1,457 research outputs found
Increasing Microcystis cell density enhances microcystin synthesis: a mesocosm study
An experimental protocol using mesocosms was established to study the effect of Microcystis sp. cell abundance on microcystin production. The mesocosms (55 L) were set up in a shallow eutrophic lake and received either no (control), low (to simulate a moderate surface accumulation), or high (to simulate a dense surface scum) concentrations of Microcystis sp. cells collected from the lake water adjacent to the mesocosms. In the low- and high-cell addition mesocosms (2 replicates of each), the initial addition of Microcystis sp. cells doubled the starting cell abundance from 500 000 to 1 000 000 cells mL⁻¹, but there was no detectable effect on microcystin quotas. Two further cell additions were made to the high-cell addition mesocosms after 60 and 120 min, increasing densities to 2 900 000 and 7 000 000 cells mL-1, respectively. Both additions resulted in marked increases in microcystin quotas from 0.1 pg cell-1 to 0.60 and 1.38 pg cell⁻¹, respectively, over the 240 min period. Extracellular microcystins accounted for <12% of the total microcystin load throughout the whole experiment. The results of this study indicate a relationship between Microcystis cell abundance and/or mutually correlated environmental parameters and microcystin synthesis
Hindcasting cyanobacterial communities in Lake Okaro with germination experiments and genetic analyses
Cyanobacterial blooms are becoming increasingly prevalent worldwide. Sparse historic phytoplankton records often result in uncertainty as to whether bloom-forming species have always been present and are proliferating in response to eutrophication or climate change, or if there has been a succession of new arrivals through recent history. This study evaluated the relative efficacies of germination experiments and automated rRNA intergenic spacer analysis (ARISA) assays in identifying cyanobacteria in a sediment core and thus reconstructing the historical composition of cyanobacterial communities. A core (360 mm in depth) was taken in the central, undisturbed basin of Lake Okaro, New Zealand, a lake with a rapid advance of eutrophication and increasing cyanobacteria populations. The core incorporated a tephra from an 1886 volcanic eruption that served to delineate recent sediment deposition. ARISA and germination experiments successfully detected akinete-forming nostocaleans in sediment dating 120 bp and showed little change in Nostocales species structure over this time scale. Species that had not previously been documented in the lake were identified including Aphanizomenon issatschenkoi, a potent anatoxin-a producer. The historic composition of Chrococcales and Oscillatoriales was more difficult to reconstruct, potentially due to the relatively rapid degradation of vegetative cells within sediment
Fidelity for imperfect postselection
We describe a simple measure of fidelity for mixed state postselecting
devices. The measure is most appropriate for postselection where the task
performed by the output is only effected by a specific state.Comment: 8 Pages, 8 Figure
Staying in place during times of change in Arctic Alaska: The implications of attachment,alternatives, and buffering
The relationship between stability and change in social-ecological systems has received considerable attention in recent years, including the expectation that significant environmental changes will drive observable consequences for individuals, communities, and populations. Migration, as one example of response to adverse economic or environmental changes, has been observed in many places, including parts of the Far North. In Arctic Alaska, a relative lack of demographic or migratory response to rapid environmental and other changes has been observed. To understand why Arctic Alaska appears different, we draw on the literature on environmentally driven migration, focusing on three mechanisms that could account for the lack of response: attachment, the desire to remain in place, or the inability to relocate successfully; alternatives, ways to achieve similar outcomes through different means; and buffering, the reliance on subsidies or use of reserves to delay impacts. Each explanation has different implications for research and policy, indicating a need to further explore the relative contribution that each makes to a given situation in order to develop more effective responses locally and regionally. Given that the Arctic is on the front lines of climate change, these explanations are likely relevant to the ways changes play out in other parts of the world. Our review also underscores the importance of further attention to the details of social dynamics in climate change impacts and responses
Further characterization of glycine-containing microcystins from the McMurdo Dry Valleys of Antarctica
Microcystins are hepatotoxic cyclic peptides produced by several cyanobacterial genera worldwide. In 2008, our research group identified eight new glycine-containing microcystin congeners in two hydro-terrestrial mat samples from the McMurdo Dry Valleys of Eastern Antarctica. During the present study, high-resolution mass spectrometry, amino acid analysis and micro-scale thiol derivatization were used to further elucidate their structures. The Antarctic microcystin congeners contained the rare substitution of the position-1 D-alanine for glycine, as well as the acetyl desmethyl modification of the position-5 Adda moiety (3S-amino-9S-methoxy-2S,6,8S-trimethyl-10-phenyldeca-4E,6E-dienoic acid). Amino acid analysis was used to determine the stereochemistry of several of the amino acids and conclusively demonstrated the presence of glycine in the microcystins. A recently developed thiol derivatization technique showed that each microcystin contained dehydrobutyrine in position-7 instead of the commonly observed N-methyl dehydroalanine
Solar Particle Acceleration at Reconnecting 3D Null Points
Context: The strong electric fields associated with magnetic reconnection in
solar flares are a plausible mechanism to accelerate populations of high
energy, non-thermal particles. One such reconnection scenario occurs at a 3D
magnetic null point, where global plasma flows give rise to strong currents in
the spine axis or fan plane. Aims: To understand the mechanism of charged
particle energy gain in both the external drift region and the diffusion region
associated with 3D magnetic reconnection. In doing so we evaluate the
efficiency of resistive spine and fan models for particle acceleration, and
find possible observables for each. Method: We use a full orbit test particle
approach to study proton trajectories within electromagnetic fields that are
exact solutions to the steady and incompressible magnetohydrodynamic equations.
We study single particle trajectories and find energy spectra from many
particle simulations. The scaling properties of the accelerated particles with
respect to field and plasma parameters is investigated. Results: For fan
reconnection, strong non-uniform electric drift streamlines can accelerate the
bulk of the test particles. The highest energy gain is for particles that enter
the current sheet, where an increasing "guide field" stabilises particles
against ejection. The energy is only limited by the total electric potential
energy difference across the fan current sheet. The spine model has both slow
external electric drift speed and weak energy gain for particles reaching the
current sheet. Conclusions: The electromagnetic fields of fan reconnection can
accelerate protons to the high energies observed in solar flares, gaining up to
0.1 GeV for anomalous values of resistivity. However, the spine model, which
gave a harder energy spectrum in the ideal case, is not an efficient
accelerator after pressure constraints in the resistive model are included.Comment: 15 pages, 14 figures. Submitted to Astronomy and Astrophysic
COVID-19 and the UK Live Music Industry: A Crisis of Spatial Materiality
For the live music industry, and those who work in it, the COVID-19 outbreak has been predominantly framed as an economic crisis, one in which the economic systems through which revenue is derived from music-based products and practices have been abruptly closed off by a crisis of public health. Using Lefebvre’s trialectics of spatiality as a theoretical lens, we will argue that, for live music, the COVID-19 outbreak can be seen as a crisis of spatial materiality. During a time of lockdown and social distancing, spaces of music production (rehearsal spaces, studios) and consumption (venues, nightclubs) have found themselves suddenly unfit for purpose. Drawing upon empirical data from ongoing research projects in Scotland and the Midlands, we will highlight the ways in which COVID-19 has disrupted the spatial practice of music. From there, we will argue that there is a need for new representational spaces of music, and the creation of new forms of musical-spatial practice, appropriating spaces of the domestic and the everyday, and fusing / overlaying them with new cultural meaning and (crucially for musicians) a reconsideration of value by potential consumers
Crisis as a Catalyst for Change: COVID-19, Spatiality and the UK Live Music Industry
Since the advent of the COVID-19 pandemic, live music spaces – and the practices which produce them as economically viable – have found themselves in crisis. In spite of a UK government announcement on the 25th of July 2020 which allocated £2.25 million to support 150 music venues across the country, the processes of allocation, the conditions under which this emergency funding is allocated, and capacity to secure medium-to-long-term sustainability of the live music industries in the UK, remains unclear. In this paper, we present a Lefebvrian analysis of live music, highlighting the complex ways in which space is produced and consumed within a live music environment. By extending this framing to consider Lefebvre’s conceptualisation of dominated and appropriated space, we argue that the economic viability of live music stems from its spatiality, and that ongoing responses to the crisis require greater sensitivity to the spatial practices of music production and consumption
A plea for scale, and why it matters for invasive species management, biodiversity and conservation
Invasive species are suspected to be major contributors to biodiversity declines worldwide. Counterintuitively, however, invasive species effects are likely scale dependent and are hypothesized to be positively related to biodiversity at large spatial scales. Past studies investigating the effect of invasion on biodiversity have been mostly conducted at small scales (\u3c100 m2) that cannot represent large dynamic landscapes by design. Therefore, replicated experimental evidence supporting a negative effect of invasive plants on biodiversity is lacking across many landscape types, including large grasslands.
We collected data across eight large (333–809 ha) grassland landscapes managed with pyric herbivory—that is the recoupling of fire and grazing—to test how an invasive legume Lespedeza cuneata affected plant and bird communities at spatial grains ranging from 0.1 m2 to \u3e3,000,000 m2.
Lespedeza cuneata invasion effects on grassland plant diversity and composition changed with scale, being negative at small spatial grains (0.1 m2) and neutral or positive at large spatial grains (\u3e3,000,000 m2).
Lespedeza cuneata abundance did not significantly affect bird diversity at any spatial grain measured.
Lespedeza cuneata may negatively affect biodiversity if abundances are greater than those observed in this study. However, previous research suggests that Lespedeza cuneata may not be capable of exceeding 20% canopy cover across large landscapes (\u3e400 ha). Control and eradication strategies can be costly and are fraught with risk. If data do not clearly support a negative Lespedeza cuneata abundance–biodiversity relationship, and if invasion is spatially limited across large landscapes, ongoing control and eradication efforts may be unwarranted and ineffective.
Synthesis and applications: Invasive species effects gleaned from small-scale studies may not reliably predict their effects at larger scales. Although we recognize the importance of small-scale studies in potentially isolating individual mechanisms, management strategies based solely on results from small-scale studies of invasion are unlikely to increase or conserve biodiversity across large landscapes. Rather, processes that generate landscape heterogeneity—like pyric herbivory—are probably more important for promoting biodiversity across all scales. Scale is a central problem in ecology, and defining scale in management objectives is essential for effective biodiversity conservation
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