Dissimilatory nitrate reductionpathways in an oligotrophic aquatic ecosystem: spatial and temporal trends

Elevated nitrate (NO3−) concentrations can cause eutrophication, which may lead to harmful algal blooms, loss of habitat and reduction in biodiversity. Denitrification, a dissimilatory process that removes NO3− mainly as dinitrogen gas (N2), is believed to be the dominant NO3− removal pathway in aquatic ecosystems. Evidence suggests that a less well-studied process, dissimilatory nitrate reduction to ammonium (DNRA), which retains nitrogen (N) in the system, may also be important under favorable conditions. Using stable isotope tracers in sealed microcosms, we measured the potential for NO3− losses due to DNRA and denitrification in an oligotrophic freshwater ecosystem. We took sediment and water samples at runoff and baseflow, across several ecotypes. Our objective was to quantify the relative importance of DNRA compared to denitrification with changes in ecotype and season. Potential denitrification rates ranged from 0 to 0.14 ± 0.03 µgN gAFDM−1 d−1. ­Potential DNRA rates ranged from 0 to 0.0051 ± 0.0008 µgN gAFDM−1 d−1. Denitrification losses peaked at the inflow stream ecotype at 96.2% of total dissimilatory NO3− removal, whereas losses due to DNRA peaked in the lake ecotype at 34.4%. When averaged over the entire system, denitrification peaked at baseflow (31.2%), while DNRA peaked at runoff (2.9%). Although NO3− transformations due to denitrification were higher than DNRA in all ecotype and temporal comparisons, our results suggest that DNRA is also important under favorable conditions

Biogeochemistry of “pristine” freshwater stream and lake systems in the western Canadian Arctic

Climate change poses a substantial threat to the stability of the Arctic terrestrial carbon (C) pool as warmer air temperatures thaw permafrost and deepen the seasonally-thawed active layer of soils and sediments. Enhanced water flow through this layer may accelerate the transport of C and major cations and anions to streams and lakes. These act as important conduits and reactors for dissolved C within the terrestrial C cycle. It is important for studies to consider these processes in small headwater catchments, which have been identified as hotspots of rapid mineralisation of C sourced from ancient permafrost thaw. In order to better understand the role of inland waters in terrestrial C cycling we characterised the biogeochemistry of the freshwater systems in a c. 14 km2 study area in the western Canadian Arctic. Sampling took place during the snow-free seasons of 2013 and 2014 for major inorganic solutes, dissolved organic and inorganic C (DOC and DIC, respectively), carbon dioxide (CO2) and methane (CH4) concentrations from three water type groups: lakes, polygonal pools and streams. These groups displayed differing biogeochemical signatures, indicative of contrasting biogeochemical controls. However, none of the groups showed strong signals of enhanced permafrost thaw during the study seasons. The mean annual air temperature in the region has increased by more than 2.5 °C since 1970, and continued warming will likely affect the aquatic biogeochemistry. This study provides important baseline data for comparison with future studies in a warming Arctic

Urban agriculture in the Gauteng City-Region’s green infrastructure network

As cities in developing countries contend with the challenges of urbanisation, they need to rethink the traditional modes of urban planning and development. Part of this logic is the need to cater for growing populations without compromising urban environments or social development. A green infrastructure approach can help meet infrastructure and service needs while ensuring the proper functioning of natural ecological systems. As part of the green infrastructure network, urban agriculture can create multifunctional green assets in the form of urban farms and food gardens. When planned accordingly, urban agriculture can contribute to addressing a range of issues in the Gauteng City-Region (GCR). The aim of this occasional paper is to gain a better understanding of urban agriculture within the green infrastructure network in the City of Johannesburg and to identify the range of ecosystem services that could be delivered when maintaining and investing in these assets. The analysis in this paper adopts a multi-method approach to (1) identify the interlinkages between urban agriculture and social, economic and environmental systems in the City of Johannesburg; (2) validate these critical interlinkages with stakeholder input and ground-level experience of urban agriculture; and (3) visualise these interlinkages through a spatial analysis of food gardens in the City of Johannesburg. This paper builds the argument that urban agriculture is a multifunctional element of the green infrastructure network in the GCR. It is worth maintaining and investing in food gardens because they contribute to a number of development imperatives in Gauteng. Food gardens may enhance food security by broadening the range of locally produced food sources that improve the potential to help the poor to access fresh food. Productive food gardens may provide economic opportunities, particularly in areas with minimal access to retail outlets and where unemployment is high. Lastly, as a component of a green infrastructure network, food gardens also help strengthen the provision of a range of key ecosystem services. Inter alia they help address climate change and build disaster resilience through flood management and carbon capture. Of course, urban agriculture will not deal with any of these challenges in their entirety, but within a wider green infrastructure approach, it has the potential to contribute significantly if it can be mainstreamed into municipal development processes. Realising the benefits of green infrastructure hinges on integrating this approach into municipal planning in a way that aims to improve the productivity of ecosystem service delivery. The paper concludes with recommendations for strengthening policy, management, planning and operational support for food gardens in the GCR

Gestational hypercalcemia: Prevalence and biochemical profile

Gestational hypercalcemia is associated with an increased risk of maternal, fetal and neonatal morbidity and mortality. Hypercalcemia may develop during pregnancy in individuals who were previously asymptomatic. The increased sensitivity during pregnancy may be related to physiological, gestational alterations in vitamin D and calcium metabolism and may be influenced by gene variants. The prevalence is unknown. We investigated the prevalence of hypercalcemia in trimester 3 (T3) in a population representative prospective cohort study (n = 1832) in South-West Sweden. Women with serum albumin (Alb) adjusted calcium (CaAlb) ≥ 2.65 mmol/L in T3 (n = 30) were matched to normo-calcemic controls, and markers of calcium and vitamin D metabolism were investigated in trimester 1 (T1) and T3. Serum concentrations of Ca, phosphate (P), Magnesium (Mg), Alb and creatinine (Cr), parathyroid hormone (PTH; T3 only), vitamin D metabolites (total 25(OH)D, 1,25(OH)2D, 24,25(OH)2D, and free 25(OH)D) were analysed in T1 and T3. CaAlb (Payne; inter-laboratory difference: UEA = 0.15 + 0.9*UGOT; UEA 2.54 = UGOT 2.65) and estimated glomerular filtration rate (eGFR; modified 4-variable MDRD) and vitamin D metabolites ratios (VMR) were calculated. Normally and non-normally distributed data were presented as mean (SD) or median (95%CI). Group differences in relationships between vitamin D metabolites and with PTH were investigated with multiple regression analyses. Hypercalcemia in T3 was found in 1.7% of women. PTH concentrations suggestive of primary hyperparathyroidism was found in 1 woman and none had 25(OH)D or 24,25(OH)2D concentrations in the toxicity range or suggestive of mutations in the CYP24A1 gene. CaAlb was significantly higher in hypercalcemic cases compared to controls in T1 (2.44 (2.30-2.80) vs 2.37 (2.25-2.49) mmol/L) and T3 (2.63 (2.52-2.78) vs 2.46 (2.31-2.58) mmol/L). Serum P was higher among cases than controls in T3 (1.12 (0.16) vs 1.07 (0.18) mmol/L) but not in T1 (1.12 (0.18) and 1.12 (0.16) mmol/L). PTH in T3 was lower in cases (1.6 (1.6-2.8) vs 2.3 (2.1-2.8) pmol/L) but 1,25(OH)2D concentrations were similar. There were no significant group differences in serum 25(OH)D, free 25(OH)D, 24,25(OH)2D, Mg, Alb, Cr and eGFR. Regression analyses did not show significant differences between cases and controls in relationships between vitamin D metabolites and with PTH, except for the free 25(OH)D-PTH relationship and a higher free:total 25(OH)D ratio in cases at T1. In conclusion, most common causes of hypercalcemia were excluded in the majority of women. Hypercalcemic women had a relatively high serum 1,25(OH)2D concentration despite an appropriately suppressed PTH, suggestive of abnormal gestational adaptions

Aquatic carbon and GHG export from a permafrost catchment; identifying source areas and primary flow paths

The aquatic pathway is increasingly being recognized as an important component of landscape scale greenhouse gas (GHG) budgets. Due to low temperatures and short residence times limiting in-stream production in northern headwater catchments, much of the exported carbon is likely to be allochthonous, transported via throughflow to the surface drainage system. Identifying sources and primary flow pathways is therefore essential in understanding and predicting changes in the aquatic flux magnitude. Arctic landscapes are now widely recognised as being particularly vulnerable to climate driven changes. The HYDRA project (“Permafrost catchments in transition: hydrological controls on carbon cycling and greenhouse gas budgets”) aims to understand the fundamental role that hydrological processes play in regulating landscape-scale carbon fluxes, and predict how changes in vegetation and active layer depth in permafrost environments influence the delivery and export of aquatic carbon. In this study we present aquatic concentrations and fluxes of carbon and GHG species collected across two field seasons (2013, 2014) from an arctic headwater catchment in northern Canada. Measured species include dissolved organic (DOC) and inorganic carbon (DIC), CO2, CH4 and N2O. Measurements were made across a range of freshwater types within the tundra landscape, including lakes, ice-wedge polygons, and the ‘Siksik’ stream which drains the (c.a. 1 km2) primary study catchment. A nested sub-catchment approach was used along the ‘Siksik’ stream; ‘snapshot’ sampling of eight points along the stream length allowed specific vegetation communities to be targeted to assess individually their contribution to aquatic export. A combination of stable isotopes and major ion concentrations measured at each sampling point provide additional information to trace source areas and flow paths within the main study catchment. Catchment scale evasion and downstream export were calculated and an initial comparison between the relative importance of different water body types presented

Utilising conservative tracers and spatial surveys to identify controls on pathways and DOC exports in an Arctic catchment

Dissolved organic carbon (DOC) is typically the predominant form of carbon exported from headwater streams, it therefore represents a major carbon export from Arctic catchments. The projected deepening of thaw depth in permafrost regions, due to an increase in air temperature, may have a significant effect on the amount of DOC exported from these systems. However, quantification of the impacts of climate driven changes on DOC export are still highly uncertain. Understanding the processes controlling DOC export is therefore crucial in predicting the potential impact of projected environmental changes. The controls of DOC production and transport are heavily influenced by soil and vegetation, which are highly variable across the landscape. To completely understand these systems information regarding spatial variability of plants, soils and thaw depths must be taken into account. In this study sub-weekly sampling of DOC was undertaken throughout 2014 in a headwater (<1 km2) catchment in the Northwest Territories, Canada. Spatial surveys of soil properties, active thaw depth and normalised difference vegetation index (NDVI) were collected and used in conjunction with conservative stable water isotopes tracers and major ions to understand sources, flow pathways and timing of DOC exports from the catchment. Stable isotope tracers act as fingerprints of water allowing sources and pathways to be assessed. Observations reveal changing DOC concentrations throughout the season as the active layer deepens and the connectivity of the soils to the stream network throughout the catchment increases. Linking the DOC data with the conservative tracer response improves the identification of carbon pathways and fluxes from the soils; preliminary analysis indicates DOC is being delivered via deeper more mineral soils later in the season. The results indicate that the active layer depth has a strong influence on the amount of DOC exported from the system, independent of the amount of carbon stored in these deeper soils

The global politics of a ‘poncy pillowcase’: Migration and borders in Coronation Street

This article examines the ways in which popular culture stages and supplies resources for agency in everyday life, with particular attention to migration and borders. Drawing upon cultural studies, and specific insights originating from the Birmingham Centre for Contemporary Cultural Studies, we explore how intersectional identities such as race, ethnicity, class, and gender are experienced in relation to the globalisation of culture and identity in a 2007 Coronation Street storyline. The soap opera genre offers particular insights into how agency emerges in everyday life as migrants and locals navigate the forces of globalisation. We argue that a focus on popular culture can mitigate the problem of isolating migrant experiences from local experiences in migrant-receiving areas

Mammalian cell transfection: the present and the future

Transfection is a powerful analytical tool enabling study of the function of genes and gene products in cells. The transfection methods are broadly classified into three groups; biological, chemical, and physical. These methods have advanced to make it possible to deliver nucleic acids to specific subcellular regions of cells by use of a precisely controlled laser-microcope system. The combination of point-directed transfection and mRNA transfection is a new way of studying the function of genes and gene products. However, each method has its own advantages and disadvantages so the optimum method depends on experimental design and objective

Activity-Dependent Shedding of the NMDA Receptor Glycine Binding Site by Matrix Metalloproteinase 3: A PUTATIVE Mechanism of Postsynaptic Plasticity

Functional and structural alterations of clustered postsynaptic ligand gated ion channels in neuronal cells are thought to contribute to synaptic plasticity and memory formation in the human brain. Here, we describe a novel molecular mechanism for structural alterations of NR1 subunits of the NMDA receptor. In cultured rat spinal cord neurons, chronic NMDA receptor stimulation induces disappearance of extracellular epitopes of NMDA receptor NR1 subunits, which was prevented by inhibiting matrix metalloproteinases (MMPs). Immunoblotting revealed the digestion of solubilized NR1 subunits by MMP-3 and identified a fragment of about 60 kDa as MMPs-activity-dependent cleavage product of the NR1 subunit in cultured neurons. The expression of MMP-3 in the spinal cord culture was shown by immunoblotting and immunofluorescence microscopy. Recombinant NR1 glycine binding protein was used to identify MMP-3 cleavage sites within the extracellular S1 and S2-domains. N-terminal sequencing and site-directed mutagenesis revealed S542 and L790 as two putative major MMP-3 cleavage sites of the NR1 subunit. In conclusion, our data indicate that MMPs, and in particular MMP-3, are involved in the activity dependent alteration of NMDA receptor structure at postsynaptic membrane specializations in the CNS

Optimisation of Over-Expression in E. coli and Biophysical Characterisation of Human Membrane Protein Synaptogyrin 1

Progress in functional and structural studies of integral membrane proteins (IMPs) is lacking behind their soluble counterparts due to the great challenge in producing stable and homogeneous IMPs. Low natural abundance, toxicity when over-expressed and potential lipid requirements of IMPs are only a few reasons for the limited progress. Here, we describe an optimised workflow for the recombinant over-expression of the human tetraspan vesicle protein (TVP) synaptogyrin in Escherichia coli and its biophysical characterisation. TVPs are ubiquitous and abundant components of vesicles. They are believed to be involved in various aspects of the synaptic vesicle cycle, including vesicle biogenesis, exocytosis and endocytotic recycling. Even though TVPs are found in most cell types, high-resolution structural information for this class of membrane proteins is still missing. The optimisation of the N-terminal sequence of the gene together with the usage of the recently developed Lemo21(DE3) strain which allows the balancing of the translation with the membrane insertion rate led to a 50-fold increased expression rate compared to the classical BL21(DE3) strain. The protein was soluble and stable in a variety of mild detergents and multiple biophysical methods confirmed the folded state of the protein. Crosslinking experiments suggest an oligomeric architecture of at least four subunits. The protein stability is significantly improved in the presence of cholesteryl hemisuccinate as judged by differential light scattering. The approach described here can easily be adapted to other eukaryotic IMPs