THE EFFECT OF NITROGEN DEPOSITION AND SEASONAL VARIABILITY ON METHANEOXIDATION AND NITROUS-OXIDE EMISSION RATES IN AN UPLAND SPRUCE PLANTATION AND MOORLAND
Ja. Macdonald et al., THE EFFECT OF NITROGEN DEPOSITION AND SEASONAL VARIABILITY ON METHANEOXIDATION AND NITROUS-OXIDE EMISSION RATES IN AN UPLAND SPRUCE PLANTATION AND MOORLAND, Atmospheric environment, 31(22), 1997, pp. 3693-3706
Rates of CH4 oxidation (-) and N2O emission were measured at upland mo
orland and coniferous forest sites in Southern Scotland to investigate
seasonal Variations in flux and the influence of atmospheric N inputs
on the land atmosphere exchange of these two gases. CH4 oxidation rat
es ranged from -0.4 to -16.7 ng CH4 m(-2)s(-1) and showed a strong sea
sonal response with a summer maxima. Total annual uptake of CH4 was es
timated at 1.8, 0.7 and 1.3 kg ha(-1)yr(-1) at the moorland, high alti
tude forest and low altitude forest sites, respectively. Highly signif
icant correlations were observed between CH4 oxidation rates and soil
temperature, with activation energies between 60 and 140 kJ mol(-1). C
H4 oxidation rates were on average 46 and 61% smaller al the high alti
tude forest site than at the the low altitude forest and moorland site
s, respectively, coincident with a large concentration of soil NH4+ -N
caused by large rates of N deposition at the hill summit. Addition of
N as NO3 to soil cores resulted in a 86% reduction in oxidation rates
and addition of N as NH4Cl in a 70% reduction. However, even for NaCl
treated cores, a 75% reduction in oxidation rates was observed. N2O f
luxes ranged from -0.8 to 15.5 ngNm(-2)s(-1) Fluxes were significantly
higher in 1994 than in 1995, corresponding to less rainfall during th
e week prior to flux measurements in 1995. In 1994 significant correla
tions were observed between N2O emission rates, soil temperature, soil
available NH4+ -N concentrations and CH4 oxidation rates. N2O fluxes
were greatest at the hill summit. Total annual emissions were estimate
d at 0.3 kg N ha(-1)yr(-1) at the high altitude forest and moorland si
te compared to 0.1 kg N ha(-1)yr(-1)at the low altitude forest sites.
It was calculated that 1% of the N deposited in the forest at the hill
summit was emitted as N2O. (C) 1997 Elsevier Science Ltd.