Presentation Title

Rates and Drivers of Methane Production and Consumption in Bioretention Facility Soils Across Six U.S. Cities

Start Date

February 2018

End Date

February 2018

Abstract

Urban bioretention facilities are one form of low impact development intended to manage stormwater. These facilities are designed in part to retain organic and inorganic contaminants and in some cases, promote their removal. One such removal process is denitrification; in anoxic, saturated conditions, denitrification converts nitrate to nitrous oxide or dinitrogen gas. However, these conditions also promote the production of methane, a potent greenhouse gas. Preliminary studies measuring in-situ methane emissions indicate bioretention facilities can be a strong source of methane. We compared both potential methane production and consumption rates between 36 bioretention facilities across six U.S cities: Portland, Phoenix, Charlotte, Baltimore, New York City, and Syracuse. Soil cores were collected and shipped overnight to our laboratory in Portland, OR. CH4 production incubations were carried out within an 8-day window; consumption assays, a 48-hour series. Soil characterization includes bulk density, moisture, total organic carbon, conductivity, pH, WHC, texture, C:N ratio, and soil temperature. Within-city variables include management and climactic regime. We determined whether the rates of potential methane production and potential methane consumption varied between cities and to what extent.Results indicate strong differences in production between Portland and Phoenix, with maximum daily average rates of 0.12 ng CH4/g/day in Portland and 8.81 ng CH4/g/day in Phoenix. Soil characteristics varied as predictors of methane production between cities. Linking methane production and consumption with their predictive variables will inform the next generation of design for low impact development to balance tradeoffs between contaminant retention and methane emissions.

Subjects

Climate Change, Soil science, Sustainable development

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Rates and Drivers of Methane Production and Consumption in Bioretention Facility Soils Across Six U.S. Cities

Urban bioretention facilities are one form of low impact development intended to manage stormwater. These facilities are designed in part to retain organic and inorganic contaminants and in some cases, promote their removal. One such removal process is denitrification; in anoxic, saturated conditions, denitrification converts nitrate to nitrous oxide or dinitrogen gas. However, these conditions also promote the production of methane, a potent greenhouse gas. Preliminary studies measuring in-situ methane emissions indicate bioretention facilities can be a strong source of methane. We compared both potential methane production and consumption rates between 36 bioretention facilities across six U.S cities: Portland, Phoenix, Charlotte, Baltimore, New York City, and Syracuse. Soil cores were collected and shipped overnight to our laboratory in Portland, OR. CH4 production incubations were carried out within an 8-day window; consumption assays, a 48-hour series. Soil characterization includes bulk density, moisture, total organic carbon, conductivity, pH, WHC, texture, C:N ratio, and soil temperature. Within-city variables include management and climactic regime. We determined whether the rates of potential methane production and potential methane consumption varied between cities and to what extent.Results indicate strong differences in production between Portland and Phoenix, with maximum daily average rates of 0.12 ng CH4/g/day in Portland and 8.81 ng CH4/g/day in Phoenix. Soil characteristics varied as predictors of methane production between cities. Linking methane production and consumption with their predictive variables will inform the next generation of design for low impact development to balance tradeoffs between contaminant retention and methane emissions.