Taxonomic composition and spatio-temporal variability of macroinvertebrates inhabiting snags were examined from an 8-km segment of the Elm Fork of the Trinity River. Seventy-seven macroinvertebrate taxa were collected from submerged wood during the study. Assemblages were highly variable spatially and temporally, especially among seasons. An ordination of species and environment did not find snag taxa to have striking correlations with many of the selected environmental variables, although there were some trends in flow-mediated species distributions. There were significant seasonal differences in the abundances of some taxa, particularly among the Chironomidae (Diptera). The Tribe Orthocladiini was numerically abundant during the winter, while the Tribes Chironomini and Tanytarsini dominated the summer and autumn. Additionally, this study included a secondary production and microdistribution analysis of a population of the caddisfly Cyrnellus fraternus. Distributions of C. fraternus were restricted to snags, the most stable substratum for retreat building and for resisting periodic high waters. Larvae were not found in the soft sand and mud benthic habitats near submerged wood. The insects were multivoltine with a minimum of three generations per year. Pupae were collected July through September and adults emerged from May through October. The population overwintered as larvae. Estimated annual production was 1,015.4 mg/m2/yr. Mean standing stock biomass was 61.24 mg/m2, the cohort production/biomass ratio was 4.59, and the annual production/biomass rate was 16.58/yr for this population. Standing stock biomass ranged from 1.6 to 349.1 mg/m2 during the year and was significantly higher in autumn and summer than winter. Larvae were more abundant in the lower portions of the study area where flow was reduced for much of the year, than in the upper reaches, characterized by higher current velocities. C. fraternus larvae were found in their highest numbers on snags with dense deposits of silt and sand.

A major inventory of tardigrades in the Great Smoky Mountains National Park was conducted and we compared tardigrade species composition in moss and lichen samples and analysed environmental correlates of tardigrade community structure. We also compared these tardigrades with those collected from soil. The basic dataset from tree mosses and lichens consisted of 336 samples, 9200 individuals and 43 species. The supplemental dataset from rock mosses and lichens consisted of 29 samples, 811 individuals, and 41 species. Collectively, there were 57 species present in mosses and lichens. Eleven species were found uniquely on rock habitats. Two-way ANOVAs for various community metrics showed no significant differences between substrate (moss versus lichen) or height (ground level versus breast height); however, there were significant differences between ATBI plots. Tardigrade communities were not significantly different between mosses and lichens, but soil tardigrade communities were quite distinct from these moss/lichen communities. We analysed the impact of 17 environmental variables on community structure using partition tree analyses. SOx deposition explained most of the variation in species richness and evenness in moss tardigrades. Forest disturbance regime had the greatest impact on abundance in lichen tardigrades. Other environmental factors influencing community structure are discussed.

Les milieux aquatiques en zone urbaine sont reconnus comme des îlots de biodiversité qui offrent de nombreux services écologiques. Dans cette étude, nous avons utilisé les macroinvertébrés comme bioindicateurs de la qualité écologique des étangs, petits lacs et marais de l’Île de Montréal. Les macroinvertébrés ont été récoltés durant l’été 2011 dans la zone littorale de 20 sites variant par leur urbanisation et leurs caractéristiques limnologiques. Nous avons évalué la variation dans la richesse en taxa, les indices de diversité et plusieurs métriques basées sur la composition taxonomique ou les traits fonctionnels. Nous avons déterminé la réponse des métriques aux changements dans l’urbanisation, l’aménagement et les conditions des plans d’eau. Notre étude montre que les étangs, marécages et petits lacs constituent des réserves importantes de biodiversité en zone urbaine. Les marécages naturels et les étangs et lacs permaments avaient une meilleure qualité écologique et supportaient des communautés de macroinvertébrés plus diverses et abondantes que les petits étangs temporaires aménagés. Le couvert de végétation aquatique, l’enrichissement en nutriments et en matière organique ainsi que la biomasse des algues expliquaient le plus de variation dans les macroinvertébrés. Les aménagements, la densité urbaine et la permanence de l’eau avaient aussi une bonne influence. Les métriques univariées avaient moins de potentiel que les métriques multivariées. Nous avons discuté les implications de notre étude pour le suivi environnemental de la biodiversité et la qualité écologique des milieux aquatiques en zone urbaine. / Aquatic ecosystems in urban landscapes are now recognized as good islets of biodiversity and valuable environments providing ecological services. However, more knowledge is needed to assess their ecological quality. Benthic macroinvertebrates are widely used as bioindicators, but rarely for urban ecosystems. In this study, we used macroinvertebrates to evaluate the ecological quality of urban ponds and lakes in the island of Montreal. We collected macroinvertebrates during summer 2011 in the littoral zone of 20 waterbodies varying in urban and limnological characteristics. We evaluated spatio-temporal variation in several diversity and biotic indices and multiple metrics based on taxonomic composition and functional traits. We investigated if macroinvertebrate metrics responded to variation in urban land-use, pond management and limnological conditions. Our study showed that small waterbodies, as ponds, lakes and marshes are important resources for sustaining aquatic biodiversity in urban landscapes. Natural wetlands and artifical permanent ponds had higher ecological quality and supported more diverse and abundant macroinvertebrates than artificial managed temporary ponds in municipal parks. Vegetation cover, nutrient and organic contents, and algal biomass were the most important factors explaining spatial variation in macroinvertebrate metrics. Pond management, urban density, and water permanence were also influencial factors. Univariate metrics had less potential than multivariable metrics to assess the responses of macroinvertebrates to environmental features. We discussed the implications of our study for management and quality assessment of urban ponds.