CLASSIC and CTCD joint project
Measuring carbon fluxes in an upland moorland : Moor House NNR

One of the main soil carbon stores in the UK are upland peatlands such as the Moor House NNR. It is a great concern that those carbon stocks might become sources under a changing climate. Consequently, it is important to model net ecosystem exchange (NEE), including soil respiration, correctly. However, so far there are only limited data of low quality available. This joint project aims to fill this data gap, combining Eddy covariance with continuous long-term soil respiration measurements.

Fig. 1: Field site at Moor House NNR, UK




We deploy an Eddy covariance system for NEE flux measurements and a state-of-the-art multiplexed (up to 16 chambers) soil respiration system at the Moor House NNR site (Fig.1). We are aiming to (i) separate the soil flux into its components (i.e. autotrophic: roots & mycorrhizas, heterotrophic: soil only) and (ii) to determine their individual environmental responses (e.g. temperature, light, phenology). The Eddy flux system will provide long-term NEE data and soil respiration data will be used for correction of night time NEE fluxes etc.






The soil respiration system (Fig. 2) delivers continuous high temporal resolution data (1 hourly mean values). We now have the first continuous soil flux data for a UK moorland site, growing every day. We also measure transects along the site in order to assess spatial variability throughout the year. However, so far the site shows a very uniform mean variance in soil respiration of about 1-2 µmol m^-2
s^-1μmol m^-2s^-1, regardless of distance between collar measurements (Fig. 2).

     
Fig. 2: left: Field sampling of soil respiration with the automated Li-Cor 8100 long-term chambers; right: Sampling for the transect data with the survey chamber and the resulting semivariogram data for 26th June and July 2006.

The shallow collars we use allow us to (i) measure the total soil respiration flux (not cutting any roots) on a fine temporal resolution and (ii) correlate the soil CO2 fluxes to environmental data (Fig. 3). These are the first UK long-term soil respiration measurements on a peatland site and the data show vegetation related differences in soil respiration, with mossy patches respiring less than heather or grass dominated fluxes. However, most interesting is the high soil respiration, similar to our Wheldrake forest site near York (CTCD), also notes the very high July air temperatures. Further, soil respiration seems to be very much related to air temperature, but this differs considerably between vegetation patches (Fig. 3).

     
Fig. 3: left: Sample of hourly (1-hour cycles) mean values of soil respiration treatments (either predominantly heather, grass or moss) over one week; right: Correlation of soil respiration with air temperatures for the means of different vegetation patches; (n=3).

Interestingly, we do not see a time-lag function of soil respiration component (Fig. 3) as in the Wheldrake forest data (CTCD), i.e. fluxes peak during midday when temperatures are highest. However, despite the very hot weather in July, the Q₁₀ values (measure of temperature sensitivity; i.e. rise in respiration per 10°C temperature increase) were quite low (Q₁₀≤ 2). Moreover, as we measure total soil respiration (i.e. including root respiration) data will enable us to model soil CO₂ fluxes at this moorland site better than ever before, which relates to collar design, e.g. soil collar insertion depth, which will be addressed in experiments later this year.

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