Duration of extraction determines CO 2 and CH 4 emissions from an actively extracted peatland in eastern Quebec, Canada

[摘要] Draining and extracting peat alters the conditions thatcontrol CO 2 and CH 4 emissions. Carbon (C) emissions from peatlandsundergoing horticultural peat extraction are not well constrained due to alack of measurements. We determine the effect that production duration(years of extraction) has on the CO 2 and CH 4 emissions from anactively extracted peatland over 3 years of measurements (2018–2020). Westudied five sectors identified by the year when extraction began (1987,2007, 2010, 2013, 2016). Greater average CO 2 and CH 4 emissionswere measured from the drainage ditches (CO 2 :2.05  ±  0.12 g C m −2  d −1 ; CH 4 :72.0  ±  18.0 mg C m −2  d −1 )compared to the field surface (CO 2 : 0.9  ±  0.06 g C m −2  d −1 ; CH 4 : 9.2  ±  4.0 mg C m −2  d −1 ) regardless ofsector. For peat fields, CO 2 fluxes were highest in the youngestsector, which opened in 2016 (1.5  ±  0.2 g C m −2  d −1 ). Thefour older sectors all had similar mean CO 2 fluxes( ∼  0.65 g C m −2  d −1 ) that were statistically different from the mean2016 CO 2 flux. A spatial effect on CO 2 fluxes was observed solelywithin the 2016 sector, where CO 2 emissions were highest from thecentre of the peat field and declined towards the drainage ditches. Theseobservations occur due to operators contouring surfaces to facilitatedrainage. The domed shape and subsequent peat removal resulted in adifference in surface peat age hence different humification and lability.In addition, 14 C dating confirmed that the peat contained within the 2016 sector wasyounger than peat within the 2007 sector and that peat age is younger towardthe centre of the field in both sectors. Humification indices derived frommid-infrared spectrometry (MIRS) ( 1630 / 1090  cm −1 ) indicated that peathumification increases with increasing years of extraction. Laboratoryincubation experiments showed that CO 2 production potentials of surfacepeat samples from the 2016 sector increased toward the centre of the fieldand were greater than for samples taken from the 1987 and 2007 sectors. Ourresults indicate that peatlands under extraction are a net source of C, whereemissions are high in the first few years after opening a field forextraction and then decline to about half the initial value and remain atthis level for several decades, and the ditches remain a 2 to 3 timesgreater source than the fields but represent 3.5  % of the totalarea of a field.

[学科分类] 大气科学