Decay Dynamics\nof Hydrophyte and Nutrient Release\nin a Lake System: Experimental and Predicting Modeling

This research focuses on Nansi Lake, an important regulating\nreservoir\nin China’s South-to-North Water Diversion Project. It studies\nthe natural decay process of five major hydrophytes in the lake and\nanalyzes the impact of this process on water quality. The results\nshow that the decay patterns of the five plants are similar, each\nbeing divided into three stages. In the initial stage, easily decomposable\norganic matter rapidly breaks down, releasing large amounts of nitrogen\nand phosphorus into the overlying water, quickly consuming dissolved\noxygen and significantly lowering the pH. In the middle stage, the\ndecomposition rate of organic matter slows down, and the nitrogen\nand phosphorus content in the water gradually decreases while dissolved\noxygen and pH slowly rise. In the final stage, the organic matter\nwithin the plants is completely consumed, leaving primarily lignin,\nand the concentrations of various substances in the water stabilize,\nreaching a steady state. Additionally, this study establishes a Monod-type\nkinetic model to simulate changes in ammonia nitrogen in water during\nthe decay process. By adjusting the parameters <i>K</i><sub>1</sub>, <i>K</i><sub>2</sub>, and <i>K</i><sub>3</sub>, we obtained fitted curves consistent with the decay data\ntrends for five plants. This helps to understand the impact of plant\ndecay on water quality in Nansi Lake and provides a basis for plant\ndisposal strategies and water quality management across different\nseasons in Nansi Lake.