Methane emissions from groundwater pumping in the USA

J. T. Kulongoski,P. B. McMahon

doi:10.1038/s41612-019-0068-6

J. T. Kulongoski, P. B. McMahon

Open Access

https://doi.org/10.1038/s41612-019-0068-6

Copy DOI

Abstract

Atmospheric methane accumulation contributes to climate change, hence quantifying methane emissions is essential to assess and model the impacts. Here, we estimate methane emissions from groundwater pumping in the Los Angeles Basin (LAB), north-eastern Pennsylvania, and the Principal aquifers of the USA using the average concentrations of methane in groundwater and annual groundwater pumping volumes. High average methane concentrations, 44.1 mg/L, and extensive groundwater pumping, ~3.1 × 1011 L/a in the LAB, result in the annual emission of ~2.9 × 10−3 Tg of microbial methane. Ethane emissions in the LAB were 3.5 × 10−6 Tg/a. Lower methane emissions estimated for NE Pennsylvania, ~3.0 × 10−6 Tg/a, reflect lower methane concentrations and groundwater pumping, 0.7 mg/L and 4.27 × 109 L/a, respectively. Methane concentrations and groundwater withdrawals, 1.06 × 1014 L/a, across the USA enabled the estimation of the total emissions of methane from Principal aquifers (92% of total pumping) of 0.044 Tg/a in the year 2000, which represents a small percentage (~0.2%) of the total annual US methane emissions, but a previously unquantified flux in the global methane budget. Globally, groundwater-pumping methane emissions were estimated to be 0.53 Tg/a, 0.2% of global methane emissions, by adopting a global estimate for groundwater extraction, and an average methane concentration in older groundwater of 0.44 mg/L.

Highlights

Methane, a reduced form of carbon, is a minor component of the atmosphere at ~1840 parts per billion in the year 2016
We estimate the emission of methane from the Los Angeles Basin (LAB) at 2.9 × 10−3 Tg/a, by multiplying the annual groundwater abstraction for each aquifer by the average methane concentration of each unit (Table 1), similar to approaches estimating the flux of nitrous oxide[15,16] and methane from groundwater pumping.[12]
Groundwater-pumping methane emissions for the LAB, an area of 1088 km[2], are ~0.7% of methane emitted annually from all sources in the South Coast Air Basin (SoCAB), an area of 17,469 km[2], which includes urbanized portions of Los Angeles, Orange, Riverside, and San Bernardino Counties, and ~3% of the methane released from the Aliso Canyon storage facility leak in 2015–2016 (Table 2)

Summary

Introduction

A reduced form of carbon, is a minor component of the atmosphere at ~1840 parts per billion in the year 2016. Methane’s atmospheric residence time is 12–17 years, and methane has a global warming potential of 25 over 100 years (GWP100 of 25), compared with carbon dioxide, which has a GWP100 of 1.1 From 2000 to 2006, atmospheric concentrations of methane remained relatively constant, from 2007 to 2013, atmospheric methane increased by more than 5%, and in 2014 and 2015, concentrations increased by more than 10%,2 and are approaching high greenhouse-gas scenarios, which could exacerbate climate change. Proposed drivers of methane emissions include growth in fossil fuel use, increased agricultural production, thawing arctic permafrost, increased precipitation and tropical flooding, and the decrease in hydroxyl radicals in the atmosphere. Identification and quantification of previously unidentified sources of methane emissions is crucial for improving methane budget estimates, and modeling climate change.[3]. Thermogenic methane forms when organic matter is buried and heated, usually at considerable depths over long periods of time, and includes methane associated with coal, gas, and oil formations

Methods

Results

Conclusion