Hydrologic influences on soil properties along ephemeral rivers in the Namib Desert

Soils were examined along three ephemeral rivers in the Namib Desert to ass ess the influence of their hydrologic characteristics on soil properties. S oils consisted of layers of fluvially deposited, organic-rich silts, inters tratified with fluvial and aeolian sands. The most significant influence of the ephemeral hydrologic regime upon soils was related to the downstream a lluviation associated with hydrologic decay. This alluviation increased the silt proportion of soils in the lower reaches of the rivers. Organic carbo n, nitrogen and phosphorous were correlated with silt content, and silt dep osition patterns influenced patterns of moisture availability and plant roo ting, creating and maintaining micro-habitats for various organisms. Locali zed salinization occurred in association with wetland sites and soluble sal t content tended to increase downstream. Because of the covariance between silt and macronutrients, and the influence of silt upon moisture availabili ty and habitat suitability, alluviation patterns associated with the hydrol ogic regime strongly influence the structure, productivity, and spatial dis tribution of biotic communities in ephemeral river ecosystems. (C) 2000 Aca demic Press.