Maximum likelihood environmental calibration and the compute program WACALIB a correction

A recently discovered error in the part of the computer program WACALIB that implements maximum likelihood (ML) calibration has been discovered and corrected. The new version of WACALIB has been re-run with all the data-sets from which results based on the earlier version of WACALIB had been published. The new results suggest that ML regression and calibration perform as well or even better than weighted averaging (WA), at least when judged by the apparent root mean squared error. Further work involving cross-validation is required to evaluate more fully the relative performance of WA and ML approaches.     

Controls on the nature and distribution of an alga in coal mine-waste environments and its potential impact on water quality

 A dominant non-bacterial microorganism that may strongly impact environmental conditions in acid mine drainage at several Indiana coal mine sites is a single-celled protozoan, Euglena mutabilis. Field data suggest E. mutabilis has high tolerance for elevated total dissolved solids (TDS), to 18 g/l, and acid conditions to pH 1.7. Distribution is restricted to unmixed effluent pH<4.6, with prolific growth between pH 3.0 and 3.5. Additional factors influencing E. mutabilis include preference for areas with lower mineral/colloidal precipitation rates and a stable substrate of iron-rich precipitates. Initial studies indicate that in areas of prolific growth it contributes to oversaturation of dissolved oxygen by up to 200%. The presence of small orange intracellular crystalline-like structures, similar in color to iron oxyhydroxides, suggests that E. mutabilis may be sequestering iron, and possibly other metals. Further work is needed to determine if E. mutabilis contributes to natural mitigation of poor water quality at these and other coal mine sites. Received: 13 January 2000 · Accepted: 2 May 2000     

Groundwater contamination: risk management and assessment for landfills in Mar del Plata, Argentina

 This study presents a program for risk management in the contamination of groundwater resulting from leachate in landfills at Mar del Plata (Argentina). The program includes prediction, prevention, monitory observation and mitigation as actions that must be taken prior to, during, and after contamination occurs. This routine aids in the identification of weak points and failures of the program for those who are in charge of making decisions, and will allow better use of limited financial and technical resources based on planning, thus minimizing disconnected determinations. Results of the prediction stage were confirmed through monitoring. The presence of a plume of contamination more than 100 m from the landfill was shown, thus proving that implementation of a monitoring plan to follow the development of the contaminated plume must be implemented, particularly in populated areas which depend on residential wells for their water supply. Received: 8 May 2000 · Accepted: 14 August 2000     

Reply to comments by G. Kosarev, N. Petersen and L. P. Vinnik on 'The use of velocity spectrum for stacking receiver functions and imaging upper mantle discontinuities

We thank the editors of GJI for the opportunity to respond to the comment in this issue by Kosarev, Petersen & Vinnik 11996: hereafter referred to as KPV), which disputes the historical and technical accuracy of the paper by Gurrola, Minster & Owens (1994; henceforth referred to as GMO).     

An extreme value analysis of the flow of Burbage Brook

An extreme value analysis of the flow of Burbage Brook is carried out by modelling peaks over a high threshold. The aims are to illustrate recently developed statistical techniques and to report on interesting features of the flow of the brook over a 58-year period. Peak flows are found to show marked seasonal variation and a downward trend. Then-year return level is estimated for various values ofn, and the reliability of the estimates is assessed.