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A multivariate measure of stream quality, the Index of Biotic Integrity (IBI), was adapted to southern Ontario and calibrated to watershed land use on a variety of spatial scales. The fish fauna at 209 stream locations on 10 watersheds near Toronto, Ontario, was sampled with a backpack electrofisher in the summers of 1984 and 1985 to provide biological information for the IBI. Watershed urbanization, forest cover, and riparian forest were measured from 1:50,000 scale topographic maps and related to IBI estimates by linear regression. Of the biological measures tested, species richness, local indicator species (brook trout (Salvelinus fontinalis) and Rhinichthys spp.), abundance of large piscivores, fish abundance, and incidence of blackspot disease were found to contribute significantly to IBI estimates. Variation in IBI estimates at the same location ranged from 0 to 8% within the sample season and from 0 to 24% between years. Linear models based on measures of watershed urbanization and forest cover accounted for 11–78% of the variation in IBI scores, depending on the spatial scale of the analysis. Significant IBI/land use relationships were found with whole-basin IBI estimates and for IBI estimates from individual stream reaches. Land use immediately upstream of sample stations was most strongly associated with stream quality as measured by the IBI.

Water quality was monitored in three 30-ha stratified headwater Precambrian Shield lakes for 5 years before and 3 years after moderate to extensive catchment deforestation. These lakes, which had water renewal times of about a decade, showed only minor changes in water quality by the third year after logging. Water quality response in a lake with moderate deforestation and intact shoreline forest was similar to that in two lakes with extensive upland and shoreline deforestation. By the second and third years after logging, May-September average volume-weighted concentrations of dissolved organic carbon, chlorophyll, total nitrogen, K + , Cl -, and Si had all increased, generally by about 10-40% over predisturbance levels, while Ca 2+ and Mg 2+ had declined by 10-25%. Dry weather the first year after logging was associated with temporary declines of 10-20% in dissolved organic carbon and chlorophyll.Résumé : Nous avons surveillé la qualité de l'eau dans trois lacs de 30 ha de tête stratifiés du bouclier précambrien, pendant 5 ans avant et 3 ans après une déforestation modérée à généralisée des bassins versants. Ces lacs, dont la pé-riode de renouvellement était d'une décennie environ, ne présentaient que de faibles changements de la qualité de l'eau trois ans après la coupe. La réaction sur le plan de la qualité de l'eau dans un lac à bassin modérément déboisé et à rivage intact était la même que celle de deux lacs à bassin fortement déboisé sur les pentes et sur le rivage. Dès la deuxième et la troisième année après le déboisement, les concentrations moyennes de mai à septembre (après pondéra-tion pour le volume) du carbone organique dissous (COD), de la chlorophylle, de l'azote total, de K + , de Cl -et de Si avaient augmenté, généralement de 10 à 40% environ par rapport aux niveaux avant perturbation, tandis que le Ca 2+ et le Mg 2+ avaient baissé de 10 à 25%. La sécheresse qui a sévi la première année après le déboisement explique des baisses temporaires de 10 à 20% du COD et de la chlorophylle.[Traduit par la Rédaction] Steedman 96

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SUMMARY. This study documents the life history of the xylophagous elmid beetle, Lara avara, and estimates its contribution to wood degradation in Oregon streams. The life cycle was found to be 4 to 6 or more years long, with all but 2–3 months of that spent in the larval stage. Larvae grow through seven instars, taking about 1 year for instars 1–3, and from 3 to 5 or more years for instars 4–7. Last‐instar larvae leave the water to pupate. Adults live approximately 3 weeks and occur from May to August. The eggs are deposited on submerged wood. Larvae probably obtain their nutrition by absorbing substances liberated into decaying wood by microbial activity. They do not produce their own cellulase, nor do they have a symbiotic gut flora similar to that of xylophagous cranefly (Tipulidae) larvae. Faecal production by L. avara larvae averaged 13% dry body wt d‐1. This yields an estimate of faecal production of 1.6 g m‐2 y‐1 in Oregon Coast Range streams (about 0.3% y‐1 of wood standing crop).