Environmental effects on constructed wetland microbial diversity and function in the context of wastewater management

Background/Question/Methods

An important gap in our understanding is how environmental change affects microbial Biodiversity-Ecosystem Function relationships (BEF). To address this question, our study investigates the BEF relationships between microbial diversity and ammonia removal at the Arcata Wastewater Treatment Facility (AWTF) both spatially and temporally. The AWTF utilizes several natural treatment systems consisting of Oxidation Ponds and constructed wetlands for secondary wastewater treatment. These natural treatment systems provide a unique opportunity to study microbial community BEF relationships because they are interconnected by the flow of nutrients in the wastewater and are exposed to seasonal changes. We conducted a field study where we sampled the AWTF natural treatment system from Autumn to Spring. Based on classical BEF studies, we expected a positive relationship between biodiversity and function, but anticipated a potential effect of seasonal and spatial factors in strengthening or weakening the relationship. To test this hypothesis, we measured microbial community diversity via next generation sequencing with richness and evenness as the biodiversity metrics. The change in ammonia concentration served as the ecosystem function variable and as the response variable for its relationship with locality, seasonality, and diversity.

Results/Conclusions

Contrary to our expectations, we found a significant negative BEF relationship between microbial community richness and ammonia removal. Ammonia concentration significantly decreased through the wastewater purification system, yet microbial diversity was unrelated to location, suggesting that other factors besides microbial community richness and evenness are reducing the ammonia along the treatment train. In turn, seasonality significantly affected the microbial community diversity where richness was lower in Spring. These results imply that nutrient cycling capabilities of natural wastewater treatment systems are most efficient when fewer species dominate the microbial communities and seasonality influences microbial community dynamics. Furthermore, environmental change has an impact on microbial community diversity and ecosystem functioning in natural and humanized systems. The results of this study inform the AWTF that the dominance of a few bacterial taxa may increase the ammonia removal capabilities of the natural treatment system. These findings contribute to our understanding of local and global systems by strengthening our framework to predict and manage microbial functions for ecosystem resiliency.