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CR 12:29-37 (1999)  -  doi:10.3354/cr012029

Surface conductance and energy exchange in an intensively managed peat pasture

B. O. M. Dirks1,*, A. Hensen2

1Wageningen Agricultural University, Dept of Theoretical Production Ecology, PO Box 430, 6700 AK Wageningen, The Netherlands
2Netherlands Energy Research Foundation, PO Box 1, 1755 ZG Petten, The Netherlands

ABSTRACT: Aerodynamic measurements of latent (λE) and sensible heat (H) exchange were made in an intensively managed peat pasture during 2 consecutive years; the fetch was approximately 1.5 km. The surface conductance (gs) was calculated from the Penman-Monteith equation. The analysis focused on 2 successive aspects of gs: gs as a function of environment (primarily vapour pressure deficit [D]) and the energy balance as a function of gs. The effect of D on gs consisted of 2 components: the range of D over which gs was reduced (beyond inflection point Di) and the reducing effect per unit D. As average D increased, so did inflection point Di and the range of D over which gs was reduced; the reducing effect per unit D decreased. gs was a strong mediator in the energy balance. λE increased with D upto the inflection point Di, beyond which gs increasingly offset the positive effect of D. As gs impaired λE, the surface to air temperature difference (ΔT) and consequently H increased. With increasing gs, λE and H added up to progressively lower values, suggesting an increasing soil heat flux. Hysteresis in the diurnal patterns of the energy balance showed that the positive effect of D on λE remained stronger than the consequent negative effect of gs. λE was higher after than before noon, whereas ΔT and H were lower.

KEY WORDS: Aerodynamic technique · Surface conductance · Energy exchange · Latent heat · Sensible heat · Pasture · Grassland

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