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Samples of chironomid pupal exuviae were collected by drift netting in the River Chew, Somerset, over a period of 4 years. The samples were analysed for percentage composition of types, and in some cases for numbers of exuviae per unit volume of water sampled. Surface samples were shown to contain many more exuviae per unit volume sampled than subsurface samples in the same place, and the catch taken by adjacent nets varied by up to four times. On the other hand, the percentage composition of exuvial types remained very consistent under all sampling conditions. Hourly samples from midday to midnight were made at four seasons in the year, showing that the variation in numbers and proportion of types remained approximately constant throughout the afternoon, but altered at the time of the evening emergence of adults. Samples taken from other rivers show both similarities and differences between themselves and the River Chew in percentage composition of types. In the River Biss, Wiltshire, a marked change in the exuvial types collected downstream from a sewage effluent outfall was shown after improvements had been made to the sewage works. Spring samples from the River Chew showed a change from Tanytarsini- to Orthocladiinae-dominated populations between 1970 and 1972. In the River Chew, exuviae suspended in the stream disintegrated after approximately 1–2 weeks. Coloured polystyrene balls were used to investigate the downstream movement of floating material in the River Chew. In August, balls released 400 m upstream of the sampling nets failed to reach them in 3 h sampling. The average stream flow rate was 0.36 m/s. Some evidence is presented to show that the exuviae float for only about 2 h in the River Chew before sinking. It is suggested that the area from which most of the sampled exuviae are derived is limited on the River Chew to, at most, 400 m upstream. Provisional identification to genus is given for those exuvial types mentioned in the paper. The possibility of using chironomid exuvial analysis as a method of characterizing streams is discussed. [ABSTRACT FROM AUTHOR]

Gametophyte material of the aquatic moss Eurhynchium riparioides was placed into suspensions of coal-dust ranging from 100 to 5000 mg/1 in concentration. After 1 week, concentrations above 500 mg/1 were causing severe abrasive damage to the leaves—however, this effect was observed at 100 mg/1 after 3 weeks. The higher concentrations of coal-dust were affecting growth by limiting the increase in length which was observed in the control flasks. Also, after a period of 3 weeks the production of side branches decreased with increase in coal-dust concentration, and at 500 mg/1, lateral shoots were almost absent. The production of chlorophyll a was also limited by the presence of coal-dust but even at the high concentration of 5000 mg/1 chlorophyll a production was not prevented entirely. A possible mechanism for the action of coal-dust is postulated. [ABSTRACT FROM AUTHOR]

Due to erosion and leaching the great rivers contain considerable quantities of silt (mud). It is estimated that the Rhine carries a mean value of 60–70 g.m-3; the variation of the mud content as a function of water discharge shows values up to several hundreds of grams per m3. The annual supply of mud from these sources is around 4⊗106 tons of dry matter. Near the river mouth, changes in water current velocity and other water movements result in deposition of the river silts. A further important factor is the change in salinity, which causes flocculation and deflocculation. Of course the geological history of the river delta is an important factor for the distribution of sediments over a given area. Chemical analysis of the river silts shows that SiO2 (or other eroded silicates) is a major constituent. Other inorganic compounds are iron and aluminium oxides and calcium (bi)carbonate. Organic matter may form an important part of the silts. Its chemical nature is not yet well described. Part of the silicon compounds are clays of the type of montmorillonite (Al2Si4O10(OH)2) and kaolinite (Al2Si2O5(OH)4). As may be expected from their chemical nature, these compounds are strong ion-exchangers, which may contain Mg, Ca and Fe ions and even anions such as phosphates. The large deposits of the Rhine silt is therefore rather fertile, which has a great influence on the growth of both the rooted and the suspended vegetation. The first has caused enormous amounts of peat, which can be found as layers formed in periods of a relatively low sea level, in which the sediments were comparatively dry. Due to a temporary elevation of the sea level, new layers of silt have been formed on top of the peat. Since the years 1000–1200, man has stimulated the formation of new lands by building dikes. Originally only lands that fell dry during low sea level were reclaimed; later on, lands a few metres below sea level were reclaimed. In these reclaimed areas groundwater level is always near the soil surface. Lakes have been formed mostly by human action; in the older days peat digging, and nowadays sand digging have created large but shallow lakes, of which the water is more or less ‘standing groundwater’. The water may still contain a large quantity of humic acids from the remaining peat. Due to the influence of the sea deposits, CaC03 is also present in large amounts. These factors together render the lake waters rich in humus and alkaline (pH 7–10). Most of the lakes serve as reservoirs for the surrounding agricultural areas. The water movement in spring and summer is therefore opposite to that in fall and wintertime. This fact and the short renewal times of these lakes cause large chemical and biological changes in which the influence of the sediments on the chemistry of the overlying water plays an important role. For instance in the spring, when water flows in from the IJselmeer, the pH and the concentrations of Cl-, Ca++, HCO3- and CO3 = increase. In autumn, when the rainy season begins, and water is admitted from the polder, the concentrations of phosphate, ammonia, silicate and iron increase. However, primary production becomes low due to the decreasing light intensities and the turbidity of the water. When the light increases again in spring a great part of the nutrients disappear from the lake, in which process the sediments play a not unimportant part. [ABSTRACT FROM AUTHOR]

The vertical distribution of some ciliated Protozoa in the plankton of a pond in north-west England was investigated during August 1971. At this time, when the pond was stratified with an oxygen deficient hypolimnion, ciliates were counted at 10-cm depth intervals every 5 h over 25 h. The most common species (Loxodes magnus and L. striatus) were confined to the hypolimnion; there was no diurnal migration into the epilimnion. Earlier work had shown that Loxodes species require oxygen; it is therefore possible that these ciliates, which inhabited the oxygen deficient hypolimnion, migrated vertically, from time to time, to an oxygen supply at the boundary with the well-oxygenated epilimnion. To test this, Loxodes populations were confined in cellophane tubes both in the hypolimnion (at 3 m) and epilimnion (0.5 m) for 12 and 24 h (earlier trials had shown that the tubes were not markedly toxic). The ciliates died at both depths, and in a further experiment when Loxodes were confined at 3 m and 0.5 m and sampled at 5-h intervals up to 25 h it was found that they survived longer in the hypolimnion. It is suggested that ciliates confined at 3 m died because they were unable to migrate vertically to an oxygen supply, while those at 0.5 m died because some other adverse factor was operating in the epilimnion. Laboratory experiments showed that Loxodes died in water in which phytoplankton photosynthesis took place and it is suggested that side effects of photosynthesis in the epilimnion (e.g. a rise in pH) caused the death of ciliates exposed at 0.5 m. [ABSTRACT FROM AUTHOR]

In the course of investigations on the ecology of submerged aquatic macrophytes a narrow-bandwidth spectroradiometer has been used to measure underwater spectral intensity (390–750 nm) in a series of lochs approaching the extremes in optical and chemical properties of Scottish fresh waters. Cosine response and immersion-effect properties of the collector were determined in the laboratory with a collimated light source. Diffuse attenuation coefficients, Ee, ranged from 0.55 in Loch Croispol, a calcareous loch, to 2.9 in Loch Leven, a lowland eutrophic loch. Underwater spectral intensity (1 m) relative to subsurface values show a proportional increase in shortwave radiation in the blue-green water of Loch Croispol, while the converse is true of the peaty brown water of Loch Uanagan. Attenuation coefficients were derived over 25 nm wavebands in Lochs Croispol, Leven and Uanagan. The water in the latter two lochs is optically similar although Leven is rich in phytoplankton and has an extinction peak at 675 nm. Uanagan represents the brown-water type of loch most common in Scotland. Loch Croispol has attenuation coefficients for shorter wavelengths at least ten times lower than the other two lochs and only approaches their values at 750 nm. Croispol resembles Crater Lake, Oregon. The colour range at the maximum colonizable depths by rooted macrophytes of brown (Uanagan 4 m) to blue-green (Croispol 6 m) water is equivalent to 196.0 and 230.6 kJ/Einstein (48.2 and 55.6 kcal/Einstein). Red/far-red ratios even in plankton-rich water (Leven) were at least three times the value for sunlight (1.3) and within the total photic zone reached three-figure proportions. Possible implications for light-sensitive seeds of aquatic species and for morphogenesis and zonation are discussed. [ABSTRACT FROM AUTHOR]