An inexpensive, optical (infrared) detector to locate the sediment/water interface in lakes with unconsolidated sediments

Unconsolidated, flocculent sediments that are frequently resuspended by win d action are found in many shallow-water lakes. Collecting sediment/water i nterface cores in such lakes for paleolimnological study may be problematic because it is difficult to determine the depth to the water/sediment inter face. Accurately determining this water depth is necessary to guarantee tha t a piston corer does not penetrate the sediments prior to the drive and to maximize the core length. A simple instrument constructed with inexpensive , readily available components is described. This infrared floc detector (I FD) is used to sense the increased optical density of unconsolidated sedime nts as the detector is lowered into a lake. The IFD, in effect, yields a pr ecise as well as an accurate measure of water depth. The depth to the water /sediment interface can be measured with an accuracy of approximately 1 cm, provided surface waters are relatively calm.