Estimation of the contribution of chromophoric dissolved organic matter to total light absorption by remote sensing in Lake Taihu

Abstract

有色溶解有机物(CDOM)是决定自然水体水色的主要溶解物质,其吸光能力和光化降解产物对水体初级生产力和碳循环过程具有重要影响.以太湖为研究区,2004年10月、2008年10月、2010年4月和2011年1月和3月共5期实测数据,采集了333个有效样点,分析不同时期CDOM对水体总吸收的贡献,并利用遥感技术估算[a_CDOM/a_t](412).结果表明:不同时期[a_CDOM/a_t](412)均值变化明显,2011年[a_CDOM/a_t](412)的均值最大(0.369),高于所有样点[a_CDOM/a_t](412)均值(0.295±0.139);201004期的[a_CDOM/a_t](412)在0.046~0.455之间变化,其均值最小(0.236±0.108);200410和200810两期数据[a_CDOM/a_t](412)均值相差不大.竺山湾、梅梁湾与整个太湖相比,竺山湾[a_CDOM/a_t](412)均值较高,对太湖[a_CDOM/a_t](412)的贡献较大,而梅梁湾[a_CDOM/a_t](412)均值与整个太湖相差较小.利用多元线性模型估算[a_CDOM/a_t](412)精度较高(n=333,RMSE=34.60%).悬浮泥沙和浮游色素是影响[a_CDOM/a_t](412)遥感估算精度的主要原因,浮游色素的吸收造成[a_CDOM/a_t](412)的值被低估,而悬浮泥沙的吸收使得[a_CDOM/a_t](412)的值被高估,并且悬浮泥沙是影响CDOM吸收的主要原因.;Chromophoric dissolved organic matter (CDOM) mainly absorbs light in water which may influence the nature water color in lakes. Its absorption and photochemical degradation products play an important role in the primary productivity of water and carbon cycle. In Lake Taihu, a total of 333 sites were sampled in October 2004, October 2008, April 2010 and January and March 2011 to analyze the contribution of CDOM to total light absorption and estimate [a_CDOM/a_t](412) from remote sensing. It was found that the average of [a_CDOM/a_t](412) exhibited highly temporal variations during the five cruises. The maximum (0.369) was determined in 2011, comparing with all samples in Lake Taihu (0.295 ± 0.139). The minimum average of [a_CDOM/a_t] (412) in the dataset 201004 was 0.236 ± 0.108, varing from 0.046 to 0.455. No significant difference was observed in the dataset 200410 and 200810. The mean of[a_CDOM/a_t](412) in Zhushan Bay was higher than that in both whole Lake Taihu and Meiliang Bay. For Meiliang Bay, it had almost the same value with the whole lake. A multi-band algorithm was adopted to estimate the [a_CDOM/a_t](412) by remote sensing and acceptable results were detected (n=333, RMSE=34.60%). Suspended sediments and pigments had an important impact on determination of [a_CDOM/a_t](412) from remote sensing. It was underestimated because of pigments and overestimated as the suspended sediments in water and the latter was worse. The results also showed that the CDOM and detritus optically dominate the water color in Lake Taihu.