Physical+Limnology

TO INVOLVE THE ADDITION OF A KNOWN QUANTITY OF AN EXOTIC TAXON, IN THIS CASE //LYCOPODIUM CLAVATUM// SPORE, TO THE SEDIMENT SAMPLES BEFORE CHEMICAL PREPARATION. GRAINS OF L. //CLAVATUM// WERE COUNTED WITH THE FOSSIL POLLEN, AND PROPORTIONS OF EACH IN A WEIGHTED SAMPLE ALLOWED THE CALCULATION OF THE NUMBER OF FOSSIL GRAINS PER GRAM OF SEDIMENT, USING THE FOLLOWING EQUATION.

THE GRAIN SIZE OF THE MINERAL FRACTION IN THE LACUSTRINE SEQUENCE IS DOMINANTLY CLAYEY SILT TO SILTY CLAY THAT NORMALLY CONTAINS SOME SAND. THE PRESENCE OF SAND AND THE WIDE RANGE OF GRAIN SIZES THROUGHOUT MOST OF THE SEDIMENT IN THIS DEEP LAKE IS A REFLECTION OF THE STEEP SLOPES BOUNDING THE LAKE, THE HIGH RAINFALL, AND THE SMALL DRAINAGE BASIN AREA, ALL OF WHICH COMBINES TO HELP DELIVER COARSE SEDIMENT TO THE VALLEY FLOOR AND TO LIMIT THE AMOUNT OF SORTING THAT OCCURS TO THE ERODED SOIL. LAMINA THAT CONTAINS A HIGH PERCENTAGE OF CLAY-SIZE MATERIAL PROBABLY REFLECTS PERIODS OF REDUCED RUNOFF TO THE LAKE OR LESS CATCHMENT DISTURBANCE. THE SEDIMENTATION RATE, BASED ON RADIOCARBON DATES OF 540 YR BP FROM NEAR THE BASE OF CORE VHB AND 320 YR BP FROM MIDWAY IN THE CORE, IS ABOUT 1 CM YRˉ¹ IN THE LOWER HALF AND 0.8 CM YR ˉ¹IN THE UPPER HALF. THIS IS A HIGH RATE OF SEDIMENTATION, ALTHOUGH NOT REASONABLE, GIVEN THE CLIMATE AND TOPOGRAPHY OF THE WATERSHED. THE HIGH WATER CONTENT OF THE SEDIMENT IS TYPICAL OF RELATIVELY FINE-GRAINED MATERIALS THAT ARE RAPIDLY DEPOSITED IN A STANDING BODY OF WATER. = =