Critical Research Gaps for Understanding Environmental Impacts of Discharging Treated Municipal Wastewater into Assimilation Wetlands

Abstract

Assimilation wetlands are natural, non-constructed, wetlands that are used for the removal of nutrients from treated municipal wastewater. This passive process is comparatively less expensive than other conventional forms of tertiary treatment of wastewater, making it desirable for municipalities. Assimilation wetlands are monitored for a number of environmental parameters, yet limited research has been conducted to understand the ecological impact of this water treatment process. Studies from a variety of systems throughout the United States provide conflicting evidence of the responses of wetland ecosystems to increased inundation and nutrient enrichment. Through an extensive review of existing literature, we summarize the impacts of increasing nutrient loading and inundation on receiving wetlands. Importantly, we address current research gaps and identify directions for future scientific study on this topic. Comprehensive ecosystem monitoring conducted at larger spatial and temporal scales, as well as controlled experimentation, are needed to fully understand ecosystem responses to long-term use of wetlands to remediate wastewater nutrients. Our intent is neither to promote nor detract from this process, but rather to bring attention to potential drivers of environmental change and inform those who manage these systems.