Stream Temperature Trends in Turkey

Stream temperature is an important property of water and affects most other water quality constituents. It is also a property which is very much influenced by exogenous factors like air temperature and stream flow. This study investigates long‐term trends in stream temperatures measured at various stream monitoring stations in Turkey to better understand links with climate change. It was found by statistical trend analysis that more streams have experienced decreasing trends than increasing ones. Moreover, stream temperatures show a rising tendency in most stations over Turkey. Flow‐adjusted temperatures were computed to eliminate flow dependency and these show more positive than negative trends. Management plans of streams and watersheds need to take this into account and incorporate the implications into plans.     

Transient release of Ni,Mn and Fe from mixed metal sulphides under oxidising and reducing conditions

The potential release of metals from anoxic sediments exposed to oxygen was investigated by using a synthetic preparation of metal sulphides dominated by solid phase FeS. The technique of DGT (diffusive gradients in thin-films) was used to measure sulphide and Fe, Mn and Ni in the anoxic metal-sulphide slurry, which had a pH of 6.4. Speciation calculations based on these data showed there was moderate supersaturation with respect to amorphous FeS in the solution phase. Measurements made using DGT with a range of diffusion layer thicknesses showed that when Fe, Mn and Ni are removed from solution there is fairly rapid (minutes) release from the solid phase, that is reasonably well sustained. This presumed desorptive release will be responsible for elevated concentrations of some metals in solution when sediments are resuspended. Oxidation of the slurry by bubbling with air rapidly (hours) removed Fe, Mn and Ni from the pore water solution. While Fe concentrations in solution remained low after the removal, Mn and Ni were transiently released. These results were consistent with initial rapid oxidation of Fe(II) to oxyhydroxides, which remove Mn(II) and Ni by adsorption. The slower oxidation of FeS then releases Mn and Ni, but these too are eventually removed by adsorption to iron oxyhydroxides. These data suggest that oxidation of metal sulphides will contribute to the release of metals from sediment disturbed by dredging or remedial aeration, but it is likely to be short lived, with complete removal within a day.     

Towards non-linear inversion for characterization of time-lapse phenomena through numerical modelling

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non-linear problem, the so-called ‘multiplicative regularized contrast source inversion’ (MR-CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non-linear inversion algorithm for large-scale computation problems. The numerical results show that by taking into account the non-linear nature of the problem, interpretation of the time-lapse data can be significantly improved, compared with that obtained using linear inversion.     

The effects of in-cloud mass production on atmospheric light scatter

Direct physical measurements of particle mass and number concentration indicate an increase in overall aerosol mass resulting from cloud processing, most likely through aqueous-phase chemistry (e.g., SO₂ oxidation). Measurements conducted in the Pennines of Northern England reveal an average increase of 14 to 20% in dry aerosol mass (0.003<particle diameter<0.9 μm) after aerosol passage through an orographic cloud. The rate of in-cloud mass production is most sensitive to changes in upwind particle size distributions, SO₂ concentration, and cloud water acidity. Newly-formed mass appears in size range between 200 and 600 nm and enhances the bimodality of the particle number distribution after cloud processing. Furthermore, the cloud-produced mass is estimated to increase total light scattering, b_sp, by 18 to 24%. The scattering efficiency of the dry, cloud-generated aerosol is 5.0±0.3 m² g⁻¹ and increases to 7.4±0.7 m² g⁻¹ when adjusted to 90% relative humidity by incorporating particle hygroscopicity data.     

A 20cm 2 CCD mosaic camera for a dark matter search part II : Electronics,data acquisition and performance

Conclusion To summarize, the readout and the control system of the CCD mosaic camera are running since December 1991 at the La Silla Observatory (ESO). The overall performance of the camera has been good. About 12000 pictures (data and flat-fields) have been successfully registered up to now. We will report in the near future preliminary scientific results of the EROS experiment.     

Iron-hydroxide clogging of public supply wells receiving artificial recharge: near-well and in-well hydrological and hydrochemical observations

Clogging of water wells by iron-hydroxide incrustations due to mixing of anoxic and oxic groundwater is a common well-ageing problem. The relation between well operation (on and off), the spatial and temporal variations in hydrochemistry outside and inside a supply well, and the distribution of clogging iron-hydroxides were studied in an artificial recharge well field in the Netherlands. Camera inspection, high-resolution multi-level water sampling outside the well and detailed in-well pH/EC/O₂ profiles revealed remarkable patterns. During pumping, the top of the upper well screen abstracted oxic filtrate, although the larger part of the in-well water column was anoxic. The column rapidly turned oxic after shutdown due to a downward short-circuiting of oxic water via the well. Within 15 d it became anoxic due to the slow advance of anoxic lake filtrate created by local changes in flow direction as the neighboring wells continued to pump. Severe clogging occurred where the oxic filtrate entered the well, while half-clogging of the upper well screen occurred due to less inflow of oxic filtrate on the lake side. Transport of iron flocs and bacterial slimes after shutdown seemed to clog the lower part of the well screen. Frequent on/off switching should be avoided in iron-clogged wells.     

Hydrogeochemical investigation of geothermal springs in Erzurum,East Anatolia (Turkey)

Geothermal water sources located within The Erzurum province were identified and hot water samples were taken from four different geothermal areas. The results of in situ and hydrogeochemical analyses of these hot water samples were interpreted and the properties of hot water, water–rock associations, estimated reservoir temperature and hot water usage areas were determined. The temperatures of the samples collected from the study area vary between 26.2 and 57.7 °C, while pH values change from 6.09 to 7.33, EC values obtained from in situ measurements are between 1829 and 9480 µS/cm and Eh values are (??190) to (26.3) mV. Total dissolved solids of the hot waters have a range from 838.7 to 3914.1 mg/l. The maximum estimated reservoir temperature is calculated as 250 °C by applying chemical geothermometers. However, considering the actual temperatures of Pasinler, Köprüköy, Horasan and Il?ca thermal waters and wells, the most reliable temperature range depending on the applied geothermometers’ results indicate minimum and maximum reservoir temperatures 85–158.9 °C, respectively, taking in account the errors. According to the isotope analysis, the waters circulating within the geothermal system are of meteoric origin and modern waters. In addition, two samples taken from clayey levels observed in the field were analyzed and the mineralogy of the clays was evaluated.     

Autogenic avulsion,channelization and backfilling dynamics of debris‐flow fans

Alluvial fans develop their semi‐conical shape by quasi‐cyclic avulsions of their geomorphologically active sector from a fixed fan apex. On debris‐flow fans, these quasi‐cyclic avulsions are poorly understood, partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas. In this study, debris‐flow fans were experimentally created under constant extrinsic forcing, and autogenic sequences of backfilling, avulsion and channelization were observed. Backfilling, avulsion and channelization were gradual processes that required multiple successive debris‐flow events. Debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia. In the channelization phase, debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed, resulting in longer run‐out and deeper channels. Backfilling commenced when debris flows reached their maximum possible length and channel depth, as defined by channel slope and debris‐flow volume and composition, after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated. The terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low‐gradient zone forcing deposition. Consequently, the next debris flow was shorter which led to more in‐channel sedimentation, causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout. This topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas. Debris‐flow avulsion cycles are governed by the same large‐scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans, although the detailed processes are unique to debris‐flow fans. This novel result provides a basis for modelling of debris‐flow fans with applications in hazards and stratigraphy.     

Sensitivity of GRACE-derived estimates of groundwater-level changes in southern Ontario,Canada

Amidst changing climates, understanding the world’s water resources is of increasing importance. In Ontario, Canada, low water conditions are currently assessed using only precipitation and watershed-based stream gauges by the Conservation Authorities in Ontario and the Ministry of Natural Resources and Forestry. Regional groundwater-storage changes in Ontario are not currently measured using satellite data by research institutes. In this study, contributions from the Gravity Recovery and Climate Experiment (GRACE) data are compared to a hydrogeological database covering southern Ontario from 2003 to 2013, to determine the suitability of GRACE total water storage estimates for monitoring groundwater storage in this location. Terrestrial water storage data from GRACE were used to determine monthly groundwater storage (GWS) anomaly values. GWS values were also determined by multiplying groundwater-level elevations (from the Provincial Groundwater Monitoring Network wells) by specific yield. Comparisons of GRACE-derived GWS to well-based GWS data determined that GRACE is sufficiently sensitive to obtain a meaningful signal in southern Ontario. Results show that GWS values produced by GRACE are useful for identifying regional changes in groundwater storage in areas with limited available hydrogeological characterization data. Results also indicate that GRACE may have an ability to forecast changes in groundwater storage, which will become useful when monitoring climate shifts in the near future.