Rising sea levels and changing water quality pose a growing threat to the coastal communities of the San Francisco Bay. Innovative nature-based solutions, such as the horizontal levee, offer the opportunity to reduce the impact of rising sea levels alongside multiple ecosystem services. A gradual incline of vegetation abutting traditional levee infrastructure, the horizontal levee naturally protects against flooding while providing native ecosystem habitat and improving water quality in the region.
Observations from the demonstration-scale horizontal levee at the Oro Loma Sanitary District (referred to as the Oro Loma Horizontal Levee) have illustrated the horizontal levee’s ability to remove excess nutrients and contaminants from secondary wastewater effluent. Research to date at the Oro Loma Horizontal Levee has sought to describe the physical and chemical perspectives of nutrient cycling and pharmaceutical transformations. However, there have been no investigations into the microbial interactions that are fundamental to driving biogeochemical processes. An incomplete understanding of how these systems function hinders the widespread implementation of horizontal levees and similar technologies in the San Francisco Bay area.
This project used advanced environmental genetics techniques to clarify the microbial role in nutrient cycling and contaminant transformation within the horizontal levee. Gene abundance analyses on the assembled DNA supported important nutrient cycling hypotheses in the wetland. First, there were no anammox specific genes present along the entire length of the slope, diminishing the likelihood that anammox played a significant role in nitrogen cycling. Second, the ubiquity of dissimilatory sulfur reduction and oxidation genes along the length of the wetland support the likelihood that sulfide-driven denitrification and/or DNRA processes play a critical role in nitrogen and sulfur cycling in the wetland.
The insights gained from this project will offer a more complete understanding of the mechanisms responsible for improving water quality in the horizontal levee, promoting broader acceptance of horizontal levees as an adaptive management tool for designing a more resilient California coastline.