Abstract:

Aims: Understanding how urbanization alters the taxonomic and functional diversity of aquatic communities is essential for assessing urban river environments and conserving biodiversity. Macroinvertebrates play a crucial role in maintaining the functions and integrity of river ecosystems, yet the ecological variables and mechanisms through which urbanization influences their functional diversity remain poorly understood.

Methods: In 2019, macroinvertebrate samples were collected during both the wet and dry seasons from 62 sites distributed across five major watersheds in Shenzhen, covering a gradient of urbanization intensity. Taxonomic and functional diversity was quantified using species richness and the RaoQ index, respectively. The Mann-Whitney U test was used to compare these two diversity indices between urban and suburban rivers. Furthermore, multivariate stepwise regression analysis was performed to identify key environmental variables shaping macroinvertebrate taxonomic and functional diversity. Finally, variation partitioning was applied to assess the relative contributions of local physical environmental conditions, water chemistry variables, and land-use variables.

Results: Taxonomic and functional diversity were consistently higher in suburban rivers (with lower levels of urbanization) than in urban rivers (with higher levels of urbanization) during both the wet and dry seasons. This disparity was more pronounced during the wet season, suggesting that urbanization exerts stronger impacts on macroinvertebrate diversity during periods of higher water flow. In contrast, functional redundancy was higher in urban rivers than in their suburban counterparts. Stepwise regression and variation partitioning analyses revealed that land-use variables, local physical environmental variables, and water chemistry variables collectively accounted for 37%-57% of the variation in taxonomic and functional diversity. However, the relative influence of these ecological variables varied depending on the biodiversity dimension and the season. Among them, local physical environmental (explaining 4%-23% of the variation) and water chemistry variables (0-9%) emerged as the primary variables, followed by land-use variables (0-4%). Specifically, water chemistry variables—such as permanganate index and conductivity—had the greatest influence on taxonomic and functional diversity during the dry season, whereas local physical environmental variables—such as substrate composition and water depth—played a more significant role in shaping functional diversity during the wet season.

Conclusions: Urbanization significantly reduces the taxonomic and functional diversity of river macroinvertebrates, primarily through changes in local environmental conditions. The lower taxonomic and functional diversity, coupled with higher functional redundancy observed in urban rivers, suggests more homogeneous macroinvertebrate community compositions in these systems. The findings of this study enhance our understanding of the processes and mechanisms underlying the decline of aquatic ecosystem functioning caused by urbanization, and provide a scientific basis for biodiversity conservation and land-use planning in the rivers of the Greater Bay Area of Guangdong-Hong Kong-Macao.

Key words: Shenzhen area, rivers, macroinvertebrate, taxonomic diversity, functional diversity, environmental variables