Measuring Evapotranspiration of five Alley Cropping systems in Germany using the Eddy-Covariance- and Bowen-Ratio Energy-Balance methods

Measuring evapotranspiration (ET) of heterogeneous ecosystems using methods like the eddy-covariance- (ECEB) and Bowen-Ratio energy-balance (BREB) methods is challenging due to their restrictions to horizontally homogeneous terrain and steady state conditions. The unfavorable ambient conditions lead to a site-specific non-closure of the energy-balance, which is a balance between the incoming net radiation and the ground-, latent- and sensible heat fluxes. Thus, an underestimation of measured heat fluxes leads to an overestimation of the latent heat fluxes inferred from the ECEB method. The aim of our study is to 1) quantify the site-specific non-closure of the energy-balance and 2) characterize the performance of both methods, compared to direct eddy-covariance measurements using a high-frequency infra-red gas analyzer (LI-7200, Licor Inc.). To assess continuous ET rates on a 30-minute time scale we installed a combined ECEB and BREB system at five alley cropping and five agricultural reference sites across Germany. For time periods of four weeks, we performed direct eddy covariance flux measurements for H2O and CO2 over one crop- and one grassland alley cropping- and their respective reference systems during the growing season of 2016. We found a non-closure between 21 and 26 % for all sites, with the residual energy being highest during the morning and lowest in the afternoon. Related to that the energy-balance ratio (EBR), i.e. the ratio between the turbulent heat fluxes and available energy, was below one in the morning hours and increased slightly during the day up to 1.8, until the EBR decreased sharply after sunset. The EBR correlated to the daily cycle of solar radiation, the main driver of turbulent fluxes. Corresponding, we found an increasing EBR with increasing friction velocity, indicating, that the energy-balance closure improves under turbulent condition. Further our analysis reveal that turbulent fluxes estimated by the BREB method compared well with direct eddy-covariance measurements. An accuracy improvement was found with increasing sensor distance. We conclude, when calculating ET rates on a 30-minute time scale using the ECEB method the site-specific non-closure should be assessed beforehand by eddy-covariance. In the current study, ignoring the non-closure would have lead to an overestimation of the ET rates of about 25 % for the ECEB method

Single phase nanocrystalline GaMnN thin films with high Mn content

Ga₁ˍₓ Mnₓ Nthin films with a Mn content as high as x=0.18 have been grown using ion-assisted deposition and a combination of Rutherford backscattering spectroscopy and nuclear reaction analysis was used to determine their composition. The structure of the films was determined from x-ray diffraction,transmission electron microscopy, and extended x-ray absorption fine structure(EXAFS). The films are comprised of nanocrystals of random stacked GaMnN and there is no evidence of Mn-rich secondary phases or clusters. EXAFS measurements at the Mn and Ga edge are almost identical to those at the Ga edge from Mn-free nanocrystallineGaNfilms, showing that the Mn occupies the Ga lattice sites, and simulated radial distribution functions of possible Mn-rich impurity phases bear no resemblance to the experimental data. The results indicate that these are the most heavily Mn-doped single phase GaNfilms studied to date.The authors gratefully acknowledge financial support from the New Zealand Foundation for Research Science and Technology through its New Economy Research Fund, and through a postdoctoral fellowship of one of the authors B.J.R.. The work of the MacDiarmid Institute is supported by a New Zealand Centre of Research Excellence award. Another author S.G. wishes to thank Education New Zealand for financial support of the EXAFS measurements

Does increased spatial replication above heterogeneous agroforestry improve the representativeness of eddy covariance measurements?

Spatial heterogeneity in terrestrial ecosystems compromises the accuracy of eddy covariance measurements. Examples of heterogeneous ecosystems are temperate agroforestry systems, which have been poorly studied by eddy covariance. Agroforestry systems have been getting increasing attention due to their potential environmental benefits, e.g. a higher carbon sequestration, improved microclimate and erosion reduction compared to open-cropland agricultural systems. Lower-cost eddy covariance setups might offer an opportunity to better capture spatial heterogeneity by allowing for more spatial replicates of flux towers. The aim of this study was to quantify the spatial variability of carbon dioxide (FC), latent heat (LE) and sensible heat (H) fluxes above a heterogeneous agroforestry system in northern Germany using a distributed network of three lower-cost eddy covariance setups across the agroforestry system. Fluxes from the three towers in the agroforestry were further compared to fluxes from an adjacent open-cropland site. The campaign took place from March 2023 until September 2024. The results indicated that the spatial variability of fluxes was largest for FC, attributed to the effect of different crops (rapeseed, corn and barley) within the flux footprints contributing to the measured fluxes. Differences between fluxes across towers were enhanced after harvest events. However, the temporal variability due to the seasonality and diurnal cycles during the campaign was larger than the spatial variability across the three towers. When comparing fluxes between the agroforestry and the open-cropland systems, weekly sums of carbon and evapotranspiration fluxes followed similar seasonality, with peak values of −50 g C m−2 week−1 and 40 mm week−1 during the growing season, respectively. The variation of the magnitude depended on the phenology of the different crops. The effect size, which is an indicator of the representativeness of the fluxes across the distributed network of three eddy covariance towers compared to only one, showed, in conjunction with the other results, that the spatial heterogeneity across the agroforestry was better captured by the network of three stations. This supports previous findings that spatial heterogeneity should be taken into account in eddy covariance studies and that lower-cost setups may offer the opportunity to bridge this gap and improve the accuracy of eddy covariance measurements above heterogeneous ecosystems.</p

Magmatic nickel sulfide mineralization in Zimbabwe: Review of deposits and development of exploration criteria for prospectivity analysis

Significant magmatic nickel sulfide deposits in Zimbabwe occur in Archean greenstone belts and Archean to Proterozoic mafic–ultramafic intrusions, such as Madziwa and the Great Dyke. Here, we review exploration criteria for magmatic nickel sulfide deposits, taking into account nickel sulfide mineral systems in general, Zimbabwe's cratonic evolution and the geological setting of the deposits. We propose that the essential ingredients for nickel sulfide mineral systems in Zimbabwe are (i) proximity to greenstone belts, craton margins and orogenic belts; (ii) large mafic–ultramafic intrusions and their feeders; (iii) crustal contamination of basic–ultrabasic magma with sulfidic crustal lithologies; and (iv) the vicinity to major fault zones that allowed fertile magma to ascend into the upper crust. We suggest that there is potential for new nickel sulfide discoveries, both within and outside the greenstone belts; including the Karoo flood basalt province, the Mashonaland dolerites, and the Limpopo, Magondi and Zambezi orogenic belts

Carbonaceous aerosols in a wood burning community in rural New Zealand

AbstractParticulate matter (PM) in Masterton, New Zealand, a rural community with a population of 20 000, was studied during the winter to gain an understanding of the carbonaceous species and their influence on PM concentrations. The average PM10 concentration during the winter was 21.0±14.8 µg m–3, of which 64% was PM2.5. PM2.5 concentrations were found to be the main cause of elevated PM10 concentrations, and were responsible for exceedances of the New Zealand National Environmental Standard for PM10. Carbonaceous species were 47 and 77% of the total PM10 and PM2.5, respectively. Organic carbon (OC) concentrations were always higher than elemental carbon (EC) concentrations. OC and EC concentrations showed excellent correlation with PM2.5 concentrations, suggesting that combustion processes were the dominant source of PM. Stable isotope analysis yielded δ13C values ranging from –24.9 to –27.6‰, which is indicative of wood combustion. Analysis of particle–phase PAHs by thermal desorption GC/MS yielded an average total PAH concentration of 38.9±25.9ng m–3, accounting for 0.3% of the PM2.5. Analysis of all of the results revealed that residential wood burning for domestic heating was the main source of PM pollution in Masterton. The results of this study suggest that a PM10 standard alone, particularly in areas where wood combustion is common, may not be providing an adequate level of protection for the exposed population

Composition and source contributions of air particulate matter pollution in a New Zealand suburban town

AbstractWainuiomata, a suburban town located at the southern end of the North Island of New Zealand, is subject to air particulate matter pollution episodes during the winter. The results of fine (PM2.5) and coarse (PM2.5–10) particulate matter monitoring in Wainuiomata from July 2006–September 2008 are presented. Receptor modeling was used to determine the sources contributing to particulate matter pollution and mass contributions to ambient particle concentrations from emission sources were estimated. PM10 concentrations displayed a seasonal pattern, with peak concentrations occurring during the winter. The results demonstrate that marine aerosol and crustal matter sources were the primary contributors to the coarse particle fraction, while the fine particle fraction was dominated by biomass burning with smaller contributions from marine aerosol and secondary sulfate particles. Arsenic was found to be present in the fine particle fraction and was associated with biomass burning, suggesting the use of copper chrome arsenate treated timber for domestic heating. Analysis of seasonal differences revealed that biomass burning was largely responsible for fine particle pollution episodes during the winter. Marine aerosol featured significantly as a PM10 source all year due to New Zealand’s remote oceanic location