Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of River

  • Charle river
  • alluvial river
  • alpine river
  • amazon river
  • braided river
  • canadian river
  • colorado river
  • columbia river
  • danube river
  • ebro river
  • elbe river
  • european river
  • floodplain river
  • freshwater river
  • hudson river
  • joaquin river
  • large river
  • lawrence river
  • lower river
  • lower tana river
  • lowland river
  • main river
  • major river
  • mekong river
  • mississippi river
  • missouri river
  • mountain river
  • murray river
  • new zealand river
  • nile river
  • ohio river
  • other river
  • paraná river
  • peace river
  • pearl river
  • platte river
  • regulated river
  • ross river
  • san joaquin river
  • small river
  • st. lawrence river
  • tana river
  • upper mississippi river
  • warta river
  • yangtze river
  • yellow river
  • zealand river

  • Terms modified by River

  • river area
  • river bank
  • river basin
  • river basin management
  • river basin scale
  • river bend
  • river capture
  • river catchment
  • river channel
  • river confluence
  • river corridor
  • river course
  • river delta
  • river delta region
  • river district
  • river dolphin
  • river downstream
  • river drainage
  • river ecosystem
  • river estuary
  • river fish
  • river flood
  • river floodplain
  • river flow
  • river form
  • river habitat
  • river health
  • river incision
  • river management
  • river morphology
  • river mouth
  • river network
  • river otter
  • river outlet
  • river plume
  • river population
  • river reach
  • river region
  • river regulation
  • river reserve
  • river restoration
  • river restoration project
  • river runoff
  • river sand
  • river section
  • river sediment
  • river segment
  • river site
  • river source
  • river stage
  • river stretch
  • river system
  • river tributary
  • river type
  • river valley
  • river water
  • river water sample
  • river watershed
  • river width
  • river worldwide

  • Selected Abstracts


    ABSTRACT. The catchment of the River Partnach, a torrent situated in a glacial valley in the Northern Calcareous Alps of Bavaria/Germany, was affected by a high-magnitude flood on 22/23 August 2005 with a peak discharge of more than 16 m3s -1 at the spring and about 50 m3s -1 at the catchment outlet. This flood was caused by a long period of intense rainfall with a maximum intensity of 230 mm per day. During this event, a landslide dam, which previously held a small lake, failed. The flood wave originating from the dam breach transported a large volume of sediment (more than 50 000 m3) derived from bank erosion and the massive undercutting of a talus cone. This caused a fundamental transformation of the downstream channel system including the redistribution of large woody debris and channel switching. Using terrestrial survey and aerial photography, erosional and depositional consequences of the event were mapped, pre- and post-event surfaces were compared and the sediment budget of the event calculated for ten consecutive channel reaches downstream of the former lake. According to the calculations more than 100 000 tonnes of sediment were eroded, 75% of which was redeposited within the channel and the proximal floodplain. A previous large flood which occurred a few weeks prior to the August 2005 event had a significant effect on controlling the impact of this event. [source]


    Article first published online: 24 SEP 200
    Lee, J. A.1, Choi, A. R.1, Park, J. H.1 & Chung, I. K2 1Department of Environmental Science, Inje University, Kimhae 621-749, Korea; 2Departement of Marine Science, Pusan National University, Pusan 609-735, Korea Seasonal and spatial variations of phytoplankton community were monitored at 16 sites along the Naktong River. Blue-green algae appeared from May through November with dominant genera of Microcystis, Anabaena, Oscillatoria and Gomphosphaeria. Frequency and biomass of the genera became greater at lower reaches. The Microcystis were observed from May to October up to 85,750cells/ml. Six species of Microcystis were identified with morphological characteristics and M. aeruginosa was most dominant. There were significant relationships between biomass of Microcystis and NO -3, TP and pH in water column. However, NH4+, PO4 -3 and N/P were not critical in successions to the Microcystis dominated community. Microcystis blooms were notable at water temperature higher than 25°C. Microcystis density in sediment was 3 orders of magnitude higher than water column. Anabaena density ranged up to 11,220cells/ml. Four species of Anabaena were identified and A. flos-aquae was most dominant. Anabaena biomass was not related to temperature, NO3 - , TN, PO4 -3, TP and N/P of water column and the frequency of trichome with akinete and/or heterocyte were not related to these parameters. Microcystins were detected from May to November with yearly fluctuations. Microcystin-RR was most dominant. Total 84.2% of algal materials with Microcystis exhibited toxicity of microcystin with maximum of 3,292,g/g dry wt. Total 12.5% of water column with Microcystis exhibited dissolved microcystin up to 3.3,g/l. Microcystin concentrations were positively related to Microcystis biomass and pH of water column. Anatoxin-a was determined by FD-HPLC analysis with NBD-F and all concentrations were below the detection limit of 0.1,g/l. [source]


    David M. Coley
    ABSTRACT: The Peace River at Arcadia, Florida, is a municipal water supply supplement for southwestern Florida. Consequently, probabilities of encountering low flows during the dry season are of critical importance. Since the association between Pacific Ocean sea surface temperatures (SSTs) and seasonal streamflow variability in the southeastern United States is well documented, it is reasonable to generate forecasts based on this information. Here, employing historic records of minimum, mean, and maximum flows during winter (JFM) and spring (AMJ), upper and lower terciles define "above normal,""normal," and "below normal" levels of each variable. A probability distribution model describes the likelihood of these seasonal variables conditioned upon Pacific SSTs from the previous summer (JAS). Model calibration is based upon 40 (of 50) years of record employing stratified random sampling to ensure equal representation from each decade. The model is validated against the remaining 10 samples and the process repeated 100 times. Each conditional probability distribution yields varying probabilities of observing flow variables within defined categories. Generally, a warm (cold) Pacific is associated with higher (lower) flows. To test model skill, the forecast is constrained to be the most probable category in each calibration year, with significance tested by chi-square frequency tables. For all variables, the tables indicate high levels of association between forecast and observed terciles and forecast skill, particularly during winter. During spring the pattern is less clear, possibly due to the variable starting date of the summer rainy season. This simple technique suggests that Pacific SSTs provide a good forecast of low flows. [source]


    Steven W. Effler
    ABSTRACT: The conspicuous shifts in summertime values of common measures of water qualify that have persisted for 10 years (1993 to 2002) in the Seneca River, New York, as a result of the zebra mussel invasion are documented. Resolution of patterns in time and space is supported by water quality monitoring that extends back to the late 1970s. Patterns are evaluated to describe the stability of impacts and quantify metabolic activity of the invader. The water quality impacts that have persisted unabated for 10 years since the invasion are the most severe documented for a river in North America. Changes in summer median conditions since the invasion include: (1) a 16-fold decrease in chlorophyll concentration (Chi), (2) a 2.5-fold increase in Secchi disc transparency, (3) a 17-fold increase in soluble reactive phosphorus concentration, (4) a 3.7-fold increase in total ammonia concentration, (5) a greater than 25 percent decrease in dissolved oxygen (DO) concentration, and (6) a decrease in pH of 0.55 units. The strength of these signatures has been driven by anthropogenic influences that include upstream nutrient loading and morphometric modifications of the river, and the functioning of Cross Lake, through which the river flows. This hypereutrophic lake sustains dense zebra mussel populations and related water quality impacts in the river downstream of the lake outflow by acting as a source of veligers and suitable food for this bivalve. Evidence is presented that levels of metabolic activity of the zebra mussel in this river have been resource limited, manifested through increased consumption of Chl and DO with increased delivery of these constituents in the lake's outflow. [source]


    Baxter E. Vieux
    ABSTRACT: A synthetic relationship is developed between nutrient concentrations and discharge rates at two river gauging sites in the Illinois River Basin. Analysis is performed on data collected by the U.S. Geological Survey (USGS) on nutrients in 1990 through 1997 and 1999 and on discharge rates in 1988 through 1997 and 1999. The Illinois River Basin is in western Arkansas and northeastern Oklahoma and is designated as an Oklahoma Scenic River. Consistently high nutrient concentrations in the river and receiving water bodies conflict with recreational water use, leading to intense stakeholder debate on how best to manage water quality. Results show that the majority of annual phosphorus (P) loading is transported by direct runoff, with high concentrations transported by high discharge rates and low concentrations by low discharge rates. A synthetic relationship is derived and used to generate daily phosphorus concentrations, laying the foundation for analysis of annual loading and evaluation of alternative management practices. Total nitrogen (N) concentration does not have as clear a relationship with discharge. Using a simple regression relationship, annual P loadings are estimated as having a root mean squared error (RMSE) of 39.8 t/yr and 31.9 t/yr and mean absolute percentage errors of 19 percent and 28 percent at Watts and Tahlequah, respectively. P is the limiting nutrient over the full range of discharges. Given that the majority of P is derived from Arkansas, management practices that control P would have the most benefit if applied on the Arkansas side of the border. [source]


    Marty D. Matlock
    ABSTRACT: The lower reaches of the Arroyo Colorado have historically failed to meet their use under subsection 303(b) of the U.S. Clean Water Act due to fecal coliform bacteria and low dissolved oxygen (DO). Fish kills, especially at the tidal confluence at the Port of Harlingen, Texas, have been reported. Oxygen demand from sediment (SOD) for a river typically has two states-diffusion limited SOD (SOD) and potential SOD (pSOD), expressed when sediment is resuspended through increased flow or other disturbances. The objective of this research was to measure SOD in the Arroyo Colorado River in situ, estimate pSOD ex situ, and evaluate the relationship between SOD and the depositional environment. We measured SOD and pSOD in the Arroyo Colorado River at up to eight sites over three sampling events. We identified the sample sites based on a modified Rosgen geomorphic index for streambed stabilization. Sites with high sediment deposition potential had high SOD. The average values of SOD between sites were 0.62 g/m2/day (standard deviation 0.38 g/m2/day) and ranged from 0.13 to 1.2 g/m2/day. Potential SOD values ranged from as low as 19.2 to as high as 2,779 g/m3 sediment/ day. Potential SOD can serve as an indicator of the possible impact of SOD from resuspended sediment in stream systems. [source]


    Jo Beth Mullens
    ABSTRACT: Once referred to as America's "best landscaped sewer," the Connecticut has undergone a dramatic transformation in the last three decades. During this time, a number of public agencies and private organizations have worked diligently to implement policies and measures aimed at improving the river's quality. Ample data collected over the years indicate that the actual water quality conditions of the Connecticut River, as measured by empirical parameters, have improved. However, prior to this study, no data existed regarding the public's perceptions of these changes. This paper will address this issue by presenting the results of a multiyear survey designed to assess the public's perceptions regarding the Connecticut's current quality, and its suitability in supporting various recreational activities. The results suggest that the majority of individuals perceive the Connecticut's water quality to be high enough to support a wide range of recreational activities including those involving physical contact with the water. Additionally, this research concludes that the vast majority of individuals who have recreated on the river for 20 years or more do perceive a significant improvement in the river's overall quality. Thus, it appears that policies and actions taken to improve the Connecticut's quality have been successful in the public's eye. [source]


    Keith H. Nislow
    ABSTRACT: Understanding the effects of dams on the inundation regime of natural floodplain communities is critical for effective decision making on dam management or dam removal. To test the implications of hydrologic alteration by dams for floodplain natural communities, we conducted a combined field and modeling study along two reaches in the Connecticut River Rapids Macrosite (CRRM), one of the last remaining flowing water sections of the Upper Connecticut River. We surveyed multiple channel cross sections at both locations and concurrently identified and surveyed the elevations of important natural communities, native species of concern, and nonnative invasive species. Using a hydrologic model, HEC-RAS, we routed estimated pre-and post-impoundment discharges of different design recurrence intervals (two year through 100 year floods) through each reach to establish corresponding reductions in elevation and effective wetted perimeter following post-dam discharge reductions. By comparing (1) the frequency and duration of flooding of these surfaces before and after impoundment and (2) the total area flooded at different recurrence intervals, our goal was to derive a spatially explicit assessment of hydrologic alteration, directly relevant to natural floodplain communities. Post-impoundment hydrologic alteration profoundly affected the subsequent inundation regime, and this impact was particularly true of higher floodplain terraces. These riparian communities, which were flooded, on average, every 20 to 100 years pre-impoundment, were predicted to flood at 100 , 100 year intervals, essentially isolating them completely from riverine influence. At the pre-dam five to ten year floodplain elevations, we observed smaller differences in predicted flood frequency but substantial differences in the total area flooded and in the average flood duration. For floodplain forests in the Upper Connecticut River, this alteration by impoundment suggests that even if other stresses facing these communities (human development, invasive exotics) were alleviated, this may not be sufficient to restore intact natural communities. More generally, our approach provides a way to combine site specific variables with long term gage records in assessing the restorative potential of dam removal. [source]


    Kent D. Becher
    ABSTRACT: The introduction of nutrients from chemical fertilizer, animal manure, wastewater, and atmospheric deposition to the eastern Iowa environment creates a large potential for nutrient transport in watersheds. Agriculture constitutes 93 percent of all land use in eastern Iowa. As part of the U.S. Geological Survey National Water Quality Assessment Program, water samples were collected (typically monthly) from six small and six large watersheds in eastern Iowa between March 1996 and September 1997. A Geographic Information System (GIS) was used to determine land use and quantify inputs of nitrogen and phosphorus within the study area. Streamliow from the watersheds is to the Mississippi River. Chemical fertilizer and animal manure account for 92 percent of the estimated total nitrogen and 99.9 percent of the estimated total phosphorus input in the study area. Total nitrogen and total phosphorus loads for 1996 were estimated for nine of the 12 rivers and creeks using a minimum variance unbiased estimator model. A seasonal pattern of concentrations and loads was observed. The greatest concentrations and loads occur in the late spring to early summer in conjunction with row-crop fertilizer applications and spring nmoff and again in the late fall to early winter as vegetation goes into dormancy and additional fertilizer is applied to row-crop fields. The three largest rivers in eastern Iowa transported an estimated total of 79,000 metric tons of total nitrogen and 6,800 metric tons of total phosphorus to the Mississippi River in 1996. The estimated mass of total nitrogen and total phosphorus transported to the Mississippi River represents about 19 percent of all estimated nitrogen and 9 percent of all estimated phosphorus input to the study area. [source]


    EVOLUTION, Issue 2 2010
    Nathan D. Jackson
    Rivers can act as both islands of mesic refugia for terrestrial organisms during times of aridification and barriers to gene flow, though evidence for long-term isolation by rivers is mixed. Understanding the extent to which riverine barrier effects can be heightened for populations trapped in mesic refugia can help explain maintenance and generation of diversity in the face of Pleistocene climate change. Herein, we implement phylogenetic and population genetic approaches to investigate the phylogeographic structure and history of the ground skink, Scincella lateralis, using mtDNA and eight nuclear loci. We then test several predictions of a river,refugia model of diversification. We recover 14 well-resolved mtDNA lineages distributed east,west along the Gulf Coast with a subset of lineages extending northward. In contrast, ncDNA exhibits limited phylogenetic structure or congruence among loci. However, multilocus population structure is broadly congruent with mtDNA patterns and suggests that deep coalescence rather than differential gene flow is responsible for mtDNA,ncDNA discordance. The observed patterns suggest that most lineages originated from population vicariance due to riverine barriers strengthened during the Plio,Pleistocene by a climate-induced coastal distribution. Diversification due to rivers is likely a special case, contingent upon other environmental or biological factors that reinforce riverine barrier effects. [source]


    Russell J. Anderson
    ABSTRACT: An extensive group of datasets was analyzed to examine factors affecting widths of streams and rivers. Results indicate that vegetative controls on channel size are scale dependent. In channels with watersheds greater than 10 to 100 km2, widths are narrower in channels with thick woody bank vegetation than in grass lined or nonforested banks. The converse is true in smaller streams apparently due to interactions between woody debris, shading, understory vegetation, rooting characteristics, and channel size. A tree based statistical method (regression tree) is introduced and tested as a tool for identifying thresholds of response and interpreting interactions between variables. The implications of scale dependent controls on channel width are discussed in the context of stable channel design methods and development of regional hydraulic geometry curves. [source]


    Roslyn A. Case
    ABSTRACT: Information regarding long term hydrological variability is critical for the effective management of surface water resources. In the Canadian Prairie region, growing dependence on major river systems for irrigation and other consumptive uses has resulted in an increasing vulnerability to hydrological drought and growing interprovincial tension. This study presents the first dendrochronological records of streamflow for Canadian Prairie rivers. We present 1,113-year, 522-year, and 325-year reconstructions of total water year (October to September) streamflow for the North Saskatchewan, South Saskatchewan, and Saskatchewan Rivers, respectively. The reconstructions indicate relatively high flows during the 20th Century and provide evidence of past prolonged droughts. Low flows during the 1840s correspond with aridity that extended over much of the western United States. Similarly, an exceptional period of prolonged low flow conditions, approximately 900 A.D. to 1300 A.D., is coincident with evidence of sustained drought across central and western North America. The 16th Century megadrought of the western United States and Mexico, however, does not appear to have had a major impact on the Canadian rivers. The dendrohydrological records illustrate the risks involved if future water policy and infrastructure development in the Canadian Prairies are based solely on records of streamflow variability over the historical record. [source]


    R. Peter Richards
    ABSTRACT: A computerized technique was developed to identify storm runoff episodes and calculate storm discharges, storm loads, and storm average concentrations for each event in datasets with up to 10,000 records. This technique was applied to four watersheds within the Lake Erie drainage basin and identified between 160 and 250 runoff events in each. Storm event loads and storm event mean concentrations were calculated for each runoff event for suspended solids, total phosphorus, soluble reactive phosphorus, nitrate, and total Kjeldahl nitrogen. The basic characteristics of the resulting data are described, as are systematic differences as a function of watershed size, seasonal differences, and trends over time. Many of the results of this study reflect the importance of nonpoint processes and improvements in agricultural best management practices in these watersheds. [source]

    Management and Recovery Options for Ural River Beluga Sturgeon

    caviar; CITES; criadero; Mar Caspio; puntos de referencia; sobrepesca Abstract:,Management of declining fisheries of anadromous species sometimes relies heavily on supplementation of populations with captive breeding, despite evidence that captive breeding can have negative consequences and may not address the root cause of decline. The beluga sturgeon (Huso huso), a species threatened by the market for black caviar and reductions in habitat quality, is managed through harvest control and hatchery supplementation, with an emphasis on the latter. We used yield per recruit and elasticity analyses to evaluate the population status and current levels of fishing and to identify the life-history stages that are the best targets for conservation of beluga of the Ural River. Harvest rates in recent years were four to five times higher than rates that would sustain population abundance. Sustainable rates of fishing mortality are similar to those for other long-lived marine species such as sharks and mammals. Yield per recruit, which is maximized if fish are first harvested at age 31 years, would be greatly enhanced by raising minimum size limits or reducing illegal take of subadults. Improving the survival of subadult and adult females would increase population productivity by 10 times that achieved by improving fecundity and survival from egg to age 1 year (i.e., hatchery supplementation). These results suggest that reducing mortality of subadults and adult wild fish is a more effective conservation strategy than hatchery supplementation. Because genetics is not factored into hatchery management practices, supplementation may even reduce the viability of the beluga sturgeon. Resumen:,El manejo de pesquerías de peces anádromos en declinación a veces depende estrechamente de la suplementación de poblaciones mediante la reproducción en cautiverio, no obstante la evidencia de que la reproducción en cautiverio puede tener consecuencias negativas y no abordar la causa principal de la declinación. El esturión beluga (Huso huso), una especie amenazada por el mercado de caviar negro y por reducciones en la calidad del hábitat, es manejado mediante el control de la cosecha y suplementación de poblaciones, con énfasis en esta. Utilizamos análisis de producción por recluta y de elasticidad para evaluar el estatus de la población y los niveles de pesca actuales y para identificar las etapas de la historia de vida que son los mejores blancos para la conservación del beluga en el Río Ural. Las tasas de cosecha en años recientes fueron cuatro a cinco veces mayores que las tasas que sustentarían la abundancia de la población. Las tasas sustentables de mortalidad por pesca son similares a las de otras especies marinas longevas como tiburones y mamíferos. La producción por recluta, que es maximizada si los peces son cosechados a la edad de 31 años, podría incrementar significativamente elevando los límites de talla mínima o reduciendo la captura ilegal de subadultos. La mejora de la supervivencia de hembras subadultas y adultas incrementaría la productividad de la población 10 veces más que la mejora obtenida incrementando la fecundidad y supervivencia de huevo a 1 año de edad (i. e., suplementación de poblaciones mediante reproducción en cautiverio). Estos resultados sugieren que la reducción de la mortalidad de peces silvestres subadultos y adultos es una mejor estrategia de conservación que la suplementación. Debido a que la genética no es considerada en las prácticas de manejo en los criaderos, la suplementación incluso puede reducir la viabilidad del esturión beluga. [source]

    Using Population Count Data to Assess the Effects of Changing River Flow on an Endangered Riparian Plant

    análisis de viabilidad poblacional; gestión ribereña; método de difusión; presas; riesgo de extinción Abstract:,Methods for using simple population count data to project extinction risk have been the focus of much recent theoretical work, but few researchers have used these approaches to address management questions. We analyzed 15 years of census data on the federally endangered endemic riparian plant Pityopsis ruthii (Small) with the diffusion approximation (DA). Our goals were to evaluate relative extinction risk among populations in two different watersheds (in Tennessee, U.S.A.) and potential effects of variation in managed river flow on population dynamics. Populations in both watersheds had high projected risks of extinction within 50 years, but the causes of this risk differed. Populations of P. ruthii on the Hiwassee River had higher initial population sizes but significantly lower average growth rates than those on the Ocoee River. The only populations with low predicted short-term extinction risk were on the Ocoee. Growth rates for populations on both rivers were significantly reduced during periods of lower river flow. We found only marginal evidence of a quadratic relationship between population performance and flow. These patterns are consistent with the idea that low flows affect P. ruthii due to growth of competing vegetation, but the degree to which very high flows may reduce population growth is still unclear. Simulations indicated that populations were most sensitive to growth rates in low-flow years, but small changes in the frequency of these periods did not strongly increase risk for most populations. Consistent with results of other studies, DA estimates of extinction risk had wide confidence limits. Still, our results yielded several valuable insights, including the need for greater monitoring of populations on the Hiwassee and the importance of low-flow years to population growth. Our work illustrates the potential value of simple methods for analyzing count data despite the challenges posed by uncertainty in estimates of extinction risk. Resumen:,Los métodos que utilizan datos de conteos simples de la población para proyectar el riesgo de extinción han sido el foco reciente de mucho trabajo teórico, pero pocos investigadores han utilizado estos métodos para responder preguntas de gestión. Analizamos 15 años de datos de censos de la planta ribereña, endémica y federalmente en peligro Pityopsis ruthii (Small) mediante el método de difusión. Nuestras metas fueron evaluar el riesgo de extinción de poblaciones en dos cuencas hidrológicas distintas y con dos efectos potenciales de la variación del flujo de agua sobre la dinámica de la población. Las poblaciones en ambas cuencas tenían alto riesgo de extinción proyectado a 50 años, pero las causas de este riesgo difirieron. Las poblaciones de P. ruthii en el Río Hiwassee tuvieron poblaciones iniciales más grandes, pero tasas de crecimiento significativamente menores, que las poblaciones en el Río Ocoee. Las únicas poblaciones con bajo riesgo de extinción pronosticado estaban en el Ocoee. Las tasas de crecimiento de las poblaciones en ambos ríos se redujeron significativamente durante períodos de bajo flujo en el río. Sólo encontramos evidencia marginal de la relación cuadrática entre el funcionamiento de la población y el flujo. Estos patrones son consistentes con la idea de que los bajos flujos afectan a P. ruthii debido al crecimiento de vegetación competitiva, pero aun no es claro el grado en que flujos muy grandes pueden reducir el crecimiento poblacional. Las simulaciones indicaron que las poblaciones son más sensibles a las tasas de crecimiento en años con bajo flujo en los ríos, pero pequeños cambios en la frecuencia de esos períodos no aumentaron el riesgo en la mayoría de las poblaciones. Consistentemente con los resultados de otros estudios, las estimaciones del riesgo de extinción mediante el método de difusión tienen amplios límites de confianza. Aun así, nuestros resultados aportaron varios conocimientos valiosos, incluyendo la necesidad de mayor monitoreo de las poblaciones en el Hiwassee y la importancia para el crecimiento poblacional de los años con bajo flujo. Nuestro trabajo ilustra el valor potencial de métodos sencillos de análisis de datos de conteo a pesar de los retos impuestos por la incertidumbre en las estimaciones del riesgo de extinción. [source]

    A Freshwater Classification Approach for Biodiversity Conservation Planning

    biodiversidad de agua dulce; clasificación; planificación de conservación; representativo Abstract:,Freshwater biodiversity is highly endangered and faces increasing threats worldwide. To be complete, regional plans that identify critical areas for conservation must capture representative components of freshwater biodiversity as well as rare and endangered species. We present a spatially hierarchical approach to classify freshwater systems to create a coarse filter to capture representative freshwater biodiversity in regional conservation plans. The classification framework has four levels that we described using abiotic factors within a zoogeographic context and mapped in a geographic information system. Methods to classify and map units are flexible and can be automated where high-quality spatial data exist, or can be manually developed where such data are not available. Products include a spatially comprehensive inventory of mapped and classified units that can be used remotely to characterize regional patterns of aquatic ecosystems. We provide examples of classification procedures in data-rich and data-poor regions from the Columbia River Basin in the Pacific Northwest of North America and the upper Paraguay River in central South America. The approach, which has been applied in North, Central, and South America, provides a relatively rapid and pragmatic way to account for representative freshwater biodiversity at scales appropriate to regional assessments. Resumen:,La biodiversidad de agua dulce está en peligro y enfrenta amenazas crecientes en todo el mundo. Para ser completos, los planes regionales que identifican áreas críticas para la conservación deben incluir componentes representativos de la biodiversidad de agua dulce así como especies raras y en peligro. Presentamos un método espacialmente jerárquico para clasificar sistemas de agua dulce para crear un filtro grueso que capte a la biodiversidad de agua dulce en los planes regionales de conservación. La estructura de la clasificación tiene cuatro niveles que describimos utilizando factores abióticos en un contexto zoogeográfico y localizamos en un sistema de información geográfico. Los métodos para clasificar y trazar mapas son flexibles y pueden ser automatizados, donde existen datos espaciales de alta calidad, o desarrollados manualmente cuando tales datos no están disponibles. Los productos incluyen un inventario completo de unidades mapeadas y clasificadas que pueden ser usadas remotamente para caracterizar patrones regionales de ecosistemas acuáticos. Proporcionamos ejemplos de procedimientos de clasificación en regiones ricas y pobres en datos en la cuenca del Río Columbia en el noroeste de Norte América y del Río Paraguay en Sudamérica central. El método, que ha sido aplicado en Norte, Centro y Sudamérica, proporciona una forma relativamente rápida y pragmática de contabilizar biodiversidad de agua dulce representativa en escalas adecuadas para evaluaciones regionales. [source]

    Conservation Strategies for Endemic Fish Species Threatened by the Three Gorges Dam

    diseño de reserva; especies endémicas; modelo de comunidad; peces; presa Three Gorges Abstract: The largest damming project to date, the Three Gorges Dam has been built along the Yangtze River (China), the most species-rich river in the Palearctic region. Among 162 species of fish inhabiting the main channel of the upper Yangtze, 44 are endemic and are therefore under serious threat of global extinction from the dam. Accordingly, it is urgently necessary to develop strategies to minimize the impacts of the drastic environmental changes associated with the dam. We sought to identify potential reserves for the endemic species among the 17 tributaries in the upper Yangtze, based on presence/absence data for the 44 endemic species. Potential reserves for the endemic species were identified by characterizing the distribution patterns of endemic species with an adaptive learning algorithm called a "self-organizing map" (SOM). Using this method, we also predicted occurrence probabilities of species in potential reserves based on the distribution patterns of communities. Considering both SOM model results and actual knowledge of the biology of the considered species, our results suggested that 24 species may survive in the tributaries, 14 have an uncertain future, and 6 have a high probability of becoming extinct after dam filling. Resumen: El proyecto de represa más grande a la fecha, la Presa Three Gorges fue construida en el Río Yangtze (China), el río con mayor riqueza de especies en la región Paleártica. Entre las 162 especies de peces que habitan el canal principal del alto Yangtze, 44 son endémicas y por tanto están seriamente amenazadas de extinción global por la presa. Consecuentemente, es urgente desarrollar estrategias para minimizar los impactos de los cambios ambientales drásticos asociados con la presa. Tratamos de identificar las reservas potenciales para las especies endémicas entre los 17 afluentes en el alto Yangtze, en base a datos de presencia y ausencia de las 44 especies endémicas. Se identificaron las reservas potenciales para la especies endémicas caracterizando los patrones de distribución de especies endémicas con un algoritmo de aprendizaje adaptivo denominado "mapa auto-organizante" (MAO). Con este método, también predijimos las probabilidades de ocurrencia de especies en reservas potenciales en base a los patrones de distribución de las comunidades. Tomando en cuenta tanto los resultados del modelo MAO como el conocimiento actual de la biología de especies en consideración, nuestros resultados sugieren que 24 especies pueden sobrevivir en los afluentes, 14 tienen un futuro incierto y 6 tienen una alta probabilidad de extinguirse después del llenado de la presa. [source]

    Prescribing Flood Regimes to Sustain Riparian Ecosystems along Meandering Rivers

    Brian D. Richter
    By managing river flows for water supplies and power generation, water management agencies have inadvertently caused considerable degradation of riverine ecosystems and associated biodiversity. New approaches for meeting human needs for water while conserving the ecological integrity of riverine ecosystems are greatly needed. We describe an approach for identifying the natural flooding characteristics that must be protected or restored to maintain riparian ( floodplain) ecosystems along meandering rivers. We developed a computer model to simulate flood-driven changes in the relative abundance of riparian patch types along the Yampa River in Colorado ( U.S.A.). The model is based on research suggesting that the duration of flooding at or above 209 m3 per second (125% of bankfull discharge) is particularly important in driving lateral channel migration, which is responsible for initiating ecological succession in the Yampa's riparian forest. Other hydrologic variables, such as the magnitude of annual peak flows, were not as strongly correlated with lateral channel migration rates. Model simulations enabled us to tentatively identify a threshold of alteration of flood duration that could lead to substantial changes in the abundance of forest patch types over time should river flows be regulated by future water projects. Based on this analysis, we suggest an ecologically compatible water management approach that avoids crossing flood alteration thresholds and provides opportunity to use a portion of flood waters for human purposes. Recommended improvements to the Yampa model include obtaining additional low-elevation aerial photographs of the river corridor to enable better estimation of channel migration rates and vegetation changes. These additional data should greatly improve the model's accuracy and predictive capabilities and therefore its management value. Resumen: La composición y estructura de ecosistemas ribereños están fuertemente ligadas a la variabilidad hidrológica natural. Al manejar el flujo de ríos para abastecer agua y generar energía, las agencias de manejo de agua han causado inadvertidamente una degradación considerable de los ecosistemas ribereños y la biodiversidad asociada a ellos. Se necesitan nuevas estrategias para satisfacer las necesidades humanas de agua al mismo tiempo que se conserva la integridad de los ecosistemas ribereños. Describimos una estrategia para identificar las características de inundaciones naturales que deben ser protegidas o restauradas para mantener ecosistemas riparios ( planicies de inundación) a lo largo de ríos sinuosos. Desarrollamos un modelo de computadora para simular los cambios causados por inundaciones en la abundancia relativa de tipos de parche ripario a lo largo del río Yampa, en Colorado ( Estados Unidos de Norteamérica). Este modelo se basa en investigación que sugiere que la duración de la inundación a, o mayor a, 209 m3 por segundo (125% de descarga del banco lleno a su capacidad) es particularmente importante en la conducción de la migración de canales laterales, lo cual es responsable de la iniciación de la sucesión ecológica en el bosque ripario del río Yampa. Otras variables hidrológicas, como lo es la magnitud del pico de los flujos anuales no estuvieron tan fuertemente correlacionadas con las tasas de migración lateral de canales. Las simulaciones del modelo nos permitieron identificar límites tentativos de alteración de la duración de la inundación que podrían conducir a cambios sustanciales en la abundancia de tipos de parches forestales en el tiempo si los flujos de los ríos son regulados en proyectos de agua futuros. En base a este análisis, sugerimos una estrategia de manejo de agua ecológicamente compatible que evita sobrepasar los límites de alteración de las inundaciones y provee la oportunidad de usar una porción del agua de las inundaciones para fines humanos. Las recomendaciones de mejoras al modelo del río Yampa incluyen la necesidad de obtener fotografías aéreas de baja elevación adicionales del corredor del río, que permitan una mejor estimación de las tasas de migración de los canales y los cambios en la vegetación. Estos datos adicionales deberán mejorar en gran medida la precisión del modelo y sus capacidades predictivas y, por lo tanto, su valor de manejo. [source]

    Changing household responses to drought in Tharaka, Kenya: vulnerability, persistence and challenge

    DISASTERS, Issue 2 2008
    Thomas A. Smucker
    Drought is a recurring challenge to the livelihoods of those living in Tharaka District, Kenya, situated in the semi-arid zone to the east of Mount Kenya, from the lowest slopes of the mountain to the banks of the Tana River. This part of Kenya has been marginal to the economic and political life of Kenya from the colonial period until the present day. A study of more than 30 years of change in how people in Tharaka cope with drought reveals resilience in the face of major macro-level transformations, which include privatisation of landownership, population growth, political decentralisation, increased conflict over natural resources, different market conditions, and environmental shifts. However, the study also shows troubling signs of increased use of drought responses that are incompatible with long-term agrarian livelihoods. Government policy needs to address the challenge of drought under these new macro conditions if sustainable human development is to be achieved. [source]

    GIS-based niche models identify environmental correlates sustaining a contact zone between three species of European vipers

    F. Martínez-Freiría
    ABSTRACT The current range of European vipers is mostly parapatric but local-scale allopatric distribution is common and few cases of sympatry are known. In the High Course of Ebro River, northern Spain, there is a contact zone between Vipera aspis, V. latastei, and V. seoanei. Sympatry was detected between aspis and latastei and also specimens with intermediate morphological traits. Presence-data at a local scale (1 × 1 km) and ecological niche-based models manipulated in a GIS were used to (1) identify how environmental factors correlate with the distribution of the three vipers and with the location of the sympatry area, and (2) identify potential areas for viper occurrence and sympatry. Ensemble for casting with 10 Maximum Entropy models identified a mixture of topographical (altitude, slope), climatic (precipitation, evapotranspiration, and minimum and maximum temperature), and habitat factors (land cover) as predictors for viper occurrence. Similar predicted probabilities according to the variation of some environmental factors (indicating probable sympatry) were observed only for aspis-latastei and aspis-seoanei. In fact, areas of probable occurrence of vipers were generally allopatric but probable sympatry between vipers was identified for aspis-latastei in 76 UTM 1 × 1 km squares, for aspis-seoanei in 23 squares, and latastei-seoanei in two squares. Environmental factors correlate with the location of this contact zone by shaping the species range: some enhance spatial exclusion and constrain distribution to spatially non-overlapping ranges, while others allow contact between species. The distribution in the contact zone apparently results from the balance between the pressures exerted by the different environmental factors and in the sympatry area probably by interspecific competition. Further ecological and genetical data are needed to evaluate the dynamics of the probable hybrid zone. GIS and niche-modelling tools proved to be powerful tools to identify environmental factors sustaining the location of contact zones. [source]

    Tracing recent invasions of the Ponto-Caspian mysid shrimp Hemimysis anomala across Europe and to North America with mitochondrial DNA

    Asta Audzijonyte
    ABSTRACT The mysid crustacean Hemimysis anomala (,bloody-red shrimp') is one of the most recent participants in the invasion of European inland waters by Ponto-Caspian species. Recently the species also became established in England and the Laurentian Great Lakes of North America. Using information from mitochondrial cytochrome oxidase I (COI) gene sequences, we traced the invasion pathways of H. anomala; the inferences were enabled by the observed phylogeographical subdivision among the source area populations in the estuaries of the Ponto-Caspian basin. The data distinguish two routes to northern and western Europe used by distinct lineages. One route has been to and through the Baltic Sea and further to the Rhine delta, probably from a population intentionally introduced to a Lithuanian water reservoir from the lower Dnieper River (NW Black Sea area) in 1960. The other lineage is derived from the Danube delta and has spread across the continent up the Danube River and further through the Main,Danube canal down to the Rhine River delta. Only the Danube lineage was found in England and in North America. The two lineages appear to have met secondarily and are now found intermixed at several sites in NW Europe, including the Rhine and waters linked with the man-made Mittellandkanal that interconnects the Rhine and Baltic drainage systems. [source]

    Spatial autocorrelation of assemblages of benthic invertebrates and its relationship to environmental factors in two upland rivers in southeastern Australia

    Natalie J. Lloyd
    ABSTRACT The nature of spatial autocorrelation of biota may reveal much about underlying ecological and biological factors responsible for producing those patterns, especially dispersal processes (drift, adult flight, etc.). We report here on assemblage-level autocorrelation in the benthic-invertebrate assemblages (retained in sieves of 300 µm mesh) of riffles in two adjacent, relatively pristine rivers in southeastern Victoria, Australia (40-km reaches of the Wellington and Wonnangatta Rivers). These are related to patterns of autocorrelation in physical and catchment conditions (,environmental variables') in the vicinity of the sampling points. Both the invertebrate assemblages and environmental variables were autocorrelated at small scales (= 8 km) in the Wellington River in one of the sampling years (1996). Dissimilarities of invertebrate assemblages were correlated with dissimilarities of environmental variables in both sampling years (1996 and 1997) in that river. Environmental variables were autocorrelated in the Wonnangatta River, but this was not expressed as autocorrelation in the assemblages of invertebrates, which were not autocorrelated at any scale studied. Individual environmental variables showed different spatial patterns between the two rivers. These results suggest that individual rivers have their own idiosyncratic patterns and one cannot assume that even similar, geographically adjacent rivers will have the same patterns, which is a difficulty for ecological assessment and restoration. [source]

    A morphological reappraisal of Tubifex blanchardi Vejdovský, 1891 (Clitellata: Tubificidae)

    ACTA ZOOLOGICA, Issue 2 2009
    Roberto Marotta
    Abstract Tubifex blanchardi Vejdovský, 1891 is a freshwater tubificid, often living in sympatry with Tubifex tubifex (Müller 1774). Although considered from its discovery as a species on its own, its biological status is debated. During the early seventies T. blanchardi was reduced to a mere form of T. tubifex, as a particular case of polymorphism in chaetal pattern. Using classical histological techniques, microdissections of portions of the male genital apparatus and phalloidin staining of dissected copulatory organs we investigated 163 mixed individuals of T. blanchardi and T. tubifex belonging to sympatric populations from the Lambro River (Milan, Northern Italy). The internal morphology of T. blanchardi is described for the first time. Our results show that T. tubifex and T. blanchardi differ in several characters concerning both their external and internal morphology, and in the fine organization of their copulatory organs. Several independent character sets support the separation of T. blanchardi from T. tubifex, suggesting that it is an independent species. This study also supports the idea that T. blanchardi and T. bergi (Hrab,, 1935), another species closely related to T. tubifex, are not conspecific. The observed morphological differences between allopatric populations of T. tubifex are discussed. [source]

    Size at the onset of sexual maturity in the anomuran crab, Aegla uruguayana (Aeglidae)

    ACTA ZOOLOGICA, Issue 4 2006
    Verónica E. Viau
    Abstract The size at maturity was studied in the crab Aegla uruguayana from the Areco River (31°14, S, 59°28, W), Argentina. Size at sexual maturity was determined according to three criteria: morphometric (change in the relative growth of reproductive characters), histological (first maturation of gonads) and functional (capability to mate and carry eggs). Regarding females, morphometric maturity occurred at a carapace length (CL) of 11.50 mm, considering abdomen width as a reproductive character. Gonad maturity of females could be observed at a minimum size ranging from 15 to 17 mm CL. The smallest ovigerous female observed in the field was 15.60 mm CL, although a relevant population incidence of ovigerous females (86.6%) has just been observed at values higher than 17 mm CL. As for males, the relative growth of the left chela length changed at a value of 15.40 mm CL, while morphological changes in sexual tube occurred between CL of 14 and 16 mm. Testicular maturation occurred at a CL ranging from 17 to 19 mm. The smallest size of males having spermatozoids in their vasa deferentia was 18.70 mm CL. The results obtained indicated that, in both sexes, functional maturity occurred after morphometric maturity and at a size similar to that of gonad maturity. Comparing sexes, females acquired sexual maturity (morphometric, gonad and functional maturity) at sizes statistically smaller than those of males. [source]

    Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies,

    J. Le Coz
    Abstract The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cutoff meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava River (Slovakia). Field measurements were performed in the exit of the Port-Galland cutoff meander, Ain River (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cutoff meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel. Copyright © 2010 John Wiley & Sons, Ltd [source]

    Channel sedimentation and erosion of the Jiangsu reach of the Yangtze River during the last 44 years

    Wang Jian
    Abstract River channel sedimentation in the lower reaches of the Yangtze River can be affected by both changes in sea level and changes in solid discharge from the upper river. To evaluate dynamic changes of sedimentation and erosion in the Jiangsu reach of the Yangtze River (about 330 km in length) from 1959 to 2003, databases were designed and constructed using a digital elevation model (DEM) of channel topography based on the Jiangsu River Relief Map for 1959, 1970, 1985, 1992, and 2003. The results indicated that the main course of the Yangtze River in Jiangsu Province had experienced an obvious switch from sedimentation to erosion status around 1985 because of the decreasing amount of solid load from the upper parts of the river channel after that year. The sedimentation process in the main course of the Jiangsu reach of the Yangtze River demonstrated the propulsive process of ,downstream-ward aggradations.' Between 1985 and 2003, the erosion rate of the lower segment was greater than those of the middle and upper segments; this is probably because both channel flow and tide current had influenced the lower segment. When channel flow combines with tide current in the same direction, channel erosion can be intensified, especially if there is a solid load shortage in the channel. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Elevation adjustments of paired natural levees during flooding of the Saskatchewan River

    Norman D. Smith
    Abstract Natural levees control the exchange of water between an alluvial channel and its floodplain, but little is known about the spatial distribution and evolution of levee heights. The summer 2005 flood of the Saskatchewan River (Cumberland Marshes, east-central Saskatchewan) inundated large areas of floodplain for up to seven weeks, forming prominent new deposits on natural levees along main-stem channels. Measurements of flood-deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre-flood levee in 80% of the sites, though no clear relationship exists between deposit thickness and magnitude of height difference. Only 16% of the pairs displayed thicker deposits on the higher levee, half of which occurred at sites where relatively clear floodbasin waters re-entered turbid channels during general flooding. Difference in crest elevation (,E) between paired levees is approximately log-normally distributed, both before and after the flood, though with different mean values. Supplemental observations from tank experiments indicate that during near-bankfull flows, temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension. During floods, preferential deposition in lows tends to even out crest heights. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Forest blowdown impacts of Hurricane Rita on fluvial systems

    Jonathan D. Phillips
    Abstract Hurricane Rita, a category three hurricane which struck the US Gulf Coast near the Louisiana/Texas border in 2005, did not cause extensive river flooding. However, the storm did result in extensive forest damage and tree blowdown. High-resolution post-storm aerial photography allowed an inventory of river bank trees blown into the channel along the lower Neches and Sabine Rivers of southeast Texas and southwest Louisiana. Blowdowns directly into the channel averaged 9·3 per kilometer in the lower Neches and 13·4 in the lower Sabine River, but individual reaches 10 to 20 km in length had rates of 20 to 44 blowdowns per kilometer. Though large woody debris (LWD) from Hurricane Rita was widely perceived to reduce the capacity of channels to convey flow, no strong evidence exists of increased flooding or significant reductions in channel conveyance capacity due to LWD from the storm. The Rita blowdown inventory also allowed an assessment of whether similar blowdown events could account for major logjams and rafts on Red, Atchafalaya, and Colorado Rivers on the Gulf Coast, which blocked navigation from tens to hundreds of kilometers in the 1800s. Results from Hurricane Rita suggest that blowdown into channels alone , not withstanding blowdown elsewhere in the river valleys or along tributaries which could deliver LWD to the river , is sufficient to completely block channels, thus providing a plausible mechanism for initiating such (pre)historic log rafts. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Scale-dependent controls upon the fluvial export of large wood from river catchments

    Jung Il Seo
    Abstract The annual fluvial export of large wood (LW) was monitored by local reservoir management offices in Japan. LW export per unit watershed area was relatively high in small watersheds, peaked in intermediate watersheds, and decreased in large watersheds. To explain these variations, we surveyed the amount of LW with respect to channel morphology in 78 segments (26 segments in each size class) in the Nukabira River, northern Japan. We examined the differences in LW dynamics, including its recruitment, transport, storage, and fragmentation and decay along the spectrum of watershed sizes. We found that a large proportion of LW produced by forest dynamics and hillslope processes was retained because of the narrower valley floors and lower stream power in small watersheds. The retained LW pieces may eventually be exported during debris flows. In intermediate watersheds, the volume of LW derived from hillslopes decreased substantially with reductions in the proportion of channel length bordered by hillslope margins, which potentially deliver large quantities of LW. Because these channels have lower wood piece length to channel width ratios and higher stream power, LW pieces can be transported downstream. During transport, LW pieces are further fragmented and can be more easily transported. Therefore, the fluvial export of LW is maximized in intermediate watersheds. Rivers in large watersheds, where the recruitment of LW is limited by the decreasing hillslope margins, cannot transport LW pieces because of their low stream power, and thus LW pieces accumulate at various storage sites. Although these stored LW pieces can be refloated and transported by subsequent flood events, they may also become trapped by obstacles such as logjams and standing trees on floodplains and in secondary channels, remaining there for decades and eventually decaying into fine organic particles. Thus, the fluvial export of LW pieces is low in large watersheds. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchment

    Guan-Wei Lin
    Abstract Patterns and rates of landsliding and fluvial sediment transfer in mountain catchments are determined by the strength and location of rain storms and earthquakes, and by the sequence in which they occur. To explore this notion, landslides caused by three tropical cyclones and a very large earthquake have been mapped in the Chenyoulan catchment in the Taiwan Central Range, where water and sediment discharges and rock strengths are well known. Prior to the MW 7·6 Chi-Chi earthquake in 1999, storm-driven landslide rates were modest. Landslides occurred primarily low within the landscape in shallow slopes, reworking older colluvial material. The Chi-Chi earthquake caused wide-spread landsliding in the steepest bedrock slopes high within the catchment due to topographic focusing of incoming seismic waves. After the earthquake landslide rates remained elevated, landslide patterns closely tracking the distribution of coseismic landslides. These patterns have not been strongly affected by rock strength. Sediment loads of the Chenyoulan River have been limited by supply from hillslopes. Prior to the Chi-Chi earthquake, the erosion budget was dominated by one exceptionally large flood, with anomalously high sediment concentrations, caused by typhoon Herb in 1996. Sediment concentrations were much higher than normal in intermediate size floods during the first 5 years after the earthquake, giving high sediment yields. In 2005, sediment concentrations had decreased to values prevalent before 1999. The hillslope response to the Chi-Chi earthquake has been much stronger than the five-fold increase of fluvial sediment loads and concentrations, but since the earthquake, hillslope sediment sources have become increasingly disconnected from the channel system, with 90 per cent of landslides not reaching into channels. Downslope advection of landslide debris associated with the Chi-Chi earthquake is driven by the impact of tropical cyclones, but occurs on a time-scale longer than this study. Copyright © 2008 John Wiley & Sons, Ltd. [source]