Recent Paleolimnology of Upper Klamath Lake Eilers et al. 2001 ABSTRACT Sediment cores were collected from Upper Klamath Lake in October, 1998 and analyzed for 210Pb, 14C, 15N, N, P, C, Ti, Al, diatoms, Pediastrum, and cyanobacterial akinetes. These results were used to reconstruct changes in water quality in Upper Klamath Lake over the last 150 years. The results showed that there was substantial mixing of the upper 10 cm of sediment, representing the previous 20 to 30 years. However, below that, 210Pb activity declined monotonically, allowing reasonable dating for the period from about 1850 to 1970. The sediment accumulation rates (SAR) showed a substantial increase in the 20th century. The increase in SAR corresponded with increases in erosional input from the watershed as represented by the increases in sediment concentrations of Ti and Al. The upper 20 cm of sediment (representing the last 150 years) also showed increases in C, N, P, and 15N. The increases in nutrient concentrations may be affected to various degrees by diagenetic reactions within the sediments, although the changes in concentrations also were marked by changes in the N:P ratio and in a qualitative change in the source of N as reflected in increasing S15N. The diatoms showed modest changes, particularly in the upper sediments, with increases in Asterionellaformosa, Stephanodiscus hantzschii, and S. parvus. Pediastrum, a green alga, was well-preserved in the sediments and exhibited a sharp decline in relative abundance in the upper sediments. Total cyanobacteria, as represented by preserved akinetes, exhibited only minor changes in the last 1000 years. However, a taxon which was formerly not present in the lake 150 years ago, Aphanizomenon, has shown major increases in recent decades. Although the mixing in the upper sediments prevents high-resolution temporal analysis of the recent history (e.g. last 30 years) of Upper Klamath Lake, the results demonstrate that major changes in water quality likely have occurred leading to a major modification of the phytoplankton assemblage. The changes in sediment composition are consistent with land use activities during this period that include substantial deforestation, drainage of wetlands, and agricultural activities associated with livestock and irrigated cropland.
"Submitted to the U.S. Bureau of Reclamation, Klamath Falls, Oregon by JC Headwaters, Inc., Roseburg, Oregon, March 16, 2001."