Substances released during the decomposition of Vallisneria natans and Thalia dealbata

Two types of aquatic plants commonly used for the ecological restoration of rivers and lakes, Vallisneria natans (Lour.) Hara and Thalia dealbata Fraser ex Roscoe, were selected and grouped by plant parts (root, stem and foliage), and decomposing release experiments were conducted. The influence of the released substances on the water quality was analyzed, as well as the amount of nutrients released by each part of these two plants. The calculated maximum chemical oxygen demand releases from the foliage of V. natans and the foliage of T. dealbata were approximately 5.4 g/kg and 22.65 g/kg, respectively. Through three-dimensional fluorescence spectrum and parallel factor analyses, the different material compositions of the decomposing liquids from the plants were determined, and the main dissolved organic components of the decomposing liquid of V. natans were amino-acid-like and microbially derived humics, and those T. dealbata were soluble microbial by-product-like substances. The carbon-to-nitrogen ratio and humification index of each experimental group were compared. The experimental results showed that different parts of V. natans and T. dealbata had different rates of nutrient release. The dissolved organic matter in the decomposed solution can be utilized by microorganisms, which have the potential to become additional carbon sources. This study provides a new method for the treatment of aquatic plant litter. Different plant species can be used in combination according to their characteristics to ensure that better results are achieved during water treatment processes that use plant decomposing liquids as additional carbon sources.