Responses of benthic macroinvertebrates to thin-layer disposal of dredged material in Mississippi Sound, USA

Benthic community responses to thin-layer disposal of dredged material were assessed at three sites in Mississippi Sound, USA. Community composition differed between disposal and reference sites (ANOSIM) for each disposal event. Oweniid sand worms, Amphinomid fire worms, and brittle stars (Ophiuriodea) contributed the most to community distinctions between disposal and reference sites (SIMPER), with higher abundances at the disposal sites. Total infaunal abundance was similar to pre-disposal and reference conditions within 3-10 months of thin-layer disposal. Distinctions in community composition between disposal and reference sites (nMDS) persisted throughout the 16-month study period, but were less pronounced at the site where sediment composition was unchanged by disposal. Size distributions of some taxa (e.g., gastropod and hemichordate) suggest adults recolonized the newly deposited sediments either through vertical migration or lateral immigration from adjacent areas. Thin-layer disposal offers a viable alternative to conventional open-water disposal practices and warrants further exploration for other areas with deeper bathymetries and different hydrodynamic regimes.     

A comparison of the effectiveness of the roots of two grass species in reducing soil erosion on alluvial fans in south-east China

The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility, and critical shear stress on alluvial fans of benggang in south-east China. A 4-m-long and 0.12-m-wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39 × 10⁻³ to 4.19 × 10⁻³ m² s⁻¹. The mean detachment capacities of P. mandiocanum and P. giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0- to 5-cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE = 0.90). With the increase in soil depth, rill erodibility increased, whereas shear stress decreased. The mean rill erodibilities of P. mandiocanum and P. giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE = 0.88). The mean critical shear stress of P. mandiocanum and P. giganteum lands was 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE = 0.76). This study demonstrated that planting of the two grasses P. mandiocanum and P. giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of P. giganteum being more effective than the shallow roots of P. mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process.     

Stormflow threshold behaviour in a subtropical mountainous headwater catchment during forest recovery period

Forest ecohydrological feedbacks complicate the threshold behaviour of stormflow response to precipitation or wetting conditions on a long-term scale (e.g. several years). In this study, the threshold behaviours in an evergreen-deciduous mixed forested headwater catchment in southern China were examined during 2009–2015, when damaged vegetation was recovering after the great 2008 Chinese ice and snowstorm. The non-uniqueness of the thresholds and the slow and rapid responses of stormflow at the outlet of the catchment in different hydro-climate datasets with different maximum values of gross precipitation (P) and sums of precipitation and antecedent soil moisture index (P + ASI) were assessed. The thresholds of P and P + ASI required to trigger stormflows (i.e. ‘generation thresholds’) and the transition from slow to rapid responses of stormflow (i.e. ‘rise thresholds’) were compared both seasonally and annually. The results indicated significant differences in the analysed datasets, highlighting the need to compare thresholds with care to avoid misinterpretation. Seasonal variations in threshold behaviours in the catchment suggested that vegetation canopy interception contributed to higher rise thresholds, and wetter conditions resulted in higher runoff sensitivity to precipitation during the growing and rainy seasons. Furthermore, the generation thresholds were higher in the dormant season, possibly due to drier soil moisture conditions in the near-channel areas. During the vegetation recovery period, the annual generation thresholds increased, however the rise thresholds did not exhibit a similar trend. The rapid stormflow response above the threshold decreased, possibly due to transpiration and interception of the recovered vegetation. However, the slow stormflow response to small rainfall events below the thresholds was higher in wetter years but lower in drier years, suggesting that the total water input dominated the stormflow response during small rainfall events. In conclusion, the seasonal and annual variations in threshold behaviours highlight that vegetation recovery and hydro-climatic conditions had a notable impact on the stormflow response.     

The impact of dredge-fill on Posidonia oceanica seagrass meadows: regression and patterns of recovery

Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows.     

Determining short-term changes in the hydraulic properties of a sandy-loam soil by a three-run infiltration experiment

ABSTRACT

Soil structure-dependent parameters can vary rapidly as a consequence of perturbing events such as intense rainfall. Investigating their short-term changes is therefore essential to understand the general behaviour of a porous medium. The aim of this study is to gain insight into the effects of wetting, perturbation and recovery processes through different sequences of Beerkan infiltration experiments performed on a sandy-loam soil. Two different three-run infiltration experiments (LHL and LLL) were carried out by pouring water at low (L, non-perturbing) and high (H, perturbing) heights above the soil surface and at short time intervals (hours, days). The results demonstrate that the proposed method allows one to capture short-term variations in soil structure-dependent parameters. The developed methodology is expected to simplify the parameterization of hydrological models with temporally variable soil hydraulic properties.     

Changes in overland flow and infiltration after a rangeland fire in a Mediterranean scrubland

Changes in overland flow and infiltration after a wildfire (summer 1989) in a typical Mediterranean scrubland were measured during the winters of 1990, 1991, 1992 and 1995 by means of simulated rainfall. Infiltration increases gradually from 1990 (sixth months after the forest fire) to 1995 (five and a half years after the forest fire). Overland flow decreases from 45% of rainfall after the forest fire to less than 6% five and a half years later. The reduction in overland flow was greatest in the first two years after the fire because of the quick recovery of vegetation. The steady-state infiltration capacity increased every year after the fire. Runoff and infiltration changes are mainly determined by the gradual recovery of vegetation. © 1998 John Wiley & Sons, Ltd.     

鲁科一井上白垩统沉积岩岩石磁学和天然剩磁分析:兼论利用剩磁方向恢复钻孔岩芯原始方位的可行性

本文对"鲁科一井"（CCSD-LK-Ⅰ）768.9~1112.3 m之间的上白垩统沉积岩样品进行了岩石磁学、磁化率各向异性（AMS）以及天然剩磁组分的研究.在此基础上,分析了利用特征剩磁（ChRM）和黏滞剩磁（VRM）方向恢复岩芯原始方位的可行性.三轴等温剩磁热退磁曲线、磁滞回线、反向场退磁曲线、一阶反转曲线等岩石磁学测量结果表明,沉积岩的主要载磁矿物为磁铁矿和赤铁矿.335块样品的AMS测量结果表明磁化率椭球主轴的最大轴K1和中间轴K2与水平面夹角较小,最小轴K3接近垂直于水平面分布,说明沉积岩保留了原始沉积磁组构特征.系统热退磁实验表明,多数样品在25~350℃和500~690℃温度段分别获得VRM和ChRM分量.利用ChRM偏角方向,并考虑构造旋转量校正,对VRM偏角方向进行恢复,Fisher统计得到DVRM=-1.3°,IVRM=59.6°,与当地现代地磁场方向（D=-6.7°,I=53.9°）基本一致.用ChRM偏角方向对磁化率主轴K1偏角方向进行校正,校正的结果为：Dch_K1=349.2°,Ich_K1=-0.7°.本文研究结果对于地质勘探中利用古地磁学方法恢复钻孔岩芯原始方位具有一定参考意义.     

新疆数字化地震前兆数据的多重保护探讨

对新疆数字化地震前兆数据的安全解决方案进行了探讨.在实际工作中采取有效的预防措施,预防任何原因造成的数据丢失的可能,讨论在灾难性数据发生时,第一时间内恢复数据的可行方案,降低数据丢失或损坏造成的影响,为新疆数字化地震前兆数据加上多重安全保险.     

The 1991 Mount Pinatubo eruption and Eastern South China Sea foraminifera: occurrence, composition and recovery

Abstract Analysis of the 12 samples taken from two horizons (the pre-1991 Mount Pinatubo eruption and the post-1991 Mount Pinatubo eruption layers) of the six deep water cores that were collected along the Eastern South China Sea shows that the absolute abundance of Recent benthic foraminifera (total assemblage) in the post-eruption layer is much lower compared to the pre-eruption layer. The post-eruption layer also shows lower diversity with relative high abundance of Quinqueloculina spp., which probably form part of the recolonization fauna. These observations suggest that environmental stability plays a vital role in the distribution of foraminifera in the eastern margin of the South China Sea. The disturbance created by the immense amount of pyroclastic materials that originated from the 1991 eruption of Mount Pinatubo has resulted in the dilution and, eventually, the decimation of most of the benthic foraminifera. The species that were able to survive might have taken advantage of the small amounts of available nutrient supply. These might also be the species that were able to adapt quickly to the changes in the environmental conditions.     

一种用于篡改定位及近似恢复的水印算法

针对遥感影像易被非法篡改的问题,提出了一种用于篡改定位及近似恢复的遥感影像半脆弱水印方案。首先将二值伪随机矩阵作为认证水印,通过量化Contourlet变换各方向子带中绝对值最大的系数将其嵌入,然后采用影像4×4分块后的灰度平均值作为恢复水印,将其嵌入到最低有效位。水印检测不需要原始遥感影像参与,实现了盲提取。实验结果表明,算法对于噪声、JPEG压缩等合理性失真具有一定的鲁棒性,而对于恶意篡改等攻击具有脆弱性,能够实现篡改区域的精确定位和近似恢复,使恢复后的遥感影像满足基本的视觉要求,可有效保护遥感影像的安全。