Abstract Light attenuation is considered as a sentinel for environmental change in lakes and has a profound influence on aquatic ecosystems. However, the spatial distribution of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) attenuation, and the underlying mechanisms are still not fully understood. We carried out a field investigation with 60 sampling sites covering the entire Lake Qiandaohu from November 29 to December 1, 2013, during the weak stratification period to elucidate the spatial pattern and driving mechanisms. The diffuse attenuation coefficient of UVB (Kd(313)), UVA (Kd(340)) and PAR (Kd(PAR)) varied from 1.48 to 4.63 m−1, 1.09 to 3.43 m−1, and 0.26 to 0.94 m−1, respectively. The corresponding ranges for the 1% attenuation depths were from 0.10 to 3.11 m, 1.34–4.21 m and 4.87–17.58 m, respectively. Total suspended matter (TSM) concentration was highly significantly correlated with Kd(313), Kd(340) and Kd(PAR) indicating that TSM was the main driver of UVR and PAR attenuation in Lake Qiandaohu in the late autumn and early winter. TSM concentration, Kd(313), Kd(340) and Kd(PAR) had obvious horizontal spatial heterogeneity presenting a decreasing trend from the estuary area to the center area in the lake. These results suggested that the spatial distribution of TSM from the inflow drived the spatial distribution of UVR and PAR attenuation. Significantly positive correlations were also observed between the chromophoric dissolved organic matter (CDOM) absorption coefficient and Kd(313). TSM and CDOM absorption spectra showed that in the UVR waveband (350–400 nm), the mean relative contribution rates of CDOM (ag(λ)), non-algal particles (anap(λ)), phytoplankton (aph(λ)) and pure water (aw(λ)) to the total absorption were 67.5 %, 24.0 %, 5.0 % and 3.5 %, respectively. In the PAR waveband, the mean relative contribution rates of ag(λ), anap(λ), aph(λ) and aw(λ) to the total absorption were 25.4 %, 18.6 %, 9.4 % and 46.6 %, respectively. Our findings could provide support for ecological environment protection in Lake Qiandaohu considering the importance of UVR and PAR attenuation in aquatic ecosystems.

中文翻译：

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清澈深湖中UVR和PAR的衰减：空间分布及影响因素

摘要 光衰减被认为是湖泊环境变化的哨兵，对水生生态系统有着深远的影响。然而，紫外线辐射（UVR）和光合有效辐射（PAR）衰减的空间分布及其潜在机制仍未完全了解。我们于 2013 年 11 月 29 日至 12 月 1 日在弱分层时期对覆盖整个千岛湖的 60 个采样点进行了实地调查，以阐明空间格局和驱动机制。UVB (Kd(313))、UVA (Kd(340)) 和 PAR (Kd(PAR)) 的漫衰减系数从 1.48 到 4.63 m-1、1.09 到 3.43 m-1 和 0.26 到 0.94 m- 1、分别。1% 衰减深度的相应范围分别为 0.10 至 3.11 m、1.34-4.21 m 和 4.87-17.58 m。总悬浮物(TSM)浓度与Kd(313)、Kd(340)和Kd(PAR)显着相关，表明TSM是千岛湖晚秋初冬UVR和PAR衰减的主要驱动因素。TSM浓度、Kd(313)、Kd(340)和Kd(PAR)水平空间异质性明显，从河口区向湖心区呈递减趋势。这些结果表明来自流入的 TSM 的空间分布驱动了 UVR 和 PAR 衰减的空间分布。在发色溶解有机物 (CDOM) 吸收系数和 Kd(313) 之间也观察到显着的正相关。TSM和CDOM吸收光谱表明，在UVR波段（350-400 nm），CDOM（ag(λ)）、非藻类颗粒（anap(λ)）、浮游植物 (aph(λ)) 和纯水 (aw(λ)) 的总吸收量分别为 67.5%、24.0%、5.0% 和 3.5%。在PAR波段，ag(λ)、anap(λ)、aph(λ)和aw(λ)对总吸收的平均相对贡献率分别为25.4%、18.6%、9.4%和46.6%。考虑到 UVR 和 PAR 衰减在水生生态系统中的重要性，我们的研究结果可为千岛湖的生态环境保护提供支持。