Comparison of benthic macroinvertebrate fauna and substratum composition in riffles and pools in the impounded River Elan and the unregulated River Wye, mid-Wales

SUMMARY. The macro-invertebrate fauna and substrate were studied in a riffle and pool from a regulated (Elan) and an unregulated (Wye) river in summer. There were some differences in the substrate particle size distribution of the two rivers and between the riffle and the pool on the Wye. There was more detritus in pools than in riffles in both rivers and generally more in the Elan than the Wye. Deposits on the bed of the Elan were rich in iron and manganese.
On the Wye. there was a greater density of invertebrates in the riffle than in the pool, but species richness was similar. Most species showed some preferences for either the riffle or the pool. The riffle contained a substantial number of Ephemeroptera, Trichoptera, Plecoptera and Simuliidae (52%) whilst the pool was dominated by chironomids (71%). Compared with the Wye, total invertebrate density and species richness were reduced in the Elan. Some species characteristic of riffles were reduced or absent on the Elan. Invertebrate density on the Elan was similar in the riffle and pool; species richness was greater in the riffle. The distribution and abundance of invertebrates is discussed in relation to such environmental factors as water velocity through the substrate and dissolved oxygen supply in interstitial habitats.     

Macroinvertebrate drift in the upper Wye catchment,Wales

Drift samples collected at five sites in the upper catchment of the River Wye yielded 99 taxa (excluding Chironomidae and Simuliidae). Significantly fewer taxa were collected from a site on the impounded River Elan (W4) compared with nearby River Wye sites. Mean daily density of drifting macroinvertebrates ranged from 6.3 × 10^-2 to 782.9 × 10^-2m^-3, with greatest densities during the summer months, and Ephemeroptera, Coleoptera and Diptera generally comprised the greatest proportion of animals collected. Chironomids formed a considerable proportion of collections at W4 and the relative abundance of ephemeropterans, coleopterans and trichopterans was generally significantly less at W4 than at other sites. Estimates of the total numbers of invertebrates drifting past each site varied from 8.3 × 10³ to 1 373.1 × 10³day^-1. Total numbers drifting were significantly related to estimates of total benthic density and similar relationships were established for some major taxonomic groups and some species.     

The Epipelic Algal Flora of the River Wye System,Wales, U.K. 1. Productivity and Total Biomass Dynamics

The spatial and temporal fluctuations of the phytopigment content, “potential” primary productivity and total biomass of the epipelic algae of the River Wye System were studied during June 1979 to May 1981. Chlorophyll-a and productivity values showed a downstream increase, much less obvious for the total biomass. Phaeophytin-a values followed almost similar spatial and temporal fluctuations to those of chlorophyll-a. High chlorophyll-a productivity and total biomass values were recorded during warmer months due to favourable environmental conditions for algal growth, but lower values during unfavourable winter and flood periods.     

Primary productivity of the River Ely,South Wales,U.K.

The present study was carried out on the non-tidal reaches of the River Ely, South Wales, from October 1979 to October 1980. The seasonal variations of the chlorophyll-a content of the phytoplankton was unimodal with one maximum in May and a minimum in December. The chlorophyll-a content varied from 0.277 to 41.259 mg m^?3. The primary productivity showed a bimodal seasonal distribution with two maxima in May and September and lower values throughout the remainder of the year, particularly in winter. The value for the primary productivity varied from 0.269 to 24.302 mg C m^?3 h^?1. A positive correlation was obtained between chlorophyll-a content and primary productivity. The seasonal distribution of the dominant algal species and the saprobity of the River Ely were also studied. The diatom species almost showed a similar seasonal periodicity. Their concentrations were low during the winter months and high during most of the spring and summer months. Many of the dominant diatom species found in the phytoplankton populations were either considered by the other authors as saprobic (Nitzchia palea) or as inhabitants of eutrophic waters (Gomphonema parvulum, Navicula cryptocephala and Synedra ulna). Chlamydomonas spp. were the most abundant green algae followed by Chlorella vulgaris. The effect of sewage effluent disposal and cattle excreta at three of the sampling sites might partly explain the presence of high Chlamydomonas spp. populations at those sites. Physical factors (low flow rates, high transparency and water temperature) and organic pollution at some sampling sites seemed to play an important role in increasing the number of algal species during spring and summer. The non-tidal reaches of the River Ely were found to be β-mesosaprobic above and below Station 5 and α-mesosaprobic at the latter station and therefore, the river can be considered as polluted at Station 5 and mildly polluted at the others.     

A survey of the macro-invertebrate riffle fauna of the River Wye

SUMMARY. Surveys of the Wye catchment in March and September 1975, and July and September 1976 and 1977, yielded 227 macro-invertebrate taxa, 77 of which were Chironomidae. Total macro-invertebrate density ranged from 520 to 22020 m⁻². Total density estimates in July 1976. during a period of severe drought, were significantly higher than in July 1977 but no differences were established between estimates on other comparable dates in 1975, 1976 and 1977. The total number of taxa and total macro-invertebrates collected from sites with total dissolved solids concentrations less than 50 mg I⁻¹ were significantly lower than at sites with higher concentrations. In general, upstream sites were dominated numerically by Plecoptera in March; Ephemeroptera, Trichoptera and Diptera were relatively more abundant during the summer months. Sites lower in the catchment were more variable in composition with Oligochaeta, Ephemeroptera, Trichoptera and Diptera all abundant at certain sites and times. The densities of Ecdyonuridae (Ephemeroptera). Hydropsychidae (Trichoptera) and Elminthidae (Coleoptera) in the impounded R. Elan, a tributary of the R. Wye, were significantly lower than at nearby sites on the Wye although no differences in total macro-invertebrate density were established. Average linkage clustering of Spearman rank correlation coefficients between selected taxa allowed the comparison of taxa groups with contemporary site groups by nodal analysis. Six major taxa groups were established and these characterized five site groupings.     

Plant reproductive phenology over four years including an episode of general flowering in a lowland dipterocarp forest,Sarawak, Malaysia

The first systematic observation of a general flowering, a phenomenon unique to lowland mixed-dipterocarp forests in Southeast Asia, is presented. During general flowering, which occurs at irregular intervals of 3–10 yr, nearly all dipterocarp species together with species of other families come heavily into flower. We monitored reproductive phenology of 576 individual plants representing 305 species in 56 families in Sarawak, Malaysia. Observations continued for 53 mo from August 1992 and covered one episode of a general flowering cycle. Among 527 effective reproductive events during 43 mo, 57% were concentrated in the general flowering period (GFP) of 10 mo in 1996. We classified 257 species into flowering types based on timing and frequency of flowering. The most abundant type was “general flowering” (35%), which flowered only during GFP. The others were “supra-annual” (19%), “annual” (13%), and “sub-annual” (5%) types. General flowering type and temporal aggregation in reproductive events were commonly found among species in various categories of taxonomic groups, life forms, pollination systems, and fruit types. Possible causes for general flowering, such as promotion of pollination brought about by interspecific synchronization and paucity of climatic cues suitable for flowering trigger, are proposed, in addition to the predator satiation hypothesis of Janzen (1974) .     

Use of Macrophytes in Assessing the Ecological Status of Small River (by the Example of the Okhta River,St. Petersburg)

Hydrochemical and hydrobiological characteristics have been studied at 13 sites in the Okhta River within the precincts of St. Petersburg in 2010. The Water Pollution Index (WPI), calculated according to hydrochemical parameters, characterizes the river water quality as “very polluted” to “extremely polluted.” According to the Pantle–Buck–Sláde?ek Saprobity Index, obtained on the basis of macrozoobenthos characteristics, polysaprobic and α-mesosaprobic zones can be distinguished in the watercourse. The species richness of river macrophytes is low (18 species). The Macrophyte Water Quality Index makes it possible to assess water quality in the range from “polluted” to “very polluted” water. Macrophyte trophic indexes MTR, IBMR and TIM indicate a high trophy level in the watercourse sites. Based on the analysis of hydrochemical materials and the data on macrozoobenthos and macrophytes, the general tendency is similar: deterioration of water quality downstream. Macrophyte characteristics reflect changes in hydrochemical parameters downstream the river course. А strong correlation (r =–0.76) is found between the Macrophyte Water Quality Index and WPI. The possibility of using the data on macrophytes in small rivers for assessing water quality is demonstrated.     

Miocene invertebrate trace fossils from a braided river environment,western Nebraska,U.S.A

Lower Miocene cross-stratified sands of the Gering and Monroe Creek Formations exposed on Scotts Bluff National Monument in western Nebraska, U.S.A., were deposited by migrating sand bars in a braided river system similar to the modern Platte River in eastern Nebraska and, like the Platte, contain local lenses of parallel stratified sediment that accumulated in ponded areas of abandoned channels. During times of low discharge, broad areas of river bar sands and abandoned channel sediments were subaerially exposed on the Miocene river plain. These sediments, like those exposed in the Platte River today, were subjected to burrowing by insects and other animals.Trace fossils in Lower Miocene braided river deposits are: vertical shelter burrows, horizontal deposit-feeding burrows, bioturbated layers, and vertical passageways between bioturbated layers. The burrows are cylindrical to sub-cylindrical in cross-section, internally meniscate or massive, generally non-branching, and smooth walled. Shelter burrows are similar in shape and size to recent burrows dug by beetles in river sediment for protection from day-time temperatures, to pass the night, and to hibernate. The shelter burrows, deposit-feeding burrows, and vertical passageways in the Lower Miocene sediments occur in four distinct “populations” with modal diameters of 1–2, 3–4, 7–8, and 10–12 mm. The occurrence of both vertical and horizontal burrows in all four “populations” suggests that they could have been made by the same insect. “Populations” with modal diameters of 1–2, 3–4, and 7–8 mm also occur in modern Platte River sediment and are made by tiger-beetle larvae (3–4 mm) and heterocerid (1–2 mm) beetles. Miocene shelter burrows, deposit-feeding burrows, bioturbated layers, and vertical passageways, therefore, could have been formed by different types of beetles, and/or larval instars and adults of the same beetle species.     

安庆西江浮游动物群落结构及江豚生存状况评估

为了解安庆西江浮游动物群落结构, 进而评价江豚(Neophocaena asiaeorientalis asiaeorientalis)的生存状况, 于2015年4月至2016年1月对西江浮游动物和环境因子进行了季节性调查。研究结果表明: (1)共采集浮游动物55种, 其中原生动物13种、轮虫27种、枝角类9种、桡足类6种。4个季节间浮游动物种类数差异较大, 夏季种类数最多, 为39种; 冬季种类数最少, 仅为16种。(2)全年浮游动物平均密度和生物量分别为4115 ind./L和1.735 mg/L, 且均以原生动物和轮虫为主。方差分析结果表明, 不同季节间浮游动物密度和生物量均存在显著差异, 且夏季浮游动物密度和生物量均显著高于其他3个季节。(3)全年共记录优势种12种, 其中原生动物4种、轮虫6种、桡足类2种; 不同季节间浮游动物优势种的组成差异明显。(4)采用浮游动物生物量对水质的评价结果显示西江水体处于中营养状态; 运用Shannon多样性指数和Margalef多样性指数对水质的评价结果显示西江水体处于α-中污状态, 表明西江水质基本上满足江豚生存需求。(5)依据浮游动物的现存量, 估算出西江食浮游动物鱼类的渔产力为54340.2 kg, 相应地可满足36头江豚的营养需求。研究结果不仅有助于了解长江故道这种特殊水体浮游动物的群落特征, 还对迁地保护区江豚的保护有重要意义。     

Diatoms and pollen in a trial core from Sandwich Harbour,South West Africa (Namibia)

Sandwich Harbour forms a largely enclosed bay and extensive lagoon system that receives a limited subsurface, freshwater inflow from the Kuiseb River. It has been suggested that the Kuiseb River contributed more freshwater to Sandwich Harbour in the past, and that the river has since been displaced northwards towards Walvis Bay. Pollen and diatom analyses were carried out on a trial core from the central inshore region of the harbour to determine whether sufficient biological material for extensive studies had been preserved, whether the sediments were undisturbed and whether changes in salinity were evident. Pollen was not preserved in sufficient quantities to analyse but diatoms were abundant in the upper portion of the core. Diatom analysis indicated that the sediments were relatively undisturbed. The earliest sediments were dominated by a freshwater soil flora, and this was displaced by a marine littoral flora with brackish and freshwater diatoms increasing in frequency in the uppermost sediments. The increase in brackish forms is correlated with the formation of a sandbar across the harbour at the end of the last century. Further analyses of the present day flora and sediment cores from different parts of the harbour should provide a clear indication of the history and development of the area, especially the role played by the Kuiseb River.     

新疆阿勒泰地区额尔齐斯河和乌伦古河流域鱼类多样性演变和流域健康评价

为了解阿勒泰地区额尔齐斯河和乌伦古河流域的鱼类多样性现状和历史演变, 本研究于2013-2016年间在该流域的鱼类多样性进行了连续调查, 并结合历史资料和标本, 以Margalef丰富度指数、Shannon-Wiener多样性指数、Pielou均匀度指数分析评估了流域内鱼类的多样性水平和时空变化。该流域历史上分布有土著鱼类23种, 当前记录到19种, 流域内还有外来鱼类15种。阿勒泰鱼类的区系组成以鲤科种类为主, 其中特有和珍稀濒危物种占比高, 具有重要的保护价值。多样性指数计算结果显示, 2013-2016年鱼类多样性情况整体稳定, 额尔齐斯河鱼类物种数多于乌伦古河。研究还基于鱼类生物完整性指数(Fish Index of Biological Integrity, F-IBI)对34个采集点的河流健康状况进行了评价, 结果显示额尔齐斯河流域大多数调查点的健康状况处于“亚健康”或“一般”水平, 乌伦古河流域多数调查点的健康状况处于“健康”水平。水利工程、外来物种、过度捕捞是影响阿勒泰地区鱼类多样性的重要因素。未来应通过水利工程的联合调度、下泄合理生态流量、布设鱼类通道、规范养殖渔业、严控外来物种、本地土著鱼类的人工增殖放流, 以及合理的就地保护措施对阿勒泰地区的鱼类多样性加以保护, 提升水体健康程度。     

THE ECOLOGY OF EPIPELIC ALGAE OF FIVE WELSH LAKES,WITH SPECIAL REFERENCE TO VOLVOCALEAN GREEN FLAGELLATES (CHLOROPHYCEAE)1

The ecology of epipelic algae on the marginal sediments of five Welsh lakes was studied over an annual cycle. The lakes, Llydaw, Cwellyn, Padarn, Maelog and Coron ranged from very oligotrophic to nutrient-rich. Attention was focussed on chlamydomonad flagellates, diatoms, blue-green algae and euglenoids and the different proportions of these in algae in the epipelon of lakes of contrasting water quality. A total of 75 algal taxa was found in the five lakes, 25 were species of volvocalean flagellates. Mean annual population density of these flagellates differed by an order of magnitude between the lakes. The greatest population density was recorded for Chlamydomonas anticontata Schiller in nutrient-rich Llyn Maelog. Twenty species of pennate diatoms were recorded frequently in the epipelon. In the nutrient-rich lakes, Maelog and Coron, pennate diatoms were dominant on the sediments, where they exhibited population maxima in spring and autumn. Increase in numbers of epipelic diatoms was recorded when silica concentrations were minimum in the overlying lake waters. Navicula hungarica Grun. achieved the maximum population density, 260 000 cells · cm^?2. Euglenoids formed large epipelic populations during late-summer and autumn in these nutrient-rich lakes. Blue-green algae were more important, proportionally, in the nutrient-poor mountain lakes, which had sediments of higher organic content. Chlamydomonads were the major algal component of the epipelon in the mountain lakes, Llydaw and Cwellyn, where the sediments were characterized by larger particle size, and higher organic content. In the nutrient-rich lakes, where the sediments had higher calcium content, chlamydomonads formed significant populations only during spring and summer, when nutrient levels were minimal in the overlying lakewaters.     

Preliminary Observations on the Nature,Taxonomic Composition,Distribution, Behaviour and Nutrient Requirements of the “Unusual” Algal “Jellies” of Oguta Lake in Southeastern Nigeria

Preliminary observations were made between October 1982 and May 1983 on the nature, taxonomic composition, spatial distribution, buoyancy behaviour and nutrient requirements of some unusual planktonic algal “jellies” in Oguta Lake in Southeastern Nigeria. These “jellies” are macroscopic, blue-green algal masses whose excessive mucilage of high consistency acts as substrata for other epiphytic components viz. diatoms and green algae. They are more abundant in the lentic areas of the lake, undergo diurnal vertical movements and have their growth enhanced by spikes of nitrogen and phosphorus salts into their aquatic medium. The effects of these “jellies” on the ecology and general water use of the lake are discussed. Speculations on the reasons for their occurrence are given and possible control measures outlined.     

Distribution and abundance of zooplankton in the Waikato River,New Zealand

Potamoplankton is often a well developed component in large lowland rivers, yet little is known about its structure in New Zealand's longest river, the Waikato River. To redress this gap we sampled bimonthly at seven sites along the length of the river over 12 months. Rotifers were the dominant zooplankton in the Waikato River making up 85% of the total densities. Cladocerans represented 9% and copepods only 6%. Rotifers were also the most taxonomically rich group with 41 species in 20 genera identified throughout the study. Thirty rotifer species and nine genera represent new records for the river – two cladoceran species were also recorded for the first time. The highest densities of crustaceans and rotifers were found in the hydro lakes. Densities of crustaceans decreased with increasing distance downstream and densities of rotifers were on average 15 times greater than crustaceans in the lower river. The seasonality of Crustacea was similar to that in New Zealand lakes and rivers with high densities in summer and minimum densities over the winter period. Total rotifer densities showed a similar trend although there were marked seasonal differences between individual species.     

Nutrient and Sediment Retention in a Temperate Marsh Ecosystem

The Wye marsh, an undeveloped wetland of 639.9 ha, serves as a receiving water for a 19,600 ha agricultural watershed before discharging into the Great Lakes. Seasonal and diel changes in limnological variables, most notably nitrogen, phosphorus, silica and turbidity, have been examined in the Wye river, marsh and discharge waters over an 11-month period and related to the composition of marsh sediments. Retention rates of the marsh ecosystem for incoming nutrients and suspended solids have been estimated by calculations of mean monthly inflow to outflow ratios using the levels of these factors in the Wye River and the marsh discharge. Calculated mean monthly retention rates of the marsh for incoming nutrients is estimated at no less than 61% for nitrogen-N, 36% for total phosphate, and 14% for soluble silica during the ice-free period. Based on observed turbidity levels, the retention of incoming suspended solids is estimated at 65% for the same period. The Wye marsh is a substantial sump for inorganic and organic materials which are retained within the water column, biomass and unconsolidated sediments.     

Algal flora of certain gravel pits in the Thames Valley,U.K.

Summary Detailed analyses are presented of the phytoplankton of two pairs of gravel pits in the Surrey-Middlesex area of the Thames Valley. One of each pair has been recently excavated while the other is much older.Gravel dredging was fairly localised during the investigation, so that it was possible to study an area of disturbed water and an area of undisturbed water in each pit.The distribution of the algae in general and the frequency of the principal members of the phytoplankton were correlated, as far as possible with the physical and chemical features of the environment.Certain algae were found to favour the new or alternatively the old pits and there was some indication that some of the algae recorded in larger numbers thrived best in the disturbed or otherwise the undisturbed water of a pit.The total number of species observed in the new pits was considerably smaller than that in the old pits. Estimates of the total phytoplankton indicates that the new pits are richer, but less varied than the old pits.All the pits were flooded once by Thames water during the course of the investigation. Reasons are given for concluding that this flooding did not cause undue contamination with river phytoplankton.     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

The rate of downstream displacement of macroinvertebrates in the upper Wye, Wales

Quantitative data describing drift rates and benthic density of macroinvertebrates are utilised to estimate the rates of downstream displacement of invertebrate populations in the Wye, Wales. Calculations are based upon two models, one a classical exponential relationship between drift catch and distance travelled and the other derived from a solute balance equation. Results from the two models were significantly correlated. Estimates of the rate of benthic community displacement ranged from 2.8 to 70.7 m d^-1, with highest rates recorded in she summer period. There were considerable differences in rates between taxa and between sites. It was estimated that a displacement of 10 km downstream could be achieved by certain taxa during a generation period.     

Effects of artificial freshets on substratum composition,benthic invertebrate fauna and invertebrate drift in two impounded rivers in mid-Wales

Artificial discharges of water from reservoirs caused a six-fold and three-fold increase in discharge in the R. Tywi and R. Elan respectively but did not significantly alter particle size composition (by weight) and the porosity of the substratum or the organic matter content of fine particles (<0.5 mm). Freshets in both rivers resulted in a consistent, though not significant, reduction in total densities of invertebrates and the densities of many major taxa and abundant species. During the freshet in the R. Elan, maximum concentration and total load of suspended solids were about 11 and 35 times greater than pre-release values respectively while invertebrate drift was dominated by Chironomidae (65%) and Plecoptera (25%). Total numbers and densities of drifting chironomids increased immediately in response to the flow increase; in contrast, numbers and densities of plecopterans increased later, during the night.     

Temporal dynamics of gastropod fauna on subtidal sandy sediments of the Ensenada de Baiona (NW Iberian Peninsula)

The temporal variation of the gastropod fauna inhabiting sandy sediments of the Ensenada de Baiona (Galicia, Spain) was studied at three subtidal sites from February 1996 to February 1997 by means of quantitative sampling. A total of 5,463 individuals representing 51 gastropod species and 22 families were found. The family Pyramidellidae was the most diverse in number of species (11 species), followed by Rissoidae and Trochidae (4 species each). The dogwhelk, Nassarius reticulatus, and the rissoid snail, Rissoa parva, were the numerically dominant species at the three studied sites; those and other abundant species showed their greatest densities by the end of summer and the beginning of autumn. In general, univariate measures of the assemblage (number of species, abundance, diversity and evenness) showed variations through time; greater values were recorded between summer and autumn depending on the site. Multivariate analyses done on abundance data showed certain seasonality in the evolution of the assemblage as expected for shallow subtidal sandy sediments at temperate latitudes; those seasonal changes were mostly related to variations in abundance of numerically dominant species. Although the measured sedimentary variables did not show significant correlations with faunal univariate parameters, sediment heterogeneity due to the presence of mats of Zostera marina L. and shells of dead bivalves might explain the differences in composition of the gastropod assemblage among sampling sites.