The Effect of the Potamogeton crispus on Phosphorus Changes throughout Growth and Decomposition: A Comparison of Indoor and Outdoor Studies

Phosphorus (P) transport and transformation in water were investigated using Potamogeton crispus. To compare and evaluate our indoor experiment with outdoor data, we used the simultaneous indoor experiment and field observation approach. The effects of P. crispus growth and decomposition on P concentrations were investigated. P. crispus significantly reduced the P content of different forms in the water during the growth period, and significantly increased the P content of different forms in the water during the decomposition period, according to the findings. As a result, the P level of the water varied seasonally and regularly. The pH and dissolved oxygen (DO) of environmental factors in the water revealed an increasing trend during the P. crispus growth period and a negative trend during the decomposition period. The changing trend of chlorophyll a (Chl-a) and alkaline phosphatase activity (APA) was inverse, decreasing during the growth period of P. crispus and increasing during the decomposition period. In the P. crispus growth environment, all forms of P in water were positively related to Chl-a, APA, and pH, and negatively related to DO. The comparison of the indoor experiment with field data revealed that the indoor experiment number has a larger standard deviation, indicating that the indoor experiment data fluctuated substantially. The indoor simulation experiment has the disadvantage of large data fluctuation. As a result, this study demonstrated that P. crispus regulated the P cycle in water via absorption and changes in environmental factors during the growth period, and released nutrients via decomposition during the decomposition period, thereby influencing the migration and transformation of P in the water. This work may be used as a reference for future research into the process of P exchange between sediments and water interfaces caused by P. crispus.