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Simon Hoeg - One of the best experts on this subject based on the ideXlab platform.
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quantifying uncertainties in tracer based hydrograph separations a case study for two three and five component hydrograph separations in a mountainous catchment
Hydrological Processes, 2003Co-Authors: S Uhlenbrook, Simon HoegAbstract:The hydrograph separation technique using natural tracers, in which different runoff components are quantified according to their chemical signature, is a widely used method for investigating runoff generation processes at the catchment scale. The first objective of this study is to demonstrate a modified methodology for separating three and five runoff components using 18 O and Dissolved Silica as tracers. The second is to evaluate, with an uncertainty propagation technique using Gaussian error estimators, the hydrograph separation uncertainties that arise due to different error effects. During four summer storm events, an interaction among three main runoff components having distinct Dissolved Silica concentrations was demonstrated for the mountainous Zastler catchment (18.4 km 2 , southern Black Forest Mountains, southwest Germany). The three main runoff components are surface storage (low Silica, saturated and impermeable areas), shallow ground water (medium Silica, periglacial and glacial drift cover), and deep ground water (high Silica, crystalline detritus and hard rock aquifer). Together with the event and pre-event water fractions of surface runoff and shallow ground water runoff, five runoff components are considered in all. Pre-event water from shallow ground water storage dominated the total discharge during floods and was also important during low flows Event water from shallow ground water was detectable only during the falling limb of a larger flood with high antecedent moisture conditions and during the peaks of three events with low antecedent moisture conditions. Runoff from surface storage is only significant during floods and can be composed of event and pre-event water. The latter reacts later and is important only during the peak of the large event with high antecedent moisture conditions. Runoff from the deeper ground water behaves quite consistently (pure pre-event water). It is demonstrated that large relative uncertainties must he considered for the quantification of runoff components. Uncertainties are caused by: (i) tracer analysis and discharge measurement; (ii) intra-storm variability of 18 O; (iii) elevation effect of 18 O and Silica; (iv) solution of minerals during runoff formation; and (v) general spatial heterogeneity of tracer concentrations. The last source of error was the most significant. The error structure was analysed in detail and showed varying error significance within an event and for different events. It is shown that, for the meso-scale catchment investigated, only qualitative results of the contribution of a runoff component can be obtained by the hydrograph separation technique. The importance of reducing errors that have the largest impact is clearly demonstrated; therefore, a targeted sampling strategy is required.
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hydrograph separation in a mountainous catchment combining hydrochemical and isotopic tracers
Hydrological Processes, 2000Co-Authors: S Uhlenbrook, Simon Hoeg, Ch LeibundgutAbstract:Runoff components of the Zastler catchment (18\4 km2, southern Black Forest, Germany) were analysed with hydrograph separations using stable oxygen isotopes and Dissolved Silica. It was shown that event water and components with low Silica contributed only small amounts to total runoff. In addition, comparison of the two-component hydrograph separations showed that the low-Silica components are generated by both event water and pre-event water fractions, depending on the state of the system. A modified three-component hydrograph separation method was introduced using Dissolved Silica and 18O. During storm events an interaction of three runoff components having distinct Silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was appropriate to assign (i) the low Silica component to the riparian zones and impermeable areas, (ii) the medium Silica component to the periglacial debris cover and (iii) the high Silica component to the crystalline detritus and crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium Silica concentrations reacted very sensitively and intensely. The contribution of this component to total runoff is comparatively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runoff generation processes occurring in this reservoir. Copyright © 2000 John Wiley & Sons, Ltd.
Eric Struyf - One of the best experts on this subject based on the ideXlab platform.
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tracing silicon cycling in the okavango delta a sub tropical flood pulse wetland using silicon isotopes
Geochimica et Cosmochimica Acta, 2014Co-Authors: Patrick J Frings, Eric Struyf, Keotsheple Mosimane, Christina L De La Rocha, Dimitri Van Pelt, Jonas Schoelynck, Mike Murray Hudson, Mangaliso J Gondwe, Piotr Wolski, William R GrayAbstract:Chemical weathering of Silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of Silicate weathering rates. Silicon isotopes (d30Si) may be a useful tool to investigate these processes. Here, we present 82 d30Si measurements from surface waters, pore waters, biogenic Silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. d30Si in Dissolved Silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19&), imply- ing the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi d30Si (n = 30) ranges from (Less)
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Fluxes of water, sediments, and biogeochemical compounds in salt marshes
Ecological Processes, 2013Co-Authors: Sergio Fagherazzi, Eric Struyf, Patricia L Wiberg, Stijn Temmerman, Yong Zhao, Peter A RaymondAbstract:Tidal oscillations systematically flood salt marshes, transporting water, sediments, organic matter, and biogeochemical elements such as Silica. Here we present a review of recent studies on these fluxes and their effects on both ecosystem functioning and morphological evolution of salt marshes. We reexamine a simplified model for the computation of water fluxes in salt marshes that captures the asymmetry in discharge between flood and ebb. We discuss the role of storm conditions on sediment fluxes both in tidal channels and on the marsh platform. We present recent methods and field instruments for the measurement of fluxes of organic matter. These methods will provide long-term data sets with fine temporal resolution that will help scientists to close the carbon budget in salt marshes. Finally, the main processes controlling fluxes of biogenic and Dissolved Silica in salt marshes are explained, with particular emphasis on the uptake by marsh macrophytes and diatoms.
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tidal marshes and biogenic Silica recycling at the land sea interface
Limnology and Oceanography, 2006Co-Authors: Eric Struyf, Armel Dausse, Stefan Van Damme, Britta Gribsholt, Henricus T S Boschker, Jack J Middelburg, Patrick MeireAbstract:We studied the seasonal exchange of biogenic Silica (BSi) and Dissolved Silica (DSi) between a freshwater and a saltwater tidal marsh and the adjacent coastal waters. Export of DSi was observed from both tidal marshes, whereas BSi was imported in association with suspended solids. The export of DSi was highest (23.4% and 123.8% in the freshwater and saltwater marsh, respectively) in summer when DSi concentrations were low in the nearby coastal waters. Combined data from both marshes suggested a logarithmic decrease in DSi export with increasing DSi concentrations in the inundating waters. BSi import was observed year round in the freshwater marsh, but only in summer in the saltwater marsh. The results show that DSi export from tidal marshes, both freshwater and salt water, contributes significantly to estuarine Si availability in summer and provide new insights regarding potential linkages between tidal marshes and secondary production in nearby coastal waters.
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freshwater marshes as Dissolved Silica recyclers in an estuarine environment schelde estuary belgium
Hydrobiologia, 2005Co-Authors: Eric Struyf, Britta Gribsholt, S Van Damme, Patrick MeireAbstract:Compared to knowledge about N and P processing in the aquatic continuum of lakes, wetlands and estuaries, knowledge concerning transport and cycling of Si is only fragmentary. Furthermore, Si research in estuaries has mainly been focused on subtidal benthic sediments and uptake and recycling by diatom communities. The biogeochemical cycling of Si in tidal wetlands, which can contain large amounts of Si, has thus far been neglected. We have conducted several whole ecosystem Si mass-balances on a freshwater marsh located in the Schelde estuary (6 tidal cycles, 2 with BSi included). Our measurements show that the freshwater marsh acts as an important source of Dissolved Si to the main river (1–18% more export than import, on average 0.114 g m−2). This export is compensated by import of amorphous Silica into the marsh (19–55% more import than export). The marsh was shown to act as Silica recycler, resupplying biologically available Dissolved Si to the estuarine ecosystem. Extrapolations show that during summer and spring months, when Dissolved Silica is depleted due to diatom growth, almost half of the total Dissolved Silica load in the main river channel could result from marsh recycling.
Patrick Meire - One of the best experts on this subject based on the ideXlab platform.
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tidal marshes and biogenic Silica recycling at the land sea interface
Limnology and Oceanography, 2006Co-Authors: Eric Struyf, Armel Dausse, Stefan Van Damme, Britta Gribsholt, Henricus T S Boschker, Jack J Middelburg, Patrick MeireAbstract:We studied the seasonal exchange of biogenic Silica (BSi) and Dissolved Silica (DSi) between a freshwater and a saltwater tidal marsh and the adjacent coastal waters. Export of DSi was observed from both tidal marshes, whereas BSi was imported in association with suspended solids. The export of DSi was highest (23.4% and 123.8% in the freshwater and saltwater marsh, respectively) in summer when DSi concentrations were low in the nearby coastal waters. Combined data from both marshes suggested a logarithmic decrease in DSi export with increasing DSi concentrations in the inundating waters. BSi import was observed year round in the freshwater marsh, but only in summer in the saltwater marsh. The results show that DSi export from tidal marshes, both freshwater and salt water, contributes significantly to estuarine Si availability in summer and provide new insights regarding potential linkages between tidal marshes and secondary production in nearby coastal waters.
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freshwater marshes as Dissolved Silica recyclers in an estuarine environment schelde estuary belgium
Hydrobiologia, 2005Co-Authors: Eric Struyf, Britta Gribsholt, S Van Damme, Patrick MeireAbstract:Compared to knowledge about N and P processing in the aquatic continuum of lakes, wetlands and estuaries, knowledge concerning transport and cycling of Si is only fragmentary. Furthermore, Si research in estuaries has mainly been focused on subtidal benthic sediments and uptake and recycling by diatom communities. The biogeochemical cycling of Si in tidal wetlands, which can contain large amounts of Si, has thus far been neglected. We have conducted several whole ecosystem Si mass-balances on a freshwater marsh located in the Schelde estuary (6 tidal cycles, 2 with BSi included). Our measurements show that the freshwater marsh acts as an important source of Dissolved Si to the main river (1–18% more export than import, on average 0.114 g m−2). This export is compensated by import of amorphous Silica into the marsh (19–55% more import than export). The marsh was shown to act as Silica recycler, resupplying biologically available Dissolved Si to the estuarine ecosystem. Extrapolations show that during summer and spring months, when Dissolved Silica is depleted due to diatom growth, almost half of the total Dissolved Silica load in the main river channel could result from marsh recycling.
Jeff P Raffensperger - One of the best experts on this subject based on the ideXlab platform.
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modelling transport of Dissolved Silica in a forested headwater catchment the effect of hydrological and chemical time scales on hysteresis in the concentration discharge relationship
Hydrological Processes, 2001Co-Authors: George M Hornberger, Todd M Scanlon, Jeff P RaffenspergerAbstract:The relationship between concentration c and discharge Q in a stream is one of the aspects of hydrochemical catchment response that has been used widely as a diagnostic. In particular, loops in the c-Q curve, commonly referred to as hysteresis loops, are used to infer particular mixing patterns. At the South Fork of Brokenback Run (SFBR) in the Shenandoah National Park, Virginia, we have evidence that stream dynamics reflect a system composed of an ephemeral subsurface stormflow zone perched above a perennial water table. The relationship between Dissolved Silica and stream discharge exhibits hysteresis in the clockwise (CW) direction. Modelling this relationship in the context of three-component mixing with constant-concentration end members failed to reproduce the observed c-Q pattern. In this paper we examine the possibility that temporal variation in soil-water concentrations of Silica can explain how CW hysteresis loops in the c-Q curve can arise. In particular, we examine the role of the ratio of a hydrological time scale to a chemical time scale in determining the nature of hysteresis loops. The CW loops that we observe in SFBR can be explained by time variability in soil-water concentrations only if the chemical (leaching) time constant is less than (or only slightly greater than) the hydrological time constant. The near equality of these time constants is consistent with reports from hydrological measurements and leaching experiments.
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modeling transport of Dissolved Silica in a forested headwater catchment implications for defining the hydrochemical response of observed flow pathways
Water Resources Research, 2001Co-Authors: Todd M Scanlon, Jeff P Raffensperger, George M HornbergerAbstract:Groundwater, subsurface stormflow, and overland flow components of discharge, derived from a hydrological model that was applied to a forested headwater catchment in north central Virginia, were used with measured stream water and lysimeter concentrations of Dissolved Silica to investigate the hydrochemical behavior of the catchment. Concentrations in base flow, taken to be a reflection of groundwater, vary with discharge, an observation in conflict with the typical assumption of constant concentration used in end-member mixing analyses. This observed flow dependence was modeled by considering the concentration in groundwater to be related to the saturation deficit in this zone. A positive correlation between the average groundwater saturation deficit and base flow Dissolved Silica concentrations is consistent with batch experiments and petrographic analysis of regolith core samples, which both indicate an increase in Silica available for dissolution with depth in the groundwater zone. In the absence of subsurface storm flow zone sampling during rainfall events a constant concentration was assumed for this zone. Concentration-discharge (C-Q) paths in the stream were used to evaluate the modeled stream Silica concentrations. An inconsistency in the direction of the modeled C-Q rotations suggests that the storm flow zone Dissolved Silica concentration may also vary with time, because of the “flushing” of high-concentration, preevent soil water on the rising limb of the storm hydrograph. For this catchment in Virginia the assumption of a constant concentration for subsurface storm flow, as well as for base flow, appears to be invalid.
George M Hornberger - One of the best experts on this subject based on the ideXlab platform.
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modelling transport of Dissolved Silica in a forested headwater catchment the effect of hydrological and chemical time scales on hysteresis in the concentration discharge relationship
Hydrological Processes, 2001Co-Authors: George M Hornberger, Todd M Scanlon, Jeff P RaffenspergerAbstract:The relationship between concentration c and discharge Q in a stream is one of the aspects of hydrochemical catchment response that has been used widely as a diagnostic. In particular, loops in the c-Q curve, commonly referred to as hysteresis loops, are used to infer particular mixing patterns. At the South Fork of Brokenback Run (SFBR) in the Shenandoah National Park, Virginia, we have evidence that stream dynamics reflect a system composed of an ephemeral subsurface stormflow zone perched above a perennial water table. The relationship between Dissolved Silica and stream discharge exhibits hysteresis in the clockwise (CW) direction. Modelling this relationship in the context of three-component mixing with constant-concentration end members failed to reproduce the observed c-Q pattern. In this paper we examine the possibility that temporal variation in soil-water concentrations of Silica can explain how CW hysteresis loops in the c-Q curve can arise. In particular, we examine the role of the ratio of a hydrological time scale to a chemical time scale in determining the nature of hysteresis loops. The CW loops that we observe in SFBR can be explained by time variability in soil-water concentrations only if the chemical (leaching) time constant is less than (or only slightly greater than) the hydrological time constant. The near equality of these time constants is consistent with reports from hydrological measurements and leaching experiments.
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modeling transport of Dissolved Silica in a forested headwater catchment implications for defining the hydrochemical response of observed flow pathways
Water Resources Research, 2001Co-Authors: Todd M Scanlon, Jeff P Raffensperger, George M HornbergerAbstract:Groundwater, subsurface stormflow, and overland flow components of discharge, derived from a hydrological model that was applied to a forested headwater catchment in north central Virginia, were used with measured stream water and lysimeter concentrations of Dissolved Silica to investigate the hydrochemical behavior of the catchment. Concentrations in base flow, taken to be a reflection of groundwater, vary with discharge, an observation in conflict with the typical assumption of constant concentration used in end-member mixing analyses. This observed flow dependence was modeled by considering the concentration in groundwater to be related to the saturation deficit in this zone. A positive correlation between the average groundwater saturation deficit and base flow Dissolved Silica concentrations is consistent with batch experiments and petrographic analysis of regolith core samples, which both indicate an increase in Silica available for dissolution with depth in the groundwater zone. In the absence of subsurface storm flow zone sampling during rainfall events a constant concentration was assumed for this zone. Concentration-discharge (C-Q) paths in the stream were used to evaluate the modeled stream Silica concentrations. An inconsistency in the direction of the modeled C-Q rotations suggests that the storm flow zone Dissolved Silica concentration may also vary with time, because of the “flushing” of high-concentration, preevent soil water on the rising limb of the storm hydrograph. For this catchment in Virginia the assumption of a constant concentration for subsurface storm flow, as well as for base flow, appears to be invalid.