We present a record of monsoon variations for the early and middle Holocene that is inferred from the geochemistry of sediment cores from Ahung Co, a lake in central Tibet. The resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal, which eliminates errors associated with the lake hard-water effect. We made down-core geochemical measurements of % carbonate, % organic carbon, C/N and δ13C of bulk organic matter, δ13C and δ18O of carbonate, and % dolomite. Proxy calibration and modern water-balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation. We find that lake level and monsoon precipitation have been decreasing at Ahung Co since the early Holocene (∼7500 cal yr B.P.). Superimposed on this trend are rapid declines in monsoon rainfall at 7000–7500 and 4700 cal yr B.P. and seven century-scale wet–dry oscillations. The cores do not contain sediment from the last ∼4000 yr. Surface sediments from the lake accumulated during the 20th century, however. From this, we argue that lake levels have risen again recently following a late Holocene dry period.

The impact of Elodea canadensis on aquatic macrophyte biodiversity in (Lake) Steinsfjord has been studied through extensive lake-wide surveys and photographic sampling. E. canadensis greatly expanded in Steinsfjord since its appearance in 1978 and still dominated the macrophyte community in 2004. The areal distribution of E. canadensis peaked within 6 years from invasion and has remained relatively stable since; however, stands no longer reach the water surface. E. canadensis significantly increased its depth range, but the cover-weighted mean depth remained unchanged, suggesting that 3–4 m is its optimal depth in Steinsfjord. Species richness has not changed significantly since the earliest survey in 1936–38. However, species composition has changed remarkably, from isoetid dominance in 1936–38 to a diverse community dominated by Najas flexilis in 1979–80 to a less diverse community dominated by E. canadensis in 2004, with Potamogeton berchtoldii and Myriophyllum alterniflorum as lake-wide subdominants. Regardless of their abundance at the onset of the E. canadensis invasion, taxa whose cover-weighted mean depth overlapped with E. canadensis's in 1979–80 greatly reduced their abundance in 2004, shifted to deeper or shallow water or disappeared from sampling stations. Our survey indicates that E. canadensis may be the reason for the decrease of N. flexilis, likely through depletion of CO2 in the water column and reduced nutrients in sediments. The abilities to survive and grow in periodically exposed shallow areas, combined with minor herbivory by waterfowl, are likely important factors for the increase of M. alterniflorum in Steinsfjord's shallow waters.

The aim of the study was to design and put together a compact, easy-to-assemble and cost-efficient incubation system for aquatic plant photosynthesis measurements. Incubation tank consisting of glass sidewalls and mirror inner walls was constructed. The tank was split into six incubation cells and two water collecting cells. Each incubation cell was built of mirror with reflective side turned into the incubation cells to prevent the self shading of plants and minimized the variance of light intensity within the cell. The wall of each incubation cell facing the source of light was made of 3 mm glass and was covered by light absorbing film. To produce different light intensities single light source (fluorescent tubes) and light absorbing film (3M Scotchtint™ Sun Control RE50NEARL) were chosen. The sidewall of each incubation cell was covered with metal-coated neutral sun control film to produce six distinct light intensities. The different transparency of the sidewalls was achieved by lamination of the chosen film in increasing numbers of layers. The effect of the lamination on optical properties of the film was also studied. The variation of photon flux density within a cell was 3.9%. Continuous use of the system and occasional repetitive measurements of film's transparency showed that it maintained its neutral optical properties over a long period of time.