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Drainage Basins (drainage + basin)
Selected AbstractsExtent of Nontimber Resource Extraction in Tropical Forests: Accessibility to Game Vertebrates by Hunters in the Amazon BasinCONSERVATION BIOLOGY, Issue 2 2003Carlos A. Peres We conducted a basin-wide geographic information system analysis of the nonmotorized accessibility of Amazonian NTFP extraction and estimated the proportion of the Amazon drainage basin within Brazil ( 3.74 million km 2 ) that can be accessed on foot from the nearest navigable river or functional road. We use a long-term series of standardized line-transect vertebrate censuses conducted throughout the region to illustrate the effects of physical accessibility on wildlife densities in terms of hunting pressure as a function of distance from the nearest point of access. Population abundance in large-bodied, prime-target species preferred by game hunters tended to increase at greater distances from the access matrix, whereas small-bodied species ignored by hunters usually showed the reverse trend. In addition, we estimated the proportion of presumably inviolate core areas within nature, extractive, and indigenous reserves of Brazilian Amazonia that are prohibitively remote and unlikely to be overhunted; for instance, only 1.16% of the basin-wide area is strictly protected on paper and is reasonably safe from extractive activities targeted to game vertebrates and other valuable NTFPs. Finally, we discuss the concept of truly undisturbed wildlands in the last major tropical forest regions by distinguishing potentially overharvested areas from those that remain largely or entirely pristine and that maintain viable populations of a full complement of harvest-sensitive species. Resumen: Las actividades de extracción enfocadas en un amplio rango de productos forestales no maderables ( NTFPs ) son omnipresentes en los bosques tropicales. Sin embargo, la extensión de bosques estructuralmente intactos en una determinada región afectada por esta forma de perturbación críptica ha sido escasamente documentada. Realizamos un análisis GIS del acceso no motorizado para la extracción NTFP en el Amazonas y estimamos la proporción de la desembocadura de la cuenca amazónica ( ,3.74 millones de km2 ) a la cual se puede acceder a pie a partir del río navegable o la carretera funcional más cercana. Utilizamos series de censos de vertebrados a largo plazo empleando transectos en línea estandarizados a lo largo de la región para ejemplificar los efectos del acceso físico sobre las densidades de vida silvestre en términos de presión de caza como función de la distancia al punto de acceso más cercano. La abundancia poblacional de especies de cuerpo grande que son blancos preferidos por los cazadores tendió a crecer a mayores distancias de la matriz de acceso, mientras que las especies de cuerpo pequeño ignoradas por los cazadores generalmente muestran la tendencia inversa. Además, estimamos la proporción de áreas medulares presuntamente inviolables dentro de las reservas naturales, extractivas e indígenas del Amazonas brasileño que son prohibitivamente remotas y poco probables de ser sobreexplotadas: por ejemplo, solo el 1.16% del área de la cuenca estrictamente proyectada en papel está razonablemente a salvo de las actividades extractivas de los vertebrados de caza y otras NTFPs valiosas. Finalmente, discutimos el concepto de tierras silvestres verdaderamente no perturbadas en las grandes regiones de bosque tropical restantes diferenciando las áreas potencialmente sobreexplotadas de aquellas que son en su mayor parte o totalmente prístinas y que mantienen poblaciones viables de un complemento total de especies sensibles a la cosecha. [source] Evolution of channel morphology and hydrologic response in an urbanizing drainage basinEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2006Peter A. Nelson Abstract The Dead Run catchment in Baltimore County, Maryland, has undergone intense urbanization since the late 1950s. Reconstruction of the channel planform from topographic maps dating back to the 1890s and aerial photographs dating back to the 1930s indicates that the channel has remained stable in planform since at least the 1930s. The relative stability of Dead Run contrasts with the alterations in channel morphology reported for other urbanizing streams in the Piedmont physiographic province of the eastern United States. Trend analyses of discharge records in Dead Run show that urban development and stormwater control measures have had significant impacts on the hydrologic response of the catchment. The flood hydraulics of the Dead Run catchment are examined for the event that occurred on 22 June 1972 in association with Hurricane Agnes. A two-dimensional hydraulic model, TELEMAC-2D, was used with a finite-element mesh constructed from a combination of high-resolution LiDAR topographic data and detailed field survey data to analyse the distribution of boundary shear stress and unit stream power along the channel and floodplain during flooding from Hurricane Agnes. The spatial and temporal distributions of these parameters, relative to channel gradient and channel/valley bottom geometry, provide valuable insights on the stability of the Dean Run channel. The stability of Dead Run's channel planform, in spite of extreme flooding and decades of urban development, is most likely linked to geological controls of channel and floodplain morphology. Copyright © 2006 John Wiley & Sons, Ltd. [source] Tilting neotectonics of the Guadiamar drainage basin, SW SpainEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2004Josep M. SalvanyArticle first published online: 23 DEC 200 Abstract The Guadiamar river ,ows from the southern Iberian Massif to the Guadalquivir foreland basin, SW Spain. Its drainage basin displays asymmetries in the stream network, the arrangement of alluvial terraces and the con,guration of the trunk river valley. The stream network asymmetry was studied using morphometric measures of transverse topographic sym-metry, asymmetry factor and drainage basin shape. The alluvial terraces were studied through the lithologic logs of more than a hundred boreholes and ,eld mapping. The morphometric methods demonstrate a regional tectonic tilting toward the SSE, causing both the migration of the Guadiamar river toward the east and the migration of the Guadiamar tributaries toward the southwest. As a consequence of the Guadiamar river migration, an asymmetric valley developed, with a steep eastern margin caused by river dissection, and a gentle western margin where the main alluvial deposits are found. The ages obtained using the 14C analysis of samples from several alluvial deposits show that the river migration, and thus tilting, has occurred during the Holocene as well as earlier in the Quaternary. This interpretation revises the Guadiamar longitudinal fault assumed by previous studies. Copyright © 2003 John Wiley & Sons, Ltd. [source] Comparison of soil moisture and meteorological controls on pine and spruce transpirationECOHYDROLOGY, Issue 3 2008Eric E. Small Abstract Transpiration is an important component of the water balance in the high elevation headwaters of semi-arid drainage basins. We compare the importance of soil moisture and meteorological controls on transpiration and quantify how these controls are different at a ponderosa pine site and a spruce site in the Jemez river drainage basin of northern New Mexico, a sub-basin of the Rio Grande. If only soil moisture controls fluctuations in transpiration, then simple hydrologic models focussed only on soil moisture limitations are reasonable for water balance studies. If meteorological controls are also critical, then more complex models are required. We measured volumetric water content in the soil and sap velocity, and assumed that transpiration is proportional to sap velocity. Ponderosa sap velocity varies with root zone soil moisture. Nearly all of the scatter in the ponderosa sap velocity,soil moisture relationship can be predicted using a simple model of potential evapotranspiration (ET), which depends only on measured incident radiation and air temperature. Therefore, simple hydrologic models of ponderosa pine transpiration are warranted. In contrast, spruce sap velocity does not clearly covary with soil moisture. Including variations in potential evapotranspiration does not clarify the relationship between sap velocity and soil moisture. Likewise, variations in radiation, air temperature, and vapour pressure do not explain the observed fluctuations in sap velocity, at least according to the standard models and parameters for meteorological restrictions on transpiration. Both the simple and more complex models commonly used to predict transpiration are not adequate to model the water balance in the spruce forest studied here. Copyright © 2008 John Wiley & Sons, Ltd. [source] Variance estimation for spatially balanced samples of environmental resourcesENVIRONMETRICS, Issue 6 2003Don L. Stevens Jr Abstract The spatial distribution of a natural resource is an important consideration in designing an efficient survey or monitoring program for the resource. We review a unified strategy for designing probability samples of discrete, finite resource populations, such as lakes within some geographical region; linear populations, such as a stream network in a drainage basin, and continuous, two-dimensional populations, such as forests. The strategy can be viewed as a generalization of spatial stratification. In this article, we develop a local neighborhood variance estimator based on that perspective, and examine its behavior via simulation. The simulations indicate that the local neighborhood estimator is unbiased and stable. The Horvitz,Thompson variance estimator based on assuming independent random sampling (IRS) may be two times the magnitude of the local neighborhood estimate. An example using data from a generalized random-tessellation stratified design on the Oahe Reservoir resulted in local variance estimates being 22 to 58 percent smaller than Horvitz,Thompson IRS variance estimates. Variables with stronger spatial patterns had greater reductions in variance, as expected. Copyright © 2003 John Wiley & Sons, Ltd. [source] Stocking piscivores to improve fishing and water clarity: a synthesis of the Lake Mendota biomanipulation projectFRESHWATER BIOLOGY, Issue 12 2002R. C. Lathrop SUMMARYY 1.,A total of 2.7 × 106 walleye fingerlings and 1.7 × 105 northern pike fingerlings were stocked during 1987,99 in eutrophic Lake Mendota. The objectives of the biomanipulation were to improve sport fishing and to increase piscivory to levels that would reduce planktivore biomass, increase Daphnia grazing and ultimately reduce algal densities in the lake. The combined biomass of the two piscivore species in the lake increased rapidly from < 1 kg ha,1 and stabilised at 4,6 kg ha,1 throughout the evaluation period. 2.,Restrictive harvest regulations (i.e. increase in minimum size limit and reduction in bag limit) were implemented in 1988 to protect the stocked piscivores. Further restrictions were added in 1991 and 1996 for walleye and northern pike, respectively. These restrictions were essential because fishing pressure on both species (especially walleye) increased dramatically during biomanipulation. 3.,Commencing in 1987 with a massive natural die-off of cisco and declining yellow perch populations, total planktivore biomass dropped from about 300,600 kg ha,1 prior to the die-off and the fish stocking, to about 20,40 kg ha,1 in subsequent years. These low planktivore biomasses lasted until a resurgence in the perch population in 1999. 4.,During the period prior to biomanipulation when cisco were very abundant, the dominant Daphnia species was the smaller-bodied D. galeata mendotae, which usually reached a biomass maximum in June and then crashed shortly thereafter. Beginning in 1988, the larger-bodied D. pulicaria dominated, with relatively high biomasses occurring earlier in the spring and lasting well past mid-summer of many years. 5.,In many years dominated by D. pulicaria, Secchi disc readings were greater during the spring and summer months when compared with years dominated by D. galeata mendotae. During the biomanipulation evaluation period, phosphorus (P) levels also changed dramatically thus complicating our analysis. Earlier research on Lake Mendota had shown that Daphnia grazing increased summer Secchi disc readings, but P concentrations linked to agricultural and urban runoff and to climate-controlled internal mixing processes were also important factors affecting summer readings. 6.,The Lake Mendota biomanipulation project has been a success given that high densities of the large-bodied D. pulicaria have continued to dominate for over a decade, and the diversity of fishing opportunities have improved for walleye, northern pike and, more recently, yellow perch. 7.,Massive stocking coupled with very restrictive fishing regulations produced moderate increases in piscivore densities. Larger increases could be realised by more drastic restrictions on sport fishing, but these regulations would be very controversial to anglers. 8.,If the lake's food web remains in a favourable biomanipulation state (i.e. high herbivory), further improvements in water clarity are possible with future reductions in P loadings from a recently initiated non-point pollution abatement programme in the lake's drainage basin. [source] Effects of high-magnitude/low-frequency fluvial events generated by intense snowmelt or heavy rainfall in arctic periglacial environments in northern Swedish Lapland and northern SiberiaGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2004A. A. Beylich Abstract In the Latnjavagge drainage basin (68°21,N, 18°29,E), an arctic-oceanic periglacial environment in northernmost Swedish Lapland, the fluvial sediment transport and the characteristics and importance of high-magnitude/low-frequency fluvial events generated by intense snowmelt or heavy rainfall have been investigated and compared with snowmelt- and rainfall-induced discharge peaks in the Levinson-Lessing Lake basin (Krasnaya river system) on the Taimyr Peninsula, an arctic periglacial environment in northern Siberia (74°32,N, 98°35,E). In Latnjavagge (9 km2) the intensity of fluvial sediment transport is very low. Most of the total annual sediment load is transported in a few days during snowmelt generated runoff peaks. Due to the continuous and very stable vegetation covering most areas below 1300 m a.s.l. in the Latnjavagge catchment, larger rainfall events are of limited importance for sediment transport in this environment. Compared to that, in the c. 40 times larger Krasnaya riversystem rainfall-generated runoff peaks cause significant sediment transport. The main sediment sources in the Latnjavagge drainage basin are permanent ice patches, channel debris pavements mobilized during peak discharges and exposing fines, and material mobilized by slush-flows. In the Krasnaya river system river bank erosion is the main sediment source. In both periglacial environments more than 90% of the annual sediment yield is transported during runoff peaks. The results from both arctic periglacial environments underline the high importance of high-magnitude/low-frequency fluvial events for the total fluvial sediment budgets of periglacial fluvial systems. Restricted sediment availability is in both arctic environments the major controlling factor for this behaviour. [source] Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake TorneträskGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002Hans Andrén Several small river deltas are found within the Abisko area. This study deals with the Abiskojokka delta in Lake Torneträsk. The aim is to describe the recent delta and its morphological development since the middle 1960s. In the apex of the delta, bars consist of boulders and cobbles while the mouth,bars are built by pebbles, gravel and to some extent sand. Birch vegetation is found on the sandy levées while willows and sedges dominate the interlevée basins. Mouth bars close to the lake generally lack vegetation. A comparison of the map in the present study with a map from 1965 shows comparatively small changes since 1964. Similar results are achieved when comparing aerial photographs from 1959 and 2000. Thus, the growth of the Abiskojokka delta is rather small compared to several other deltas in the Scandinavian mountains. This low growth rate is a result of upstream lakes trapping the major part of the fluvial sediments. Therefore, most of the delta sediment is redistributed old glaciofluvial material from the terraces within the Abiskojokka valley. Some material might also emanate from the Abiskojokka canyon. Formation of the main part of the delta is probably associated with the lowering of the Torneträsk ice,lakes, during and after the deglaciation of the region. Although some extreme rainstorm events have occurred in the area during recent decades, the effects of these on the delta are small. The result of such events is, however, visible as deposition of sand and silt on the levées after flooding. On the other hand, the shoreline and the mouth bars are continuously changing due to rather high wave energy especially during northerly winds. Along several mouth bars, spits are formed and reformed due to wave action. Minor changes of, and within, the two main distributaries have also been noticed, especially as bank erosion and redistribution of bars. The project will continue with a survey of the distal slope (foreset slope) of the delta as well as a study (including X,ray radiography) of the bottom sediments in Lake Torneträsk close to the delta front. The upstream deltas within this drainage basin as well as other deltas within the Torneträsk region will be studied. [source] Geomorphic and dendroecological impacts of slushflows in central Gaspé Peninsula (Québec, Canada)GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2001Sonya J. Larocque Slushflows are rare phenomena in southeastern Canada. Here we report for the first time the occurrence of slushflows in a subalpine environment in eastern Canada (Mt. Albert, Gaspé Peninsula, Québec). Because nothing is known of their frequency- magnitude in the area, we reconstructed the chronology of slushflow events over the past century using dendrogeomorphic techniques based on impact scars, reaction wood and traumatic resin ducts. Slushflows contributed to the formation of a tongue-shaped accumulation of 17900 m2 at the outlet of a firstorder drainage basin. The slushflow boulder tongue was composed of heterogeneous-sized, angular and unoriented clasts, which are markedly different from the sediments of an adjacent alluvial fan. Although movements were initiated above the subalpine forest limit, slushflows induced forest fragmentation along the treed slope. Three slushflow events were identified over the past century, in 1925, 1964 and 1988, respectively, which indicate exceptional initiation conditions and considerable geomorphic activity of individual events. [source] Merkel cell carcinoma of the head and neck: A retrospective case series,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 11 2002Anthony E. Brissett MD Abstract Background. Eighty-five percent of all Merkel cell carcinomas appear on sun-exposed areas, with 50% to 55% occurring on the head and neck. Methods. A chart review was performed on 22 patients treated for Merkel cell carcinoma of the head and neck between 1981 and 1998. Results. Fifteen patients were men (68%). The average age at operation was 69.9 years (range, 24,84 years). The average duration of follow-up was 3.6 years (range, 3 days,8.6 years). Overall survival at 1, 2, and 3 years postoperatively was 78%, 68%, and 68%, respectively. The only independent predictor of survival was the type of surgical therapy. All patients who underwent wide local excision (WLE) of the primary tumor with dissection of the lymphatic drainage basin were alive at 2 years as opposed to 68% who had WLE alone and 33% who had Mohs surgery. Conclusions. WLE and dissection of the lymphatic drainage basin provided the best overall survival. © 2002 Wiley Periodicals, Inc. Head Neck 24: 982,988, 2002 [source] Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment, southern United KingdomHYDROLOGICAL PROCESSES, Issue 9 2010A. L. Collins Abstract Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub-catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time-integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub-catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub-catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02,27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub-catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub-catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15,20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley & Sons, Ltd. [source] Tectonic control of erosion and sedimentation in the Amazon Basin of BoliviaHYDROLOGICAL PROCESSES, Issue 22 2009Patrice Baby Abstract The western Amazon drainage basin, which extends from southern Colombia to northern Bolivia, comprises the Cordillera Oriental of the Andes and its adjacent foreland basin system. In northern Bolivia, the orogenic wedge of the eastern Andes is very large, and its forward propagation controls the morphology of the Madeira drainage basin. We consider here the erosion and sedimentation mass balance in this part of the Amazon Basin, estimated on the basis of recent sediment yield data, within the current tectonic and geomorphic framework. The total suspended sediment (TSS) flux exported from the present orogenic wedge of northern Bolivia has been estimated at 500,600 million t year,1. More than 50% of the total sediment load crossing the Madeira foreland basin system is deposited. The rest of the sediments (less than 46%) reaches the eastern Amazon Basin, bypassing the Brazilian craton to the north. The average mass of sediment that has been deposited from the late Miocene to the present in the Madeira foreland basin sedimentation system is less than that intercepted today, by a factor of about 2·4. These results can be interpreted as an increase in Bolivian foreland basin flexural subsidence over time, associated with crust thickening and orogenic loading, and accentuated by the growing mass of retained sediments. They are consistent with the uplift rates of the Cordillera Oriental, obtained from fission-track dating, which began increasing significantly around 10,15 Ma. Copyright © 2009 John Wiley & Sons, Ltd. [source] Snow-distribution and melt modelling for glaciers in Zackenberg river drainage basin, north-eastern GreenlandHYDROLOGICAL PROCESSES, Issue 24 2007Sebastian H. Mernild Abstract A physically based snow-evolution modelling system (SnowModel) that includes four sub-models: MicroMet, EnBal, SnowPack, and SnowTran-3D, was used to simulate eight full-year evolutions of snow accumulation, distribution, sublimation, and surface melt from glaciers in the Zackenberg river drainage basin, in north-east Greenland. Meteorological observations from two meteorological stations were used as model inputs, and spatial snow depth observations, snow melt depletion curves from photographic time lapse, and a satellite image were used for model testing of snow and melt simulations, which differ from previous SnowModel tests methods used on Greenland glaciers. Modelled test-period-average end-of-winter snow water equivalent (SWE) depth for the depletion area differs by a maximum of 14 mm w.eq., or ,6%, more than the observed, and modelled test-period-average snow cover extent differs by a maximum of 5%, or 0·8 km2, less than the observed. Furthermore, comparison with a satellite image indicated a 7% discrepancy between observed and modelled snow cover extent for the entire drainage basin. About 18% (31 mm w.eq.) of the solid precipitation was returned to the atmosphere by sublimation. Modelled mean annual snow melt and glacier ice melt for the glaciers in the Zackenberg river drainage basin from 1997 through 2005 (September,August) averaged 207 mm w.eq. year,1 and 1198 mm w.eq. year,1, respectively, yielding a total averaging 1405 mm w.eq. year,1. Total modelled mean annual surface melt varied from 960 mm w.eq. year,1 to 1989 mm w.eq. year,1. The surface-melt period started between mid-May and the beginning of June and lasted until mid-September. Annual calculated runoff averaged 1487 mm w.eq. year,1 (,150 × 106 m3) (1997,2005) with variations from 1031 mm w.eq. year,1 to 2051 mm w.eq. year,1. The model simulated a total glacier recession averaging , 1347 mm w.eq. year,1 (,136 × 106 m3) (1997,2005), which was almost equal to previous basin average hydrological water balance storage studies , 244 mm w.eq. year,1 (,125 × 106 m3) (1997,2003). Copyright © 2007 John Wiley & Sons, Ltd. [source] Snow density variations: consequences for ground-penetrating radarHYDROLOGICAL PROCESSES, Issue 7 2006A. Lundberg Abstract Reliable hydrological forecasts of snowmelt runoff are of major importance for many areas. Ground-penetrating radar (GPR) measurements are used to assess snowpack water equivalent for planning of hydropower production in northern Sweden. The travel time of the radar pulse through the snow cover is recorded and converted to snow water equivalent (SWE) using a constant snowpack mean density from the drainage basin studied. In this paper we improve the method to estimate SWE by introducing a depth-dependent snowpack density. We used 6 years measurements of peak snow depth and snowpack mean density at 11 locations in the Swedish mountains. The original method systematically overestimates the SWE at shallow depths (+25% for 0·5 m) and underestimates the SWE at large depths (,35% for 2·0 m). A large improvement was obtained by introducing a depth,density relation based on average conditions for several years, whereas refining this by using separate relations for individual years yielded a smaller improvement. The SWE estimates were substantially improved for thick snow covers, reducing the average error from 162 ± 23 mm to 53 ± 10 mm for depth range 1·2,2·0 m. Consequently, the introduction of a depth-dependent snow density yields substantial improvements of the accuracy in SWE values calculated from GPR data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Landscape influences on aluminium and dissolved organic carbon in streams draining the Hubbard Brook valley, New Hampshire, USAHYDROLOGICAL PROCESSES, Issue 9 2005Sheila M. Palmer Abstract Concentrations of both aluminium (Al) and dissolved organic carbon (DOC) in stream waters are likely to be regulated by factors that influence water flowpaths and residence times, and by the nature of the soil horizons through which waters flow. In order to investigate landscape-scale spatial patterns in streamwater Al and DOC, we sampled seven streams draining the Hubbard Brook valley in central New Hampshire. We observed considerable variation in stream chemistry both within and between headwater watersheds. Across the valley, concentrations of total monomeric aluminium (Alm) ranged from below detection limits (<0·7 µmol l,1) to 22·3 µmol l,1. In general, concentrations of Alm decreased as pH increased downslope. There was a strong relationship between organic monomeric aluminium (Alo) and DOC concentrations (R2 = 0·92). We observed the highest Alm concentrations in: (i) a watershed characterized by a steep narrow drainage basin and shallow soils and (ii) a watershed characterized by exceptionally deep forest floor soils and high concentrations of DOC. Forest floor depth and drainage area together explained much of the variation in ln Alm (R2 = 0·79; N = 45) and ln DOC (R2 = 0·87; N = 45). Linear regression models were moderately successful in predicting ln Alm and ln DOC in streams that were not included in model building. However, when back-transformed, predicted DOC concentrations were as much as 72% adrift from observed DOC concentrations and Alm concentrations were up to 51% off. This geographic approach to modelling Al and DOC is useful for general prediction, but for more detailed predictions, process-level biogeochemical models are required. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simulating pan-Arctic runoff with a macro-scale terrestrial water balance modelHYDROLOGICAL PROCESSES, Issue 13 2003Michael A. Rawlins Abstract A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described, along with comparisons with observed data across the pan-Arctic drainage basin. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The pan-Arctic water balance model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw,freeze model (TFM) driven by air temperature, modelled soil moisture content, and physiographic data. Climate time series (precipitation and air temperature) are from the National Centers for Environmental Prediction (NCEP) reanalysis project for the period 1980,2001. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1,) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year,1. The highest runoffs are found across northeastern Canada, southern Alaska, and Norway, and lower estimates are noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer,fall) runoff to the ten Arctic sea basins (r = 0·84). Model water budgets are most sensitive to changes in precipitation and air temperature, whereas less affect is noted when other model parameters are altered. Increasing daily precipitation by 25% amplifies annual runoff by 50 to 80% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model leads to runoffs that are 7 to 27% lower than the control run. The results of these model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities (particularly climate time series) to estimate terrestrial Arctic hydrological budgets better. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effects of hydrological processes on the chemical composition of riverine suspended sediment in the Zhujiang River, ChinaHYDROLOGICAL PROCESSES, Issue 12 2003Quanzhou Gao Abstract The chemical composition of riverine suspended sediment is the integration of the weathering crust minerals, soil organic matter and erosion agency within a specific drainage basin, which has been largely disturbed by the human activities. Selected metal elements of the riverine suspended sediment in the Zhujiang River were analysed using inductively coupled plasma,atomic emission spectrometry (ICP,AES) in three different hydrological phases from 1997 to 1998 at Makou and Sanshui hydrographic gauge stations, located at the lower reaches of the two main tributaries of the Zhujiang River, i.e. the Xijiang and the Beijing Rivers respectively. Organic carbon and nitrogen were also analysed using a conventional element analyser. The results demonstrate that the chemical composition of the riverine suspended sediment show obvious variability in different hydrological phases, which closely correlate to the organic matter content in suspended sediment. Intensified erosion in the flood phase results in lower concentration of the organic matter than that in the lower water level phase. The riverine suspended sediment with rich organic matter in the lower water level phase adsorbs some metal elements from the river water. Copyright © 2003 John Wiley & Sons, Ltd. [source] The geochemical characteristics of the Paraná River suspended sediment load: an initial assessmentHYDROLOGICAL PROCESSES, Issue 7 2003Pedro J. Depetris Abstract Most water in the Paraná River drainage basin is supplied by the tropical Upper Paraná (over 60% of the total annual water discharge, 550 km3). The total suspended solids (TSS) load (c. 80 × 106 t year,1), however, is essentially furnished (50,70%) by the mountainous, arid and mostly sediment-mantled upper Bermejo River drainage basin. This characteristic suggests that the Paraná River solid load (TSS, 600 km upstream from the mouth) is largely recycled sedimentary material, whose discharge-weighted mean chemical index of alteration is c. 71. The extended UCC-normalized multi-elemental diagrams are similar to those of other world rivers. Nevertheless, the detailed inspection of UCC-normalized rare earth element (REE) ,spidergrams' reveals a lithological source for the Paraná River TSS that might be compatible with either tholeiitic flood basalts (widespread in the upper drainage) or with young Andean intermediate volcanic rocks. In view of the Bermejo River's dominant role as a sediment contributor, we feel that the signature preserved in the Paraná's TSS is the latter. Conversely, the Uruguay River TSS REE signature is certainly determined by the extensive weathering products of Jurassic,Cretaceous tholeiitic basalts. Copyright © 2003 John Wiley & Sons, Ltd. [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] Geomorphic characteristics of the Minjiang drainage basin (eastern Tibetan Plateau) and its tectonic implications: New insights from a digital elevation model studyISLAND ARC, Issue 2 2006Hui-Ping Zhang Abstract The Minshan Mountain and adjacent region are the major continental escarpments along the eastern Tibetan Plateau. The Minjiang drainage basin is located within the plateau margin adjacent to the Sichuan Basin. Based on the analysis of the digital elevation model (DEM) acquired by the Shuttle Radar Topography Mission (SRTM), we know that the Minjiang drainage basin has distinct geomorphic characteristics. The regular increasing of local topographic relief from north to south is a result of the Quaternary sediment deposition within the plateau and the holistic uplift of the eastern margin of the Tibetan Plateau versus the Sichuan Basin. Results from DEM-determined Minjiang drainage sub-basins and channel profiles show that the tributaries on the opposite sides are asymmetric. Lower perimeter and area of drainage sub-basins, total channel length and bifurcation ratio within eastern flank along the Minjiang mainstream are the result of the Quaternary differential uplift of the Minshan Mountain region. Shorter stream lengths and lower bifurcation ratio might be the indications of the undergrowth and newborn features of these eastern streams, which are also representative for the eastern uplift of the Minshan Mountain. [source] Patterns in diversity of anurans along an elevational gradient in the Western Ghats, South IndiaJOURNAL OF BIOGEOGRAPHY, Issue 5 2007Rohit Naniwadekar Abstract Aim, To examine patterns in anuran species richness along an elevation gradient and identify factors that govern anuran species richness on a tropical elevational gradient. Location, Sampling for anurans was carried out in Kalakad Mundanthurai Tiger Reserve (KMTR) in the southern Western Ghats, India. Methods, Night-time sampling for anuran species richness was carried out from 20 November 2004 to 20 April 2005, during the north-east monsoon and dry seasons, using transects (50 × 2 m) and visual encounter surveys along the streams. The entire gradient was classified into thirteen 100-m elevation zones. Sampling at the alpha (single drainage basin) level was carried out in the Chinnapul River drainage basin (40,1260 m a.s.l.) and at the gamma (landscape) level in four drainage basins. Additionally, published records were used to arrive at an empirical species richness (S) for the entire landscape. Mid-Domain Null software was used to test for the possible influence of geometric constraints on anuran species at both the alpha and gamma levels. The influence of area under each elevation zone on empirical S was tested. The pattern in anuran species richness along the elevational gradient was investigated using: (1) species boundaries in each elevation zone and their habitat correlates, (2) abiotic factors as predictor variables, (3) mean snout vent lengths of anurans, and (4) correlation between the matrices of distance in the elevation zones based on microhabitat parameters and species composition. Cluster analysis on species presence,absence in the elevation zones was used to categorize the entire gradient into high, middle and low elevations. In these three elevation categories, pattern in composition of species was examined for endemism in Western Ghats,Sri Lanka biodiversity hotspot, uniqueness to an elevation zone, adaptations of adults and modes of breeding. Results, Species richness at the alpha level increased linearly with elevation, while at the gamma level there were three peaks. Maximum species richness was observed at the highest elevation (1200 m) at both the alpha and the gamma levels. The observed patterns differed significantly from mid-domain null predictions. The multi-modal pattern in species richness was a consequence of overlapping species range boundaries. Soil temperature was the best single measure in explaining the majority of variation in species richness at the alpha level (r2 = 0.846, P < 0.01). However, soil moisture was the best predictor when both the alpha and the gamma sites were pooled (r2 = 0.774, P < 0.01). Anuran body size decreased with an increase in elevation. The highest proportions of endemic and unique species were found at high elevations (> 700 m). The proportion of arboreal anurans increased from low to high elevation. Anurans exhibiting direct development were predominantly found at high elevations. Main conclusions, Geometric constraints did not influence anuran species richness along the elevational gradient. Overlapping range boundaries influenced species richness at the gamma level. Abiotic factors such as soil temperature and moisture influenced anuran species richness in the mountain range. The ,Massenerhebung effect' could be responsible for range restriction and endemism of anurans, differences in guilds and mode of reproduction. These findings highlight the importance of cloud forests for endemic anurans. [source] Microgeographic population structure of brook charr: a comparison of microsatellite and mark-recapture dataJOURNAL OF FISH BIOLOGY, Issue 3 2003B. K. Adams Polymorphism at five microsatellite genetic markers (genotyped n = 496) and mark-recapture tagging data (tagged n = 9813) were used to define the population structure of brook charr, Salvelinus fontinalis from the Indian Bay watershed, Newfoundland, Canada. Despite the absence of physical barriers to migration among lakes, both genetic and tagging data suggest that brook charr in each lake represent reproductively isolated populations. Exact tests comparing allele frequencies, , (global value = 0·063), Rst (global value = 0·052), individual assignment tests, and Nei's genetic distance provided congruent estimates of population subdivision in agreement with the tagging data (only 2·2% of recaptures were lake-to-lake). The genetic structure of the brook charr populations corresponded with the geographic structure of the drainage basin on a qualitative level, although linear distance over water was not significantly correlated with the tagging data or the genetic distance measures. The agreement between the tagging and the genetic data suggest that microsatellite markers can be useful tools for defining real biological units. The results also suggest that brook charr exhibit microgeographic population structure at the watershed scale, and that this is the scale at which conservation and management of this salmonid might best be implemented. [source] STORM DISCHARGE, LOADS, AND AVERAGE CONCENTRATIONS IN NORTHWEST OHIO RIVERS, 1975,1995,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2001R. 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] Wheat field erosion rates and channel bottom sediment sources in an intensively cropped northeastern Oregon drainage basin,LAND DEGRADATION AND DEVELOPMENT, Issue 1 2004G. N. Nagle Abstract Sediment tracers were used to quantify erosion from cultivated fields and identify major source areas of channel bottom sediment within the Wildhorse Creek drainage, an intensively cropped tributary of the Umatilla River in northeastern Oregon, USA. Available data indicated that Wildhorse Creek was one of the largest sediment yielding tributaries of the Umatilla River. Carbon, nitrogen and the nuclear bomb-derived radionuclide 137Cs were used as tracers to fingerprint sediment sources. Sediment was collected from the stream bottom and active floodplain and compared to samples from cultivated fields and channel banks. Samples were characterized on the basis of tracer concentrations and a simple mixing model was used to estimate the relative portion of bottom sediment derived from cultivated surface and channel banks. The results indicate that the amount of bottom sediment derived from cultivated surface sources was less than 26,per,cent for the 1998 winter season, although this estimate has a high margin of error. Cesium-137 was also used to estimate surface erosion from three cultivated fields in the watershed. Annual estimates of erosion since 1963 from the three sampled fields were from 3 to 7,5,t,ha,1 yr,1. For the 1998 season, it appears that most channel-bottom sediment was of subsurface origin with much of it likely coming from channel and gully banks indicating that significant reductions in sediment in Wildhorse Creek might be accomplished by the stabilization of eroding riparian areas and swales on the lower slopes of agricultural fields. Published in 2004 by John Wiley & Sons, Ltd. [source] Reproductive ecology of the freshwater red alga Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in three tropical streamsPHYCOLOGICAL RESEARCH, Issue 3 2005Orlando Necchi Junior SUMMARY Batrachospermum delicatulum specimens from three stream segments were analyzed from a tropical region in south- eastern Brazil (20°18,, 20°49,S, 49°13,, 49°46,W). Physical and chemical parameters and the spatial placement of thalli were investigated along with the reproductive characteristics of the gametophytic phase. Sequence data of the cox 2- 3 spacer region was also utilized to evaluate genetic variation in individuals within and among stream segments. Gametophyte occurred under relatively diverse environmental conditions, whereas thalli abundance was weakly or not correlated to environmental variables within the stream segments. All specimens examined were dioecious. The ratio of male/female plants was relatively low (0.5 to 1.3) and male plants tended to occur as clumps (two or three plants together). High reproductive success was observed, as indicated by the occurrence of 100% fertilized (carposporophytic) female plants. This is similar to previous reports for this and other dioecious species, which is remarkable considering the relatively low proportion of male/female plants. Results support the two hypotheses to explain the high reproductive success in dioecious species. The occurrence of male plants in clumps was evidence for a strict spatial relationship (i.e. male plants located in upstream position of female plants in order to release spermatia, which would be carried by eddies through female plants). In contrast, the occurrence of male and female plants adjacent to each other allowed outcrossing among neighboring plants with intermingled male and female branches, which seemed more applicable to some situations (low turbulence habitats). The cox 2- 3 spacer region from the 18 individuals sequenced was 376 bp and the DNA sequence was identical with no base pair substitutions. Likewise, a previous study of another Batrachospermum species showed that the same haplotypes were present in all stream segments from the same drainage basin, even though the stream segments were a considerable distance apart. Short distance dispersal either by small birds or waterway connectivity might explain these findings. [source] Evaluation of Selective Lymph Node Sampling in the Node-Negative Neck,THE LARYNGOSCOPE, Issue 6 2002Richard O. Wein MD Abstract Objective To determine whether intraoperative selective lymph node sampling before neck dissection in the node-negative (N0) neck accurately reflects the disease content of the neck and can be used to assist in treatment selection. Study Design A prospective clinical study at a university medical center. Methods Over a 2-year period, 36 patients with head and neck squamous cell carcinoma scheduled to undergo 41 elective neck dissections were enrolled. At the initiation of the neck dissection, biopsy of the "most suspicious" lymph node within the tumor's primary nodal drainage basin was performed, and the specimen was measured and sent for frozen-section evaluation. The results of lymph node sampling were compared with the final histopathologic interpretation of the resected primary and neck dissection. Results Of the 41 N0 necks, 29% (12 of 41) were positive for occult metastases. Results of selective lymph node biopsy correlated with the results of neck dissection in 34 of 41 specimens (83%). The specificity and positive predictive value of node sampling were both 100%. The proportion of cases with a positive neck dissection with a positive sampled node (sensitivity) was 42% (5 of 12). Conclusion The results of selective lymph node biopsy with frozen-section analysis in the N0 neck, as defined in the current study, did not reflect a technique with adequate sensitivity to alter intraoperative treatment strategy. [source] Three-Dimensional Optimization of Urban Drainage SystemsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 6 2000A. Freire Diogo A global mathematical model for simultaneously obtaining the optimal layout and design of urban drainage systems for foul sewage and stormwater is presented. The model can handle every kind of network, including parallel storm and foul sewers. It selects the optimal location for pumping systems and outfalls or wastewater treatment plants (defining the natural and artificial drainage basins), and it allows the presence of special structures and existing subsystems for optimal remodeling or expansion. It is possible to identify two basic optimization levels: in the first level, the generation and transformation of general layouts (consisting of forests of trees) until a convergence criterion is reached, and in the second level, the design and evaluation of each forest. The global strategy adopted combines and develops a sequence of optimal design and plan layout subproblems. Dynamic programming is used as a very powerful technique, alongside simulated annealing and genetic algorithms, in this discrete combinatorial optimization problem of huge dimension. [source] Quantifying sediment storage in a high alpine valley (Turtmanntal, Switzerland)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2009Jan-Christoph Otto Abstract The determination of sediment storage is a critical parameter in sediment budget analyses. But, in many sediment budget studies the quantification of magnitude and time-scale of sediment storage is still the weakest part and often relies on crude estimations only, especially in large drainage basins (>100,km2). We present a new approach to storage quantification in a meso-scale alpine catchment of the Swiss Alps (Turtmann Valley, 110,km2). The quantification of depositional volumes was performed by combining geophysical surveys and geographic information system (GIS) modelling techniques. Mean thickness values of each landform type calculated from these data was used to estimate the sediment volume in the hanging valleys and the trough slopes. Sediment volume of the remaining subsystems was determined by modelling an assumed parabolic bedrock surface using digital elevation model (DEM) data. A total sediment volume of 781·3×106,1005·7×106,m3 is deposited in the Turtmann Valley. Over 60% of this volume is stored in the 13 hanging valleys. Moraine landforms contain over 60% of the deposits in the hanging valleys followed by sediment stored on slopes (20%) and rock glaciers (15%). For the first time, a detailed quantification of different storage types was achieved in a catchment of this size. Sediment volumes have been used to calculate mean denudation rates for the different processes ranging from 0·1 to 2·6,mm/a based on a time span of 10,ka. As the quantification approach includes a number of assumptions and various sources of error the values given represent the order of magnitude of sediment storage that has to be expected in a catchment of this size. Copyright © 2009 John Wiley & Sons, Ltd. [source] Morphometric indices as indicators of tectonic, fluvial and karst processes in calcareous drainage basins, South Menorca Island, SpainEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2007Francesca S. Segura Abstract This study proposes using morphometric indices to discriminate the processes that shape calcareous drainage basins. To illustrate this, a DEM of the southern part of Menorca Island (Migjorn) was created and basin slope, drainage density, hypsometric curve and integral, and the area occupied by open and closed dolines were extracted from it. These indices show an important dependence on tectonics, which govern the morphology of these drainage basins and encourage the predominance of karst and/or fluvial processes in the different sectors. The morphometric indices are clearly influenced by the geological Migjorn structure, a carbonate Upper Miocene reef platform gently folded as an asymmetrical anticline. The hypsometric integral and curve discriminate the influence of tectonics and structure whilst the drainage density and the proportion of open dolines are associated with basins with more pronounced fluvial processes. A cluster analysis based on these indices discriminated three sectors where different forms and processes are found. In the western and eastern sectors, rounded basins without major fractures predominate. The basins slope at less than 5°, and karst processes outweigh fluvial processes. The central sector, however, has steeper slopes, a clearly defined drainage system, and a predominance of fluvial over karst processes. Greater uplift in this sector has facilitated the formation of elongated basins that follow the main fracture lines. Copyright © 2007 John Wiley & Sons, Ltd. [source] Close range digital photogrammetric analysis of experimental drainage basin evolutionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2003J. Brasington Abstract Despite the difficulties of establishing formal hydraulic and geometric similarity, small-scale models of drainage basins have often been used to investigate the evolution and dynamics of larger-scale landforms. Historically, this analysis has been restricted to planform basin characteristics and only in the last decade has the topographic similarity of experimental landscapes been explored through explicitly three-dimensional parameters such as the distributions of cumulative drainage area, area,slope and catchment elevation. The current emphasis on three-dimensional morphometry reflects a growing awareness of the descriptive paucity of planform data and the need for more robust analysis of spatial scaling relationships. This paradigm shift has been significantly facilitated by technological developments in topographic survey and digital elevation modelling (DEM) which now present the opportunity to acquire and analyse high-resolution, distributed elevation data. Few studies have, however, attempted to use topographic modelling to provide information on the changing pattern and rate of sediment transport though an evolving landscape directly by using multitemporal DEM differencing techniques. This paper reports a laboratory study in which digital photogrammetry was employed to derive high-resolution DEMs of a simulated landscape in declining equilibrium at 15 minute frequency through a 240 minute simulation. Detailed evaluation of the DEMs revealed a vertical precision of 1·2 mm and threshold level of change detection between surfaces of ±3 mm at the 95 per cent confidence level. This quality assurance set the limits for determining the volumetric change between surfaces, which was used to recover the sediment budget through the experiment and to examine local - and basin-scale rates of sediment transport. A comparison of directly observed and morphometric estimates of sediment yield at the basin outlet was used to quantify the closure of the sediment budget over the simulation, and revealed an encouragingly small 6·2 per cent error. The application of this dynamic morphological approach has the potential to offer new insights into the controls on landform development, as demonstrated here by an analysis of the changing pattern of the basin sediment delivery ratio during network growth. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||