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Km Downstream (km + downstream)
Selected AbstractsElevation of gene expression for salmon gonadotropin-releasing hormone in discrete brain loci of prespawning chum salmon during upstream migrationDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2005Takeshi Onuma Abstract Our previous studies suggested that salmon gonadotropin-releasing hormone (sGnRH) neurons regulate both final maturation and migratory behavior in homing salmonids. Activation of sGnRH neurons can occur during upstream migration. We therefore examined expression of genes encoding the precursors of sGnRH, sGnRH-I, and sGnRH-II, in discrete forebrain loci of prespawning chum salmon, Oncorhynchus keta. Fish were captured from 1997 through 1999 along their homing pathway: coastal areas, a midway of the river, 4 km downstream of the natal hatchery, and the hatchery. Amounts of sGnRH mRNAs in fresh frozen sections including the olfactory bulb (OB), terminal nerve (TN), ventral telencephalon (VT), nucleus preopticus parvocellularis anterioris (PPa), and nucleus preopticus magnocellularis (PM) were determined by quantitative real-time polymerase chain reactions. The amounts of sGnRH-II mRNA were higher than those of sGnRH-I mRNA, while they showed similar changes during upstream migration. In the OB and TN, the amounts of sGnRH mRNAs elevated from the coast to the natal hatchery. In the VT and PPa, they elevated along with the progress of final maturation. Such elevation was also observed in the rostroventral, middle, and dorsocaudal parts of the PM. The amounts of gonadotropin II, and somatolactin mRNAs in the pituitary also increased consistently with the elevation of gene expression for sGnRH. These results, in combination with lines of previous evidence, indicate that sGnRH neurons are activated in almost all the forebrain loci during the last phases of spawning migration, resulting in coordination of final gonadal maturation and migratory behavior to the spawning ground. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005 [source] Stream geomorphology in a mountain lake district: hydraulic geometry, sediment sources and sinks, and downstream lake effectsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2007C. D. Arp Abstract Lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels. Lakes in the Sawtooth Mountains, Idaho, USA, were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions. First, we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake. To expand on these observations and understand the role of glacial legacy, we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes, meadows (filled lakes), and no past or present lakes. Downstream hydraulic geometry relationships were weak for both the single catchment and regionally. Our data show that downstream patterns in sediment size, channel shape, sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources (hillslopes and tributaries) and sediment sinks (lakes). Stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size, where outlets are wide and shallow with coarse sediment, and inlets are narrow and deep with finer sediment. Meadow outlets and lake outlets show similarities in the coarse-sediment fraction and channel capacity, but meadow outlets have a smaller fine-sediment fraction and nearly mobile sediment. Estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2,4 km downstream, but full recovery may not be reached within 20 km downstream. These results suggest that sediment sinks, such as lakes, in addition to sources, such as tributaries, are important local controls on mountain drainage networks. Copyright © 2006 John Wiley & Sons, Ltd. [source] Lateral movement of common carp (Cyprinus carpio L.) in a large lowland river and floodplainECOLOGY OF FRESHWATER FISH, Issue 1 2009M. J. Jones Abstract,,, Common carp (Cyprinus carpio L.) are a major freshwater invader and knowledge of their movements is important for planning control efforts. To investigate the movement patterns of common carp, radio-tags were implanted into 46 adult fish; 37 near a large floodplain wetland, the Barmah-Millewa forest, and 9 in the Murray River approximately 175 km upstream. Tagged fish were located every second week between August 1999 and March 2001. Common carp occupied total linear ranges (TLR) between 0.4 and 238 km (mean 30 ± 61 km), with 25 fish (62.5%) occupying a TLR < 10 km. Two fish made large distance movements approximately 650 km downstream. Fish sex, the number of locations, time at large, or tagging location explained little variability (P > 0.05) in TLR. Monthly distance from release varied from 0.04 to 238 km (mean 15 ± 44 km), and was not significantly related to river discharge and water temperature, but 29 of 31 (93.5%) fish tagged at Barmah moved from the Murray River into adjacent floodplain habitats upon flooding. Five fish (12.5%) moved large distances (>127 km) upstream of the Barmah-Millewa forest. Fourteen fish (35%) showed site fidelity to within 20 m and usually occupied one or two home sites. Twenty-six fish (65%) showed site fidelity to within 100 m occupying up to five sites during the study period. Movement patterns of common carp were complex, and individuals exhibited different strategies, which is typical of invasive species. Efforts to control and potentially reduce common carp populations in regulated river-floodplain environments should target key floodplain access points and over-wintering habitats to reduce adult biomass, spawning and recruitment levels. [source] Biomarker study of a municipal effluent dispersion plume in two species of freshwater musselsENVIRONMENTAL TOXICOLOGY, Issue 3 2002F. Gagné Abstract The toxicological effects of a primary-treated municipal effluent plume were investigated in two species of freshwater mussels, Elliptio complanata and Dreissena polymorpha, exposed for 62 days at sites upstream and downstream of an effluent outfall in the St. Lawrence River (Quebec, Canada). Levels of metallothioneins (MT), cytochrome P4501A1 activity, DNA damage, total lipids, relative levels of vitellins, and phagocytic activity (in E. complanata hemocytes) were determined after the exposure period. A parallel analysis measured heavy metals and coprostanol in mussel tissues. The results show that significant levels of coprostanol and some metals (specifically, Cu, Hg, Sb, Se, and Zn) had accumulated in mussels caged 5 km downstream of the effluent plume. Mixed-function oxidase activity, MT in gills, total lipids, DNA damage (in D. polymorpha only), and total hemolymph bacteria (in E. complanata only) had increased in these mussels, while levels of total cadmium (Cd), MT in digestive glands or whole soft tissues, phagocytic activity, and DNA damage in the digestive gland (in E. complanata only) were diminished. The exposure of mussels to surface waters contaminated by a municipal effluent led to many stress responses, depending on both the tissues and the species being examined. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 149,159, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10046 [source] Immunocompetence of bivalve hemocytes as evaluated by a miniaturized phagocytosis assayENVIRONMENTAL TOXICOLOGY, Issue 3 2002C. Blaise Abstract Immune function in bivalves can be adversely affected by long-term exposure to environmental contaminants. Investigating alterations in immunity can therefore yield relevant information about the relationship between exposure to environmental contaminants and susceptibility to infectious diseases. We have developed a rapid, cost-effective, and miniaturized immunocompetence assay to evaluate the phagocytic activity, viability, and concentration of hemocytes in freshwater and marine bivalves. Preliminary experiments were performed to optimize various aspects of the assay including 1) the time required for adherence of hemocytes to polystyrene microplate wells, 2) the time required for internalization of fluorescent bacteria, 3) the ratio of hemocytes to fluorescent bacteria in relation to phagocytosis, 4) hemolymph plasma requirements, and 5) the elimination of fluorescence from (noninternalized) bacteria adhering to the external surface of hemocytes. The results of these experiments showed the optimal adherence time for hemocytes in microplate wells to be 1 h, that phagocytosis required at least 2 h of contact with fluorescently labeled E. coli cells, that the number of fluorescent E. coli cells had a positive effect on phagocytic activity, that at least 2.5 million cells/mL were required to measure a significant intake, and that a linear increase in uptake of bacteria (R = 0.91; p < 0.01) could be obtained with concentrations of up to 1.3 × 106 hemocytes/mL. Afterward, the assay was used in two field studies to identify sites having the potential to affect the immunocompetence of bivalves. The first study was conducted on Mya arenaria clams collected at selected contaminated sites in the Saguenay River (Quebec, Canada), and the second examined Elliptio complanata freshwater bivalves that had been exposed to a municipal effluent plume in the St. Lawrence River (Quebec, Canada). In the Saguenay River field study a significant increase in phagocytosis was observed at sites closest to polluted areas. Phagocytotic activity varied over time and was highest during the warmest months (June, July, and August), closely paralleling the spawning period of Mya arenaria clams. In contrast, a drop in phagocytic activity was observed in Elliptio complanata mussels exposed to surface water 4 km downstream of a major municipal effluent plume, with a concomitant increase in the number of hemocytes in the hemolymph. It appears that both immunosuppressive and immunostimulative effects are likely to occur in the field and that responses will be influenced by the type and intensity of contaminants at play. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 160,169, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10047 [source] Occurrence and fate of micropollutants in the Vidy Bay of Lake Geneva, Switzerland.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2010Part II: Micropollutant removal between wastewater, raw drinking water Abstract The occurrence and removal of 58 pharmaceuticals, endocrine disruptors, corrosion inhibitors, biocides, and pesticides, were assessed in the wastewater treatment plant (WWTP) of the city of Lausanne, Switzerland, as well as in the effluent-receiving water body, the Vidy Bay of Lake Geneva. An analytical screening method to simultaneously measure all of the 58 micropollutants was developed based on ultra performance liquid chromatography coupled to a tandem mass spectrometer (UPLC-MS/MS). The selection of pharmaceuticals was primarily based on a prioritization study, which designated them as environmentally relevant for the Lake Geneva region. Except for the endocrine disruptor 17,-ethinylestradiol, all substances were detected in 24-h composite samples of wastewater entering the WWTP or in the treated effluent. Of these compounds, 40% were also detected in raw drinking water, pumped from the lake 3,km downstream of the WWTP. The contributions of dilution and degradation to micropollutant elimination between the WWTP outlet and the raw drinking water intake were established in different model scenarios using hypothetical residence times of the wastewater in Vidy Bay of 1, 4, or 90 d. Concentration decrease due to processes other than dilution was observed for diclofenac, beta-blockers, several antibiotics, corrosion inhibitors, and pesticides. Measured environmental concentrations (MECs) of pharmaceuticals were compared to the predicted environmental concentrations (PECs) determined in the prioritization study and agreed within one order of magnitude, but MECs were typically greater than the corresponding PECs. Predicted no-effect concentrations of the analgesic paracetamol, and the two antibiotics ciprofloxacin and sulfamethoxazole, were exceeded in raw drinking water samples and therefore present a potential risk to the ecosystem. Environ. Toxicol. Chem. 2010; 29:1658,1668. © 2010 SETAC [source] Antidepressants and their metabolites in municipal wastewater, and downstream exposure in an urban watershedENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2010Chris D. Metcalfe Abstract Antidepressants are a widely prescribed group of pharmaceuticals that can be biotransformed in humans to biologically active metabolites. In the present study, the distribution of six antidepressants (venlafaxine, bupropion, fluoxetine, sertraline, citalopram, and paroxetine) and five of their metabolites was determined in a municipal wastewater treatment plant (WWTP) and at sites downstream of two WWTPs in the Grand River watershed in southern Ontario, Canada. Fathead minnows (Pimephales promelas) caged in the Grand River downstream of a WWTP were also evaluated for accumulated antidepressants. Finally, drinking water was analyzed from a treatment plant that takes its water from the Grand River 17 km downstream of a WWTP. In municipal wastewater, the antidepressant compounds present in the highest concentrations (i.e., >0.5 µg/L) were venlafaxine and its two demethylation products, O - and N -desmethyl venlafaxine. Removal rates of the target analytes in a WWTP were approximately 40%. These compounds persisted in river water samples collected at sites up to several kilometers downstream of discharges from WWTPs. Venlafaxine, citalopram, and sertraline, and demethylated metabolites were detected in fathead minnows caged 10 m below the discharge from a WWTP, but concentrations were all <7 µg/kg wet weight. Venlafaxine and bupropion were detected at very low (<0.005 µg/L) concentrations in untreated drinking water, but these compounds were not detected in treated drinking water. The present study illustrates that data are needed on the distribution in the aquatic environment of both the parent compound and the biologically active metabolites of pharmaceuticals. Environ. Toxicol. Chem. 2010;29:79,89. © 2009 SETAC [source] Trout density and health in a stream with variable water temperatures and trace element concentrations: Does a cold-water source attract trout to increased metal exposure?ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2009David D. Harper Abstract A history of hard-rock mining has resulted in elevated concentrations of heavy metals in Prickly Pear Creek (MT, USA). Remediation has improved water quality; however, dissolved zinc and cadmium concentrations still exceed U.S. Environmental Protection Agency water-quality criteria. Physical habitat, salmonid density, fish health, and water quality were assessed, and metal concentrations in fish tissues, biofilm, and macroinvertebrates were determined to evaluate the existing condition in the watershed. Cadmium, zinc, and lead concentrations in fish tissues, biofilm, and invertebrates were significantly greater than those at the upstream reference site and an experimental site farther downstream of the confluence. Fish densities were greatest, and habitat quality for trout was better, downstream of the confluence, where water temperatures were relatively cool (16°C). Measures of fish health (tissue metal residues, histology, metallothionein concentrations, and necropsies), however, indicate that the health of trout at this site was negatively affected. Trout were in colder but more contaminated water and were subjected to increased trace element exposures and associated health effects. Maximum water temperatures in Prickly Pear Creek were significantly lower directly below Spring Creek (16°C) compared to those at an experimental site 10 km downstream (26°C). Trout will avoid dissolved metals at concentrations below those measured in Prickly Pear Creek; however, our results suggest that the preference of trout to use cool water temperatures may supersede behaviors to avoid heavy metals. [source] Risk assessment of Magnacide® H herbicide at Río Colorado irrigation channels (Argentina). tier 3: Studies on native speciesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007Andrés Venturino Abstract We evaluated the potential environmental risk of the herbicide Magnacide® (Baker Petrolite, TX, USA) using native species from Argentina, representing the ecosystem at the Irrigation Corporation (CORFO) channels at the Colorado River mouth, Buenos Aires, Argentina. Six species including fish, toads, snails, crustaceans, and insects were selected to perform studies on acute toxicity and repeated exposure effects. Magnacide H susceptibility ranking was Bufo arenarum (lethal concentration 50 [LC50] = 0.023 mg/L), Onchorhynchus mykiss (LC50 = 0.038 mg/L), Heleobia parchappii (LC50 = 0.21 mg/L), Hyalella curvispina (LC50 = 0.24 mg/L), Simulium spp. (LC50 = 0.60 mg/L), and Chironomus spp. (LC50 = 2.83 mg/L). The risk limit of 10th percentile (0.013 mg/L) determined by probit analysis on sensitivity distribution was similar to the one calculated from literature data. Risk assessment based on field application data suggested lethal exposures for more than 70 to 90% of the species up to 20 km downstream from the application point. Repeated exposures to Magnacide H of amphibian larvae at the lowest-observed-effect concentration caused some effects during the first exposure, but without cumulative effects. Amphipods were insensitive to repeated exposures, showing no cumulative effects. Whether short-term exposures may result in long-term sublethal effects on the organism's life history was not addressed by these laboratory tests. In conclusion, tier 3 studies indicate that Magnacide H application schedule is extremely toxic for most native species at CORFO,Río Colorado channels, representing a high potential risk in the environment. The real environmental impact must be addressed by field studies at tier 4 giving more information on population effects and communities. [source] Distribution of degradation products of alkylphenol ethoxylates near sewage treatment plants in the lower Great Lakes, North AmericaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000Erin R. Bennett Abstract Degradation of alkylphenol ethoxylate (APEO) surfactants in the environment leads to the formation of relatively hydrophobic compounds such as nonylphenol (NP), octylphenol (OP), nonylphenol monoethoxylate (NP1EO), and nonylphenol diethoxylate (NP2EO) that have been shown to have estrogenic activity. Previous studies have shown that sewage treatment plants (STPs) are point sources for these compounds in the aquatic environment. We collected sediment samples at several sites in the vicinity of STPs in Hamilton Harbour and in the Detroit River to determine the spatial distribution of the degradation products of APEOs. In addition, we deployed semipermeable membrane devices (SPMDs) and caged freshwater mussels (Elliptio complanata) at these locations to determine the distribution of these compounds in the dissolved phase and their potential to bioaccumulate in aquatic organisms. The NP, OP, NP1EO, and NP2EO were found at ,g/g (dry wt.) concentrations in sediments and accumulated to ng/g (wet wt.) concentrations in caged mussels near the STPs. However, in the Detroit River, the concentrations of these compounds declined to near background levels in the sediments, water column (i.e., SPMDs), and biota at stations about 1 km downstream from STPs. At stations in Hamilton Harbour, concentrations of APEO degradation products also declined markedly in sediments and SPMDs located a few hundred meters from the STP. These data indicate that degradation products of APEOs can be accumulated by biota near STPs. However, the environmental distribution of these compounds is localized to areas close to the point of discharge. [source] Stochastic Study of Solute Transport in a Nonstationary MediumGROUND WATER, Issue 2 2006Bill X. Hu A Lagrangian stochastic approach is applied to develop a method of moment for solute transport in a physically and chemically nonstationary medium. Stochastic governing equations for mean solute flux and solute covariance are analytically obtained in the first-order accuracy of log conductivity and/or chemical sorption variances and solved numerically using the finite-difference method. The developed method, the numerical method of moments (NMM), is used to predict radionuclide solute transport processes in the saturated zone below the Yucca Mountain project area. The mean, variance, and upper bound of the radionuclide mass flux through a control plane 5 km downstream of the footprint of the repository are calculated. According to their chemical sorption capacities, the various radionuclear chemicals are grouped as nonreactive, weakly sorbing, and strongly sorbing chemicals. The NMM method is used to study their transport processes and influence factors. To verify the method of moments, a Monte Carlo simulation is conducted for nonreactive chemical transport. Results indicate the results from the two methods are consistent, but the NMM method is computationally more efficient than the Monte Carlo method. This study adds to the ongoing debate in the literature on the effect of heterogeneity on solute transport prediction, especially on prediction uncertainty, by showing that the standard derivation of solute flux is larger than the mean solute flux even when the hydraulic conductivity within each geological layer is mild. This study provides a method that may become an efficient calculation tool for many environmental projects. [source] Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater streamHYDROLOGICAL PROCESSES, Issue 14 2008Daniel H. Doctor Abstract The stable isotopic composition of dissolved inorganic carbon (,13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed ,13C-DIC increased between 3,5, from the stream source to the outlet weir approximately 0·5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in ,13C-DIC of 2·4 ± 0·1, per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased ,13C-DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream ,13C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in ,13C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, ,13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrological importance of an unusual hazard in a mountainous basin: flood and landslideHYDROLOGICAL PROCESSES, Issue 14 2006Umesh K. Haritashya Abstract The Bhagirathi River, a proglacial melt water stream of the Gangotri Glacier, is the principal source of the Ganges river system. The upper part of the basin lies in the high altitude region of the Garhwal Himalayas and is extensively covered by glaciers. We provide hydro-meteorological insight into a severe storm that produced unusual high rains in June 2000 in the uppermost part of the Bhagirathi River. This storm was concentrated upstream of Gangotri town and triggered landslides/rockslides at several locations between the glacier snout and Gangotri town. One of the major rockslides blocked the Bhagirathi River at Bhujbas, about 3 km downstream of the Gangotri Glacier snout, creating an artificial lake at this location. High stream flow in the river, generated by rapid runoff response from mountain slopes along with melt runoff from the glacier, quickly increased the level of water stored in the artificial lake. Daily rainfall in this region rarely exceeds 10 mm, while total rainfall during this 6-day storm was 131·5 mm. This unusual rain event occurred during the tourist season in June, consequently trapping a large number of tourists and vendors in this area. Sudden release of stored water generated floods that created havoc downstream of the artificially created lake. This paper presents the hydrological and meteorological information related to such an unusual and devastating event observed in the high altitude region of the Himalayas. Copyright © 2006 John Wiley & Sons, Ltd. [source] Patternizing of impoundment impact (1985,2002) on fish assemblages in a lowland river using the Kohonen algorithmJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2005T. Penczak Summary Impoundment impact on fish assemblage structure was investigated in the dammed middle course of the Warta River. A backwater site (AB) was located 2 km upstream of the Jeziorsko Reservoir, and a tailwater site (CD) 1.5 km downstream of the dam. Both sites were studied for 3 years in the pre-impoundment period (1985,1987) and 15 years after damming (1988,2002). Quantitative electrofishing in spring and autumn assured obtaining yearly average biomass for each population. Most of the data analysis aimed to assess the dam impact on the fish assemblage structure but other accompanying impacts such as discharge manipulations, revetment, different forms of engineering, and water quality improvement in the tailwater and backwater reaches were also discussed. The Kohonen algorithm (self-organizing map, SOM) was used for the analysis, and perfectly separated AB and CD samples into two clusters. Samples from the backwater (AB) proved that this reach of the Warta River had maintained its almost natural character and that fish assemblages had changed moderately, now occupying only five neighbouring hexagons out of a total of 16. In the tailwater (CD), however, because of considerable fluctuations in fish assemblages the SOM produced three subclusters, which engaged nine hexagons: (i) the pre-impoundment period (1985,1987, two hexagons); (ii) 7 years after the definite closure of dam sluices (1988,1994, five hexagons); and (iii) the past 8 years of sampling (1995,2002, two hexagons), when stabilization in the assemblage was observed. The SOM also definitely proved profound changes in fish assemblage composition: most lithophilous species declined and many phytolithophilous and phytophilous species became dominants, particularly in the tailwater site where downstream migration of 0+ of successfully spawned species from the reservoir took place. [source] Riverine, estuarine and marine migratory behaviour and physiology of wild and hatchery-reared coho salmon Oncorhynchus kisutch (Walbaum) smolts descending the Campbell River, BC, CanadaJOURNAL OF FISH BIOLOGY, Issue 3 2008C. M. Chittenden Eighty coho salmon Oncorhynchus kisutch smolts (40 wild and 40 hatchery-reared) were surgically implanted with acoustic transmitters and released into the Quinsam River over 2 days. Differences in physiology, travel time and migratory behaviour were examined between wild and hatchery-reared fish. In addition, tagged and control fish of both wild and hatchery-reared stock were raised for 3 months following surgery to compare survival and tag retention. Detection ranges of the acoustic receivers were tested in the river, estuary and ocean in a variety of flow conditions and tide levels. Receivers were placed in the river, estuary and up to 50 km north and south from the river mouth in the marine environment. Wild smolts were significantly smaller by mass, fork length and condition factor than hatchery-reared smolts and exhibited significantly higher levels of sodium, potassium and chloride in their blood plasma than hatchery-reared smolts. The gill Na+K+ -ATPase activity was also significantly higher in the wild coho smolts at the time of release. Ninety-eight per cent of wild and 80% of hatchery-reared fish survived to the estuary, 8 km downstream of the release site. No difference was found in migration speed, timing or survival between smolts released during daylight and those released after dark. Wild smolts, however, spent less time in the river and estuary, and as a result entered the ocean earlier than hatchery-reared smolts. Average marine swimming speeds for wild smolts were double those of their hatchery-reared counterparts. While hatchery smolts dispersed in both a northward and southward direction upon entering the marine environment, the majority of wild smolts travelled north from the Campbell River estuary. The wild coho salmon smolts were more physiologically fit and ready to enter sea water than the hatchery-reared smolts, and as a result had higher early survival rates and swimming speeds. [source] Nitrogen Sources and Sinks Within the Middle Rio Grande, New Mexico,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2007Gretchen P. Oelsner Abstract:, Relationships between discharge, land use, and nitrogen sources and sinks were developed using 5 years of synoptic sampling along a 300 km reach of the Rio Grande in central New Mexico. Average river discharge was higher during 2001 and 2005 "wet years" (15 m3/s) than during the drought years of 2002-04 "dry years" (8.9 m3/s), but there were no differences in nitrogen loading from wastewater treatment plants (WWTPs) which were the largest and most consistent source of nitrogen to the river (1,330 kg/day). Average total dissolved nitrogen (TDN) concentrations remained elevated for 180 km downstream of the Albuquerque WWTP averaging 1.2 mg/l in wet years and 0.52 mg/l in dry years. Possible explanations for the constant elevated TDN concentrations downstream of the major point source include reduced nitrogen retention capacity, minimal contact with riparian or channel vegetation, large suspended sediment loads, and low algal biomass. Somewhat surprisingly, agricultural return flows had lower average nitrogen concentrations than river water originally diverted to agriculture in both wet (0.81 mg/l) and dry years (0.19 mg/l), indicating that the agricultural system is a sink for nitrogen. Lower average nitrogen concentrations in the river during the dry years can be explained by the input of agricultural returns which comprise the majority of river flow in dry years. [source] The sodium tail of MercuryMETEORITICS & PLANETARY SCIENCE, Issue 9 2002A. E. POTTER However, when the angle of the ecliptic is near maximum in the northern hemisphere, and Mercury is near its greatest eastern elongation, it can be seen against the western sky for about a half hour after sunset. During these times, we were able to map sodium D2 emission streaming from the planet, forming a long comet-like tail. On 2001 May 26 (U.T.) we mapped the tail downstream to a distance of ,40 000 km. Sodium velocities in the tail increased to ,11 km s,1 at 40 000 km as the result of radiation pressure acceleration. On 2000 June 5 (U.T.) we mapped the cross-sectional extent of the tail at a distance of ,17 500 km downstream. At this distance, the half-power full-width of the emission was ,20 000 km. We estimated the transverse velocity of sodium in the tail to range from 2 to 4 km s,1. The velocities we observed imply source velocities from the planet surface of the order of 5 km s,1, or 4 eV. Particle sputtering is a likely candidate for production of sodium atoms at these velocities. The total flux of sodium in the tail was ,1 times 1023 atoms s,1, which corresponds to 1 to 10% of the estimated total production rate of sodium on the planet. [source] | ||||||||||||||||