A review of the effects of plant harvesting on constructed wetland systems

Under the background of environmental protection, constructed wetland, an ecological technology, is widely used in advanced treatment and ecological purification of various surface water bodies because of its low carbon, low consumption and high efficiency. Plants are considered to be important parts of constructed wetlands and play an important role in the process of water purification. Due to the growth characteristics of wetland plants, if the withered wetland plants can not be harvested in time, they will lead to secondary pollution, and even cause wetland blockage, which will affect the stable operation of wetland system. This paper summarized the influence of plant harvesting on the operation effect of constructed wetland system, analyzed the mechanism of plant harvesting affecting pollutant removal, and finally summarized the harvesting management strategies of different kinds of plants. This paper makes up the blank of this part through narration, which will better guide the harvesting process of constructed wetland plants. The seasonal fluctuation of plant harvesting on water quality is significant. Harvesting in spring and summer can stably improve the removal effect of pollutants such as chemical oxygen demand and total nitrogen in the system, while harvesting in autumn and winter is beneficial to the removal of total phosphorus and ammonia nitrogen, but the impact on chemical oxygen demand and total nitrogen fluctuates greatly. In terms of plant species, harvesting submerged plants is more conducive to removing four conventional pollutants (chemical oxygen demand, total nitrogen, total phosphorus, and ammonia nitrogen) compared to emergent plants, which facilitates better purification of constructed wetland water bodies. At the same time, through the second excavation of the article, it is found that there is a certain correlation between wetland plant species and seasons during harvesting. In addition, harvesting not only directly affects the productivity and biological characteristics of plants, but also indirectly affects the physical and chemical environment and microbial metabolism process of wetlands by changing the oxygen secretion level of plant roots and the activity of substrate enzymes, thus affecting the plant-microorganism-substrate coupling effect and the geochemical cycle process of pollutants, which makes the change of water purification efficiency in constructed wetlands. The influence of plant harvesting on the operation of constructed wetland mainly depends on harvesting time, harvesting mode, harvesting frequency, harvesting degree and plant species. When harvesting plants, appropriate harvesting strategies should be selected according to plant types and actual conditions of constructed wetlands, striving to achieve the optimal solution.