Is ecohydrology one idea or many?

Abstract

Examples cited by Kundzewicz (2002) to provoke discussion of ecohydrology reveal divergent notions of the fundamental nature of the concept. At issue is the answer to this question—does the term “ecohydrology” refer to a single idea or does it encompass many different ideas? Here, I argue that ecohydrology encompasses diverse ideas at the interface between hydrology and ecosystem science. Zalewski’s (2000) definition captures the competing views of ecohydrology, even as it attempts to reconcile them; “Ecohydrology, the study of the functional interrelationships between hydrology and biota at the catchment scale, is a new approach to achieving sustainable management of water.” First, ecohydrology is introduced as an area of study directed toward understanding the interdependence of hydrological and ecological processes. Next, ecohydrology provides a single, overarching paradigm for water management based on a holistic vision of water’s role in the environment. Can ecohydrology be both of these things? Traditional water management depends on information derived from hydrological science. A holistic approach to water management similarly depends on integrated study of hydrological and ecological processes (Fig. 1). However, science alone does not determine management. Other factors, besides scientific knowledge, combine to determine the overall approach to water management. Therefore, ecohydrology is either an overarching paradigm for water management, or it is the study of the interaction of hydrological and ecological processes. It cannot be both. I suggest that ecohydrology is the sub-discipline shared by the ecological and hydrological sciences that is concerned with the effects of hydrological processes on the distribution, structure, and function of ecosystems, and on the effects of biotic processes on elements of the water cycle (Nuttle, 2002). This combines RodriguezIturbe’s (2000) view of ecohydrology as “the science which seeks to describe the hydrological mechanisms that underlie ecologic pattern and processes” with his subsequent observation that “the connection between the role of plants in the water balance is central to ecohydrology” (Rodriguez-Iturbe et al., 2001). This definition focuses on the role of hydrological processes in ecosystems, consistent with Rodriguez-Iturbe’s reference to “ecologic pattern and processes.” As Kundzewicz (2002) observes, the etymology of “ecohydrology” links hydrology with the relatively broad field of ecology. However, the study of hydrological processes makes little or no contribution in some areas of ecology, e.g. population ecology.