Ecohydrology is a cross-disciplinary field that emerged in the early 2000s as a result of recognition of the need to better understand complex, multifaceted interactions occurring in terrestrial ecosystems and their connection to the water cycle. In this article, ecohydrology is viewed as the science that studies how water in all its forms links living organisms and their abiotic environment to define their function, interactions, structure, and distribution. As a highly interdisciplinary field, ecohydrology draws from hydrology, ecology, atmospheric sciences, plant ecophysiology, biophysics, hydrodynamics, soil science, geomorphology, biogeochemistry, agronomy, and even landscape architecture. Basic science questions and land and water resource management issues are addressed in the field. A range of temporal scales, from minutes (such as in stomatal response to a changing environment) to millennia (such as that characteristic of landscape evolution period), is relevant to studies in ecohydrology. Likewise, spatial extent of analysis covers a spectrum ranging from ~10–6 m (e.g., concerned with leaf stomatal cavities or soil pores), to regional scales at ~106 m. As other sciences, ecohydrologic research relies on theoretical analysis, observation-based inference and experimentation, and computational approaches. The latter are becoming powerful, permitting experimentation and tests of mathematical descriptions of relevant processes and mechanisms. As evidenced by the publication record, one the main scopes of ecohydrology has been to understand how water available to ecosystems is used by vegetation and impacts the water cycle through the process of evapotranspiration. This review draws from this literature thus having a prevailing emphasis on vegetation control of water fluxes (i.e., transpiration) and the bilateral interactions between vegetation and abiotic environment. This perspective is justified by the key role of transpiration in the water cycle: it is the largest water flux from vegetated land to the atmosphere. The field of ecohydrology has analyzed different climatic regions and areas. Arid and semiarid ecosystems, where water is the major limiting factor of ecosystem functioning, are viewed as one of the key foci in ecohydrologic studies, largely driving the establishment of the field. The role that transpiration has on rainfall via water recirculation and the potential effects of deforestation are the emphasis of tropical ecohydrology. The large changes in the hydrologic budget associated with urbanization are addressed in urban ecohydrologic studies. One may expect that future focus will be on understanding of the transformation of terrestrial ecosystems, as we know them, due to ongoing and anticipated changes in the hydrologic cycle.
Use of Water Isotopes in Hydrological Processes
