Linking dynamics of dissolved organic carbon in a forested lake with environmental factors

Dynamics of dissolved organic carbon concentration (DOC) and capacity toabsorb light (color) are determined by in-lake and external properties andprocesses. In this study, the influence of external factors such as rainfallandsolar radiation on DOC and color dynamics was assessed for a small forestedlake. DOC and absorption coefficients at 440 nm (a440)ranged 4-fold from 0.46 to 1.62 mM and from 3.4 to 14.8m−1, respectively. DOC and a440 variedsynchronously, but an important percentage of the variability (26%) ina440 was not explained by DOC. The resulting twofold variation inthemolar absorption coefficient of DOC suggested significant seasonal changes inchromophoric content. Both DOC and a440 were positive andsignificantly related to cumulative rainfall. Solar radiation, however, onlyappeared to influence a440 dynamics. This influence was mediated byphotobleaching. Photobleaching coefficients (kb) were higher in falland spring relative to the summer. This seasonal variability in kbvalues was related to monthly rainfall. The influence of photobleaching ona440 dynamics was evaluated by comparing the half life ofa440 in the water column with water residence time (WRT). For thestudy lake, photobleaching contributed notably to a440 dynamicsduring the dry periods when WRT was longer than the a440 half life .DOC dynamics, however, were not related to solar radiation becausephotomineralization was considerably slower than photobleaching.