Impact of dams, dam removal and dam-related river engineering structures on sediment connectivity and channel morphology of the Fugnitz and the Kaja Rivers

In terms of changing flow and sediment regimes of rivers, dams are often regarded as the most dominant form of human impact on fluvial systems. Dams can decrease the flux of water and sediments leading to channel changes such as upstream aggradation and downstream degradation. The opposite effects occur when dams are removed. Channel degradation often requires further intervention in terms of river bed and bank protection works. The situation evolves more complex in river systems that are impacted by a series of dams due to feedback processes between the different system compartments. A number of studies have recently investigated geomorphic systems using connectivity approaches to improve the understanding of geomorphic system response to change. This paper presents a case study investigating the impact of dam construction, dam removal and dam-related river bed and bank protection measures on the sediment connectivity and channel morphology of the Fugnitz and the Kaja Rivers using a combination of DEM analyses, field surveys and landscape evolution modelling. For both river systems the results revealed low sediment connectivity accompanied by a fine river bed sediment facies in river sections upstream of active dams and of removed dams with protection measures. Contrarily, high sediment connectivity which was accompanied by a coarse river bed sediment facies was observed in river sections either located downstream of active dams or of removed dams with upstream protection. In terms of channel changes, significant channel degradation was examined at locations downstream of active dams and of removed dams. Channel bed and bank protection measures prevent erosion and channel slope recovery after dam removal. Landscape evolution modeling revealed a complex geomorphic response to dam construction and dam removal as sediment output rates and therefore geomorphic processes have been shown to act in a non-linear manner. These insights are deemed to have major implications for river management and conservation, as quality and state of riverine habitats are determined by channel morphology and river bed sediment composition.

Sexually Different Growth Histories of the American Eel in Four Rivers in Maine

Growth histories of yellow-phase American eels Anguilla rostrata collected in four rivers in Maine, were back-calculated from sagittal otolith increments. Our objectives were to first determine whether sexually dimorphic growth rates exist and then compare the growth histories of American eels from four rivers within a geographic region. For female eels, the maximum growth rate was 31.9 +/- 1.7 mm/year at age 8, decreasing to 25.1 +/- 2.9 mm/year at age 14. Males attained a maximum of 29.8 +/- 1.6 min/year at age 3, decreasing to a minimum of 17.9 +/- 1.3 mm/year at age 11. Females grew faster than males after age 4 and had a slower reduction in growth rate with age. These faster growth rates among females were similar in all four rivers. The observed growth rates are not consistent with current life history hypotheses and may indicate an alternative life history strategy. Because female eels benefit from a larger size (i.e., size refuge, increased fecundity, and greater niche breadth), they would benefit from a higher-risk growth strategy that increases growth rate during their earlier years and reduces the amount of time spent in an unfavorable size-class. The tradeoffs (i.e., mortality, developmental rate, pathogen resistance, and longevity) associated with this faster growth rate may not favor the males' life history requirements. Male eels do not achieve the size of females and therefore are not subject to the advantages associated with being larger. Therefore, they may use a risk-averse strategy that maintains submaximum growth rates to obtain the minimum size necessary to mature and complete the spawning migration while reducing the adverse affects of faster growth rates. We postulate that, in eels, intrinsic growth rates should be considered a life history trait that has evolved to meet the life history requirements of each sex.

Modelling woody material transport and deposition in alpine rivers

Recent flood events in Switzerland and Western Austria in 2005 were characterised by an increase in impacts and associated losses due to the transport of woody material. As a consequence, protection measures and bridges suffered considerable damages. Furthermore, cross-sectional obstructions due to woody material entrapment caused unexpected flood plain inundations resulting in severe damage to elements at risk. Until now, the transport of woody material is neither sufficiently taken into account nor systematically considered, leading to prediction inaccuracies during the procedure of hazard mapping. To close this gap, we propose a modelling approach that (1) allows the estimation of woody material recruitment from wood-covered banks and flood plains; (2) allows the evaluation of the disposition for woody material entrainment and transport to selected critical configurations along the stream and that (3) enables the delineation of hazard process patterns at these critical configurations. Results from a case study suggest the general applicability of the concept. This contribution to woody material transport analysis refines flood hazard assessments due to the consideration of woody material transport scenarios.

Bedload composition, transport and modification in rivers of Westland, New Zealand, with implications for the distribution of alluvial pounamu (jade)

River bedload surveyed at 50 sites in Westland is dominated by Alpine Schist or Torlesse Greywacke from the Alpine Fault hanging wall, with subordinate Pounamu Ultramafics or footwall-derived Western Province rocks. Tumbling experiments found ultramafics to have the lowest attrition rates, compared with greywacke sandstone and granite (which abrade to produce silt to medium-sand), or incompetent schist (which fragments). Arahura has greater total concentrations (103–105 t/km2) and proportions (5–40%) of ultramafic bedload compared with Hokitika and Taramakau catchments (101–104 t/km2, mostly <10%), matching relative areas of mapped Pounamu Ultramafic bedrock, but enriched relative to absolute areal proportions. Western Province rocks downthrown by the Alpine Fault are under-represented in the bedload. Enriched concentrations of ultramafic bedload decrease rapidly with distance downstream from source rock outcrops, changing near prominent ice-limit moraines. Bedload evolution with transport involves both downstream fining and dilution from tributaries, in a sediment supply regime more strongly influenced by tectonics and the imprint of past glaciation. Treasured New Zealand pounamu (jade) is associated with ultramafic rocks. Chances of discovery vary between catchments, are increased near glacial moraines, and are highest near source-rock outcrops in remote mountain headwaters.

Bursting Boilers and the Federal Power Redux: The Evolution of Safety on the Western Rivers

Using newly constructed data series on explosions, deaths, and steamboat traffic, we examine econometrically the causes of increased safety in steamboat boilers in the nineteenth century. Although the law of 1852 (but not that of 1838) did have a dramatic initial effect in reducing explosions, that reduction came against the background not of a system out of control but of a system that from the beginning was steadily increasing boiler safety per person- mile. The role of the federal government in conducting and disseminating basic research on boiler technology may have been more significant for increased safety than its explicit regulatory efforts.

Abundance and biomass of bacterioplankton in waters of the Kara Sea and the Ob and Yenisey Rivers

Bacterial cell number in the water column of the Kara Sea and estuary areas of the Ob and Yenisey Rivers was determined in water samples collected at 32 stations at depths from the surface to 200 m. The samples were analyzed by direct microscopy. In most parts of the sea microorganism concentrations ranged generally from 103 to 104 cells per ml and their biomasses from milligrams to tens of mg/m**3. Bacterioplankton concentration of river waters was much higher than in the open sea, especially in Ob waters. The highest bacteria concentrations, hundreds of thousands cells per ml with biomass exceeding 200 mg/m**3, were found in the southern part of the Ob section. Minimal concentrations were observed in the northeastern part and near the southeastern part of the Ob section and the southeastern coast of Novaya Zemlya. Dark CO2 fixation rates determined at some stations indicated low bacteria biomass production.

Geochemistry of rivers in norther Germany

In den Jahren 1973 bis 1978 erfolgten umfangreiche mikrobiologische-ökologische Untersuchungen in der Elbe und in einigen kleineren Flüssen Schleswig-Holsteins sowie im Nordostseekanal. In diesem Zusammenhang wurden verschiedene bateriologische und eine Reihe von hydrographisch-chemischen Parametern bestimmt. Die Daten geben Auskunft über den bakteriologischen Zustand der Gewässer in Abhängigkeit von Schwankungen der wichtigsten hydrographischen Faktoren insbsosondere der Temperatur und Wasserführung. Weiter ermöglichen sie Aussagen über die Abwasserbelastung der untersuchten Flüsse.

Mineral content, major oxides and trace elements concentrations in clay from different IODP Holes of 331-C0013, 331-C0017, East China sea shelf and different Taiwan rivers

The Okinawa Trough (OT) in the East Asian continental margin is characterized by thick terrigenous sediment and ubiquitous volcanic-hydrothermal activities. In this study, the clays collected during IODP Expedition 331 to the middle OT (Iheya North Knoll) were analyzed for mineralogical and geochemical compositions. By comparing with the clays from the East China Sea shelf and surrounding rivers, we examine different clay origins. The hydrothermal field in the mid-OT is dominated by Mg-rich chlorite, while the recharge zone has clay mineral assemblages similar to the shelf and rivers, showing high content of illite, subordinate chlorite and kaolinite and scarce smectite. Compared to the terrigenous clays, the hydrothermal clays in the OT have high concentrations of Mg, Mn and Zr but low Fe, Na, K, Ca, Ba, Sr, P, Sc and Ti, while the hydrothermal clays in the mid-ocean ridge are relatively enriched in Fe and V and depleted in Al, Mg, Zr, Sc and Ti. Different fractionation patterns of rare earth elements also register in the terrigenous and hydrothermal clays, diagnostic of variable clay origins. We infer that the OT hydrothermal clay was primarily formed by the chemical alteration of detrital sediments subject to the hydrothermal fluids. The remarkably different compositions of hydrothermal clays between the sediment-rich back arc basin like OT and the sediment-starved ocean ridge suggest different physical and chemical processes of hydrothermal fluids and fluid-rock/sediment reactions under various geologic settings.