Fine-Scale Relief in the Amazon Drives Large Scale Ecohydrological Processes

Abstract:

Access to soil water by roots is a key ecophysiological factor for plant productivity in natural systems. Periodically during dry seasons or critically during episodic climate droughts, shortage of water supply can reduce or severely impair plant life. At the other extreme persistent soil waterlogging will limit root respiration and restrict local establishment to adapted species, usually leading to stunted and less productive communities. Soil-water availability is therefore a very important climate variable controlling plant physiology and ecosystem dynamics. Terra-firme, the non-seasonally floodable terrain that covers 82% of the landscape in Amazonia,[1] supports the most massive part of the rainforest ecosystem. The availability of soil water data for terra-firme is scant and very coarse. This lack of data has hampered observational and modeling studies aiming to develop a large-scale integrative ecohydrological picture of Amazonia and its vulnerability to climate change. We have mapped the Amazon basin with a new terrain model developed in our group (HAND, Height Above the Nearest drainage[2]), delineating soil water environments using topographical data from the SRTM digital elevation model (250 m horizontal interpolated resolution). The preliminary results show that more than 50% of Terra-firme has the water table very close to the surface (up to 2 m deep), while the remainder of the upland landscape has variable degree of dependence on non-saturated soil (vadose layer). The mapping also shows extremely heterogeneous patterns of fine-scale relief across the basin, which implies complex ecohydrological regional forcing on the forest physiology. Ecoclimate studies should therefore take into account fine-scale relief and its implications for soil-water availability to plant processes.

[1] Melack, J. M., & Hess, L. L. (2011). Remote sensing of the distribution and extent of wetlands in the Amazon basin. In W. J. Junk & M. Piedade (Eds.), Amazonian floodplain forests: Ecophysiology, ecology, biodiversity and sustainable management (pp. 1–28). Ecological Studies-Springer.

[2] Nobre, A. D., Cuartas, L. A., Hodnett, M., … Saleska, S. (2011). Height Above the Nearest Drainage – a hydrologically relevant new terrain model. Journal of Hydrology, 404(1-2), 13–29

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