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Steven M Wondzell - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal variation in river corridor exchange across a 5th order Mountain Stream network
Hydrology and Earth System Sciences, 2019Co-Authors: Adam S Ward, Steven M Wondzell, Noah M Schmadel, Skuyler Herzog, Jay P Zarnetske, Viktor Baranov, Phillip J BlaenAbstract:Abstract. Although most field and modeling studies of river corridor exchange have been conducted at scales ranging from tens to hundreds of meters, results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchanges are expected to vary with hydrologic forcing and the local geomorphic setting. While we desire predictive power, we lack a complete spatiotemporal relationship relating discharge to the variation in geologic setting and hydrologic forcing that is expected across a river basin. Indeed, the conceptual model of Wondzell (2011) predicts systematic variation in river corridor exchange as a function of (1) variation in baseflow over time at a fixed location, (2) variation in discharge with location in the river network, and (3) local geomorphic setting. To test this conceptual model we conducted more than 60 solute tracer studies including a synoptic campaign in the 5th-order river network of the H. J. Andrews Experimental Forest (Oregon, USA) and replicate-in-time experiments in four watersheds. We interpret the data using a series of metrics describing river corridor exchange and solute transport, testing for consistent direction and magnitude of relationships relating these metrics to discharge and local geomorphic setting. We confirmed systematic decrease in river corridor exchange space through the river networks, from headwaters to the larger main stem. However, we did not find systematic variation with changes in discharge through time or with local geomorphic setting. While interpretation of our results is complicated by problems with the analytical methods, the results are sufficiently robust for us to conclude that space-for-time and time-for-space substitutions are not appropriate in our study system. Finally, we suggest two strategies that will improve the interpretability of tracer test results and help the hyporheic community develop robust datasets that will enable comparisons across multiple sites and/or discharge conditions.
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simulation of dynamic expansion contraction and connectivity in a Mountain Stream network
Advances in Water Resources, 2018Co-Authors: Adam S Ward, Noah M Schmadel, Steven M WondzellAbstract:Abstract Headwater Stream networks expand and contract in response to changes in Stream discharge. The changes in the extent of the Stream network are also controlled by geologic or geomorphic setting – some reaches go dry even under relatively wet conditions, other reaches remain flowing under relatively dry conditions. While such patterns are well recognized, we currently lack tools to predict the extent of the Stream network and the times and locations where the network is dry within large river networks. Here, we develop a perceptual model of the river corridor in a headwater Mountainous catchment, translate this into a reduced-complexity mechanistic model, and implement the model to examine connectivity and network extent over an entire water year. Our model agreed reasonably well with our observations, showing that the extent and connectivity of the river network was most sensitive to hydrologic forcing under the lowest discharges (Qgauge 10 L s−1) the extent of the network was relatively insensitive to hydrologic forcing and was instead determined by the network topology. We do not expect that the specific thresholds observed in this study would be transferable to other catchments with different geology, topology, or hydrologic forcing. However, we expect that the general pattern should be robust: the dominant controls will shift from hydrologic forcing to geologic setting as discharge increases. Furthermore, our method is readily transferable as the model can be applied with minimal data requirements (a single Stream gauge, a digital terrain model, and estimates of hydrogeologic properties) to estimate flow duration or connectivity along the river corridor in unstudied catchments. As the available information increases, the model could be better calibrated to match site-specific observations of network extent, locations of dry reaches, or solute break through curves as demonstrated in this study. Based on the low initial data requirements and ability to later tune the model to a specific site, we suggest example applications of this parsimonious model that may prove useful to both researchers and managers.
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evaluation of alternative groundwater flow models for simulating hyporheic exchange in a small Mountain Stream
Journal of Hydrology, 2009Co-Authors: Steven M Wondzell, Justin Lanier, Roy HaggertyAbstract:summary Groundwater flow models have been used to estimate the amount of exchange flow and the residence time distribution of Stream water in the hyporheic zone. However, reliability of these predictions have not been tested. We ask the questions: (1) how reliable are hyporheic groundwater models in typical applications examining hyporheic exchange flows? and (2) how does the reliability change with increased data availability and model sophistication? We developed groundwater flow models of the hyporheic zone for a Mountain Stream in the HJ Andrews Experimental Forest, Oregon. The models are based on surveyed topography and hydraulic conductivity (K) measurements from both slug tests and a well-to-well tracer test. We developed several models using different methods to estimate two of the most uncertain parameters – K and the depth and shape of the bedrock boundary. We first tested the goodness of fit of each model to the water levels observed in a network of wells and piezometers. Results showed that differences among models in predicted heads were quite small, whereas differences among estimated hyporheic fluxes varied by a factor of two. We then tested the model predictions of tracer arrival times to each well in the network during a Stream-tracer injection. Comparison of simulated and observed travel times showed that increased model sophistication did not lead to improved model reliability, because travel time predictions from the homogeneous model were equal to, or better than, the predictions from the heterogeneous models. While general trends in solute breakthrough were correct in the models, K data from even 37 wells in a 15 m by 50 m model domain were insufficient to characterize detailed arrival times accurately. This suggests that geomorphic data may be sufficient to predict water fluxes through the subsurface and approximate travel times. However, for detailed analysis of solute transport pathways and breakthroughs, intensive sampling of the subsurface may be necessary. Published by Elsevier B.V.
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a modelling study of hyporheic exchange pattern and the sequence size and spacing of Stream bedforms in Mountain Stream networks oregon usa
Hydrological Processes, 2006Co-Authors: M N Gooseff, Steven M Wondzell, Justin Lanier, Justin K Anderson, Roy HaggertyAbstract:Studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale, namely slope breaks in the longitudinal profile of Streams that generate subsurface head distributions. We recently completed a field study that suggested channel unit spacing in Stream longitudinal profiles can be used to predict the spacing between zones of upwelling (flux of hyporheic water into the Stream) and downwelling (flux of Stream water into the hyporheic zone) in the beds of Mountain Streams. Here, we use two-dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of Stream flow in second-, third-, and fourth-order Mountain Stream reaches. Modelling allowed us to (1) represent visually the effect that the shape of the longitudinal profile has on the flow net beneath Streambeds; (2) isolate channel unit sequence and spacing as individual factors controlling the depth that Stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones; (3) evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real Streams. We simulated hyporheic exchange in two sets of idealized Stream reaches and one set of observed Stream reaches. Idealized profiles were constructed using regression equations relating channel form to basin area. The size and length of channel units (step size, pool length, etc.) increased with increasing Stream order. Simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased (from 2Ð 7mt o 7 Ð6 m), and downwelling lengths increased (from 2Ð 9mt o 6 Ð0 m) with increase in Stream order from second to fourth order. Step spacing in the idealized reaches increased from 5Ð 3mt o 13Ð7 m as Stream size increased from second to fourth order. Simulated downwelling lengths increased from 4Ð 3m in second-order Streams to 9Ð7 m in fourth-order Streams with a POOL–RIFFLE–STEP channel unit sequence, and increased from 2Ð 5m to 6 Ð1 m from second- to fourth-order Streams with a POOL–STEP–RIFFLE channel unit sequence. Upwelling lengths also increased with Stream order in these idealized channels. Our results suggest that channel unit spacing, size, and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling. Though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed Stream reaches than in idealized Stream reaches, similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches. This article replaces a previously published version (Hydrological Processes, 19(17), 2915–2929 (2005) [DOI:10.1002/hyp.5790]. Copyright 2006 John Wiley & Sons, Ltd.
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power law residence time distribution in the hyporheic zone of a 2nd order Mountain Stream
Geophysical Research Letters, 2002Co-Authors: Roy Haggerty, Steven M Wondzell, Matthew A. JohnsonAbstract:[1] We measured the hyporheic residence time distribution in a 2nd-order Mountain Stream at the H. J. Andrews Experimental Forest, Oregon, and found it to be a power-law over at least 1.5 orders of magnitude in time (1.5 hr to 3.5 d). The residence time distribution has a very long tail which scales as t−1.28, and is poorly characterized by an exponential model. Because of the small power-law exponent, efforts to characterize the mean hyporheic residence time (ts) in this system result in estimates that are scale invariant, increasing with the characteristic advection time within the Stream channel (tad). The distribution implies the hyporheic zone has a very large range of exchange timescales, with significant quantities of water and solutes stored over time-scales very much longer than tad. The hyporheic zone in such Streams may contribute to short-time fractal scaling in time series of solute concentrations observed in small-watershed studies.
Roy Haggerty - One of the best experts on this subject based on the ideXlab platform.
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evaluation of alternative groundwater flow models for simulating hyporheic exchange in a small Mountain Stream
Journal of Hydrology, 2009Co-Authors: Steven M Wondzell, Justin Lanier, Roy HaggertyAbstract:summary Groundwater flow models have been used to estimate the amount of exchange flow and the residence time distribution of Stream water in the hyporheic zone. However, reliability of these predictions have not been tested. We ask the questions: (1) how reliable are hyporheic groundwater models in typical applications examining hyporheic exchange flows? and (2) how does the reliability change with increased data availability and model sophistication? We developed groundwater flow models of the hyporheic zone for a Mountain Stream in the HJ Andrews Experimental Forest, Oregon. The models are based on surveyed topography and hydraulic conductivity (K) measurements from both slug tests and a well-to-well tracer test. We developed several models using different methods to estimate two of the most uncertain parameters – K and the depth and shape of the bedrock boundary. We first tested the goodness of fit of each model to the water levels observed in a network of wells and piezometers. Results showed that differences among models in predicted heads were quite small, whereas differences among estimated hyporheic fluxes varied by a factor of two. We then tested the model predictions of tracer arrival times to each well in the network during a Stream-tracer injection. Comparison of simulated and observed travel times showed that increased model sophistication did not lead to improved model reliability, because travel time predictions from the homogeneous model were equal to, or better than, the predictions from the heterogeneous models. While general trends in solute breakthrough were correct in the models, K data from even 37 wells in a 15 m by 50 m model domain were insufficient to characterize detailed arrival times accurately. This suggests that geomorphic data may be sufficient to predict water fluxes through the subsurface and approximate travel times. However, for detailed analysis of solute transport pathways and breakthroughs, intensive sampling of the subsurface may be necessary. Published by Elsevier B.V.
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a modelling study of hyporheic exchange pattern and the sequence size and spacing of Stream bedforms in Mountain Stream networks oregon usa
Hydrological Processes, 2006Co-Authors: M N Gooseff, Steven M Wondzell, Justin Lanier, Justin K Anderson, Roy HaggertyAbstract:Studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale, namely slope breaks in the longitudinal profile of Streams that generate subsurface head distributions. We recently completed a field study that suggested channel unit spacing in Stream longitudinal profiles can be used to predict the spacing between zones of upwelling (flux of hyporheic water into the Stream) and downwelling (flux of Stream water into the hyporheic zone) in the beds of Mountain Streams. Here, we use two-dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of Stream flow in second-, third-, and fourth-order Mountain Stream reaches. Modelling allowed us to (1) represent visually the effect that the shape of the longitudinal profile has on the flow net beneath Streambeds; (2) isolate channel unit sequence and spacing as individual factors controlling the depth that Stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones; (3) evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real Streams. We simulated hyporheic exchange in two sets of idealized Stream reaches and one set of observed Stream reaches. Idealized profiles were constructed using regression equations relating channel form to basin area. The size and length of channel units (step size, pool length, etc.) increased with increasing Stream order. Simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased (from 2Ð 7mt o 7 Ð6 m), and downwelling lengths increased (from 2Ð 9mt o 6 Ð0 m) with increase in Stream order from second to fourth order. Step spacing in the idealized reaches increased from 5Ð 3mt o 13Ð7 m as Stream size increased from second to fourth order. Simulated downwelling lengths increased from 4Ð 3m in second-order Streams to 9Ð7 m in fourth-order Streams with a POOL–RIFFLE–STEP channel unit sequence, and increased from 2Ð 5m to 6 Ð1 m from second- to fourth-order Streams with a POOL–STEP–RIFFLE channel unit sequence. Upwelling lengths also increased with Stream order in these idealized channels. Our results suggest that channel unit spacing, size, and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling. Though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed Stream reaches than in idealized Stream reaches, similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches. This article replaces a previously published version (Hydrological Processes, 19(17), 2915–2929 (2005) [DOI:10.1002/hyp.5790]. Copyright 2006 John Wiley & Sons, Ltd.
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power law residence time distribution in the hyporheic zone of a 2nd order Mountain Stream
Geophysical Research Letters, 2002Co-Authors: Roy Haggerty, Steven M Wondzell, Matthew A. JohnsonAbstract:[1] We measured the hyporheic residence time distribution in a 2nd-order Mountain Stream at the H. J. Andrews Experimental Forest, Oregon, and found it to be a power-law over at least 1.5 orders of magnitude in time (1.5 hr to 3.5 d). The residence time distribution has a very long tail which scales as t−1.28, and is poorly characterized by an exponential model. Because of the small power-law exponent, efforts to characterize the mean hyporheic residence time (ts) in this system result in estimates that are scale invariant, increasing with the characteristic advection time within the Stream channel (tad). The distribution implies the hyporheic zone has a very large range of exchange timescales, with significant quantities of water and solutes stored over time-scales very much longer than tad. The hyporheic zone in such Streams may contribute to short-time fractal scaling in time series of solute concentrations observed in small-watershed studies.
Adam S Ward - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal variation in river corridor exchange across a 5th order Mountain Stream network
Hydrology and Earth System Sciences, 2019Co-Authors: Adam S Ward, Steven M Wondzell, Noah M Schmadel, Skuyler Herzog, Jay P Zarnetske, Viktor Baranov, Phillip J BlaenAbstract:Abstract. Although most field and modeling studies of river corridor exchange have been conducted at scales ranging from tens to hundreds of meters, results of these studies are used to predict their ecological and hydrological influences at the scale of river networks. Further complicating prediction, exchanges are expected to vary with hydrologic forcing and the local geomorphic setting. While we desire predictive power, we lack a complete spatiotemporal relationship relating discharge to the variation in geologic setting and hydrologic forcing that is expected across a river basin. Indeed, the conceptual model of Wondzell (2011) predicts systematic variation in river corridor exchange as a function of (1) variation in baseflow over time at a fixed location, (2) variation in discharge with location in the river network, and (3) local geomorphic setting. To test this conceptual model we conducted more than 60 solute tracer studies including a synoptic campaign in the 5th-order river network of the H. J. Andrews Experimental Forest (Oregon, USA) and replicate-in-time experiments in four watersheds. We interpret the data using a series of metrics describing river corridor exchange and solute transport, testing for consistent direction and magnitude of relationships relating these metrics to discharge and local geomorphic setting. We confirmed systematic decrease in river corridor exchange space through the river networks, from headwaters to the larger main stem. However, we did not find systematic variation with changes in discharge through time or with local geomorphic setting. While interpretation of our results is complicated by problems with the analytical methods, the results are sufficiently robust for us to conclude that space-for-time and time-for-space substitutions are not appropriate in our study system. Finally, we suggest two strategies that will improve the interpretability of tracer test results and help the hyporheic community develop robust datasets that will enable comparisons across multiple sites and/or discharge conditions.
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solute transport and transformation in an intermittent headwater Mountain Stream with diurnal discharge fluctuations
Water, 2019Co-Authors: Adam S Ward, Noah M Schmadel, Marie J Kurz, Julia L A Knapp, Phillip Blaen, C J Harman, Jennifer D Drummond, David M HannahAbstract:Time-variable discharge is known to control both transport and transformation of solutes in the river corridor. Still, few studies consider the interactions of transport and transformation together. Here, we consider how diurnal discharge fluctuations in an intermittent, headwater Stream control reach-scale solute transport and transformation as measured with conservative and reactive tracers during a period of no precipitation. One common conceptual model is that extended contact times with hyporheic zones during low discharge conditions allows for increased transformation of reactive solutes. Instead, we found tracer timescales within the reach were related to discharge, described by a single discharge-variable StorAge Selection function. We found that Resazurin to Resorufin (Raz-to-Rru) transformation is static in time, and apparent differences in reactive tracer were due to interactions with different ages of storage, not with time-variable reactivity. Overall we found reactivity was highest in youngest storage locations, with minimal Raz-to-Rru conversion in waters older than about 20 h of storage in our study reach. Therefore, not all storage in the study reach has the same potential biogeochemical function and increasing residence time of solute storage does not necessarily increase reaction potential of that solute, contrary to prevailing expectations.
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simulation of dynamic expansion contraction and connectivity in a Mountain Stream network
Advances in Water Resources, 2018Co-Authors: Adam S Ward, Noah M Schmadel, Steven M WondzellAbstract:Abstract Headwater Stream networks expand and contract in response to changes in Stream discharge. The changes in the extent of the Stream network are also controlled by geologic or geomorphic setting – some reaches go dry even under relatively wet conditions, other reaches remain flowing under relatively dry conditions. While such patterns are well recognized, we currently lack tools to predict the extent of the Stream network and the times and locations where the network is dry within large river networks. Here, we develop a perceptual model of the river corridor in a headwater Mountainous catchment, translate this into a reduced-complexity mechanistic model, and implement the model to examine connectivity and network extent over an entire water year. Our model agreed reasonably well with our observations, showing that the extent and connectivity of the river network was most sensitive to hydrologic forcing under the lowest discharges (Qgauge 10 L s−1) the extent of the network was relatively insensitive to hydrologic forcing and was instead determined by the network topology. We do not expect that the specific thresholds observed in this study would be transferable to other catchments with different geology, topology, or hydrologic forcing. However, we expect that the general pattern should be robust: the dominant controls will shift from hydrologic forcing to geologic setting as discharge increases. Furthermore, our method is readily transferable as the model can be applied with minimal data requirements (a single Stream gauge, a digital terrain model, and estimates of hydrogeologic properties) to estimate flow duration or connectivity along the river corridor in unstudied catchments. As the available information increases, the model could be better calibrated to match site-specific observations of network extent, locations of dry reaches, or solute break through curves as demonstrated in this study. Based on the low initial data requirements and ability to later tune the model to a specific site, we suggest example applications of this parsimonious model that may prove useful to both researchers and managers.
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identifiability of transient storage model parameters along a Mountain Stream
Water Resources Research, 2013Co-Authors: Christa Kelleher, M N Gooseff, Thorsten Wagener, Brian L Mcglynn, Adam S Ward, Robert A PaynAbstract:[1] Transient storage models are widely used in combination with tracer experiments to characterize Stream reaches via calibrated parameter estimates. These parameters quantify the main transport and storage processes. However, it is implicitly assumed that calibrated parameters are uniquely identifiable and hence provide a unique characterization of the Stream. We investigate parameter identifiability along with the Stream conditions that control identifiability for 10 breakthrough curves (BTC) for 100 m pulse injections along Stringer Creek, Montana, USA. Identifiability is assessed through global, variance-based sensitivity analysis of the one-dimensional transport with inflow and storage model (OTIS). Results indicate that the main channel area parameter A and the dispersion coefficient D were the most sensitive parameters and, therefore, likely to be identifiable across all timescales and reaches. Identifiability of transient storage zone size As fell into two categories along Stringer Creek. As was identifiable for lower elevation regions, corresponding to a constrained valley, higher Stream slopes, and in-channel roughness, but not for upper Stream regions, corresponding to a wider valley floor, flatter Stream slopes, and low roughness. The storage zone exchange parameter α was nonidentifiable across all study reaches. Our results suggest that only some of the processes represented in the model will be relevant and, therefore, identifiable for pulse injection data. As such, calibrated parameter estimates should be accompanied by an assessment of parameter sensitivity or uncertainty. We also show that parameter identifiability varies with Stream setting along Stringer Creek, suggesting that physical characteristics directly influence the identification of dominant Stream processes.
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hydrologic and geomorphic controls on hyporheic exchange during base flow recession in a headwater Mountain Stream
Water Resources Research, 2012Co-Authors: Adam S Ward, Michael N Gooseff, Michael Fitzgerald, T J Voltz, Andrew Binley, Kamini SinghaAbstract:Hyporheic hydrodynamics are a control on Stream ecosystems, yet we lack a thorough understanding of catchment controls on these flow paths, including valley constraint and hydraulic gradients in the valley bottom. We performed four whole-Stream solute tracer injections under steady state flow conditions at the H. J. Andrews Experimental Forest (Oregon, United States) and collected electrical resistivity (ER) imaging to directly quantify the 2-D spatial extent of hyporheic exchange through seasonal base flow recession. ER images provide spatially distributed information that is unavailable for Stream solute transport modeling studies from monitoring wells alone. The lateral and vertical extent of the hyporheic zone was quantified using both ER images and spatial moment analysis. Results oppose the common conceptual model of hyporheic "compression'' by increased lateral hydraulic gradients toward the Stream. We found that the extent of the hyporheic zone increased with decreasing vertical gradients away from the Stream, in contrast to expectations from conceptual models. Increasing hyporheic extent was observed with both increasing and decreasing down-valley (i.e., parallel to the valley gradient) and cross-valley (i.e., from the hillslope to the Stream, perpendicular to the valley gradient) hydraulic gradients. We conclude that neither cross-valley nor down-valley hydraulic gradients are sufficient predictors of hyporheic exchange flux nor flow path network extent. Increased knowledge of the controls on hyporheic exchange, the temporal dynamics of exchange flow paths, and their the spatial distribution is the first step toward predicting hyporheic exchange at the scale of individual flow paths. Future studies need to more carefully consider interactions between spatiotemporally dynamic hydraulic gradients and subsurface architecture as controls on hyporheic exchange.
Mario Aristide Lenzi - One of the best experts on this subject based on the ideXlab platform.
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geomorphic effects of large wood jams on a sub antarctic Mountain Stream
River Research and Applications, 2008Co-Authors: Luca Mao, Andrea Andreoli, Francesco Comiti, Mario Aristide LenziAbstract:Dead wood pieces, especially when organized in jams, play an important geomorphic role in Streams because of the effects on flow hydraulics, pool formation and sediments storage. The increase in Stream morphological diversity and complexity also exerts an important ecological role. This work reports on geomorphic role of large wood (LW) pieces and jams in a third-order Mountain Stream located in the Southern Tierra del Fuego (Argentina), and draining an old-growth Nothofagus-forested basin not influenced by the beavers damming activity. Even if the in-Stream number of wood pieces (length >1 m; diameter >0.1 m) is comparable to that observed in other climatic areas, the slow growth of the Nothofagus forest causes a lower wood abundance in terms of volumetric load. Because of the relatively small dimensions of the surveyed LW pieces, almost 70% of them demonstrated to have been fluvial transported and also the wood jams reflect the apparent dynamic nature of wood in the channel. Wood jams exert a significant influence on the channel morphology, representing almost half of the drop caused by steps and being responsible for the creation of 30% of the pools. LW-forced pool volume is strongly and positively correlated to the height of the LW jam. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity. Copyright © 2008 John Wiley & Sons, Ltd.
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characteristics distribution and geomorphic role of large woody debris in a Mountain Stream of the chilean andes
Earth Surface Processes and Landforms, 2007Co-Authors: Andrea Andreoli, Francesco Comiti, Mario Aristide LenziAbstract:The paper presents an analysis of amounts, characteristics and morphological impact of large woody debris (LWD) in the Tres Arroyos Stream, draining an old-growth forested basin (9·1 km2) of the Chilean Southern Andes. Large woody debris has been surveyed along a 1·5 km long channel section with an average slope of 0·07 and a general step–pool/cascade morphology. Specific wood storage is very high (656–710 m3 ha−1), comparable to that recorded in old-growth forested basins in the Pacific Northwest. Half of the LWD elements were located on the active floodplain, and around two-thirds of LWD elements were found in accumulations. Different types of log jam were observed, some heavily altering channel morphology (log-steps and valley jams), while others just line the channel edges (bankfull bench jams). Log-steps represent approximately 22% of all steps, whereas the elevation loss due to LWD (log-steps and valley jams) results in 27% loss of the total Stream potential energy. About 1600 m3 of sediment is stored in the main channel behind LWD structures, corresponding to approximately 150% of the annual sediment yield. Copyright © 2007 John Wiley & Sons, Ltd.
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displacement and transport of marked pebbles cobbles and boulders during floods in a steep Mountain Stream
Hydrological Processes, 2004Co-Authors: Mario Aristide LenziAbstract:In a small experimental catchment of the Dolomites (Rio Cordon, 5 km2) field observations have been carried out on the movement of various sized bed material particles. Displacement length of 860 marked pebbles, cobbles and boulders (0·032 < D < 0·512 m) has been measured along the river bed during individual snowmelt and flood events in the periods 1993–1994 and 1996–1998. Floods were grouped into two categories. The first includes ‘ordinary’ events, which are characterized by peak discharges with a return period of 1–5 years and by an hourly bedload rate not exceeding 20 m3 h−1. The second refers to ‘exceptional’ events with a return period of 50–60 years. A flood of this latter type occurred on 14 September 1994, with a peak discharge of 10·4 m3 s−1 and average hourly bedload rate of 324 m3 h−1. The variation according to grain size of total displacement length Li depends on the degree of mobilization of the individual fractions of the bed surface: Li is independent of Di for smaller, fully mobile grain sizes and decreases rapidly with Di for larger fractions in a state of partial transport. Sustained selective transport without a supply of sediment from upStream leads to the development of a stable coarse armoured surface through progressive winnowing of finer material from the bed surface. With supply unlimited conditions for transport, both the occurrence of extreme events and the duration of a sequences of ‘ordinary’ floods play an important role in the degree of mobilization of the individual fractions of the bed. Copyright © 2004 John Wiley & Sons, Ltd.
Regis Cereghino - One of the best experts on this subject based on the ideXlab platform.
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stable isotope evidence of trophic interactions between introduced brook trout salvelinus fontinalis and native brown trout salmo trutta in a Mountain Stream of south west france
Journal of Fish Biology, 2007Co-Authors: Julien Cucherousset, J C Aymes, Frederic Santoul, Regis CereghinoAbstract:The potential trophic impact of introduced brook trout Salvelinus fontinalis on native brown trout Salmo trutta in a Mountain Stream (south-west France) was investigated using stable isotope analysis (SIA). The isotopic signatures (δ13C and δ15N) of S. fontinalis were similar regardless of the absence or presence of S. trutta, and SIA mixing models revealed that S. fontinalis diet consisted mainly of terrestrial invertebrates. Conversely, a significant shift in S. trutta isotopic signatures (depletion of 1·6‰δ13C and enrichment of 0·6‰δ15N) was observed in sympatry with S. fontinalis; this may be due to a dietary shift towards terrestrial invertebrates. Contrary to an expected dietary divergence in sympatry, an elevated level of dietary overlap was observed between the non-native and native salmonids when in co-occurrence. This dietary convergence is more likely to be due to behavioural interactions than to variations in food availability or fish displacements.
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Influence of intermittent hydropeaking on the longitudinal zonation patterns of benthic invertebrates in a Mountain Stream
International Review of Hydrobiology, 2002Co-Authors: Regis Cereghino, Pierre Cugny, Pierre LavandierAbstract:The longitudinal zonation patterns of invertebrate species were studied in the River Oriege (Pyrenees, France) from 920 to 819 m a.s.l. At 912 m a.s.l., the river receives hypolimnetic water diverted from a nearby reservoir lake, and the natural flow may be enhanced several times a day from 1 to 11 m 3 s -1 in summer and winter, and from 5 to 15 m 3 s -1 during spring spates. During hydropeaking, the water was cooled in summer and slightly warmed in winter, but this was attenuated 3500 m downStream from the plant. Invertebrate densities were recorded in July (end of spates) and October (low flow period) at ten sampling sites : a reference site upStream of the hydrostation's discharge point (site 1), and nine sites each 400m below the outlet (sites 2-10). The longitudinal distribution of invertebrate taxa was studied using Factorial Analyses, taxa and sites were clustered using Analysis of Dynamic Cluster. The hydroelectric facility did not clearly modify the qualitative composition of the benthic fauna, but clearly affected the longitudinal zonation of several populations. The low abundance of several species below the outlet reflected the impact of both hydropeaking and zonation. These species were high Mountain species, the density of which decreases towards downStream sites in the Pyrenees, and low Mountain species, the density of which naturally decreases towards upStream sites. Some taxa disappeared in the regulated section, so their distribution in the River Oriege was primarily influenced by hydropeaking. Finally, some taxa preferentially lived in the lower section of the river where the impact of peaking flows was strongly attenuated, so their longitudinal distribution was first governed by their natural longitudinal zonation. Under this kind of river regulation (natural discharge and temperature except during periods of power generation, intermittent hydropeaking from a separate reservoir) modifications of the thermal regime had a minor effect on the population dynamics, unlike hydraulic disturbances which strongly influenced the structural attributes of benthic communities.
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use and partition of space and resources by two coexisting rhyacophila species trichoptera in a high Mountain Stream
Hydrobiologia, 1995Co-Authors: Pierre Lavandier, Regis CereghinoAbstract:Life history, distribution, drift and food habits of two coexisting Rhyacophila species, Rhyacophila evoluta and Rhyacophila intermedia were studied in a high Mountain Stream in the Pyrenees.