Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/68

The Lowland Equatorial Monsoon Ecozone surface and groundwater from neighbouring ecosystems, rainforests of the lowland equatorial monsoon (the LEM) depend upon rainfall and are more subject to rainfall fluctuations.

However the net amount of rainfall actually available may be reduced by evaporation before it enters the biological regime.

Moreover, rainfall not lost by evaporation may be lost by leaching through the soil and by run-off. Nonetheless a healthy rainforest ecosystem acts like a sponge: the soil system (including litter, detritus and humus) soaks up the water, subsequently releasing it slowly to plants and to rivers by percolation.

Evapotranspiration is greatest in a clearing in the tropical rainforest, where a lot of vegetation are disturbed and exposed to the heat of the sun; it is least (as one would expect) in the shaded undergrowth. Also, as one would expect, for any given season, daily evapotranspiration potential is at its maximum at noon.

Temperature varies during the day but also within the vertical space of the forest. These inequalities create localised rainfall, when transpired vapour from one area condenses back to water in a cooler area or on a cooler surface. On a still day 66