PROPUESTA DEL PROGRAMA DE PROCESOS OPERATIVOS ESTANDARIZADOS DE SANITIZACIÓN (POES)

Since the two research sites were located in the same peatland complex, they share similar Ta and precipitation regimes. For much of the study period Ta was near long-term (1981-2010) averages

(i.e., within  1 standard deviation) (Table 5.1). Anomalous periods include higher than normal Ta in July 2014 and September 2015 and colder than normal co nditions in March, April, June, July and November 2015 and April 2016 (Table 5.1). Rainfall was lower than normal in

September 2015, but higher than normal in three consecutive winter months from November

2014 to January 2015 (Table 5.1). Seasonal trends in environmental variables for the two study

years showed expected patterns and were similar between sites (Fig.5.2). The daily average Ta was near zero before 20th April (day110) and increased above 5 oC after 15th May (day 135) in both years, peaking at late July in 2014 (day 183-212) and mid- to late-August (day 229-237) in

2015 and then dropped below 5 oC on 8th November (day 312) in 2014 and 15th November (day 319) in 2015. The highest Ta of 24 °C in 2014 was about 2 °C higher than that in 2015. The seasonal pattern of T1 followed the seasonal variation in Ta and the highest values coincided with the peak in Ta in each year (Fig.5.2: b1-b3). The lowest values of T1 for both years were reached near the end of December and remained near zero until the end of April the following spring.

The daily average PPFD was highly variable during the growing season for both sites, ranging

from less than 100 µmol m-2 s-1 to a maximum of about 720 µmol m-2 s-1 in May of 2014 and 680 µmol m-2 s-1 in June of 2015 (Fig.5.2f). Daily rainfall ranged from 0 mm to 89 mm in the first study year and from 0 mm to 53 mm in the second study year (Fig.5.2: e1-e3). Maximum WTs at

the pasture site (-61 cm in 2014-15 and -52 cm in 2015-16) in were deeper than those at the bog

(-33 cm in 2014-15 and -36 cm in 2015-16). Soil moisture at 30 cm remained in a narrow range

between ~0.76 and 0.88 m3 m-3 at the bog and between 0.61 and 0.67 m3 m-3 at the pasture site in both study years (Fig.5.2: c1-c3). Soil moisture and WT were high in the non- growing season

showed periodic sharp rises and decreases corresponding to summer rain events greater than 10

mm and the subsequent drawdowns (Fig.5.2: d1-d3).

Table 5.1 Comparison of monthly average temperature and cumulative monthly rainfall

measured at Robinson Pasture during measurement periods from May, 2014 to April, 2016 with

the long-term (1981-2010 average ± SD) measurements from the nearby, climate station in

Stephenville, Newfoundland and Labrador. Please note that bog and pasture had similar rainfall.

Month Rainfall (mm) Air temperature (ºC)

Bog & Pasture Bog Pasture Bog Pasture Bog Pasture

2014 2015 2016 1981- 2010 2014 2015 2016 1981-2010 Jan 54 14 29 ± 24 -6.7 -6.8 -5.2 -5.3 -6 ± 1.6 Feb 20 45 27 ± 30 -9.2 -9.2 -3.9 -3.9 -6.7 ± 2.9 Mar 12 30 37 ± 29 -6.9 -6.9 -5 -5 -3.5 ± 2.5 Apr 41 88 62 ± 42 -0.8 -0.8 0.6 0.6 2.6 ± 1.8 May 129 118 94 ± 44 6.5 6.5 7 7.1 7.6 ± 1.4 Jun 65 64 104 ± 45 12.3 12.2 10.1 10.2 12.1 ± 1.3 Jul 97 119 118 ± 45 19.3 19 14.2 14.1 16.4 ± 1.1 Aug 105 125 130 ± 65 16.7 16.5 18.1 17.9 16.7 ± 0.9 Sep 83 55 128 ± 48 12.4 12.2 13.8 13.7 12.8 ± 1.1 Oct 85 101 124 ± 45 8.6 8.5 6.5 6.4 7.4 ± 1.3 Nov 133 82 94 ± 31 1.6 1.5 1.2 1.2 2.7 ± 1.3 Dec 105 54 49 ± 42 -1.4 -1.5 -2.1 -2.1 -2.4 ± 1.7 Overall 845 995 ± 133 3.7 3.7 5.0 ± 1

Fig.5.2. The daily average air temperature (a1-a3), soil temperature at 1 cm (b1-b3), volumetric

soil water content at depth of 30 cm (c1-c3), water table depth (d1-d3), cumulative rainfall (e1-

e3) and photosynthetic photon flux density (PPFD) during the measurement periods for both bog

and abandoned peatland pasture.

5.4.2. Comparison of the temporal variation in CO2 flux

Although NEE displayed a strong diel pattern from May to October in both 2014 and 2015 for

both sites, the abandoned peatland pasture had substantially larger half- hourly fluxes than at the

bog (both daytime and nighttime values) during months from June to September (Fig.5.3). Only

during the shoulder months of May and October were the diel magnitudes of NEE similar for

both sites. Peak daytime CO2 uptake and nighttime emission occurred in the warmest months (July and August) at both sites (Fig.5.3). NEE, ER and GPP showed strong seasonal patterns for

both sites with significantly larger daily fluxes observed at the abandoned peatland pasture

(Figs.5.4, 5.5). The daily average NEE ranged from -2.61 to 1.77 µmol m-2 s-1 in 2014-15 at the bog, and from -5.88 to 4.22 µmol m-2 s-1 in 2014-15 and from -6.38 to 4.12 µmol m-2 s-1 in 2015- 16 at the pasture (Fig.5.4a, 5.5a). The highest daily net CO2 uptake occurred in early August of 2014 at the bog, but in early July of both years at the pasture. ER ranged from 0.23 to 3.40 µmol

m-2 s-1 in 2014-15 at the bog, and between 0.28 and 8.64 µmol m-2 s-1 in 2014-15 and between 0.20 and 8.43 µmol m-2 s-1 in 2015-16 at the pasture (Fig.5.4b, 5.5b). ER at both sites was low during the non-growing season (from November to April), generally less than 1 µmol m-2 s-1, and increased steadily after snowmelt, peaking in the summer months. Peak daily ER fluxes of 8.64

µmol m-2 s-1 in early August of 2014 and 8.43 µmol m-2 s-1 in late August of 2015 at the pasture were significantly larger than maximum ER at the bog (3.40 µmol m-2 s-1) which occurred in

mid- to late-July 2014. GPP followed a similar seasonal pattern as ER for both sites, with the

highest daily average GPP of 3.70 µmol m-2 s-1 in 2014 at the bog and 10.17 µmol m-2 s-1 in 2014 and 9.75 µmol m-2 s-1 in 2015 at the pasture. The GPP peak occurred in early August for the bog and early- to mid-July in both years at the pasture (Fig.5.4c, 5.5c).

Monthly totals emphasized the much larger fluxes observed at the pasture compared to the bog

during the growing season months, while the between-site differences were small during non-

growing season months (Fig.5.6). The monthly mean GPP from June to September ranged from

4.91 to 10.02 µmol m-2 s-1 in 2014-15 and from 4.63 to 9.75 µmol m-2 s-1 in 2015-16 at the abandoned peatland pasture, whereas at the bog the range was 2.04-3.66 µmol m-2 s-1 in 2014-15 (Fig.5.6c). Monthly ER at the abandoned peatland pasture during June to September ranged from

4.27 to 6.97 µmol m-2 s-1 in 2014 and from 3.73 to 6.84 µmol m-2 s-1 in 2015 and was 1.52-2.72 µmol m-2 s-1 at the bog in 2014 (Fig.5.6b). Net CO2 sinks occurred in June to September in both years at the abandoned peatland pasture, NEE ranged from -0.64 to -3.05 µmol m-2 s-1 in 2014 and from -0.20 to -3.78 µmol m-2 s-1 in 2015, and in 2014 at the bog NEE ranged from -0.27 to - 1.91 µmol m-2 s-1 (Fig.5.6a).

Ecosystem light use efficiency of the pasture was significantly larger than that at the bog in June

and July of 2014, but was similar at the two sites from August onward. In 2015, α was larger at

the pasture from June to August (Fig.5.7a). Conversely, GPPmax of the abandoned peatland pasture was significantly larger than that of the bog in all growing season months in both years,

except May when GPPmax was different between the two sites in 2014, but not in 2015. These contrasting results for May were attributed to a delay of ~15 days in the start of growing season

in 2015 for the abandoned peatland pasture compared to that in 2014 (Fig.5.7b).

Fig. 5.3 Comparison of average diel variation in net ecosystem exchange of CO2 (NEE) in different growing season months for the bog and abandoned peatland pasture sites. Data points

are average values for all available measurements in each 30- minute period of the month and

Fig. 5.4. Seasonal variation of half- hourly (gray dots) and daily average (black dots) NEE (a1-

a3), ER (b1-b3) and GPP (c1-c3) during the period between April 2014 and August 2015 at the

Fig. 5.5. Seasonal variation of half- hourly (gray dots) and daily average (black dots) NEE (a1-

a3), ER (b1-b3) and GPP (c1-c3) during the period between April 2014 to April 2016 at the

Fig.5.6 Monthly average NEE and its component fluxes GPP and ER for the bog and abandoned

Fig.5.7 Monthly light use efficiency (α) and maximum carbon fixation rate (GPPmax) for the bog and abandoned peatland pasture.