Fish in the littoral zone: ecology, threats and management

The importance of the littoral zone of lakes to a diversity of fish species has been appreciated for many centuries, although the complexity and heterogeneity of this habitat have resulted in a poorer understanding of local fish ecology compared with that achieved for typically much larger but simpler offshore habitats. Lake fish species may occupy the littoral zone permanently or visit it on diel, seasonal or ontogenetic timescales in response to a range of intrinsic and extrinsic factors. The purposes of such occupations include feeding, refuge from predation and, most importantly for many species, reproduction. The primary environmental threats to fish in the littoral zone arise from eutrophication, which may directly or indirectly alter feeding conditions through the loss of macrophytes, from increases or decreases in water level variations and from siltation rates, both of which may interfere with spawning or egg incubation, and from the introduction of alien species, many of which preferentially colonise the littoral zone where they may act as predators, competitors or environmental degraders. The management of these threats is best accomplished through general lake management measures such as the control of nutrient levels, but some actions specific to the littoral zone or its fish populations are also feasible. These include the replacement of lost or damaged spawning substrata, the active management of water levels at appropriate times of year, and, at least potentially, the deployment of artificial structures to provide appropriate physical habitat for adult fish.     

Offshore oil platforms and fouling communities in the southern Arabian Gulf (Abu Dhabi)

This study examined the fouling organisms on the legs of offshore oil platforms at two sites in the southern Arabian Gulf (offshore Abu Dhabi, United Arab Emirates). 100% of the metal structures was colonized by encrusting organisms. Both the number of individuals and the total biomass tended to decrease with depth. The total weight of dead shells always exceeded that of living organisms. Sessile filter feeders dominated the biomass, whereas small mobile forms had the largest number of individuals. The biomass at the deeper platform (22 m) was dominated by bivalves, barnacles and bryozoans, while polychaetes and amphipods had the greatest number of individuals. Biomass values here ranged from 1 g/0.1 m2 at 20 m to 147 g/0.1 m2 at 5 m; the corresponding individual numbers were 266 (20 m) and 11,814 indiv./0.1 m2 (5 m). The results at the shallower platform (11 m) differed in several respects: barnacles clearly dominated over bivalves, and sponges exceeded byrozoans, while total individual numbers fell due to a decline in polychaete dominance. Biomass values here ranged from 84 g/0.1 m2 at 10 m to 153 g/0.1 m2 at 0 m; the corresponding individual numbers were 695 (10 m) and 3,125 indiv./0.1 m2 (0 m). The potential role of such fouling communities on artificial structures in the Gulf is discussed.     

浅水湖泊植被分布格局及草-藻型生态系统转化过程中植物群落演替特征:安徽菜子湖案例

2005年9月-2009年10月对菜子湖湿地植被分布格局及种类组成进行调查,结合近十年的监测数据.分析了菜子湖水生植物群落的演替过程和驱动因素.结果表明:菜子湖维管植物共有147种,隶属于42科101属.植被分布格局为:①中部水位较深的区域.以马来眼子菜群丛,黑藻群从等沉水植物群落和野菱群丛等根生浮叶植物群落为主;②靠...     

新疆巴音布鲁克高寒沼泽湿地植物群落空间分布与环境解释

为探明巴音布鲁克高寒沼泽湿地植物群落与环境因子的关系,采用样线与样方结合的方法,于2014-2015年在天鹅湖沼泽湿地进行植物群落调查与环境因子测定.结果显示,巴音布鲁克天鹅湖沼泽湿地植物共有35种,隶属于19科27属.方差分析表明,地表积水条件显著影响植物群落物种多样性,随着地表积水减少,物种丰富度和ShannonWiener指数呈现上升趋势,Pielou指数呈现下降趋势,说明随着地表积水的减少,植物群落的物种多样性逐渐增加.冗余分析与偏冗余分析表明,所有环境因子共解释了植物群落物种组成变异的67.9%.水位与土壤全氮含量对物种组成的总效应达到显著水平,土壤全氮含量的净效应达到极显著水平,但全磷含量和有机碳含量的总效应与净效应均未达到显著水平.研究表明,积水条件和土壤氮含量是巴音布鲁克天鹅湖沼泽湿地植物群落物种组成和分布的主要环境驱动因子.     

Abiotic features and macroinvertebrate colonization of the hyporheic zones of two tributaries of the river Elbe (Germany)

Whole-ecosystem experiments may reach statistical pertinence when reference and treatment sites are compared. Therefore at least two similar systems must be found. To this aim we tried to answer the question if the hyporheic zones of both streams have similar features. We postulated that both streams would be unsuitable for a comparison in an ecosystem experiment if the structure of their hyporheic invertebrate communities differs significantly. Although pH, electrical conductivity and nitrate concentration differed in the surface water, variability of all chemical criteria studied in the hyporheic zones was much lower between the two streams compared to the variability within each stream. Thus the structure of both hyporheic invertebrate communities did not differ significantly. Because of this uniformity both streams are regarded to be suitable for a comparison in a whole-ecosystem experiment.     

热带水库消落区植物群落物种组成与结构特征——以海南松涛水库为例

消落区是河流、湖泊和水库因阶段性或长期性的水位涨落而反复淹没或出露而形成的一种特殊的季节性湿地.消落区植被在维持水陆生态系统的动态平衡、生物多样性、生态安全及生态服务功能等方面发挥着重要作用.通过样方法调查分析了海南松涛水库消落区植物组成、区系特点以及群落分布特征.结果显示：松涛水库消落区共有维管植物40科101属115种,其中被子植物36科97属111种,蕨类植物4科4属4种.植物区系以热带性为主,外来入侵种较多,且既耐水淹又耐干旱植物众多;群落以草本、灌木植物为主,乔木较少且大多以幼苗形式存在.主要群落类型为以铺地黍（Panicum repens）为优势种的复合群落,个别区域零散分布有美洲蟛蜞菊（Wedelia trilobata）、光荚含羞草（Mimosa sepiaria）、猪屎豆（Crotalaria pallida）、马松子（Melochia corchorifolia）、假臭草（Praxelis clematidea）和铺地黍等单优群落.消落区不同海拔区间群落分布存在明显差异,物种多样性从高到低呈显著递减趋势.研究结果可为松涛水库消落区植被恢复工作提供科学指导.     

Pelagic ciliates (Protozoa, Ciliophora) of different brackish and freshwater lakes — a community analysis at the species level

The pelagic ciliate communities from 58 north German lakes differing in their origin (natural lakes and artificial ponds), morphology (from shallow ponds with a maximum depth of below 0.5 m to relatively deep lakes with a maximum depth of more than 10 m, surface areas from below 10 ha to more than 100 ha), trophic state (from mesotrophic to hypertrophic) and salinity (freshwater lakes and brackish water lakes) are described and compared at species level. Each lake was comprehensively sampled quarterly in the years 1996 and 1997, respectively. Applying a quantitative protargol stain, about 140 ciliate species could be identified and quantified in all investigated lakes. 35 species, mainly members of the Prostomatida and Oligotrichida, were found commonly in all types of lakes at all seasons and dominated the pelagic ciliate communities. 3 species were common in freshwaters, but never occurred in brackish lakes. In the brackish waters a mixture of common freshwater species and marine species was found with 13 species exclusively occurring in brackish waters. Lowest ciliate cell numbers were observed for deep freshwater lakes, highest cell numbers were determined for brackish waters. Highest species richness was found in artificial peat ponds with an average of 24 pelagic ciliate species in spring samples. The range of occurrence for the identified species was wide for most common species. However, the influence of some environmental factors could be enlightened.     

Riffle‐pool morphometry and stage‐dependant morphodynamics of a large floodplain river (Vereinigte Mulde,Sachsen‐Anhalt,Germany)

Riffle‐pool sequences are a common feature of gravel‐bed rivers. However, mechanisms of their generation and maintenance are still not fully understood. In this study a monitoring approach is employed that focuses on analysing cross‐sectional and longitudinal channel geometry of a large floodplain river (Vereinigte Mulde, Sachsen‐Anhalt, Germany) with a high temporal and spatial resolution, in order to conclude from stage‐dependant morphometric changes to riffle and pool maintaining processes. In accordance with previous authors, pool cross‐sections of the Mulde River are narrow and riffle cross‐sections are wide suggesting that they should rather be addressed as two general types of channel cross‐sections than solely as bedforms. At high flows, riffles and pools in the study reaches changed in length and height but not in position. Pools were scoured and riffles aggraded, a development which was reversed during receding flows below the threshold of 0·4Q_bf (40% bankfull discharge). An index for the longitudinal amplitude of riffle‐pool sequences, the bed undulation intensity or bedform amplitude, is introduced and proved to be highly significant as a form parameter, its first derivative as a process parameter. The process of pool scour and riffle fill is addressed as bedform maintenance or bedform accentuation. It is indicated by increasing longitudinal bed amplitudes. According to the observed dynamics of bed amplitudes, maintenance of riffle‐pool sequences lags behind discharge peaks. Maximum bed amplitudes may be reached with a delay of several days after peak discharges. Increasing bed undulation intensity is interpreted to indicate bed mobility. Post‐flood decrease of the bed undulation intensity indicates a retrograde phase when transport from pools to riffles has ceased and bed mobility is restricted to riffle tails and heads of pools. This type of transport behaviour is referred to as disconnected mobility. The comparison of two river reaches, one with undisturbed sediment supply, the other with sediment deficit, suggests that high bed undulation intensity values at low flows indicate sediment deficit and potentially channel degrading conditions. It is more generally hypothesized that channel bed undulations constitute a major component of form roughness and that increased bed amplitudes are an important feature of channel bed adjustment to sediment deficit be it temporally during late floods or permanently due to a supply limitation of bedload. Copyright © 2011 John Wiley & Sons, Ltd.     

Flood effects on phosphorus immobilisation in a river water filled pit lake—Case study Lake Goitsche (Germany)

Between 1999 and 2002, a former open-cast mine was filled with river water forming the recent Lake Goitsche. During filling initially acid water was neutralised. Phosphorus (P) imported from Mulde River was nearly completely removed from the water column by co-precipitation with iron (Fe) and aluminium (Al) and deposited in the sediment.During extremely high waters of the Mulde River in 2002, a dike breach facilitated a second high import of P into Lake Goitsche with suspended and dissolved matter. The analysis of total phosphorus (TP), however, showed that P again had been eliminated from the water body a few months after the flood event. Sediment investigations before filling with river water, during filling, and after the flood event were used to analyse the process of P immobilisation in a lake with acid mine drainage history.The ratios of Fe to soluble reactive P (SRP) of sediment pore water were up to three orders of magnitudes higher than in natural lakes and can serve as an indicator for potential internal P loading from sediments. The SRP concentrations at the oxic/anoxic boundary were near or below the limit of quantification (< 0.2 μmol/L). Fe and manganese (Mn) redox cycling were responsible for hindering P dissolution from sediment to lake water.Finally it can be stated, that the risk of eutrophication for such a lake seems to be low.     

Effects of reduced salt concentrations on plant communities in the River Werra (Germany)

The reduction and equalization of the salt concentrations in the River Werra have resulted in a gradual recovery of the aquatic flora. Spatial high-resolution macrophyte mappings document the spread of the aquatic vascular plants in the middle and lower River Werra. Simultaneously, the plankton blooms have declined. Changes in the composition of the algal communities including diatoms also indicated lower salinity. In addition to the salinity, high nutrient concentrations, waste water discharges and structural degradation are important stressors in the River Werra as shown by e.g. low species richness of vascular plants and the common occurrence of pollution tolerant diatoms. From the existing data it is clear that an encompassing improvement of the ecological conditions in the River Werra can only be achieved by further restoration measures considering all stressors.     

Heavy metal inflow into the floodplains at the mouth of the river Weiße Elster (Central Germany)

From 1998 to 2002 investigations were carried out to estimate both the quantity and quality (heavy metal contents) of suspended matter loads discharged into a floodplain area measuring approx. 5 km² of the Central German river Weiße Elster, a tributary of the river Saale in the Elbe river basin. Flood sediments, suspended particulate matter, and floodplain soils were investigated especially for the main pollutants Cd, Zn, Cu, Pb, Cr, and Hg. Supplementary gamma spectroscopy examinations were performed to help to identify the age of deposits in order to estimate sedimentation rates for last decades. The recent flood sediments are contaminated by up to 33 times the geogenic background (Cd). Up to 55% of the total annual SPM load of the river Weiße Elster is relocated into the investigated retention area in the flood‐stricken year 2002. The sedimentation rates for the last 50 years vary between 0.5 mm/a and 1 mm/a in far away and rarely flooded parts and between 1 mm/a and 2 mm/a in the frequently flooded parts of the inflow of the retention area.     

Discharge regime and the effect of drying on macroinvertebrate communities in a temporary karst stream in East Westphalia (Germany)

The special hydrological situation of temporary streams has a great influence on the abiotic processes and other habitat conditions for organisms. To monitor possible impacts of stream drying on the composition of lotic communities, streamflow measurements and collections of the macrozoobenthos were conducted in a temporary and an adjacent upstream permanent section of the karst stream Sauer (East Westphalia, Germany) in 1996. The Sauer has a summer-dry temporary flow regime. The seasonal dry phase can last from spring to early autumn, so the duration of the dry phase varies from one to several months, increasing with distance downstream from the upstream permanent section. The number of invertebrate taxa and individuals decreases with increasing duration of the dry phase. The permanent section is characterized by taxa typical of montane and submontane streams, whereas the fauna of the temporary section is quite different, composed of representatives of various zonal areas. Limnephilid caddisflies are particularly characteristic of this section. Life cycle strategies and specific adaptations with respect to habitat drying are discussed for several species. It can be concluded that the temporary discharge regime of the karst stream Sauer has a clear effect on the invertebrate communities. They mainly consist of species which can be seen as characteristic faunal elements of temporary streams.     

Site-specific response spectra from the combination of microzonation with probabilistic seismic hazard assessment—An example for the Cologne (Germany) area

Seismic noise was measured at some 20 sites in the Cologne area (Germany) aligned nearly perpendicular to a graben structure. The H/V spectral noise ratio for each site was used to derive realistic S-wave velocity profiles down to the bedrock by means of a genetic algorithm inversion. Numerical simulations were performed for different combinations of source and propagation path parameters: focal depth, epicentral distance, attenuation and fault mechanism. Synthetic seismograms were produced and converted to Fourier and response spectra. Finally, the site-specific values from response spectral ratios, with their uncertainties, were used to modify attenuation functions entering the logic-tree algorithm of the probabilistic seismic hazard assessment (PSHA). The site-specific response spectra show the significance of taking into account the local S-wave velocity structure in PSHA.     

太湖贡湖湾虾类种类组成与时空分布特征

分别于2005年4月、7月、10月利用蹦网对贡湖湾虾类种类组成和时空分布进行调查.共采集到虾类9605尾,属于2科3属5种,分别是秀丽白虾(Exopalaemon modestus)、日本沼虾(Macrobrachium nipponense)、锯齿新米虾中华亚种(Neocaridina denticulata sin...     

Estimating distributional patterns of non-marine Ostracoda (Crustacea) and habitat suitability in the Burdur province (Turkey)

We explored distributional patterns and habitat preferences of ostracods in the Burdur province (Turkey). At 121 sites we recorded 35 taxa (22 recent, 13 sub-recent), of which 23 represent new records for the province. According to the Index of Dispersion and d-statistics, the individual species exhibited clumped distributions. Cosmopolitan species dominated (63.64%). A direct effect of regional factors (e.g., elevation) was not observed, while local factors (e.g., water temperature) best explained species distribution among habitats. Based on alpha diversity values, natural habitats (springs, ponds, creeks) were more suitable than artificial habitats (e.g., troughs, dams), suggesting that natural habitats define regional species diversity. Twenty-two of the recorded species had wider ecological ranges than previously reported. Cosmopolitan species appeared to suppress non-cosmopolitan species due to their wider ecological range.     

Factors structuring phytoplankton community in a large tropical river: Case study in the Red River (Vietnam)

Algal assemblages have been widely used as an ecological indicator of aquatic ecosystem health conditions because of their specific sensitivity to a wide variety of environmental conditions. In turbid rivers, as in other aquatic systems, phytoplankton structure plays an important role in structuring aquatic food webs. Worldwide, phytoplankton is less studied in turbid, large tropical rivers compared to temperate river systems. The present study aimed to describe the phytoplankton diversity and abundance in a turbid tropical river (the Red River, northern part of Vietnam from 20°00 to 25°30 North; from 100°00 to 107°10 East) and to determine the importance of a series of environmental variables in controlling the phytoplankton community composition. Phytoplankton community was composed of 169 phytoplankton taxa from six algal groups including Bacillariophyceae, Chlorophyceae, Cryptophyceae, Euglenophyceae, Dinophyceae and Cyanobacteria. Community composition varied both spatially and with season. Sixteen measurement environmental variables were used as input variables for a three-layer backpropagation neural network that was developed to predict the phytoplankton abundance. Phytoplankton abundance was successfully predicted using the tagsig transfer function and the Levenberg-Marquardt backpropagation algorithm. The network was trained to provide a good overall linear fit to the total data set with a slope (R) and mean square error (MSE) of 0.808 and 0.0107, respectively. The sensitivity analysis and neutral interpretation diagram revealed that total phosphorus (TP), flow discharge, water temperature and P-PO₄³⁻ were the significant variables. The results showed that the developed ANN model was able to simulate phytoplankton abundance in the Red River. These findings can help for gaining insight into and the relationship between phytoplankton and environmental factors in this complex, turbid, tropical river.