An investigation the optical properties and spatial distribution of dissolved organic matter (DOM) in an ecological purification system and the primary factors that affect the optical properties of the DOM was conducted. Taking the Yanlong Lake ecological purification system as an example, data from spring 2017 and 2018 were compared. The results show that the concentrations of total phosphorus and total nitrogen and the permanganate index in Yanlong Lake were 0.05-0.25, 1.25-2.75, and 3.99-7.17 mg·L-1, respectively. In addition, the dissolved oxygen in the effluent of Yanlong Lake increased to (11.93±1.31) mg·L-1, and the turbidity decreased to (13.23±2.24) NTU, while the change in the permanganate index was not significant. Principal component analysis (PCA) showed that the water quality of the Yanlong Lake raw water and water in the pre-treatment area was closely related to the inflow of exogenous sources, while the water quality in submerged plant areas and deep purification areas was dependent on endogenous effects. According to the fluorescence index, humification index, and biological source index analysis, it was found that there are new spontaneous sources of DOM in this body of water, the degree of humification is lower, and endogenous biological DOM is dominant. The PARAFAC model can be used to classify DOM into UV-fulvic acid-like components (239 nm, 304 nm/407 nm), visible light fulvic acid-like components (256 nm, 352 nm/439 nm), tryptophan-like protein (276 nm/327 nm) and humic acid (292 nm, 395 nm/491 nm). The UV absorption index indicates that the spectral intensity of DOM in the raw water, pretreatment unit, and emergent water plant area of Yanlong Lake fluctuates greatly, and the DOM spectral intensity of the submerged plant area and deep purification area is relatively stable. The factors affecting the optical properties of the DOM in terms of water quality parameters are mainly transparency, dissolved oxygen, conductivity, total nitrogen, and algae cell number.
Keywords: dissolved organic matter (DOM); ecological purification system; influencing factor; optical properties; spring.