Using Chlorine Dioxide for Drinking Water Disinfection by the Application of the Chlorite/Chlorine Process

Chlorine dioxide stock solutions for the disinfection of drinking water are made by the application of chlorite/chlorine process in many waterworks. In such cases the stock solution is always characterised by a mixture of chlorine and chlorine dioxide. The disinfection of waters of different origin with a mixture of chlorine dioxide and chlorine showed the formation of odours of different intensity. The reasons are the re‐formation of chlorine dioxide and the formation of odorous disinfection by‐products. Applying the chlorine dioxide for disinfection, its re‐formation caused by the reaction of chlorite with chlorine is the dominant reason of odour formation. When chlorine is used, the formation of odorous by‐products becomes more relevant. In order to quantify the sensitivity of water concerning odour, the odour indicator coefficient OI was defined. The decreased demand of chlorine dioxide by applying chlorine and chlorine dioxide in combination is recognised to be the key in order to avoid the formation of odour after the disinfection of drinking water with chlorine dioxide.     

From seamount to oceanic island, Porto Santo, central East-Atlantic

The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice- and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surf-rounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta: 1. closely-packed pillow lava and massive tabular lava flows along the southwestern coast of Porto Santo, and 2. a steeply inclined pillow-hyaloclastite breccia prism composed of foreset-bedded hydroclastic breccia, variably-shaped pillows, and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of Porto Santo.The facies architectures indicate emplacement: 1. on a gently sloping platform in southwestern Porto Santo, and 2. on steep offshore slopes along high energy shorelines in eastern Porto Santo.Growth of the pillow-hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn-volcanic intrusions contributed significantly. Submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern Porto Santo. The island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession. Volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity.     

A graphical approach to polar paths: Paleomagnetic cycles and global tectonics

Some problems of the conventional “minimum polar distance” approach to Precambrian pole path construction are discussed. An alternative technique, based on a less restricted approach, is proposed and assessed by using all presently-available Precambrian and Paleozoic data from the world. In the construction of any pole path, assumptions are always made on the shape of the path through regions of apparently missing data. Many different assumptions are possible. Assuming that the Precambrian tectono-stratigraphic record conforms to repeated sequences of geological events suggests we should observe cycles in the paleomagnetic data. Empirically, it is found that the pole paths for the periods Cambrian-Devonian, and 750–1000 Ma, define cycles of pole motion from equator, up to and over the pole, and back down to the equator. Similar cycles of 250-Ma periodicity can be identified in paleomagnetic data back to 2500-Ma. Global wide changes in the phase of the cycles appears to be coincident with the major subdivisions of geological time i.e., Phanerozoic + Hadrynian, Helikian, Aphebian, and Archean. Finally, the geological implications of these cyclic changes in Precambrian pole paths are briefly discussed.     

Streamflow regulation and multi-level flood plain formation: channel narrowing on the aggrading Green River in the eastern Uinta Mountains, Colorado and Utah

The style and degree of channel narrowing in aggrading reaches downstream from large dams is dependent upon the dominant geomorphic processes of the affected river, the magnitude of streamflow regulation, and the post-dam sediment transport regime. We measured different magnitudes of channel adjustment on the Green River downstream from Flaming Gorge Dam, UT, USA, that are related to these three factors. Bankfull channel width decreased by an average of about 20% in the study area. In reaches with abundant debris fans and eddy deposited sand bars, the amount of channel narrowing was proportional to the decrease in specific stream power. The fan–eddy-dominated reach with the greatest decrease in stream power narrowed by 22% while the reach with the least decrease in stream power narrowed by 11%. In reaches with the same magnitude of peak flow reduction, meandering reaches narrowed by 15% to 22% and fan–eddy-dominated reaches narrowed by 11% to 12%. Specific stream power was not significantly affected by flow regulation in the meandering reaches.In the diverse array of reach characteristics and deposit types found in the study area, all pre- and post-dam deposits are part of a suite of topographic surfaces that includes a terrace that was inundated by rare pre-dam floods, an intermediate bench that was inundated by rare post-dam floods, and a post-dam floodplain that was inundated by the post-dam mean annual flood. Analysis of historical photographs and tree-ring dating of Tamarix sp. shows that the intermediate bench and post-dam floodplain are post-dam landforms in each reach type. Although these two surfaces occur at different levels, they are forming simultaneously during flows of different magnitude. And while the relative elevation and sedimentologic characteristics of the deposits differ between meandering reaches and reaches with abundant debris fans and eddies, both reach types contain deposits at all of these topographic levels.The process of channel narrowing varied between fan–eddy-dominated and meandering reaches. In the meandering reaches, where stream power has not changed, narrowing was accomplished by essentially the same depositional processes that operated prior to regulation. In fan–eddy-dominated reaches, where significant reductions in stream power have occurred, channel narrowing has been accompanied by a change in dominant depositional processes. Mid-channel sand deposits are aggrading on deposits that, in the pre-dam era, were active gravel bars. These deposits are creating new islands and decreasing the presence of open-framework gravel bars. In eddies, bare sand bars are replaced with vegetated bars that have a simpler topography than the pre-dam deposits.     

Reaction pathways and reaction progress for the smectite-to-chlorite transformation: evidence from hydrothermally altered metabasites

The transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite/smectite mixed‐layering sequence, or an equilibrated discontinuous sequence involving smectite–corrensite–chlorite. Here, analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving (i) a continuous mixed‐layer chlorite/smectite series; (ii) a discontinuous smectite–corrensite–chlorite series and (iii) a direct smectite to chlorite transition. Such contrasting pathways are not in accord with an equilibrium mineral reaction series, suggesting that these pathways record kinetically controlled reaction progress. In the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization, and not to differences in thermal gradients or clay grain size. This suggests a kinetic effect linked to variation in fluid/rock ratios and/or a contrast between advective or diffusive fluid transport. The mode of fluid transport provides a means by which the rates of dissolution/nucleation/growth can control the reaction style and the reaction progress of the smectite to chlorite transition. Slow rates of growth are linked to the first reaction pathway involving mixed‐layering, while increasing rates of growth, relative to nucleation, promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition, representative of the third pathway.     

Snowfall into a forest and clearing

Experiments in February–March 1987 at Fraser Experimental Forest in Colorado, U.S.A., compared the number flux of snow particles above the center of an 80-m wide clearing with simultaneous samples in and above the forest 85 m upwind. Numbers of snow particles counted with electronic sensors on towers decreased with decreasing height below the canopy top in the forest and also nearer the surface in the clearing. Average fluxes were greater in the clearing than in the forest, and these differences increased with increasing average wind speed, in the 0–6 m s⁻¹ range, measured during the experiments. The greater flux at the tower in the clearing could not be completely explained by interception of snow in the forest canopy, indicating that aerodynamics may have played a part in creating the difference, even in those light winds. A plumer or concentration of snow particles appeared to have developed near the top of the canopy and spread into the clearing.     

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.