ALBERT

Notes: The design and use of a tow net for sampling coarse fish fry in rivers are described, and its performance over a year is discussed with regard to species selectivity and size selectivity. The extent to which it can be used to provide data on the comparative abundance of the fry and their mean lengths and associated variances are described.

Notes: A population of Gobius niger in a south-coast bay was sampled over a 12-month period. The bay received the cooling water discharge from Fawley power station. Four year-classes were recorded of which the 1+ group was found to be responsible for the bulk of egg production. The main spawning period was from April to May although some evidence of batch spawning was found. Growth was found to be faster than has been reported for populations elsewhere, possibly because of the raised water temperature. Despite higher temperatures the growing season was not extended beyond that of other comparable black goby populations, being restricted to a 4–5 months period after the main spawning period. Seasonal changes in diet were believed to be the result of the effect of water temperature on fish movement. Feeding occurred throughout the year.

Notes: Abstract 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.

Notes: Abstract 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.

Notes: Summary 1. The River Severn at Ironbridge is warmed by cooling-water from Ironbridge “A” power station. Water temperatures over the years 1965–1967 were raised by values ranging from 0.5 to 7.2°C above ambient. 2. Collections of Plecoptera and Ephemeroptera were taken from three reaches in the vicinity of the cooling water discharge. “A” was situated 400 m upstream, “C” 800 m downstream and “E”, 2 km downstream of the outfalls. 3. The river at all three stations was fast flowing and normally fairly shallow with a stony substratum. 4. The water was alkaline with B.O.D. values of 0.9—5.0 ppm. There were no significant chemical changes from “A” to “E”. 5. Natural water temperatures varied from 0°C to 20.6°C. Downstream of the warm water outfalls the range was 0°C to 24.8°C. Mean weekly temperatures were raised by between 0.2°C to 4°C. There was no temperature stratification at the three sampling stations. 6. Thirteen species of Plecoptera and twenty-one species of Ephemeroptera were recorded. Ten species of Ephemeroptera (including three Caenis spp) constituted 95% of the total numbers collected. 7. Distribution of nymphs at “A”, “C” and “E” changed with river level and season. Species found commonly in the marginal grasses were those most active and common in invertebrate drift. 8. When compared with the faunas of other rivers and streams, the Severn at Ironbridge is a transitional area, with species common to hill streams and larger rivers. 9. The use of fine nets (24 meshes/cm) facilitated the more accurate determination of life-histories. 10. Life-histories of Taeniopteryx nebulosa, Ephemerella ignita, Heptagenia sulphurea, Baetis pumilus, Baetis bioculatus, Baetis rhodani, Baetis vernus and Baetis buceratus are described for both heated and unheated reaches. 11. Under natural conditions at “A”, three distinct types of life-history were defined among the eight species and the relationships between their life-histories and the natural temperature cycles differ. (a) T. nebulosa is a winter grower, nymphs only develop to maturity after September, though some were found in May and June at “A”. Temperature range for nymphs was approximately 17°C to 0°C. (b) E. ignita and B. bioculatus are both summer growers. Nymphs occur over a range of about 6.5°C to 22°C naturally. (c) The other species had more complex hatching, growth and emergence periods. H. sulphurea, B. rhodani, B. pumilus and B. buceratus nymphs grew quickly during February–May. Numbers were low in the height of summer and the controlling factor is probably competition for food and space with the “summer” species. 12. All species show a range of temperature tolerance during each life-history phase. This tolerance is considered to be a mechanism evolved to give the species some flexibility to withstand natural variations in climate from year to year. 13. E. ignitanymphs were larger and B. bioculatus better grown in May 1965 than in May 1966. This difference was probably related to the date on which 6°C was first reached and not to the time/temperature factor during the whole winter. 14. There was no really obvious “succession” of species in the Severn as found in small streams. 15. Effects of the power station effluent are considered from two aspects. There is some evidence that small, early hatched nymphs of Taeniopteryx were absent from “C” and “E” in June, but not from “A”. Later nymphs grew and hatched simultaneously at all three stations. There is no evidence of any other effects on the distribution and abundance of species. There may have been a small advance, of up to one week in the hatching times of Taeniopteryx and E. ignita in April 1967 but the data are not highly significant. The advances of 3–5 weeks in temperature shown by LANGFORD (1970) are not reflected in the life-histories of Plecoptera or Ephemeroptera. 16. All the evidence indicates that the heated effluent from Ironbridge “A” has no significant effects on the distribution and ecology of any of the eight species. Nymphs of some of the Ephemeroptera were collected over the whole range of river temperature, i.e. 0°C to 24.8°C, while the summer species were recorded over the whole summer range, i.e. 6°C to 24.8°C. T. nebulosa was restricted in its hatching and growth by temperatures over about 17°C both upstream and downstream of the power station. 17. It is suggested that the ability of each species to tolerate wide temperature range in different life-history stages is sufficient to enable the species to withstand and survive unnatural temperature conditions, provided that these temperatures are not sustained, or lethal to all stages, i.e. egg, nymph or adult. 18. Further studies on the long-term variations in life-histories in relation to river conditions are in progress.

Notes: Summary o| li]1.|Biological Surveys of rivers and streams were carried out in Lincolnshire during 1961\2-67. li]2.|Lincolnshire is a lowland region, with calcareous rocks and soils intensively farmed. Pollution is mainly from small sewage disposal works and farms. li]3.|The rainfall is low, up to 27.5\rd (70 cm) annually. li]4.|Most river systems are less 50 km long and have sources from \s+ 33 m to 125 m above Mean Tide Level (ODN). There are two main types of watercourse a. Free flowing “streams” with sandy or stony substrata b. Canalised impounded “rivers” with clay banks and silt or mud substrata. li]5.|The temperature of the streams is less variable throughout the year than that of rivers. li]6.|The two types of watercourse are chemically similar, but the rivers have higher B.O.D.'s and some reaches are affected by salt water during low freshwater flows. li]7.|The vegetation of streams differs from that of rivers. Plant species common in rivers are also found in pools and ponds. li]8.|Collections of invertebrates were made with a hand net in two standardised methods depending on the type of watercourse. li]9.|The distribution and habitat of each species is described and habitats are compared with those in other regions. Altitude ranges are higher in other regions but basic habitats are very similar. li]10.|Comparisons are drawn between the Plecoptera and Ephemeroptera faunas of a. Clean Lincolnshire streams and clean rivers b. Clean and polluted reaches c. Chalk and limestone river systems d. Stations with different substrata e. Lincolnshire and other regions of Britain 10a. Plecoptera are not usually found in rivers. Two groups of Ephemeroptera are defined — a “river” group and a “stream” group. b. Plecoptera are rare as pollution occurs. T. nebulosa, I. grammatica and A. standfussi are most tolerant. Ephemeroptera are also suppressed by pollution. B. rhodani, C. moesta and B. bioculatus are fairly tolerant. c. Plecoptera were more common in chalk streams. Of the mayflies, B. pumilus and H. fusca were only found in the chalk streams, B. bioculatus and C. macrura were only found in limestone streams. d. Few differences were found between the distribution of species in sandy and stony substrata, though only 3 species of Plecoptera and 3 of Ephemeroptera occurred in small, shingly headwaters. e. The Plecoptera fauna of Lincolnshire is sparse compared to the mountain regions. Of the Ephemeroptera, Ecdyonuridae were notable absentees, owing to the lack of suitable substrata. Distribution of species is in many cases inexplicably sporadic within the region as it is in other regions.

Notes: Summary 1. The River Severn is 320 km long from its source to the sea. It is warmed in its lower-middle reaches by the cooling-water from Ironbridge \ldA\rd power station. 2. Hourly records of natural river temperature have been collected for 20 years. Temperatures in the river 2 km downstream of the cooling water outfalls were measured using a continuous recorder in 1966. Surveys showed that complete mixing of warm and cold water occurred at the recorder. 3. The Severn at Ironbridge is fairly swift, and shallow, turbulent rapids (A, C and E on Fig. 1) alternate with slower, deeper reaches. Current velocities varied from 0.5 to 0.8 m/sec. Daily flow rates during the period from January 1965 \2- June 1967 varied from 5.6 cu m/sec. to 480 cu m/sec. The power station normally circulated between 5% and 50% of the available river flow. 4. Records of natural temperature from January 1965 \2- June 1967 are analysed with respect to seasonal and short-term changes in weather conditions. Data obtained from the recorder are used to compute an equation from which \lddownstream\rd temperatures were calculated for periods when the recorder was not in use. 5. Four natural \ldseasons\rd are described covering periods of \ldlow\rd, \ldrising\rd, \ldhigh\rd and \ldfalling\rd temperatures. The rate of change varied from year to year but a mean weekly temperature of 10\dgC was reached in the same week (week 18) in 1965, 66 and 67. Lowest water temperatures were recorded in December and January, the highest in June, July or August. Winter temperatures varied from 0\dg to 8\dg with a mean around 4\dgC. Highest temperature over ten years was 22.8\dgC in 1957, 59 and 60, but the maximum during 1965\2-67 was 20.6\dg in 1965. 6. Mean air and water temperature move generally in the same direction, but in summer water temperature is consistently the higher. 7. Daily records show that there is a regular diurnal variation in water temperature on sunny days in early summer, probably due to the direct warming influence of the sun. No variation occurs in winter. The largest single daily increase was 2.5\dgC, though summer rainfall caused a fall in temperature of 3.5\dgC. This was due to a direct localized cooling effect of the rain. Steady river temperatures were associated with overcast skies and mean air temperatures close to that of the water. 8. Water temperature followed the trends of air temperature during the equinoxes, with some time lag. Other weather conditions during spring and autumn were similar. 9. The effect of a short summer spate was to depress the normal diurnal variation without causing a sharp change in river temperature. 10. Compared with small streams and a Lake District tarn, the temperature of the Severn is relatively stable, with less weekly and diurnal variation. Of the three types of water body, the tarn was generally warmer in summer and cooler in winter. Of the running waters the Severn was slightly warmer in summer and cooler in winter. Maximum stream temperatures were almost always lower than 20\dgC. 11. The short term effects of the cooling water on the river were to exaggerate normal summer diurnal variation by up to 100% and to establish diurnal patterns in other seasons when these were not found naturally. The greatest daily rise 2 km downstream of the station was 7.2\dgC above ambient. More normally the daily increase was 0.5\dgC to 3.5\dgC above ambient. Maximum downstream temperature was 24.5\dgC in the summer of 1965. 12. Long term effects were to produce certain river temperatures, e.g., 10\dgC for short periods some weeks before they occurred naturally, though during the night downstream temperatures fell to ambient. If degree-hours above 0\dgC were totalled over the year there were increases in the downstream reaches of some 29% in 1965 and 11% in 1966. Arbitrary total numbers of degree hours could be reached some 2\2-5 weeks earlier downstream than upstream. The rate of accumulation of degree hours varied with season and the effects of the cooling water on this \ldrate\rd were more marked in winter than in summer. 13. The stability of the natural water temperature in the River Severn compared with that of Hodson's Tarn and small streams, means that single daily measurements or weekly maximum and minimum recordings can be of considerable value in determining temperature patterns.