Study on zooperiphyton and zoobenthos of a small river

The special traits of zooperiphyton and zoobenthos structures in a small river were studied. Under conditions of maximal proximity of niches, these groups of invertebrates retain taxonomic and ecological heterogeneity. Differences in zooperiphyton and zoobenthos taxonomic structures are most pronounced in terms of presence of dipterans, oligochetes, and mollusks. In the periphyton, the dominant groups are chironomid (orthocladines, chironomines, and tanitarsines) larvae, oligochetes of fam. Naididae and mollusks of fam. Limnaeidae. In the benthos chironomid (chironomines and tanirodines), oligochetes of fam. Tubificidae, and mollusks of fam. Pisidiidae are dominant. On average, the bottom invertebrates are considerably larger than fouling organisms. At similar abundance values, the biomass of benthos is by an order of magnitude higher compared to zooperiphyton. Ranging of average biomasses of zooperiphyton and zoobenthos revealed that the leader common for both communities is the large and mobile predatory leech, Erpobdella octoculata (Linnaeus). The anthropogenic impact and zoogenic (beavers) impact upon the river biota are comparable to each other.     

Spatial structure of zooperiphyton in a small river (West Siberia)

Basic quantitative characteristics of zooperiphyton from the Uk River are presented. Factors effecting the composition and structure of invertebrates have been found. The effect that the current velocity, water level, and different types of pollution have on zooperiphyton in the small river is shown. The pollution of the river reduces taxonomic diversity. The maximum effect is caused by the discharge of mineralized waters. In clean portions of the river, Trichoptera dominate in biomass; in polluted parts, their role decreases and the larvae of chironomids and leeches prevail in zooperiphyton.     

Peculiarities of the zooperiphyton succession in beaver ponds of a small river

The increase in the species diversity of the zooperiphyton and intensifying succession due to the increase of the abundance of chironomid larvae (stage I) was observed upstream along the small Latka River (a tributary of Rybinsk Reservoir) during the first year after the appearance of the beaver dam, when the depth increased and the flow velocity decreased. In the beaver pond, which was overgrown by yellow water-lily, the zoocenose succession depended greatly on the abundance of the vegetating and fading plants. During the vegetation period, at high abundance of the yellow water-lily, the species richness of the zoocenose decreased, and then it increased again the next year, when new vegetation was low, and the old plants were decomposing en masse. Directly downstream from one of the beaver dams, the mollusks affected negatively the seasonal succession of the zoocenoses under an instable water level and current regime, when they removed nearly all the fouling from the substrates.     

Changes in the zooperiphyton structure in a small river along the spatial gradient

A total of 165 taxa have been recorded in the zooperiphyton of the Sestra River, among which larvae of chironomids (40), nematodes (24), and oligochaetes (21) have the highest species richness. The increase in the taxonomic richness of zoocenoses from the river head to its mouth is weakly expressed. The highest diversity of zoocenoses is characteristic for the contact zones of the river water with its tributaries and receiving waters. The discreteness of spatial characteristic of the taxonomic composition of zooperiphyton reflects the heterogeneity and diversity of habitat conditions of invertebrates. In regards to its effect on zoocenoses, anthropogenic pollution can exceed the impact of many environmental factors (including the current velocities) which affect the formation of rheophilic communities in river ecosystems. The dominant complexes of zooperiphyton include all trophic groups of invertebrates, among which the group of detritophages-collectors has the highest taxonomic diversity. The group of phytodetritophages-filterers + collectors mainly includes chironomid larvae of the genus Chironomus, which are associated with strongly polluted zones. Invertebrate filterers, sponges, and bryozoans prevail mainly in zooperiphyton in the lower reaches of the river, which are not subjected to the pollution.     

Factors affecting river entry of adult Atlantic salmon in a small river

In this study, effects of stock origin, fish size, water flow and temperature on time of river ascent of adult Atlantic salmon Salmo salar were tested. Brood stocks were collected in eight Norwegian rivers situated between 59 and 69° N. The fish were reared to smolts, individually tagged and released in the River Imsa, south-west Norway (59° N). Adults from all stocks approached the Norwegian coast concurrently, but Atlantic salmon ≥70 cm in natural tip length entered coastal water slightly earlier during summer than smaller fish. Atlantic salmon <70 cm, however, ascended the river significantly earlier and at lower water flow and higher water temperature than larger fish. Although largest in size, the fish from the northern populations (62–69° N) ascended the River Imsa almost 1 month earlier than those from the south (59–60° N). They seemed less restricted by the environmental factors than the fish originating from the more southern rivers. There was no apparent trend among years in time of river ascent. Maximum ascent per day occurred at water discharges between 12·5 and 15 m³ s⁻¹ and at water temperatures between 10 and 12·5° C. There was a significant positive correlation between water flow and river ascent during the first part of the upstream run from July to September with best correlation for September, when multiple regression analysis indicated that water temperature had an additional positive effect. Stock origin, fish size and water discharge were important variables influencing the upstream migration of Atlantic salmon in small rivers.     

Transported material in a small river with multiple impoundments

SUMMARY.

• 1 The transport of particulate material in a multiply-impounded southern African river was studied from source to mouth over a period of 2 years during base flow conditions.
• 2 More than 95% of the dissolved and particulate material in transport was ultra fine (<80 μm). We conclude that too much emphasis has been placed on coarse material (>1 mm) in theories of river ecosystem functioning.
• 3 The ratio of CPOM:FPOM (1000–4000:250–1000 μm) in transport decreased with increasing stream order as a result of inputs of FPOM from pollution sources and from plankton blooms discharged from reservoirs.
• 4 The downstream effects of impoundment depended largely on the type of release and the quality of the inflowing water: surface-releasing reservoirs in the clean, upper reaches of the river had the least effect on transported material. A polluted surface-release impoundment in the mid-reaches of the river converted the particle size spectrum of the river from small (<80 μm) to large (250–1000 μm). Bottom-released water carried high concentrations (36–190 g m³) of small (<5 μm) and largely inorganic (86–93%) material.
• 5 The distance required for zooplankton densities to reduce by 95% was between 4 and 8 km downstream of an impoundment, except below a polluted impoundment where zooplankton densities took 32–35 km to reduce by 95%.
• 6 Most of the downstream changes in transported organic matter in the Buffalo River are due to inflows of agricultural and urban effluent. These disturbances to the river cause greater perturbations than do the impoundments.

     

Abiotic and biotic factors affecting zooperiphyton development in a waterflow of a cooling water pool

The study is concerned with invertebrates populating riffle stones in a cooling water pool. It was shown that the invertebrate community is dominated by Oligochaeta of the genus Naididae in abundance, and Plumatella emarginata bryozoans, in biomass. The study revealed the following: (1) in communities with biomass >100 g/m² abundance and biomass are affected by roughness and lightness of the substrate; (2) bryozoan biomass and Oligochaeta abundance correlate.     

Variability of photosynthesis-irradiance curves and ecosystem respiration in a small river

• 1 We investigated photosynthesis‐irradiance relationships (P‐I curves; P = oxygen production rate due to photosynthesis, I = light irradiance rate at the water surface) and ecosystem respiration in a 9 km long reach of a river that is characterised by light conditions favouring primary production, high ambient nutrient concentrations, a high re‐aeration rate, and frequent spates. We addressed the question of how disturbances (spates) and season influence photosynthesis and ecosystem respiration.
• 2 We used an oxygen mass‐balance model of the river to identify ecosystem respiration rates and the two parameters of a hyperbolic P‐I function (P_max = maximum oxygen production rate due to photosynthesis, α = the initial slope of the P‐I function). The model was fitted to dissolved oxygen concentrations quasi‐continuously recorded at the end of the reach. We estimated parameters for 137 three‐day periods (during the years 1992–97) and subsequently explored the potential influence of season and disturbances (spates) on P_max, α and ecosystem respiration using stepwise regression analysis.
• 3 Photosynthesis‐irradiance relationships and ecosystem respiration were subject to distinct seasonal variation. Only a minor portion of the variability of P‐I curves could be attributed to disturbance (spates), while ecosystem respiration did not correlate with disturbance related parameters. Regular seasonal variation in photosynthesis and ecosystem respiration apparently prevailed due to the absence of severe disturbances (a lack of significant bedload transport during high flow).

     

The distribution of invertebrate communities in a small South African river

Monthly samples of macroinvertebrates were collected from the stony-bed and marginal-vegetation habitats of a small river in the south western Cape Province, South Africa. Cluster analyses of the samples revealed assemblages of invertebrates (here referred to as communities) with clear spatial and temporal distribution patterns in the muer. The species composition of the communities, and their distribution, are described. The relation of the macroinvertebrate distribution to changes in the physico-chemical environment was investigated using stepwise multiple discriminant analysis. The results indicated a strong correlation between the two.     

Spatial heterogeneity of periphytic microbial communities in a small pesticide-polluted river

Spatial variability in the microbial community composition of river biofilms was investigated in a small river using two spatial scales: one monitored the upstream–downstream pesticide contamination gradient, referred to as the 'between-section variability', and the other monitored a 100-m longitudinal transect (eight sampling sites per section) within each sampling section, referred to as the 'within-section variability'. Periphyton samples were collected in spring and winter on artificial substrates placed in the main channel of the river. Denaturing gradient gel electrophoresis (DGGE) was used to assess the prokaryotic and eukaryotic community richness and diversity, and HPLC pigment analysis to assess the global taxonomic composition of the photoautotrophic community. In order to try to reduce the biological variability due to differences in flow velocity and in light conditions within each sampling section, and consequently to take into account only the changes due to water chemistry, nine plates (three per sampling section) subjected to similar physical conditions were chosen, and the results for these plates were compared with those obtained for all 24 plates. As shown by DGGE and by HPLC analyses, using these three substrate plates exposed to similar environmental conditions did indeed reduce the within-section variability and maximize the between-section variability. This sampling strategy also improved the evaluation of the impact of pollutants on the periphytic communities, measured using short-term sensitivity testing.     

Successions of sheathing mycorrhizal fungi

Many fungi capable of forming sheathing (ecto-) mycorrhizas are associated with trees. But what are the rules governing their occurrence? Evidence from first generation woodlands/forests, where trees grow on sites that have been treeless for many years, indicates that species of fungi occurring at early stages of woodland development ('early-stage fungi') are, in due course, superseded by others ('late-stage fungi'). There is an ordered succession which seems to reflect, in large measure, the different abilities of early- and late-stage fungi to form mycorrhizas on roots growing in soils with accumulations of recalcitrant leaf litter. In second generation woodlands/forests there seems to be little evidence of early-stage fungi. This is not so surprising as it may seem, bearing in mind that their soils are already likely to have accumulations of recalcitrant litter. Instead of classifying sheathing mycorrhizal fungi by referring to the temporal stage of woodland development, it now seems more meaningful to judge them by their abilities to colonize roots in soils with or without accumulations of different types of litter.     

Structure of hydrophilic vegetation of a small river in an urban environment

The hydrophilic vegetation of the small Korovka River has been characterized in the urban and suburban zones of the city of Rybinsk (Yaroslavl oblast). The structure and state of the vegetation within the urban territory depends mainly on the anthropogenic load and hydrological factors. The main phytocoenoses of urban and suburban zones are hydrophilic and helophilic complexes, respectively. The level of overgrowth of these zones varies within the range of 30–70% and 5–20%, respectively. The following overgrowth patterns dominate in the urban zone: mosaic thicket, border, and underwater meadow. In the case of the suburban zone, the border and thicket patterns dominate.     

Comparison of zoobenthos and zooperiphyton of large and medium rivers

The results of a study of zoobenthos and zooperiphyton of two rivers of the Ob’ River middle reaches are shown. A comparative analysis of the composition and abundance values of two ecological groups of zoobenthos and zooperiphyton hydrobionts has revealed the difference in their taxonomic compositions and dominant complexes. The similarity in total number and biomass of zoobenthos and zooperiphyton in the large river and the higher values of zooperiphyton quantitative development in a medium river have been identified.     

Spatial structure of zooperiphyton from the Ob River

Data on the qualitative and quantitative composition of zooperiphyton in the middle and lower reaches of the Ob River are reported, revealing the basic factors affecting its growth. Along most of the river, the zooperiphyton forms a continuum, which is disturbed at sites exposed to pollution. It is found that communities dominated by caddisworms prevail over most of the river; a decrease in the river stream velocity causes a change in the communities, with the replacement of Trichoptera by gastropod communities.     

Successions in the forest-steppe under climate changes: a modelling approach

The paper represents an attempt to apply the general principles of modelling vegetation dynamics under climate changes to a study of the long-term vegetation dynamics in the forest-steppe zone of the European territory of Russia, with a purpose to forecast under special climatic scenarios. An original technique is used to construct a Markov chain as a model of vegetation succession. The technique emanated from gebotanic knowledge generalized as a scheme of successional transitions with estimates of the average duration for certain stages of succession. Whenever the knowledge related the stage duration to certain (climate-sensitive) factors of the environment, the fundamental potentiality arises to model the temporal course of succession as a function of a given scenario for how the key factors change. In the formal terms, the model represents a random chain of the Markov kind with a finite number of states and discrete time of transitions by the given scheme. Relative square distributions of succession stages under concern at any time moment (within an adopted scenario) appear as the model outcome (forecasts), as well as estimates of the attainment time for certain states of the vegetation in the territory under study. A method is proposed to describe dynamics of the phytomass production and stores (and the corresponding model trajectories are obtained) for a given scenario.     

Reproductive migration of brown trout in a small Norwegian river studied by telemetry

The movement of 34 large (39–73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m³ s⁻¹) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m³ s⁻¹) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low ( c . 6° C), but not at high ( c . 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2–51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day⁻¹, respectively. All tagged brown trout that survived spawning returned to the lake after spawning.     

Spatial microhabitat selection by Biomphalaria pfeifferi in a small perennial river in Tanzania

A study was carried out in the Mlali river in south-central Tanzania with two aims. First, to determine microhabitat availability in two sites (A and B) with respect to water depth, water velocity and dominant substratum type. Second, to assess microhabitat use by Biomphalaria pfeifferi, the intermediate host snail of intestinal schistosomiasis and to investigate whether these snails show preferences for certain microhabitats. The two sites differed significantly with respect to width, water depth, water velocity and substratum composition. It is suggested that the absence of B. pfeifferi from site B is mainly associated with the high water velocities at that site, where 62% of the measurements exceeded30 cm s^-1. In site A, the microhabitat use by 327 B. pfeifferi snails was assessed by means of direct observation. No significant relationships were found between snail size and the habitat variables investigated, indicating that snail size appeared to be of no importance in spatial microhabitat selection. B. pfeifferi snails showed statistically significant preferences for shallow water (depth: 2–7 cm) and the preferred water velocities ranged between 12 and 21 cm s^-1 with an estimated optimum at13.3 cm s^-1. No statistically significant preferences for substratum type were found. This revised version was published online in August 2006 with corrections to the Cover Date.     

山西植被空间格局及演替简

在ArcGIS软件中采集1984年和2005年山西植被类型的图形,得到山西群系、森林、灌丛、草本植被及栽培植被的图形及面积,用叠置分析和景观格局分析方法研究植被的空间分布及其演替、空间格局及其变化。森林在西南部相对集中分布,在西北角增加明显,它在山西植被中所占面积及比重都最小,最为破碎。油松林在山西森林中占优势,恢复森林主要是油松林、小叶杨林、辽东栎林。1984年灌丛的面积在植被中最大,所占比例也最高,超过50%,集中连片分布面积较大,但灌丛缩减迅速,主要在中南部,在山西植被中遭破坏最为严重。沙棘、虎榛子灌丛和黄栌、连翘灌丛对灌丛的影响最大。草本植被主要在北部减少,在中南部分散增加,更加破碎。白羊草草丛在山西草本植被中占优势,蒿、禾草草原和百里香、禾草草原变化最大。栽培植被明显增加,在植被中所占比重急剧增加,成为山西优势植被。森林、栽培植被分别增加24.3%、71.5%,而灌丛、草本植被却分别减少70.3%,15.6%,演替主要是人为因素造成的。     

The distribution of zoobenthic organisms as the water level decreases in a small river

The influence of water level changes on the distribution of aquatic organisms in the channel of a small river was studied. A decrease in the water level leads to the migration of animals to deeper habitats. A further decrease in the water level results in the concentration of benthic organisms in other streams. Aquatic organisms able to survive for a long time were found on the wet bottom sediments at dried parts of the river channel.