Effects Of Different Disturbances Research Articles

Spatial variability of CH4 uptake in aerated soils of Yellow River Delta

The widespread occurrence of aerated plain soils underscores their significant role in the global soil methane (CH4) sink budget. However, plain soils are poorly characterized in terms of spatial variability of CH4 uptake and the relevant control. We investigated the intra- and inter-site spatial variability of CH4 uptake through flux measurements in intact soil cores from five non-wetland sites within the Yellow River Delta, each representing a distinct land use/cover type. Methane uptake rates were highest in undisturbed forest cores. The rates were very low, often falling below the detection limit, in cores from the other four sites. The significant correlation between CH4 uptake and bulk density across sites suggests the integrative role of bulk density for the effects of different disturbances (including salt stress and succession) on CH4 uptake. Methane uptake was heterogeneous at the within-site scale as indicated by large coefficients of variations (CVs). Soil texture variation manipulated the within-site pattern of CH4 uptake in the low-salinity sites. Salt affected the spatial variation of CH4 uptake only at high level of salinity. Neither Potter's nor Ridgwell's models effectively captured the within-site variation of CH4 uptake due to a texture-associated bias in the models. Establishing a quantitative relationship between CH4 uptake and clay content at the field scale in alluvial plain soils will facilitate the refinement of model parameters linked to texture and rectify biases in CH4 estimation. These results provide an insight for the biogeochemical control of CH4 uptake in alluvial plain soils and have important application for improving CH4 models.

Structure and Function of Fungal Community in Channel Sediments of Different Sections of Jialing River

This study aimed to explore the effects of different disturbances on the fungal communities in the sediments of the Jialing River in order to provide scientific basis for the protection of the river ecosystem. The fungal community in the sediments of the main stream of the Jialing River was taken as the research object, and high-throughput sequencing and bioinformatics techniques were used to analyze the differences in the composition and function of fungal communities in river sediment of different types of disturbance （project disturbance, tributary disturbance, sand mining disturbance, and reclamation disturbance） and non-disturbance sections. The results showed that： ① The reclamation and project disturbances significantly inhibited the diversity and richness of fungal communities （P<0.05）. The tributary disturbance increased the richness of fungal communities, whereas the impact of sand mining disturbance on sediment fungal communities was not significant. ② The diversity and composition of fungal communities tended to be similar at the different sampling sites in the section with low input of exogenous substances （non-disturbance and sand mining disturbance）, whereas there were obvious differences in the diversity of fungal communities at the different sampling sites of high input of external substances （tributary disturbance, project disturbance, and reclamation disturbance） sections. ③ Ascomycota, Rozellomycota, and Basidiomycota were the main dominant fungal phyla in the sediments of the Jialing River. The relative abundance of Rozellomycota was the highest in the sand mining interference section, and the relative abundance of Basidiomycota was the highest in the tributary interference section. Project disturbance significantly increased the relative abundance of saprotrophs, animal pathogens, plant pathogens, and dung saprotrophs, whereas other disturbances inhibited the relative abundance of fungal parasitic fungi, plant pathogens, and plant saprophytes. In conclusion, human disturbance has caused changes in fungal diversity, community structure, and function in the sediment of the Jialing River, and xenobiotic input was a key factor contributing to this phenomenon. The results can provide a reference for predicting and evaluating the ecological quality of river sediments.

Conversion Control for Remote Sensing Stable Platforms for Transient and Continuous Disturbances

An airborne electro-optical stabilized platform is a device situated between the aircraft and the imaging components, which serves to isolate external disturbances and maintain imaging axis stability for the imaging components. In light of the impact of transient and continuous attitude changes of the aircraft on the axis-stabilized imaging in visible light unmanned aerial vehicle (UAV) remote sensing missions, a control method combining a proportional-integral (PI) controller and a backpropagation neural network (BPNN) PID conversion control was devised. The specific procedure involved the following steps: firstly, the transfer mechanism of external disturbances between platforms was derived using the state transition matrix through mechanistic modelling. Secondly, the multi-rigid body dynamics equations of the airborne electro-optical platform were established based on Newton’s laws of motion and Euler’s laws. Subsequently, the relationship between the stable platform rotation angle and external disturbances was obtained using Laplace transformation, and an analysis was conducted on the effects of different disturbances on the stable platform. Lastly, conversion control was incorporated into the system model for simulation analysis. The simulation results demonstrated that transient disturbances could be effectively and rapidly isolated by the PI controller, while continuous disturbances exhibited improved performance when handled by the neural network PID controller, thus validating the efficacy of the designed conversion control method.

Various disturbances propagation analysis of district heating system based on the standardized thermal resistance method

AbstractVarious heating disturbances and faults in the heating network are necessary to be controlled and handled by some intelligent heating strategies with the increasing complexity of the heating network. This paper constructed the dynamic modeling of the heating system using standard thermal resistance and obtained a dynamic heat current model of the heating system. On this basis, we analyzed the heat transfer performance of the heating system. Five disturbances are selected, including the behavior of users, indoor heat source, heat exchanger heat transfer performance deterioration, pipe blockage, and pipe leakage. The effects of different disturbances on the overall system and user side water supply temperature were obtained by establishing a dynamic model for segmented heating pipelines. Feasible control methods for the heating network and load side are sorted out, mainly changing the water supply's temperature and the water supply's flow rate to reduce the water supply's fluctuation. Five specific control strategies are proposed for five types of disturbances. Comparing the case without control and the case with control, the results show that the fluctuation of water supply temperature is significantly reduced, and the control strategies can reduce the impact of disturbances on the heat network system and customers and improve the comfort of customers in the presence of disturbances. under the disturbance of pipeline leakage, the method proposed in this article reduces the temperature fluctuation amplitude by 75% and the fluctuation duration by 60%.

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

AbstractThe relationship between biodiversity and the stability of ecosystem functioning over time has been widely studied. The current global context has refloated this topic for biodiversity's role in buffering the effects of different disturbances. In general, the results of these studies show that ecosystem functioning is more stable over time in more diverse systems. However, these results are derived from empirical research on small‐scale studies, where species and disturbances conditions are manipulated. In this work, we used climate and floristic information data obtained from surveys over an extended period on Flooding Pampa grasslands (Argentina) with a remotely sensed indicator of the stability of net primary productivity at a regional scale over a broad temporal range to evaluate the relationship between species diversity and the stability of ecosystem functioning under different water conditions. We found a close correlation between Normalized Difference Vegetation Index responses of natural grasslands and climate variability in the study area. Besides, grasslands with higher species richness and diversity showed greater stability in ecosystem functioning at different water conditions. The results obtained could be relevant in natural resource management for the close relationship between diversity–stability in a local and regional productive context characterized by a simplified landscape of space and time.

Disentangling the effects of climate and defoliation on forest growth: The case of an outbreak of a Thaumetopoea pityocampa population with a shifted phenology in a Pinus pinaster monoculture

Forests are widely affected by disturbances, both abiotic, climate related, and biotic, like insect outbreaks. However, the impact of the interaction of these disturbances on tree growth is still not well understood. On the present work the impact of climatic and long-term defoliation by Thaumetopoea pityocampa (Dennis and Schiff.) during summer on Pinus pinaster growth was evaluated. At the National Pine Forest of Leiria, in Portugal, we sampled defoliated and non-defoliated forest plots covered by monocultures of young P. pinaster trees. Growth was assessed using dendrochronological techniques, and its relationship with climatic variability, including severe droughts, and defoliation, was analysed using hierarchical partitioning models. Results suggest that long term defoliation result in trees not being able to take advantage of favourable climatic conditions, leading to a reduced radial and height growth. Droughts were the major climatic disturbance, causing growth reduction as well, although the impacts of both disturbances did not act synergistically. Additionally, models showed that previous year climatic conditions have a significant effect on annual growth, namely, previous year annual precipitation and temperature. Yet, the best model obtained include a positive effect of the previous year annual precipitation and a negative effect of the interaction between this climatic parameter and defoliation. This work illustrates the potential of defoliation and climate to reduce forest productivity and the importance of water availability for tree development in Mediterranean climates. In addition, our results also emphasise the need to simultaneously evaluate the effects of different disturbances, particularly in a time of global change when an increase in forests disturbances is expected. This approach will certainly contribute to a more informed management of production forests.

Disturbances consistently restrain the role of random migration in grassland soil microbial community assembly

Random migration often plays important roles in soil microbial community assembly. However, it remains unexplored that whether its role is affected by anthropogenic disturbances, and whether the effects of different disturbances are consistent. Here, we report a novel and general pattern that different disturbances consistently restrain the role of migration in soil bacterial community assembly. We mimicked 16 types of anthropogenic disturbances relevant to a Eurasian steppe ecosystem, including removing different number of plant functional groups, mowing, adding nitrogen, adding phosphorus, watering, warming, and some of their combinations. The estimated migration rates in soil bacterial community assembly with Stephen Hubbell’s neutral model decreased by 0.19–6.29% under these disturbances. The relative change in migration rate was correlated with the deterministic change in community composition and the relative change in soil pH. Our results suggested that the intensifying anthropogenic disturbances may restrain the random dispersal, colonization and distribution of soil microorganisms.

Karst environments and disturbance: evaluation of the effects of human activity on grassland and forest naturalness in dolines

Karst depressions (dolines) have the potential to act as safe havens for a high diversity of valuable species. We showed that local anthropogenic disturbances play a significant role in determining the naturalness of dolines. We compared the number of specialist species, competitor species, generalist species and species of disturbed habitats between natural and disturbed dolines in two Hungarian karst areas, where different types of anthropogenic disturbances have been shaping the vegetation for centuries. We found that these disturbances have the potential to negatively influence the naturalness of dolines, reducing the number of valuable species, thus affecting the conservation value of dolines. To maintain the naturalness of vegetation in these doline habitats, the populations of ruderal competitors should be eliminated, and sustainable forest management should be adapted. However, there are still open questions about the effects of different disturbances on the naturalness in dolines that need to be answered to determine which conservation strategies will be particularly suitable for valuable species in a warming climate.

Effects of different disturbances on plant growth and content of main medicinal ingredients of rhizomatous clonal plant &lt;i&gt;Glycyrrhiza uralensis&lt;/i&gt; in a natural population

Effects of different disturbances on plant growth and content of main medicinal ingredients of rhizomatous clonal plant &lt;i&gt;Glycyrrhiza uralensis&lt;/i&gt; in a natural population

Assessment of the Effects of Physical Disturbances in Simple Micro-Universes by Measurement of DOC-levels

An increasing problem with today’s way of living is the rising of anthropologically influenced pollutions. Quite recently has research been directed towards the effects and consequences these disturbances may cause within freshwater environments, which has inspired this study. Hoping to assess the effects of different disturbances that are likely to occur in lakes, DOC-levels (Dissolved Organic Carbon) were measured to get an idea of what might happen to the microbial ecology when these are introduced. The research was conducted by introducing a heavy reduction of bacteria, micro plastics, SDS (Sodium dodecyl sulfate) and micro plastics and SDS together to enclosed environments. The purpose of this, and also the aims of this study being to 1) find out of DOC-levels were affected, if 2) a difference could be observed between exposure to micro plastics + SDS versus micro plastics and SDS alone, and 3) to assess the recovery after each disturbance. Following exposure DOC-levels remained generally unchanged in the reduced bacteria and micro plastics mesocosms, whereas these levels were heavily reduced after exposure to SDS. It was also found that SDS + micro plastics required a shorter exposure time before mortality was observed than SDS alone, and resulted in a much higher mortality rate than micro plastics alone.

Simulation and Control of a Methanol-To-Olefins (MTO) Laboratory Fixed-Bed Reactor

In this research, modeling, simulation, and control of a methanol-to-olefins laboratory fixed-bed reactor with electrical resistance furnace have been investigated in both steady-state and dynamic conditions. The reactor was modeled as a one-dimensional pseudo-homogeneous system. Then, the reactor was simulated at steady-state conditions and the effect of different parameters including inlet flow rate, inlet temperature and electrical resistance temperature on reactor performance was studied. Results showed that the most effective parameter is electrical resistance temperature. Thus, it was selected as manipulating variable for controlling product quality. In the next step, dynamic simulation of the process was performed and the effect of different disturbances on the dynamic behavior of the reactor was assessed. Finally, PID and Neural Network Model Predictive (NNMP) controllers were utilized for process control, and their performances were compared to each other. The response of the control system to different disturbances and set point changes showed that both PID and NNMP control systems can maintain the process at the desired conditions. PID controller had smaller rise time and no offset compared to NNMP controller while NNMP controller had smaller overshoot.

Resiliencia de un pajonal de Panicum prionitis Nees bajo distintas alternativas de manejo

Panicum prionitis (“paja de techar”) tall grasslands are one of the most extensive vegetation types in the islands of the Parana River valley. These communities are traditionally burned in order to improve its quality forage and animal consumption. Our objective was to analyze the effect of different disturbances along two years: prescribed fire, mowing and control using multivariate analyses on vegetation variables (abundance-cover, richness, evenness and diversity). P. prionitis remained as dominant species regardless of treatment and throughout the experiment. Even though disturbances affected species composition, no significant effect was detected on richness, evenness, and diversity. Mowing and the use of prescribed fire showed the same effect on this highly resilient community.

Meiofaunal assemblages associated with native and non-indigenous macroalgae

Meiofauna is a useful tool to detect effects of different disturbances; however, its relevance in the frame of biological invasions has been almost fully neglected. Meiofaunal assemblages associated with the invasive macroalga Sargassum muticum were studied and compared with those associated with two native macroalgae (Bifurcaria bifurcata and Chondrus crispus). We used a linear mixed model to determine the influence of habitat size (i.e. macroalgal biomass) in shaping meiofaunal assemblages. Results showed that habitat size (i.e. macroalgal biomass) shaped meiofaunal assemblages influencing its abundance, richness and structure. However, the identity of macroalga (i.e. species) appears also to play a significant role, particularly the differences of complexity among the studied species may shape their meiofaunal assemblages. Finally, the invasive macroalga appears to influence positively species richness. Our results highlight the need of including different faunal components to achieve a comprehensive knowledge on effects of invasive macroalgae and that meiofaunal assemblages may be a valuable tool to examine them.

Retention forestry and prescribed burning result in functionally different saproxylic beetle assemblages than clear-cutting

In fire-susceptible boreal forests, clear-cutting has been justified as being a harvesting regime that mimics natural stand-replacing dynamics, despite obvious differences in its biological legacies. Prescribed burning and retention forestry are commonly applied to better maintain naturally occurring legacies, but the community-level effects of different disturbances on the functional characteristics of biota remains still largely unknown. In this study, we investigated the effects of prescribed fire, clear-cutting and retention forestry on the functional properties of saproxylic beetle assemblages in Eastern Finland, using stand-level data from a before-after field experiment with four levels of tree retention (0, 10 and 50m3ha−1 and control) and prescribed burning. We analyzed the functional-phylogenetic diversity and a set of species traits that link species to resources. The data include 377 beetle species and 38549 individuals. Functional-phylogenetic diversity decreased from a random to a clustered pattern after burning and logging with retention trees, indicating environmental filtering of both processes. These effects became more pronounced with increasing logging intensity. Species-level traits that were favored by burning and tree retention were connected to open-habitat conditions and fresh dead wood, whereas clear-cutting revealed a random pattern without reference to specific resources. Our functional approach thus shows that clear-cutting does not mimic the dynamics of wildfire, but leads to different functional composition of species assemblages. Therefore, prescribed burning or wildfire should be incorporated and sufficient amount of trees retained in forest management to conserve functional processes and natural composition of saproxylic species assemblages in boreal forests.

Comprehensive modeling and CFD simulation of absorption of CO2 and H2S by MEA solution in hollow fiber membrane reactors

A comprehensive mathematical model has been developed for the simulation of simultaneous chemical absorption of carbon dioxide and hydrogen sulfide by means of Monoethanolamine (MEA) aqueous solution in hollow fiber membrane reactors is described. In this regard, a perfect model considering the entrance regions of momentum, energy, and mass transfers was developed. Computational Fluid Dynamics (CFD) techniques were applied to solve governing equations, and the model predictions were validated against experimental data reported in the literature and excellent agreement was found. Effects of different disturbances on the dynamic behavior of the reactor were investigated. Moreover, effects of various parameters such as wetting fraction, gas and liquid inlet velocities, inlet temperature of the solvent, MEA concentration, and CO2 and H2S compositions were carefully studied. It was found that for large values of gas velocity or small values of liquid velocity, the thermal energy equation can play an important role in the model predictions. © 2013 American Institute of Chemical Engineers AIChE J 60: 657–672, 2014

Using a Spreadsheet Scroll Bar to Solve Equilibrium Concentrations

A simple, conceptual method is described for using the spreadsheet scroll bar to find the composition of a system at chemical equilibrium. Simulation of any kind of chemical equilibrium can be carried out using this method, and the effects of different disturbances can be predicted. This simulation, which can be used in general chemistry university courses (and also in the higher years of secondary schools due to its simplicity), is carried out by the students, avoids the solving of complex algebraic equations, and allows many of the common misconceptions and difficulties in this subject to be dealt with.

Comparative Effects of Different Disturbances in Coral Reef Habitats in Moorea, French Polynesia

Degradation and loss of critical coastal habitats has significant ramifications for marine fisheries, such that knowledge of changes in habitat quality and quantity are fundamental to effective ecosystem management. This study explores changes in the structure of coral reef habitats, specifically changes in coral cover and composition, in Moorea, French Polynesia, to assess the independent and combined effects of different disturbances since 1979. During this period, reefs on the north coast have been subject to coral bleaching, severe tropical storms, as well as outbreaks ofAcanthaster. Coral cover varied significantly among years, showing marked declines during some, but not all, disturbances. The greatest rates of coral loss coincided with outbreaks ofA. planci. Moreover, successive disturbances have had differential effects among coral genera, leading to strong directional shifts in coral composition.Acroporais declining in abundance and coral assemblages are becoming increasingly dominated byPocillopora and Porites. Observed changes in the cover and composition of corals are likely to have further significant impacts on the reef fish assemblages. Given that significant disturbances have been mostly associated with outbreaks ofA. planci, rather than climate change, effective ecosystem management may reduce and/or delay impending effects of climate change.

Effect of disturbances at inlet on hypersonic boundary layer transition on a blunt cone at small angle of attack

To investigate the effect of different disturbances in the upstream, we present numerical simulation of transition for a hypersonic boundary layer on a 5-degree half-angle blunt cone in a freestream with Mach number 6 at 1-degree angle of attack. Evolution of small disturbances is simulated to compare with the linear stability theory (LST), indicating that LST can provide a good prediction on the growth rate of the disturbance. The effect of different disturbances on transition is investigated. Transition onset distributions along the azimuthal direction are obtained with two groups of disturbances of different frequencies. It shows that transition onset is relevant to frequencies and amplitudes of the disturbances at the inlet, and is decided by the amplitudes of most unstable waves at the inlet. According to the characteristics of environmental disturbances in most wind tunnels, we explain why transition occurs leeside-forward and windside-aft over a circular cone at an angle of attack. Moreover, the indentation phenomenon in the transition curve on the leeward is also revealed.

Short Note

Using process‐orientated parameters to assess degradation.

Dissociating the effect of different disturbances on the band gap of a two-dimensional photonic crystal

In this article, we dissociate the effect of the three generic disturbances on the band gap of a bidimensional metallic photonic crystal made of parallel rods. The disturbances are investigated separately. They are deviations from the perfectly periodic position, the angle between rods constituting the photonic crystal and different sizes in rod diameters. Numerical simulations and experimental measurements have been performed in the microwave region and the results compared. The effects of these disturbances on a localized state are discussed as well. When the disturbance level is weak (i.e., a few percent), the band structure is conserved: the slopes at the edge and the band-gap width are the same as for the perfect structure. By contrast, the bandpass is reduced by about −1 dB. For an important disturbance the crystal becomes practically unusable due to the deep random modifications of its band structure. In all cases when the band gap exists, the transmission peak associated with the localized state is present.