Flooding depths and burial effects on seedling emergence of five California weedy rice (Oryza sativa spontanea) accessions

Weedy rice (Oryza sativa f. spontanea Roshev.) has recently become a significant botanical pest in California rice (Oryza sativa L.) production systems. The conspecificity of this pest with cultivated rice, Oryza sativa (L.), negates the use of selective herbicides, rendering the development of non-chemical methods a necessary component of creating management strategies for this weed. Experiments were conducted to determine the emergence and early growth responses of O. sativa spontanea to flooding soil and burial conditions. Treatment combinations of four flooding depths (0, 5, 10, and 15 cm) and four burial depths (1.3, 2.5, 5, and 10 cm) were applied to test the emergence of five O. sativa spontanea accessions as well as ‘M-206’, a commonly used rice cultivar in California, for comparison. Results revealed that burial depth had a significant effect on seedling emergence. There was a 43-91% decrease in emergence between seedlings buried at 1.3 and 2.5 cm depending on the flooding depth and accession, and an absence of emergence from seedlings buried at or below 5 cm. Flooding depth did not affect emergence, but there was a significant interaction between burial and flooding treatments. There was no significant difference between total O. sativa spontanea emergence from the soil and water surfaces regardless of burial or flooding depths, implying that once the various accessions have emerged from the soil they will also emerge from the floodwater. Most accessions had similar total emergence compared to M-206 cultivated rice, but produced more dry weight than M-206 when planted at 1.3 cm in the soil. The results of this experiment can be used to inform stakeholders of the flooding conditions necessary as well as soil burial depths that will promote or inhibit the emergence of California O. sativa spontanea accessions from the weed seedbank.

Geochemical characteristics and origins of biodegraded oils in the Bongor Basin (Chad) and their implications for petroleum exploration

The Bongor Basin is a typical lacustrine passive-rifted basin situated in the West and Central African Rift System (WCARS). It has experienced two phases of tectonic inversion and features a complex process of petroleum generation and accumulation. A total of 41 crude oil samples from the basin were geochemically analyzed to investigate their compositions of molecular markers. The results show that the oils have similar origins and are likely to belong to the same oil population. However, there are significant differences in geochemical characteristics and physical properties, caused by the secondary alteration. The relative contents and distribution patterns of normal alkanes and acyclic isoprenoids indicate that some of the oils have suffered biodegradation to varying degrees. The samples can be divided into three categories according to their relative degrees of degradation: normal oil, slightly biodegraded oil (PM 1–3), and severely biodegraded oil (PM 5–7). The burial depth of oil reservoirs in this area is the predominant factor impacting on the level of biodegradation. Crude oils in reservoirs with burial depths of less than 800 m are all severely biodegraded, while oils in reservoirs with burial depths greater than 1300 m have experienced no evident biodegradation. In reservoirs with burial depths between 800 m and 1300 m, the biodegradation degrees vary from normal to severely biodegraded. Oil reservoirs with burial depths less than 1300 m and adjacent to major faults are readily subject to biodegradation, while reservoirs with similar burial depths, but a certain distance away from major faults, have suffered no evident biodegradation. Moreover, if primary reservoirs have been modified by tectonic activity after accumulation, the crude oils are more likely to be biodegraded. Faulted anticline traps may create more favorable geological conditions for preservation of crude oil than reverse extrusion anticline reservoirs. This study may provide practical guidance for the assessment and prediction of oil quality in future oil exploration.

Seedbank persistence of four summer grass weed species in the northeast cropping region of Australia

Summer grass weed species are a particular problem in the northeast cropping region of Australia because they are prolific seeders and favor no-till systems. Information on weed seed persistence levels can be used for the development of effective and sustainable integrated weed management programs. A field study was conducted over 42 months to evaluate the seedbank persistence of Chloris truncata, C. virgata, Dactyloctenium radulans, and Urochloa panicoides as affected by burial depth (0, 2, and 10 cm). Regardless of species, buried seeds persisted longer than surface seeds and there was no difference in seed persistence between 2 and 10 cm depths. Surface seeds of C. truncata depleted completely in 12 months and buried seeds in 24 months. Similarly, C. virgata seeds placed on the soil surface depleted in 12 months. Buried seeds of this species took 18 months to completely deplete, suggesting that C. truncata seeds persist longer than C. virgata seeds. Surface seeds of D. radulans took 36 months to completely deplete, whereas about 7% of buried seeds were still viable at 42 months. U. panicoides took 24 and 42 months to completely exhaust the surface and buried seeds, respectively. These results suggest that leaving seeds on the soil surface will result in a more rapid depletion of the seedbank. Information on seed persistence will help to manage these weeds using strategic tillage operations.

Prediction and Treatment of Water Leakage Risk Caused by the Dynamic Evolution of Ground Fissures in Gully Terrain

Groundwater leakage in the loess gully terrain is one of the main hazards of coal seam mining at shallow burial depth. The burial depth of the 5−2 coal seam is less than 50 m from the ground in the gully of the study site. The fissures that expand upward after mining can easily penetrate the ground to form a water-conducting channels. During rainy periods, there is a potential risk of groundwater leakage. In order to reveal the characteristics of plane development and the dynamic evolution of gully ground fissures, the typical U-shaped gully in the northern Shaanxi coal mine was studied using the field measurement methods of “On-site measurement” and UAV aerial photography. Based on the experimental platform of ground fissure leakage developed and designed by the team, an indoor test model corresponding to the actual situation was established. In addition, the mathematical models of actual flood inrush, fissure width, and flood flow in the channel were established. The actual mine water flow and the mine drainage capacity were compared and analyzed, thus proposing criteria for classifying gully mining ground fissure collapsed water hazards. These criteria can provide theoretical references for predicting fissure leakage hazard zones in the ground gully of shallow buried coal seams. According to the development height of the water-conducting fissure zone (WCFZ), the treatment methods of ground fissures in gullies under different security conditions were designed, which was applied in the field with good results. The results showed that the treatment methods in this paper could effectively prevent the leakage of groundwater in the gullies along the ground fissures.

An Impact-Echo Experimental Approach for Detecting Concrete Structural Faults

For the current problem of detection of grouting defects in posttensioned prestressed concrete members, the paper takes a single-layer arrangement of prestressed pipes as the object of study. The influence law of the main factors such as pipe material, defect size, defect critical surface location, and prestressing reinforcement location on the results of the impact-echo method for detecting concrete grouting defects was studied. Firstly, the ABAQUS finite element software was used to simulate these factors to obtain the influence law on the detection results, and a modal test was conducted to verify them. The results show that the impact-echo method can effectively test the location of defects and the degree of burial depth, and the pipe material influences the test results, and the impact of corrugated metal pipe is smaller and more accurate than the PVC pipe. In addition, the greater the plate thickness frequency drift rate, the larger the transverse size of the defect, so the plate thickness frequency drift rate and the measured defect depth are combined to quantitatively determine the depth of the defect.

Archaeological investigations in the shallow seawater environment with electrical resistivity tomography

This work explores the applicability and effectiveness of electrical resistivity tomography in mapping archaeological relics in the shallow marine environment. The approach consists of a methodology based on numerical simulation models validated with comparison to field data. Numerical modelling includes the testing of different electrode arrays suitable for multi-channel resistivity instruments (dipole–dipole, pole–dipole, and gradient). The electrodes are placed at fixed positions either floating on the sea surface or submerged at the bottom of the sea. Additional tests are made concerning the resolving capabilities of electrical resistivity tomography with various seawater depths and target characteristics (dimensions and burial depth of the targets). Although valid a priori information, in terms of water resistivity and thickness, can be useful for constraining the inversion, it should be used judiciously to prevent erroneous information leading to misleading results. Finally, an application of the method at a field site is presented not only for verifying the theoretical results but also at the same time for proposing techniques to overcome problems that can occur due to the special environment. Numerical and field electrical resistivity tomography results indicated the utility of the method in reconstructing off-shore cultural features, demonstrating at the same time its applicability to be integrated in wider archaeological projects.

Design and Analysis of Earthing System for Wind Turbine Generators from Lightning Discharge Currents

<p>Currently, wind power production is undergoing rapid growth due to the escalating interest in green energy generation. As a result, generators are now choosing to locate wind turbine generators (WTGs) in areas where there is more lightning activity, and earthing problems can be exacerbated further by the soil resistivity being higher than where turbines are usually located. In addition, the desire to capture more energy from the wind has given way to larger WTGs, further increasing the probability of lightning strikes to the structure. This heightened regularity has emphasized the need for an effective grounding system, capable of dissipating the large currents discharged by the lightning into the lightning protection system. This “effective grounding system” must offer a low impedance by limiting the ground potential rise, which is critical due to the wider frequency content of the lightning discharge currents (ranging from DC to several MHz). The design of an effective grounding system for WTGs depends on the calculation of the minimum length of the earth electrodes, soil resistivity and its frequency-dependency, and the impact of WTG foundation. The calculation of the length of earth electrodes needs an accurate measurement of soil resistivity and modeling of the measured resistivity. Hence, this research considers the measured soil resistivity values of an Australian wind farm and presents an analysis of the soil stratification to identify the optimum soil models. The influence of the soil layers on the WTG grounding system is also investigated to install the earth electrodes. As the resistivity of the soil is frequency-dependent, an analysis is performed to evaluate the effect of the frequency-dependent soil parameters on the WTG grounding system at various frequencies of lightning discharge current. In addition, the impact of the rebar of the WTG foundation on the grounding system is evaluated as the rebar shares the lightning discharge currents. The effective length of the earth electrodes is frequency-dependent, and rebar determines the impedance of the grounding system at high-frequencies. The next step in the grounding design is the design of earth electrodes. The current dissipating capacity of the earth electrodes depends on soil resistivity, dimensions of the earth electrodes, and burial depth of the electrodes. However, the traditional practice of designing earth electrodes is based on the soil resistivity alone, considering the uniform soil resistivity model. The conventional method of designing earth electrodes based on the uniform soil resistivity is not practical due to non-homogeneous behavior of the soil resistivity. To enhance the WTG earthing system design, this research proposes a novel method to calculate the minimum length of an earth electrode for uniform and two-layer based soil models considering electrode dimensions and burial depth. The grounding impedance achieved when electrode lengths are calculated using the proposed method is compared to grounding impedance values computed using the conventional method. This comparison shows that the proposed method is an improvement on the current convention. In particular, the proposed method gives a grounding impedance value of less than 10 Ω at low frequencies for all soil resistivity values. This results in a reduction in the potential rise of up to 64% compared to the peak potential value in the conventional method. The benefits offered by the proposed method mean that it can be employed to calculate electrode lengths for the required resistance values based on soil resistivity, electrode dimensions, and burial depth. Such a design may serve as a starting point for an engineer wishing to design a WTG earthing system. Another challenge noted is the practice of assessing the effectiveness of the WTG grounding system. The conventional method is based on achieving a low-frequency resistance of 10 Ω according to the standard IEC 61400-24 and the performance of the grounding system at high frequencies is not considered. Hence, identification of the high-frequency components of the relevant lightning discharge currents is important to understand the performance of the grounding system. An analysis of the wind turbine earthing system for different lightning discharge current wave shapes is performed considering the lightning current waveforms and parameters mentioned in the IEC 61400-24 standard and evaluated the various frequency components and their influence on the WTG grounding system. It is identified that the impedance of the grounding system is minimum for the first short positive stroke current parameters for all the soil resistivity values compared to the first short negative and the subsequent short current wave shapes, although the peak current magnitude is highest for this wave shape. From the analysis of WTG grounding system based on various parameters, this research presents a procedure for assessing the effectiveness of WTG lightning protection system with a focus on the grounding system. It is identified that the effectiveness of the grounding system can be improved by proper design of earth electrodes, optimum soil stratification, and selecting low resistivity soil sites. Finally, various earth electrode configurations are evaluated to identify the better electrode configuration for WTG grounding system. This thesis provides an in-depth analysis of WTG grounding systems to protect WTGs from lightning strikes. The contributions of this research will help wind farm architects to design effective grounding systems leading to effective lightning protection systems. Finally, the contributions will help to increase the adoption of wind power, resulting in more renewable energy generation. The outcome of this research can be realized to reduce the downtime of WTGs by incorporating the effectiveness of lightning protection system component into the wind farm optimization process. Also, a generalized procedure for calculating the minimum length of earth electrodes for all the soil models can be developed in the future.</p>

Design and Analysis of Earthing System for Wind Turbine Generators from Lightning Discharge Currents

<p>Currently, wind power production is undergoing rapid growth due to the escalating interest in green energy generation. As a result, generators are now choosing to locate wind turbine generators (WTGs) in areas where there is more lightning activity, and earthing problems can be exacerbated further by the soil resistivity being higher than where turbines are usually located. In addition, the desire to capture more energy from the wind has given way to larger WTGs, further increasing the probability of lightning strikes to the structure. This heightened regularity has emphasized the need for an effective grounding system, capable of dissipating the large currents discharged by the lightning into the lightning protection system. This “effective grounding system” must offer a low impedance by limiting the ground potential rise, which is critical due to the wider frequency content of the lightning discharge currents (ranging from DC to several MHz). The design of an effective grounding system for WTGs depends on the calculation of the minimum length of the earth electrodes, soil resistivity and its frequency-dependency, and the impact of WTG foundation. The calculation of the length of earth electrodes needs an accurate measurement of soil resistivity and modeling of the measured resistivity. Hence, this research considers the measured soil resistivity values of an Australian wind farm and presents an analysis of the soil stratification to identify the optimum soil models. The influence of the soil layers on the WTG grounding system is also investigated to install the earth electrodes. As the resistivity of the soil is frequency-dependent, an analysis is performed to evaluate the effect of the frequency-dependent soil parameters on the WTG grounding system at various frequencies of lightning discharge current. In addition, the impact of the rebar of the WTG foundation on the grounding system is evaluated as the rebar shares the lightning discharge currents. The effective length of the earth electrodes is frequency-dependent, and rebar determines the impedance of the grounding system at high-frequencies. The next step in the grounding design is the design of earth electrodes. The current dissipating capacity of the earth electrodes depends on soil resistivity, dimensions of the earth electrodes, and burial depth of the electrodes. However, the traditional practice of designing earth electrodes is based on the soil resistivity alone, considering the uniform soil resistivity model. The conventional method of designing earth electrodes based on the uniform soil resistivity is not practical due to non-homogeneous behavior of the soil resistivity. To enhance the WTG earthing system design, this research proposes a novel method to calculate the minimum length of an earth electrode for uniform and two-layer based soil models considering electrode dimensions and burial depth. The grounding impedance achieved when electrode lengths are calculated using the proposed method is compared to grounding impedance values computed using the conventional method. This comparison shows that the proposed method is an improvement on the current convention. In particular, the proposed method gives a grounding impedance value of less than 10 Ω at low frequencies for all soil resistivity values. This results in a reduction in the potential rise of up to 64% compared to the peak potential value in the conventional method. The benefits offered by the proposed method mean that it can be employed to calculate electrode lengths for the required resistance values based on soil resistivity, electrode dimensions, and burial depth. Such a design may serve as a starting point for an engineer wishing to design a WTG earthing system. Another challenge noted is the practice of assessing the effectiveness of the WTG grounding system. The conventional method is based on achieving a low-frequency resistance of 10 Ω according to the standard IEC 61400-24 and the performance of the grounding system at high frequencies is not considered. Hence, identification of the high-frequency components of the relevant lightning discharge currents is important to understand the performance of the grounding system. An analysis of the wind turbine earthing system for different lightning discharge current wave shapes is performed considering the lightning current waveforms and parameters mentioned in the IEC 61400-24 standard and evaluated the various frequency components and their influence on the WTG grounding system. It is identified that the impedance of the grounding system is minimum for the first short positive stroke current parameters for all the soil resistivity values compared to the first short negative and the subsequent short current wave shapes, although the peak current magnitude is highest for this wave shape. From the analysis of WTG grounding system based on various parameters, this research presents a procedure for assessing the effectiveness of WTG lightning protection system with a focus on the grounding system. It is identified that the effectiveness of the grounding system can be improved by proper design of earth electrodes, optimum soil stratification, and selecting low resistivity soil sites. Finally, various earth electrode configurations are evaluated to identify the better electrode configuration for WTG grounding system. This thesis provides an in-depth analysis of WTG grounding systems to protect WTGs from lightning strikes. The contributions of this research will help wind farm architects to design effective grounding systems leading to effective lightning protection systems. Finally, the contributions will help to increase the adoption of wind power, resulting in more renewable energy generation. The outcome of this research can be realized to reduce the downtime of WTGs by incorporating the effectiveness of lightning protection system component into the wind farm optimization process. Also, a generalized procedure for calculating the minimum length of earth electrodes for all the soil models can be developed in the future.</p>

Seed germination ecology of Conyza sumatrensis populations stemming from different habitats and implications for management

Conyza sumatrensis (Retz.) E. H. Walker is an obnoxious weed, emerging as an invasive species globally. Seed germination biology of four populations of the species stemming from arid, semi-arid, temperate, and humid regions was determined in this study. Seed germination was recorded under six different environmental cues (i.e., light/dark periods, constant and alternating day and night temperatures, pH, salinity, and osmotic potential levels) in separate experiment for each cue. Populations were main factor, whereas levels of each environmental cue were considered as sub-factor. The impact of seed burial depths on seedling emergence was inferred in a greenhouse pot experiment. Seed germination was recorded daily and four germination indices, i.e., seed germination percentage, mean germination time, time to reach 50% germination, and mean daily germination were computed. Tested populations and levels of different environmental cues had significant impact on various seed germination indices. Overall, seeds stemming from arid and semi-arid regions had higher seed germination potential under stressful and benign environmental conditions compared to temperate and humid populations. Seed of all populations required a definite light period for germination and 12 hours alternating light and dark period resulted in the highest seed germination. Seed germination of all populations occurred under 5–30°C constant and all tested alternate day and night temperatures. However, the highest seed germination was recorded under 20°C. Seeds of arid and semi-arid populations exhibited higher germination under increased temperature, salinity and osmotic potential levels indicating that maternal environment strongly affected germination traits of the tested populations. The highest seed germination of the tested populations was noted under neutral pH, while higher and lower pH than neutral had negative impact on seed germination. Arid and semi-arid populations exhibited higher seed germination under increased pH compared to temperate and humid populations. Seed burial depth had a significant effect on the seedling emergence of all tested populations. An initial increase was noted in seedling emergence percentage with increasing soil depth. However, a steep decline was recorded after 2 cm seed burial depth. These results indicate that maternal environment strongly mediates germination traits of different populations. Lower emergence from >4 cm seed burial depth warrants that deep burial of seeds and subsequent zero or minimum soil disturbance could aid the management of the species in agricultural habitats. However, management strategies should be developed for other habitats to halt the spread of the species.