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A population of Tubifex tubifex in an organically rich stream was found to have an annual life-cycle with a prolonged period of reproductive activity throughout the winter and spring. Cocoons were produced mainly during the late winter and early spring. No cocoons were found during August and September, and there were few mature worms at this time. The population density ranged between 5420 m-2 in mid-September and 613000 m-2 in mid-May. The maximum population biomass (Bmax) recorded was 106 g dry wt m-2 (March) and the minimum was 10 g dry wt m-2 (September), Total annual production (P) was 139 g dry wt m-2 and the average annual biomass (B) was 46 g dry wt m-2 giving an annual P/B ratio of 3.0, and a P/Bmax ratio of 1.3. [ABSTRACT FROM AUTHOR]

(1) A survey of the macro-invertebrates and fish in the River Cynon, a trout stream in south-east Wales receiving industrial and domestic wastes, and nine of its tributaries, was carried out in the summer of 1970. Its principal purpose was to describe the structure of these communities before waste treatment facilities, in course of construction, reduce the degree of pollution. (2) The macro-invertebrate communities changed dramatically at station C4, there being a very varied fauna upstream and one dominated by chironomids and oligochaetes downstream, principally Nais barbata, Cricotopus bicinctus and Syncricotopus rufiventris. It seems likely that coal particles, influencing the substrate, are largely responsible for this change. Further downstream, and below substantial organic discharges, tubificids and the enchytraeid, Lumbricillus rivalis, became increasingly abundant. The total density of macro-invertebrates increased from about 2000/m² in the headwaters to over 20,000/m² in the lower reaches. (3) The fauna of the clean tributaries, Hir (C16) and Wenallt (C19) was similar to that of the unpolluted upper reaches of the Cynon (C1–C3) whereas that of tributaries affected by coal particles was similar to the fauna of the Cynon downstream of C4. (4) Six species of fish were recorded (bullhead, eel, minnow, trout, stickleback and stoneloach) of which three (bullhead, eel and trout) were confined to reaches upstream (C8 and above) of industrial effluents at Abercwmboi. For 0.8 km downstream of these effluents the river was fishless and further downstream, to the confluence with the River Taff, fish density and biomass were reduced. (5) In the upper Cynon and its tributaries the density and biomass of trout were within the range recorded elsewhere in the British Isles. The growth rate of trout in the catchment is low. Differences in growth rate and shape of trout in the main river and tributaries suggest that there is little interchange between these areas, except perhaps with very young fish. 0 + ∗ fish were only caught in abundance at two tributary stations and their numbers, even if widely distributed, could not permanently support the current density of older fish throughout the upper catchment. (6) Stone loach and minnow reached a very large size and individuals caught of the latter species approached the maximum recorded length for the British Isles. [ABSTRACT FROM AUTHOR]

The acute toxicity of phenol and ammonia, singly and in combination,to larvae of the ephemeropteran, Baetis rhodani, was examined using a computerized continuous flow system in the laboratory. The 24 h LC50 values (with 95% confidence intervals) were calculated to be 29.9 (17.3-51.5) mg phenol liter-1 and 8.2 (2.0-33.0)mg un-ionized ammonia liter-1. When phenol and ammonia were together in low concentration (< 20 mg liter-1 and < 3 mg liter-1 [un-ionized], respectively), they expressed their toxicity additively, but at higher concentrations they behaved in a greater-than-additive manner. When the 24 h LC50 values were used to predict the toxicity of a coking plant effluent, containing principally ammonia and phenol, it was found that the B. rhodani larvae died quicker than expected indicating the presence of other toxic chemicals. This exemplifies the value of using direct toxicity assessments to detect the presence of unknown toxicants. [ABSTRACT FROM AUTHOR]