夏季东太湖光合有效辐射衰减特征及其对沉水植物恢复的指示

水下光照分布是影响水生态系统的重要因素,研究光合有效辐射衰减特征对于沉水植物恢复具有一定的指导意义.根据沉水植物生物量资料,将东太湖划分为沉水植物茂盛区、沉水植物稀疏区和无植物区3种区域.基于2019年夏季原位水下光场资料,探讨了东太湖光衰减特性和光照衰减因子的空间差异以及不同区域内的主导衰减因子,分析了东太湖的稳态阶段和富营养化水平,并阐述了真光层深度与透明度的关系,以期为东太湖沉水植物恢复和保护提供相关资料.结果表明:东太湖不同区域光衰减特性差异显著,光合有效辐射衰减系数(k d(PAR))在0.73~11.80 m^-1之间变化,真光层深度范围为0.39~6.31 m.不同区域的无机悬浮物和有机悬浮物浓度存在显著性差异,稀疏区叶绿素a浓度显著高于茂盛区,而与无植物区没有显著差异,有色可溶性有机物(CDOM)吸收系数在3种区域无显著性差异.k d(PAR)与无机、有机悬浮物的线性拟合效果较好,而与叶绿素a、CDOM拟合较差.水体吸收和散射作用是茂盛区光衰减的主要原因,无植物区域主导衰减因子仅有无机悬浮物,稀疏区由叶绿素a和无机悬浮物共同主导,是生态修复需要重点关注的区域,有机悬浮物和CDOM对东太湖光照衰减没有太大影响.东太湖目前正处于从草型稳态向藻型稳态过渡的阶段,整个湖泊属于富营养水平,真光层深度大约为透明度的2.7倍.

Attenuation characteristics of photosynthetically active radiation in summer eastern LakeTaihu and implications for submerged plants restoration

The underwater light distribution is an important factor affecting aquatic ecosystems. The study on the attenuation characteristics of photosynthetically active radiation is of guiding significance for the restoration of submerged plants. In this study, based on the biomass data of submerged plants, eastern Lake Taihu was divided into submerged plants sparse region, submerged plants lush region, and no-plant region. Spatial difference in light attenuation characteristics and light attenuation factors of eastern Lake Taihu, dominant attenuation factors in different regions, regime shift phases and eutrophication level, and the relationship between euphotic depth and transparency were studied by applying in situ measurement data in August 2019. Results were analyzed to provide relevant optical data for the restoration and protection of submerged plants in eastern Lake Taihu. The results showed that the light attenuation characteristics are significantly different in three regions. The diffuse attenuation of photosynthetically active radiation varied from 0.73 m^-1 to 11.80 m^-1 and the corresponding euphotic depth was 0.39-6.31 m. There were significant differences in the concentrations of suspended particulate inorganic matter and suspended particulate organic matter in different regions. The concentration of chlorophyll-a in the sparse region was significantly higher than that in the lush region, but not significantly different from that in no-plant region. Chromophoric dissolved organic matter (CDOM) absorption coefficient had no significant difference in three regions. The linear fitting effect of k_d(PAR) with suspended particulate inorganic matter and suspended particulate organic matter was better, but it was worse with chlorophyll-a and CDOM. Water absorption and scattering were the main cause of light attenuation in the lush region and suspended particulate inorganic matter was the dominant attenuation factor in no-plant region. The sparse region was dominated by chlorophyll-a and suspended particulate inorganic matter, which was a region that needs to be focused on for ecological restoration. Suspended particulate organic matter and CDOM had little effect on the light attenuation. Eastern Lake Taihu was currently in the transition stage from a macrophytes-dominated state to a phytoplankton-dominated state, and the entire lake was at eutrophic level. Euphotic depth was about 2.7 times of the transparency.