Downstream Decrease Research Articles

Simulation of Facet Dendritic Shape of Isothermal Alloy in a Forced Flow by Phase Field Method

Numerical simulation based on a new regularized phase field model was performed to describe the dendritic growth of an isothermal alloy with a strong anisotropy in the presence of a forced flow. These results indicate that a crystal grow into an equiaxial facet dendritic in the absence of a forced flow and into an asymmetrical facet dendritic in the presence of a forced flow. With increasing a flow velocity, the tip steady velocity of upstream dendritic arm increases, that of the downstream arm decreases, and that of the perpendicular arms increases at first, and then decreases, the perpendicular arms gradually grow toward the incoming flow direction. In the certain range of anisotropy parameter, when γ is larger than 0.14, dendritic tip steady velocities in all direction are expected to reach their own saturation values. In addition, the effect of a compound forced flow on an isothermal facet dendritic is similar to experimental results.

Plasma transition at the flanks of the Venus ionosheath: Evidence from the Venus Express data

[1] Measurements conducted with the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) instrument in the Venus Express spacecraft reveal the presence of a plasma transition within a boundary layer that extends along at the flanks of the Venus ionosheath and where the solar wind exhibits changes similar to those reported from previous missions (Mariner 5, Venera, and Pioneer Venus). At the plasma transition there is a sharp downstream decrease in the density of the solar wind electrons and a sudden increase in their temperature embedded within the boundary layer where more gradual changes in the speed, temperature, and density of the solar wind ions are observed. The ASPERA-4 data also show important fluxes of planetary ions measured downstream from the plasma transition and whose dominant velocity component is in the Sun-Venus direction. The speed of those ions is slower than the local solar wind speed and thus is different from that expected from the convective electric field acceleration in which both speed values should be comparable. The boundary layer is interpreted as representing a feature that results from the transport of solar wind momentum to the Venus upper ionosphere, and the ASPERA-4 data provide information on the kinetic properties of the eroded planetary ion population that is seen to stream mostly in the Sun-Venus direction. From the comparison of the ASPERA-4 measurements with those of the magnetic field obtained with the magnetometer of the Venus Express, it is found that in the near wake crossing of the plasma transition the magnetic field intensity decreases to lower values with downstream distance from the planet in agreement with measurements conducted with the Mariner 5 and the PVO. From the analysis of data for orbits with evidence of the plasma transition within the boundary layer, it is found that the momentum flux of planetary ions measured in the wake can be accounted for from the incident momentum flux of the solar wind protons implying an approximate balance as would result from the transport of solar wind momentum to the planetary particles.

Sedimentary Characteristics of the Gravel-Sand Transition in the River Rhine

Abstract A gravel-bed river often changes abruptly into a sand-bed river. The causes of such so-called gravel–sand transitions have been elucidated in recent years, but detailed observations of gravel–sand transitions in large rivers are scarce. The present study fills this knowledge gap by investigating the sedimentary characteristics of the gravel–sand transition in the river Rhine. Data on bed composition and flow characteristics are used, in combination with a novel method for the evaluation of the bed structure. The analysis shows that, in contrast to common belief, the bed structure in the gravel–sand transition zone does not change from fully clast supported to fully matrix supported. Instead, there is a strong cross-stream variation in bed structure, especially upstream of the transition zone. The analysis also shows that the downstream decrease in gravel mobility in the gravel–sand transition zone, which is usually attributed to the change in bed structure and the so-called patchiness effect, is at least partly caused by the larger-scale bend sorting process, which concentrates gravel in outer bends where it is only infrequently mobile. Dune sorting, which has been suggested to have an effect on the gravel mobility similar to that of bend sorting, was found to be relatively unimportant in the Rhine, partly because it is strongly counteracted by armoring processes that affect an uncommonly thick sediment layer. The gravel–sand transition in the Rhine, with its length of 50 km, is much less abrupt than the gravel–sand transitions of smaller rivers reported on in the literature. Although the dependence of the transition length on river size intuitively is correct, the exact causes remain unclear.

Diel cycling and stable isotopes of dissolved oxygen, dissolved inorganic carbon, and nitrogenous species in a stream receiving treated municipal sewage

Diel and synoptic studies were undertaken in Silver Bow Creek, a small, highly eutrophic stream receiving municipal sewage from the city of Butte, Montana, USA. During mid-summer baseflow conditions, oxidation of ammonium from the Butte wastewater treatment plant created a 2-km long reach marked by nightly hypoxia and extreme growth of aquatic plants and algae. Large diel cycles in the concentrations and isotopic compositions of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were inversely related, and are explained by the daily cycle of photosynthesis and respiration, modified by the effects of nitrification. Nitrification rates were higher during the day than at night due to a combination of higher water temperatures and higher DO concentrations. Changes in nitrification rate imparted diel cycles in the concentrations and N-isotopic compositions of NO 3 − and NH 4 +, whereas total dissolved inorganic nitrogen (DIN) concentrations and δ 15N-DIN values showed minimal diel variation. δ 15N-NH 4 steadily increased with distance downstream over a 5 km reach, whereas δ 15N-NO 3 showed a more complex spatial pattern. Plant assimilation caused downstream decreases in DIN and soluble reactive phosphorous: however, it was not possible to determine whether the plants assimilated NO 3 −, NH 4 +, or both. An important new finding of this study is the recognition that synoptic and diel changes in δ 18O-DO in the zone of active nitrification imparted a corresponding change in δ 18O-NO 3. Future studies examining the O-isotope composition of nitrate need to consider whether DO has a constant or shifting isotopic composition at the source of nitrification. The results of this study underscore the complex and dynamic interactions between biologically-active solutes in nutrient-rich streams, and also emphasize the importance of recognizing these cycles when collecting samples for scientific or monitoring purposes.

Longitudinal zonation of macroinvertebrates in an Ecuadorian glacier‐fed stream: do tropical glacial systems fit the temperate model?

Summary1. The ecology of glacier‐fed streams at temperate latitudes has been intensely studied in recent years, leading to the development of a well‐validated conceptual model on the longitudinal distribution of macroinvertebrate communities downstream of the glacier margin (Freshwater Biology, 2001a; 46, 1833). However, to our knowledge, the ecology of tropical glacier‐fed streams has not yet been studied.2. We sampled benthic macroinvertebrates and measured environmental variables at nine sites between 4730 and 4225 m altitude along a 4.3 km stretch of a glacier‐fed stream 40 km south of the equator in the Ecuadorian Andes. Our goal was to study the longitudinal distribution of the fauna in relation to environmental factors and to compare this with the conceptual model based on temperate–arctic glacier‐fed streams.3. Total density of invertebrates differed considerably at the two highest altitude sites; 4600 m−2 at a pro‐glacial lake outlet and only 4 m−2 at a site originating directly from the glacier snout. Otherwise, there was a downstream decrease in density to about 825 m−2 at the three lowest sites. Taxon richness increased with distance from the glacier, very similar to the pattern predicted. A total of 28 taxa were collected; two at the glacier snout, seven at the nearby pro‐glacial lake outlet, 13 at site 2 (<400 m from the glacier) and 20 at the lowest sites.4. The numerical percentage of Chironomidae (Diptera) decreased downstream from 100 to 44%. The subfamily Podonominae was numerous at the highest sites but became much less important further downstream. The Orthocladiinae were important both in numbers and species at all sites, while Diamesinae were numerous only in the middle of the reach studied and were completely absent from the upper three sites. The limited importance of the Diamesinae, and its replacement by Podonominae, is different from the pattern typically observed in north‐temperate glacier‐fed streams. This could be because of the fact that the genus Diamesa is missing from the Neotropics.5. Stream temperature and channel stability explained most of the variability in faunal composition and richness, supporting the model. Stability increased systematically downstream while temperature did not. Surprisingly, no classical kryal zone (Tmax < 4 °C) was found, as even the site closest to the glacier snout (50 m) had a Tmax of 15 °C and no site had Tmax < 8 °C. We propose that this might be a general feature of equatorial glacial streams.

Evaluation of the ecological status of an impaired watershed by using a multi-index approach

The objective of this study was to use an integrative approach to assess the ecological status of a small river impacted by multiple sources of disturbance. The River Febros (NW Portugal) is a small and highly impacted non-regulated river; approximately 44% of the watershed area is dedicated to agriculture, but there is also some urbanization. Environmental status was evaluated using a new multi-index approach, combining quality indices for water (Water Quality Index (WQI)), benthic macroinvertebrates (Iberian Biological Monitoring Working Party Index (IBMWP)), and human modification (Riparian Forest Quality Index (QBR)); Ecological Status River Mediterranean Index (ECOSTRIMED); River Habitat Survey (RHS)). Surveys were carried out between October 2002 and 2003, along four stretches of the main course of the river for physicochemical characteristics, as well as water microbiology and macroinvertebrates. Water quality was poor at all sites (WQI averaged 30.4%) and decreased downstream. The RHS (assessment of instream habitats and the river corridor) and the QBR quantification displayed the same trend. Macroinvertebrates diversity was permanently low with only the most tolerant insects taxa present; oligochaetes dominated. The ecological status of River Febros was well represented using the experimental assessment system, where a downstream decrease in condition was noticeable (in spite of a lower water quality upstream). Our results emphasize the importance of assessing several components of disturbed ecosystems in order to ascertain overall quality and the importance of promoting improvement of the riparian gallery as a buffer against multiple agents of disturbance.

3-Hydroxymethyl coenzyme A reductase inhibition attenuates spontaneous smooth muscle tone via RhoA/ROCK pathway regulated by RhoA prenylation

RhoA prenylation may play an important step in the translocation of RhoA in the basal internal anal sphincter (IAS) smooth muscle tone. Statins inhibit downstream posttranslational RhoA prenylation by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibition (HMGCRI). The role of statins in relation to RhoA prenylation in the pathophysiology of the spontaneously tonic smooth muscle has not been investigated. In the present studies, we determined the effect of classical HMGCRI simvastatin on the basal IAS tone and RhoA prenylation and in the levels of RhoA/Rho kinase (ROCK) in the cytosolic vs. membrane fractions of the smooth muscle. Simvastatin produced concentration-dependent decrease in the IAS tone (via direct actions at the smooth muscle cells). The decrease in the IAS tone by simvastatin was associated with the decrease in the prenylation of RhoA, as well as RhoA/ROCK in the membrane fractions of the IAS, in the basal state. The inhibitory effects of the HMGCRI were completely reversible by geranylgeranyltransferase substrate geranylgeranyl pyrophosphate. Relaxation of the IAS smooth muscle via HMGCRI simvastatin is mediated via the downstream decrease in the levels of RhoA prenylation and ROCK activity. Studies support the concept that RhoA prenylation leading to RhoA/ROCK translocation followed by activation is important for the basal tone in the IAS. Data suggest that the role of HMG-CoA reductase may go beyond cholesterol biosynthesis, such as the regulation of the smooth muscle tone. The studies have important implications in the pathophysiological mechanisms and in the novel therapeutic approaches for anorectal motility disorders.

Nutrient dynamics in streams and the role ofJ-NABS

Nutrient dynamics in streams has been an important topic of research since the 1960s. Here we review this topic and the significant role played by J-NABS in its development. We limit this review almost exclusively to studies of N and P because these elements have been shown to limit productivity in streams. We use the expression nutrient dynamics for studies that included some measures of biological processes occurring within streams. Prior to the 1970s, instream biological processes were little studied, but through 1985 conceptual advances were made, and 4 types of studies made important contributions to our understanding of instream processes: 1) evidence of increased plant production and decomposition in response to nutrient addition, 2) studies showing a downstream decrease in nutrient concentrations, 3) studies using radioisotopes, and 4) budget studies. Beginning with the first paper printed in its first issue, J-NABS has been the outlet for key papers advancing our understanding of rates and controls of nutrient dynamics in streams. In the first few years, an important review and a conceptual model for conducting experiments to study nutrient dynamics in streams were published in J-NABS. In the 1990s, J-NABS published a number of papers on nutrient recycling within algal communities, the role of the hyporheic zone, the role of spawning fish, and the coupling of data from field 15 N additions and a N-cycling model to provide a synoptic view of N dynamics in streams. Since 2000, J-NABS has published influential studies on nutrient criteria for streams, rates of and controls on nitrification and denitrification, uptake of stream nutrients by riparian vegetation, and nutrient dynamics in urban streams. Nutrient dynamics will certainly continue to be an important topic in J-NABS. Topics needing further study include techniques for studying nutrient dynamics, nutrient dynamics in larger streams and rivers, the ultimate fate of nutrients taken up by plants and microbes in streams, ecological stoichiometry, the effects of climate change, and the role of streams and rivers in nutrient transformation and retention at the landscape scale.

Effects of sediment pollution on food webs in a tropical river (Borneo, Indonesia)

The impact of pollution on the trophic ecology of the Kelian River (Borneo, Indonesia) was studied by comparing food webs (on the basis of gut analysis and field and laboratory observations) at six sites. The upper sites were in pristine rainforest but the river became increasingly polluted downstream, largely owing to sedimentation from alluvial gold mining activities. Four previous studies all showed a downstream decrease in macroinvertebrates (mean abundance: 272 per 400 cm2 at Site 1 dropped to 2.6 at Site 6; mean number of taxa: 37.6 at Site 1 down to 1.6 at Site 6), and this was highly correlated with suspended solids. Food webs also reflected the effect of pollution. Cleaner sites had more complex food webs, with more elements, links, higher linkage density and higher complexity than did downstream polluted sites, which lacked grazers, shredders and filterers. Several taxa that were grazers at clean sites became collector-gatherers at polluted sites. Despite the enormous impact of pollution, cessation of alluvial mining activities resulted in some recovery. The resilience of the fauna is likely to be enhanced by the tropical conditions with high rainfall, rapid flow rates and high temperatures, coupled with rapid life cycles. Fish distribution and diets did not appear to be affected by pollution.

Longitudinal assessment of the effect of concentration on stream N uptake rates in an urbanizing watershed

We examined the effect of concentration on nitrogen uptake patterns for a suburban stream in Maryland and addressed the question: How does NO3 − uptake change as a function of concentration and how do uptake patterns compare with those found for NH4 +? We applied a longitudinal (stream channel corridor) approach in a forested stream section and conducted short-term nutrient addition experiments in late summer 2004. In the downstream direction, NO3 − concentrations decreased because of residential development in headwaters and downstream dilution; NH4 + concentrations slightly increased. The uptake patterns for NO3 − were very different from NH4 +. While NH4 + had a typical negative relationship between first-order uptake rate constant (K c ) and stream size, NO3 − had a reverse pattern. We found differences for other metrics, including uptake velocity (V f ) and areal uptake rate (U). We attributed these differences to a stream size effect, a concentration effect and a biological uptake capacity effect. For NO3 − these combined effects produced a downstream increase in K c , V f and U; for NH4 + they produced a downstream decrease in K c and V f , and a not well defined pattern for U. We attributed a downstream increase in NO3 − uptake capacity to an increase in hyporheic exchange and a likely increase in carbon availability. We also found that K c and V f were indirectly related with concentration. Similar evidence of ‘nutrient saturation’ has been reported in other recent studies. Our results suggest that higher-order uptake models might be warranted when scaling NO3 − uptake across watersheds that are subject to increased nitrogen loading.

Spatial and temporal evolution of a terminal fluvial fan system: the Permian Organ Rock Formation, South‐east Utah, USA

AbstractThe recognition of terminal fluvial systems, otherwise termed ‘terminal fans’ or ‘distributary fluvial fan systems’, preserved in the ancient rock record is based primarily on the recognition of facies characteristics indicative of a progressive downstream decrease in: (i) fluvial discharge; (ii) channel depth and width; (iii) lateral and vertical connectivity of channel‐fill elements; and (iv) evidence for channellized flow and a systematic increase in: (i) evidence for sheetflood deposition; (ii) aeolian and/or playa deposits; and (iii) channel bifurcation. However, despite these criteria having been applied previously to a variety of outcrop successions, there is still no unifying facies model that adequately accounts for the complex stratigraphic architectural relationships expected for such systems, based on the varied styles of fluvial activity and system interaction known from modern examples. Moreover, few previous studies have given significant consideration to the long‐term temporal evolution of terminal fluvial fans. These issues are addressed by this study of the Permian (Leonardian/Artinskian) Organ Rock Formation of the Paradox Basin, South‐east Utah. A detailed stratigraphic framework based on 84 sedimentary logs demonstrates proximal to distal variations in sedimentary style. Integration of these data with high‐resolution architectural panels depicting the geometry and facies characteristics of individual fluvial elements has enabled the development of a series of depositional models that account for both the spatial and temporal evolution of the system and which are representative of: (i) initial progradation of the fluvial system into the Paradox foreland basin; (ii) retreat of the fluvial system and expansion of a distal aeolian dune system; (iii) the final phase of fluvial progradation following aeolian dune deflation; and (iv) the final retrogradation of the fluvial system back towards the hinterland.

Downstream trends in sediment size and composition of channel-bed, bar, and bank deposits related to hydrologic and lithologic controls in the Llano River watershed, central Texas, USA

The downstream fining of fluvial sediments is a fundamental tenet of drainage systems and, for decades, has been the subject of considerable research. Most of this research has focused on variability in channel-bed material. Other sedimentological components such as channel bars and banks, however, represent distinctively different processes occurring at various flow magnitudes and durations and thus provide an opportunity to examine a more comprehensive set of controls on the larger fluvial system. This study analyses downstream patterns of sediment size and composition for channel-bed material, bars, and banks in the Llano River watershed (11,568 km 2) in central Texas, USA. Fluvial deposits in the study area were characterized through field, laboratory, and statistical analyses and standard sedimentary indices ( d 16, d 50, d 84, sorting) were computed. Two hundred thirty-eight sediment samples were collected at 15 sites along the main-stem channel with sampling occurring at the low-flow channel (thalweg), lateral bars, banks, and overbank locations. Channel-bar deposits are characterized by a downstream reduction in particle size, but low-flow-channel deposits have a substantially weaker trend, a discrepancy possibly attributed to uniformity and continuity of hydraulic sorting mechanisms during moderate and high flows. Channel-bar deposits reveal an abrupt downstream reduction in gravel size in the upper watershed, which is attributed to an increase in drainage area. Further, an abrupt gravel-to-sand transition occurs immediately downstream of a distinct lithologic change from mostly carbonate rocks to igneous and metamorphic rocks. The downstream decrease in channel-bar particle size occurs despite an increasingly constricted alluvial valley, commonly associated with greater unit stream power and relatively coarse sediment. Contrasting with channel-bed material, particle size of channel banks increases downstream, which is attributed to the addition of sand-sized sediment from igneous and metamorphic rocks. The consideration of distinctive sedimentological components of a dynamic fluvial system represents a more comprehensive and nuanced study of the topic of downstream sediment trends than prior studies, which is important to a range of engineering, biological, and planning issues at the watershed scale.

Dissolved inorganic carbon concentrations and stable carbon isotope ratios in streams polluted by variable amounts of acid mine drainage

Summary Dissolved inorganic carbon (DIC) concentrations and stable carbon isotopes of DIC (δ13CDIC) were determined in streams polluted by acid mine drainage (AMD). The aim was to assess the effects of variable AMD contamination on DIC dynamics and δ13CDIC. The stream with relatively high metal (e.g., Fe, Al, Mn) concentrations exhibited downstream decreases in pH because production of protons by the chemical evolution of AMD exceeded the stream’s buffering capacity. DIC dynamics in this stream was driven by proton-enhanced CO2 degassing. In the stream with lower metal concentrations, the protons were neutralized by HCO 3 - and pH increased in the downstream direction. In this stream, DIC dynamics was driven by CO2 loss due to higher partial pressure of CO2 (pCO2) in stream water compared to atmospheric. In both contaminated watersheds, CO2 loss resulted in seasonal exports of HCO 3 - was dehydrated to CO2(aq), how CO2 was lost from the streams, and if carbon in DIC was exchanged with atmospheric CO2. The δ13CDIC was enriched by 3.0‰ when CO2 loss was neutralization induced and CO2 loss was accompanied by partial exchange of carbon between DIC and atmospheric CO2. We conclude that DIC loss and δ13CDIC enrichment in AMD-contaminated streams depends on the rate of production and amount of protons produced by metal hydrolysis, the stream’s buffering capacity, and the mechanism of CO2 loss.

A conceptual model for the longitudinal distribution of wood in mountain streams

AbstractWood load, channel parameters and valley parameters were surveyed in 50 contiguous stream segments each 25 m in length along 12 streams in the Colorado Front Range. Length and diameter of each piece of wood were measured, and the orientation of each piece was tallied as a ramp, buried, bridge or unattached. These data were then used to evaluate longitudinal patterns of wood distribution in forested headwater streams of the Colorado Front Range, and potential channel‐, valley‐ and watershed‐scale controls on these patterns. We hypothesized that (i) wood load decreases downstream, (ii) wood is non‐randomly distributed at channel lengths of tens to hundreds of meters as a result of the presence of wood jams and (iii) the proportion of wood clustered into jams increases with drainage area as a result of downstream increases in relative capacity of a stream to transport wood introduced from the adjacent riparian zone and valley bottom. Results indicate a progressive downstream decrease in wood load within channels, and correlations between wood load and drainage area, elevation, channel width, bed gradient and total stream power. Results support the first and second hypotheses, but are inconclusive with respect to the third hypothesis. Wood is non‐randomly distributed at lengths of tens to hundreds of meters, but the proportion of pieces in jams reaches a maximum at intermediate downstream distances within the study area. We use these results to propose a conceptual model illustrating downstream trends in wood within streams of the Colorado Front Range. Copyright © 2009 John Wiley & Sons, Ltd.

Numerical simulation of facet dendritic growth in a forced flow

A numerical simulation based on a new regularized phase-field model is developed to describe the silicon solidification in a forced flow. The effect of forced flow, anisotropy, and mesh grid on dendritic growth shape is investigated. These results indicate that crystals grow into an equiaxial facet dendritic without flow and into an asymmetrical facet dendritic with flow, that is, upstream arm growth is promoted, and downstream inhibited, however, there is no such effect on perpendicular arms. It is also found that the asymmetrical growth feature becomes noticeable with increase in the flow velocity. With the increase in the anisotropy value, the tip velocities of upstream and downstream decrease gradually.

Surface complexation effects on phosphate adsorption to ferric iron oxyhydroxides along pH and salinity gradients in estuaries and coastal aquifers

Non-conservative behavior of dissolved inorganic phosphate (DIP) in estuaries is generally ascribed to desorption from iron and aluminum (hydr)oxides with increasing salinity. Here, we assess this hypothesis by simulating the reversible adsorption of phosphate onto a model oxide (goethite) along physico-chemical gradients representative of surface and subsurface estuaries. The simulations are carried out using a surface complexation model (SCM), which represents the main aqueous speciation and adsorption reactions of DIP, plus the ionic strength-dependent coulombic interactions in solution and at the mineral–solution interface. According to the model calculations, variations in pH and salinity alone are unlikely to explain the often reported production of DIP in surface estuaries. In particular, increased aqueous complexation of phosphate by Mg 2+ and Ca 2+ ions with increasing salinity is offset by the formation of ternary Mg-phosphate surface complexes and the drop in electrical potential at the mineral–water interface. However, when taking into account the downstream decrease in the abundance of sorption sites, the model correctly simulates the observed release of DIP in the Scheldt estuary. The sharp increase in pH accompanying the admixing of seawater to fresh groundwater should also cause desorption of phosphate from iron oxyhydroxides during seawater intrusion in coastal aquifers. As for surface estuaries, the model calculations indicate that significant DIP release additionally requires a reduction in the phosphate sorption site density. In anoxic aquifers, this can result from the supply of seawater sulfate and the subsequent reductive dissolution of iron oxyhydroxides coupled to microbial sulfate reduction.

The river before damming: distribution and ecological notes on the endemic species Echinogammarus cari (Amphipoda: Gammaridae) in the Dobra River and its tributaries, Croatia

The endemic species Echinogammarus cari (Karaman 1931) is the only species of this genus present in the Black Sea drainage basin of Croatia. The species is known only from its type locality, the Bistrac spring. Since little is known about the distribution and ecology of this amphipod species, research was conducted to determine the extent of its distribution in the Dobra River and its tributaries, part of which will be flooded on the completion of a 52.5 m high dam in 2009. Sampling was conducted at 10 study sites in the drainage area of the sinking Gornja Dobra and at 19 study sites in the Gojacka Dobra, including measurement of physicochemical parameters. To examine microdistribution of this species, samples were collected on moss and on stony substrate. The species is confined to first 15 km of the Gojacka Dobra, its tributary streams Bistrica and Ribnjak, while it is absent in the drainage area of the Gornja Dobra. At all sites where it was recorded, it coexists with Gammarus fossarum, and its relative abundance was significantly higher on moss microhabitats, while G. fossarum was more abundant on a stony substrate. The downstream decrease in the relative abundance of E. cari could be related to the longitudinal decrease in conductivity and the increase of water temperature fluctuations. After the completion of the dam, 60% of the presently known distribution area of E. cari will be flooded. Consequently, the species is likely to become endangered.

Channel incision, evolution and potential recovery in the Walla Walla and Tucannon River basins, northwestern USA

AbstractWe evaluated controls on locations of channel incision, variation in channel evolution pathways and the time required to reconnect incised channels to their historical floodplains in the Walla Walla and Tucannon River basins, northwestern USA. Controls on incision locations are hierarchically nested. A first‐order geological control defines locations of channels prone to incision, and a second‐order control determines which of these channels are incised. Channels prone to incision are reaches with silt‐dominated valley fills, which have sediment source areas dominated by loess deposits and channel slopes less than 0·1(area)−0·45. Among channels prone to incision, channels below a second slope–area threshold (slope = 0·15(area)−0·8) did not incise. Once incised, channels follow two different evolution models. Small, deeply incised channels follow Model I, which is characterized by the absence of a significant widening phase following incision. Widening is limited by accumulation of bank failure deposits at the base of banks, which reduces lateral channel migration. Larger channels follow Model II, in which widening is followed by development of an inset floodplain and aggradation. In contrast to patterns observed elsewhere, we found the widest incised channels upstream of narrower reaches, which reflects a downstream decrease in bed load supply. Based on literature values of floodplain aggradation rates, we estimate recovery times for incised channels (the time required to reconnect to the historical floodplain) between 60 and 275 years. Restoration actions such as allowing modest beaver recolonization can decrease recovery time by 17–33 per cent. Published in 2007 by John Wiley & Sons, Ltd.

Particulate and dissolved amino acids in the lower Mississippi and Pearl Rivers (USA)

In this study, we present seasonal changes (monthly samples from September 2001 to August 2003) in the abundance and composition of dissolved and particulate amino acids, at one station in the lower Mississippi and Pearl Rivers (LA, MS: USA). Spatial changes over a 4-day transmit from river km 390 to river mouth (Head of Passes, LA) in the Mississippi River, and a two-day downstream sampling from Jackson (MS) to Stennis Space Center (MS) were also determined. Temporal data in the lower Mississippi River showed significantly lower concentrations of dissolved combined amino acids (DCAA, 0.8 to 2.2 μM) and dissolved amino acids in high molecular weight fraction (HMW DAA, 0.2–0.4 μM) than in the Pearl River (DCAA, 1.4–4.3 μM; HMW DAA, 0.4–1.4 μM). Dissolved free amino acids (DFAA) were significantly lower than DCAA in both rivers, and displayed minimal seasonal variability. DCAA, HMW DAA, and particulate amino acids (PAA) were generally higher during high-flow periods, which may have suggested dominance in terrestrial sources. Carbon-normalized yield of PAA (%C-PAA) was generally higher during low-flow conditions and positively correlated with chlorophyll-a (chl-a), reflective of in situ sources. Downstream variability in the lower Mississippi River showed stable DCAA concentrations, a decline in PAA (from 1.06 to 0.43 μM), and a gradual increase in mole percent of non-protein amino acids (%NPAA). This likely reflected bacterial degradation of phytoplankton biomass during falling discharge. Nitrogen-normalized yield of PAA (%N-PAA) was inversely correlated with PAA ( R = − 0.7, n = 48), indicative of short-term sedimentation and resuspension events. Conversely, downstream decreases in DCAA and middle-reach peaks of PAA and %N-PAA in the Pearl River, likely resulted from photochemical degradation of DOM as well as algal production during base-flow conditions. The comparisons in abundance and composition of DAA and PAA in these different river systems provides important information on in situ nitrogen and carbon cycling as related to riverine inputs of organic matter to coastal ocean.

Silibinin’s effect on total EGFR, Erb-b2, and Erb-b3 expression in human colon cancer

14124 Purpose: Flavonoid, silibinin, has been shown to have strong chemotherapeutic activity in prostate, breast, bladder, skin, ovarian, and colon cancer. It has no documented LD50 and has been proven safe in multiple animal models and human trials. Cell cycle arrest and inhibition of protein levels of various cyclins are commonly reported in silibinin’s mechanism of action. We investigated silibinin’s activity on upstream cell-signaling targets, EGFR, Erb-b2, Erb-b3, Akt, Erk1/2, and mTOR, using three human colon cancer cells lines: Fet, Geo, HCT 116. Methods: The MTT cell-viability assay and FACS analysis were performed after silibinin treatment to substantiate its effect on proliferation and cell-cycle. Western blots for EGFR, Erb-b2, Erb-b3, Erk1/2, Akt, and mTOR were completed and quantified with densitometry. Standardization of protein loading was confirmed with cytoskeletal and house-keeping proteins, B-actin and GAPDH. Means were contrasted using analysis of variance with Dunnet’s correction for multiple testing. All statistical testing was two-sided with a significance level of 5%. Results: The MTT assay revealed a dose-dependent inhibitory effect. Treatment of FET and GEO at 75 micrograms/ml resulted in 50% inhibition of cell-viability (IC-50) at 72 hrs. An IC50 dose of 40 ug/ml was established for HCT116. FACS analysis demonstrated statistically significant cell-cycle arrest in all cell lines. G2-M phase arrests in Fet and Geo cell lines (p<0.001) and a G1 arrest in HCT116 (p=0.005) were noted. Western blots showed decreased protein level expressions of total and phospho-EGFR, Erb-b2, Erb-b3, Akt, Erk1/2, and mTOR. Conclusions: Inhibition of protein expression levels of the Erb-b family of receptor tyrosine kinases plays a role in the mechanism of silibinin’s action. Strong inhibition of protein levels of total EGFR, Erb-b2, and Erb-b3 was noted as well as downstream decreases in total Erk1/2, Akt, and mTOR. Given silibinin’s inhibition of cancer proliferation and its safety profile, it is a promising compound requiring further mechanistic study, and applications in cancer therapy should be pursued given its effects on the Erb-b class of receptor tyrosine kinases and intermediary proteins, Erk1/2, Akt, and mTOR. No significant financial relationships to disclose.