Biomat Resilience to Desiccation and Flooding Within a Shallow, Unit Process Open Water Engineered Wetland

Adam Brady,Evelyn Lundeen,Jonathan Sharp,Michael Vega,Julia Siegmund,Kimberly Riddle,Henry Peel

doi:10.3390/w13060815

Adam Brady, Evelyn Lundeen + Show 5 more

Open Access

https://doi.org/10.3390/w13060815

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Journal: Water	Publication Date: Mar 16, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: United States Military Academy, Colorado School of Mines

Abstract

Projections of increased hydrological extremes due to climate change heighten the need to understand and improve the resilience of our water infrastructure. While constructed natural treatment analogs, such as raingardens, wetlands, and aquifer recharge, hold intuitive promise for variable flows, the impacts of disruption on water treatment processes and outcomes are not well understood and limit widespread adoption. To this end, we studied the impact of desiccation and flooding extremes on demonstration-scale shallow, unit process open water (UPOW) wetlands designed for water treatment. System resilience was evaluated as a function of physical characteristics, nitrate removal, photosynthetic activity, and microbial ecology. Rehydrated biomat that had been naturally desiccated re-established nitrate removal consistent with undisrupted biomat in less than a week; however, a pulse of organic carbon and nitrogen accompanied the initial rehydration phase. Conversely, sediment intrusion due to flooding had a negative impact on the biomat’s photosynthetic activity and decreased nitrate attenuation rates by nearly 50%. Based upon past mechanistic inferences, attenuation potential for trace organics is anticipated to follow similar trends as nitrate removal. While the microbial community was significantly altered in both extremes, our results collectively suggest that UPOW wetlands have potential for seasonal or intermittent use due to their promise of rapid re-establishment after rehydration. Flooding extremes and associated sediment intrusion provide a greater barrier to system resilience indicating a need for proactive designs to prevent this outcome; however, residual treatment potential after disruption could provide operators with time to triage and manage the system should a flood occur again.

Highlights

Two extremes of field-scale disruption events within the unit process open water (UPOW) wetland cells at Prado formed the foundation of this study
In September 2018, after ~15 months of growth, the Little Bubbs were isolated from the flow and dried in an autumnal Mediterranean climate. Materials harvested from this system served as the source for desiccated biomat experiments designed to assess the capability of these systems to go through oscillating dry/dormant and wet-weather treatment conditions
The entire engineered wetland footprint, including both conventional vegetated and UPOW cells, were in turn inundated with storm surge associated river-type flows rather than the traditional controlled flows that otherwise supplied water to the wetland

Summary

Introduction

Existing water and wastewater infrastructure in the United States and beyond is collectively nearing the end of its projected lifespan and was not designed to address uncertainties and stressors associated with the impacts of climate change. Of particular concern is the magnitude and frequency of hydrologic extremes. Flows estimated for 200-year floods are expected to increase while the timing between such events should decrease [1,2]. Increases in runoff associated with melting snowpack may further intensify the potential for flooding and shift timing from historic norms [3]. Climate change is expected to impact the regional frequency and severity of droughts [4]

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