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In a number of disciplines including ecology, ecotoxicology, water quality management, water resource management, fishery biology etc., there is significant interest in the testing of new materials, environmental samples (of water or sediments) and specific sites, in terms of their effects on biota. In the first instance, we consider various sources of aquatic pollution, sources typically associated with developed areas of the world. Historically, much water quality assessment has been performed by researchers with a background in chemistry or engineering, thus chemical analysis was a dominant form of assessment. However, chemical analyses, particularly of such materials as organochlorines and polyaromatic hydrocarbons can be expensive, and local environmental factors may cause the actual exposure of an organism to be little correlated with chemical concentrations in the surrounding water or sediments. To a large extent toxicity testing has proceeded independently of environmental quality assessment in situ, and the work has been done by different, and differently-trained researchers. Here we attempt to bring together the various forms of biological assessment of aquatic pollution, because in our opinion it is worth developing a coherent framework for the application of this powerful tool. Biotic assessment in its most primitive form involves the simple tracking of mortality in exposed organisms. However, in most natural environments it is extended, chronic exposure to contaminants that has the most wide-ranging and irreversible repercussions--thus measures of sub-lethal impairment are favoured. From an ecological standpoint, it is most valuable to assess ecological effects by direct study of in situ contaminant body burdens and impairment of growth and reproduction compared with 'clean' sites. A distinction is made here between bioindication and biomonitoring, and a case is made for including aquatic macrophytes (angiosperms) in studies of contaminant levels and effects in the biota. It is apparent that there is a concurrent need for laboratory-based testing of new industrial by-products before any are released in the environment, and such studies should aid the investigation of mechanisms and modes of toxicity, but environmental assessment, and tracking of improvements in environmental quality are most effectively achieved by active biomonitoring experiments.

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The hypothesis that male—biased sex ratios result from the greater costs of reproduction for females was examined at various modular levels in a study of the dioecious clonal shrub, staghorn sumac (Rhus typhina). The population of flowering trunks was male—biased, though male and female clones proved to be of similar ages. Trunks within apparent female clones were more likely to be vegetative or dead than in male clones, though the density of living plus dead trunks was comparable in male and female clones. Females of given ages had the same mean trunk diameter as similarly aged males. Overall, the average female trunk diameter was the same as the average male diameter. Differential costs and patterns of reproduction for males and females were revealed through destructive harvests and separate analysis of trunks and branches. An abrupt discontinuity n the performance (growth) of male trunks and branches. An abrupt discontinuity in the performance (growth) of male trunks was found; those with a diameter less than °4 cm had greater total numbers of leaves, branches, and inflorescences than females of comparable diameter, whereas larger males and females did not differ from each other. Flowering males branches had significantly fewer leaves than those of flowering females. The number of leaves per branch was highly correlated with the number of fruits produced in the corresponding terminal inflorescence. The average (±SE) male inflorescence had 4099 ± 312 flowers, whereas the average female inflorescence bore 1575 ± 67.2 fruits. There was a sixfold difference in the biomass of these terminal reproductive units (female infructescences being heavier.) This study suggests the importance in a clonal species of defining the modular level at which costs are assessed. The hypothesis that females suffer greater reproductive costs as a consequence of fruit production is supported by the finding of diminished survivorship of daughter trunks in female clones. However, it is not supported by data on annual trunk diameter increments. Reproductive costs in sumac are shown at the level of the clone (ramet survivorship) or the branch, rather than at the level of the flowering trunk module.