Community shift of aquatic insects following waste-water treatment implementation at Dongda Creek, Taichung City, Taiwan

Abstract

Urbanization and industrialization have severely degraded Taiwan’s freshwater ecosystems, including Dongda Creek in Taichung City, which received 10,000 tons of wastewater daily. To address this, a wastewater treatment plant (WWTP) was constructed by Tunghai University and the Taichung City Government, and its ecological impact was assessed through water quality and aquatic insect diversity monitoring before (2019–2020) and after implementation (2021–2023). Water quality measurements included temperature, pH, nutrients, and dissolved oxygen, while aquatic insect communities were analyzed using diversity indices and multivariate techniques. Results revealed significant water quality improvements, including reduced fat content and total nitrogen levels, although nitrate concentrations increased. The dominance of pollution-tolerant Chironomidae declined post-WWTP, while sensitive taxa such as Baetidae, Hydrophilidae, and Libellulidae emerged, accompanied by significant increases in diversity indices (taxa richness, Shannon, and Simpson). Seasonal patterns in insect diversity became more pronounced after the WWTP became operational. Environmental variables such as pH, temperature, and biochemical oxygen demand significantly influenced insect distributions, with Chironomidae thriving under poor conditions and sensitive taxa increasing as water quality improved. This study demonstrates that WWTP implementation can enhance water quality and foster ecological recovery, as evidenced by the recolonization of sensitive aquatic insect taxa and increased diversity. These findings highlight the effectiveness of restoration projects like WWTPs in improving ecosystem health and underscore the importance of ecological monitoring in freshwater management and conservation. Dongda Creek serves as a valuable case study for guiding urban river restroration efforts in similar contexts.