.

SPECIES LEVEL PHOSPHORUS ACQUISITI ON AND INTERNAL UTILIZATION EFFICIENCY AND THEIR RELATION WITH BOTTOM - UP AND TOP - DOWN FACTORS

Ecosystem level nutrient use efficiency (NUE) generally increases with the richness of species or life forms in a community, though, discrepancies may exist at species level. Existence of such discrepancies, phosphorus acquisition efficiency (PAE), phosphorus internal utilization efficiency (PUTIL), phosphorus use efficiency (PUE), quotient of phosphorus utilization (QUTIL) and phosphorus harvest index (PHI) were assessed at species (Corchorus depressus) level with various spatial and temporal factors within the arid area of the Thar Desert, India. These P variables were ordinate and regressed with various bottom up (species richness, relative importance of C. depressus, Shannon and Wiener index, Simpson index, evenness, seed output, percent cover of C. depressus, root length and root collar diameter) and with top down factors (soil organic carbon, nitrogen, moisture, pH and electric conductivity). The relative importance of PAE and PUTIL in the PUE as well as the QUTIL and PHI in the PUTIL were also assessed. ANOVA analysis revealed that all the factors undertaken in the present study (i.e. spatial and temporal events and their interaction) brought significant variation (P<0.001) in PAE, PUTIL, PUE and QUTIL. However, for PHI spatial and temporal events individually brought significant variations, their interaction was non-significant. It emerged that for PUE at low P environmental conditions, PAE was 10-37 times more important than PUTIL. Similarly for PUTIL, QUTIL was 17-56 times more important than PHI. Kaiser-Meyer-Olkin test (0.597) and Bartlett's test of sphericity indicated appropriate use of factor analysis (PCA) and significant correlation between variables in the present study, respectively. Ordination analysis showed lack of correlation between PAE and PUTIL, indicating that selection of one of these should not affect the other. Percent cover of plant, seed output, root length and root collar diameter exhibit various relationships with different P variables. Regression analysis between P variables and community factors revealed that at species level dominance of C. depressus reflects its higher P acquisition efficiency; however as the community diversity (richness, Shannon and Wiener index and evenness) increases the P internal utilization and PUE were inhibited. It can be concluded that P internal utilization and PUE of C. depressus are largely influenced by temporal factors (increase and decrease of community diversity during pulse and non-pulse events, respectively). As a result this species achieved effective nutrient use through temporal partitioning, through which it fulfilled P requirements during low resource availability. Among the soil variables soil nitrogen supported PUTIL, PUE and QUTIL, while soil moisture and soil pH favoured PHI and soil N and PHI showed

‘New conservation’ or surrender to development?

Ecologists have concluded that diversity per se in ecosystems is important to ecosystem function and ecological services. Meta-analyses of several hundred investigations showed that a loss of diversity negatively affected ecosystem function (Balvanera et al., 2006; Cardinale et al., 2006, 2011; Tilman, 2012). Specifically, research showed that loss of species diversity decreased productivity, resilience, nutrient cycling, drought tolerance, options for water management, resistance to pests and efficiency of ecosystems while increasing chances of catastrophic disease (Keesing et al., 2010; Tilman, 2012; Washington, 2013). Yet, the planet’s biodiversity is affected by explosions in human population, advancing technology and increasing per capita consumption (Wilson, 2002). Lately, some propose that the future of conservation lies in managing nature for human benefit (Kareiva & Marvier, 2007; Kareiva et al., 2007; Nordhaus & Shellenberger, 2007; Marris, 2011; Kareiva, Lalasz & Marvier, 2012a; Duncan, 2013). Directing conservation action for human benefit is nothing new. It recycles the ideas of Gifford Pinchot, maximum sustainable yield and the Brundtland Commission. Here, we critique some recent assumptions in the various forms of this ideology (hereafter, ideology), many of which use human exceptionalism as a justification: (1) nature is a warehouse for human use; (2) humans can construct new ecosystems from non-native species; (3) humans do not have to live within limits; (4) nature is resilient; (5) nature is a social construct; (6) conservationists preach too much doom and gloom; (7) people can manage nature intensively while preserving biodiversity.

RELICS OF ANCIENT POST-AGB STARS IN A PRIMITIVE METEORITE

Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low $^{12}$C/$^{13}$C isotopic ratios in these grains are a result of abundant $^{12}$C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of $\sim 10^{15}$ cm$^{-3}$, typical of the $i$-process, are achieved during this phase in post-AGB stars. The large $^{42,43,44}$Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from $^{46,48}$Ca, which cannot be resolved from the isobars $^{46,48}$Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a very late thermal pulse.