EXECUTIVE SUMMARY – AETE
A literature review on the techniques of sonar profiling and grid sampling, using a grab sampler was undertaken as an evaluation step for environmental lake sediment monitoring. The sonar systems to be evaluated include the sub-bottom acoustic profiling system, with or without side-scan, and the echo sounding system.
The sub-bottom acoustic profiling system operates at low frequencies with great sediment penetration depth (up to 100 m) and provides information on (1) morphological features present on the lake bottom, (2) paleofluvial regimes, (3) present day control on sedimentation and erosional processes and (4) tectonic activity. This information simplifies sediment sampling surveys and help to interpret geochemical results. The sub-bottom acoustic profiler in conjunction with the side-scan sonar system generate an accurate representation of the lake bottom recording vertical, lateral sedimentological variations along with topographical features present at the lake bottom. The echo sounding system is a high frequency system which records water depth. Most modern system combine low and high frequency sound range satisfying both resolution and depth penetration requirements for mapping lacustrine sediments. The incorporation of the side-scan sonar along with the sub-bottom acoustic profiling system is not a cost effective alternative for the purpose of lake sediment monitoring.
Grid sampling using a grab sampler can be used to assess the distribution of geochemical elements in a lake basin. Sampling over a regularly spaced square or triangular grid simplifies and helps to keep track on the sampling site location for a uniform coverage of the sampled area. The Wildco-Dredge or the Petite Ponar type grab sampler can be used to sample surficial lake sediments. The Petite Ponar sampler seems to be more reliable and flexible to sample all types of sedimentogical environments (shallow-deep waters and/or high inorganic sediments).
