Future Field Investigations Research Articles

Enhancing citrus fruit yield investigations through flight height optimization with UAV imaging

Citrus fruit yield is essential for market stability, as it allows businesses to plan for production and distribution. However, yield estimation is a complex and time-consuming process that often requires a large number of field samples to ensure representativeness. To address this challenge, we investigated the optimal altitude for unmanned aerial vehicle (UAV) imaging to estimate the yield of Citrus unshiu fruit. We captured images from five different altitudes (30 m, 50 m, 70 m, 90 m, and 110 m), and determined that a resolution of approximately 5 pixels/cm is necessary for reliable estimation of fruit size based on the average diameter of C. unshiu fruit (46.7 mm). Additionally, we found that histogram equalization of the images improved fruit count estimation compared to using untreated images. At the images from 30 m height, the normal image estimates fruit numbers as 73, 55, and 88. However, the histogram equalized image estimates 88, 71, 105. The actual number of fruits is 124, 88, and 141. Using a Vegetation Index such as IPCA showed a similar estimation value to histogram equalization, but I1 estimation represents a gap to actual yields. Our results provide a valuable database for future UAV field investigations of citrus fruit yield. Using flying platforms like UAVs can provide a step towards adopting this sort of model spanning ever greater regions at a cheap cost, with this system generating accurate results in this manner.

Ground Validation Reveals Limited Applicability of Species Distribution Models for Dakota Skipper (Hesperia dacotae, Lepidoptera: Hesperiidae) Recovery Efforts in Canada.

Species distribution models (SDMs) use spatial relationships between species occurrence and habitat (predictor) variables to generate maps of habitat suitability across a region of interest. These maps are frequently used in recovery planning efforts for endangered species, but they are influenced by data availability, selection of predictor variables, and choice of model type. Ground validation is necessary to robustly evaluate map accuracy, but it is rarely done, making it difficult to determine which modeling approach is best-suited for a given species or region. To address this uncertainty, we used two SDM types (Maxent and GLM) and two methods of selecting predictor variables to build four SDMs for an endangered prairie butterfly (Dakota skipper, Hesperia dacotae) in two regions of Manitoba, Canada. We then conducted field-based habitat suitability assessments at 120 locations in each region to enable direct comparisons of model output and accuracy. We found that soil type and surrounding landcover (grassland versus cropland) were important predictors of species occurrence regardless of region, predictor selection method, or model type. Cross-validation statistics indicated that most SDMs performed well (AUC > 0.7), but ground validation revealed that the habitat suitability maps they generated were inaccurate (Cohen's kappa < 0.4). Maxent models produced more accurate maps than GLMs, likely because false species absences adversely affected the latter, but only one Maxent-based map was accurate enough to help locate sites for future field investigations (Cohen's kappa > 0.3). Our results emphasize the importance of ground-validating SDM-based habitat suitability maps before incorporating them into species recovery plans.

Investigation of chigger mites on small mammals in Ruili, Yunnan Province, China.

Chigger mites are arthropods and are the sole vectors of scrub typhus, and rodents as well as other small mammals are the most common hosts of chigger mite larvae. Therefore, it is of great medical significance to study the ecology of chigger mites. In this study, a detailed analysis of chigger mites was conducted based on field survey data. A total of 4,941 chigger mites were collected from 86 hosts at 34 survey sites in Ruili, Yunnan Province, China. Among the 4,941 chiggers, five genera in one subfamily were identified; Schoengastiella ligula was the dominant chigger species with the highest infestation index, prevalence (Pm, 42.86%) and mean intensity (MI, 59.09%) (P<0.001). The association coefficient (V) between S. ligula and Gahrliepia radiopunctata was positively correlated (P<0.05), indicating the tendency of chiggers to select and coexist on the same host at the same time. The dominant species Leptotrombidium kunmingense, Ascoschoengastia indica, S. ligula and G. radiopunctata showed aggregation distribution patterns, indicating that the distribution of chiggers among different hosts was not uniform. Low altitudes and low latitudes appeared to be more favorable for the growth and reproduction of chigger mites (P<0.05). It is suggested to collect as many host samples as possible in future field investigations to better understand the dynamics of chigger mite populations and their primary hosts.

Degradation and adsorption of synthetic DNA water tracers in environmental matrices

Synthetic DNA tracers are gaining interest as tools for tracking contamination pathways and hydraulic connections in surface water and groundwater systems. However, few quantitative data exist that describe DNA tracer degradation and adsorption in environmental matrices. We undertook laboratory experiments to quantify the degradation of multiple double-stranded DNA tracers in stream water, groundwater, and domestic and dairy-shed effluent, and adsorption to stream sediments, soils, coastal sand aquifer media and alluvial sandy gravel aquifer media. Faster DNA tracer degradation seemed to be associated with high bacterial concentrations in the liquid phase. Overall, the degradation of the 352 base pair (bp) DNA tracers in the aqueous phase was significantly (P = 0.018) slower than that of the 302 bp DNA tracers. Although the tracers' internal amplicon lengths were similar, the longer non-amplified flanking regions of the 352 bp tracers may better protect them from environmental degradation. Thermodynamic analysis suggests that longer flanking regions contribute to greater tracer stability. This finding may explain our previous field observations that 352 bp tracer mass reductions were often lower than 302 bp tracer mass reductions. The 2 sets of DNA tracers did not differ significantly regarding their adsorption to stream sediment-stream water or aquifer media-groundwater mixtures (P > 0.067), but the 352 bp tracers showed significantly less adsorption to soil-effluent mixtures than the 302 bp tracers (P = 0.005). The DNA tracers' adsorption to soil-effluent mixtures was comparatively less than their adsorption to the aquifer media-groundwater and stream sediment-stream water mixtures, suggesting that DNA tracers may compete with like-charged organic matter for adsorption sites. These findings provide insights into the fate of DNA tracers in the environment. The DNA tracers' degradation rate constants determined in this study for a range of environmental conditions could assist the design of future field investigations.

The glacial geomorphology of sub-Antarctic Marion Island

ABSTRACT Since the discovery of glacial features on sub-Antarctic Marion Island, the character and extent of a historic glacial period have remained an important research focus for earth science investigations. Previous glacial reconstructions were limited to mostly pre-GPS field observations and pre-digital mapping through a Geographic Information System. With the aid of GPS field mapping, high-resolution satellite imagery and a digital surface model with a 1 × 1 m cell resolution, this paper provides a comprehensive, geo-rectified spatial geodatabase and map of Marion Island’s glacial geomorphology. The geodatabase includes an inventory of glacial erosional (e.g. striations) and depositional (e.g. moraines) features compiled from existing records as well as new features mapped from recent field observations. The final map and the geodatabase, which is downloadable as ESRI layer-package files, will aid future field investigations and modelling applications to understand Marion Island’s Quaternary landscape evolution and post-glacial ecological succession.

Potassium isotopic fractionation during clay adsorption

Clay adsorption is a critical process responsible for the mobilization and cycling of potassium (K) on Earth’s surface. Recent studies emphasized the potential of using stable K isotopes (δ41K) to understand chemical weathering. However, the direction, degree, and mechanism of K isotopic fractionation linked to clay K uptake during chemical weathering remain poorly constrained.This work investigated the mechanism of K adsorption on clays (kaolinite and smectite) and the isotopic fractionation in three experimental sets with K-containing solutions. The time-series experiments revealed that the adsorption and isotope equilibria were attainedafter less than 12-hour reaction. Potassium adsorption rate slowed down and its isotopic fractionation approached the steady-state during 15-day reaction. The pH-dependent experiments demonstrated that the percentage of clay K adsorption and the isotopic composition of adsorbed K (and aqueous K) display negative linear correlations. Net isotopic fractionation between adsorbed and aqueous phases (Δ41Kad-aq) remained near-constant (0.6–0.8‰), regardless of variations in pH ranging from 4 to 10. The concentration-control experiments demonstrated that the percentage of K adsorption decreased with increasing KCl concentrations from 0.005 to 20 mM. The δ41K values of aqueous K reached the minimum of −0.53‰ after 92.7% K adsorbed (initial KCl of 0.005 mM). Potassium adsorption was substantially suppressed as ionic strength (fixed by Na+) increased from 0.001 to 0.5 M without apparent Δ41Kad-aq variations. The K K-edge XANES demonstrated that primary K incorporated in clay lattice and surface KCl derived from sorbed K+ and Cl− synchro-dehydration can be identified after drying of clays. These features indicate that adsorbed K+ was bounded onto clays as outer-sphere complexes, which can be replaced with excess Na+ at high ionic strength. Based on experimental results, we cannot distinguish specific mineralogy regulation on K isotopic fractionation. In sum, isotopically heavy K is preferentially sorbed on clay minerals. The results confirm an equilibrium fractionation path independent of reaction time, pH, ionic strength, and initial KCl concentration. Observed K isotopic fractionation is best fitted by an equilibrium isotopic fractionation law with a fractionation factor αad-aq of 1.00075. We highlight the opposite direction of K isotopic fractionation in clay adsorption and structural incorporation during chemical weathering, and their comparative contributions should be considered for future field investigations.

Species distribution models advance our knowledge of the Neanderthals\u2019 paleoecology on the Iranian Plateau

Neanderthals (Homo neanderthalensis) were distributed across a vast region from Europe to western and Central Asia. The Neanderthals’ paleoecology and distribution has been extensively studied in Europe where the species originated. However, very little is known about their paleoecology in south-western Asia. Here, we employed species distribution modelling and 45 Middle Palaeolithic (c. 200,000–40,000 years BCE) sites location associated with fossil and/or lithic artefacts made by the Neanderthals to examine the expansion of the Neanderthals on the Iranian Plateau in south-western Asia. We estimated the niche overlap between Neanderthals and wild goat, wild sheep and Persian gazelle by modelling their past distribution using 200, 143 and 110 occurrence records respectively. The results show that Neanderthals had highest niche overlap with wild goat in the study area. This analysis revealed that the most suitable Neanderthals’ habitats in south-western Asia were located in the Zagros Mountains stretches from north-western and western and some isolated patches in the central parts of the Iranian Plateau. The annual precipitation and maximum temperature of the warmest month were the most important predictor of the species’ distribution. This finding shows that the southern edge of the Neanderthals distribution was limited by warm summer. Our results provide important information for future field investigations and excavations in the area.

Modeling Current and Future Potential Geographical Distribution of Carpinus tientaiensis, a Critically Endangered Species from China

Future climate change will have serious impacts on species survival and distribution and will likely lead to the extinction of some species classified as endangered. Carpinus tientaiensis (Betulaceae), a unique and endangered species in China, has restricted distribution and a small population, indicating an urgent need for its protection. However, research on its current distribution or the influence that climate change will have on its future survival and distribution is limited. We used a MaxEnt model and ArcGIS software to predict the current and future niches of C. tientaiensis. The current suitable distribution area of C. tientaiensis is small, mainly in east China, south Zhejiang and Anhui, and central and southern mountainous areas of Taiwan province. The core suitable areas are concentrated in the Xianxialing and Kuocang mountains in south Zhejiang, the southern mountains of Taiwan, and the Dabie, Huangshan and Jiuhua mountains in south Anhui. Among the 15 BIOCLIM variables examined, the precipitation of the driest quarter (bio17) was found to be the most important factor limiting C. tientaiensis survival and distribution. Future field investigations will focus on the Xianxialing and Kuocang mountains, as they may have unidentified wild C. tientaiensis communities. In the future, the Kuocang, Dapan and Tiantai mountains in east Zhejiang, and the high-altitude areas of Dabie and Jiuhua mountains in south Anhui, will be suitable for C. tientaiensis ex situ conservation and cultivation. However, the suitable distribution and core suitable areas for C. tientaiensis will decrease sharply as they are susceptible to climate shocks. Moreover, the suitable distribution area of C. tientaiensis is predicted to move slightly north and obviously eastward. Therefore, we suggest that strengthen conservation and management efforts for C. tientaiensis in its original habitats, and actively carry out ex situ conservation and artificial breeding in botanical gardens.

Spatial-temporal variations and source contributions to forest ozone exposure in China

As surface ozone (O3) concentrations have significantly increased in many regions of China, it is concerned that O3 may cause negative impacts on forests in the country. To estimate the risks of O3 exposure to forest health, several frequently used O3 exposure indices (M7, M24, N100, SUM60, W126, and AOT40f) were calculated for the entire year of 2013 and the source contributions to exposure in April and August were quantified using a source-oriented version of the Community Multiscale Air Quality (CMAQ) model. Critical loads for natural ecosystems (12 ppm-h for SUM60) and for moderately sensitive plant species (23.8 ppm-h for W126) are exceeded in 85% and 75% of the forest areas in China, respectively. About 90% of the forest areas have AOT40f higher than the critical load of 10 ppm-h. Forests in the western rim of the Sichuan Basin (WSCB), parts of the southern rim of the Qinghai-Tibetan Plateau (SQTP), Yunnan Province, and the North China Plain (NCP) have higher O3 exposure than that of other areas. In spring, transport of O3 and precursors from Southeast Asia have significant contributions to O3 exposure for forests in Yunnan, SQTP and to a less extent in WSCB. In both spring and summer, industries and transportation sectors have large contributions to O3 exposure along the WSCB and in the NCP. A higher priority in future field investigations to assess O3 impacts on forests in China should be given to these regions. The results also suggest that O3 production in China is much more due to nitrogen oxides (NOx) than due to volatile organic compounds (VOCs). In order to protect China's forest from O3, it would be most efficient to reduce NOx emissions from industries, transportation, and other countries in general.

Application of Numerical Tools to Investigate a Leaky Aquitard beneath Urban Well Fields

Memphis aquifer is the primary drinking water source in Shelby County (Tennessee, USA), and it supplies industrial, commercial, and residential water. Memphis aquifer is separated from the Shallow aquifer by a clayey layer known as the Upper Claiborne confining unit (UCCU). All of the production wells in the Memphis area are screened in the Memphis aquifer, or even deeper in the Fort Pillow aquifer. Traditionally, it was assumed that the UCCU could fully protect the Memphis aquifer from the contaminated Shallow aquifer groundwater. However, recent studies show that at some locations, the UCCU is thin or absent, which possibly leads to the contribution of Shallow aquifer to the Memphis aquifer. Accurately locating the breaches demands expensive and difficult geological or geochemical investigations, especially within an urban area. Hence, a pre-field investigation to identify the locations where the presence of breaches is likely can significantly reduce the cost of field investigations and improve their results. In this study, to identify the locations where the presence of breaches in the UCCU is likely, we develop a reliable MODFLOW-based numerical model, and use three different analyses: (1) pilot-point calibration (PPC), (2) velocity and flow budget (VFB), and (3) particle tracking (PT), to post-process the developed groundwater model results. These pre-field numerical investigations provide relevant and defensible explanations for groundwater flow anomalies in an aquifer system for informed decision-making and future field investigations. In this study, we identify five specific zones within the broad study area which are reasonable candidates for the future field investigations. Finally, we test the results of each analysis against other evidence for breaches, to demonstrate that the results of the numerical analyses are reliable and supported by previous studies.

Assessment of Antarctic moss health from multi-sensor UAS imagery with Random Forest Modelling

Moss beds are one of very few terrestrial vegetation types that can be found on the Antarctic continent and as such mapping their extent and monitoring their health is important to environmental managers. Across Antarctica, moss beds are experiencing changes in health as their environment changes. As Antarctic moss beds are spatially fragmented with relatively small extent they require very high resolution remotely sensed imagery to monitor their distribution and dynamics. This study demonstrates that multi-sensor imagery collected by an Unmanned Aircraft System (UAS) provides a novel data source for assessment of moss health. In this study, we train a Random Forest Regression Model (RFM) with long-term field quadrats at a study site in the Windmill Islands, East Antarctica and apply it to UAS RGB and 6-band multispectral imagery, derived vegetation indices, 3D topographic data, and thermal imagery to predict moss health. Our results suggest that moss health, expressed as a percentage between 0 and 100% healthy, can be estimated with a root mean squared error (RMSE) between 7 and 12%. The RFM also quantifies the importance of input variables for moss health estimation showing the multispectral sensor data was important for accurate health prediction, such information being essential for planning future field investigations. The RFM was applied to the entire moss bed, providing an extrapolation of the health assessment across a larger spatial area. With further validation the resulting maps could be used for change detection of moss health across multiple sites and seasons.

Assessment of offshore oil/gas platform status in the northern Gulf of Mexico using multi-source satellite time-series images

Accurate knowledge of the detailed status (location and lifetime) of each oil/gas platform is crucial for ocean management and for understanding its potential environmental impact. However, this requirement is often compromised due to incomplete data records, especially when platform abandonment is not properly planned, designed, and/or executed. The availability of multi-source optical and SAR images provides the possibility of a systematic assessment, but the ubiquitous false positives and frequent geocoding errors make it technically challenging. Here, we develop a time-series remote sensing approach (TSRS) for detecting offshore platforms and determining their status, where the technical challenges are overcome using two strategies, as follows: (i) A stepwise optimization strategy applied to individual images and time-series images to mitigate numerous noises, to select platforms from candidates, and to assess platform status; and (ii) A cross geo-correction strategy using platforms derived from high-geometric accuracy images as ground control points to rectify poorly geo-referenced images. We applied the TSRS approach to the northern Gulf of Mexico using about 26,000 moderate-resolution optical/SAR images from eight satellites spanning the period from 1982 to 2017. TSRS detected a total of 9260 (5556) platforms in both Federal and State waters, including 3140 (1803) existing platforms, 5044 (3426) removed platforms, and 1076 (327) status-to-be-determined platforms where the numbers in parentheses represent those from Federal waters. Of these TSRS platforms, 4751 coincide spatially with 5476 (77.68%) of platform records of the Bureau of Safety and Environmental Enforcement (BSEE) platform database; 2846 (387 in Federal waters) are not found in the BSEE platform database but are convincingly supported by data from other sources (including BSEE-pipeline-database, time-series VIIRS nighttime light products, and littoral ground-truth images), meaning that 82.04% of the TSRS-derived platforms can be directly/indirectly confirmed. A site-specific validation in East Bay using multi-temporal ground-truth aerial images indicates that, for this site, the false negative rate (FNR) is ~9.63% and the false positive rate (FPR) is only 4.44%. The detailed beginning/end dates of the TSRS platforms are mostly confirmed by the corresponding Installation/Site-clear dates recorded in the BSEE platform database. Our findings suggest that the TSRS approach is a robust and cost-effective way to assess oil/gas platform status in large regions, and our results here may complement the official database, narrow down locations for future field investigations, and provide critical information for future assessment of the potential impacts of active and decommissioned platforms on the marine environments.

Field- and Lab-Based Potentiometric Titrations of Microbial Mats from the Fairmont Hot Spring, Canada

ABSTRACTPotentiometric titrations are an effective tool to constrain the protonation constants and site concentrations for microbial surface ligands. Protonation models developed from these experiments are often coupled with data from metal adsorption experiments to calculate microbial ligand-metal binding constants. Ultimately, the resulting surface complexation models can be used to predict metal immobilization behavior across diverse chemical conditions. However, most protonation and metal-ligand thermodynamic constants have been generated in laboratory experiments that use cultured microbes which may differ in their chemical reactivity from environmental samples. In this study, we investigate the use of in situ field potentiometric titrations of microbial mats at a carbonate hot spring located at Fairmont Hot Springs, British Columbia, with the aim to study microbial reactivities in a natural field system. We found that authigenic carbonate minerals complicated the potentiometric titration process due to a “carbonate spike” introduced by the contribution of inorganic carbonate mineral dissolution and subsequent carbonate speciation changes during the transition from low to high pH. This inhibits the determination of microbial surface ligand variety and concentrations. Our preliminary study also highlights the need for developing novel probes to quantify in situ microbial mat reactivity in future field investigations.

Does the Arctic charr Salvelinus alpinus produce sounds in a captive setting?

Arctic charr Salvelinus alpinus did not appear to invest in acoustic communication during courtship and agonistic interactions in captivity. Salvelinus alpinus did, however, produce four different types of sounds which were found to be associated with three different types of air exchange behaviours which probably have a swimbladder regulation function. Since air passage sounds appear to be common among Salmonidae, it is suggested that the potential of passive acoustics techniques for behavioural and ecological monitoring should be further investigated in future field and laboratory investigations.

In situ Laser Induced Breakdown Spectroscopy as a tool to discriminate volcanic rocks and magmatic series, Iceland

This study evaluates the potentialities of a lab-made pLIBS (portable Laser-Induced Breakdown Spectroscopy) to sort volcanic rocks belonging to various magmatic series. An in-situ chemical analysis of 19 atomic lines, including Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Na, Si, Sr and Ti, from 21 sampled rocks was performed during a field exploration in Iceland. Iceland was chosen both for the various typologies of volcanic rocks and the rugged conditions in the field in order to test the sturdiness of the pLIPS. Elemental compositions were also measured using laboratory ICP-AES measurements on the same samples. Based on these latter results, which can be used to identify three different groups of volcanic rocks, a classification model was built in order to sort pLIBS data and to categorize unknown samples. Using a reliable statistical scheme applied to LIBS compositional data, the classification capability of the pLIBS system is clearly demonstrated (90–100% success rate). Although this prototype does not provide quantitative measurements, its use should be of particular interest for future geological field investigations.

Estimation of uncertainty in the sampling and analysis of polychlorinated biphenyls and polycyclic aromatic hydrocarbons from contaminated soil in Brighton, UK

The heterogeneity of environmental samples is increasingly recognised, yet rarely examined in organic contamination investigations. In this study soil samples from an ex-landfill site in Brighton, UK were analysed for polychlorinated biphenyl (PCB) and polycyclic aromatic hydrocarbon (PAH) contamination by using a balanced sampling protocol. The analytical technique of gas chromatography–mass spectrometry was found to be fit for purpose by the use of duplicate samples and the statistical analysis of variances, as well as of certified reference materials. The sampling uncertainty was found to significantly overweigh the analytical uncertainty, by a factor of 3 and 6 for PCBs and PAHs, respectively. The soil samples showed a general trend of PCB concentration that was under the recommended target level of 20ng/g dry weight. It is possible that one site alongside the main road may exceed the 20ng/g target level, after taking into consideration the overall measurement uncertainty (70.8%). The PAH contamination was more severe, with seven sites potentially exceeding the effect-range medium concentrations. The soil samples with relatively high PCB and PAH concentrations were all taken from the grass verge, which also had the highest soil organic carbon content. The measurement uncertainty which was largely due to sampling can be reduced by sampling at a high resolution spacing of 17m, which is recommended in future field investigations of soil organic contamination.

Ectoparasitic insects and mites on Yunnan red-backed voles (Eothenomys miletus) from a localized area in southwest China

Ectoparasitic insects and mites on Yunnan red-backed voles (Eothenomys miletus) in Dali prefecture, Yunnan Province, southwest China, were studied between 2003 and 2004. In total, 34,389 individuals of 86 species of ectoparasitic insects (seven species of fleas and five species of sucking lice) and mites (23 species of gamasid mites and 51 species of chigger mites) were collected from 916 individual hosts. The diversity of ectoparasites on this single rodent species in such a small area was much higher than in previous reports, which concerned more host species and greater geographical areas. The majority of the ectoparasites were chigger mites, which accounted for 59.3% of the parasite species and 87.4% of the individual parasites. Most voles harbored parasites with an overall prevalence (P) of 82.5% and mean abundance (MA) of 37.5 parasites per host. The dispersion coefficient (C) and patchiness index (m*/m) were used to study the spatial patterns of the seven dominant parasite species, and all seven had aggregated distributions. The species abundance distribution of the ectoparasites on the vole was fitted by Preston's lognormal distribution (R (2) = 0.82), and the total expected parasite species was estimated from this plot as 167 species. Yunnan red-backed voles harbor many ectoparasites as revealed by examination of a large host population. Future field investigations should sample large numbers of host individuals to assess ectoparasite populations.

Applications of laser scanning to structures in laboratory tests and field surveys

SUMMARY The capabilities and advantages of laser scanners used for structural engineering applications to assess structural damage in laboratory tests and post-earthquake field survey are discussed. High definition laser scans have many advantages over conventional instrumentation in laboratory setting: (i) capture three dimensional global deformations of large objects with accuracy; (ii) enable graphical post-processing based on a location of the acquired points in space and utilizing the light intensity red–green–blue (RGB) values of scanned images; (iii) access to objects without spatial constraint and remote monitoring by scanning from a distance; and (iv) reduce workload for installing instruments. Therefore, high definition laser scans have been successfully used in laboratory tests, and several case studies are presented to demonstrate the accuracy of laser scanner measurements. In addition, this paper makes the first attempt to demonstrate the use of high-definition laser scanning technology in field surveys of structures damaged during January 2010 Haiti earthquake. Damage assessments were performed for several structures using the scans, and the results were compared with qualitative results of visual ground survey. The techniques of gathering and disseminating critical information employed herein is expected to have major impact on future structural laboratory tests and field investigations. Copyright © 2013 John Wiley & Sons, Ltd.

Contributions of individual reactive biogenic volatile organic compounds to organic nitrates above a mixed forest

Abstract. Biogenic volatile organic compounds (BVOCs) can react in the atmosphere to form organic nitrates, which serve as NOx (NO + NO2) reservoirs, impacting ozone and secondary organic aerosol production, the oxidative capacity of the atmosphere, and nitrogen availability to ecosystems. To examine the contributions of biogenic emissions and the formation and fate of organic nitrates in a forest environment, we simulated the oxidation of 57 individual BVOCs emitted from a rural mixed forest in northern Michigan. Key BVOC-oxidant reactions were identified for future laboratory and field investigations into reaction rate constants, yields, and speciation of oxidation products. Of the total simulated organic nitrates, monoterpenes contributed ~70% in the early morning at ~12 m above the forest canopy when isoprene emissions were low. In the afternoon, when vertical mixing and isoprene nitrate production were highest, the simulated contribution of isoprene-derived organic nitrates was greater than 90% at all altitudes, with the concentration of secondary isoprene nitrates increasing with altitude. Notably, reaction of isoprene with NO3 leading to isoprene nitrate formation was found to be significant (~8% of primary organic nitrate production) during the daytime, and monoterpene reactions with NO3 were simulated to comprise up to ~83% of primary organic nitrate production at night. Lastly, forest succession, wherein aspen trees are being replaced by pine and maple trees, was predicted to lead to increased afternoon concentrations of monoterpene-derived organic nitrates. This further underscores the need to understand the formation and fate of these species, which have different chemical pathways and oxidation products compared to isoprene-derived organic nitrates and can lead to secondary organic aerosol formation.

Interactions of Colletotrichum musae and Lasiodiplodia theobromae and their biocontrol by Pantoea agglomerans and Flavobacterium sp. in expression of crown rot of “Embul” banana

Previous research has shown that two local isolates of bacteria (Pantoea agglomerans and Flavobacterium sp.) are capable of biocontrol of the two main pathogens (Colletotrichum musae and Lasiodiplodia theobromae) known to cause crown rot on “Embul” (Musa, AAB) banana. In this investigation an attempt was made to elucidate the comparative virulence of these pathogens and to determine the underlying biocontrol mechanisms. L. theobromae was more virulent, causing faster spread of the disease, whereas C. musae was more resistant to the bacterial antagonists. Viable cells of the antagonists were more effective at suppressing conidial germination than cell-free culture media. It seemed that antifungal compounds acting on conidial germination may be heat stable and those acting on mycelia may include heat labile compounds also. Considering the specialized roles observed for each pathogen in terms of causing the disease, and in modes of control by antagonists, future field investigations on biocontrol should consider the roles played by the pathogens and the antagonists.