Studies On The Effects Of Plant Diversity On Ammonia Volatilization In Constructed Wetlands

Ammonia volatilization from wastewaters with high-concentration ammonium has become a major environmental and health problem. Constructed wetlands (CWs) have been widely used in treating wastewaters with high-concentration ammonium. Although CWs can effectively remove nitrogen in the wastewaters, there is a lot of ammonia volatilization, which is closely related to formation of haze and nitrogen deposition, in the process of wastewater treatment. Plant diversity has proved to improve ecosystem functioning such as wastewater nitrogen removal and biomass productivity in CWs. However, the effect of plant diversity on ammonia volatilization is still unknown in CWs. To investigate the effects of plant species richness and identity on ammonia volatilization, this study conducted a microcosm experiment system simulating CWs, and assembled 4 richness gradient and all possible 15 combinations. This study carried out 4 ammonia volatilization measurements at different hydraulic retention time (HRT). Results showed that (1) higher species richness decreased ammonia volatilization:for HRT=1 and 4 d (P < 0.05), for HRT=7 and 8 d (P<0.10), but the effects of species richness on nitrogen removal and biomass production were relatively lower; (2) species identity significantly affected ammonia volatilization and related ecosystem functioning, and systems containing Rumex japonicus had lower ammonia volatilization flux than others (P<0.05); (3) the effects of species identity on ammonia volatilization and related ecosystem functioning were larger than species richness; (4) the complementarity effect occurred in mixtures containing R. japonicus and contributed to the suppression effect of diversity on ammonia volatilization in initial stage of wastewater supply (HRT=1 d) when wastewater nitrogen concentration was relatively higher, but became weaker in later stage (HRT=4,7, 8 d) when wastewater nitrogen concentration had decreased; (5) ammonia volatilization flux positively related to wastewater ammonium nitrogen concentration and negatively related to plant biomass production in mixture systems. This study indicated that assembling plant diversity (especially selecting suitable plant combinations) can be applied to suppress ammonia volatilization, and meanwhile improve nitrogen removal efficiency and plant biomass production in CWs.