Free water surface constructed wetlands (FSW) are established from interconnected wastewater treatment ponds, and their environment are characterized by gradients of bio-physiochemical variables and stress factors across ponds. However, change in macroinvertebrate community in response to various environmental conditions within- and between-FSWs in subtropical region remained unclear. This research investigated the spatial and temporal variation of macroinvertebrate biodiversity and community structure in three successive wastewater treatment ponds along environmental gradients in two FSWs in northern Taiwan. Sampling of macroinvertebrates was conducted by deploying colonization tiles and retrieved for every 7–14 d for 5 times in the study ponds during dry and wet seasons. Community composition of macroinvertebrates was similar between the two FSWs and major taxa included Oligochaeta, Hirudinea, Diptera, Gastropoda and Ostracoda, with Oligochaeta being the most abundant taxon. Colonization abundance of macroinvertebrates was gradually increased in the two FSWs throughout the whole study period. Analysis of variance revealed Oligochaeta and Ostracoda were similar between dry and wet season, but abundance of Diptera, Gastropoda and Hirudinea showed significant seasonal variation and their abundance were ~ 3–10× higher in wet season than dry season. Multivariate analysis indicated the successive change in wastewater treatment with increasing NO3-N and decreasing TP concentrations across the treatment ponds represented the most important environmental gradient in FSWs as this demonstrated highest explanatory the most influential environmental factors on the increase of macroinvertebrate biodiversity in FSWs based on BVSTEP algorithm. Macroinvertebrates showed significant increases in taxon richness and abundance along wastewater treatment gradient suggesting they can serve as simple and direct community indicators used for monitoring the environmental changes. Results from this study provide important insights on sustainable management strategies that introducing environmental disturbances such as hydrological changes (i.e., seasonal changes in water levels, water temperature and water chemistry) in FSWs can help reducing the possibility of wetland terrestrialization, enhancing macroinvertebrate biodiversity and avoiding over-dominance tolerant taxa in FSWs.
Man-made wetlands, Bioindicator, Macrozoobenthos, Biodiversity, Wastewater Purification, Eutrophication
