VEGETATION EFFECT UPON MACROINVERTEBRATE COMMUNITIES IN A VERTICAL-FLOW CONSTRUCTED WETLAND TREATING DOMESTIC WASTEWATER

Constructed wetlands play an important role in wastewater pollutants removal. Thus, several investigations have been carried out about the different components of the system in order to acquire scientific knowledge on the pollutants removal processes that take place there. However, there is little knowledge about the biodiversity that can be found in these artificial environments, especially concerning the invertebrate community level. Our study investigate the effect of different plants species (i.e. Andropogon gayanus, Chrysopogon zizanioides, Echinochloa pyramidalis, Pennisetum purpureum, and Tripsacum laxum) upon macroinvertebrates communities and their abundance in the sediments of a vertical flow constructed wetland treating synthetic domestic wastewater. The experiment was performed in a pilot-scale composed of six beds constructed with bricks. Each bed was filled from the bottom to the top with 0.1 m of gravel covered with cloth and 0.6 m of white lagoon sand. Five beds were transplanted wile one unplanted was used as control. 80 L of domestic synthetic wastewater was then applied on the beds intermittently during six months. All the five plant species have well developed, improving the removal of total nitrogen (TN), total phosphorus (TP) and total suspended solid (TSS) from domestic wastewater in the constructed wetlands. However, P. purpureum provided highest above ground biomass and favored the best TSS, COD, TN and TP removal efficiencies. As for macroinvertebrates, 12 taxa belonging to 12 families, 6 classes and 6 orders were recorded. The community structure was influenced by plant species. Macroinvertebrates were significantly more diversified in the planted beds than in the control. Insects dominated all the planted beds, while Oligochaeta were the most abundant in unplanted bed. The bed planted with P. purpureum housed the largest number of organisms and was follow by those planted with T. laxum, E. pyramidalis, A. gayanus and C. zizanioides, respectively. Following the vertical profile, macroinvertebrates abundance decreased from the upper layer to the bottom layers and only Oligochaeta (Lumbricidae) were recorded in all beds sediments layers of the CW.