藻源性湖泛发生过程CDOM变化对水色的影响

利用Y-型沉积物再悬浮发生装置模拟湖泛发生过程,分析其中有色可溶性有机物(CDOM)的变化特征及其对水色的影响.结果表明,藻类死亡过程消耗大量的氧气,水中溶解氧在短时间内消失殆尽,形成厌氧环境;并同时分解产生大量CDOM,使得水中CDOM显著增多.前期阶段,CDOM浓度随时间一直升高,第6 d时CDOM浓度达到峰值,CDOM在443 nm处的吸收系数a_g(443)为4.48 m^-1.水体黑度值(FeS浓度)呈先增大后减小的趋势,最大值0.35mmol/L同样出现在第6 d,整个过程中,CDOM浓度和黑度值变化趋势一致,a_g(443)与水体黑度呈显著正相关.利用Hydrolight和CIE颜色匹配函数模拟不同梯度的CDOM对水色的影响,发现随a_g(443)增大,水体颜色也逐渐由绿色转为棕色,整体向长波方向移动,水色逐渐变暗.因此,可以认为CDOM浓度变化是引起湖泛水体发黑的重要原因之一,可作为定量监测湖泛强度的指示性参数.

The changes of water color induced by chromophoric dissolved organic matter(CDOM) during the formation of black blooms

In this study, we developed a laboratory scale mesocosm to study the conditions that favour the formation of black water blooms. Using water samples and sediment from an eutrophic lake, we analyzed the daily transformation of physical, biological and chemical conditions over several weeks. The results showed that a transformation of oxic-hypoxic-anoxic conditions characterized the formation of the black bloom. In anaerobic conditions, chromophoric dissolved organic matter (CDOM) increased due to the production of degradation products from decaying algae. CDOM reached a maximum on day 6 with the value of 4.48 m^-1. The blackness (FeS concentration) increased initially, then decreased to a constant concentration of 0.35mmol/L. CDOM values were significantly correlated with the blackness of water color. Water-leaving radiance was simulated under different CDOM conditions by Hydrolight and transposed using the CIE color matching functions. This showed a transition from green to brown which closely followed the increase in CDOM absorption. Results above clearly show that CDOM is a major factor leading to the formation of black blooms, and can be used to monitor their dynamics over time.