Reconstruction of long-term changes of the underwater light field in large shallow lakes Peipsi and Võrtsjärv, North-East Europe

Proceedings of the Estonian Academy of Sciences

Toomas Kõiv¹  Peeter Nõges¹  Helgi Arst¹  Kaire Toming¹  Tiina Nõges¹ 

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

DOI  :  10.3176/proc.2013.3.06

学科分类：化学（综合）

来源: Teaduste Akadeemia Kirjastus

【 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 Kd,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.

【 授权许可】

Unknown