Growth rates of bacteria in rivers

Three different methods for determining bacterial growth rate in rivers are described. Two of the methods are for bacteria in suspension: a recirculating experimental channel method and a radioactive tracer technique using super(35)SO sub(4). The third method is for bacteria attached to surfaces and specifically considers the surface of the common duckweed Lemna minor).

Organic detritus and its role as a food source in chalk streams

This review deals with the variation in populations of invertebrates and the relationships between invertebrate production and detrital food material in chalk streams. The total quantity of detrital material processed by invertebrate consumers is many times greater than the production of these consumers. The amount of detritus ingested each year by chalk stream invertebrates may well be similar to the annual input of autochthonous primary production plus that from allochthonous tree cover.

Saprolegnia infections of salmonid fish

This paper deals firstly with the identification and characteristics of fungal pathogens that colonize salmonids and then considers the relative importance of the condition of the host fish and the environmental factors which may influence the interaction between pathogen and host.

Population dynamics of Windermere perch

This paper looks briefly at some of the more recent analyses and interpretations of the changes that have occurred in the population dynamics of Windermere perch and at the present level of understanding. The long-term study has shown how flexible the population is and how it has behaved in different ways over successive periods of time since 1939. Through one of these periods it was possible to account for nearly all the variance in recruitment by a relatively simple explanatory model. The reduction in numbers on the outbreak of disease in 1976 started a natural experiment which will form a baseline for future studies.

Phytoplankton periodicity: its motivation, mechanisms and manipulation

This review summarizes some recent work to find a generalized explanation of phytoplankton periodicity in lakes. Much of the observational and experimental evidence is drawn from work centred on the large enclosures (Lund Tubes) installed in Blelham Tarn, English Lake District. Observations on the phytoplankton in the tubes are related to the periodic changes that occur in natural lakes and it is suggested that such changes have common patterns, that they are due to common causes, that they are affected by similar processes and that they are therefore predictable and, potentially, manipulable.

Acid precipitation and its effects on aquatic systems in the English Lake District

There is no evidence of an increase in the acidity (lower pH or alkalinity) of water-bodies in the Lake District over the last 50 years. Brown trout occur in acid streams and upland tarns where pH is 4.5-5.2 throughout the year. Their occurrence in such waters in Britain and Ireland has been known for most of this century and there is no previous evidence of harmful effects on salmonid fisheries, though numbers of fish are naturally low. However, many benthic invertebrates that are common in hill-streams where pH is above 5.7 do not occur in more acid streams. This phenomenon occurs in the headwaters of several western rivers in Cumbria. It is not a recent response to "acid rain". Harmful effects of pH are undoubtedly more pronounced in waters that are poor in other dissolved ions. Low concentrations of sodium, potassium, calcium and chloride are especially important and may limit the distributions of some aquatic animals even where pH is above 5.7. The concentration of sulphate ions is usually relatively high but this is not important to the fauna; concentrations are at least two times higher in productive alkaline water-bodies than they are in unproductive acid waters.

Experiments using an artificial stream to investigate the seasonal growth of chalk-stream algae

Research into the production ecology of chalk streams using a large artificial recirculating stream is described. Physical chemical processes including calcium and inorganic phosphate levels, and exchange of gaseous carbon dioxide in both a simple closed system and a circulating system with gravel substrate have been monitored in both light and dark conditions. Further experiments were concerned with the seasonal changes in algal growth over the gravel substrate with constant water velocities and replenishment. The algal population, composed mainly of the diatoms Achnanthes minutissima, Meridion circulare, Nitzschia fonticola and Synedra ulna reached a peak in mid May and declined rapidly during June. Concentrations of phosphate phosphorus fell as the diatoms grew but was not thought to limit growth. Silicate concentrations followed the diatom cycle closely but never fell below 0.8 mg/l Si. It is possible that one of the nutrients may have been limiting the rate of growth due to steep diffusion gradients through the algal mat. In the last summer and autumn a hard calcareous crust composed of the green alga Gongrosira incrustans and the blue green alga Homeothrix varians , developed. The channel stream is compared with the natural conditions found in chalk streams.

The bullhead Cottus gobio , a versatile and successful fish

A series of studies on the ecology of the bullhead, Cottus gobio is described. Habitat choice, growth rate and longevity, population density, biomass and production, reproduction, life history and feeding is compared at 8 sites in England and 1 site in Wales. Evidence suggests that in Cottus gobio the prevailing environmental conditions result in considerable modifications in longevity, growth rate and egg production. It also indicates that the advantages of fast growth and high reproductive effort in favourable habitats are offset, at least partially by increases in mortality.

Effects of Cow Green Reservoir upon downstream fish populations

Post impoundment observations on the fish populations of the River Tees, downstream from the Cow Green Reservoir were made between 1971 and 1980. Both bullhead (Cottus gobio L.) and brown trout (Salmo trutta L.) population densities increased in the river after impoundment but changes in growth rate were small. Investigations into the stomach contents of the two species reflects the results of other work on increases of benthos in the river. Following regulation there was an increase in the quantity of Ephemerella ignita found in trout stomachs while in the bullhead, regulation caused an increase in the importance of Mollusca and a decrease in importance of Ephemeroptera and Plecoptera.

Monitoring the trophic status of reservoirs

The current situation of regional, rather' than national, problems of eutrophication in standing waters has been widely aired in recent reports. A reliable, quantitative data base is a prerequisite to future trend monitoring, a concensus view of those reports. The objective of this report is to establish requirements, methodology and a minimal data set for nutrient and algae status in water supply reservoirs in England which may be used as a protocol for future trend monitoring.A pilot study has been carried out to assess the relative merits of different sampling strategies, the choice of which has major implications for the cost of sample collection. This short report suggests that consider the possibility of designating a few sites as ”baseline sites” at which detailed changes in trophic status as monitored by the more labour-intensive parameters would be collected on a regular, long term basis to help in the interpretation of the low cost survey results.

Automatic identification and enumeration of algae

A good understanding of the population dynamics of algal communities is vital in many ecological and pollution studies of freshwater and oceanic systems. Present methods require manual counting and identification of algae and can take up to 90 min to obtain a statistically reliable count on a complex population. Several alternative techniques to accelerate the process have been tried on marine samples but none have been completely successful because insufficient effort has been put into verifying the technique before field trials. The objective of the present study has been to assess the potential of in vivo fluorescence of algal pigments as a means of automatically identifying algae. For this work total fluorescence spectroscopy was chosen as the observation technique.

Nitrates - loss processes in raw water

This project investigated the production of nitrate (nitrification) by bacteria in lakes. The work was undertaken as nitrification is a key process in the nitrogen cycle and previous estimates of rates of nitrification were unreliable. When different methods were used to estimate rates of nitrification within sediment deposits different results were obtained. Investigation' of specific aspects of these methodologies has allowed some rationalization of these observations and also enabled comparisons of previously published data which, beforehand, was not possible. However, it was not clear which methods gave the most reliable rate estimates. Calculation of a nitrate budget for Grasmere lake indicated that the use of methods which involved the mixing of surface sediments (and therefore disrupted preformed nutrient gradients) overestimated the rate of nitrification. The study concludes that slight changes in the method used to prepare sediment slurries can result in large changes, in the measured nitrifying activity. This makes comparisons between studies, using different methods, extremely difficult. Methods to study sediment nitrification processes which do not disrupt preformed substrate gradients within the sediment provide the most reliable rate estimates.

Nitrates in surface waters, inputs and seasonality: Progress report for the period April - December 1987

The objective of this short project progress report is to investigate, in a catchment on which earlier nitrate data are available for comparison, seasonality and budgets, in relation to land use, of nitrate inputs, concentrations and loads. Sampling was undertaken from 1984-87 in the River Frome catchment and data on nitrate concentrations analysed.

Impact of watercress cultivation on river water quality: progress report for the period, January - December 1987

The objective of this short project progress report is to investigate the possible water quality implications of modern watercress growing practices. Chalk receiving watercourses are usually of high supply, amenity, game fishing and fish farming value. Any headwater pollution load, therefore, needs characterising and quantifying. Two sites of watercress farming were studied in 1986-87 and nutrient levels examined. Different approaches of watercress farmers in Dorset and Hampshire are summarised.

The effects of environmental stress on the physiology of growth in rainbow trout, Salmo gairderi Richardson

There is little doubt that both mammalian and teleost growth hormones can accelerate growth and increase food conversion efficiency in all commonly-reared species of salmonid fish. In those vertebrates that have been closely studied (predominantly mammals), the pituitary hormone somatotropin (GH or growth hormone) is a prime determinant of somatic growth. The hormone stimulates protein biosynthesis and tissue growth, enhances lipid utilization and lipid release from the adipose tissues (a protein-sparing effect) and suppresses the peripheral utilization of glucose. The present study is a prerequisite for future work on growth hormone physiology in salmonids and should contribute to our understanding of the mechanisms of growth suppression in stressed fish. Plasma growth hormone (GH) levels were measured in rainbow trout using a radioimmunoassay developed against chinook salmon growth hormone.