Littoral and shoreline wood in mid‐continent great rivers (USA)

Woody debris has several important roles in running water. Less is known about the ecology of wood in great rivers than in smaller rivers and streams. We used a probability survey to estimate the abundance of littoral and shoreline wood along the following mid‐continent great rivers of the United States in summer 2004–2006: the Missouri River, Upper Mississippi River, and the Ohio River. We counted wood pieces >0.3 m in diameter from a zone between the bank full level out into the river 10 m. We categorized wood according to its origin and function as “beached” (transported from upriver but not providing aquatic habitat), “wet” (origin unknown and providing aquatic habitat; includes snags), or “anchored” (attached to the bank at its current location and providing aquatic habitat). We counted 5900 pieces of wood at 447 sites across rivers. Approximately 56 percent of pieces were beached, 30 percent were wet, and 14 percent were anchored. Overall, mean abundance of wood was 2.6 pieces of wood 100 m^?1 of shoreline (approximately 3.0 m³ 100 m^?1). Abundance of wood (pieces per unit distance of river) was much lower than has been reported for many smaller streams and rivers. There was more wood along the Upper Mississippi River (3.3 pieces 100 m^?1) than elsewhere (≤2.4 pieces 100 m^?1). The mean abundance of wood on the Ohio River decreased significantly between the 2004 and 2005 survey periods due to high flows. Longitudinal patterns in wood abundance were weak. There was less anchored and wet wood along shorelines protected by revetment (e.g., rip rap). There was generally more wood along shorelines where the riparian land use was characterized as forest rather than agriculture or developed. Mean abundance of wood along forested, un‐revetted shorelines was approximately four pieces 100 m^?1 of shoreline (= 80 pieces km^?1 of river). This estimate of mean wood abundance for what amounts to least disturbed riparian and shoreline conditions is relevant for great river bioassessment and management. Published in 2009 John Wiley & Sons, Ltd.     

Asymmetric Hybridization of Pink (Oncorhynchus gorbuscha) and Chinook (O. tshawytscha) Salmon in the St. Marys River,Michigan

Natural hybridization between pink salmon (Oncorhynchus gorbuscha) and Chinook salmon (O. tshawytscha) has been observed only in the Great Lakes, where both species have been introduced. The direction of hybridization between these species is poorly understood, thus the present study analyzed mitochondrial DNA (mtDNA) to determine whether the maternal parents were pink or Chinook salmon. During annual salmon population surveys on the St. Marys River (1998–2002), fifty putative hybrids of pink salmon and Chinook salmon were identified from meristic, morphometric and color characters. We designed primers to amplify a fragment of the mitochondrial D-loop control region that included both a variable and a control restriction site (BstNI). Polymerase chain reaction, restriction endonuclease digestion and capillary electrophoresis of mtDNA were used in order to identify the maternal parent of each hybrid salmon. In addition, the amplified fragments from the three fish species were sequenced to further verify the results. All hybrid salmon specimens were found to possess Chinook salmon mtDNA, indicating that hybridization between Chinook salmon and pink salmon is asymmetrical and likely unidirectional, occurring only between male pink salmon and female Chinook salmon. Influences contributing to the hybridization of these salmonid species could include limited spatial and temporal segregation of spawners, sexual selection, a limiting number of Chinook males, and/or physiological factors.     

Temporal and spatial trends of organochlorines and mercury in fishes from the St. Clair River/Lake St. Clair corridor,Canada

The temporal and spatial relationships of a suite of organochlorine contaminants and mercury were examined in various fish species of the St. Clair River/Lake St. Clair corridor, Canada, in order to evaluate the effectiveness of remediation efforts and to assess the risk to human and wildlife fish consumers. In Lake St. Clair, fish tissue concentrations of mercury, polychlorinated biphenyls (PCBs), octachlorostyrene (OCS), hexachlorobenzene (HCB), and dichlorodiphenyltrichloroethane (DDT) decreased consistently from the 1970s until the 1980s and 1990s, after which the rate of contaminant decline slowed or concentrations stabilized. This trend was consistent in up to 13 species (both young-of-the-year and adult fishes) comprising different trophic positions and dietary habits, suggesting that the changes were reflective of ambient conditions rather than food web processes. Elevated concentrations of mercury, PCBs, OCS, HCB, and DDT were detected in St. Clair River young-of-the-year spottail shiner compared with fish from Lake Huron, indicating that non-atmospheric inputs of these chemicals, likely originating from sediment, remain in the St. Clair River. Current concentrations of mercury and PCBs, and mercury, PCBs, and DDT remain of concern to human and wildlife fish consumers, respectively. Given that contaminant decreases have generally stabilized in fish, we suggest that further natural recovery of contaminants in St. Clair corridor fishes will be slow since contaminants will likely continue to be influenced by sediment levels.     

Investigation of viruses in Diporeia spp. from the Laurentian Great Lakes and Owasco Lake as potential stressors of declining populations

The benthic amphipod Diporeia is an ecologically and biogeochemically important constituent of deep freshwater lakes in North America. The proliferation of dreissenid mussels in the mid-1990s coincided with a sharp decrease in Diporeia populations in several Laurentian Great Lakes; however the ultimate cause and mechanisms of their decline are still unknown. Here we examined the composition of DNA viruses associated with Diporeia collected from populations of Lake Michigan that had declined and stable populations in Lake Superior and Owasco Lake (Finger Lake in central New York State). Viral metagenomic libraries from Owasco Lake and Lake Superior were comprised primarily of bacteriophages, which may infect bacteria within the amphipod microbiome. In contrast, the metagenomic library from Lake Michigan contained well-represented ssDNA circular viral genomes. The prevalence and viral load of one putative Type V ssDNA circular virus (LM29173) that recruited almost 30% of total viral sequence reads in the Lake Michigan library was analyzed by quantitative PCR. The prevalence of LM29173 was over two orders of magnitude greater in Lake Michigan compared to the other two lakes. Although further research is necessary to establish the pathology and epidemiological extent of viral-Diporeia interactions, our data suggest that viruses may be numerically significant constituents of the Diporeia microbiome, and if pathogenic some of these viruses may be a stressor of Great Lakes Diporeia populations. Our data further indicate that special attention should be given to the circovirus that was prevalent in the declining Michigan population but uncommon in the other two lakes.     

探索南水北调西线工程两利双赢方案——原西南电管局局长、资深专家王尊相访谈录

南水北调西线工程是被称为世界上规模最大的调水工程。西线调水将会严重影响西电东送。西水北调是解决问题的两利双赢方案。这样浩大的工程必须遵照党中央的指导方针,尊重科学、尊重实践、尊重专家,广泛听取意见,多方论证,使决策符合实际,减少失误。     

Comparison of the interannual and interdecadal variability of heavy flood characteristics upstream and downstream from dams in inversed hydrologic regime: Case study of Matawin River (Québec,Canada)

Erected in 1930, the Matawin Dam caused an inversion of the hydrologic regime of the Matawin River: snow‐melt water in spring (April to June) is stored in the reservoir and then released in winter (January to March) to feed the hydroelectric generating stations built downstream on the Saint‐Maurice River. Thus, heavy floods occur upstream from the dam in spring but downstream in winter. We compared the interannual and interdecadal variability of the heavy flood characteristics (magnitude, duration, frequency and variability) both upstream (spring floods) and downstream (winter floods) from the dam during the 1934–1994 period. This comparison revealed that the principal change observed downstream from the dam translates into a strong increase in the duration (in days) of heavy floods. The average duration of these floods quintupled. This change in duration occurred around the mid‐1960s and thus led to a significant decrease in the magnitude, frequency and variability of heavy floods. It also altered the relationship between the climate indices and these fundamental characteristics (magnitude, frequency and duration). Downstream from the dam, the magnitude and frequency are positively correlated to the Atlantic multidecadal oscillation (AMO), whereas upstream they are negatively correlated to the same index. However, the AMO index is negatively correlated to the duration downstream from the dam, whereas upstream this characteristic is no longer significantly correlated to any climatic index. Two factors have been invoked to explain this change observed downstream from the dam.

• The cooling observed since the 1960s at the station located at the dam. However, this cooling was not observed on the scale of the entire watershed. This reduces its plausibility.
• The increase in hydroelectric power production in the watershed after nationalization of hydroelectric power in 1962. This increase would be explained by the expansion of the market for hydroelectric power (national and international markets). Before nationalization, the hydroelectric power produced in the watershed was intended only for regional industries.

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