Macrobenthic fauna in Thale Sap Songkla, a brackish lake in southern Thailand

The macrobenthic fauna in Thale Sap Songkhla was investigated at 2–3 month intervals from October 1991 to October 1993. The abundance of the benthic fauna ranged from 53 to 9529 individuals m^?2. The abundance and species composition were generally higher during the late southwest monsoon (October) than during the mid-northeast monsoon (December). One hundred and twenty-two species belonging to six phyla were found. Three major groups of macrobenthic fauna consisted of 44 species of Polychaeta (36%), 44 species of Crustacea (36%) and 28 species of Mollusca (28%). The other six species (5%) were minor groups belonging mainly to the Nematoda, Oligochaeta, Sipunculida and Pisces (fish larvae). The predominant polychaetes were Diopatra neapolitana and Heteromastus filiformis. Diopatra neapolitana was found only at two stations close to the sea (20–1440 individuals m^?2), while H. filiformis was found at all stations (6-2255 individuals m^?2). Apseudes sp. 1 (Tanaidacea), Apanthura africana (Isopoda), Amphipoda (many species) and Eupogebia sp. (Anomura) were the main groups of Crustacea. The most abundant crustacean was Apseudes sp. 1., with a maximum density of 5726 individuals m^?2. The dendrogram of Jaccard's coefficient shows two clusters of communities. An increase of polychaetes was observed in the second year of the study.     

Changes in the quantitative distribution of Caspian Sea polychaetes: Prolific fauna formed by non-indigenous species

Although considered major players in many ecosystems around the world, the ecology of Caspian Sea polychaetes is currently understudied. This study describes the species composition and quantitative distribution of polychaetes in the southern Caspian Sea and relates the distribution to seasonal changes in environmental parameters of water (temperature, salinity, and surface current speed) and sediments (organic matter and grain size composition) at four depths (2, 5, 9 and 14 m) on the Noshahr coast in the southern Caspian Sea in 2010. Four species were found: Alitta succinea, Hediste diversicolor, Hypania invalida, and Streblospio gynobranchiata. Among them, the non-indigenous S. gynobranchiata was the dominant species, accounting for 87% of the total abundance. Significant differences in abundance across the four species were observed among depths and seasons. Additionally, significant correlations between species abundances and the tested environmental factors were evident. This study highlights the potential consequences of established non-indigenous species in the southern Caspian Sea.     

Mesocosm observations on the ecological response of an aquatic community to sediment contamination

Between 1992 and 1997 the effects of contaminated sediment on an aquatic community were studied in outdoor mesocosms (2m³), one filled with ‘naturally’ polluted sediment from the sedimentation area ‘Ketelmeer’, the other with relatively clean sediment from the shallow lake ‘Oostvaardersplassen’. Negative effects of the contaminated sediment were observed on the population development of the amoeba species Arcella megastoma and Diflugia accuminata, the mysid shrimp Neomysis integer, the microlepidopteran Cataclysta lemnata and the cladoceran community, whereas the biting midge Culex sp. showed a preference for the contaminated system. The reduction of the grazing capacity of the cladoceran community resulted in higher algal densities in the ‘Ketelmeer’ mesocosm despite the fact that nutrient concentrations in the water column of both mesocosms were comparable.     

Tree colonization trends on a sediment bar after a major flood

Tree mortality and regeneration in riparian areas are greatly influenced by flooding. The elevational distribution of Salix spp. and Robinia pseudoacacia were investigated by observing densities and standing conditions before and after a major flood on a sediment bar in the middle reaches of the Arakawa River in Kumagaya, Japan. The subsequent tree recruitment was also examined. R. pseudoacacia was easily washed away with the eroded sediment, whereas Salix spp. was found to be more tolerant. Both species were able to survive even after collapsing, provided that their roots were fully or partially embedded in the sediment. Re‐shooting of collapsed trees, rather than emergence from saplings (either by seeds or vegetative fragments), was observed to be the major method of recruitment after the flood. Therefore, tree density before the flood was unchanged, unless the trees were subject to washing away. Salix spp. recruitment was mainly observed in low‐lying areas and R. pseudoacacia in elevated areas. Recruitment from saplings was species‐specific. Salix spp. at high elevations originated mainly from shoot fragments as they need high levels of moisture for seed germination and at higher elevations, sediment moisture content is very low. R. pseudoacacia, on other hand, originated mainly from roots and seeds. At a given elevation, past recruitment patterns indicated that the annual recruitment of trees increased with tree density up to a particular threshold of recruitment density. Further increases in tree density beyond that optimum value resulted in a decline in recruitment. Furthermore, threshold density was observed to increase along with elevation for R. pseudoacacia while declining with Salix spp. Copyright © 2010 John Wiley & Sons, Ltd.     

Seasonal variation in the phytoplankton of a saline lowland river (Buenos Aires,Argentina) throughout an intensive sampling period

The aim of this survey was to analyse seasonal variations in phytoplankton composition and abundance with respect to temperature and conductivity values at two sampling sites in the Salado River's lower basin: El Destino and Guerrero. Samples were taken twice a week from 9 March 2004 to 20 July 2004. A total of 145 and 143 species were identified for these two sites, respectively. Infrequent species were discarded to avoid statistical misinterpretations. Autocorrelation analyses (Ljung‐Box Q‐statistic) were performed in order to establish seasonal patterns for species abundance. Similar significant (p < 0.05) autocorrelation patterns were observed for phytoplankton species composition, temperature and conductivity, thus, illustrating correlations with seasonal behaviour. On the basis of these data, species were grouped as (1) late‐summer: with 34 species well represented in warm waters (>22°C) (e.g. Planctonema lauterbornii and Chroococcus spp.); (2) winter: with 10 species that reached their highest densities in cold waters (<12°C) (e.g. Binuclearia eriensis and Microcystis firma); (3) transitional: of only four species with abundance peaks during intermediate conditions (15.5°C average) such as Closteriopsis acicularis and Nodularia spumigena and (4) independent: with 22 species of random behaviour whose autocorrelations remain within confidence limits. These four classifications pertain to species with similar presence at both sampling sites; the rest of the species evinced slightly different patterns. An apparent season‐associated succession of species was detected with those adapted to the warm, stagnant water of the late summer being replaced by others acclimated to the cold water of the winter. Copyright © 2009 John Wiley & Sons, Ltd.     

Distribution of macrobenthic fauna in Phawong and U-Taphao canals flowing into a lagoonal lake, Songkhla, Thailand

The macrobenthic fauna of two discharge ecosystems, Phawong Canal and U-Taphao Canal flowing into Songkhla Lake in Thailand, were studied from August 1994 to August 1995. The salinity of Phawong Canal and U-Taphao Canal ranged from 0.1 to 27.8 and 0.1 to 17.0 practical salinity units (PSU), respectively. The biochemical oxygen demand (BOD) of Phawong Canal ranged from 2.5 to 33.0 mg L⁻¹, while that of U-Taphao Canal ranged from 1.1 to 12.6 mg L⁻¹. Temporal changes in the number of species and individuals were determined throughout a year. During the season of heavy rains (November– December), the density and number of most species decreased markedly. Only chironomid larvae increased and these were distributed in the uppermost reaches of the canals during this period. Sixty-two and 52 species of macrobenthic fauna were found in Phawong Canal and U-Taphao Canal, respectively; however, the abundance and number of species collected at each sampling was very low in the upper reaches of the canals. The most numerous benthic fauna in the Phawong Canal were polychaetes, followed by amphipods. Pelecypods and gastropods were the dominant groups in U-Taphao Canal. A distribution pattern of macrobenthic fauna associated with pollution gradients (BOD) was observed only at Phawong Canal. In addition, species diversity according to the Shannon-Wiener index only was not applicable to the assessment of benthic environmental health when the few individuals found were evenly distributed among the few species present at U-Taphao Canal. It is recommended that a coastal care project be established by the appropriate government agencies in the study areas.     

Distribution of macrobenthic fauna in Phawong and U-Taphao canals flowing into a lagoonal lake, Songkhla, Thailand

The macrobenthic fauna of two discharge ecosystems, Phawong Canal and U-Taphao Canal flowing into Songkhla Lake in Thailand, were studied from August 1994 to August 1995. The salinity of Phawong Canal and U-Taphao Canal ranged from 0.1 to 27.8 and 0.1 to 17.0 practical salinity units (PSU), respectively. The biochemical oxygen demand (BOD) of Phawong Canal ranged from 2.5 to 33.0 mg L⁻¹, while that of U-Taphao Canal ranged from 1.1 to 12.6 mg L⁻¹. Temporal changes in the number of species and individuals were determined throughout a year. During the season of heavy rains (November– December), the density and number of most species decreased markedly. Only chironomid larvae increased and these were distributed in the uppermost reaches of the canals during this period. Sixty-two and 52 species of macrobenthic fauna were found in Phawong Canal and U-Taphao Canal, respectively; however, the abundance and number of species collected at each sampling was very low in the upper reaches of the canals. The most numerous benthic fauna in the Phawong Canal were polychaetes, followed by amphipods. Pelecypods and gastropods were the dominant groups in U-Taphao Canal. A distribution pattern of macrobenthic fauna associated with pollution gradients (BOD) was observed only at Phawong Canal. In addition, species diversity according to the Shannon-Wiener index only was not applicable to the assessment of benthic environmental health when the few individuals found were evenly distributed among the few species present at U-Taphao Canal. It is recommended that a coastal care project be established by the appropriate government agencies in the study areas.     

Distribution of Macrobenthic Species in Lake Ontario in Relation to Sources of Pollution and Sediment Parameters

Bottom samples were collected in Lake Ontario during the International Field Year for the Great Lakes (IFYGL) in November 1972. Samples were collected in triplicate at 55 stations located throughout the lake.Sand prevailed at the shallow areas but silt dominated the intermediate and deep-water areas. Total carbon and total Kjeldahl nitrogen content of the sediment increased with increased depth, but no trend was evident in the total phosphorus content.Oligochaetes and the amphipod Pontoporeia affinis accounted for 92% of all organisms collected. The former group dominated the shallow areas while the latter dominated the intermediate and deep-water zones. Stylodrilus heringianus and Limnodrilus hoffmeisteri were the most widely distributed species, being collected at 51 of the 55 stations.Several approaches were used to evaluate trophic conditions in the lake - the indicator species approach, the oligochaete-density index, a modified “Goodnight-Whitley” index, and the Brinkhurst % L. hoffmeisteri index. The indicator species approach proved to be the most sensitive index because inconsistencies arose when the other indices were applied.The most obviously eutrophic areas were near the mouth of the Niagara River and off Toronto. These areas were characterized by high oligochaete densities dominated by either L. hoffmeisteri or T. tubifex. Mesotrophic conditions were evident along the southern shoreline from the mouth of the Niagara River to Rochester, New York.Stylodrilus heringianus, L. hoffmeisteri, T. tubifex, and P. affinis were significantly related to some of the measured sediment parameters in either the intermediate or deep-water areas.     

The storage and provenance of fine sediment on the channel bed of two contrasting lowland permeable catchments,UK

Fine sediment (<63 µm) storage in river channels frequently represents a significant term in catchment sediment budgets and plays an important role in diffuse pollution problems. A combination of a sediment remobilization technique and the fingerprinting approach was used to examine the storage and provenance of fine sediment on the channel bed of two contrasting lowland permeable catchments in the UK. In the upper Tern (∼231 km²) study catchment, estimates of mean fine sediment storage on the channel bed ranged between 860–5500 g m⁻², with an overall average of 2391 g m⁻², compared to 470–2290 g m⁻² and 1065 g m⁻² in the Pang (∼166 km²) and 770–1760 g m⁻² and 1255 g m⁻² in the Lambourn (∼234 km²) sub‐catchments. Mean total fine sediment storage on the bed of the main channel was equivalent to 37% (upper Tern), 38% (Pang) and 21% (Lambourn) of the mean annual suspended sediment loads measured at the catchment outlets. Over the study period, the total gain (1427 t) and loss (1877 t) to fine sediment storage on the channel bed in the upper Tern catchment were equivalent to 82% and 108% of the mean annual suspended sediment load, respectively, compared to 149% (740 t) and 136% (678 t) in the Pang sub‐catchment, and 39% (422 t) and 49% (528 t) in the Lambourn sub‐catchment. The source of the fine sediment stored on the channel bed within each study area varied. In the upper Tern catchment, the weighted mean relative contributions from individual source types were estimated to be 35 ± 5% (pasture), 51 ± 5% (cultivated) and 14 ± 3% (channel banks and subsurface sources). The corresponding estimates were 49 ± 8%, 33 ± 5% and 18 ± 5% for the Pang sub‐catchment, compared to 19 ± 6%, 64 ± 5% and 17 ± 5% for the Lambourn sub‐catchment. These sediment source estimates have important implications for the design and implementation of targeted sediment control policies within the study areas. Copyright © 2007 John Wiley & Sons, Ltd.     

Composition of the seed bank in drawdown areas of Navigation Pool 8 of the Upper Mississippi River

In an effort to enhance aquatic plant production and habitat diversity on the Upper Mississippi River (UMR), resource managers considered water level reduction as a management tool to increase the area of emergent and submersed aquatic vegetation by natural seed germination. To quantify the availability of seed, we assessed the potential seed bank of selected areas of Navigation Pool 8 of the UMR from substrate samples collected in spring 2000. We tested these samples for viable seed content under four hydrologic conditions: dry, moist, shallow flooded and submerged. Forty‐seven species were identified in the seed bank, including 27 obligate wetland, 10 facultative wetland and 7 upland species. Dominant taxa within the seed bank included Sagittaria spp., Lindernia dubia, Zosterella dubia, Cyperus spp., Eragrostis spp. and Leersia oryzoides. Of the four hydrologic treatments, moist substrates had the greatest species diversity and were the most productive, yielding an average density of 1420 seedlings m^?2. Emergent and submersed aquatic species were widely distributed, each type occurring in more than 90% of the samples. Timing of seedling germination varied among species and has implications for scheduling drawdowns to promote establishment of desired species. Seed bank results were correlated with the vegetation response on substrates exposed during a reduction of water levels of Pool 8 during summer 2001. Experimentally determining the composition and viability of seed banks from drawdown areas provides information useful in predicting the types of vegetation that may develop on exposed substrates. Further, these findings provide resource managers a better understanding of the potential for achieving desired vegetation response through water level reductions. Published in 2008 by John Wiley & Sons, Ltd.     

Relative abundance of mosquitoes and snails associated with water hyacinth and hippo grass in the Nyanza gulf of Lake Victoria

This study was conducted from September to December 2008 to investigate the relative abundance of malaria vectors and schistosomiasis host snails associated with aquatic weeds in Nyanza Gulf (Lake Victoria). Larval and adult’s stages of mosquitoes, lakeflies and snails were collected and identified with standard entomological and malacological techniques. The relative species composition and abundance of fish associated with macrophytes were also determined. Physico‐chemical parameters were determined with standard analytical methods. Community‐based surveys were also conducted, using standard questionnaires, focused group discussions and direct observations. The results of this study indicated that the abundance of malaria‐causing mosquitoes was low, accounting for only 0.4% of the total number of mosquitoes and lake flies collected from the gulf. Lake flies (Chaoborus and Chironomus spp.) were the most abundant flying insects associated with aquatic macrophytes (84.2%), followed by Culicines Culex spp. (12.2%) and Aedes spp. mosquitoes (3.2%). Biomphalaria sudanica and Bulinus africanus, the two most common hosts for schistosomiasis in the gulf, were detected in both types of macrophytes, but were most significantly attached to water hyacinth (P < 0.0001) and hippo grass (P = 0.0003). There were significantly fewer snails attached to the hippo grass, compared with those unattached in the open water (P < 0.05, GENMOD). Different habitats exhibited low Secchi disc transparency values, but elevated total phosphorous (TP), total nitrogen (TN), chlorophyll‐a concentrations, as well as algal cell counts. Furthermore, Oreochromis niloticus and Haplochromine fishes were more abundant in water hyacinth mats compared with hippo grass mats and open‐water habitats. The low mosquito abundance indicated that the sampled habitats were unsuitable for mosquito breeding, likely attributable to water turbulence and/or predation by larvivorous fish. The strong association between B. sudanica and B. africanus and aquatic macrophytes, and the observation that local communities perform many lakeshore‐related activities that bring them into contact with water, can potentially lead to a higher prevalence of schistosomiasis in the Nyanza Gulf region.     

AN EVALUATION OF THE RELATIVE QUALITY OF DIKE POOLS FOR BENTHIC MACROINVERTEBRATES IN THE LOWER MISSOURI RIVER,USA

A habitat‐based aquatic macroinvertebrate study was initiated in the Lower Missouri River to evaluate relative quality and biological condition of dike pool habitats. Water‐quality and sediment‐quality parameters and macroinvertebrate assemblage structure were measured from depositional substrates at 18 sites. Sediment porewater was analysed for ammonia, sulphide, pH and oxidation–reduction potential. Whole sediments were analysed for particle‐size distribution, organic carbon and contaminants. Field water‐quality parameters were measured at subsurface and at the sediment–water interface. Pool area adjacent and downstream from each dike was estimated from aerial photography. Macroinvertebrate biotic condition scores were determined by integrating the following indicator response metrics: % of Ephemeroptera (mayflies), % of Oligochaeta worms, Shannon Diversity Index and total taxa richness. Regression models were developed for predicting macroinvertebrate scores based on individual water‐quality and sediment‐quality variables and a water/sediment‐quality score that integrated all variables. Macroinvertebrate scores generated significant determination coefficients with dike pool area (R² = 0.56), oxidation–reduction potential (R² = 0.81) and water/sediment‐quality score (R² = 0.71). Dissolved oxygen saturation, oxidation–reduction potential and total ammonia in sediment porewater were most important in explaining variation in macroinvertebrate scores. The best two‐variable regression models included dike pool size + the water/sediment‐quality score (R² = 0.84) and dike pool size + oxidation–reduction potential (R² = 0.93). Results indicate that dike pool size and chemistry of sediments and overlying water can be used to evaluate dike pool quality and identify environmental conditions necessary for optimizing diversity and productivity of important aquatic macroinvertebrates. A combination of these variables could be utilized for measuring the success of habitat enhancement activities currently being implemented in this system. Published in 2011 by John Wiley & Sons, Ltd.     

Nutrient concentrations in the surface sediments of Lake Chivero,Zimbabwe: A shallow,hypereutrophic, subtropical artificial lake

A lake‐wide survey in Lake Chivero, Zimbabwe, was performed to (i) examine the spatial distribution of three sediment grain sizes; (ii) determine their nutrient concentrations; and (iii) analyse the relationships between the measured surface sediment variables in the three sediment grain sizes. The results of this study indicated sand, silt and mud sediments occupied about 24, 22 and 54%, respectively, of the lake area. All the measured physicochemical variables varied significantly among the three sediment grain sizes (P < 0.05, anova ). High values for pH, dissolved oxygen and NO₃ were observed in the sand sediments, while water depth, electrical conductivity, soluble reactive phosphorus, NH₄, total phosphorus, total nitrogen and total organic carbon were observed in the mud sediments. In the silt sediments, most measured variables showed intermediate values. Intervariable correlation indicated varied correlation patterns among the three sediment grain sizes. Information generated in this study is essential for an accurate delineation of the spatial extent of nutrient and contaminant distribution in the sediment of Lake Chivero and will facilitate the ability of lake managers to derive a comprehensive nutrient budget of the lake as a means of establishing realistic target conditions for lake restoration.     

Biodiversity characteristics of small high-altitude tropical man-made reservoirs in the Eastern Rift Valley, Kenya

The biodiversity characteristics in eight small (0.065–0.249 km²) public man‐made reservoirs in the central part of the Eastern Rift Valley, Kenya, were studied between 1995 and 1998. A total of 71 phytoplankton species belonging to approximately 50 taxa were identified. Chlorophytes and cyanobacteria dominated the crop. The dominant taxa included Botryococcus, Syunura, Microsystis, Anabaena, and Cosmarium. A total of over 40 zooplankton species were identified. The community was composed mainly of crustacea, rotifers and protozoa. The most dominant group was Keratella but Brachionus and Nauplius were equally abundant. The diversity and abundance of benthic invertebrates was not high, and only 18 species were identified throughout the study period with the range of species number being 1–7 per reservoir. The benthic fauna was mainly composed of Lumbriculidae and Chironomid worms. A total of six monthly bird counts found an average of 60 birds per reservoir, and a total of 49 species was identified. Ducks, geese and coots dominated the waterfowl, especially during the dry season. Large‐scale breeding by Black‐headed Heron (Ardea melanocephala ) and Little Egret (Egretta garzetta ) was observed in one of the sites, and other species were also breeding in the reservoirs. The population of waterbirds in reservoirs was closely related to the biomass of benthic invertebrates, and the findings of the study indicate that the structure and dynamics of life forms within small man‐made reservoirs can serve as excellent sensors and indicators of the state of watershed health.     

Spatial and seasonal variations in phytoplankton community structure in alkaline–saline Lake Nakuru,Kenya

Spatial and seasonal variations of phytoplankton, expressed in terms of species composition, cell density, biovolumes and biomass, collected at 10 sampling sites in alkaline–saline Lake Nakuru, Kenya, were investigated monthly from March 2004 to February 2005, in relation to selected physical and chemical water quality parameters. A total of eight species, belonging to five genera and three classes, were recorded. The Cyanophyceae comprised the bulk of the phytoplankton, followed by Euglenophyceae, while Bacillariophyceae were the least abundant. Arthrospira fusiformis was the most dominant species, in terms of density, among the Cyanophyceae, while Euglena spp. and Navicula elkabs dominated the Euglenophyceae and Bacillariophyceae density, respectively. Seasonal variations in phytoplankton species composition, density and biomass were significant (P < 0.05) with minimum cell density and biomass occurring during the dry season, and being maximum following the end of the two rainy seasons from May to November 2004, suggesting the possible influence of various environmental factors on the lake. Sampling sites located close to the inlets of inflowing rivers exhibited significantly (P < 0.05) higher phytoplankton cell density and biomass than those by the inshore sites. Soluble reactive phosphorus, ammonia‐nitrogen, conductivity and total alkalinity accounted for most of the variations in the cell densities of phytoplankton species.     

Littoral zooplankton diversity in Himayat Sagar Reservoir,Telangana, India

The present study investigated zooplankton composition and diversity, along with physicochemical parameters from the littoral regions of Himayat Sagar Reservoir, Telangana, India. A total of 84 zooplankton species were found, including 60 rotifer species, 16 cladoceran species and eight copepod species. Keratella tropica, Lecane bulla, Coronatella rectangula and Mesocyclops sp. were observed frequently throught the study period. The Shannon Diversity Index ranged between H′ = 1.8 and 2.1, with a high diversity observed during the summer season. Dominance was greater during the monsoon and winter seasons, being represented by Brachionus calyciflorus, B. angularis, B. falcatus, Keratella tropica, Ceriodaphnia cornuta, Diaphanosoma sarsi and Mesocyclops sp. Correlation coefficients and principal component analysis indicated temperature, pH and nutrients had a major influence on zooplankton community changes in this reservoir. The environmental variables and diversity indices indicated seasonally fluctuating trophic conditions. Himayat Sagar Reservoir requires long‐term monitoring for assessment and better management of its faunal diversity and water quality.     

Spatial and temporal tree colonization in a midstream sediment bar and the mechanisms governing tree mortality during a flood event

Reduced disturbances in regulated rivers can result in stable tree colonisation in downstream reaches. We examined spatial and temporal tree colonisation on a midstream sediment bar, focussing on three dominant taxa: Salix spp. (primarily Salix gilgiana), Robinia pseudoacacia and Albizia julibrissin. We developed allometric relationships for tree height, tree age and tree diameter at breast and knee height, as well as relationships between above and below‐ground biomass. The spatial profiles for all individual trees of these taxa were obtained before and after a major flood in September 2007. Pre‐flood data indicate that R. pseudoacacia colonize the highest elevations, A. julibrissin lower elevations and Salix spp. the lowest elevations of the three taxa. The oldest trees at each elevation were found to have survived 1.8–2.5 m inundation in past floods. Results of investigations subsequent to the flood event in September 2007 suggest that trees can survive flooding as long as their roots remain embedded in the soil. Individuals of Salix spp. experienced higher levels of inundation, but showed the greatest survival. This is probably due to morphological acclimations, particularly deep root systems and high elasticity of shoots. Considering inundation depths, erosion depths and sediment particle sizes in tree habitats, we found that sediment mobilization was the major cause of tree mortality. Thus, the ability of Salix spp. to colonize coarse sediments greatly contributed to its survival, as coarse sediments result in significantly less tractive force. Copyright © 2009 John Wiley & Sons, Ltd.     

A new method to determine interstitial flow patterns in flume studies of sub‐aqueous gravel bedforms such as fish nests

Flume studies often seek to measure and record the interstitial flow within plane‐bed sediment bodies and within sediment beds with wavy surfaces, such as those typified by salmonid fish spawning nests and river‐dunes. A simple, inexpensive method is described to record and map, at discrete points, the spatial variation in interstitial flow speeds in experimental fine gravel beds. The procedure uses activated carbon granules to capture a tracer: Rhodamine WT dye. Calibration of the uptake of dye by the carbon for known interstitial flow speeds allows mapping of point flow speed data initially in the nominal x‐dimension. Using interpolation procedures available in a range of commercial ‘mapping’ software packages, the point data can be used to produce quasi two‐dimensional ‘slices’ along sampling planes within the three‐dimensional gravel bed. Similarly, three‐dimensional representations can be produced within which lines of equal current speed (‘isovels’) are interpolated such that the flow vectors (in x, y and z coordinates) may be inferred. Copyright © 2006 John Wiley & Sons, Ltd.     

淮北采煤塌陷区两个小型湖泊轮虫的群落结构特征

于2017年4月、7月、10月和2018年1月对淮北采煤塌陷区东湖和刘桥湖两个小型湖泊进行采样调查,探讨轮虫群落结构的季节变化及其与环境因子的关系。东湖共记录轮虫13科15属32种,刘桥湖共记录10科12属25种。东湖轮虫的年平均密度和生物量(2 722个/L和3.04 mg/L)明显高于刘桥湖(1 311个/L和1.30 mg/L);东湖主要优势种为刺盖异尾轮虫、暗小异尾轮虫、长肢多肢轮虫、长三肢轮虫、广布多肢轮虫和螺形龟甲轮虫,刘桥湖主要优势种为暗小异尾轮虫、长肢多肢轮虫、小链巨头轮虫、广布多肢轮虫、螺形龟甲轮虫和迈氏三肢轮虫;东湖和刘桥湖水体呈中度富营养状态;水温、总氮、总磷和叶绿素a质量浓度是影响两湖轮虫群落结构变化的重要因素,鲢、鳙鱼的捕食压力间接影响了两湖轮虫群落结构的变化。     

POPULATION DEMOGRAPHICS OF CATOSTOMIDS IN LARGE RIVER ECOSYSTEMS: EFFECTS OF DISCHARGE AND TEMPERATURE ON RECRUITMENT DYNAMICS AND GROWTH

Catostomids are among the most widespread and ecologically important groups of fishes in North America, particularly in large river systems. Despite their importance, little information is available on their population demographics and even less is known about factors influencing their population dynamics. The objectives of this study were to describe annual mortality, recruitment variation, and growth of eight catostomid species, and to evaluate the effects of discharge and temperature on year‐class strength and growth in Iowa rivers. Catostomids were sampled from 3‐km reaches in four nonwadable rivers during June–August 2009. Northern hogsucker, Hypentelium nigricans, golden redhorse, Moxostoma erythrurum, and shorthead redhorse, M. macrolepidotum, typically lived 6–8 years, had very stable recruitment, and had high total annual mortality (i.e., 40–60%). Golden redhorse exhibited the fastest growth of all species. Growth of northern hogsucker and shorthead redhorse was intermediate to the other catostomids. Highfin carpsucker, Carpiodes velifer, quillback, Carpiodes cyprinus, and white sucker, Catostomus commersonii, had high growth rates, low mortality (i.e., 25–30%), and relatively stable recruitment. River carpsucker, Carpiodes carpio, and silver redhorse, M. anisurum, had higher maximum ages (up to age 11), slower growth, lower total annual mortality (20–25%), and higher recruitment variability than the other species. Neither discharge nor temperature was strongly related to recruitment of catostomids. In contrast, several interesting patterns were observed with regard to growth. Species (e.g., carpsuckers, Carpiodes spp.) that typically consume prey items most common in fine substrates (e.g., chironomids) had higher growth rates in reaches dominated by sand and silt substrate. Species (e.g., northern hogsucker) that consume prey associated with large substrates (e.g., plecopterans) had much faster growth in reaches with a high proportion of rocky substrates. Temperature was weakly related to growth of catostomids; however, discharge explained a substantial amount of the variation in growth of nearly all species. Results of this study provide important information on the autecology of catostomids that can be used for comparison among species and systems. These data also suggest that connection of rivers with their floodplain is an important feature for catostomids in temperate river systems. Published in 2011 by John Wiley & Sons, Ltd.