A New Method for Finding Small Vertebrate Fossils: Ultraviolet Light At Night

Vertebrate fossils from many different formations fluoresce when exposed to ultraviolet (UV) light. In this paper field observations and controlled experiments in the Chadron Formation (White River Group, late Eocene) of Wyoming are used to assess the utility of searching for fossils at night using ultraviolet light. The results indicate that, especially for very small teeth and egg-shell fragments, searching with ultraviolet light at night can result in significantly more specimens than searching during daylight hours. This method has the potential to increase sample sizes for small vertebrate specimens that are often overlooked when using standard collecting techniques.     

Utility of field-based artificial streams for assessing effluent effects on riverine ecosystems

Experimentation using field-based artificial streams provides a promising, complimentary approach to biomonitoring assessments because artificial streams provide control over relevant environmental variables and true replication of treatments. We have used large and small artificial stream systems, based in the field, to examine the effect of treated bleached kraft pulp mill effluent (BKME) on the benthos of three large rivers in western Canada. Under natural regimes of temperature, water chemistry, and insolation, these artificial streams provide current velocities and substrata to food chains or food webs that are representative of those in the study river. With these tools we have shown that BKME stimulated mayfly growth in the Thompson River above that which could be accounted for by fertilization of their algal food supply. In contrast, moulting frequency was inhibited at high BKME concentrations. Results from artificial streams also indicate that increased algal biomass and abundances of benthic communities downstream of BKME outfalls were induced by nutrient enrichment from the effluent. BKME treatments did not change diatom species richness in the Fraser River, or diatom species diversity in either the Athabasca or Fraser Rivers. Artificial streams provide a means of understanding the mechanisms of stressor effects over a continuum ranging from single stressor effects on specific taxa to the effects of multiple stressors on communities and ecosystems. Because riverside deployment provides environmental realism within a replicated experimental design, this approach can (i) address questions that cannot be examined using laboratory tests or field observations, (ii) improve our mechanistic understanding of stressor effects on riverine ecosystems, and (iii) can contribute directly to the development, parameterization, and testing of models for predicting ecosystem-level responses.     

Influence of flood timing on the recovery of macrophytes in a former river channel

Over two vegetation cycles we compared the recovery of macrophytes from flood disturbances that occured at different seasons (July vs December) on patches of a former channel of the Rhône River, France. Some patches were disturbed twice; others were disturbed either in summer or in winter; others were never disturbed and were used as controls.The recovery rate of the vegetation was estimated from the duration of recolonization of the disturbed areas and of growth of the recolonizing species. The influence of the summer disturbance appeared to be strong because the disturbance occurred when the development of the vegetation was maximum. The influence of the winter disturbance was apparently much lower since most species had already declined at this time because of their phenology. The repetition of the two disturbances on the same patch had little influence on the vegetation community.In all cases, the recovery of the vegetation occurred rapidly, both for total vegetation cover and species richness. By the following spring, no significant differences appeared between disturbed and reference patches. The effect of the disturbances varied according to the phenology of the plants, and the macrophyte community studied was more sensitive in summer than in winter.     

River/land ecotones: scales and patterns

On a continental scale a river system itself is an ecotone, mediating between the terrestrial system and the sea. On the landscape scale, ecotones appear between terrestrial and river systems. At decreasing scales, the number and diversity of ecotones increases. Ecotone processes are discussed in relation to the entire river ecosystem, on scales ranging from the activity range of fish fry up to that of adult fish.The introduction of patch theory into the River Continuum Concept (RCC) allows for the proper consideration of hydraulics and time. The relationships between stream order and patch distribution, patch size and lifetime and age diversity of patches are described. This combination model is much better adjusted to the situations occurring in nature than the original, very abstract RCC-model.Dedicated to Professor Franz Berger on the occasion of his 90th birthday     

HARBOR SEAL (PHOCA VITULINA) PREDATION ON SEINED SALMONIDS IN THE LOWER KLAMATH RIVER, CALIFORNIA

Feeding activity of harbor seals ( Phoca vitulina ) was monitored while the California Department of Fish and Game seined and tagged migrating adult salmonids between 1984 and 1988. The number of predations observed each week of observation was significantly correlated with the number of fish seined during that week. There was a significantly higher number of predations observed on days when seining took place than on days when no seining occurred. Our observations suggest that most, if not all, predations we observed on days when seining occurred involved fish that had been recently seined and released. The estimated percentage of seined fish taken by seals was relatively constant over the five years of the study, ranging from 3.1% to 5.5%. Various strategies for reducing the level of predation on seined salmonids in the lower Klamath River are discussed.     

Hydrologic,vegetation, and substrate characteristics of floating marshes in sediment-rich wetlands of the Mississippi river delta plain,Louisiana, USA

Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l^–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1^–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham     

南水北调与生态平衡

水是人类赖以生存繁衍的重要资源。我国人口逐年增长,而淡水资源数量有限。多变的自然降水及频繁的旱涝灾害,一直决定着我国农业收成乃至整个国民经济的盛衰。     

Decomposition and nutrient liberation rates of plant material in the Parana medio River (Argentina)

The degradation of plant material was studied in order to obtain degradation coefficients and nutrient release kinetics of the vegetation that will be submerged during the filling of the future Parana Medio man-made lake. A group of 13 plant species representative of the whole vegetation of the area were chosen.The plant samples (submerged at 2.5–4 m in the Setubal lagoon), were periodically analyzed during 97 days. The experimental data were fitted to an exponential decomposition model. The plants were classified according to their velocities of degradation into three groups: fast (K>0.01), mean (0.01>K>0.005) and slow (K<0.005). The curves of release of P, N, Ca, Mg, Na and K in function of time are presented and discussed.     

Sphagna of the 1979 Projeto Flora Amazônica expedition

Within the great expanse of the Brazilian Amazon Basin,Sphagnum has been greatly overlooked, in part because of its scarcity and in part because of the paucity of trained bryological collectors in the area. During a Projeto Flora Amazônica expedition in 1979, seven specimens ofSphagnum were collected, representing six species, five of which are newly described:S. amazonicum, S. dimorphophyllum, andS. subsecundoides in sectionSphagnum;S. curicuriariense andS. ripense in sect.Subsecunda. Also discussed areS. negrense Mitt. andS. sanguinale Warnst.