Vapour pressure deficit modulates hydraulic function and structure of tropical rainforests under nonlimiting soil water supply.

Atmospheric conditions are expected to become warmer and drier in the future, but little is known about how evaporative demand influences forest structure and function independently from soil moisture availability, and how fast-response variables (such as canopy water potential and stomatal conductance) may mediate longer-term changes in forest structure and function in response to climate change. We used two tropical rainforest sites with different temperatures and vapour pressure deficits (VPD), but nonlimiting soil water supply, to assess the impact of evaporative demand on ecophysiological function and forest structure. Common species between sites allowed us to test the extent to which species composition, relative abundance and intraspecific variability contributed to site-level differences. The highest VPD site had lower midday canopy water potentials, canopy conductance (gc ), annual transpiration, forest stature, and biomass, while the transpiration rate was less sensitive to changes in VPD; it also had different height-diameter allometry (accounting for 51% of the difference in biomass between sites) and higher plot-level wood density. Our findings suggest that increases in VPD, even in the absence of soil water limitation, influence fast-response variables, such as canopy water potentials and gc , potentially leading to longer-term changes in forest stature resulting in reductions in biomass.

The Role of Hydraulic Failure in a Massive Mangrove Die-Off Event.

Between late 2015 and early 2016, more than 7,000 ha of mangrove forest died along the coastline of the Gulf of Carpentaria, in northern Australia. This massive die-off was preceded by a strong 2015/2016 El Niño event, resulting in lower precipitation, a drop in sea level and higher than average temperatures in northern Australia. In this study, we investigated the role of hydraulic failure in the mortality and recovery of the dominant species, Avicennia marina, 2 years after the mortality event. We measured predawn water potential (Ψpd) and percent loss of stem hydraulic conductivity (PLC) in surviving individuals across a gradient of impact. We also assessed the vulnerability to drought-induced embolism (Ψ50) for the species. Areas with severe canopy dieback had higher native PLC (39%) than minimally impacted areas (6%), suggesting that hydraulic recovery was ongoing. The high resistance of A. marina to water-stress-induced embolism (Ψ50 = -9.6 MPa), indicates that severe water stress (Ψpd < -10 MPa) would have been required to cause mortality in this species. Our data indicate that the natural gradient of water-stress enhanced the impact of El Niño, leading to hydraulic failure and mortality in A. marina growing on severely impacted (SI) zones. It is likely that lowered sea levels and less frequent inundation by seawater, combined with lower inputs of fresh water, high evaporative demand and high temperatures, led to the development of hyper-salinity and extreme water stress during the 2015/16 summer.

Drivers of nocturnal stomatal conductance in C3 and C4 plants.

Nocturnal water losses were for long considered negligible, but it is now known that incomplete stomatal closure during the night leads to significant water losses at leaf, plant and ecosystem scales. However, only daytime transpiration is currently accounted for in evapotranspiration studies. Important uncertainties on the drivers of nocturnal water fluxes hinder its incorporation within modelling frameworks because some studies indicate that night-time stomatal drivers may differ from day-time responses. Here, we synthesise the studies on nocturnal stomatal conductance (gn) to determine underlying drivers through a systematic literature review and, whenever possible, meta-analytical techniques. Similar to daytime responses, we found negative effects of vapour pressure deficit, predawn water potential, air temperature, and salinity on gn across the plant species. However, the most apparent trend was an increase of gn from the beginning until the end of the night, indicating significant and widespread endogenous regulation by the circadian clock. We further observed how neither elevated CO2 nor nutrient status affected gn significantly across species. We also did not find any significant associations between gn and elevated ozone or increasing plant age. There was a paucity of studies on climatic extremes such heat waves and also few studies connected gn with anatomical features such as leaf specific area or stomatal density. Further studies are also needed to address the effects of plant sex, abscisic acid concentrations and genotypic variations on gn. Our findings solve the long-term conundrum on whether stomatal responses to daytime drivers are the same as those that during the nighttime.

Assessment of health risks associated with potentially toxic element contamination of soil by end-of-life ship dismantling in Bangladesh.

Ship breaking and recycling industry (SBRI) loops back scarce ferrous and non-ferrous materials from dismantled ships and also renews the global shipping fleet by treating the end-of-life (EoL) ships. Currently, SBRIs in Bangladesh, India, and Pakistan are dismantling the majority of the EoL ships by open beaching method. Accordingly, ship dismantling carries the blame of releasing potentially toxic elements (PTEs) to the coastal and marine environment risking the food chain through potential bioaccumulation and biomagnification. Health risk assessment associated with PTEs from open beach ship dismantling is scarce. This study aimed at assessing concentrations and seasonal variations of PTEs in soils exposed to the activities of SBRIs for their source apportionment by using contamination factor (CF) and multivariate statistical analysis, while carcinogenic and non-carcinogenic health risks due to the PTEs have also been determined. Soil samples were collected twice-during pre-monsoon and post-monsoon seasons-from three working zones of each of the 15 different ship breaking yards spanning the entire SBRI zone in Bangladesh. Soil contamination was assessed by using the CF, and inverse distance weighting interpolation mapping showed the spatial distribution of metals at SBRI zone in Bangladesh. Multivariate statistical analysis, principal component analysis, and correlation matrix yielded the source apportionment of PTEs. Subsequently, carcinogenic and non-carcinogenic health risks were assessed following the approach recommended by the United States Environmental Protection Agency (USEPA) with uncertainty estimation through Monte Carlo simulation. Contamination levels of PTEs followed Cd > Zn > Cr > Cu > Pb > Ni > Mn > As. Concentrations of Cd, Cr, Mn, and Zn were higher than the maximum allowable regulatory limits at storage zone and also higher as compared with the beaching and cutting zones in general. The contamination index indicated extreme Cd contamination in the area with elevated levels in pre-monsoon. Two principal components (PC) were identified-PC1 (Cd, Cu, Mn, Pb, Zn) and PC2 (As, Cr, Ni) inferring their source segmentation. Indirect soil ingestion is the major possible exposure path to PTEs. The health index indicated the absence of any obvious health effects on the people active at SBRI yards in Bangladesh. The carcinogenic risk was for 6 to 7 persons per 100,000 people which was within the USEPA acceptable range.

Environmental hazards associated with open-beach breaking of end-of-life ships: a review.

End-of-life (EOL) ships contribute significantly to the flow of recycled industrial Fe and non-Fe metal materials in resource-poor developing countries. The ship scrapping (breaking) and recycling industry (SBRI) recycles 90-95% of the total weight of EOL ships and is currently concentrated in Bangladesh, India, Pakistan, Turkey, and China, due to the high demand for recyclable and reusable materials there, an abundance of low-cost labor, and lenient environmental regulations. However, the SBRI has long been criticized for non-compliance with standards relating to occupational health, labor safety, and to the management of hazardous materials. Among the different EOL recycling options, Bangladesh, India, and Pakistan use open beaching, a technique that exposes all spheres of the environment to the release of hazardous materials from EOL ships. This article summarizes the current state of knowledge on the environmental exposure of hazardous materials from SBRI, to judge the risks associated with the dismantling of EOL ships on open beaches. Our work includes an overview of the industry and its recent growth, compares available ship-breaking methods, provides an inventory of hazardous releases from EOL ships, and reviews their movement into different spheres of the environment. The economic dynamics behind open beaching, and apportionment of responsibility for hazards related to it, are discussed, in order to generate policy and legal recommendations to mitigate the environmental harm stemming from this industry.

Liquid electrode plasma-optical emission spectrometry combined with solid-phase preconcentration for on-site analysis of lead.

A relatively rapid and precise method is presented for the determination of lead in aqueous matrix. The method consists of analyte quantitation using the liquid electrode plasma-optical emission spectrometry (LEP-OES) coupled with selective separation/preconcentration by solid-phase extraction (SPE). The impact of operating variables on the retention of lead in SPEs such as pH, flow rate of the sample solution; type, volume, flow rate of the eluent; and matrix effects were investigated. Selective SPE-separation/preconcentration minimized the interfering effect due to manganese in solution and limitations in lead-detection in low-concentration samples by LEP-OES. The LEP-OES operating parameters such as the electrical conductivity of sample solution; applied voltage; on-time, off-time, pulse count for applied voltage; number of measurements; and matrix effects have also been optimized to obtain a distinct peak for the lead at λmax=405.8nm. The limit of detection (3σ) and the limit of quantification (10σ) for lead determination using the technique were found as 1.9 and 6.5ng mL-1, respectively. The precision, as relative standard deviation, was lower than 5% at 0.1µg mL-1 Pb, and the preconcentration factor was found to be 187. The proposed method was applied to the analysis of lead contents in the natural aqueous matrix (recovery rate:>95%). The method accuracy was verified using certified reference material of wastewaters: SPS-WW1 and ERM-CA713. The results from LEP-OES were in good agreement with inductively coupled plasma optical emission spectrometry measurements of the same samples. The application of the method is rapid (≤5min, without preconcentration) with a reliable detection limit at trace levels.