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Watershed Area (watershed + area)
Selected AbstractsEffects of Habitat Fragmentation by Damming on the Persistence of Stream-Dwelling Charr PopulationsCONSERVATION BIOLOGY, Issue 5 2002Kentaro Morita We assessed the effect of habitat fragmentation by damming on the population persistence of a stream-dwelling fish, the white-spotted charr (Salvelinus leucomaenis), in streams of southwestern Hokkaido, Japan. We sampled for charr at 52 dammed-off sites by electrofishing or snorkeling and measured five habitat characteristics: isolation period, watershed area, gradient, elevation, distance from sea. Of the 52 study sites above dams, white-spotted charr were absent at 17 sites and were present at 35 sites. Because the charr occupied all undammed upstream reaches, the damming would cause the absence of charr upstream. Among five habitat characteristics examined, stepwise logistic-regression analysis showed that disappearance was promoted with increasing isolation period, with decreasing watershed area (i.e., habitat size), and with decreasing gradient. The resulting logistic model explained 82.7% of the present white-spotted charr occurrence and forecasted that 12 of 35 extant populations will disappear after 50 years. Our findings imply that extirpation of small, dammed-off populations is inevitable unless efficient fish ladders are installed or dams are removed. Resumen: La construcción de presas tiene serias consecuencias sobre los ecosistemas acuáticos y uno de los mas serios es el "efecto de barrera" ( la prevención de que un organismo migre a través del sistema). Evaluamos los efectos de la fragmentación del hábitat ocasionados por la construcción de presas en la persistencia de un pez morador de arroyos, la trucha de montaña de manchas blancas ( Salvelinus leucomaenis), en arroyos del suroeste de Hokkaido, Japón. Muestreamos en 52 sitios con represas empleando electropesca o buceo con esnórquel y medimos cinco características del hábitat ( periodo de aislamiento, área de la cuenca, gradiente, elevación y distancia al mar). De los 52 sitios de estudio ubicados arriba de las represas las truchas de montaña estuvieron ausentes en 17 sitios y presentes en 35 sitios. Debido a que las truchas de montaña ocupaban todos los rangos sin represas arroyo arriba, la creación de represas pudo causar la ausencia de truchas de montaña arroyo arriba. Dentro de las cinco características del hábitat examinadas, el análisis de regresión logística mostró que la desaparición era promovida por un incremento en el periodo de aislamiento, con una disminución en el área de la cuenca (i.e. tamaño del hábitat) y con una disminución del gradiente. El modelo logístico resultante explicó 82.7% de la presencia de truchas de montaña y pronosticó que 12 de la 35 poblaciones actuales desaparecerían después de 50 años. Nuestros resultados implican que la extirpación es pequeña y que la exclusión por construcción de represas es inevitable a menos que se instalen desvíos para peces o que se remuevan las presas. [source] Scale-dependent controls upon the fluvial export of large wood from river catchmentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2009Jung 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] Assessment of shallow landslide susceptibility by means of multivariate statistical techniquesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2001Cristina Baeza Abstract Several multivariate statistical analyses have been performed to identify the most influential geological and geomorphological parameters on shallow landsliding and to quantify their relative contribution. A data set was first prepared including more than 30 attributes of 230 failed and unfailed slopes. The performance of principal component analysis, t-test and one-way test, allowed a preliminary selection of the most significant variables, which were used as input variables for the discriminant analysis. The function obtained has classified successfully 88·5 per cent of the overall slope population and 95·6 per cent of the failed slopes. Slope gradient, watershed area and land-use appeared as the most powerful discriminant factors. A landslide susceptibility map, based on the scores of the discriminant function, has been prepared for Ensija range in the Eastern Pyrenees. An index of relative landslide density shows that the results of the map are consistent. Copyright © 2001 John Wiley & Sons, Ltd. [source] Relative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern MesoamericaECOLOGY OF FRESHWATER FISH, Issue 3 2010P. C. Esselman Esselman PC, Allan JD. Relative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica. Ecology of Freshwater Fish 2010: 19: 439,454. © 2010 John Wiley & Sons A/S Abstract,,, While the abiotic factors important to freshwater fish assemblages at a reach scale are well understood, studies of larger scale constraints have yielded variable conclusions, spurring a need for further studies in new biogeographic contexts. This study investigated the importance of catchment- and reach-scale abiotic factors to variation in freshwater fish assemblages in rivers of northeastern Mesoamerica. Abiotic variables and fish data from 72 sampling sites on main stem rivers of Belize were used with partial constrained ordination to determine the proportion of spatially structured and unstructured variation in fish presence and absence, relative abundance, and community metrics explained by catchment- and reach-scale environmental factors. Results showed that, combined, catchment and reach variables explained a large portion of the total variation in the fish assemblage data (54,75%), and that catchment environment explained a greater portion of variation (42,63%) than reach environment (34,50%). Variables representing landscape position (local elevation, watershed area) and their reach-level correlates (channel width, depth variation, and substrate) correlated strongly to the fish assemblage data. Our results suggest that landscape-scale factors have a stronger relative influence on assemblages than environmental conditions at the reach scale within our study area. These results contrast with past findings that showed greater local scale influence in landscapes with low anthropogenic disturbance levels. Our findings suggest that biodiversity conservation efforts should consider assemblage variation across a longitudinal gradient, and that a multi-catchment region is a biologically relevant scale for fish conservation planning and coordination in northeastern Mesoamerica. [source] Tectonics and quaternary evolution of the Northern Apennines watershed area (upper course of Arno and Tiber rivers, Italy)GEOLOGICAL JOURNAL, Issue 1 2009Marco Bonini Abstract This work examines the connection between Quaternary tectonics and erosion/incision processes in the primary Tuscan-Romagna watershed of the Northern Apennines, which essentially coincides with the topographic culmination of the Nero Unit structural ridge. Tectonic and geomorphic information were collected in the area where this ridge is crossed by the upper Tiber River course forming a deep gorge. Structural analysis and field mapping have revealed that the region experienced polyphase tectonics with superposed thrust folding events identifiable both at the map and mesoscopic scales. Hinterland-SSW-verging thrusts and thrust-related folds deformed the whole thrust pile during the latest deformation phase. Backthrusts/backfolds controlled the development of intermountain basins nearby the main watershed during the Early Pleistocene and seemingly deformed, in the Tiber gorge, a low-relief landscape developed in the Early Pleistocene (ca. 1.1,Ma). Successively, the upper Tiber River course area and Apennines axial zone underwent a generalized uplift, which is manifested by the deep incision of palaeo-morphologies. This proposed sequence of events correlates well with the major geodynamic change of the Apennines revealed by an acceleration of uplift rates in the Middle,Late Pleistocene. This latter event may also correlate with increased rates of river incision recorded in Europe as a consequence of uplift and/or climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Controls on surface water chemistry in two lake-watersheds in the Adirondack region of New York: differences in nitrogen solute sources and sinksHYDROLOGICAL PROCESSES, Issue 10 2007Mari Ito Abstract The southwestern Adirondack region of New York receives among the highest rates of atmospheric nitrogen (N) deposition in the USA. Atmospheric N deposition to sensitive ecosystems, like the Adirondacks, may increase the acidification of soils through losses of exchangeable nutrient cations, and the acidification of surface waters associated with enhanced mobility of nitrate (NO3,). However, watershed attributes, including surficial terrestrial characteristics, in-lake processing, and geological settings, have been found to complicate the relationships between atmospheric N deposition and N drainage losses. We studied two lake-watersheds in the southwestern Adirondacks, Grass Pond and Constable Pond, which are located in close proximity (,26 km) and receive similarly high N deposition, but have contrasting watershed attributes (e.g. wetland area, geological settings). Since the difference in the influence of N deposition was minimal, we were able to examine both within- and between-watershed influences of land cover, the contribution of glacial till groundwater inputs, and in-lake processes on surface water chemistry with particular emphasis on N solutes and dissolved organic carbon (DOC). Monthly samples at seven inlets and one outlet of each lake were collected from May to October in 1999 and 2000. The concentrations of NO3, were high at the Grass Pond inlets, especially at two inlets, and NO3, was the major N solute at the Grass Pond inlets. The concentrations of likely weathering products (i.e. dissolved Si, Ca2+, Mg2+, Na+) as well as acid neutralizing capacity and pH values, were also particularly high at those two Grass Pond inlets, suggesting a large contribution of groundwater inputs. Dissolved organic N (DON) was the major N solute at the Constable Pond inlets. The higher concentrations of DON and DOC at the Constable Pond inlets were attributed to a large wetland area in the watershed. The DOC/DON ratios were also higher at the Constable Pond inlets, possibly due to a larger proportion of coniferous forest area. Although DON and DOC were strongly related, the stronger relationship of the proportion of wetland area with DOC suggests that additional factors regulate DON. The aggregated representation of watershed physical features (i.e. elevation, watershed area, mean topographic index, hypsometric-analysis index) was not clearly related to the lake N and DOC chemistry. Despite distinctive differences in inlet N chemistry, NO3, and DON concentrations at the outlets of the two lakes were similar. The lower DOC/DON ratios at the lake outlets and at the inlets having upstream ponds suggest the importance of N processing and organic N sources within the lakes. Although an inverse relationship between NO3, and DOC/DON has been suggested to be indicative of a N deposition gradient, the existence of this relationship for sites that receive similar atmospheric N deposition suggest that the relationship between NO3, and the DOC/DON ratio is derived from environmental and physical factors. Our results suggest that, despite similar wet N deposition at the two watershed sites, N solutes entering lakes were strongly affected by hydrology associated with groundwater contribution and the presence of wetlands, whereas N solutes leaving lakes were strongly influenced by in-lake processing. Copyright © 2006 John Wiley & Sons, Ltd. [source] Visual Analysis or Semi-Automated Gray-Scale-Based Color Mapping of the Carotid Plaque: Which Method Correlates the Best with the Presence of Cerebrovascular Symptoms and/or Lesions on MRI?JOURNAL OF NEUROIMAGING, Issue 2 2009Isabelle Momjian MD ABSTRACT BACKGROUND AND PURPOSE To determine the correlation between carotid plaque morphology, assessed by two different ultrasonographic methods, and presence of cerebrovascular events and/or lesions on magnetic resonance imaging (MRI). PATIENTS AND METHODS Visual analysis of plaque echogenicity using a five-type classification was performed. Further, a semi-automated gray-scale-based color mapping of the whole plaque and of its surface was achieved. RESULTS There were 31 (35%) symptomatic (23 strokes and 8 transitory ischemic attacks [TIAs]) and 58 (65%) asymptomatic carotid stenoses. MRI lesions related to the carotid stenosis if located in the ipsilateral cortical, subcortical, or watershed area, were present in 27 cases (30%). In a multivariate logistic regression model, degree of stenosis (P= .03) and a predominant red color on the surface (P= .04) were independent factors associated with the presence of cerebrovascular events and/or lesions on MRI. Sensitivity and specificity were, respectively, 80% and 63% by combining degree of stenosis and color mapping of plaque surface. CONCLUSION Degree of stenosis and a predominant red color on plaque surface were independent factors associated with the presence of cerebrovascular events and/or lesions on MRI. No correlation was observed with any particular type of plaque based on visual analysis alone. [source] INFLUENCES OF WATERSHED URBANIZATION AND INSTREAM HABITAT ON MACROINVERTEBRATES IN COLD WATER STREAMS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2003Lizhu Wang ABSTRACT: We analyzed data from riffle and snag habitats for 39 small cold water streams with different levels of watershed urbanization in Wisconsin and Minnesota to evaluate the influences of urban land use and instream habitat on macroinvertebrate communities. Multivariate analysis indicated that stream temperature and amount of urban land use in the watersheds were the most influential factors determining macroinvertebrate assemblages. The amount of watershed urbanization was nonlinearly and negatively correlated with percentages of Ephemeroptera-Plecoptera-Trichoptera (EPT) abundance, EPT taxa, filterers, and scrapers and positively correlated with Hilsenhoff biotic index. High quality macroinvertebrate index values were possible if effective imperviousness was less than 7 percent of the watershed area. Beyond this level of imperviousness, index values tended to be consistently poor. Land uses in the riparian area were equal or more influential relative to land use elsewhere in the watershed, although riparian area consisted of only a small portion of the entire watershed area. Our study implies that it is extremely important to restrict watershed impervious land use and protect stream riparian areas for reducing human degradation on stream quality in low level urbanizing watersheds. Stream temperature may be one of the major factors through which human activities degrade cold-water streams, and management efforts that can maintain a natural thermal regime will help preserve stream quality. [source] Selling the Public on Sustainable Watershed ConservationBULLETIN OF LATIN AMERICAN RESEARCH, Issue 3 2004Jeff Pugh Abstract:, The city of Quito, Ecuador, began working in 2000 to protect the ecologically fragile watershed area for its drinking water. In order to protect the Papallacta watershed, the independent Fund for the Conservation of Watersheds (FONAG) was launched to finance and manage economically sound sustainability projects in the area. FONAG is funded in part through start up grants from several organisations and a 1 per cent fee on all Quito water bills, but it has been unable to build an endowment sizeable enough to begin implementing conservation projects. We measure perceptions of the fund among Quito's university,based residents in two settings and evaluate the quality of the fund's proposed communication campaign based on existing communication theory. Further, we propose an adapted environmental education model based on a synthesis of existing theory and the empirical findings from our examination of the FONAG example. The Papallacta case study illuminates the potential strengths and weaknesses of the cultural ecology and political will of this type of collaborative sustainability project for addressing water problems in a developing country in a mountainous setting, centred around the themes of water conservation and sustainable development. [source] The cation and silica chemistry of a Subandean river basin in western AmazoniaHYDROLOGICAL PROCESSES, Issue 7 2002J. A. Sobieraj Abstract We sampled river water at 13 locations in the Pichis basin, a 10 500 km2 large rainforest-covered drainage basin in Peru, to assess the influence of lithological variability and seasonality on water chemistry. The concentrations of major cations and silica show a strong seasonal dependence and a remarkable variability over short distances that is only weakly reduced in the wet season; cation concentrations in streams differ by up to 100% within a few kilometres. The lowest cation concentrations were associated with relatively cation-depleted upper Tertiary and lower Quaternary formations, whereas relatively cation-rich lower Tertiary and Jurassic formations left a clear calcium and sodium signal in the respective rivers. Cluster analysis, in conjunction with boxplots, suggests that the sampling locations can be segregated into three groups based on similarities of their geochemical signals. According to the previously defined criteria, one river is classified as a Group 2 river with 200 < TZ+ < 450 µeq/L, whereas all other rivers fall into Group 3 with 450 < TZ+ < 3000 µeq/L (where TZ+ refers to the total cation charge). Based on a comparison with other studies at different sections of the Amazon mainstem, the river chemistry of our study area is relatively enriched in K+, Mg2+ and Ca2+, and, consequently, has a higher TZ+ value, while being relatively depleted in silica. The influence of lithological variability on water chemistry must be considered in land-use change studies even at watershed areas of 26,3382 km2. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||||||||