Pa. Meyers et al., SEDIMENTARY RECORD OF SOURCES AND ACCUMULATION OF ORGANIC-MATTER IN PYRAMID-LAKE, NEVADA, OVER THE PAST 1,000 YEARS, Limnology and oceanography, 43(1), 1998, pp. 160-169
We have examined the organic matter contents of two Pb-210-dated cores
of sediment from Pyramid Lake for consequences of the historic enviro
nmental and limnological changes that have occurred since modern settl
ement of this region began in the 1850s. Agricultural diversion of Tru
ckee River water has diminished the volume of this saline, terminal la
ke by one-fourth since 1905. Organic C:N ratios, organic delta(13)C va
lues, and terrigenous:aquatic n-alkane ratios indicate that the propor
tion of land-derived organic matter in sediments has decreased as rive
r how has decreased. Algal productivity also appears to have decreased
since 1930. Some prehistorical variations in the delivery of organic
matter are evident in older sediments. Elevations in the proportion of
land plant wax and in C:N ratios in sediments deposited A.D. 1200-140
0 suggest that contributions of land-derived organic matter were enhan
ced at this time. Proportions of biomarker n-alkanes indicate that gra
sses were more important than trees and shrubs as the dominant source
of land plant waxes during this period, suggesting an interlude of reg
ionally wetter climate.