A field experimental study on recolonization and succession of subtidal macrobenthic community in sediment contaminated with industrial wastes

A field experiment was carried out in Hong Kong to study the patterns of recolonization and succession of subtidal macrobenthos in defaunated sediment contaminated with industrial wastes and to determine the time required for benthic recovery in the industrial-contaminated sediment. A total of 50 species was found with an average of 172 animals/tray and 24 species/tray recorded one month after deployment. Initial colonizers were predominantly polychaetes (96 animals/tray, accounting for 55.7%) and gastropods (47 animals/tray, accounting for 27.2%). Abundance of macrobenthos increased quickly to a peak (505 animals/tray) after four months, declined afterwards, and increased again till the end of the experiment. Species number peaked (57 species/tray) in the same month as abundance did, and gradually declined thereafter. Abundance, species number and diversity were significantly lower in the industrial-contaminated sediment as compared to the controls during the early successional stages, indicating the harmful effects of industrial wastes on recolonization and succession of macrobenthos. Although no significant differences in community parameters between the industrial-contaminated and the control sediments were found after eleven months, significant difference in species composition still existed after fourteen months, showing a relatively long-term impact of industrial wastes on macrobenthic community structure.     

Relationship between macrobenthos and physical habitat characters in tidal flat in eastern Seto Inland Sea, Japan

The investigations were carried out at 6 tidal flats located on the eastern part of the Seto Inland Sea, Japan. This study was focused on physical characteristics of sediments, namely as particle size of sediment and difference in elevation, and generalizes the relationship between sediments and macrobenthos. A total of 192 species were collected at 187 stations at 6 tidal flats. Physical characteristics of sediment were classified into 9 groups by cluster analysis in relation to sediment particle size and difference in elevation. Those groups had also significant difference in physical characteristics of sediments, and were characterized by some specific macrobenthos species. Distribution of macrobenthos can be explained by the classification of physical characteristics of sediment. These findings show the possibility to predict the variety of macrobenthos community using the physical characteristics of sediment.     

Seasonal changes of the profundal macrobenthic community in a polluted lake

Late summer and winter structures of the profundal macrobenthos in a polluted lake (Lake Nemi, Central Italy) were compared to verify the relative differences in the faunal structure and the magnitude of the winter recovery of this community. Densities of Oligochaetes and Chironomids did not vary significantly from summer to winter, the latter not showing any recolonization of the profundal zone. Structure and diversity of the total fauna, and Oligochaete/Chironomid ratio were very similar in the two periods. Our results suggest that in a severely polluted lake, with a strong and lasting oxygen deficit in the hypolimnic zone, a lack of recovery of profundal macrobenthos may be expected in improved environmental winter conditions.     

Macrobenthic associations in a South Atlantic Brazilian enclosed bay: the historical influence of shrimp trawling

This study characterized the macrobenthos of Tijucas Bay and related the distribution and dominance patterns with historical trawling activities. Fifteen sampling sites were established in the bay and were sampled in summer and winter for the characterization of the macrobenthos. To evaluate the trawling effects, three passages were established at each site with control and impacted areas analyzed before and after trawl-net action in impacted area. Seasonal differences occurred in macrobenthos, possibly influenced by rainfall where the relative water level of the Tijucas River was directly associated with the discharge of freshwater and particulate matter. The associations identified in the bay were distinct in comparison with the Zimbros Embayment. The trawling assessment showed no significant variation in the macrobenthos after the trawl, possibly due to decades of shrimp exploitation in the bay. Trawling and instable environmental conditions inside the bay make the establishment of a stable macrobenthic community difficult.     

寒区湿地春、夏浮游植物群落划分——以三江平原安邦河湿地为例

运用多元分析方法对安邦河湿地春、夏浮游植物群落进行划分,结果表明,两季节均可分为3个组群:(1)核心区组群,春季为绒毛平板藻.四角盘星藻群落,夏季为四角盘星藻群落;(2)边缘区组群,春季为梅尼小环藻-尖针杆藻群落,夏季为鱼腥藻-铜绿微囊藻.梅尼小环藻群落;(3)莲花池组群,春季为地中尖头藻群落,夏季为银灰平裂藻群落.各群落的种类组成、数量及多样性存在季节差异,与寒区环境因子季节变化相关.     

Sediment features, macrozoobenthic assemblages and trophic relationships (delta13C and delta15N analysis) following a dystrophic event with anoxia and sulphide development in the Santa Giusta lagoon (western Sardinia, Italy)

Macrozoobenthic assemblages and stable carbon (delta(13)C) and nitrogen (delta(15)N) isotope values of various primary producers (macroalgae and angiosperms) and consumers (macroinvertebrate filter/suspension feeders, deposit feeders, detritivores/omnivores and carnivores and fishes) were studied in the Santa Giusta lagoon (Sardinia, Italy) before (spring) and after (autumn) a dystrophic event which occurred in the summer of 2004. A few days after the dystrophy, the physico-chemical characteristics of sediments and macrozoobenthic assemblages were also investigated. In the latter occasion, high total organic carbon (3.9%) and organic matter (15.9%) contents of surface sediments went together with peaks in acid-volatile sulphide concentrations. Certain immediate effects were quite extreme, such as the drastic reduction in macrozoobenthos and the massive fish kill in August 2004. Among the macrozoobenthos, there were few individuals of chironomid larvae and Capitella cf. capitata left. However, by October, chironomid larvae were numerous, indicating a lack of predators (e.g. fish) and competitors. In addition, some bivalve species and polychaetes which were absent, or present in small numbers before the event, became relatively numerous. The results are discussed based on a knowledge of the sulphide tolerance of these species. Stable isotope analysis clearly showed that the basal level of the food web for most consumers consisted mainly of macroalgae and sedimentary organic matter, and that the values before and after the dystrophic event were not significantly different from one another. This indicates that the relations among different trophic levels were quickly restored following the dystrophic event.     

Hydrochemistry of Three Dystrophic Lakes in Northeastern Poland

A hydrochemical investigation was carried out in spring, summer, and autumn, in the years 1991–1994, in three dystrophic lakes of the Wigry National Park (NE Poland). In spite of the fertile catchment basin, the developing ombrofile peat bogs of lake environment results in the acidification of lakes, the presence of small concentrations of dissolved mineral substances (below 50 mg L^–1), and exceptionally high DOC concentrations, exceeding 10 mg L^–1 C. During summer, a strong thermic stratification develops in the lakes, with constant conditions of oxygen deficiency prevailing below 3 m. In the course of the spring and autumn mixing of dystrophic lakes, the deterioration of oxygen conditions occurs in the epilimnion. In spite of high TP and NH₄⁺ concentrations, which increase from spring to autumn, the conditions developing in the lakes are unfavourable, for the functioning of aquatic organisms, on account of the strong shading. The increased direct irradiation of water bodies caused by deforestation or favourable atmospheric conditions results in an increased trophy of lakes.     

Macrobenthic community structure in the northern Saudi waters of the Gulf, 14 years after the 1991 oil spill

The 1991 Gulf oil spill heavily impacted the coastal areas of the Saudi waters of the Arabian Gulf and recent studies have indicated that even 15 years after the incident, macrobenthos had not completely recovered in the sheltered bays in the affected region such as, Manifa Bay. This study investigates the community conditions of macrobenthos in the open waters in one of the impacted areas, Al-Khafji waters, about 14 years after the spill. Diversity measures and community structure analyses indicate a healthy status of polychaete communities. The BOPA index reveals that oil sensitive amphipods were recolonized in the study area. This confirms that the benthic communities of the oil spill impacted area had taken only <14 years to recover in the open waters of the impacted areas. The study also reveals the existence of three distinct polychaete communities along the depth and sediment gradients.     

Some aspects of the life history,structure and movement of monsoon depressions

Summary Monsoon depression is one of the most important synoptic scale disturbances on the quasi-stationary planetary scale monsoon trough over the Indian region during the summer monsoon season (June to September). Salient features of the climatology of the depressions with regard to frequency of cyclogenesis, life expectancy, horizontal scale and tracks are discussed. Rainfall aspects of the depressions are discussed in some detail and the role of local, dynamical and sub-synoptic scale factors are brought out. Work done on the life history such as formation, intensification and maintenance of depressions has been reviewed based on synoptical and theoretical approaches. Structure of the depression based on composited, synoptical and dynamical studies is discussed. Wind circulation, thermal and moisture patterns, vertical motion field, vorticity budget etc., of a recent case study are brought out in some detail. The problem of movement of the depression against the low level basic westerly wind is briefly discussed and the results of several numerical and climatological prediction models are presented.     

Recovery of macrobenthos in defaunated tropical estuarine sediments

In the estuarine environment, hypoxia and/or anoxia have become a major cause of benthic defaunation and are strongly associated with increased eutrophication. Mesoscale field experiments were carried out to examine the recolonization and recovery time of macrobenthos after defaunation. Azoic sediments were achieved by covering four areas with polyethylene sheeting. Temporal changes and depth distribution of macrobenthos within the defaunated sediments were compared with those in undisturbed natural sediments at the same site. Within 3 days, annelids appeared as the first immigrants. After 153 days, the process of recovery had not yet been completed in terms of species richness. Whereas diversity and evenness showed no significant differences between treatments during the entire experiment, multivariate analyses proved that differences between treatments were still significant 93 days after the start of the experiment.     

夏季短期调水对太湖贡湖湾湖区水质及藻类的影响

贡湖湾作为"引江济太"工程长江来水进入太湖的第一站,湖湾水体生态环境的变化是对调水工程净水效果的最好响应,因此本文针对贡湖湾一次夏季短期调水展开调查研究,分别取2013年7月24日(调水前)和2013年8月18日(短期调水后)两次监测水样的水体理化指标和浮游藻类群落数据进行了对比分析,并对浮游藻类群落与环境因子做了相关性分析.结果表明:受来水影响,短期调水后监测区水体的p H略有下降,溶解氧、浊度、硝态氮、总氮、总磷以及高锰酸盐指数等水体理化指标浓度均较调水前有所升高;其中受调水影响最为显著的区域为望虞河的入湖口区、湾心区.两次监测调水前后湖区水体优势藻种属未发生变化,仍以微囊藻为主,但蓝藻种属比例有所下降,绿藻和硅藻等种属比例则有所上升.望虞河入湖口区和贡湖湾湾心区的Shannon-Wiener多样性指数和Pielou均匀度指数受调水的影响升高.同时,浮游藻类群落结构与受水水体理化参数的冗余分析结果表明,此次监测的短期调水后,太湖贡湖湾监测湖区水体p H、溶解氧、硝态氮、总氮、总磷、高锰酸盐指数等环境因子与浮游藻类的群落分布呈显著相关,是影响受水水体中藻类群落的主要环境因子.     

The influence of geomorphological position and vegetation cover on the erosional and hydrological processes on a Mediterranean hillslope

Soil erosion and runoff rates are assumed to be highly dependent on slope position. However, little knowledge exists about the hydrogeomorphological processes at the pedon scale that support this idea. In order to assess the hydrological and erosional behaviour of soils at different slope positions, simulated rainfall experiments (55 mm was applied during one hour) were carried out on a south-facing slope with underlying limestone in south-east Spain. In the mean terms, the erosion rates (9 g m² hr⁻¹) and the runoff coefficients (12%) were very low at the scale of measurement (0·25 m²). The slope position does not affect erosion rates when the measurements are carried out under extreme dry conditions during summer. The low runoff rates found in summer under thunderstorms of high intensity (5 year return period) and the runon into surfaces with higher infiltration rates resulted in no detectable direct surface runoff (Hortonian) at the slope scale. This implies that erosion as a consequence of surface overland flow will only take place during events of high magnitude (55 mm hr⁻¹) and low frequency (>5 years). Vegetation is the most important factor determining the soil erosion and runoff rates within the slope. © 1998 John Wiley & Sons, Ltd.     

Observations on the Bottom Fauna of the Ganga River (between Buxar and Ballia) with Special Reference to Its Role in the Seasonal Abundance of Fresh Water Prawn Macrobrachium birmanicum choprai (Tiwari)

The paper deals with the changes in composition and density of bottom fauna of the Ganga river at Buxar and Ballia in relation to soil texture and water quality observed between March 1984 and Feb. 1986 with its possible role in the seasonal abundance of M. birmanicum choprai. No marked differences were noted in the quality of water at the two centres. The texture of bottom was sandy at both the centres, but the soil at Ballia was found to consist almost of sand with a negligible quantity of clay content. The benthic fauna mainly consisted of dipterans, amphipods and annelids and exhibited a higher abundance at Buxar. It showed a major pulse in the month of March with a minor one in December. The macrobenthos including gastropods and bivalves were abundant during summer (March–June). The bottom fauna on which the prawns generally feed becomes a potential source of food during winter when the prawns get confined to a unit area.     

A neurocomputing approach to predict monsoon rainfall in monthly scale using SST anomaly as a predictor

A relationship between summer monsoon rainfall and sea surface temperature anomalies was investigated with the aim of predicting the monthly scale rainfall during the summer monsoon period over a section (80°–90°E, 14°–24°N) of eastern India that depends heavily upon the rainfall during the summer monsoon months for its agricultural practices. The association between area-averaged rainfall of June over the study zone and global sea surface temperature (SST) anomalies for the period 1982–2008 was examined and the variability of rainfall in monthly scale was calculated. With a view to significant variability in the rainfall in the monthly scale, it was decided to implement the artificial neural network (ANN) for forecasting the monthly scale rainfall using the SST anomalies as a predictor. Finally, the potential of ANN in this prediction has been assessed.     

1975年海城地震与1976年唐山地震前后的重力变化

1975年2月4日海城7.3级地震前后在震中以西不远的一条长约250公里的北西—南东向剖面上进行了五次重力测量,震前三次,震后两次.剖面上相邻两个测点的重力差的测量均方误差小于40微伽.自1972年6月至1973年5月的一年期间的三次观测结果表明,剖面东南段重力值显著下降,最大达352微伽.地震以后,1975年3月的第四次重力测量发现,剖面东南段的重力值回升到第一次测量时的水平.1975年7月的第五次测量则表明剖面东南段的重力值继续上升.1976年7月28日唐山7.8级地震前后也观测到重力的变化,不过地震前重力是增加而不是减少.震前和震后,在震中以北不远的一条长约270公里的东西向剖面上各进行过两次重力测量.结果表明,主震后整个剖面,特别是靠近唐山的那些测点的重力也有逐渐恢复到震前第一次测量时的数值的趋势.由这些结果可以看到,重力的变化与地震的发生似有密切的关系.根据重复大地水准测量资料估计的地面高程变化所能引起的重力变化远比所观测到的变化为小.因此,我们推测某些大地震可能与地壳和上地幔内的质量迁移有关,认为所观测到的重力变化大部份是质量迁移引起的.我们对质量迁移的重力效应作了理论分析,但是,对迁移的物理过程我们还很不清楚.      

三峡水库香溪河鱼类群落结构特征及历史变化

由于自然和人为因素的影响,三峡水库鱼类资源一直在发生变化,为掌握三峡水库蓄水后典型支流香溪河鱼类群落的现状及历史变化,于2020年7月—2021年4月使用多网目复合刺网和地笼对香溪河鱼类群落进行实地采样,并结合历史数据进行比较分析。研究期间共采集到鱼类55种,隶属于7目14科,鲤科鱼类种类数最多,以杂食性鱼类和湖泊定居性鱼类为主,优势种为贝氏?(Hemiculter bleekeri)、短颌鲚(Coilia bratchygnahus)、似鳊(Pseudobrama simoni)和翘嘴鲌(Culter alburnus),其相对重要性指数(IRI)分别为5502、3828、2567和1109。鱼类物种多样性指数在春季最高,夏季最低。刺网单位捕捞努力量渔获个体数和单位捕捞努力量渔获量在夏季最高,冬季最低。与三峡水库蓄水前相比,香溪河鱼类中长江上游特有鱼类减少4种,外来鱼类增加3种。湖泊定居性种类持续增加,喜流水性种类减少,鱼类优势种发生较大变动。2020—2021年香溪河鱼类组成与1987年的相似性指数为0.29,与2012—2013年的相似性指数为0.53,反映三峡水库蓄水前后香溪河...     

Colonisation of epilithic diatom population of the River Taff, South Wales, U.K.

1. A light and scanning electron microscopic study of the structure of epilithic diatom communities was carried out at two sites on the River Taff, South Wales, an upstream unpolluted site (Site 1) and a downstream polluted site (Site 2). 2. Community structure at the micro-scale revealed that, although communities at both sites were similar in terms of species present (similarity indices ranging between 0.44 and 0.96), they were very different with respect to their physical structure. 3. The traditional approach in studying epilithic diatom communities ignores information relating to community structure. The combination of light and scanning electron microscopy proved to be most useful for studying the epilithic diatom communities. 4. The examination of community succession on stone substrata showed that communities were highly dynamic on a weekly time scale, which suggests that the “age” of a substratum is a very important determinant of the attaching communities. A change from a prostate, two-dimensional community structure to an erect, three-dimensional community structure, and a shift from the dominance of epilithic diatoms to the dominance of epiphytic diatoms were noted. Such a change was more noticed at the polluted downstream site, possibly due to a higher rate of surface pre-conditioning and biofilm production at this site than at the unpolluted upstream site.     

Variations of gravity before and after the Haicheng earthquake, 1975, and the Tangshan earthquake, 1976

Before and after the Haicheng earthquake of magnitude 7.3 which occurred on February 4, 1975, five repeated gravimeter surveys were carried out, three before and two after the earthquake, along a northwest-southeast profile of about 250 km in length not far on the west of the epicenter. The mean-square error of the measurements of the gravity differences between two consecutive points on the profile is less than 40 μGal. From June, 1972 to May, 1973, within a period of about one year, the results of three surveys indicated a clear decrease of the gravity values at points on the southeastern portion of the profile, amounting to about 352 μGal. After the earthquake, the fourth survey, which was carried out in March, 1975, revealed that the gravity values had recovered to the levels of the first survey and continued to increase as was shown by a fifth survey carried out in July of the same year.Variations of gravity were also observed before and after the Tangshan earthquake of magnitude 7.8 which occurred on July 28, 1976, but in this case, gravity was increasing instead of decreasing before the earthquake. Along an east-west profile of about 270 km in length and not far on the north of the epicenter, two gravity surveys were made before and two after the earthquake. The results showed that after the main shock, the gravity values of the whole profile, especially at those points closer to Tangshan, tended to return gradually to their values of the first survey before the earthquake.From these results, there seems to be a close relationship between these gravity variations and the occurrences of earthquakes. Based on results of repeated levelling work done in these regions, the estimated amount of gravity change caused by the change of elevation of the ground surface is far too small to account for the observed value. Therefore we speculate that some large earthquakes might be associated with some sort of mass transfer under ground, within the crust or in the upper mantle. This transfer would cause a large part of the gravity variation observed. We have made a theoretical analysis of this effect and attempted to obtain some estimate of the magnitude of this mass transfer, even though we are not yet clear about the physics of it.