HR: 0830h
AN: S51C-0070    [PDF]
TI: Environmental Impact of Controlled-Source Explosions in Ethiopia (Project EAGLE): Geochemical Effects on Lakes and Streams
AU: * Cash, M
EM: michelec@stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215 United States
AU: Klemperer, S L
EM: sklemp@stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215 United States
AU: Mengistou, S
EM: seyoumen@yahoo.com
AF: Department of Biology, Addis Ababa University, Addis Ababa, o Ethiopia
AB: Controlled-source seismologists seek to detonate charges in lakes or rivers because source coupling is an order of magnitude larger in water than in drill holes. Previous studies have documented the biological impact of dynamite explosions on small fish populations; however, little attention has been paid to the potential chemical changes associated with the dispersal of a dynamite charge in a body of water. At the request of the Ethiopian Environmental Protection Authority, we sought to examine the effects on water chemistry resulting from the detonation of one tonne dynamite charges used during the Ethiopia-Afar Geoscientific Lithospheric Experiment (EAGLE), an active source seismic survey of the Main Ethiopian Rift. Water samples from two Ethiopian lakes and six Ethiopian streams were collected in January 2003. Samples were collected immediately preceding and following the detonation of the 2 lake shots and those 6 of our 19 borehole shots for which a stream was present in the surrounding area. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis has provided concentrations of 16 elements, including: As, B, Ba, Be, Ca, Cd, Co, Cu, Mg, Mn, Mo, Na, Ni, Sr, V, Zn. Additional elements were also examined, however elements such as Cr, Fe, and Pb, had concentrations residing close to the detection limits of the ICP-OES, and the certainty of these numbers is not reliable. We plan to make measurements of Cl and S using the Ion Chromatograph (IC) method. The sites from which the water samples were collected include: (1) Lake Shala, a 12 by 15 km lake, 266 meters deep, (2) Lake Arenguade, an approximately 800m diameter crater lake, 32 m deep, and (3) six streams, each located within close proximity to one of the 19 borehole shots. All samples were filtered using a 2 micron nalgene filter to remove any biotic material. Prior to each shot, water samples were collect. To the extent possible, lake samples were taken 1 hour before the shot, 10 minutes post shot, 1 day after the shot, and 10 days later. Samples where collected every 10 meters in depth from 1 to 30 m, and for the deeper lake, Shala, samples were also taken at 60 m and 90 m. Samples were collected both at the location of the shot as well as 300 m away from the shot (Lake Arenguade) and 1 km from the site of the shot (Lake Shala). Elemental concentrations were plotted both as a function of time and as a function of depth. Preliminary results suggest that while some elemental concentrations varied slightly after each shot, no concentrations were drastically altered from their pre-shot values. The elemental concentrations tended to revert to pre-shot values within a few hours to a few days after the initial explosion. The explosions of the two dynamite lake shots and the borehole shots do not seem to have significantly impacted the water chemistry of the surrounding lakes and streams.
DE: 0935 Seismic methods (3025)
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 9305 Africa
SC: Seismology [S]
MN: 2003 Fall Meeting