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Sediment cores were collected from deep-water areas of Lake Chenghai, China in June 1997. The vertical profile of 137Cs activity gives reliable geochronological results. The results also indicate that sediment accumulation rates in deep-water areas of Lake Chenghai were relatively constant in recent decades, averaging 0.43 g cm− 2 y− 1, despite a variable organic carbon influx. 210Pbeq (= 226Ra) activity was relatively constant also, with an average value of 54.3 ± 3.2 Bq kg− 1. Vertical profiles of 210Pbex (= 210Pbtotal − 226Ra) decreased exponentially, resulting in somewhat lower sediment accumulation rates (0.3 g cm− 2 y− 1). These lower rates are likely less reliable, as the relatively large fluctuations in 210Pbex activities correlate closely to the organic carbon (Corg) content of the sediments. For example, the vertical profile of 210Pbex activity displays peaks at mass depths of 3.7–4.7 g cm− 2 (10–12 cm) and 10–11 g cm− 2(25–28 cm), similar to the maxima in the vertical profile of Corg. This phenomenon must be related to the delivery of particulate organic matter (POM) from the water to the sediments, or to watershed soil erosion. Since the mean atomic ratios of Horg / Corg and Corg / Norg in Lake Chenghai sediments are 5.5 and 7.0, respectively, indicating that POM was predominantly derived from the remains of authigenic algae, this eliminates watershed erosion rates as a primary control on lake sedimentation rates as resolved by 210Pbex. Sedimentation fluxes (F(Corg)) of particulate organic carbon since 1970 varied between 60 to 160 g m− 2 y− 1, and appeared to closely influence variations in 210Pbex concentrations. For example, sedimentation fluxes of 210Pbex (F(210Pbex)) showed maxima in the years 1972–1974 and 1986–1989, likely reflecting historical variations of lake biological productivity or carbon preservation.

The uplifting of the Himalayas has resulted in the development of a three-tiered landform in Southern China, the Yunnan–Guizhou Plateau is the middle tier of this landform on the eastern slope of the Himalayas. Lake Hongfeng and Lake Baihua in central Guizhou are about 1000 km away from Lake Erhai in western Yunnan. Sediment cores were collected from Lakes Erhai and Lugu in west Yunnan and Lakes Hongfeng and Baihua in central Guizhou, along with 28 surface soil cores from the watersheds of these lakes. The accumulation characteristics of 7xxxx Be and 137yyyy Cs show that: (1) 137 Cs activities in the soil cores of central Guizhou were higher than that in the western Yunnan. The activities and maximum penetrative depth of 7 Be were similar for the two regions. The activity ratio of 7 Be/ 137 Cs in surface soil reached 100–1000 in western Yunnan, but only 10–100 for central Guizhou region. (2) 7 Be inventories in soil cores at most sampling sites of central Guizhou were low, reflecting severe soil erosion. 7 Be inventories in the soil cores of Lake Lugu watershed in summer–autumn were higher than that in Lake Hongfeng/Baihua watershed and also higher than that in Lake Erhai watershed. This could be related to high 7 Be precipitation in summer and altitude. (3) 7 Be inventories in sediment cores of Lake Erhai, Lake Lugu and Lake Baihua were 237±73, 322±19 and 783±44 Bq m −2 , respectively. Based on activity values that were corrected to deposition, prior to 1986, 137 Cs inventories in these lakes were 519±26, 937±13 and 3704±56 Bq m −2 , respectively. (4) Modeling indicated that 7 Be and 137 Cs accumulations in Lake Hongfeng and Lake Baihua were dominated by watershed erosion, and controlled by the retention factor in Lake Erhai and Lake Lugu, but the 137 Cs inventory ratios obtained in the sediment core and from direct atmospheric fallout were similar, and the ratios were smaller for 7 Be. (5) 7 Be inventories from direct atmospheric fallout in Lake Erhai, Lake Lugu and Lake Baihua were 0.07±0.02, 0.29±0.02 and 0.08±0.01 Bq m −2 , respectively. Prior to 1986, 137 Cs inventories were 0.11±0.01, 0.22±0.01 and 0.37±0.01 Bq m −2 , respectively, showing that 137 Cs deposition has a regional difference. This phenomenon may reflect that uplift of the Himalayas has a screening effect on the fallout of globally distributed atmospheric pollutants in western Yunnan, China.