Quantifying bubbles – using point process models to understand ebullition variability

July 30, 2013 • Filed under: News — melanie.rohr

A newly published paper in the Journal of Geophysical Research – Biogeosciences by WERC researcher Katey Walter Anthony provides a new understanding on the variability of methane ebullition in thermokarst lakes and discusses how these findings apply to whole lake emission estimates collected from field data.

Walter Anthony, K. M., and P. Anthony (2013), Constraining spatial
variability of methane ebullition seeps in thermokarst lakes using
point process models, J. Geophys. Res. Biogeosci., 118,
doi:10.1002/jgrg.20087

Abstract

Ebullition is an important but highly heterogeneous mode of methane
emission in lakes. Variability in both spatial distribution and
temporal flux creates difficulty in constraining uncertainties in
whole lake emission estimates. Analysis of short- and long-term flux
measurements on 162 ebullition seeps in 24 panarctic lakes confirmed
that seep classes, identified a priori according to bubble patterns in
winter lake ice, have distinct associated fluxes irrespective of lake
or region. To understand the drivers of ebullition’s spatial
variability and uncover ways to better quantify ebullition in field
work, we combined point-process modeling with field measurements of
2679 GPS-marked and classified ebullition seeps in three Alaskan
thermokarst (thaw) lakes that varied by region, permafrost type, and
seep distribution. Spatial analysis of field data revealed that seeps
cluster above thawed permafrost soil mounds in lake bottoms. Seep
density and clustering, determined from field observations, were used
as parameters in a Poisson cluster process model to simulate seeps
across entire lake surfaces. Sampling results indicated that (1)
applying seep-class mean flux values to unmeasured seeps counted on
ice-bubble surveys does not compromise accuracy of whole lake flux
estimates; (2) three distributed 50 m2 ice-bubble survey transects
more accurately estimate mean lake ebullition than 17 dispersed 0.2 m2
bubble traps; and (3) the uncertainty associated with whole lake mean
ebullition estimated by lake-ice survey transects is inversely related
to seep density. Findings suggest that transect field data collected
on a large number of widely distributed lakes can be combined to
provide a well-constrained, bottom-up estimate of regional lake
ebullition.

The full version of this paper can be accessed via the publisher’s online library.