Soil–Atmosphere Exchange of Nitrous Oxide, Nitric Oxide, Methane, and Carbon Dioxide in Logged and Undisturbed Forest in the Tapajos National Forest, Brazil

Abstract

Selective logging is an extensive land use in the Brazilian Amazon region. The soil-atmosphere fluxes of nitrous oxide (N 2 O), nitric oxide (NO), methane (CH 4 ), and carbon dioxide (CO 2 ) are studied on two soil types (clay Oxisol and sandy loam Ultisol) over two years in both undisturbed forest and forest recently logged using reduced impact forest management in the Tapajos National Forest, near Santarem, Para, Brazil. In undisturbed forest, annual soil-atmosphere fluxes of N 2 O (mean ± standard error) were 7.9 ± 0.7 and 7.0 ± 0.6 ng N cm −2 h −1 for the Oxisol and 1.7 ± 0.1 and 1.6 ± 0.3 ng N cm −2 h −1 for the Ultisol for 2000 and 2001, respectively. The annual fluxes of NO from undisturbed forest soil in 2001 were 9.0 ± 2.8 ng N cm −2 h −1 for the Oxisol and 8.8 ± 5.0 ng N cm −2 h −1 for the Ultisol. Consumption of CH 4 from the atmosphere dominated over production on undisturbed forest soils. Fluxes averaged −0.3 ± 0.2 and −0.1 ± 0.9 mg CH 4 m −2 day −1 on the Oxisol and −1.0 ± 0.2 and −0.9 ± 0.3 mg CH 4 m −2 day −1 on the Ultisol for years 2000 and 2001. For CO 2 in 2001, the annual fluxes averaged 3.6 ± 0.4 mol m −2 s −1 on the Oxisol and 4.9 ± 1.1 mol m −2 s −1 on the Ultisol. We measured fluxes over one year each from two recently logged forests on the Oxisol in 2000 and on the Ultisol in 2001. Sampling in logged areas was stratified from greatest to least ground disturbance covering log decks, skid trails, tree-fall gaps, and forest matrix. Areas of strong soil compaction, especially the skid trails and logging decks, were prone to significantly greater emissions of N 2 O, NO, and especially CH 4 . In the case of CH 4 , estimated annual emissions from decks reached extremely high rates of 531 ± 419 and 98 ± 41 mg CH 4 m −2 day −1 , for Oxisol and Ultisol sites, respectively, comparable to wetland emissions in the region. We calculated excess fluxes from logged areas by subtraction of a background forest matrix or undisturbed forest flux and adjusted these fluxes for the proportional area of ground disturbance. Our calculations suggest that selective logging increases emissions of N 2 O and NO from 30% to 350% depending upon conditions. While undisturbed forest was a CH 4 sink, logged forest tended to emit methane at moderate rates. Soil-atmosphere CO 2 fluxes were only slightly affected by logging. The regional effects of logging cannot be simply extrapolated based upon one site. We studied sites where reduced impact harvest management was used while in Earth Interactions • Volume 9 (2005) • Paper No. 23 • Page 2 typical conventional logging ground damage is twice as great. Even so, our results indicate that for N 2 O, NO, and CH 4 , logging disturbance may be as important for regional budgets of these gases as other extensive land-use changes in the Amazon such as the conversion of forest to cattle pasture.

Atmospheric methane uptake by tropical montane forest soils and the contribution of organic layers

“…Annual CH 4 fluxes at the 1,000 m site were larger than previously reported for other premontane forests in Africa (Delmas et al 1992), Australia (Kiese et al 2008), Indonesia (Purbopuspito et al 2006) and China (Werner et al 2006) and were also larger than those reported from lowland forests in Costa Rica (Keller and Reiners 1994;Reiners et al 1998) and Brazil (Keller et al 2005). The 5.4-5.9 kg CH 4 -C ha -1 year -1 CH 4 uptake rates at our 1,000 m site were also on the high end of the methane consumption ranges for temperate ecosystems (Fiedler et al 2005;Smith et al 2000).…”

“…Anaerobic microsites in upland soils may occur during wet periods or due to consumption of soil oxygen because of high microbial activity (Verchot et al 2000). An enhanced occurrence of anaerobic microsites can turn soils from net sinks for atmospheric CH 4 into net sources (Davidson et al 2004;Keller and Reiners 1994;Keller et al 2005).…”

Postharvest nitrous oxide emissions from a subtropical oxisol as influenced by summer crop residues and their management

“…In addition, Varner et al (2003) reported that mortality of fine roots, due to their fast turnover, has the potential to contribute significantly to N 2 O production and fluxes. Keller et al (2005) found that soil compaction also increased the N 2 O flux from a North Brazilian Oxisol. After maize harvest, the mean soil N 2 O emission in NT soil was 34 mg m -2 N in the evaluation period, with an N 2 O peak of 127 mg m -2 h -1 N (Figure 1), which was approximately five times below the maximum observed after soybean harvest.…”

Soil N2O fluxes along an elevation gradient of tropical montane forests under experimental nitrogen and phosphorus addition

“…TMFs usually exhibit "conservative" soil N cycling (similar rates of mineral N production and consumption), which results in low N losses. This is in contrast to tropical lowland forest soils, which typically have a more "leaky" soil N cycle; they often have relatively high soil N cycling rates (Vitousek and Matson, 1988;Corre et al, 2010), N-oxide (NO, N 2 O) fluxes (e.g., Matson and Vitousek, 1987;Keller et al, 2005;Purbopuspito et al, 2006;Koehler et al, 2009), and NO − 3 leaching (e.g., Hedin et al, 2003;Dechert et al, 2005;Schwendenmann and Veldkamp, 2005). However, N addition experiments in TMFs of Hawaii (Hall and Matson, 2003) and Panama (Koehler et al, 2009;Corre et al, 2014) have shown increases in soil mineral N production -especially nitrification rates -and N-oxide fluxes in as little as 1-2 years after the onset of N addition.…”