Comparing Multiple Approaches to Reconstructing the Phosphorus History of Marl Lakes: A Utah Lake Case Study

Freshwater lakes around the world have suffered from the increasing occurrence of harmful algal blooms in recent decades. One of the most pressing reasons water quality managers try to address harmful algal blooms is that some of the species that occur with them produce toxins which can affect humans, pets, and wildlife. In many lakes, the nutrient phosphorus controls whether these harmful algal and bacterial species can occur. Therefore, efforts to control harmful algal blooms often center around reducing inputs of phosphorus from a variety of sources within the watershed. Scientists and water quality managers have long been challenged by the problem of determining the extent of phosphorus pollution in lakes, and to what degree human activity has changed the phosphorus aspect of aquatic ecosystems. We studied the historical phosphorus record of Utah Lake in north-central Utah, USA, which has been plagued by harmful algal blooms in recent years, by taking sediment cores from four different locations around the lake. We first analyzed the CaCO3 component of one Utah Lake core for trends in phosphorus concentration over time. This approach is based on the co-precipitation of CaCO3 with phosphorus, which scales with concentrations of phosphorus in the lake water. Next, we separated the total phosphorus of samples from four different sediment cores into five different forms by extraction and analyzed each extraction to establish trends in the different fractions of phosphorus that occur in lake sediments. In order to correlate phosphorus trends with important events in the lake’s ecological history, we performed cesium and lead isotope analyses, assigning years to the various depths of these sediment cores. These analyses together support our hypothesis that phosphorus concentrations have increased in the lake due to human activity. Nearly all of the phosphorus fractions from each of the four cores increase in more recent years, agreeing with the analyses focused on CaCO3 grains from one specific core which showed an increase in phosphorus beginning around the middle of the 19th century. We recommend applying the principles of our CaCO3-phosphorus analysis performed here in other lakes with CaCO3-P-rich sediments to better understand their ecological histories

Formal-informal economy linkages: What implications for poverty in South Africa?

The idea of dualism in the South African economy, characterized by a “first” and “second” economy has come to dominate government thinking in recent years. Using the panel component of the Labour Force Survey (LFS), the authors explore linkages between the formal and informal economy. Their analysis suggests that there is a high level of interaction between formal and informal work, at the lower end of the labour market. At the household level too, access to stable employment in the formal economy is associated with higher levels of earning in the informal economy. The findings have implications for poverty analysis in South Africa. Policy which views poverty as being located outside the mainstream of the economy – in the so-called ‘second’ economy – is misleading. Instead, an integrated approach which views poverty as linked to and a product of the trajectory and growth patterns of the South African economy is suggested as a more useful conceptualisation of poverty and inequality in South Africa

Black South African families with older members: opportunities and constraints

In developing countries, the majority of elders live with children. In South Africa, the first baseline study of persons aged 60 years and older confirmed that more than nine in ten black elders live with children and/or grandchildren. The study focussed on the individual elder and did not provide information on the living conditions of multigeneration families. To fill a gap in knowledge, this paper inquires into the situation of households which shelter persons aged 60 years and over. Secondary analysis of data collected nationwide in late 1993 among close on 9 000 South African households for the Project on Statistics for Living Standards and Development (Saldru 1994) aimed to provide information for policy and planning for the care of the elderly in the family context. Statistics on geographic location, household composition, housing and infrastructure, household economy, education and health, and perceived quality of life were compiled for elderly households and young households with no older members. A comparison of the statistical profiles of older and younger households indicated that poverty was the major constraint on the wellbeing of elderly households. Elderly persons in the family were most likely to perceive their living conditions to be depressed. Elderly households were larger, poorer and more likely to be located in the rural areas than young households. The geographical division of older and younger households, which coincided with an income gap, indicates a need for further inquiries into the dynamics of household formation and the economic links between older and younger households. The paper addresses intergenerational welfare policy issues: the authors recommend that elderly households be considered as an important subcategory of the poor to ensure the wellbeing of older members of the family

The lithium depletion boundary and the age of NGC 2547

We present the results of a photometric and spectroscopic survey of cool M dwarf candidates in the young open cluster NGC 2547. Using the 2dF fiber spectrograph, we have searched for the luminosity at which lithium remains unburned in an attempt to constrain the cluster age. The lack of a population of individual lithium-rich objects towards the faint end of our sample places a very strong lower limit to the cluster age of 35 Myr. However, the detection of lithium in the averaged spectra of our faintest targets suggests that the lithium depletion boundary lies at 9.5 < M(I) < 10.0 and that the cluster age is < 54 Myr. The age of NGC 2547 judged from fitting isochrones to low-mass pre-main-sequence stars in colour-magnitude diagrams is 20-35 Myr using the same evolutionary models. The sense and size of the discrepancy in age determined by these two techniques is similar to that found in another young cluster, IC 2391, and in the low-mass pre main-sequence binary system, GJ 871.1AB. We suggest that the inclusion of rotation or dynamo-generated magnetic fields in the evolutionary models could reconcile the two age determinations, but only at the expense of increasing the cluster ages beyond that currently indicated by the lithium depletion. Alternatively, some mechanism is required that increases the rate of lithium depletion in young, very low-mass fully convective stars.Comment: 14 pages, 7 figures, 3 tables, accepted by MNRA

Mass segregation in the young open cluster NGC 2547

We present a study of mass segregation of the young (20-35 Myr isochronal age), open cluster NGC 2547. We find good evidence that mass segregation exists in NGC 2547 down to 3 Msun, and weak evidence for mass segregation down to 1 Msun. Theoretical models of an initially unsegregated model of NGC 2547 using the NBODY2 code show weaker mass segregation, implying that at least some of the observed mass segregation has a primordial origin. We also report the discovery of three possible escaped cluster members, which share the proper motion and colours of the cluster, but lie nearly a degree from the cluster centre.Comment: 7 pages, 7 figures. To appear in Monthly Notices (in press

Listening to Children and Young People’s (CYP) Experience and Perceptions During the Period of COVID-19 and Their Advice for Teachers and Schools

This research project aimed to elicit the views of children and young people (CYP) about their experience of COVID-19, and their advice to teachers and schools. The views of fourteen CYP aged between 9 and 15 years of age from within and around London were ascertained through individual semi-structured interviews and analysed through thematic analysis. There were a variety of responses from CYP, including the following: a deep appreciation for their teachers and their support throughout the pandemic; stories of positive personal growth and spending more time with their family. However, their inability to see friends and the challenges of learning from home had a considerable impact on some CYP who would have liked home learning to have been more personalised, interactive and varied and for there to have been a greater awareness of workload. A list of issues for consideration and a checklist based upon the CYP’s views have been compiled, for the use of schools and teachers. Given the small sample, the timing of the study and the fact that the pandemic is ongoing, some suggestions for further research are indicated

Seawater cycled throughout Earth's mantle in partially serpentinized lithosphere

The extent to which water and halogens have primordial origins in the Earth's mantle, or are dominated by seawater-derived components introduced by subduction, remains a matter of debate. About 90% of non-radiogenic xenon in the Earth's mantle has a subducted atmospheric origin, but the degree to which atmospheric gases and other seawater components are coupled during subduction is unclear. Here we present the concentrations of water and halogens in samples of magmatic glasses collected from global mid-ocean ridges and ocean islands. We show that water and halogen enrichment is unexpectedly associated with trace element signatures characteristic of dehydrated oceanic crust, and that the most incompatible halogens have relatively uniform abundance ratios that are different from primitive mantle values. Taken together, these results imply that Earth's mantle is highly processed and that most of its water and halogens were introduced by the subduction of serpentinised lithospheric mantle associated with dehydrated oceanic crust.Australian Research Council (FT130100141