Study on Instability in Baroclinic Vortex Symmetric Disturbance under Effect of Nonuniform Environmental Parameters

With the aid of the baroclinicity parameter M2,inertial instability parameter F2 and the stratification instability paramter N2 as the slowly varying function both spatially and temporally,an energetic equation is derived of symmetric perturbation waves in baroclinic vortices in the framework of progressively changing wavetrain theory,or WKB,alongside the examination of effects of these parameters upon the vortex disturbance.     

Acoustic interaction of humpback whales and whale-watching boats

The underwater acoustic noise of five representative whale-watching boats used in the waters of west Maui was measured in order to study the effects of boat noise on humpback whales. The first set of measurements were performed on 9 and 10 March, close to the peak of the whale season. The ambient noise was relatively high with the major contribution from many chorusing humpback whales. Measurements of boat sounds were contaminated by this high ambient background noise. A second set of measurements was performed on 28 and 29 April, towards the end of the humpback whale season. In both sets of measurements, two of the boats were inflatables with outboard engines, two were larger coastal boats with twin inboard diesel engines and the fifth was a small water plane area twin hull (SWATH) ship with inter-island cruise capabilities. The inflatable boats with outboard engines produced very complex sounds with many bands of tonal-like components. The boats with inboard engines produced less intense sounds with fewer tonal bands. One-third octave band measurements of ambient noise measured on 9 March indicated a maximum sound pressure level of about 123 dB re 1 microPa at 315 Hz. The maximum sound pressure level of 127 dB at 315 Hz was measured for the SWATH ship. One of the boats with outboard engines produced sounds between 2 and 4 kHz that were about 8-10 dB greater than the level of background humpback whale sounds at the peak of the whale season. We concluded that it is unlikely that the levels of sounds produced by the boats in our study would have any grave effects on the auditory system of humpback whales.     

A potential mechanism for disturbance-mediated channel migration in a southeastern United States salt marsh

Coastal salt marsh tidal creeks are thought to show less channel adjustment/movement relative to their terrestrial fluvial counterparts. We propose a mechanism for disturbance-mediated bank failure that may allow/initiate channel migration in these otherwise stable systems. The stability of tidal creeks is promoted by the extensive vegetation root structure along the banks. However, wrack mats (i.e., dead vegetation) deposited on creek banks can cause the death of below-ground vegetation leading to bare, unstable banks that may slump into the channel. We measured the frequency of bank failures associated with wrack-disturbed sites along three creeks on Sapelo Island, Georgia, USA to determine whether these sites were vulnerable to erosion. Approximately 81% of the disturbed sites showed signs of bank failure. Therefore, wrack-induced bank failure may potentially lead to channel migration in creeks previously believed to be static landscape features.     

The replacement of arborescent cactus species along a climatic gradient in the southern Chihuahuan Desert: competitive hierarchies and response to freezing temperatures

In the southern region of the southern Chihuahuan Desert three common species of arborescent cacti are distributed over a north-west to south-east climatic gradient; Opuntia leucotricha, O. streptacantha, and Myrtillocactus geometrizans. In general, O. leucotricha is more abundant in the colder north-west section; M. geometrizans in the warmer south-east zone, not occurring in the north-west; and O. streptacantha reaches its greatest abundance in the centre of the region. We studied the potential replacement process between the three species due to canopy interference as well as the effect of a disturbance, freezing temperature, on their survivorship. Canopy interference between adjacent individuals of M. geometrizans/O. streptacantha and O. streptacantha/O. leucotricha indicated a potential replacement sequence of O. leucotricha replaced by O. streptacantha which, in turn, is replaced by M. geometrizans. In contrast, the damage caused by an extreme low-temperature event hardly affected O. leucotricha. It did however cause severe damage to individuals of O. streptacantha in the north-west of its distribution with little or no damage to individuals in the more south-eastern populations studied. M. geometrizans had a similar pattern of damage to O. streptacantha over its range in the region but at each site where the two species occurred together, that damage was more severe. Our observations suggest that disturbance in the form of extreme freezing temperatures is the mechanism that limits the distribution of these three arborescent cacti in the southern Chihuahuan Desert and allows their co-existence regionally.     

地球局部重力场对近地卫星轨道的影响

本文重点探讨了近地卫星的受力情况,从理论上分析了司托克斯积分公式的一些特性,给出了高空扰动引力的误差量级及适当的近区域积分半径;最后,利用数值积分方法,对几种情况的卫星轨道计算进行了比较分析。     

Effects of point-source nutrient addition and mussel removal on epibiotic assemblages in Perumytilus purpuratus beds

The objective of this study was to evaluate the effects of point-source nutrient addition and mussel removal on species diversity of the epibenthic assemblage of the purple mussel Perumytilus purpuratus. It was hypothesised that mussels cushion the effects of disturbance on the associated organisms and thereby favour species diversity in patches with added nutrients. In order to test this hypothesis, a two-factorial field experiment was conducted at an exposed rocky shore of northern-central Chile in which nutrient addition and mussel removal were manipulated with two levels. Experimental units consisted of 100-cm² mussel plots that were sampled after two months of experimental manipulations. Local nutrient addition was done with coated slow-release fertilisers. Mussel removal treatments consisted in three destructive events applied throughout the experimental phase, and each event consisted in the removal of 20% of the mussel biomass from each plot. While point-source nutrient addition had only minor effects on diversity, mussel removal had significant and negative effects on faunal species richness and the abundance of suspension-feeders and sessile organisms. The abundance of predators/scavengers significantly decreased with mussel removal in the presence of nutrient addition. Grazers and mobile organisms were very abundant in the mussel assemblage but their abundance remained unaffected by treatments. Finally, species richness and total abundance of algae were also not affected by the treatments. Although the duration of our experiment was relatively short, we suggest that the effects of local nutrient addition are of minor importance at the study site in comparison to the effects of mussel removal. Based on our results and previous studies conducted in soft-bottom systems, we suggest that physical and biological stress acting on exposed hard-bottom communities overshadows the potential effects of local nutrient addition.     

Deep-sea Polymetallic Nodule Mining: Challenges Ahead for Technologists and Environmentalists

Although, offshore mining for mineral wealth is not required at present, it may be the only alternative in the future due to the continuous growing demand for certain metals that have no or limited land deposits. Risk involved in deep-sea mining is not less than that in space missions. Limited groups of mining engineers and environmental scientists are conducting studies that influence the development of mining systems and subsystems for collection, screening, lifting, and transportation of deep-sea minerals. Accepting this challenge more than 20 years ago, the National Institute of Oceanography, Goa, started surveys and exploration for polymetallic nodules in the Indian Ocean and was the first to receive "Pioneer Status" recognition from the United Nations. Experiments have also been conducted to study the potential impacts of deep-seabed mining.     

浅部不均匀体对目标体电阻率异常影响的研究

浅部不均匀体能使电阻率测深曲线产生严重的畸变. 为了从根本上消除浅部不均匀体的干扰,本文采用三维有限元数值模拟的方法,计算出浅部不均匀体异常和混合体（目标体+不均匀体）异常,通过一定的校正方法,把不均匀体影响从混合异常中校正掉,从而实现对浅部不均匀体影响的定量校正.     

Is exotic plant invasion enhanced by a traditional wildlife habitat management technique?

Soil disturbance is a wildlife habitat management tool that retards succession and promotes early seral vegetation. Our objective was to determine responses of two invasive herbaceous species (Pennisetum ciliare and Salsola iberica) and native perennial grasses to disking on different soils. Two 10 ×40 m plots were delineated within each of 4 blocks on Ramadero loams and 4 blocks on Delmita fine sandy loams. On Delmita soils, canopy cover of P. ciliare, S. iberica, and native perennial grasses averaged across all years was not affected by disking (ANOVA, P>0.05). On Ramadero soils, P. ciliare canopy cover was similar (Tukey's, P>0.05) on control and disked plots for the first 4 years post-disturbance, but P. ciliare cover was 10-fold greater (Tukey's, P=0.02) the 5th year after disking on disked versus control plots. On Ramadero soils, S. iberica canopy cover averaged across all years was 221 times greater (ANOVA, P=0.05) on disked plots than on control plots. Disking did not affect native perennial grass canopy cover. Land managers should consider soil series when disking for wildlife management, as disking disturbance may exacerbate exotic plant ingress and establishment on certain soils.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.