Isotopic evidence for axial tree stem methane oxidation within subtropical lowland forests.

Knowledge regarding mechanisms moderating methane (CH4 ) sink/source behaviour along the soil-tree stem-atmosphere continuum remains incomplete. Here, we applied stable isotope analysis (δ13 C-CH4 ) to gain insights into axial CH4 transport and oxidation in two globally distributed subtropical lowland species (Melaleuca quinquenervia and Casuarina glauca). We found consistent trends in CH4 flux (decreasing with height) and δ13 C-CH4 enrichment (increasing with height) in relation to stem height from ground. The average lower tree stem δ13 C-CH4 (0-40 cm) of Melaleuca and Casuarina (-53.96‰ and -65.89‰) were similar to adjacent flooded soil CH4 ebullition (-52.87‰ and -62.98‰), suggesting that stem CH4 is derived mainly by soil sources. Upper stems (81-200 cm) displayed distinct δ13 C-CH4 enrichment (Melaleuca -44.6‰ and Casuarina -46.5‰, respectively). Coupled 3D-photogrammetry with novel 3D-stem measurements revealed distinct hotspots of CH4 flux and isotopic fractionation on Melaleuca, which were likely due to bark anomalies in which preferential pathways of gas efflux were enhanced. Diel experiments revealed greater δ13 C-CH4 enrichment and higher oxidation rates in the afternoon, compared with the morning. Overall, we estimated that c. 33% of the methane was oxidised between lower and upper stems during axial transport, therefore potentially representing a globally significant, yet previously unaccounted for, methane sink.

The legacy and drivers of groundwater nutrients and pesticides in an agriculturally impacted Quaternary aquifer system.

Nutrient and pesticide pollution are among the major threats to groundwater quality in agriculturally impacted aquifers. Understanding their legacy effects and drivers are important to protect aquifers from exposures to contamination. However, the complexities of groundwater flowpaths make it difficult to predict the time-scales of groundwater flow and contaminant transport. To determine these controls of groundwater nutrient and pesticides in an aquifer system underlying an intensive agricultural area in the Great Barrier Reef catchment, Australia, we sampled tritium (3H) to estimate groundwater-age, nutrient and pesticide concentrations to investigate groundwater contamination, and nitrogen (ẟ15N-NO3-) and oxygen (ẟ18O-NO3-) isotopes to determine groundwater nitrate dynamics. We, then, constructed high-resolution 3D geological and groundwater flow models of the aquifer system to determine the role of the geologic heterogeneity on the observed nutrient and pesticide concentrations. Groundwater 3H derived ages, and nutrient and pesticide concentrations did not follow distinct spatial trends. ẟ15N-NO3- and ẟ18O-NO3- values indicated that nitrification and denitrification processes influenced nitrate dynamics in the aquifer system; however, they were not solely able to explain the entire 3D variability. The 3D geologic modelling identified possible preferential flowpaths and perched systems, which helped to explain the observed groundwater-age, nutrient and pesticide variabilities. Old-groundwater (~100-years) was found in shallow depths (<15 m) where perched systems were identified. In areas with preferential flowpaths, young-groundwater (⁓1-year) with significant nitrate (~12 mg-N/L) and pesticides (up to 315 ng/L) concentrations were detected at deeper depths (>25 m), below perched and locally confined systems. Downward increasing groundwater-age, and decreasing nutrient and pesticide concentrations were detected in the unconfined aquifer, while old-groundwater (~160-years) and lower nitrate (<3 mg-N/L) and pesticides (<2 ng/L) concentrations were detected in the confined systems. This study demonstrates the importance of understanding both the geology and the hydrogeology of an area before deploying monitoring studies and/or making conclusions from tritium, nutrient and pesticide data alone.

Best Guess method for age-based weight estimation in paediatric emergencies: validation and comparison with current methods.

BACKGROUND: During paediatric resuscitation, drug doses are calculated based upon weight. Age-based weight estimates are used when weighing children is impractical. The average weight of Australian children has increased, and widely used paediatric age-based formulae might underestimate weight. A modified age-based method for paediatric weight calculation, the 'Best Guess', has been described. OBJECTIVE: To validate the Best Guess formulae on a new population of paediatric emergency patients, and to compare the accuracy of this method with Advanced Paediatric Life Support (APLS) and Australian Resuscitation Council (ARC) formulae for age-based weight calculations. METHODS: A retrospective study was performed of Australasian Triage Scale (ATS) category 1 or 2 patients presenting to a tertiary paediatric ED over a 12 month period. Calculated weights using each method (APLS, ARC and Best Guess) were compared with true weights for infants (<1 year), preschool-aged (1-4 years) and school-aged (5-14 years) children. Mean actual error and mean percentage error for each was calculated. RESULTS: A total of 1843 patient weights were included in the study. The Best Guess Infant formula accurately estimated weight (mean percentage error +4.2%). The Best Guess formulae more accurately estimated weight than both APLS and ARC formulae for both preschool-aged children (mean percentage error +2.6% vs-12.1% vs-12.1%) and school-aged children (mean percentage error +7.7% vs-19.9% vs-12.4%). CONCLUSION: The Best Guess formulae is a valid method for age-based weight estimation in acutely unwell or injured children presenting to the ED and more accurately predicts mean weight than either APLS or ARC formulae.