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The fish fauna of the stony littoral in the central parts of L. Päijänne was studied by electric fishing on four occasions during 1988–1989. Ten fish species and 1681 individuals (14.5 kg) were caught in the 15 fishing sites (4096 m2) which gives a mean density of 0.41 ind. m-2 and biomass of 3.5 gm-2. Effluent from two large paper mills causes a clear zonation of the fish fauna in the area. In the most polluted shores, only burbot and perch occurred regularly and the reproduction of other species was inhibited. In the semipolluted area (5–15 km from the Kaipola paper mill), burbot and stone loach occurred regularly, but owing to low numbers of perch and bullhead the total densities were usually low.

Lake Päijänne, the second largest lake in Finland, has been seriously polluted since the 1960s due to the effluents from pulp and paper mills, notably the Äänekoski sulphate and sulphite pulp mills situated about 50 km north of the lake, and the sulphite pulp mill and paper mills of Jämsänkoski and Kaipola on Central Lake Päijänne.

The annual reproductive success of Coregonus albula and C. lavaretus in some polluted and clean areas of the central parts of L. Päijänne was estimated in 1981–90 on the basis of occurrence of larvae in shore seine and seine net samples after the ice melted. In polluted areas (0–5 km from Kaipola paper mill) larvae of coregonids were found only occasionally. In semipolluted areas (5–15 km from the paper mill) the densities of larvae were usually less than 0.1 ind m-2. In ‘clean’ areas the mean densities of larvae ranged from 0.45 to 5.34 inds m-2. A relatively high reproductive success of vendace was observed in 1984–85, moderate success in 1982–83 and low success in 1986–90. The larvae of whitefish were scarce in both polluted and semipolluted areas and their density ranged from 0.01 to 0.15 ind m-2 in clean shores. The highest density was observed in 1989. In spite of the improvement of the quality of water in the area in the 1980s, the reproductive success of coregonids is still low in a great part of the basin which may depend on adverse oxygen conditions of the hypolimnion and sediment and the toxic effects of the effluents.

Bottom fauna surveys of the Lower Sabine River in the vicinity of Orange, Texas were performed from 1967 to 1969. During this time samples were taken before and after effluent from a black-liquor paper mill was discharge into the Sabine River. Species diversity indices were determined for each station (one station above the discharge canal and four below it). The results obtained indicated that the paper mill effluent was not disturbing the river to a degree that it would cause damage. However, the proximity of Sabine Lake (an estuary) and the very low flow often encountered on the Sabine River makes it imperative that high standards be imposed in treatment of the waste water and that qualified personnel make periodic studies on the river.

The effects of a paper mill effluent on the macroinvertebrate community were assessed for the riffle areas of a large fast-flowing stream, the lower reaches of the Saranac River of northern New York State, U.S.A. The effluent caused few changes in dissolved oxygen concentration, pH, biochemical oxygen demand, temperature or nutrient content; however, significant differences in transmitted light, concentrations of particulates and accumulated debris on the substrate were observed. A moderate decrease in invertebrate diversity correlated with increased levels of particulates and substrate debris. An analysis of the response of invertebrate functional groups revealed the effluent had little effect on the density of gathering collector organisms. The functional groups most severely reduced in density were the filtering collectors and scrapers. Predators showed a moderate reduction in density in response to the effluent. The alterations in invertebrate densities were attributed largely to the alterations in seston and substrate caused by the introduction of particulates composed mainly of paper fiber and inert dye.

Four riverine animal communities were measured to assess the impact of extensively treated wastewater from a pulp and paper mill on the lower La Trobe River in Victoria, Australia. Benthic macroinvertebrates in channel and bankside habitats were sampled using a new air-lift corer. Population density was expressed in relation to substrate volume. Other communities measured at five sites upstream and downstream of the mill's wastewater outfall were the zooplankton, and the animals associated with submerged littoral vegetation. Ten environmental variables were also measured during the two sampling periods.

Eradication of aquatic weeds has been found to involve huge expenditure and is seldom practised. The present paper describes the use of dried Salvinia material in the manufacture of paper. The sheets have been checked for burst, breaking length, folding capacity, etc. Sheets prepared by a mixture of dried Salvinia and rice straw can be used safely as packing material in addition to several other uses.

Abstract: There have been almost a hundred years of continuous scientific activities at The Hydrobiological Station ‘Glubokoe Ozero’. The present volume of ‘Hydrobiologia’ contains summary papers reviewing previous and recent results of the studies on the hydrochemistry, zooplankton, zoobenthos, littoral fauna, food composition of fish, and historical biocenology (based on animal remains in bottom sediments), as well as on particular animal groups, such as Cladocera with special consideration of Daphnia, rotifers, fish, and parasitofauna. The present introductory paper provides data on the general characteristics of Lake Glubokoe, the history of its investigations and the station's modern programme which is aimed at biocenology with special consideration for morphological and physiological adaptations. Research both on general and on peculiar features of Lake Glubokoe is envisaged.

This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.

This paper presents a background description of the basin and an overview of the physical, chemical and biological limnology of Georgian Bay and the North Channel. Further, it describes the expansion of European settlement and the association of cultural impacts with urbanization, industry and transportation. The history of the fishery is briefly outlined, and changes in the structure of fish communities are related to fishing pressures and the introduction of exotics. In the concluding sections of the paper, we discuss present and future concerns which may be related to water quality and water quantity issues and, also, to the stability of re-establishing fish communities.

The first part of the paper discusses the significance of using either concentration or accumulation values for expressing the results of investigations of lake sediment cores aimed at studying the history of heavy metal pollution. Neither the values for heavy metal concentration in the lake sediment, whether expressed per gram dry sediment or per gram soluble (organic) sediment, nor the values for their total annual accumulation per unit area of the lake bottom, can, on their own, provide an accurate picture of past pollution conditions, but when considered in combination they render a fairly reliable and detailed interpretation. The second part of the paper deals with Pb, Cd and Hg analyses of cores of varved sediments from several lakes in N. Sweden. Pb and Cd pollution increased during the second half of the 19th century. In most lakes, Hg pollution seems first to have started during the 20th century. Marked increases in both concentration and accumulation of heavy metals took place during the 20th century. For recent decades, the estimated accumulation rates of heavy metals from anthropogenic sources are: Pb 0.5–1.5 µg cm-2 yr-1, Cd 15–30 ng cm-2 yr-1 and Hg 1–2 ng cm-2 yr-1, Higher values were recorded in lakes affected by local emissions.

Eighty nine fresh-water algae of various groups are described in this paper. This paper is one of the series of publications representing the studies on a series of small freshwater pools near St. John's, Newfoundland.

As a result of some field observations and laboratory experiments, a number of authors (see text) have suggested that insects living in rivers, even slightly heated by power station cooling water, may have their life-cycles altered sufficiently to lead to the elimination of species owing to early emergence into a lethally cold air, shorter emergence periods, disrupted mating behaviour, or the elimination of necessary “chill-periods” in winter. If this were so, an important food resource for fishes in some rivers might be lost. Part I of this paper (Langford and Daffern — in press) described the results of an emergence-trapping programme on the River Severn around the cooling water outfalls of Ironbridge “A” and “B” Power Stations. This paper describes in detail the emergence pattern and periods of eight species of Ephemeroptera, seven species of Trichoptera and one species of Megaloptera, upstream and downstream of the outfalls during the period July 1969–November 1971. The patterns are analysed in relation to river flows and water temperature. Although t7emperature increases reached 8°C, maximum water temperatures reached 28°C, total degree-hours were up to 24% more during spring, and there was a four-week advance in degree-hour accumulation; there was no evidence of a pattern of early emergence downstream. Emergence of most species occurred over a temperature range of 12°C to 28°C and there was no evidence of the high temperatures in 1970 halting emergence or shortening the emergence period. Captures of all species of Ephemeroptera were obviously influenced by spates, i.e. increased river levels and flows. Evidence suggests that emergence may be suppressed under such conditions. Catches of most Trichoptera species were not as markedly influenced by river flows. Implications are that future flow changes in the middle reaches of the Severn as a result of water transfers could affect emergence patterns of Ephemeroptera. There is no positive indication that temperature changes caused by the cooling-water discharge had any influence on onset or progress of emergence of either Ephemeroptera or Trichoptera. It is suggested that where early emergence has been induced experimentally in the laboratory, constant high temperatures, stable flow conditions and food have been provided. In a natural river system, it is unlikely all these conditions would be maintained consistently enough for lethally early emergence to occur. It is concluded, therefore, that before predictions about the effects of power station cooling water discharges on the emergent insects of rivers are made, based on extrapolation of laboratory data, it is essential that the relevant field conditions and relationships should be considered. Also the natural variability and adaptability of species should be investigated in more detail.

Although rather extensive bibliographies give the impression that there is a vast amount of literature on the effects of temperature on aquatic organisms, when one tries to apply this information to specific interactions, such as the effects of temperature changes on chemical toxicity to aquatic organisms, often very little of the evidence is applicable. Although the most useful information on this relationship has been acquired in laboratory situations even this body of literature (which forms the bulk of this paper) is not adequate to make any scientifically justifiable generalizations. Field data on this relationship is almost non-existent and it is unlikely that much will become available unless specific studies are initiated which are directed toward this end. This is equally true of the laboratory information although it seems more likely that this will be generated as a spinoff from other research activities. In order to develop water quality management programs for steam-electric power plants one should understand the relationship between temperature and the response of aquatic organisms to toxic chemicals. Not only do some power plants discharge chlorine and other similar materials as well as heated waste water but those that discharge the latter only may be located near discharges of toxic chemicals. Since temperature and chemical stress to aquatic organisms are most commonly discussed independently we felt a paper covering this relationship would be useful.

Abstract: Human activities generate many pollutants from different land uses. These pollutants include nutrients (e.g., phosphorus and nitrogen), toxic substances (e.g., heavy metals and pesticides), and other substances (e.g., chlorides and salts). These materials often enter a river at some upstream point and are transported downstream by the flowing water. Many substances are transported both during storms and during normal river flow and often the major portion of the transport occurs during the storms. This paper considers the quantification of transport primarily during storms. First, the characteristics of storm transport are discussed. Then, a calculation method for estimating the distance of travel for sediment related materials is presented. Third, a technique to estimate the amount of a given chemical passing a point in a stream over a specified period of time is presented. The last part of this paper contains a technique for tracing the movement of substances through a river network. In particular, this procedure yields information as to the source of given pollutants over the entire Storm period.

The assessment of the hazard associated with the introduction of chemical substances into the environment is receiving considerable attention in current ecological, political, and public forums. The purpose of this paper is to identify and evaluate the basic concepts involved in assessing the hazard of chemical substances to aquatic life. A conceptual framework for conducting a hazard assessment is elaborated. In addition, several proposed procedures for conducting aquatic hazard assessment are compared and contrasted. A discussion of the decision criteria currently utilized in hazard assessment procedures is included. The use of safety factors or ‘uncertainty factors’ as a central concept in a sequential testing approach is presented. An assessment of the ‘state-of-the-art’ in aquatic hazard assessment and recommendations for suceeding stpes in the development of procedures constitute the conclusion of the paper.

The review of the present status of limnological studies in India is based on Indian publications in Hydrobiologia since the inception of the Journal. About 325 Indian papers have appeared up to 1979; nearly two-third appeared in the last one decade. Ponds occupy first place among the freshwater bodies studied. There are only a few papers on the rivers and streams. The emphasis of studies on flora is generally on taxonomical and morphological aspects. Among the studies on fauna, several relate to different aspects of Crustacea, and taxonomy of rotifers. Fish studies published in Hydrobiologia do not reflect the trends of progress in India. Work on production, energy flow and functioning of ecosystems is limited. About thirty papers relate to estuarine and marine environments. Suggestions for future work are made in the light of present studies and the gaps.

During a programme of research on the fauna of the River Severn around Ironbridge Power Station, the emergence patterns of resident insect species were studied upstream and downstream of the cooling-water outfalls. This paper describes the traps used to catch emerging adult insects and relates their overall performance, total catches and species selectivity, to the physical characteristics of the river. Upstream temperatures during 1970 and 1971 reached maxima of 22°C and 20.6°C respectively, while downstream maxima were 27.8°C and 23.4°C. The main cause of elevated temperatures downstream was cooling-water from Ironbridge “A” Power Station. Analysis of trap catches showed that the total numbers of Ephemoptera species and of individuals were greater in certain types of trap but that catches of Trichoptera were less related to trap type. The total emergence period varied during 1969, 1970 and 1971 irrespective of the elevated temperatures and both Ephemeroptera and Trichoptera continued to emerge during and after water temperatures as high as 26–27.8°C and as low as 11°C, in June. There was some relationship between emergence rates, river level (flow) and temperatures, but evidence suggests that river level was the most significant factor. The general conclusion from this paper is that the temperature increases in the Severn, caused by normal operations at Ironbridge “A” and by sporadic operations at Ironbridge “B”, did not have a significant effect on the total numbers and overall emergence period of Trichoptera, Ephemeroptera and Megaloptera downstream of the outfalls. Also the species-composition of trap catches was very similar both upstream and downstream of the power stations. The emergence periods of individual species are described in a second paper.

The aim of this paper is to provide detailed information concerning the hardware and software needed to design and construct a system for the continuous growth of algae, employing a computer-controlled variable dynamic light regime. The light intensity is controlled by adjusting the angular displacement of slats of a Venetian blind with the help of a stepper motor. The software developed allows the simulation of nature-related light flux regimes occurring in stratified water columns, mixed water columns with optically clear water, and mixed water columns with optically dense water. The light period, circulation time and attenuation coefficient can be chosen freely. Different light regimes with equal total light doses can be generated with the help of mathematical equations developed for this purpose. The software developed is of the Terminate and Stay Resident (TSR) type and operates in the background, thus allowing the computer to be used for other tasks. The system can be used to investigate algal growth and photosynthesis in relation to a dynamic light regime. The characteristics of the light regimes applied during the Vth GAP workshop are presented. The results of these experiments will be described in subsequent papers.

a.This paper presents an account of (i) fecundity studies intoT. mossambicaunder Middle Central American conditions and (ii) limnological investigations into Lake Moyua/Nicaragua which have been performed during 1961/62.b.Data obtained as to fecundity ofT. mossambicaare discussed in the light of the term prolificy and with regard to ecological and biological characteristics of Nicaraguan waters and native fish fauna.c.A more detailed contemplation about the possible effects of a spread out or transplantation ofT. mossambicainto other Nicaraguan water concludes the paper.

Some effects of current at velocities of 9 and 38 cm/sec on periphyton communities have been determined in laboratory streams. The diatom community that developed in the faster current formed a dense, felt-like growth on the gravel and rubble substrate and usually appeared dark green or brownish in color. At the slower current velocity, the community was dominated by species of Stigeoclonium, Oedogonium, and Tribonemawhich formed long, loose oscillating filaments on the substrate and resembled the aggregations of green filamentous algae often observed in ponds. Although the accumulation of biomass on the gravel and rubble was much more rapid in fast current than slow current, by the end of the experiment, the organic matter per unit area of substrate was approximately the same at both velocities. The export of biomass was consistently greater from the community subjected to the faster current, and at a near steady-state or constant standing crop, the highest productivity was maintained at the faster velocity. Dr. HarryK. Phinneyhas provided helpful advice during this work. The author is also indebted to Dr. CharlesE. Warrenand Dr. PeterDoudorofffor their invaluable administrative assistance. This paper is a contribution of the Pacific Cooperative Water Pollution and Fisheries Research Laboratories, Oregon State University, and U. S. Public Health Service Cooperating. This investigation was supported in part by National Science Foundation Research Grant GB 467. Technical Paper 1918, Oregon Agricultural Experiment Station. Effekte von Strömungsgeschwindigkeiten von 9 and 38 cm/Sek auf Aufwuchsgesellschaften wurden unter Laboratoriumsbedingungen untersucht. Die Diatomeengesellschaft, die sich in der schnelleren Strömung entwickelte, zeigte dichten filzartigen Wuchs auf dem Kies- und Geröllsubstrat und war gewöhnlich dunkelgrün oder braun gefärbt. Die langsamere Strömungsgesch windigkeit führte ein Vorherrschen von Stigeoclonium, Oedogoniumund TribonemaArten herbei, die lange und lockere, oszillierende Filamente auf dem Substrat bildeten, welche den Ansammlungen von grünen Fadenalgen ähnelten, die man häufig in Teichen beobachtet. Die Mengen organischer Substanz pro Einheitsfläche des Substrates waren nahezu gleich am Ende des Experiments für beide Strömungsgeschwindigkeiten, obwohl die Ansammlung von Biomasse auf Kies and Geröll viel rascher in der schnellen als in der langsamen Strömung vor sich ging. Der Abtransport von Biomasse war durchwegs grösser in der schnelleren Strömung und hier wurde nach Erreichen des Gleichgewichtzustandes oder stetigen Ertragzustandes auch die höchste Produktivität verzeichnet.

This is the third of a series of papers covering the anatomy, morphology, systematics and ecology of the crustose corallines of the Gulf of Maine. Pseudolithophyllum orbiculatum, the only species of this genus in the region, is treated in this paper.

The paper describes a polluted pond from India, which exhibited a well marked thermal stratification in summer. The surface and bottom strata of water exhibited a temperature difference of 8° C. The paper also describes the diurnal movement of Eudorina elegansand Trinema linearewhich formed a bloom in the pond. The movements of these organisms are interpreted on the basis of fluctuations in temperature and light conditions. The possibility of the competition for space is also discussed. On a décrit un cas de stratification thermale bien marquée dans un étang pollué en dépit de peu de profondeur de son bassin, dans un été en Inde. Les couches superficielles et de fond de l'eau ont montré une différence de temperature de 8° C. On décrit également le mouvement diurnal d'Eudorina eleganset Trinema linearequi ont formé une floraison dans l'étang. Le déplacement de ces organismes est interprété en fonction du changement de temperature et de la luminosité. La possibilité d'une concurrence pour l'espace est discutée.

A simplified technique to trap respired carbon dioxide in a closed bottle system was developed from the technique introduced by Hobbie & Crawford in 1969. In this technique carbon dioxide was trapped in ethanolamine in a glass cup without the use of chromatographic paper. The results show that there is no need to enlarge the absorption surface with filter paper as practically complete recovery was achieved with ethanolamine alone in the cup.

This paper reports a study of fluctuations of salinity, permanence and macrophyte occurrence in a wide range of saline wetlands between 1978 and 1982.

Abstract: In Lake Glubokoe (Moscow region) five species of Daphnia have been found: D. cristata, D. cucullata, D. curvirostris, D. galeata, and D. hyalina. This paper presents descriptions of the morphology of various populations of these species, and new data on their geographical distribution, and discusses the taxonomic status of certain species. Arguments are given in favour of the assertion that D. thorata and D. balchashensis are synonyms of D. galeata. It is shown that there are no grounds for the discrimination of the subspecies D. galeata galeata and D. galeata mendotae.

Abstract: This paper briefly describes the activities of zoology professor N. Yu Zograf. He founded the Hydrobiological Station on Lake Glubokoe, participated in the organization of the Polytechnical Museum in Moscow and wrote one of the first text-books on zoology in Russia.

Abstract: This paper presents the results of studies on the benthos of Lake Glubokoe in 1980 as compared to data for 1949 and 1950. The abundance of chironomids increased at medium depths, that of oligochaetes became higher along the entire depth and that of Chaoborus remained the same. The community of Sergentia was replaced by that of Chironomus.

Abstract: This paper describes under-ice observations on the diurnal dynamics of the distribution and behaviour of roach in Lake Glubokoe in March, 1983, and in March, 1984. It presents data on the reactions of fish to external stimuli. Some factors influencing the distribution of fish in the winter period are discussed.

Abstract: This paper briefly reviews systematic, production and biocenotic studies on invertebrates of the littoral zone of Lake Glubokoe. It presents new data for a number of years on the spatial distribution and population dynamics of species (mainly cladocerans) constituting a zoocenosis confined to the lower surface of floating leaves of Nuphar luteum.

This paper reviews the results of experimental manipulations, carried out during the period 1977–1983, on the phytoplankton maintained in the limnetic enclosures at Blelham Tarn, English Lake District. Three categories of manipulations are considered.

Responses to hydrologic change are an important theme in lotic ecology, and data for Australian rivers are accumulating in a rapid, butad hoc manner. Thia paper arranges recent contributions according to the major drainage divisions, which provide reasonably coherent environmental units. The east coastal rivers are exploited for storage, power generation and waste disposal, and Tasmanian rivers are regulated to serve hydro-electric power schemes. Most information refers to the Murray-Darling river system, which supplies irrigated agriculture in semi-arid inland areas of S.E. Australia, and is intensively regulated by dams, weirs and barrages. The Murray's flows are over-committed, if variability is taken into account, and there are environmental problems (e.g. erosion and salinity) associated with irrigation. The effects of regulation are seen also in the changed distributions of plants and animals associated with the Murray and its floodplain. In Australia the national effort is uncoordinated because research and management are developing independently of one another. Ecologists must become involved in the planning and implementation of strategies that are consistent, as far as possible, with offstream and instream needs.

The present paper deals with the nematode species collected from a small deep fresh-water pool on a coral island in the Solomon Islands. 50% of the specimens recorded belong to terrestrial forms (4 species), 45% were marine forms (6 species) and only 5% belonged to fresh-water (4 species). Three species are described as new to science.

The paper attempts to combine the low oxygen content of the hypolimnion during stratification and the oxygen uptake of zoobenthos. Data of declining oxygen content in the hypolimnion and critical limits of respiration are combined for Chironomus anthracinus, Potamothrix hammoniensis and three species of Pisidium, P. casertanum, P. subtruncatum and P. henslowanum. The respiratory adaptation to low oxygen content influences both growth and population dynamics of the different species. The results have important bearing on eutrophication of the Lake Esrom ecosystem and temperate eutrophic lakes in general as well as the composition of profundal zoobenthos and its population dynamics.

This paper aims to describe the ecology and determine the distribution of Oligochaeta according to sediment type, depth and other environmental factors in 21 lakes of the National Park of the Lithuanian SSR. Diagrams are included showing the distribution of the lakes according to the index of density and biomass of Oligochaeta in the trophic structure of biocenosis of the zoobenthos. Light is thrown on the problem of sediment composition as a significant factor in the distribution and development of aquatic Oligochaeta.

This paper reports the findings of one section of a freshwater synoptic survey in the Tayside Region of Scotland and deals with the distribution and abundance of the crustacean zooplankton and other microfauna of 25 standing waters of small to medium size and 24 small running waters. The objectives were to assess the possible effects of land-use, especially afforestation, and of catchment area sub-surface geology, on such fauna. Various methods, statistical and non-statistical, have been used to assess the influence of these parameters on the presence, absence and relative abundance of the dominant taxonomic groups. The main findings indicate that the nature of the water-body is of prime importance in determining the abundance and composition of the fauna and little effect can be associated with land-use or sub-surface geology.

This paper describes the use of a continuous-flow chamber for maintaining small and fragile fish larvae and their prey in a healthy state and under suitable conditions over a 24 h period for studies on prey preferences. Survival of golden perch (Macquaria ambigua Richardson) larvae and prey was high and ten replicates on food preferences were carried out simultaneously. The larvae preferred small Daphnia carinata King (780–860 µm) over larger ones (2000–3120 and 3680–5440 µm) and preferred cladocerans (Daphnia carinata King and Moina micrura Kurz) over calanoids (Boeckella de Guerne & Richard). The chamber is also suitable for studies on feeding behaviour and diet requirements of fish larvae.

Abstract: This paper examines seasonal changes in the density and taxonomic composition of the zooplankton of a small tropical impoundment, in relation to factors of water temperature, food supply and reservoir flushing. The response of the zooplankton to management techniques designed to regulate the density of cyanobacteria in the dam are also considered. Cyclopoid copepods were the dominant zooplankters, although Cladocera became much more significant following the introduction of measures to control cyanobacteria. Planktonic Rotifera were a diverse but generally unimportant fraction of the total biomass, except following seasonal or management induced environmental perturbations, when the Rotifera often recovered most rapidly.

This paper describes the breeding biology of the Louisiana red swamp crayfish (Procambarus clarkii Girard) that has been introduced in a tropical lake, Naivasha. Notable differences in crayfish biology are found between the place of origin in Louisiana and lake Naivasha.

Nutrient and carbon budgets of the western part of the Dutch Wadden Sea are based on the concept formulated by Postma (1954): import of organic compounds from the North Sea, mineralization in the estuary ans subsequently an export of dissolved inorganic nutrients to the North Sea. In this paper the phosphorus budget of the westernmost part of the Wadden Sea (Marsdiep basin) during the period 1950–1985 is considered to evaluate this concept and to investigate whether eutrophication processes have changed these P-budgets during the last decades. Most attention is paid to the importance of the exchange of P-components between the tidal basin and the open sea. The budgets are based on a general mass balance equation in which the main entries are the loadings via the freshwater sources, the net sediment-water exchange, the exchange with the North Sea, the input from the adjacent Vlie basin, and a transformation term representing the interchange between dissolved and particulate phosphorus. Averaged over the entire period 55% of the phosphate input (SRP) to the basin is delivered by the fresh water sources, and 45% by the Vlie basin. For non-SRP components these numbers are 50% and 40% respectively, while only 10% comes from the North Sea. The import from the North Sea, as calculated by our model thus seems less important than previously documented. There is a clear effect of the eutrophication during the last decades. In the first 20 years of the period investigated there was a moderate increase in the TP input to the basin, partly caused by an increasing input of non-SRP (TP minus soluble reactive phosphorus) from the North Sea. In 1970/71 almost 30% of the non-SRP loading originated from the North Sea. From approximately 1975 onwards this import of non-SRP turns into an export, while the TP-loading from the other sources inclined, until a maximum was reached in 1981. Recently a decrease in the TP-inputs has been observed. It is concluded that the recent output of phosphorus from the Marsdiep basin may have a considerable impact on the adjacent area of the North Sea.

In an earlier study we found that the rotifer Brachionus plicatilis in Soda Lake, Nevada (USA) maintains extensive genetic variation for three isozymes. This variation was present both within and between different collections. No evidence was found that there was a seasonal succession of distinct electromorphs. In this paper we ask: is the genetic variation maintained by selective neutrality among electromorphs? Parthenogenetic females from ten clones representing seven different composite electromorphs were selected for life table analysis. Substantial main effects of genotype or interactions of genotype with experimental food quantities and temperatures, were found for the intrinsic rates of increase, net reproductive rates, and mean life spans of these clones. We conclude that these fitness differences permit us to reject the hypothesis that genetic variation is maintained because of selective neutrality among clones. Instead, it seems likely that directional selectional may be either too weak or of too brief a duration in Soda Lake for clonal exclusion to occur.

Estimating the hazard or risk to both human health and the environment has been based almost exclusively on single species toxicity tests low in environmental realism and without validation of their accuracy in more complex systems. While this may be quite appropriate for humans in a large variety of circumstances, there is no substantive body of direct experimental evidence indicating that precise predictions of harm from hazardous materials can be extrapolated from single species laboratory tests (or even multispecies laboratory tests) to the more complex highly variable natural systems. Now added to the hazardous chemical assessment problem is the accidental or deliberate release of genetically engineered microorganisms into the environment that have the additional capability of multiplying and expanding their numbers and also transferring genetic information to other organisms. This paper focuses entirely on hazard evaluation for organisms other than humans, namely predicting the potential risk or probability of harm to natural systems based on laboratory toxicity testing using single species. Not only will the basic risk assessment strategy itself be examined but also the question of determining the statistical reliability of various extrapolations from one level of biological organization to another.

This paper presents the results of several years' surveys on the vegetation of the Special Zoological Reserve of Kopacki Rit. Over this large floodplain of the Danube and Drava rivers prevail different types of hygro- and hydrophytic communities. Some of them are relatively constant, having persisted in this Reserve for many years with a relatively constant area. Some other communities, particularly aquatic ones, appear periodically, and their area is directly influenced by surface water area and duration of the flood.

145 rotifer species were previously known from Sudan, mostly from the Nile valley and the NE of the country. In the present paper planktonic, periphytic and benthic samples from the Western provinces of Darfur and Kordofan are examined. They contained 77 species, in one or different forms, of which 67% were cosmopolitan, 15% thermophilic, 14% tropicopolitan, and 4% temperate-boreal. No new taxa were found, but 23 species and one subspecies are new to Sudan, while one is new to Africa.

The paper compares three batches of brown trout (Salmo trutta Linnaeus) eggs, two batches of Atlantic salmon (Salmo salar Linnaeus) eggs and the artificial trout eggs described by Ottaway (1981), in terms of their measurable physical characteristics. Attention was given to the effects of temperature and of the stage of development of the real eggs. Comparisons were also made between brown trout eggs and artificial eggs of the rate of fall in a water column, of the value and speed of attainment of terminal velocity when falling through water and of the pattern of settlement within an experimental stream channel.

Hyperscums are crusted buoyant mats of densely packed cyanobacteria, often decimeters thick, that persist for periods of weeks to months at the same site. In Hartbeespoort Dam, a hypertrophic lake in South Africa, hyperscums of the cyanobacterium Microcystis aeruginosa that cover more than a hectare and contain up to 2 tons of chlorophyll a typically form in winter and persist for 2–3 months. This paper reports on the environmental conditions that favour hyperscum formation.

This paper examines the physical consequences of increased catchment sediment yields on the sediment budget and the hydrodynamic setting of the South Johnstone River estuary in North Queensland. A combined study involving hydrological monitoring, assessment of sediment sources, estimation of riverine sediment budget and hydro-sedimentological numerical modelling for estuarine sediment transport is currently underway. Initial field and laboratory observations indicate that the sediment delivery from highly erosion-prone sugar cane cultivations in the tropical catchment has increased dramatically during the last 10 years. This has subsequently given rise to elevated flood levels in both the lower and upper catchment areas, as well as significant modifications to the river bed morphology.