Reconstruction of Long-Term Changes of the Underwater Light Field in Large Shallow Lakes Peipsi and Võrtsjärv, North-East Europe

Veealuse Valgusvälja Pikaajaliste Muutuste Taastamine Suurtes ja Madalates Kirde-Euroopa Järvedes (Peipsi ning Võrtsjärv)

Kaire Toming ； Peeter Nõges ； Helgi Arst ； Toomas Kõiv ； Tiina Nõges

《Proceedings of the Estonian Academy of Sciences》 62卷3期 (2013/09) Pp. 202-212

並列摘要

The main objective of our study was to reconstruct the multi-decadal changes of the underwater light field in two large, shallow and polymictic Estonian lakes Võrtsjärv and Peipsi in order (i) to assess the potential role that light limitation may have had on phytoplankton growth in the past and (ii) to get an insight into the factors driving underwater light climate in shallow turbid lakes in the long term. We reconstructed the long-term variations of the diffuse attenuation coefficient of water (Kd,PAR) in the photosynthetically active region (PAR, 400-700 nm) partly on the basis of measured beam attenuation spectra and partly using regression analysis. From K d,PAR we calculated the depth of the euphotic zone (z1%) and the mean light availability in the mixed layer (Emix). The reconstructed time series of these bio-optical parameters gave a plausible picture of the long-term development of light conditions in the two lakes studied, which was in accordance with their eutrophication history and changes in their water levels. Better light availability in both lakes generally coincided with years of a low water level, and the coincidence was more distinct in the shallower Võrtsjärv. Values of Emix revealed a probable light limitation in Peipsi in autumn and in Võrtsjärv throughout the year.

並列關鍵字

large shallow lakes ； underwater light climate ； diffuse attenuation coefficient ； seasonal changes ； long-term changes