Pooling of CO₂within a small valley in a tropical seasonal rain forest

Abstract

CO 2 concentrations and related environmental factors were measured in an Asian tropical rainforest located in a small valley in Xishuangbanna, SW China, with the aim of investigating the CO 2 pooling effect and its mechanism of formation. Pooling of CO 2 was observed during the evening (1600-2200 hours local time); the accumulated CO 2 subsequently flowed away after dusk. We consider that along-slope drainage flow, soil CO 2 efflux, and temperature inversion contribute to the development of CO 2 pooling. A new model is proposed to track the mechanism of the formation and dissipation of CO 2 pooling (e.g., drainage flow, compensatory mechanisms). Given its influence on the storage term, we suggest that CO 2 pooling and subsequent disappearance should be taken into account when calculating eddy covariance and other micrometeorological measurements of carbon flux for valley sites.

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

“…The right (clockwise) shear of subcanopy flow at night was in qualitative agreement with previously observed and modeled horizontal mean wind directional shear in some forest sites [33,[45][46][47][48], but conflicted to the left shift in other sites [32,43,49]. In fact, the subcanopy wind direction in calm night was highly dependent on the local longest slope direction [18,36], which is highly local site-dependent.…”

“…The daytime drainage flows under tall and dense canopies were also observed at other sites: down-slope at sites with flat terrain [8,30] or down-valley at complex sites [9,28,51]. Interestingly, the five sites with a daytime drainage flow below canopy (the MMSF site [10], the AEF site [29], the Manaus LBA site [30], the Xishuangbanna site [47] and the Maoershan site) had two common features: (1) a tall, dense canopy; (2) closed to the valley center or at the lower part of the sidewall with relative gentle slope. There is evidence that the radiative heating/cooling of dense canopy isolated the subcanopy layer with that above canopy [26,28], which plays a key role in the formation of these decoupled subcanopy flows.…”

“…However, the below-canopy misalignment occurred much more frequent, 76% in the daytime and 71% in the nocturnal occasions. On one hand, the nocturnal misalignment of the subcanopy flow with that above canopy is a common feature of a site with a tall and dense canopy in complex terrain [8,9,12,18,43,47,50], and even at a old-growth tropical forest site with flat terrain (Santarém LBA-ECO site, ~1° slope) [8]. On the other hand, the frequent subcanopy down-slope winds during the day (Table 2) contradicts with the classical theory of diurnal mountain wind systems [15].…”

Construction and progress of Chinese terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation

“…At the same time, a series of important ecological phenomena and their controling mechanism were illustrated. For example, the 'light depress' at ecosystem scale in temperate and alpine grasslands (Fu et al, 2006(Fu et al, , 2009, the nonlinear response of ecosystem carbon flux to temperature variation , heterogeneous response of soil respiration to temperature Jia et al, 2013;Song et al, 2013), the spatio-temporal variation of ecosystem light use efficiency (Yuan et al, 2010;Zhang et al, 2006c;Wu et al, 2008), and the 'carbon pool' in mountain area (Yao et al, 2012). Such studies enhance the understanding of the biotic and abiotic controlling mechanism of ecosystem CO 2 flux across different temporal scales, and the response and adaptation of ecosystem flux to global change.…”

CO2 flux observation in various forests of Monsoon-Asia

“…CO 2 storage in valley topography is reported to be very important in forest on complex terrain (Takagi et al 2009). Yao et al (2012) report CO 2 storage in valley topography in tropical seasonal rainforest.…”