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Biogeochemical turnover in hyporheic zones is known to have the potential to affect the chemical signature of surface water cycling through shallow streambed sediments. This study investigates the impact of streambed physical properties on the fate of nitrate and dissolved oxygen in groundwater upwelling through the streambed of a lowland river. For analyzing depth-dependent patterns and zonation of nitrogen concentrations, diffuse gel probes in shallow (top 15 cm) streambed sediments have been deployed in a nested setup together with multilevel minipiezometers for streambed sediments of 15-150 cm. Spatial heterogeneity of groundwater upwelling was controlled by patterns of low-conductivity peat and clay strata that caused locally confined conditions, suggesting increased streambed residence times. Nitrate concentrations in the upwelling groundwater changed by up to 68.06 mg L-1 within the top 15 cm of streambed sediments and by up to 107.47 mg L-1 at depths of 15-150 cm, indicating that significant nitrogen turnover was not restricted to shallow streambed sediments. Intensive reduction of nitrate concentrations was found, in particular, in vicinity of low-conductivity streambed strata. The coincidence of confined groundwater upwelling and reduced oxygen concentrations at these locations suggests that increased residence times and associated depletion of dissolved oxygen create conditions favorable for nitrate reduction. Our results highlight that increased nitrogen turnover at aquifer-river interfaces is not necessarily limited to shallow streambed zones, where surface water is mixing with groundwater, but can affect upwelling groundwater in reactive hot spots that extend to greater streambed depths and beyond hyporheic mixing zones. Citation: Krause, S., C. Tecklenburg, M. Munz, and E. Naden (2013), Streambed nitrogen cycling beyond the hyporheic zone: Flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river,
This study investigates spatial patterns and temporal dynamics of aquifer-river exchange flow at a reach of the River Leith, UK. Observations of sub-channel vertical hydraulic gradients at the field site indicate the dominance of groundwater up-welling into the river and the absence of groundwater recharge from surface water. However, observed hydraulic heads do not provide information on potential surface water infiltration into the top 0-15 cm of the streambed as these depths are not covered by the existing experimental infrastructure. In order to evaluate whether surface water infiltration is likely to occur outside the 'window of detection', i.e. the shallow streambed, a numerical groundwater model is used to simulate hydrological exchanges between the aquifer and the river. Transient simulations of the successfully validated model (Nash and Sutcliff efficiency of 0.91) suggest that surface water infiltration is marginal and that the possibility of significant volumes of surface water infiltrating into non-monitored shallow streambed sediments can be excluded for the simulation period. Furthermore, the simulation results show that with increasing head differences between river and aquifer towards the end of the simulation period, the impact of streambed topography and hydraulic conductivity on spatial patterns of exchange flow rates decreases. A set of peak flow scenarios with altered groundwater-surface water head gradients is simulated in order to quantify the potential for surface water infiltration during characteristic winter flow conditions following the observation period. The results indicate that, particularly at the beginning of peak flow conditions, head gradients are likely to cause substantial increase in surface water infiltration into the streambed. The study highlights the potential for the improvement of process understanding of hyporheic exchange flow patterns at the stream reach scale by simulating aquifer-river exchange fluxes with a standard numerical groundwater model and a simple but robust model structure and parameterization. Copyright
Research has consistently shown that males play violent video games more frequently than females, but factors underlying this gender gap have not been examined to date. This approach examines the assumption that males play violent video games more because they anticipate more enjoyment and less guilt from engaging in virtual violence than females. This may be because males are less empathetic, tend to morally justify physical violence more and have a greater need for sensation and aggression in video game play than females. Results of a path model based on survey data of 444 respondents and using multi-step multiple mediation analyses confirm these assumptions. Taken together, the findings of this study shed further light on the gender gap in violent video game use.
Research has consistently shown that males play violent video games more frequently than females, but factors underlying this gender gap have not been examined to date. This approach examines the assumption that males play violent video games more because they anticipate more enjoyment and less guilt from engaging in virtual violence than females. This may be because males are less empathetic, tend to morally justify physical violence more and have a greater need for sensation and aggression in video game play than females. Results of a path model based on survey data of 444 respondents and using multi-step multiple mediation analyses confirm these assumptions. Taken together, the findings of this study shed further light on the gender gap in violent video game use.
Several longitudinal studies and meta-analytic reviews have demonstrated that exposure to violent media is linked to aggression over time. However, evidence on effective interventions to reduce the use of violent media and promote critical viewing skills is limited. The current study examined the efficacy of an intervention designed to reduce the use of media violence and aggression in adolescence, covering a total period of about 12 months. A sample of 683 7th and 8th graders in Germany (50.1% girls) were assigned to two conditions: a 5-week intervention and a no-intervention control group. Measures of exposure to media violence and aggressive behavior were obtained about 3 months prior to the intervention (T1) and about 7 months post-intervention (T2). The intervention group showed a significantly larger decrease in the use of violent media from T1 to T2 than the control group. Participants in the intervention group also scored significantly lower on self-reported aggressive behavior (physical aggression and relational aggression) at T2 than those in the control group, but the effect was limited to those with high levels of initial aggression. This effect was mediated by an intervention-induced decrease in the normative acceptance of aggression. No gender differences in program efficacy were found. The results show that a 5-week school-based intervention can produce changes in the use of media violence, aggressive norms, and behaviors sustained over several months.