First Advisor

Olyssa Starry

Date of Award

Spring 6-16-2024

Document Type

Thesis

Degree Name

Bachelor of Science (B.S.) in Environmental Science and University Honors

Department

Environmental Science and Management

Language

English

Subjects

ecoroof, stormwater runoff, leaf area index, plant selection, establishment, weeds

Abstract

Ecoroofs remove of stormwater runoff from the combined sewer system in Portland, Oregon. Reducing runoff is essential in cities considering how impervious surfaces promote flooding. A limited number of studies focus on comparing stormwater retention of ecoroof plants during their establishment period within Portlands climate. Different photosynthetic pathways in plants may impact stormwater runoff based on their water use efficiency. This study undertook a one-year study to determine the effect of plant establishment on water retention for a C4 and CAM species in six ecoroof trays. Weeds were investigated as a factor in water retention, and whether plant type within the tray impacts weed growth. Retention varied based on the season, with both species reaching about 25% at the end of the study. Plant coverage reached 63% for buffalograss and 69% for white stonecrop in by the end of the study. Across all seasons, buffalograss trays had a lower LAI than white stonecrop, but runoff did not differ between the two species. No difference was found in the weed count and species within the two types of trays. Water retention in this study had comparable observations to local ecoroof research, with winter having the lowest retention. Neither plant type outperformed the other in retention, which could be investigated further in longer studies comparing the full establishment period including many species in each pathway. Clients and ecoroof professionals may use these data to strengthen their understanding of two commonly used species and their probable interactions with weeds during establishment.

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