Abstract
Urban ponds increase biodiversity by providing essential habitats, mitigating heat, and serving as refuges for aquatic species. Macrophyte management, particularly mowing, plays a crucial role in altering vegetation structure and influencing water quality factors. However, the effects on aquatic insect communities remain unclear, as previous studies have not explicitly differentiated between direct and indirect effects. Additionally, little is known about how the total effect of mowing varies over time and with increasing water temperature. To address this gap, we conducted paired treatment experiments (with/without macrophyte mowing) from April to September in a Southeast Asian urban wetland. Using Bayesian structural causal modeling, we quantified both the total and direct effects of mowing on aquatic insect communities. Our results show that mowing primarily increases aquatic insect abundance via indirect pathways, with impacts varying by family and season. In summer, mowing increased the abundance of midge larvae (Chironomidae), likely due to their tolerance to high water temperature, whereas damselfly larvae (Coenagrionidae) require cooler conditions. Conversely, during spring and fall, mowing decreased the abundance of both midge larvae and damselfly larvae. Mowing also increases water temperature and dissolved oxygen, further affecting aquatic insect abundance. Overall, our research provides a novel mechanistic understanding of how emergent macrophyte mowing influences aquatic insect communities, addressing key methodological limitations in previous studies. These findings can inform more effective macrophyte management strategies to enhance aquatic biodiversity in urban ecosystems.