内陆水体有色溶解有机物的变化特征

有色溶解有机物(CDOM)是水体中的光学活性物质,其光化学变化对水体中碳循环过程具有重要作用。评价分析不同纬度、不同营养状况下内陆水体的CDOM吸收特性,对建立不同水体的固有光学特性数据库具有重要意义。基于太湖、石头口门水库、巢湖和鄱阳湖的现场CDOM吸收系数,分析aCDOM(412)时空变化特征,并基于不同波段拟合光谱斜率S,利用SA/aCDOM(412)判断了研究区CDOM的不同来源。结果表明,不同纬度、不同营养状况的CDOM吸光特性差异显著,高纬度水体的CDOM含量高于低纬度水体,而浮游植物大量生长的富营养化水体的CDOM吸收大于贫瘠营养水平的水体。受藻类的影响,巢湖部分样点的CDOM吸收光谱特征发生改变,在320nm和600nm处有明显的吸收峰;aCDOM(412)与SA呈较好的负相关关系;并且SA/aCDOM(412)可有效判断研究区CDOM的不同来源。

CHARACTERISTICS OF CHROMOPHORIC DISSOLVED ORGANIC MATTER IN INLAND WATERS

Chromophoric Dissolved Organic Matter (CDOM) is optically active compounds in aquatic systems, which absorb light in the ultraviolet and visible domains, controlling the water leaving radiance or remotely sensed reflectance. It is important to the carbon cycling in inland waters as the photochemical processes of CDOM producing CO2 or CO. Previous studies have focused on the CDOM absorption properties in specific water ecosystems, limiting the knowledge of biogeochemical dynamics of CDOM in different waters. For example, CDOM may suffer from changes in absorption spectra with the temperature, potential sources and residence time of water, and so on. The significant issue is to analyze the properties of CDOM absorption in inland waters at different latitudes and trophic states, which is useful to construct the IOPs database and provide spatial and temporal variations of CDOM absorptions from water color. Based on the field CDOM absorptions in Taihu Lake, Shitoukoumen Reservoir, Chaohu Lake and Poyang Lake, the temporal and spatial changes of CDOM absorption at 412 nm (aCDOM(412)) was analyzed. We found that Shitoukoumen Reservoir at the high latitude showed highest aCDOM(412) than those at low latitude, including Taihu Lake, Chaohu Lake and Poyang Lake. CDOM absorptions in the lakes at high latitude exhibited significant spatial heterogeneity in terms of trophic states, for example, aCDOM(412) in the oligotrophic lake (Poyang Lake) was lower than the eutrophic lakes (Taihu Lake and Chaohu Lake). It is noted that average of aCDOM(412) in Chaohu Lake was higher than Taihu Lake, although they both are hyper eutrophic inland waters. We also found that changes in absorption spectra of CDOM as the influence of massive phytoplankton blooms with two distinct absorptions at 320 nm and 600 nm. The spectral slopes S reveals the potential sources and fates of CDOM and may negatively correlate with CDOM absorptions. We calculated the S in different wavebands and observed that spectral slopes from the UVA (315-400 nm) showed high correlation with aCDOM(412) in different water regions. The SA/aCDOM(412) was used to detect the sources of CDOM in the four water areas. The results revealed a useful proxy, SA/aCDOM(412), to determine the potential sources and fates of CDOM in inland water ecosystems. Future work will focus on how the regulatory factors (such as, temperature, light, hydrology, etc.) characterize the CDOM absorption properties in aquatic ecosystems