Effects of Aquatic Plant Coverage on Diversity and Resource Use Efficiency of Phytoplankton in Urban Wetlands: A Case Study in Jinan, China

Simple Summary An urban wetland, a critical component of an ecosystem, provides diverse habitats and has important functions such as water purification and nutrient cycling. However, under urbanization, wetland ecosystems face serious challenges from human activities like dredging, which often removes aquatic plants and destroys their functions. Therefore, studying the contributions of aquatic plants is key to wetland conservation. The present study was conducted in 10 urban wetlands in Jinan, China, to investigate the effects of aquatic plant coverage on wetland water quality, phytoplankton diversity, and resource use efficiency. The study area was categorized into three different aquatic plant coverage groups: low coverage (0-25%), medium coverage (26-35%), and high coverage (36-66%). The relationships among water quality parameters, phytoplankton diversity, and resource use efficiency were analyzed. Data show that the increase in aquatic plant coverage could directly absorb excess nutrients (e.g., nitrogen and phosphorus) and help to reduce sediment resuspension, thus significantly reducing the nutrient and suspended solid content of the water body and improving the water quality of the wetland. Furthermore, the increase in coverage was also associated with the increase in phytoplankton diversity, including species richness and functional diversity. The present study has shown that the composition of phytoplankton functional groups is positively affected by the degree of aquatic plant coverage. Phytoplankton groups adapted to still-water conditions and low light intensity were predominant in sites with higher aquatic plant coverage. Meanwhile, lower nutrients prevented dominant species from outcompeting others, allowing increased diversity. This increased phytoplankton diversity was associated with increased resource utilization efficiency (RUE), which is the ratio of phytoplankton biomass to available nutrients such as nitrogen and phosphorus. More diversity allows for better ecological niche allocation and complementarity in the utilization of limited resources. Adequate aquatic plant coverage plays a critical role in maintaining biodiversity, water quality, and ecosystem function in urban wetlands. Conservation of aquatic plants should be a priority in management plans. The results of this study provide a scientific basis for incorporating aquatic plants into sustainable urban wetland conservation strategies.Abstract With the acceleration of urbanization, biodiversity and ecosystem functions of urban wetlands are facing serious challenges. The loss of aquatic plants in urban wetlands is becoming more frequent and intense due to human activities; nevertheless, the effects of aquatic plants on wetland ecosystems have received less attention. Therefore, we conducted field investigations across 10 urban wetlands in Jinan, Shandong Province, as a case in North China to examine the relationships between aquatic plant coverage and phytoplankton diversity, as well as resource use efficiency (RUE) in urban wetlands. Multivariate regression and partial least squares structural equation modeling (PLS-SEM) were used to analyze the water quality, phytoplankton diversity, and RUE. The results demonstrate that the increase in aquatic plant coverage significantly reduced the concentration of total nitrogen and suspended solids' concentrations and significantly increased the phytoplankton diversity (e.g., species richness and functional diversity). The aquatic plant coverage significantly affected the composition of phytoplankton functional groups; for example, functional groups that had adapted to still-water and low-light conditions became dominant. Furthermore, the increase in phytoplankton diversity improved phytoplankton RUE, highlighting the importance of aquatic plants in maintaining wetland ecosystem functions. This study may provide a scientific basis for the management strategy of aquatic plants in urban wetlands, emphasizing the key role of appropriate aquatic plant cover in maintaining the ecological stability and ecosystem service functions of wetlands.