What are the reasons for the Prussian carp expansion in the upper Elbe River, Czech Republic?

Fifty five Prussian carp Carassius auratus gibelio were radio‐tracked weekly along the course of the upper Elbe River, for 15 months. In addition, diurnal movements were observed in three different habitat types (main channel, navigation canal and floodplain areas). Fish species composition from 10 fish ladders was regularly analysed in 1996, 2000 and 2001, and patterns of juvenile (0+ year) fish distribution and abundance were collected in 2000 and 2001, to support telemetric data on longitudinal migrations, and habitat preference within the studied stretch. Downstream migrations dominated in all seasons, being most intensive in spring and reaching a maximum distance of 85 km. Migration stopped when specimens found a floodplain area, where they occupied larger home ranges compared to the main channel. Migrations upstream of up to 2 km were rare, and specimens did not enter fish ladders. Spontaneous reproduction only occurred on the floodplain and its success was very low. The results suggested that neither upstream migrations, nor spontaneous reproduction represented the key mechanism for the Prussian carp invasion into the Elbe catchment area of the Czech Republic. It can be assumed that escapes from aquaculture activities are primarily responsible for its expansion.     

Rivers as barriers for high elevation amphibians: a phylogeographic analysis of the alpine stream frog of the Hengduan Mountains

At high altitude, rivers may function as barriers for amphibians. We examined 21 populations of Scutiger boulengeri from the Hengduan Mountains with 1038 base pairs of mitochondrial cytochrome b gene sequences. The haplotypes of S. boulengeri formed three clades on the gene tree, and each clade was restricted to one mountain ridge separated by two major river systems, the Yalong River and the Dadu River. The vicariant pattern of the gene tree suggests that these rivers functioned as effective barriers during population differentiation. On the other hand, mountain ridges may have facilitated amphibian movement. Populations within the uninterrupted mountain ranges of clades II and III, revealed little genetic structure. The northern clade I, harboured a substantial amount of genetic variation, which might be the consequence of the rugged terrain and heterogeneous habitat of this area. Furthermore, one outgroup species, Scutiger glandulatus , formed the fourth clade and nested within S. boulengeri , suggesting that S. boulengeri is likely a paraphyletic species or a species complex.     

SHIFT FROM CHLOROPHYTES TO CYANOBACTERIA IN BENTHIC MACROALGAE ALONG A GRADIENT OF NITRATE DEPLETION1

A survey of the spatial distribution of benthic macroalgae in a fluvial lake of the St. Lawrence River (Lake Saint‐Pierre, Quebec, Canada) revealed a shift in composition from chlorophytes to cyanobacteria along the flow path of nutrient‐rich waters originating from tributaries draining farmlands. The link between this shift and changes in water quality characteristics was investigated by sampling at 10 sites along a 15 km transect. Conductivity, current, light extinction, total phosphorus (TP; >25 μg P · L^?1), and ammonium (8–21 μg N · L^?1) remained fairly constant along the transect in contrast to nitrate concentrations, which fell sharply. Filamentous and colonial chlorophytes [Cladophora sp. and Hydrodictyon reticulatum (L.) Bory] dominated in the first 5 km where nitrate concentrations were >240 μg N · L^?1. A mixed assemblage of chlorophytes and cyanobacteria characterized a 1 km transition zone where nitrate decreased to 40–80 μg N · L^?1. In the last section of the transect, nitrate concentrations dropped below 10 μg N · L^?1, and cyanobacteria (benthic filamentous mats of Lyngbya wollei Farl. ex Gomont and epiphytic colonies of Gloeotrichia) dominated the benthic community. The predominance of nitrogen‐fixing, potentially toxic cyanobacteria likely resulted from excessive nutrient loads and may affect nutrient and trophic dynamics in the river.     

Formation,Transport and Retention of Aggregates in a River‐Lake System (Spree,Germany)

The formation, particle size distribution, structure and retention of aggregates were studied in a river‐lake system of the lowland River Spree and factors influencing these processes were evaluated. Samples were taken from the inflow and outflow of a flushed lake, as well as along the adjacent flowing reach of the River Spree, between April 2001 and May 2002. The aim was to record the influence of the seasons and different turbulence intensities on the size, shape, composition, abundance and transport properties of the particles. As additional parameters, the phytoplankton biomass, the concentration of suspended particulate matter, the concentrations of nutrients and the discharge were measured. The abundance of the particles showed a strong seasonality in the investigated period, which closely correlated with the concentrations of suspended particulate matter and particulate organic matter in the water column. The organic carbon content of the suspended matter varied between 37% (dry weight) in summer and about 14% in winter. The concentration of particles ranged between 500 and 2500 particles/ml. The number of particles was significantly lower upstream from the lake than at the downstream transects. The majority of the aggregates in the River Spree were smaller than 500 µm, most of the particles even showing a diameter less than 50 µm. Many particles, above all algae, were washed out of the lake Neuendorfer See into the adjacent flowing reach of the River Spree. Algae influenced the abundance of the particles and contributed to the formation of aggregates with their stickiness. In the river flowing section large particles were formed by turbulence structures, whilst simultaneously the number of smaller particles decreased in the water column caused by aggregation processes. In general, an increasing flow velocity and discharge rate resulted in a larger amount of aggregates in the water column. On the other hand, particle abundance was reduced in the flow direction when the flow velocity was low. Under these conditions particles were retained by sedimentation and benthic filter‐feeding. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Aquatic Macrophyte Approach to Assess the Impact of Disturbances on the Diversity of the Ecosystem and on River Quality

Disturbance has long been recognized as an important determinant of community characteristics in aquatic systems. The aims of our study were to evaluate the impact of different disturbances on the macrophyte diversity and on river quality. To this end, we investigated the floristic composition for different stretches impacted by disturbances and we tested both diversity indices and the trophic index (IBMR) “Biological Index Macrophytes in Rivers” in the Moselle river (NE of France). The river was divided into four sections of different lengths based on uniformity of morphological characteristics, substrate conditions and flowing velocity: the upper, the wild, the resectioned and the downstream Moselle. Floristic composition and water chemical parameters were analysed from 1999 to 2001. The man‐made increase of nutrient concentration favoured the floristic richness in the last sites of the upper Moselle, whereas river dynamics and floods did not allow the development of vegetation in the wild Moselle. Disturbances caused by industrial sewage and eutrophication allowed the spreading of pollu‐tolerant and riparian alien species. The aquatic macrophyte approach is a useful means to detect impact of disturbances on diversity and on river quality. However, it was not effective in assessing disturbances such as flood overflow or chemical pollution. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

西江广东鲂天然繁殖场生态环境调查与评价

2001年在广东鲂产卵期间,对广东鲂天然繁殖场西江水系中两大渔场设立6个监测点进行水质监测分析,并对该水域水质现状作出环境评价。分析了水温、pH值、溶解氧、氨氮、磷酸盐、亚硝酸盐等二十个监测项目,其中青皮塘只有磷酸盐一项超标,超标率为100%,其余均未超标;罗旁超标项目三项,其中悬浮物、磷酸盐超标率为100%、氨氮超标率为33.3%,其余项目未超标。采用均值型综合污染指数评价法对两渔场水质进行评价,两渔场磷酸盐污染最为严重,分担率青皮塘为63.49%,罗旁为46.09%,综合污染指数均值青皮塘为0.59,罗旁为0.52,均属轻度污染。     

Pre- and post-impoundment studies (1978–1982) in the Volta River below the Akosombo Dam with particular emphasis on the microbiology

A four year's survey of the Volta River below the Akosombo Dam to determine the distributional pattern and activities of different bacterial groups during pre- and post-impoundment of the river at Kpong is reported. The bacterial numbers were high and showed variations in all the stations. Relatively low bacterial numbers were observed in the upper reaches. The different bacterial groups followed approximately the same pattern over the entire length of the river. Industrial and domestic wastes slightly affected the quality of the water. The entire system was well oxygenated. During pre-impoundment studies the oxygen condition improved as the water flows downstream. Early post-impoundment studies showed a decrease in dissolved oxygen concentration around the middle reaches and an increase below the Kpong Dam. An emergence of Ceratophyllum demersum, Potamogeton octandrus, Vallisneria aegyptica and aquatic snails, which carry bilharzia parasites, was observed in the Kpong Headpond during post-impoundment studies. There was an extensive growth of submerged aquatic plants in the lower reaches.     

Structural changes and dynamics of the phytoplankton along a highly polluted lowland river of Argentina

The phytoplankton of the Matanza-Riachuelo river (Buenos Aires, Argentina) was studied for a period of 15 months together with different physical and chemical variables, along an increasingly eutrophic in character downstream. 281 taxa were recorded within a seasonal succession, among these 49 percent were euglenophyta, 25 percent bacillariophyta, 15 percent chlorophyta and 10 percent cyanophyta. Multivariate procedures included cluster analyses and ordination by PCA of both species and samples, and stepwise multiple regression analyses were employed to assess the impact of the pollution on the phytoplankton. The effect of the alteration was different in each studied site. With one exception, the changes in the community structure described herein involved modifications of the basic species composition. According to the species present, it was deduced that the main pollutant was the high concentration of organic matter. Results of the Matanza-Riachuelo, Reconquista, and Luján Rivers studies are further discussed.