New Field Sampling Techniques And Data Description

James G. Flocks
(with technical contributions from Marci Marot, Phil McCarty,
Dana Weise, Paul Conner, Jr. and Scott Noakes)

Introduction

In 1994 the United States Geological Survey (USGS) began a multidisciplinary evaluation of the geology, geomorphology, coastal processes, and environmental quality of the Pontchartrain Basin. The primary issues involved in the study include the environmental quality of the sediments and wetland loss. The sediments in Lake Pontchartrain have a long history of contamination from surface runoff. More recently, the northern and western shorelines of the lake are undergoing erosion, along with subsidence and loss of diversity in vegetation. To adequately assess the impact of these issues, various field investigations were employed (see Table 1 below). 

Investigations

The following field investigations were conducted between 1994 and 1997 in Lakes Pontchartrain, Maurepas, Borgne and the surrounding waterways, excluding the Mississippi River. An outline of the survey techniques, their task objective and accomplishments to date will be followed by detailed descriptions of the methods involved in the techniques.

Table 1. Field investigations used in the Lake Pontchartrain Basin study.

Summary

To properly address the issues associated with sediment quality and shoreline dynamics of the Lake Pontchartrain Basin, it is necessary to understand the geologic evolution of the region as well as recent changes in the characteristics of the lake bottom and subsurface. To develop this understanding a variety of field investigative techniques must be employed. Remote sensing provides a non-invasive, multi-dimensional survey of the lake bottom and subsurface that provides data for geologic framework interpretations, computer models of lake bottom and water column dynamics and identification of features such as relic barriers, beach trends, fault lines and man-made structures. Subsurface sampling techniques such as vibracore, borehole drilling and box cores provide a means to directly sample the sediments at depths and resolutions dependant on the type of investigation. Sediments obtained by these techniques yield information on Quaternary geologic framework, regional sedimentation patterns, downcore geochonology, palynology and sediment contamination history. Finally, surficial sediment sampling such as grab samples and underway sampling are necessary to determine regional sedimentation and contaminant distribution and temporal changes in distribution during the length of the study.

References

Dunbar, J.B., Blaes, M.R., Dueitt, S.E. and May, J.R., Stroud, K.W. 1994; Geological Investigation of the Mississippi River Deltaic Plain; U.S. Army Corps Technical Report GL-84-15.

Dunbar, J.B., Blaes, M.R., Dueitt, S.E. and May, J.R., 1995; Geological Investigation of the Mississippi River Deltaic Plain; U.S. Army Corps Technical Report GL-84-15.

Johnson, H. P. and Helferty, M., 1990. The Geological Interpretation of Side-Scan Sonar. Reviews of Geophysics, vol. 28, no. 4, p. 357-380.

Kenwood, C., F.T. Manheim, S.J. Williams, and C. Polloni, 1996; An Environmental and Geological Bibliography for Lake Pontchartrain; U.S. Geological Survey Open File Report 96-527.

Manheim, F.T., this volume.

Noakes, S., this volume.