Oecologia (Berl) (1982) 54:389-397 Oecologia 9 Springer-Verlag 1982 A Case Study of Energy, Water and Soil Flow Chains in an Arid Ecosystem A. Yair 1 and M. Shachak 2 1 Institue of Earth Sciences, The Hebrew University of Jerusalem, Israel. Also Watershed Ecology Unit. Blaustein Institute for Desert Research, Ben Gurion University, Israel 2 Watershed Ecology Unit. Blaustein Institute for Desert Research and Biology Department, Ben Gurion University, Sede Boqer Campus, Israel Abstract. Little attention has been directed to the study of soil flow and the complex relationships among energy water and soil flow in terrestrial ecosystems. Soil plays an important role in arid ecosystems. After water soil is the second key factor in the development of an arid ecosystem since soil is the only part of the system capable of absorbing and storing water and nutrients during the hot and long summer period. The present work presents a case study of an ecological soil flow chain in an arid environment and analyses the relationship between this chain and the energy and water flow chains. The study was conducted at the Sde Boqer experiment site located in the northern Negev of Israel where average annual rainfall is 92 mn. Data collected during five consecutive years show that the soil movement process within the ecosystem studied cannot be considered as a purely physical phenomenon, but rather as a part of a complex system in which the burrowing and digging activity of Isopods and Porcupines plays an impor- tant role by providing disaggregated soil particles easy to remove by shallow flows. Although controlled by the spatial distribution of soil moisture the biological activity acts as a regulator of soil depth and thus of soil moisture. If this regulating role is deleted from the system a new ecosystem, more arid, can be expected to develop. It is therefore con- cluded that the study of state and flow variables of an arid ecosystem should consider altogether the water, soil, energy and mineral chains. 1 Introduction Numerous recent studies deal with flow of energy and of minerals in ecosystems. The study of energy flow (Linde- man 1942; Odum 1957; Golley 1960) deals with the conver- sion of solar energy to organic matter by the producers and the transformation of the energy to the consumers and decomposers. The mineral flow studies are concerned with the movement of minerals from the abiotic elements to the biotic and vice versa (Cole et al. 1967; Likens and Bormann 1972; Burton and Likens 1975; Gosz et al. 1976). Except for some notable exceptions (Abaturov 1972; Lofty 1974; Rusek 1975), little attention has been directed to the study of soil flow and the complex relationships among energy, water and soil flow in terrestrial ecosystems. The inclusion of soil flow in the study of ecosystems is of great impor- tance, especially in arid areas. After water, soil is the second Offprint requests to: A. Yair key factor in the development of an arid ecosystem, since soil is the only part of the system capable of absorbing and storing water and nutrients for long periods. In the absence of sufficient soil, few higher plants can become established. Therefore, the input, output and the flow of the soil through processes of soil erosion and ,deposition must be considered as part of ecological flow chains. (In this study an ecological flow chain is defined as the flow of matter and/or energy controlled by biotic and abiotic elements.) Of particular interest are the spatial distribution of soil, its depth and its salt content. The latter' indirectly influences the water holding capacity of the soils which, in an arid environment, controls the spatial distribution of plants and burrowing animals (Yair 1978). The activity of burrowing and digging animals contributes to the soil turnover within the physical structure of the ecosystem. Therefore, the study of the soil flow chain may contribute to current research on the role of consumer populations as regulators in the total ecosystem function (Kitchell et al. 1979). The main purpose of the present paper is to present a case study of an ecological soil flow chain in an arid environment and to analyze the relationships between this chain and the energy and water flow chains. Special atten- tion will be accorded to the spatial variability over limited areas of rainfall, runoff, soil moisture and their influence on the spatial distribution of soil turnover by animal activi- ty, namely isopods and porcupines. The assumed relation- ships between the abiotic and biotic factors in the soil flow chain in the ecosystem under study are presented in Fig. 1. I Sur'~ or~176 [Runo. I Soil moisture I Animal activityI (digging :faeces) L 9 I, Low energy ].1 erodable so~ Fig. 1. Assumed relationships among abiotic and biotic variables in the soil flow chain in the Northern Negev Desert ecosystem