. Bulletin. Natural history; Natural history. 256 Illinois Natural History Survey Bulletin Vol. 33, Art. 3 I%7|I968|I969|I970| 1971 |l972|l973|l974|l975|l976!l977|l978il979|l98C| 1981 |e82|l983 DAPHNIA. Fig. 10 - Variations in populations oiDaph- nia, Mysis, Bosmina, Epischura, Diaptomus, and Kellicottia in Lake Tahoe between 1967 and 1983. Mysis values from the years 1968 to 1977 are based on the per- centages of lake trout containing Mysis dur- ing creel censuses by the California Depart- ment of Fish and Game. Beginning in 1975, My- sis values were deter- mined on the basis of a lakewide av
. Bulletin. Natural history; Natural history. 256 Illinois Natural History Survey Bulletin Vol. 33, Art. 3 I%7|I968|I969|I970| 1971 |l972|l973|l974|l975|l976!l977|l978il979|l98C| 1981 |e82|l983 DAPHNIA. Fig. 10 - Variations in populations oiDaph- nia, Mysis, Bosmina, Epischura, Diaptomus, and Kellicottia in Lake Tahoe between 1967 and 1983. Mysis values from the years 1968 to 1977 are based on the per- centages of lake trout containing Mysis dur- ing creel censuses by the California Depart- ment of Fish and Game. Beginning in 1975, My- sis values were deter- mined on the basis of a lakewide average (data through 1980 from Gold- man [1981]). of the Roman road, Via Cassia, about 2,000 years ago is evident from a sedi- ment core (Cowgill & Hutchinson 1970). Sediment from erosion, ash from vol- canic eruptions, as well as that portion of the biota which is resistant to decay may lie undisturbed in sediments for thousands of years. Further, pigments (Vallentyne 1960) and evidence of water chemistry may also be retained in the paleolimnological record. One of the arguments presented for the continued development of the Tkhoe basin was that the lumbering ac- tivities of the 1860's did not appear to have done serious damage to the water quality of Lake Tahoe. By examining sediments, we were able to demonstrate that damage done during the initial re- moval of timber from the basin was small in comparison to the disturbance that has accompanied modern develop- ments. Samples taken in midlake with a large box-coring device clearly show that much more nitrogen is now enter- ing the lake relative to carbon (Fig. 11 A). Fig. IIB shows the carbon con- tent of nearshore sediments in the vicinity of extensive lumbering activity during the 1860's. Although there are insufficient lead dates to confirm the 1860 level, it is indicated by estimated sedimentation rates. Similarly, the input of another important algal nutri- ent, iron, has gi-eatly increased with erosion from the steep
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