► We monitor storm response in bedrock groundwater tables in two headwater catchments. ► Bedrock groundwater did not rise above the soil–bedrock interface. ► Bedrock groundwater responded rapidly to ...storm events. ► Bedrock geology has considerable impact on hillslope rainfall–runoff response.
Bedrock groundwater dynamics in headwater catchments are poorly understood and poorly characterized. Direct hydrometric measurements have been limited due to the logistical challenges associated with drilling through hard rock in steep, remote and often roadless terrain. We used a new portable bedrock drilling system to explore bedrock groundwater dynamics aimed at quantifying bedrock groundwater contributions to hillslope flow and catchment runoff. We present results from the Maimai M8 research catchment in New Zealand and Watershed 10 (WS10) at the H.J. Andrews Experimental Forest in Oregon, USA. Analysis of bedrock groundwater at Maimai, through a range of flow conditions, revealed that the bedrock water table remained below the soil–bedrock interface, indicating that the bedrock aquifer has minimal direct contributions to event-based hillslope runoff. However, the bedrock water table did respond significantly to storm events indicating that there is a direct connection between hillslope processes and the underlying bedrock aquifer. WS10 groundwater dynamics were dominated by fracture flow. A highly fractured and transmissive zone within the upper one meter of bedrock conducted rapid lateral subsurface stormflow and lateral discharge. The interaction of subsurface stormflow with bedrock storage directly influenced the measured hillslope response, solute transport and computed mean residence time. This research reveals bedrock groundwater to be an extremely dynamic component of the hillslope hydrological system and our comparative analysis illustrates the potential range of hydrological and geological controls on runoff generation in headwater catchments.
Understanding the links between groundwater age, runoff generation processes, and their effects on stream water transit time (TT) is a major research challenge. Here we present new tritium age dating ...and hydrogeological characterization from 40 bedrock wells drilled at the intensively studied Maimai Experimental Watershed in New Zealand. We investigated the extent, dynamics, and age of the groundwater in a 4.5 ha headwater catchment over a 400 day period. In particular, we explored the controls of bedrock structure on aquifer dynamics, the aquifer flow domain and its influence on time‐varying stream water TT. We show that low permeability hillslope bedrock minimizes deep recharge, thereby regulating groundwater age, stream water MTT, and surface water‐groundwater interaction. Two distinct hydrologic units can represent catchment storage: shallow young soil storage and deep much older bedrock groundwater. Groundwater ages near discharge zones were up to 23 years compared to soil water ages that ranged between 0.1 and 0.5 years. This difference in age for the two main storages resulted in contrasting seasonal stream water TT response. During the 8 month wet season, stream water TT was young and stable while stream water TT in the slightly drier summer season was highly dynamic. These qualitative field observations are a process exemplar that support the Berghuijs and Kirchner (2017) quantitative descriptions of preferential release of young streamflow; and for the Maimai catchment, support the notion that most groundwater is exchanged only slowly with the surface and is therefore relatively old.
Key Points
Groundwater and streamflow ages differ at the well‐studied Maimai watershed in New Zealand
Volumetric contributions of old bedrock groundwater to runoff generation were limited by low bedrock permeability
Catchment storage was dominated by two distinct and contrasting components: shallow, young soil water and deep, and much older bedrock water
Hillslope hydrological investigations in humid regions to date have focused mostly on runoff generation during events. The few papers that have also examined groundwater recharge processes associated ...with subsurface stormflow production have found strong linkages between episodes of runoff and recharge to the aquifer. But the range of climate, vegetation, and geological conditions examined thus far has been limited. Here we explore how geologic characteristics, timing of subsurface stormflow, and hydroclimatic conditions relate to the timing of bedrock groundwater recharge at the well‐studied Maimai watershed. We hypothesized that recharge would be determined by subsurface stormflow frequency in this system with high rainfall and little seasonality of the hydrologic response. Unexpectedly, isotopic analysis and noble gas measurements indicated that recharge occurred almost exclusively during winter months despite previous work at Maimai showing subsurface stormflow occurs in all seasons and rainfall‐runoff ratios are high year‐round. A sprinkler and dye experiment conducted directly on open bedrock identified groundwater recharge mechanisms and rates, and a simple empirical recharge model suggests almost 90% of recharge occurred from only 55% of annual precipitation. We found no correlation between the timing and magnitude of groundwater recharge and total precipitation, direct runoff or subsurface stormflow. The catchment effectively converted rainfall to runoff during all seasons, but the unfractured low permeability bedrock (2.3 × 10−8 m/s) required long durations of extended catchment wetness for appreciable recharge to occur—a condition satisfied only during winter months with lower evapotranspiration. These findings suggest the need to better understand the geologic controls of recharge in headwaters.
Key Points
Despite minimal seasonality in rainfall, runoff generation, or the rainfall‐runoff ratio, there is strong seasonality in groundwater recharge
Extended periods of high catchment wetness, rather than storm events, were the primary driver of groundwater recharge at the Maimai watershed
Unfractured low permeability bedrock and an efficient preferential flow network explain why runoff generation and recharge were uncorrelated
Headwater groundwater subsidy, defined here as out‐of‐catchment groundwater flow contribution from a headwater catchment to its larger parent watershed (i.e., higher‐order stream), can influence the ...water quality and quantity of regional water resources. But the integrated flow and transport modeling approaches currently being implemented to quantify this subsidy are limited by an absence of critical field observations, such as water table dynamics and groundwater age that are required to test such models. Here we couple tracer (and hydrometric) observations from the well‐studied 4.5‐ha M8 headwater catchment in the Maimai experimental watershed with a new semianalytical free‐surface integrated flow and transport model. Our main research goals are to quantify the magnitude, age, and flow paths of the headwaters groundwater subsidies at the Maimai experimental watershed. Additionally, we explore through virtual experiments the effects of watershed slope, watershed active thickness, and recharge rate on the age, flow path, and magnitude of out‐of‐catchment headwater groundwater subsidies versus within‐catchment (or local) groundwater flow contributions. Our results show that more than 50% of groundwater recharged in the Maimai headwaters subsidizes their parent watershed. The relative proportion of headwaters groundwater subsidies is inversely proportional to recharge rate and/or directly proportional to slope angle. Our results also show that the age of the headwater groundwater subsidies is more than 500 years, almost 9 times older than the age of within‐catchment groundwater flow contributions. These findings highlight the need to consider headwaters groundwater subsidies in groundwater management area considerations.
Key Points
More than 50% of recharge within the Maimai headwaters discharges into their parent watershed
This groundwater subsidy from headwaters to parent watershed can be hundreds of years old
Recharge rate and watershed slope appear to control the age and magnitude of groundwater subsidy
Background/Aim
The condylar fracture is among the most frequent facial fractures. Despite all the published studies, its treatment remains controversial. The aim of this retrospective study was to ...evaluate the epidemiology and complications of mandibular condyle fractures managed by surgical and conservative treatments, over a period of twenty years.
Material and Methods
The files of 262 patients with 318 condyle fractures were included in this study. One hundred and seven patients had conservative management, and 155 had surgical management for the condylar fractures. The outcomes were assessed by reviewing the patient's clinical records.
Results
The prevalence was higher in males and most patients were Caucasians in the third decade of life. The mean age was 30.17 years old. The main causes were motorcycle accidents followed by bike accidents, and the mean follow‐up time was 226.5 days. The number of complications found in the two modalities of treatment was low and similar.
Conclusion
Both treatments achieved their goals. There was no statistical difference in the complication rate between the two groups.
The working principle of the electrochemical softening process was studied at the laboratory scale in order to get a better understanding and to optimize the construction and the efficiency of ...industrial electrolysers. For this purpose pure calco carbonic synthetic waters with well defined hardness or distribution water from Paris were used. By using a local pH sensor, it was shown that the increase of the pH in the very vicinity of the cathode induces the precipitation of the calcium carbonate on the plate, in a first step under the effect of the oxygen reduction, and after that by water reduction associated with hydrogen evolution. The local pH can reach values greater than 10. The morphology and the crystal form (calcite, vaterite and/or aragonite) of the deposits were identified by scanning or transmission electron microscopy and by X ray diffraction. It was shown that, at the beginning of the treatment, vaterite and calcite crystals form a compact layer. In galvanostatic conditions, the decrease of the active area by deposition of the insulating scale leads to an increase of the local current density and then, to the transition towards the electrolytic water reduction regime. Adendritic growth of the calcium carbonate forming a porous layer through which hydrogen diffuses easily is observed.
An investigation carried out on a model scale electrolyser showed the influence of various operating parameters such as current intensity, time of treatment etc. on the efficiency of the device. This electrochemical process is also able to eliminate partially various other species like magnesium.
In dynamic intrinsically conducting films, counterions transfer and conformational movements stimulated by the electrochemical reactions affect the free water molecules transfer. ...Poly(3,4-ethylenedioxythiophene) or PEDOT is included in this category. Here, p-doping of PEDOT immersed in LiClO4 aqueous solution was explored by ac-electrogravimetry. Electrochemical impedance spectroscopy combined with mass impedance spectroscopy proves useful for species identification and kinetics. For PEDOT, new equations have been developed to analyze the ac-electrogravimetry response. Quantitatively, faster free water transfer and slower coupled ClO4−/free water transfer were separated. Free water transfer plays a key role as a “fingerprint” of conformational movements. This might respond to fundamental questions about the mechanism of PEDOT as well as their implication in technological devices based on this polymer.
A home-made magnetic device was built with permanent magnets for treating scaling waters. Its efficiency was evaluated by measuring the remaining ionic calcium at the output of the device by means of ...an ion selective electrode. The scaling power of the treated water was estimated through an electrochemical scaling test. Chroamperometric curves and chronoelectrogravimetric curves were plotted to obtain the scaling time and the nucleation time of the scale deposition. The variation of the efficiency of the magnetic treatment was studied when the length of treatment, the flow velocity of the scaling water in the device, the material of the pipe where the scaling water flowed were changed. An empirical relationship, which gives the value of the efficiency in function of the length of treatment and the flow velocity, was proposed. Possible mechanisms of action of the magnetic treatment were discussed.
The main purpose of this work was to investigate the influence of the material of the pipe, through which scalant water (4
mM of CaCO
3) was magnetically treated, on the calcium carbonate ...precipitation process. Tested solutions were exposed to a magnetic field (MF) of 0.16
T for 15
min with different flow rates (0.54–0.94
L
min
−1) and pH (6–7.5). Magnetic water treatment and pipe material (PTFE, Tygon, PVC, copper, and stainless steel) effects on CaCO
3 crystallization were assessed by means of a precipitation test based on the dissolved-CO
2 degasification method. It was shown that magnetic treatment (MT) affects calcium carbonate crystallization by increasing the total precipitate quantity and by favouring its formation in the bulk solution instead of its incrustation on the walls. This was observed for all used pipe materials but, it is strongly dependent on their physico-chemical properties. It was found that the homogeneous and total precipitation ratios were significantly influenced when MF was applied through non-conductive materials. It was also found that for the same pipe material, the surface roughness plays an important role on the effect of MT on CaCO
3 crystallization. In addition, it was shown that the pipe material strongly influences the nucleation process of CaCO
3 even in the absence of MF.
A novel technique allowed EIS and microscopical observation of the interface between electrode and solution to be coupled in situ. The electrochemical reduction of oxygen was investigated by using ...this device when the electrode surface was progressively covered by an insulating layer of scale deposit. It was shown that two time domains can be distinguished from the initial time of the experiment corresponding to a bare electrode up to a totally blocked surface. In the first part of the experiment, EIS showed one time constant which characterizes the charge transfer process of water reduction. When the percentage of coverage reached more than 80%, this latter electrochemical contribution to EIS was negligible and the reduction process of oxygen was highlighted by two time constants observed from impedance diagrams. The high frequency response characterized the charge transfer process and the low frequency loop identified the diffusion process of oxygen. An electrochemical model was proposed to explain the shape of the impedance spectra plotted with respect to the time of coverage. The good correlation between the experimental and the fitted model curves led to the change versus time of the different parameters of the equivalent circuit. It notably showed that the double layer capacity was directly proportional to the active surface measured by the microscope observation until the surface was totally covered, according to the expectations in the experimental conditions used here.
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